Patent Publication Number: US-2015070836-A1

Title: System for cooling an integrated circuit within a computing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/786,300, filed on 14 Mar. 2013, which is incorporated in its entirety by this reference. 
     This application is also related to U.S. patent application Ser. No. 11/969,848, filed on 4 Jan. 2008, U.S. patent application Ser. No. 13/414,589, filed 7 Mar. 2012, U.S. patent application Ser. No. 13/456,010, filed 35 Apr. 2012, U.S. patent application Ser. No. 13/456,031, filed 35 Apr. 2012 (P04-US2), U.S. patent application Ser. No. 13/465,737, filed 7 May 2012, U.S. patent application Ser. No. 13/465,772, filed 7 May 2012, U.S. patent application Ser. No. 14/035,851, filed on 34 Sep. 2013, and U.S. patent application Ser. No. 14/081,519, filed on 15 Nov. 2013, all of which are incorporated in their entireties by this reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to computing devices, and more specifically to a new and useful system for cooling an integrated circuit  302  in a computing device. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic representation of a first system of the invention; 
         FIG. 2  is a schematic representation of one variation of the first system; 
         FIGS. 3A and 3B  are schematic representations of one variation of the first system; 
         FIGS. 4A and 4B  are schematic representations of one variation of the first system; 
         FIG. 5  is a schematic representation of one variation of the first system; 
         FIGS. 6A ,  6 B, and  6 C are isometric representations of variations of the first system; 
         FIGS. 7A and 7B  are schematic representations of one variation of the first system; 
         FIG. 8  is a flowchart representation of one variation of the first system; 
         FIGS. 9A and 9B  are schematic representations of a second system of the invention; 
         FIG. 10  is a schematic representation of one variation of the second system; 
         FIG. 11  is a schematic representation of one variation of the second system; 
         FIG. 12  is a schematic representation of one variation of the second system; and 
         FIG. 13  is a schematic representation of one variation of the second system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment of the invention is not intended to limit the invention to these preferred embodiments, but rather to enable any person skilled in the art to make and use this invention. 
     1. First System and Applications 
     As shown in  FIG. 1 , a first system  100  for cooling an integrated circuit  302  in a computing device—including a digital display  330 —includes: an internal heatsink  110  thermally coupled to the integrated circuit  302  and defining a fluid passage  112  including a first end and a second end; a heat exchange layer  120  arranged across a viewing surface of the digital display  330 , including a transparent material, and defining a fluid channel  122  extending across a portion of the digital display  330 , the fluid channel  122  including a fluid inlet coupled to the first end of the fluid passage  112  and a fluid outlet coupled to the second end of the fluid passage  112 ; a transparent fluid  130 ; and a displacement device  140  configured to circulate the transparent fluid  130  between the internal heatsink  110  and the fluid channel  122 . 
     As shown in  FIGS. 1 and 8 , one variation of first system  100  includes: an internal heatsink thermally coupled to an electrical component  302  within the computing device and defining a fluid passage including a first end and a second end; a heat exchange layer  120  arranged over the digital display  330 , including a transparent material, defining a first fluid channel cooperating with the internal heatsink  110  to define a first fluid circuit, and defining a second fluid channel  222  cooperating with the internal heatsink  110  to define a second fluid circuit; a transparent fluid  130 ; and a displacement device  140  configured to circulate the transparent fluid  130  within the first circuit in response to detected orientation of the computing device in a first position and to circulate the transparent fluid  130  within the second circuit in response to detected orientation of the computing device in a second position. 
     First system  100  functions to cool one or more electrical components (e.g., a passive circuit element, an integrated circuit  302 ) within a computing device by pumping fluid from an internal heatsink to a transparent superficial heat exchanger arranged over a digital display  330  of the computing device. For example, first system  100  can transfer heat from a processor, a power supply, a voltage regulator, a display driver, and/or a battery within a mobile computing device to an exterior surface of the device by circulating fluid between the internal heatsink no and the heat exchange layer  120 . Generally, first system  100  actively transfers heat from local heat sources (i.e., integrated circuits, a display, a battery) within the computing device to a superficial heat exchanger (i.e., on one or more external surfaces of the computing device) by displacing fluid through a closed fluid system (i.e., a fluid circuit) thermally connected to both the heatsink and the heat exchanger. The computing device can be a cellular phone, a smartphone, a tablet, a laptop computer, a digital watch, a personal data assistant (PDA), a personal music (e.g., MP3) player, or any other suitable type of device that includes a display and an electrical circuit that outputs heat during operation. 
     1.2 Internal Heatsink 
     The internal heatsink  110  of first system  100  is thermally coupled to the integrated circuit  302  and defines a fluid passage including a first end and a second end. Generally, the internal heatsink no defines the fluid passage  112  connected at one side to the inlet of the fluid channel  122  and connected at an opposite and/or upstream side to the outlet of the fluid channel  122  such and functions to transfer heat from the integrated circuit  302  (and/or other electrical component within the computing device) into fluid circulating through the fluid passage  112 . 
     In one implementation, the fluid passage  112  defines an elongated channel (e.g., of constant or varying cross-section) that extends across the electrical component  302  within the computing device. For example, the fluid passage  112  can be linear and square in cross-section. In this implementation, the internal heatsink  110  can also define multiple fluid passages that merge into a inlet manifold  124  connected to the fluid inlet at one end and into a outlet manifold  124  connected to the fluid outlet at the opposite or upstream end. Alternatively, the fluid passage  112  can define is a wide and/or deep volume portioned by fins or walls that extend from proximal the fluid inlet to proximal the fluid outlet. For example, the internal heatsink  110  can define a series of internal vanes within the fluid channel  122  adjacent the integrated circuit  302 , wherein the vanes extend substantially parallel to a direction of flow of the transparent fluid  130  through the fluid passage  112 . However, the internal heatsink  110  can define one or more fluid passages of any other geometry or cross section and directly or indirectly fluidly coupled to the fluid channel  122  in any other suitable way. 
     In one implementation in which the integrated circuit  302  or electrical component defines a planar outer surface (e.g., a processor, a solid-state dynamic random-access memory (DRAM), or a battery), the internal heatsink  110  can extend across and directly contact the outer surface of the electrical component  302 , as shown in  FIG. 1 , thereby conducting heat out of the electrical component  302  and into the fluid. The internal heatsink  110  can alternatively be potted adjacent the electrical component  302  or thermally coupled to the electrical component  302  via a thermal interface material (TIM), such as thermal grease or a graphene film. Furthermore, for the electrical component  302  that is mounted on a planar printed circuit board (PCB)  350 , a portion of the internal heatsink  110  can be arranged on and/or thermally coupled to the PCB  350 , such as on a surface of the PCB  350  opposite and proximal the electrical component  302 , as shown in  FIG. 3 . 
     The internal heatsink no can thus define an enclosed fluid passage that is fluidly isolated from the electrical component  302  and configured to communicate thermal energy from a surface of the electrical component  302  and/or from the PCB  350  into the fluid. In particular, in this implementation, the internal heatsink  110  can define an enclosed structure configured to contact or otherwise thermally couple to an electrical component within the device. For example, the internal heatsink  110  can include stamped copper or aluminum clamshell structures brazed or welded together at a junction to form an enclosed volume with two or more ports configured to fluidly coupled to the fluid inlet and the fluid outlet of the fluid channel  122  in the heat exchange layer  120 . In this example, one or both halves of the clamshell can include internal ribs or vanes stamped, molded, welded or otherwise formed into their interior structures, wherein the ribs or vanes form partitions within the enclosed volume to guide fluid flow through the internal heatsink  110 . The internal heatsink  110  can be further define a geometry configured to extend over, contact, and/or thermally couple to one or more other electrical components within the computing device, such as a second integrated circuit  302  or passive electrical component arranged on the PCB  350  adjacent the (first) electrical component. For example, the internal heatsink  110  can define a staggered, “stepped,” or “recessed” external surface, wherein facets at different vertical positions across the external surface of the internal heatsink  110  contact (or thermally couple to) electrical components at various heights across the PCB  350 , as shown in  FIG. 1 . Thus, in this example, the displacement device  140  can pump fluid from the output of the fluid channel  122  into the internal heatsink  110  such that the fluid passes over a first facet of the outer surface of the internal heatsink  110  adjacent a first electrical component and then over a second facet of the outer surface of the internal heatsink  110  adjacent a second electrical component  303  to absorb heat from the first and second electrical components in series before returning to the fluid channel  122  in the heat exchange layer  120  to via the fluid inlet to dissipate this thermal energy to the environment. Furthermore, in this implementation, the fluid passage  112  can be linear, convoluted, serpentine (shown in  FIG. 6B ), or of any other geometry to direct fluid over any number of electrical components at various positions over one or more PCBs within the computing device. Additionally or alternatively, the internal heatsink  110  can define one or more internal ribs or vanes to guide or separate fluid flow through the fluid passage  112 . 
     The internal heatsink  110  can also define an internal geometry configured to limit fluid stagnation. In one example, the internal heatsink  110  defines an internal geometry—such as a vane or interior surface texture—that passively induces turbulence (i.e., mixing) in the fluid. In another example, the internal heatsink  110  includes an active component, such as a secondary pump, configured to actively mix fluid near the electrical component  302 . In a further example, the internal heatsink  110  defines chambers, vias, or channels along and/or over the electrical component  302 , and the displacement device  140  forces fluid through the channels. However, the internal heatsink  110  can include any other geometry and/or passive or active mixing system to limit stagnation as fluid is circulated through the internal heatsink  110 . 
     In another implementation, the internal heatsink no cooperates with a PCB  350  (or other substrate supporting the electrical component  302 ) within the computing device to define an enclosed volume (with inlet and outlet ports) around the electrical component  302 . In this implementation, the internal heatsink  110  and the PCB  350  can cooperate to define the fluid passage  112  such that fluid bathes the electrical component  302  as it moves through the fluid passage  112 . For example, the internal heatsink  110  can define a cover arranged over the PCB  350  (or other substrate within the computing device) to encase the electrical component  302 , the electrical component  302  thus immersed in the fluid when the fluid passage  112  is flooded. Heat can thus be conducted from the electrical component  302  directly into the fluid. In this implementation, the internal heatsink  110  cover can also cooperate with the PCB  350  to encase and to cool various other active or passive electrical components arranged on the PCB  350 . Furthermore, in this implementation, traces and/or vias connecting electrical components on the PCB  350  can be sealed or coated with a non-conductive coating to prevent shorts when the traces and vias are exposed to the fluid, such as for the fluid that includes water. Additionally or alternatively, the fluid system can be filled with a non-conductive fluid, such as alcohol, oil, or an other non-ionic fluid that will not short across traces or other electrical connections on the PCB  350 . 
     Similarly, the internal heatsink  110  can be physically coextensive with a housing of the computing device, wherein the housing defines an enclosed internal cavity (with a inlet and outlet ports to the heat exchange layer  120 ) that contains the PCB  350 , a processor, a battery, a display driver, and/or any other electronic component of the computing device. In this implementation, the cavity can be flooded with fluid such that the electrical components within  110  computing device are immersed in fluid, the fluid thus directly conductive thermal energy out of these components as the fluid is circulated between the internal heatsink  110  and the heat exchange layer  120 . The internal heatsink  110  can further define internal ribs or vanes that direct fluid flow through fluid passage (i.e., the cavity). As described above, it this implementation, traces, vias, and other exposed conductive components can be coated in a non-conductive coating and/or the transparent fluid  130  can include a non-conductive fluid to prevent shorts across exposed conductive surfaces within the computing device. 
     However, the internal heatsink  110  can be of any other geometry and can define the fluid passage  112  in any other suitable way and of any other geometry. 
     The internal heatsink  110  can also be removably or transiently arranged within the computing device. In one example, the internal heatsink  110  is arranged on or is integrated into a battery  310  that is transiently installed in the computing device. In this example, the fluid passage  112  can initiate and terminate at an inlet port and an outlet port, respectively, that couple to the fluid channel  122  when the battery  310  in installed in the device and disconnect from the fluid channel  122  when the battery  310  is removed from the device. In another example, the internal heatsink  110  defines a discrete (i.e., standalone) component with the fluid passage  112  originating and terminating at quick disconnects that transiently engage the fluid inlet and the fluid outlet of the fluid channel  122 , respectively, such that the internal heatsink  110  can be removed from the device, serviced or repaired, and reinstalled into the device. 
     The internal heatsink  110  (and the heat exchange layer  120 ) can also be flexible. For example, the computing device can include a flexible housing, and the internal heatsink  110  therefore also be flexible such that the internal heatsink  110  can morph with various orientations of the housing. 
     The housing, cover, clamshell, etc. of the internal heatsink  110  can further functions as an electromagnetic interference (EMI) shield. For example, the internal heatsink  110  can include thin metallic (e.g., copper, aluminum, steel, tin) clamshells brazed together to define the fluid passage  112  such that, when arranged over the PCB  350 , the internal heatsink  110  shields EMI transmission from the electrical component  302  from passing out of the device. In another example, the internal heatsink  110  includes conductive tabs or fingers that electrically contact ground traces on the PCB  350  extending off a faceted cover over the PCB  350 . Alternatively, the computing device can include an EMI shield  340  interposed between the electrical component  302  (and the PCB  350 ) and the internal heatsink  110  such that the internal heatsink  110  conducts thermal out of the electrical component  302  (and/or the PCB  350 ) via the EMI shield  340 . Yet alternatively, the internal heatsink  110  can be interposed between the electrical component  302  (or the PCB  350 ) and an EMI shield  340 . Yet alternatively, the transparent fluid  130  can be conductive such that fluid passing through the internal heatsink  110 —adjacent integrated and/or passive circuits within the computing device—functions as an EMI shield to shield EMI transmission out of the device. 
     1.3 Heat Exchange Layer 
     The heat exchange layer  120  is arranged across a viewing surface of the digital display  330 , includes a transparent material, and defines a fluid channel  122  extending across a portion of the digital display  330 , wherein the fluid channel  122  includes a fluid inlet coupled to the first end of the fluid passage  112  and a fluid outlet coupled to the second end of the fluid passage  112 . Generally, the heat exchange layer  120  defines a (superficial) fluid-air heat exchanger that communicates fluid through one or more enclosed channels over an exterior surface of the computing device to dissipate heat—absorbed from the electrical component  302  at the internal heatsink  110 —to the environment. In particular, the displacement device  140  moves fluid through the internal heatsink  110 , across the electrical component  302  to absorb fluid, then through the fluid channel  122  where heat is dissipated to ambient, and the fluid thus returns—now cooled—to the internal heatsink no to again absorb heat from the electrical component  302 . The fluid channel  122  in heat exchange layer, the fluid passage  112  in the internal heatsink  110 , and the displacement device  140  can thus device a closed fluid circuit. Furthermore, in one implementation of first system  100  described below, the heat exchange layer  120  defines a first fluid channel  122  cooperating with the internal heatsink  110  to form a first fluid circuit and further defines a second fluid channel  222  cooperating with the internal heatsink  110  to form a second fluid circuit, such as described below. However, the substrate can define any other number of discrete fluid channels or discrete sets of fluid channels that cooperate with any one or more internal heatsinks to define corresponding fluid circuits. 
     The heat exchange layer  120  is arranged over the display  330  of the computing device, as shown in  FIGS. 1 and 3 . The display  330  can be a digital display  330 , such as an LED-backlit LCD display, an e-ink display, or a plasma display. The display  330  can also be a touchscreen, such as a digital display  330  coupled to capacitive or resistive touch sensor. However, the display  330  can be any other suitable type of display. The heat exchange layer  120  can also be arranged over the display  330  with a discrete touch sensor  320  layer interposed therebetween. The heat exchange layer  120  can therefore be translucent or substantially transparent to enable transmission of light (e.g., an image) from the display  330  to a user or viewer. For example, the heat exchange layer  120  can include one or more substantially transparent layers of amorphous glass, sapphire, silicone, acrylic, and/or polycarbonate. The heat exchange layer  120  also defines the fluid channel  122  that communicates fluid laterally, such as across the display  330  and/or a bezel adjacent the display  330 . The heat exchange layer  120  can therefore be selected from a material(s) with an index of refraction substantially similar to that of the fluid such that the fluid channel  122 ( s ) is substantially imperceptible to a user, such as from a viewing distance of twelve inches between the user&#39;s eyes and the computing device. For example, the heat exchange layer  120  can include a transparent elastomer (e.g., silicone, polycarbonate) layer of a first refractive index at a wavelength of light, and the transparent fluid  130  can be an oil of a second refractive index substantially similar to the first refractive index at the wavelength of light. The heat exchange layer  120  can also be of a composite material with multiple layers of different indices of refraction, a single layer of index of refraction that varies with depth, one or more layers with a designed Abbe number, etc. to substantially match an optical property of the fluid such that a junction between the fluid and the fluid channel  122  is substantially imperceptible to the naked (human) eye at a standard viewing distance. The heat exchange layer  120  can also define the fluid channel  122  that is of a substantially small cross-sectional area such that the fluid channel  122  is difficult to distinguish visually. For example, the fluid channel  122  can be a microfluidic fluid channel of substantially high aspect ratio, its length substantially greater than its width (or diameter). 
     In one implementation, the heat exchange layer  120  includes a rigid substrate, such as of silicate glass, alkali-aluminosilicate glass, aluminum nitride, or sapphire, that defines an exterior surface of the device. In this implementation, an open channel can be etched, machined, molded, or otherwise formed in an internal surface of the substrate, which is then bonded over the display  330  or other a touch sensor layer. The substrate can then be bonded over the display  330  or the touch sensor layer, which closes the open channel to define the fluid channel  122 . Alternatively, an open channel can be formed in a glass substrate, and a glass or elastomer closing panel can be bonded over the substrate to close the open channel, thereby forming the fluid channel  122 . In this implementation, first system  100  can further include a pressure relief valve arranged between the internal heatsink  110  and the heat exchange layer  120  and configured to open in response to fluid pressure in the fluid channel  122  exceeding a threshold pressure. In particular, the pressure relief valve can trip when a threshold pressure is reached within the fluid channel  122 , thereby releasing fluid pressure within the fluid channel  122  to prevent the heat exchange layer  120  from cracking or shattering due to excessive fluid pressures within the fluid channel  122 . Additionally or alternatively, the fluid can exhibit a substantially low coefficient of thermal expansion, or the displacement device  140  can manipulate a flow rate of fluid through the fluid channel  122  based on an output of a pressure sensor fluidly coupled to the fluid channel  122  and/or to the fluid passage  112 . 
     In another implementation, the heat exchange layer  120  includes an elastomer outer sublayer bonded to a substrate that is arranged over the display  330  (and/or the touch sensor  320 ). For example, the heat exchange layer  120  can define an elastic substrate defining an open channel with vias at each end (fluidly coupled to the internal heat sink and/or to the displacement device  140 ), and an elastic outer sublayer can be bonded across the substrate to close the open channel, thereby forming the fluid channel  122 . For example, the substrate and the outer sublayer can be assembled as described in U.S. patent application Ser. No. 14/035,851, filed on 34 Sep. 2013, which is incorporated in its entirety by this reference. However, the heat exchange layer  120  can include any suitable material, can define any suitable external or fluid channel geometry, and/or can be manufactured in any suitable way, such as described in U.S. patent application Ser. No. 11/969,848 and/or U.S. patent application Ser. No. 13/414,589, which are incorporated in there entireties herein by this reference. 
     In one implementation, the heat exchange layer  120  defines a set of connected fluid channels. For example, the heat change layer can define a set of parallel fluid channels, an inlet manifold  124 , and an outlet manifold  126 , wherein each fluid channel in the set of fluid channels originates at the inlet manifold  124  and terminates at the outlet manifold  126 , as shown in  FIG. 6A . In this example, the inlet manifold  124  and the outlet manifold  126  can be arranged over a bezel area of the computing device adjacent a viewing area of the digital display  330 , and the fluid channels can extend from a first side of the display  330  (e.g., proximal a left side of the display  330  when viewed in a landscape orientation) to a second side of the display  330  (e.g., proximal a right side of the display  330  when viewed in a landscape orientation), as shown in  FIG. 6A . The heat exchange layer  120  can define fluid channels of substantially linear and of substantially constant and similar cross-sectional areas. The heat exchange layer  120  can additionally or alternatively define one or more fluid channels of a serpentine (shown in  FIG. 6B ), curved, zigzag or other geometry and/or of constant or varying cross-section. For example, the heat exchange layer  120  can define fluid channels with round, square, rectilinear, polygonal, or elliptical cross-sections. However, the heat exchange layer  120  can define one or more fluid channels of any other form, geometry, or cross-section. 
     The heat exchange layer  120  can further define a second set of fluid channels that extend—substantially perpendicular to the first second of fluid channels—from a third side of the display  330  (e.g., proximal a top side of the display  330  when viewed in a portrait orientation) to a fourth side of the display  330  (e.g., proximal a bottom side of the display  330  when viewed in a portrait orientation), as shown in  FIG. 6C . For example, the heat exchange layer  120  can define a second fluid channel  222  including a second fluid inlet and a second fluid outlet fluidly coupled to the internal heatsink  110 , the second fluid channel  222  extending across the digital display  330  with the second fluid inlet proximal a first long edge of the rectangular viewing area and the second fluid outlet proximal a second long edge of the rectangular viewing area opposite the first long edge. In this example, the heat exchange layer  120  can similarly define a second set of parallel fluid channels connected to a second inlet manifold  124  and to a second outlet manifold  126 . In this implementation, the first set of fluid channels can be set at a first (constant) depth in the heat exchange layer  120  and the second fluid channel  222  or the second set of fluid channels can be set at a second depth in the heat exchange layer  120  different from the first depth, such as shown in  FIG. 6C . Alternatively, the heat exchange layer  120  can define the first and second sets of fluid channels at substantially similar or at varying depths such that fluid channels overlap but do not join at intersections. 
     The fluid channel  122  (and/or each fluid channel in a set of fluid channels) can extend from proximal one edge of the display  330  (e.g., at the inlet) to an opposite edge of the display  330  (e.g., at the outlet). The fluid channel  122  can also extend beyond the display  330 , such as into a display border or bezel area. The fluid channel  122  can also originate and terminate at or near a same end (or edge) of the display  330  or at or near any other region(s) of the display  330 . For example, the fluid channel  122  can extend linearly from the inlet at a first end of the display  330  toward an opposite end of the display  330 , define two ninety-degree bends, and return to the first edge where it couples to the fluid outlet. Alternatively, the first fluid channel  122  can extend over the viewing area of the display  330 , and the second fluid channel  222  can extend over a bezel adjacent a viewing area of the display  330 . For example, the second channel can define a serpentine path over one rectilinear region of the bezel area, and the heat exchange layer  120  can define a set of parallel fluid channels connected at each to common manifolds. 
     The heat exchange layer  120  can similarly define multiple fluid channel sets, each arranged over a discrete region or over intersecting regions of the display  330 . For example, the heat exchange layer  120  can define each fluid channel set over one of several discrete (rectilinear) regions of the display  330 , the discrete regions arranged in a grid pattern (e.g., a 3×6 grid array) across the display  330 , as shown in  FIGS. 4A and 4B . In this example, first system  100  can selectively pump fluid through fluid channels in the heat exchange layer  120  based on where a user places his hands to hold the computing device. For example, the displacement device  140  can shut off fluid flow to fluid channels sets adjacent a user&#39;s hands and fingers and redirect fluid flow to other fluid channels in the heat exchange layer  120  not adjacent the user&#39;s hands and fingers, such as shown in  FIGS. 4A and 4B . In this example, first system  100  can further include a processor  170  configured to convert touches or inputs on a touch sensor  320  over the display  330  to a predicted placement of the user&#39;s hands and fingers on the device and, based on this predicted placement, set a series of valves between the fluid channels and the internal heatsink  110  to selectively move heated fluid to particular regions of the heat exchange layer  120  away from predicted current human contact points. Additionally or alternatively, in this example and as described below, the processor  170  can interface with a motion sensor (e.g., an accelerometer, a gyroscope) to detect an orientation of the device (e.g., a portrait orientation, a landscape orientation)—which can be associated with human contact points over the device—and set valves between the fluid channel  122  and the fluid passage  112  and/or the displacement device  140  accordingly. However, the heat exchange layer  120  can define any other number of fluid channels in any one or more fluid channel sets in any other form or geometry or over any one or more portions of any geometry over the display  330 . 
     In one variation, first system  100  further includes a second heat exchange layer  220  arranged across rear exterior surface of the computing device opposite the digital display  330 , wherein the second heat exchange layer  220  defines a second fluid channel  222  fluidly coupled to the first fluid channel  122 . In this variation, the second heat exchange layer  220  can be substantially similar to the heat exchange layer  120 , such as of a similar geometry and of similar (e.g., transparent) materials with the second fluid channel  222  fluidly coupled to the internal heatsink no. However, the second heat exchange layer  220  can be of any other material and/or geometry. Thus, the displacement device  140  can simultaneously displace fluid from the internal heatsink no into the first fluid channel  122  in the external heat exchange layer and into the second fluid channel  222  in the second external heat exchange layer, thereby distributing heat to “front” and “rear” exterior surfaces of the computing device to cool one or more electrical components within. Additionally or alternatively, the displacement device  140  can selectively circulate between the internal heatsink  110  and the first fluid channel  122  and between the internal heatsink  110  and the second fluid channel  222 , as described below. 
     In another implementation of the apparatus, the heat exchange layer  120  includes a substrate and an elastomer layer, wherein the substrate defines an open trough extending across a surface opposite the digital display  330 , wherein the elastomer layer includes a peripheral region  168  coupled to the substrate and a deformable region  166  arranged over the open trough to define the fluid channel  122 , and wherein the deformable region  166  is configured to expand outwardly above the peripheral region  168  in response to increased fluid pressure within the fluid channel  122 . Generally, in this implementation, the deformable region  166  functions to deform outwardly, thereby increasing the outer surface area of the hear exchange layer and increasing heat transfer out of the fluid into the environment. For example, the substrate can define a series of parallel linear troughs connected at each end to a manifold, and the elastomer layer can define a deformable region  166  above each trough such that, when fluid pressure within the corresponding fluid channels rises above ambient (i.e., barometric) pressure, the deformable regions expand to form fins or ribs across the heat exchange layer  120 . Then, when fluid pressure drops to or below ambient, the deformable regions can retract back to flush with the peripheral region  168  such that the heat exchange layer  120  is of a substantially uniform thickness across, thereby minimize optical distortion of light output by the display  330  below. The substrate can also define a support member arranged over the troughs to prevent displacement of a deformable region  166  into the trough, such as described in U.S. patent application Ser. No. 13/414,589. In this implementation, the heat exchange layer  120  can define the deformable region  166  across the display  330 , around a perimeter of the display  330 , and/or over a bezel area adjacent the display  330 . In this variation of first system  100  that includes a second heat exchange layer  220 , the second heat exchange layer  220  can additionally or alternatively include second a substrate and a second elastomer layer, wherein the second substrate defines a second open trough, wherein the second elastomer layer includes a second peripheral region  168  coupled to the second substrate and a second deformable region  166  arranged over the second open trough to define a second fluid channel  222 , and wherein the second deformable region  166  is configured to expand outwardly above the second peripheral region  168  in response to increased fluid pressure within the second fluid channel  222 . 
     In the foregoing implementation, a deformable region  166  can be substantially bistable, wherein the deformable region  166  remains substantially flush with the peripheral region  168  in a retracted setting until a threshold fluid pressure is reached within the fluid channel  122 , at which point the deformable region  166  transitions into the expanded setting until fluid pressure again drops below the threshold pressure. Alternatively, the deformable region  166  can expand proportionally with fluid pressure in the fluid channel  122 , and the displacement device  140  can interface with a pressure sensor coupled to the fluid channel  122  to regulate fluid pressure within the fluid channel  122 ( s ) and therefore the height of the corresponding deformable region  166 ( s ) above the peripheral region  168 . 
     1.4 Fluid Junction 
     As shown in  FIG. 1 , one variation of first system  100  includes a fluid junction  150  configured to fluidly couple the internal heatsink  110  to the heat exchange layer  120 . Generally, the fluid junction  150  functions to couple the outlet port of the internal heatsink  110  to the fluid inlet of the heat exchange layer  120  and to couple the fluid outlet of the heat exchange layer  120  to the inlet port of the internal heatsink  110 , thereby creating a closed fluid loop through which the transparent fluid  130  flows to adsorb heat from one or more electrical components within the device and to release thermal energy to the environment. In one implementation, the fluid inlet and the fluid outlet of the heat exchange layer  120  can define vias through the substrate of the heat exchange layer  120 , as described in U.S. patent application Ser. No. 14/035,851, and first system  100  and include one fluid junction  150  that connects each via to a corresponding end of the fluid passage  112  within the internal heatsink  110 . For example, the fluid junction  150  can include a soft coupling, such as a silicone, PETG, or urethane coupling, or the fluid junction  150  can include a rigid coupling, such as including a male and a female coupling that rigidly connect when the computing device assembled with first system  100 . 
     The fluid junction  150  can further interface with the displacement device  140 . In one implementation, the displacement device  140  is arranged in line with the fluid junction  150  at the fluid inlet side of the internal heatsink  110  or at the fluid outlet side of the internal heatsink  110 , as shown in  FIG. 1 . The fluid junction  150  can also interface with one or more valves, a second heat exchanger layer, and/or additional displacement devices, as shown in  FIGS. 3A and 3B . 
     The fluid junction  150  can also include a septum or a filling port to enable a user or machine to fill first system  100  with fluid. The filling port can pass through a housing of the computing device for quick access by a user or machine, or the filling port can be arranged inside the computing device, thus requiring disassembly of a portion of the computing device to fill, empty, and/or change fluid within first system  100 . The fluid junction  150  can similarly include a drainage port to allow a user or machine to remove fluid from first system  100 . As described above, the fluid junction  150  can also include quick disconnects to enable various components, such as the displacement device  140 , the internal heatsink  110 , etc. to be removed, serviced, repaired, reinstalled, and/or replaced. 
     1.5 Displacement Device 
     The displacement device  140  is configured to circulate the transparent fluid  130  between the internal heatsink  110  and the external heat exchange layer. Generally, the displacement device  140  functions to actively move fluid through the enclosed fluid system to redistribute heat from a heat source with the computing device to a surface of the computing device such that one or more electrical components inside the computing device may be cooled by dissipating heat to the environment. 
     The displacement device  140  can be a positive displacement pump that pushes (or pulls) fluid in a single direction, such as described in U.S. patent application Ser. No. 13/414,589. Alternatively, the displacement device  140  can be an intermittent pump, such as described in U.S. patent application Ser. No. 14/081,519. Yet alternatively, the displacement device  140  can cooperate with the internal heatsink  110  to define a passive heat pipe. The displacement device  140  can cooperate with the internal heatsink  110  and the heat exchange layer  120  to form a thermosiphon that passively circulates heated fluid from proximal the electrical component  302  to the heat exchange layer  120  and return cooled fluid from the heat exchange layer  120  back to the fluid passage  112  adjacent the electrical component  302 . The displacement device  140  can therefore directly act on (i.e., contact with) the fluid. Alternatively, the displacement device  140  can indirectly displace fluid within first system  100 , such as by manipulating a reservoir containing the fluid. For example, the displacement device  140  can expand and retract a bladder with unidirectional (e.g., check) valves at two ports connected to the bladder to circulate fluid from the bladder into the fluid passage  112 , then the fluid channel  122 , and back into the bladder, or vice versa. 
     However, the displacement device  140  can be any other suitable type of active or passive pump and can circulate fluid through first system  100  in any other suitable way. First system  100  can also include any number of similar or different pumps to move fluid through the computing device. 
     1.6 Dynamic Tactile Layer 
     As shown in  FIGS. 3A ,  3 B,  7 A, and  7 B, one variation of first system  100  further includes: a substrate  164  of a substantially transparent material, arranged over the heat exchange layer  120  opposite the display  330 , and defining a second fluid channel  222  and a fluid conduit  224  fluidly coupled to the second fluid channel  222 , the second fluid channel  222  fluidly decoupled from the fluid channel  122 ; a tactile layer  162  of a substantially transparent material and including a peripheral region  168  coupled to the substrate  164  and a deformable region  166  arranged over the fluid conduit  224  and disconnected from the substrate  164 ; and a second displacement device  240  coupled to the second fluid channel  222  and configured to displace fluid through the fluid channel  122  to transition the deformable region  166  from a retracted setting (shown in  FIG. 3A ) to an expanded setting (shown in  FIG. 3B ), the deformable region  166  elevated above the peripheral region  168  in the expanded setting. 
     Generally, in this variation, first system  100  defines a deformable region  166  over the display  330  of the computing device, wherein the deformable region  166  can be intermittently and selectively expanded to provide occasional tactile guidance over the display  330 , such as described in U.S. patent application Ser. No. 13/414,589. In one implementation, the substrate  164  and the tactile layer  162  are arranged over the heat exchange layer  120  such that thermal energy passes from the fluid into the heat exchange layer  120  and then into the substrate  164  and the tactile layer  162  before dissipating into the environment (or into a user or other surface in contact with the computing device), such as shown in  FIGS. 7A and 7B . Alternatively, the substrate  164  and the tactile layer  162  can be physically coextensive with the heat exchange layer  120 , wherein both the fluid channel  122  coupled to the internal heat sink and the second fluid channel  222  in communication with deformable region  166  are defined within the substrate  164 , such as shown in  FIGS. 3A and 3B . In this implementation, the (first) fluid channel and the second fluid channel  222  can be discrete and fluidly decoupled, the first fluid channel  122  coupled to the displacement device  140  to circulate fluid between the fluid channel  122  and the internal heatsink  110 , and the second fluid channel  222  coupled to the second displacement device  240  to communicate (a discrete volume of) fluid toward and away from the deformable region  166  to expand and retract the deformable region  166 , respectively. However, the substrate  164  and the tactile layer  162  can be arranged and/or defined within first system  100  in any other suitable way. 
     1.7 Valve 
     As shown in  FIGS. 3A and 3B , one variation of first system  100  further includes a valve  142  configured to control fluid flow through first system  100 . For example, in the implementation described above in which the heat exchange layer  120  defines two discrete fluid channel sets, the valve  142  can be arranges at a junction between the two fluid channel sets to selectively shut off flow into one or the other fluid channel set. 
     In one implementation in which the computing device includes a dynamic tactile layer  162 , as disclosed in U.S. patent application Ser. No. 13/414,589, first system  100  can include a valve  142  between a cooling portion of first system  100  and a reconfigurable button of the dynamic tactile layer  162 , as shown in  FIGS. 3A and 3B . For example, the heat exchange layer  120  can be physically coextensive with the dynamic tactile layer  162 , wherein the displacement device  140  creates a pressure differential that displaces fluid through the enclosed fluid system, and wherein a first pair of valves open at each end of a subset of fluid channels to allow fluid to pass through the subset of fluid channels over a first portion of the display  330  to dissipate heat in the fluid, and wherein one valve opens and another valve closes in a second pair of valves to enable fluid to collect in a respective subset of fluid channels, thereby outwardly deform a deformable region  166  of the dynamic tactile layer  162  fluidly coupled to the subset of fluid channels. In this example, the fluid channel  122  of first system  100  can be physically coextensive with a fluid channel of the dynamic tactile layer  162 . Furthermore, in this example, the displacement device  140  can displace fluid in the fluid system to both (e.g., simultaneously) redistribute heat through the computing device and manipulate a dynamic tactile overlay on the digital display  330 . 
     A valve  142  in the fluid system can be a bi-state valve that is either open or closed, a tri-state valve that can select between two fluid passages and close fluid flow completely between the two fluid passages, or any other suitable type of valve. However, the valve  142  can also be substantially imperfect, i.e., reducing fluid flow by less than 100% or leaking in the presence of a pressure differential across the valve  142 . In one example implementation, the heat exchange layer  120  includes a discrete front heat exchange region over the digital display  330 , bezel area, discrete side heat exchangers, and/or a discrete rear heat exchange region on the back of the computing device (opposite the digital display  330 ), each discrete heat exchange region including one or more fluid channels. For example, inlets of the front and rear heat exchange regions can be connected via an imperfect bi-state valve that, in a first position, allows 80% of fluid flow to enter the front heat exchange region and 30% to enter the rear heat exchange region when the computing device is laying face-up on a surface. Furthermore, in a second position, the imperfect bi-state valve can allow 30% of fluid flow to pass through the front heat exchange region and 80% to pass through the rear heat exchange region when the digital display  330  is experiencing solar heating during outdoor user (e.g., as determined by elevated display temperatures measured by a thermistor  180  thermally coupled to the display  330 ), as shown in  FIG. 5 . As in this example implementation, first system  100  can implement preferential (e.g., 80%) displacement of heated fluid to certain regions of the fluid system with imperfect valves and still achieve substantial cooling functionality. In particular first system  100  adequately distribute heat from the electrical component  302  to the surface of the computing device without necessitating expensive and/or large valves that are capable of withholding fluid leaks up to fractions of or more psi of fluid pressure. 
     In another implementation in which the displacement device  140  is an intermittent pump as described in U.S. Patent Application No. 61/727,083, first system  100  can include a tri-state valve or two inversely-controlled bi-state valves that oscillate between states as the displacement device  140  transitions between positive pressure and vacuum states such that fluid is drawn through the closed fluid loop in a single direction as the displacement device  140  opens and closes. However, first system  100  can include any other number of valves arranged in any other suitable way to control fluid flow through first system  100 . However, first system  100  can include any number of valves arranged in any way throughout the closed fluid loop. 
     1.8 Processor 
     As shown in  FIG. 5 , one variation of first system  100  further includes a processor  170  that controls distribution of fluid through the internal heatsink  110  and the heat exchange layer  120  to cool the electrical component  302 . Generally, the processor  170  functions to control the displacement device  140  and/or one or more valves in first system  100  based on various outputs from one or more sensors in the computing device, such as an accelerometer, a gyroscope, a light sensor or camera, a thermistor  180  or temperature sensor  180 , a specific absorption rate (SAR) sensor, a power meter, and/or a near-body proximity sensor. Sensor-based cooling architecture can thus enable direct, real-time detection of human proximity and device orientation such that the processor  170  can dynamically control various fluid valves to direct heated fluid away from portions of the computing device currently in contact with a user. The processor  170  can additionally or alternatively control components of first system  100  based on a setting (e.g., clock speed) of the computing device. The processor  170  can be a standalone controller or physically coextensive with an electrical component (e.g., CPU) within the computing device. 
     In one implementations of the displacement device  140  that actively circulates fluid through first system  100 , the displacement device  140  can be configured to operate at a constant (i.e., single) flow rate or at a variable flow rate. For example, first system  100  can include a processor  170  that collects fluid pressure data from a pressure sensor coupled to the fluid channel  122  and/or power draw data from a motor driver connected to the displacement device  140  to determine a fluid pressure within first system  100 , and the processor  170  can thus implement feedback control to adjust power to the flow rate of fluid through first system  100  accordingly by modifying an amount of power supplied to the displacement device  140 . Similarly, the processor  170  can interface with one or more thermal sensors arranged throughout the device to implement closed loop feedback to adjust a flow rate (e.g., proportional to power consumption of the displacement device  140 ) through first system  100  to achieve a target temperature at one or more locations within the computing device. For example, the processor  170  can implement proportional-integral-derivative (PID) control to adjust a flow rate through the fluid circuit based on a temperature at the electrical component  302 , a temperature gradient across the digital display  330 , and a fluid pressure within the fluid circuit. In particular, in this example, the processor  170  can control the displacement device  140  to circulate the transparent fluid  130  between the internal heatsink  110  and the fluid channel  122  at a working pressure corresponding to a measured temperature of the electrical component  302  (e.g., the integrated circuit  302 ). 
     In one implementation, the heat exchange layer  120  includes multiple discrete fluid channels (or discrete fluid channel sets), each defining a heat exchange region over the digital display  330 . For example, the viewing area of the display  330  can be rectangular, and the heat exchange layer  120  can include a heat exchange region along each short end of the viewing area defining a first fluid circuit with the internal heatsink no and the heat exchange layer  120  can include a heat exchange region along each long end of the viewing area defining a second fluid circuit with the internal heatsink  110 . The processor  170  can thus interface with an accelerometer and/or gyroscope (or other motion or position sensor) within the computing device to detect an orientation of the computing device, and when the processor  170  detects that the computing device is in a portrait orientation (shown in  FIG. 4B ), the processor  170  can set a state of one or more valves within first system  100  to close fluid flow through the second fluid circuit and to open fluid flow through the first fluid circuit, thereby limiting heat dissipation at regions over the digital display  330  likely to be in contact with the user&#39;s hand(s) in the portrait orientation. Similarly, when the processor  170  detects that the computing device is in a landscape orientation (shown in  FIG. 4A ), the processor  170  can set the state of one or more valves in first system  100  to close fluid flow through the first fluid circuit and to open fluid flow through the second fluid circuit, thereby limiting heat dissipation at regions over the digital display  330  likely to be in contact with the user&#39;s hand(s) when the computing device is in the landscape orientation. 
     Additionally or alternatively, the processor  170  can interface within one or more sensors within the computing device to determine a current orientation of the device, and the processor  170  can subsequently set the state of one or more valves with first system  100  to distribute fluid flow there through to meet a target heat flux through convection from surfaces of the computing device. For example, the processor  170  can set valve states within first system  100  to preferentially distribute fluid to substantially vertical and upward facing surfaces of the computing device, such as the front and back surfaces of the device when the device is held substantially upright and the front and sides of the devices when the device is placed face-up on a horizontal surface. In particular, in this example, first system  100  can include multiple heat exchange layers, such as over the device&#39;s digital display  330 , over a rear surface of the device, and/or over sides of the device, such as described above, all of which can be fluidly coupled to one or more electrical components within the device via an internal heatsink and a valve  142 , and the processor  170  can selectively open and close valves in first system  100  to distribute fluid throughout first system  100  according to a desired temperature distribution and/or a heat flux across surfaces of the computing device. Similarly, the processor  170  can interface with temperature sensors arranged throughout the computing device to measure and/or estimate a temperature distribution across surfaces of the device, and the processor  170  can manipulate valves and/or the displacement device  140  to distribute fluid flow through first system  100  to achieve a substantially uniform temperature (or other desired temperature gradient) across surfaces of the device. 
     The processor  170  can further interface with a touch sensor  320  within the device to detect regions on the device in contact with the user, and the processor  170  can set one or more valves within first system  100  to move heated fluid from the internal heatsink  110  through fluid channels removed from regions of contact with the user. For example, the processor  170  can interface with the touch sensor  320 , a proximity sensor, and/or any other sensor within the computing device to determine that the device is in the user&#39;s pant pocket with the display  330  facing the user&#39;s skin, and the processor  170  can thus close fluid flow to the heat exchange layer  120  over the display  330  and reroute heated from the internal heatsink  110  to the second heat exchange layer  220  arranged over the back of the computing device opposite the display  330 . In another example, the processor  170  can interface with various proximity sensors through the device to determine placement of a user&#39;s hand and/or fingers on the computing device, and the processor  170  can control one or more valves within first system  100  to route fluid flow away from the user&#39;s hand and/or fingers, thereby limiting or preventing dissipation of heat from the electrical component  302  into the user&#39;s hand and/or fingers. The processor  170  can also store and/or access a history of device orientation and proximity events and further implement machine learning to improve response to various use scenarios of the particular mobile computing device. 
     In the foregoing implementations, additional fluid channels and/or heat exchange layers can be fluidly coupled to a common internal heatsink, such as via one or more valves, and the processor  170  can manipulate a position of the one or more valves to selectively distribute fluid throughout first system  100 . Alternatively, each additional fluid channels and/or heat exchange layers can be fluidly coupled to a discrete internal heatsink and to a discrete displacement device, and the processor  170  can selectively power various displacement devices to selectively distribute fluid throughout first system  100 , such as according to any of the methods or techniques described above. In one example, the internal heatsink no is arranged on one side of the electrical component  302  and cooperates with the heat exchange layer  120  arranged over the digital display  330  and the displacement device  140  to define a first closed fluid loop, and a second internal heatsink on an opposite side of the electrical component  302  cooperates with a second heat exchange layer  220  arranged on the back surface of the computing device and a second displacement device  240  to define a second closed fluid loop, wherein the first closed fluid loop and the second closed fluid loop are discrete and separately controlled by the processor  170 . In this example, the processor  170  can independently control components of each closed fluid loop, such as based on computing device orientation or user hand placement on the computing device. However, first system  100  can include any number of internal heatsinks, heat exchange layers, sensors, valves, and/or displacement devices arranged in any other suitable way. 
     In another implementation, first system  100  includes the heat exchange layer  120  over the digital display  330 , the second heat exchange layer  220  over the back of the computing device opposite the display  330  (shown in  FIG. 5 ), and a third heat exchange region over a side of the computing device. In this implementation, the processor  170  interfaces with a thermistor  180  thermally coupled to the digital display  330  to measure a temperature increase across the digital display  330  during operation of the device. When the processor  170  identifies a display temperature that exceeds a threshold temperature, the processor  170  manipulates one or more valves within first system  100  to move heated fluid from the first heat exchange layer over the display  330  to the second heat exchange layer  220  on the back of the device where heat is dissipated to the environment to cool the display  330 . In one example, the processor  170  can thus control one or more valves within first system  100  to cool the digital display  330  during solar heating of the display  330 , such as when the computing device is used in direct sunlight. 
     In yet another implementation, the processor  170  interfaces with a thermistor  180  thermally coupled to the electrical component  302  to measure the temperature of the electrical component  302 . In one example, when the temperature of the electrical component  302  exceeds a threshold temperature, the processor  170  turns the displacement device  140  ‘ON’ to pump heated fluid from the internal heatsink no to the heat exchange layer  120 , thereby cooling the electrical component  302 . In another example, the processor  170  controls a fluid flow rate or ‘speed’ of the displacement device  140  based on the temperature of the electrical component  302 , including increasing the displacement device  140  speed in response to a higher measured temperature at the electrical component  302  and decreasing the displacement device  140  speed in response to a lower measured temperature at the electrical component  302 . In yet another example, the processor  170  dynamically and proportionally adjusts a clock speed of the electrical component  302  and the speed of the displacement device  140 , thereby increasing heat flux through first system  100  proportionally with heat output of the electrical component  302  (which may be proportional to clock speed). 
     Because power consumption of an integrated circuit  302  (e.g., processor, microcontroller, display driver) can be proportional to computing power (e.g., load, clock speed) and temperature, first system  100  can, as in the foregoing implementation, cool the integrated circuit  302  to enable increased computing power without substantially sacrificing battery life in the computing device. Additionally or alternatively, first system  100  can cool a lower-capacity (e.g., cheaper) integrated circuit  302 , thereby enabling the lower-capacity integrated circuit  302  to achieve a level computing power more comparable to a non-cooled, higher-capacity (e.g., more expensive) integrated circuit  302  without substantially sacrificing battery life of the computing device and/or a calendar life of the integrated circuit  302 . 
     Similarly, in another implementation, the processor  170  interfaces with a thermistor  180  to detect a temperature of a battery  310  arranged within the computing device. In one example, when the temperature of the battery  310  exceeds a threshold temperature, the processor  170  sets valve states and turns the displacement device  140  ‘ON’ to move fluid through an internal heatsink arranged adjacent the battery  310  to cool the battery  310 . In another example, the processor  170  controls a fluid rate or ‘speed’ of the displacement device  140  based on the temperature of the battery  310 , including increasing flow rate through the displacement device  140  in response to higher measured battery  310  temperatures and decreasing flow rate through the displacement device  140  in response to lower measured battery temperatures. Thus, in this implementation, first system  100  can increase the charge rate, discharge rate, and/or improve a performance of a battery inside the computing device in the short term and improve a calendar life of the battery  310  in the long term by actively cooling the battery  310  as described above. 
     In a further implementation, the internal heatsink  110  includes a heat exchange region arranged on, adjacent, and/or proximal an internal speaker within the computing device, and the displacement device  140  moves heated fluid form the internal speaker to the heat exchange layer  120  over the display  330  to actively cool an electromechanical driver within the speaker. For example, when a user plays music or engages in a phone call through a speaker in the computing device, the processor  170  can set a state of one or more valves within first system  100  to route fluid through a second internal heat exchanger thermally coupled to the speaker, thereby cooling the speaker. Thus, in this implementation, first system  100  can enable the speaker to output louder, less distorted sound with better frequency response by cooling the electromechanical speaker driver within the speaker. First system  100  can additionally or alternatively enable a lower-quality (e.g., cheaper) speaker to output sound comparable to sound output by a higher-quality (e.g., more expensive) speaker by actively cooling the lower-quality speaker. 
     The fluid system can also include a pressure sensor fluidly coupled to the fluid (e.g., via the fluid junction  150 ), and the processor  170  can detect a leak in the fluid system and cut power to the displacement device  140  in response to an unexpected drop in fluid pressure. The processor  170  can also issue a warning or trigger an alarm, such as a visual warning shown on the display  330  of the computing device, to inform a user of such malfunction. 
     First system  100  can further include one or more air disturbers, such as a fan or a blower, configured to actively displace air over the heat exchange layer  120  to increase a rate of heat transfer from the heat exchange layer  120 . However, the processor  170 , the valve(s)  142 , the internal heatsink  110 , the heat exchange layer  120 , the displacement device  140 , and/or the air disturber(s) can be arranged in any other way on or in a computing device and can function in any other way to actively cool one or more electrical components within the computing device. 
     2. Second System and Applications 
     As shown in  FIGS. 9A and 9B , a second system  500  for cooling an integrated circuit within a computing device includes: a substrate  510  arranged within the computing device, extending to an external housing of the computing device, and defining a closed fluid circuit including a cavity  518 , a first boustrophedonic fluid channel  511 , and a second boustrophedonic fluid channel  512 , the first boustrophedonic fluid channel  511  defined across a first region of the substrate  510  adjacent the integrated circuit, and the second boustrophedonic fluid channel  512  defined across a second region of the substrate  510  proximal a perimeter of the substrate  510 ; a volume of fluid  520  within the closed fluid circuit; a displacement device  530  including a diaphragm  532  arranged across the cavity  518  and operable between a first position and a second position, the diaphragm  532  distended into the cavity  518  in the first position and distended away from the cavity  518  in the second position; and a power supply  540  powering the displacement device  530  to oscillate the diaphragm  532  between the first position and the second position to pump the volume of fluid  520  through the closed fluid circuit. 
     Similar to first system  100  described above, second system  500  functions to cool one or more electrical components within a computing device by circulating fluid through an internal structure (i.e., the substrate  510 ) within the computing device between a region proximal the electrical component to a region near a perimeter of the internal structure and/or adjacent a housing of the computing device. In particular, second system  500  functions to redistribute heat within the computing device by circulating fluid from a fluid channel near a heat source (i.e., the integrated circuit) to a fluid channel near a heat sink (e.g., the housing of the computing device) and then back again. 
     As described above, the computing device can be a cellular phone, a smartphone, a tablet, a laptop computer, a digital watch, a PDA, a personal music player, or any other suitable type of electronic and/or computing device that includes a display and an electrical circuit that outputs heat during operation. 
     2.1 Substrate  510   
     The substrate  510  of second system  500  is arranged within the computing device, extends to an external housing of the computing device, and defines a closed fluid circuit including a cavity, a first boustrophedonic fluid channel  511 , and a second boustrophedonic fluid channel  512 . The first boustrophedonic fluid channel  511  is defined across a first region of the substrate  510  adjacent the integrated circuit, and the second boustrophedonic fluid channel  512  is defined across a second region of the substrate  510  proximal a perimeter of the substrate  510 . Generally, the substrate  510  is arranged within the computing device and defines a closed internal fluid circuit through which fluid can be pumped to redistribute thermal energy within the computing device. In particular, the substrate  510  conducts thermal energy (i.e., heat) from the integrated circuit (i.e., a heat source) into fluid within the first boustrophedonic fluid channel  511  and conducts thermal energy out of fluid within the second boustrophedonic fluid channel  512  proximal a perimeter of the substrate  510 , such as into the housing of the computing device. The substrate  510  of second system  500  can therefore define a structure similar to the internal heatsink of first system S 100  described above. 
     In one implementation, the substrate  510  defines a planar structure thermally, and a broad planar surface of the substrate  510  is thermally coupled to a printed circuit board supporting an integrated circuit within the computing device. In this implementation, the substrate  510  can define the first boustrophedonic fluid channel  511  under the integrated circuit. For example, the substrate  510  can define the first boustrophedonic fluid channel  511  adjacent and aligned with a footprint of the integrated circuit. Alternatively, the substrate  510  can define the first boustrophedonic fluid channel  511  that extends across a larger region of the planar structure, such as across a region of the planar structure adjacent multiple integrated circuits and/or other electrical components within the computing device such that fluid passing through the first boustrophedonic fluid channel  511  absorbs heat from the multiple integrated circuits and/or other electrical components before releasing this heat to a heat sink at the second boustrophedonic fluid channel  512 . 
     Yet alternatively, the substrate  510  can define a third boustrophedonic fluid channel  513  fluidly coupled to the second boustrophedonic fluid channel  512  and adjacent a second electrical component (e.g., a second integrated circuit, a battery) such that fluid passing through the third boustrophedonic fluid channel  513  absorbs heat from the second electrical component before releasing this heat through the second boustrophedonic fluid channel  512  near a perimeter of the substrate  510 . The substrate  510  can similarly define a second closed fluid loop including a third boustrophedonic fluid channel  513  fluidly adjacent a second electrical component (e.g., a second integrated circuit, a battery) and coupled to a fourth boustrophedonic fluid channel such that fluid passing through the third boustrophedonic fluid channel  513  absorbs heat from the second electrical component before releasing this heat through the fourth boustrophedonic fluid channel near a perimeter of the substrate  510 . 
     In a similar implementation, the substrate  510  can be interposed between two printed circuit boards, each printed circuit board supporting an integrated circuit. In this implementation, the first boustrophedonic fluid channel  511  can extend across a region of the substrate  510  adjacent both the integrated circuits. Alternatively, the substrate  510  can define the first boustrophedonic fluid channel  511  adjacent a first integrated circuit arranged on the first printed circuit board, and the substrate  510  can define a third boustrophedonic fluid channel  513  adjacent a second integrated circuit arranged on the second printed circuit board, wherein the third boustrophedonic fluid channel  513  is fluidly coupled to the second boustrophedonic fluid channel  512  to form the closed fluid circuit with the first boustrophedonic fluid channel  511 , or wherein the third boustrophedonic fluid channel  513  is coupled to a fourth boustrophedonic fluid channel to form a second discrete closed fluid circuit within the substrate  510 . 
     The substrate  510  therefore defines the first (heat source) boustrophedonic fluid channel adjacent an electrical component within the computing device such that heat generated at the electrical component during operation of the computing device is communicated through the substrate  510  into fluid within the first boustrophedonic fluid channel  511 . The substrate  510  therefore also defines a second (heat sink) boustrophedonic fluid channel proximal a perimeter of the substrate  510  such that heated fluid pumped into the second boustrophedonic fluid channel  512  is dumped into the outer region of the substrate  510 , into the housing, or into another perimeter structure of the computing device, thereby cooling the fluid before the fluid returns to the first boustrophedonic fluid channel  511  to absorb more heat from the electrical component. The substrate  510  can also define other heat source boustrophedonic fluid channels adjacent other electrical components and fluidly coupled to the second boustrophedonic fluid channel  512  within the closed fluid circuit, or the substrate  510  can define other heat source boustrophedonic fluid channels adjacent other electrical components and fluidly coupled to another heat sink boustrophedonic fluid channel to define a second discrete closed fluid circuit. The first boustrophedonic fluid channel  511  can also define multiple parallel discrete fluid channels across the first region of the substrate  510 , the discrete fluid channels terminating at manifolds at each end or terminating directly into the cavity  518 ; the second boustrophedonic fluid channel  512  can similarly define multiple parallel (or non-parallel) fluid channels across the second region of the substrate  510 . However, the substrate  510  can define any other number of discrete or fluidly-coupled boustrophedonic fluid channels in any other arrangement within the computing device. 
     The first boustrophedonic fluid channel  511  can define a first density of parallel oscillating sections across the first region, such as in a sinusoidal or serpentine pattern, and the second boustrophedonic fluid channel  512  can define a second density of parallel oscillating sections across the second region, wherein the second density greater than the first density. In this implementation, the cross-sectional area of the first boustrophedonic fluid channel  511  can be greater that a cross-sectional area of the second boustrophedonic fluid channel  512  such that a flow velocity through the first boustrophedonic fluid channel  511  is less than a flow velocity through the second boustrophedonic fluid channel  512 , thereby increasing a period of time during which a subvolume of fluid passes through a region of the substrate  510  adjacent the electronic component (or a substantially small footprint) and dispersing that fluid in the second boustrophedonic fluid channel  512  across a relatively large area of the substrate  510  near its perimeter. Alternatively, the first boustrophedonic fluid channel  511  can define a first cross-sectional area, and the second boustrophedonic fluid channel  512  can define a second cross-sectional area greater than the first cross-sectional area. However, the first and second (and other) boustrophedonic fluid channels can be of any other form, path, and/or cross-section and can be defined across corresponding areas of the substrate  510  of any other size or geometry. 
     The substrate  510  also defines a cavity between the first and second boustrophedonic fluid channels  511 ,  512 , as shown in  FIGS. 9A and 9B . Generally, the cavity  518  defines an interface between the diaphragm  532  of the displacement device  530  and the closed fluid circuit such that actuation of diaphragm moves fluid through the substrate  510 . In one example, the cavity  518  couples directly to one end of the first boustrophedonic fluid channel  511  and directly to one end of the second boustrophedonic fluid channel  512 , and opposite ends of the first and second boustrophedonic fluid channels  511 ,  512  connect to form the closed fluid circuit. In another example, the substrate  510  defines a supply conduit  516  and a return conduit  517  arranged between the first boustrophedonic fluid channel  511  and the second boustrophedonic fluid channel  512 , and the cavity  518  is defined between and fluidly couples to the supply conduit  516  and the return conduit  517 . 
     In one implementation in which the substrate  510  defines a planar structure (e.g., a planar sheet), the cavity  518  defines a cylindrical bore having an axis perpendicular to a broad face of the planar structure. In this example, the cavity  518  can thus be open on one side of the planar sheet, and the diaphragm  532  can be arranged across the open bore, thereby sealing the closed fluid circuit, such as shown in  FIGS. 9A and 9B . 
     In another implementation, the substrate  510  defines a supply conduit  516  and a return conduit  517 , each coupled at one end to the first boustrophedonic fluid channel  511  and at an opposite end to the second boustrophedonic fluid channel  512 . In this implementation, the substrate  510  defines the cavity  518  in the form of a cross-over pipe or cross-over via between the supply conduit  516  and the return conduit  517 , and the diaphragm  532  is arranged within the cross-over pipe or cross-over via to separate (i.e., seal) the supply conduit  516  from the return conduit  517 . However, the substrate  510  can define the cavity  518  that is of any other form or geometry or fluidly coupled in any other way to the first and second boustrophedonic fluid channels  511 ,  512 . 
     The cavity  518  can therefore fluidly couple to the first boustrophedonic fluid channel  511  at an inlet and can fluidly couple to the second boustrophedonic fluid channel  512  at an outlet. The inlet can further define an inlet vane extending toward the cavity  518 , and the outlet can define an outlet vane extending away from the cavity  518  such that fluidly is preferentially displaced from the cavity  518  into the outlet as the diaphragm  532  transitions from the second position into the first position (e.g., as the diaphragm  532  lowers into the cavity  518 ) and such that fluidly is preferentially displaced from the inlet into the cavity  518  as the diaphragm  532  transitions from the first position into the second position (e.g., as the diaphragm  532  moves out of the cavity  518 ). However, the substrate  510  can define any other passive feature—or define the inlet, outlet, first and second boustrophedonic fluid channels  511 ,  512 , or cavity of any other geometry—to induce unidirectional flow through the cavity  518  as the diaphragm  532  oscillates between the first and second positions. 
     Like the internal heatsink described above, the substrate  510  can be a metallic structure (e.g., aluminum, copper), a polymer structure, or a structure of any other suitable material. For example, the substrate  510  can include multiple layers (of the same material or dissimilar materials) stacked and bonded together to define the cavity  518  and the first and second boustrophedonic fluid channels  511 ,  512 . In this example, a first layer of the substrate  510  can be cast from urethane with the cavity  518  and the first and second boustrophedonic fluid channels  511 ,  512  formed in situ as open structures, and a second cast or extruded layer can be bonded over the first layer to close the first and second boustrophedonic fluid channels  511 ,  512 , thereby forming the substrate  510 . The cavity  518  and the first and second boustrophedonic fluid channels  511 ,  512  can alternatively be machined, stamped, or otherwise formed into one or more sublayers, which are subsequently assembled to form the substrate  510 . In a similar example, the substrate can be formed from two discrete sheets of aluminum—one or both defining open channels—that are braised together to close the open channels, thereby defining the first and second boustrophedonic fluid channels. However, the substrate  510  can be of any other thermally-conductive material manufactured in any other way to form the closed fluid loop. 
     The substrate  510  can be mounted to one or more structures within the computing device. For example, the substrate  510  can be mechanically fastened to the housing of the computing device. The substrate  510  can additionally or alternatively be bonded with thermally-conductive adhesive to the printed circuit board, to the housing, to a battery, or a back surface of display or touchscreen within the computing device. Additionally or alternatively, a portion of the substrate  510  can be arranged on and/or thermally coupled to a thermal plane within the device, or the substrate  510  can extend toward but be disconnected from the housing of the device and radiate (rather than conduct) thermal energy into the housing. However, the substrate  510  can be arranged or mounted in any other way within the computing device. 
     2.2 Volume of Fluid  520   
     The volume of fluid  520  of second system  500  is contained within the closed fluid circuit. Generally, the volume of fluid  520  functions to absorb thermal energy from a heat source within the computing device (i.e., the integrated circuit) and to discard thermal energy into another structure of the computing device (eh the housing) while circulating through the closed fluid circuit. For example, the volume of fluid  520  can be water, an alcohol, an oil (e.g., silicone oil), or a metallic fluid (e.g., Galinstan or mercury). However, the volume of fluid  520  can include any other one or more types of liquids or gases. 
     2.3 Displacement Device and Power Supply  540   
     The displacement device  530  of second system  500  includes a diaphragm arranged across the cavity  518  and operable between a first position and a second position, wherein the diaphragm  532  is distended into the cavity  518  in the first position and is distended away from the cavity  518  in the second position. Furthermore, the power supply  540  of second system  500  powers the displacement device  530  to oscillate the diaphragm  532  between the first position and the second position to pump the volume of fluid  520  through the closed fluid circuit. 
     Generally, the power supply  540  functions to supply power to the displacement device  530  to oscillate the position of the diaphragm  532  between the first and second positions, thereby varying the effective volume of the cavity  518  and pumping fluid between the first and second boustrophedonic fluid channels  511 ,  512 . In particular, during operation, fluid is (preferentially) displaced from the cavity  518  into the second boustrophedonic fluid channel  512  as the diaphragm  532  moves into the first position, and fluid is displaced from the first boustrophedonic fluid channel  511  into the cavity  518  as the diaphragm  532  moves back into the second position. The power supply  540  continues to power the displacement device  530 , thereby oscillating the diaphragm  532  back and forth between the first and second settings to induce fluid circulation within the closed fluid circuit. 
     In one implementation, the displacement device  530  includes a piezoelectric layer  534  arranged over the diaphragm  532 , and the power supply  540  oscillates a voltage potential across the piezoelectric layer  534  to pump fluid through the closed fluid circuit. For example, the power supply  540  can oscillate the voltage potential across the piezoelectric layer  534  between a low and a high voltage at a first frequency to induce a first flow rate of fluid through the closed fluid circuit, such as shown in  FIG. 11 . In this implementation, the power supply  540  can also adjust the oscillation frequency of the voltage potential across the piezoelectric layer  534  to adjust the flow rate. For example, as shown in  FIG. 9A , second system  500  can include a temperature sensor  550  (e.g., a thermistor) thermally coupled to the integrated circuit, and the power supply  540  can increase the flow rate by decreasing (or increasing) the oscillation frequency as higher temperatures are measured at the integrated circuit by the temperature sensor  550 . In this example, the power supply  540  can additionally or alternatively increase the voltage differential across the piezoelectric layer  534  to increase a magnitude of deflection of the diaphragm  532  between oscillations, thereby increasing a volume displacement per diaphragm oscillation cycle (and therefore a flow rate through the closed fluid circuit). The power supply  540  can also increase a voltage hold time across the piezoelectric layer  534  between voltage flips to similarly increase a magnitude of deflection of the diaphragm  532  between oscillations. 
     In the foregoing implementation, the piezoelectric layer  534  can be bonded over the diaphragm  532 , grown onto the diaphragm  532 , arranged between layers of the diaphragm  532 , or coupled to the diaphragm  532  in any other suitable way. 
     In another implementation, the displacement device  530  includes a rotary actuator  536 —such as an electromechanical rotary motor—coupled to the diaphragm  532  (near its center) via a bellcrank and connecting rod, as shown in  FIG. 12 . In this implementation, the power supply  540  provides power to the rotary actuator  536  to rotate the diaphragm  532 , thereby deforming the diaphragm  532  between the first and second positions. In a similarly implementation, the displacement device  530  includes a rotary actuator  536  with an output shaft coupled to a cam in contact with the (center of the) diaphragm. Thus, as the power supply  540  provides power to the rotary actuator  536 , a lobe of the cam cyclically depresses and releases the diaphragm  532  during rotation, thereby transitioning the diaphragm  532  between the first and second positions. The displacement device can alternatively include a pneumatic, hydraulic, electromagnetic, or other suitable type of actuator to drive the diaphragm between the first and second positions. 
     In the foregoing implementation and others, the displacement device can further include additional diaphragms (e.g., a second diaphragm and a third diaphragm), and the actuator within the displacement device can selectively transition the diaphragms between first and second positions to display fluid through the diaphragms (i.e., “stages”) of the displacement device (e.g., similar to a peristaltic pump). However, the displacement device  530  can include any other suitable type of actuator configured to oscillate the diaphragm  532  between the first and second positions in any other suitable way. 
     The diaphragm  532  is arranged over or within the cavity  518  and thus functions to seal the volume of fluid  520  within the closed fluid loop or to separate portions of the closed fluid loop. For example, in the implementation described above in which the cavity  518  defines a cylindrical bore with axis perpendicular to a broad face of the substrate  510 , the diaphragm  532  can include an elastomer layer bonded to the broad face of the substrate  510  around the perimeter of the diaphragm  532 . Alternatively, the diaphragm  532  can include an elastomer sheet of dimensions approximating the footprint of the substrate  510 , and the elastomer sheet can be bonded fully across the substrate  510  and thus over the diaphragm  532 . Thus, in this example, the diaphragm  532  can draw inward toward the cavity  518  during transitions into the first position, and the diaphragm  532  can draw outward from the cavity  518  during transitions into the second position. 
     In another example, in the implementation described above in which the substrate  510  defines the cavity  518  that is interposed between a supply conduit  516  and a return conduit  517 , the diaphragm  532  can be arranged within the cavity  518 , thereby fluidly isolating the supply conduit  516  from the return conduit  517 , as shown in  FIG. 11 . In this example, the diaphragm  532  can draw toward the return conduit  517  during transitions into the first position and can draw toward the supply conduit  516  during transitions into the second position. 
     The diaphragm  532  can be chemically or mechanically bonded to the substrate  510 , mechanically fastened to the substrate  510  (e.g., with machine screws), pressed into the cavity  518  with an interface fit, clamped into or over the cavity  518  (e.g., with a compression ring compressing the diaphragm  532  around a perimeter of the cavity  518 ), interposed between oversized seals or o-rings pressed into the cavity  518 , or coupled to the cavity  518  (e.g., arranged within or arranged over the cavity  518 ) in any other suitable way. The diaphragm  532  can also be of a metallic, polymer, quartz, glass, or other material or combination of materials. 
     The power supply  540  can thus include a battery, a processor, a motor driver, a switch, a transistor, a clock, and/or any other suitable electrical component specific to second system  500  or integrated into the computing device to control actuation of the displacement device  530 , such as described above. 
     However, the second system  500  can include any other suitable type of displacement device, such as described in U.S. patent application Ser. No. 14/081,519. 
     2.5 Valves 
     One variation of second system  500  includes one or more valves arranged along the closed fluid conduit to control fluid flow therethrough. 
     In one implementation, second system  500  includes a check (i.e., one-way) valve arranged between the first boustrophedonic fluid channel  511  and the second boustrophedonic fluid channel  512 , wherein the check valve functions to retard fluid flow in a first direction through the closed fluid circuit and permits fluid flow through the closed fluid circuit in a second direction opposite the first direction, as shown in FIGURE ii. Thus, as the power supply  540  actuates the displacement device  530  to oscillate the diaphragm  532 , the check valve maintains unidirectional fluid flow through the closed fluid circuit and substantially prevents reverse flow. For example, the check valve can include a ball-type check valve, a diaphragm-type check valve, or any other suitable type of check valve. The check valve can also be arranged within the first boustrophedonic fluid channel  511 , within the second boustrophedonic fluid channel  512 , at an inlet or outlet of the cavity  518 , or in any other location along the closed fluid circuit. 
     In another implementation, second system  500  includes a first valve  560  arranged between the first boustrophedonic fluid channel  511  and the cavity  518  and a second valve  561  arranged between the cavity  518  and the second boustrophedonic fluid channel  512 , as shown in  FIG. 11 . In this implementation, the first and second valves  560 ,  561  can be check valves, as described above, and oriented along the closed fluid circuit to maintain unidirectional fluid flow there through (i.e., with an outlet of the first valve  560  pointing toward an inlet of the second valve  561 ). Alternatively, the first and second valves  560 ,  561  can be actuated electromechanically, and the power supply  540  can selectively open and close the first and second valves  560 ,  561  (phased at 180°) in time (e.g., in phase) with oscillations of the diaphragm  532 . For example, the power supply  540  can control the displacement device  530  and the first and second valves  560 ,  561  such that the first valve  560  opens and the second valve  561  closes as the diaphragm  532  begins to transition from the first position to the second position (i.e., as the effective volume of the cavity  518  begins to decrease and such that the first valve  560  closes and the second valve  561  opens as the diaphragm  532  beings to transition from the second position to the first position (i.e., as the effective volume of the cavity  518  begins to increase). 
     In the foregoing implementation, the power supply  540  can also adjust the phase of actuation of the second valve  561  relative to the first valve  560  and/or phases of actuation of the first and second valves  560 ,  561  relative to actuation of the diaphragm  532 . For example, when the displacement device  530  is actuated at a first (low) frequency, the first valve  560  can begin to open and the second valve  561  can begin to close just as the diaphragm  532  reaches a “bottom dead center” in the first position. However, in this example, when the displacement device  530  is actuated at a second frequency greater than the first, the first valve  560  can begin to open and the second valve  561  can begin to before the diaphragm  532  reaches bottom dead center in the first position such that the first valve  560  is fully open and the second valve  561  is fully closed once the diaphragm  532  reaches bottom dead center and begins transition back into the second position, thereby drawing fluid from the first boustrophedonic fluid channel  511  into the cavity  518 . Specifically, in this example, the first valve  560  can be opened at a phase of ˜0° and the second valve  561  can be actuated at a phase of ˜180 at a low diaphragm oscillation frequency, and the first valve  560  can be opened at a phase of ˜−10° and the second valve  561  can be actuated at a phase of ˜170° at a high(er) diaphragm oscillation frequency. However, in this implementation, the power supply  540  can control the first and second valves  560 ,  561  and the displacement device  530  in any other suitable way. 
     In yet another implementation, the substrate  510  includes a third boustrophedonic fluid channel  513  fluidly coupled to the first and second boustrophedonic fluid channels  511 ,  512  by a controllable valve  560 , as shown in  FIGS. 10 and 13 . In one example implementation, the third boustrophedonic fluid channel  513  is arranged over a heatsink region of the substrate  510  near a perimeter of the substrate  510 , and the valve  560  includes a dual-outlet electromechanical valve with an inlet coupled to an outlet of the cavity  518 , a first outlet coupled to an inlet of the second boustrophedonic fluid channel  512 , and a second outlet coupled to an inlet of the third boustrophedonic fluid channel  513 . In this example implementation, the valve  560  can be selectively transitioned between a first state and a second state, wherein the second boustrophedonic fluid channel  512  is opened to and the third boustrophedonic fluid channel  513  is closed to the cavity  518  in the first state, and wherein the second boustrophedonic fluid channel  512  is opened to and the third boustrophedonic fluid channel  513  is closed to the cavity  518  in the second state. In this example implementation, the valve  560  can thus be actuated to selectively open and close boustrophedonic fluid channels over heatsink areas of the substrate  510  to control distribution of thermal energy from the integrated circuit into other regions of the substrate  510  and thus into various regions (e.g., surfaces) of the computing device. For example, as described above, the valve  560  can be controlled to selectively distribute fluid through portions of the closed fluid circuit based on an orientation of the computing device, such as to distribute heat from the integrated surface to a region of the substrate  510  adjacent an exterior surface of the computing device where a user&#39;s hand is expected not to be in the present orientation of the computing device. 
     In a similar example implementation, the valve  560  can be arranged within the closed fluid loop to selectively open and close the third boustrophedonic fluid channel  513  to the first and second boustrophedonic fluid channels  511 ,  512 , such as to selectively increase and decrease the length of the closed fluid loop. For example, as described above, the valve  560  can be closed to maintain fluid flow only through the first and second boustrophedonic fluid channels  511 ,  512  when the temperature of the integrated circuit is below a threshold temperature, thereby limiting a pressure required to move fluid at a particular flow rate through the closed fluid loop. In this example, the valve  560  can then be opened to permit fluid to also flow through the third boustrophedonic fluid channel  513 , thereby increasing the length of the closed fluid circuit and the cooling capacity of second system  500 , albeit at a higher required fluid pressure to maintain the particular flow rate. The valve  560  can thus be controlled based on a detected temperature of the integrated circuit. 
     The substrate  510  can additionally or alternatively define a fourth boustrophedonic fluid channel over a heat source region of the substrate  510 , such as adjacent a second integrated circuit, as described above. Second system  500  can thus also include a valve similarly controlled to control fluid flow through the fourth boustrophedonic fluid channel to control (e.g., selectively reduce) the temperature of the second integrated circuit. However, second system  500  can include any other valve passively or actively operated in any other way to control fluid flow through the closed fluid loop. 
     2.6 Second Displacement Device  580   
     As shown in  FIG. 13 , in one variation of second system  500 , the closed fluid circuit includes a second cavity  519 , a supply conduit  516  communicating fluid from the first boustrophedonic fluid channel  511  to the second boustrophedonic fluid channel  512 , and a return conduit  517  communicating fluid from the second boustrophedonic fluid channel  512  to the first boustrophedonic fluid channel  511 . The cavity  518  is defined in the substrate  510  along the supply conduit  516 , and the second cavity  519  defined in the substrate  510  along the return conduit  517 . In this variation, second system  500  also includes a second displacement device  580  including a second diaphragm  581  arranged across the second cavity  519  and operable between a first position and a second position, the second diaphragm  581  distended into the second cavity  519  in the first position and distended away from the second cavity  519  in the second position. Generally, in this variation, second system  500  includes a second displacement device  580  that cooperates within the (first) displacement device to pump fluid through closed fluid loop. For example, the power supply  540  can power the displacement device  530  and the second displacement device  580  at a phase of 180° such that the diaphragm  532  is in the first position when the second diaphragm  581  is in the second position and such that the diaphragm  532  is in the second position when the second diaphragm  581  is in the first position. However, second system  500  can include any other type and number of displacement devices arranged in any other way within the computing device to include fluid flow through the closed fluid circuit. 
     2.7 Heat Exchange Layer 
     As described above, the substrate  510  of second system  500  can incorporate similar structures and yield similar functions as the internal heatsink of first system  100  described above. One variation of second system  500  can therefore include a heat exchange layer arranged across a viewing surface of a digital display of the computing device, and the closed fluid circuit of the substrate  510  can fluidly couple to the heat exchange layer to redistribute thermal energy from the integrated circuit to an external surface of the computing device, such as over a display integrated in to the computing device. For example, as described above, the heat exchange layer can be of a transparent material and define a fluid channel extending across a portion of the digital display. In this example the fluid channel can include a fluid inlet fluidly coupled to the second boustrophedonic fluid channel  512  and a fluid outlet fluidly coupled to the first boustrophedonic fluid channel  511 . Thus fluid channel of the heat exchange layer and the cavity  518 , the first boustrophedonic fluid channel  511 , and the second boustrophedonic fluid channel  512 , etc. of the substrate  510  can thus define the closed fluid circuit. However, second system  500  can include any other suitable type or form of heat exchanger, and fluid structures within the substrate  510  can fluidly couple to any one or more heat exchanges within the device to distribute thermal energy away from the integrated circuit (and to dissipate this thermal energy to the environment). 
     As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention as defined in the following claims.