Abstract:
Cooling means for a heated surface comprising an enclosure for enclosing the heated surface and two oppositely charged interleaved radial arrays of microelectrodes positioned on the surface within the enclosure. The combined arrays have a closely spaced end and a periphery end. A volatile cooling liquid is contained in a reservoir within the enclosure but separate from the array. A slit-type restrictor is positioned between the reservoir and the array to restrict liquid flow from the reservoir toward the array. A portion of the closely spaced end of the array is positioned within the slit whereby the pumping action of the array draws only the amount of volatile liquid along the electrodes needed to form a thin evaporating film over the array area. The vapor from the thin film evaporator flows to a condenser where it is cooled, condensed to a liquid and returned to the liquid reservoir.

Description:
PRIORITY CLAIMED 
   Priority is claimed based on the Provisional Patent Application filed 18 Oct. 2002 bearing Ser. No. 60/419,690 titled “Thin Film Evaporators Having Splayed Electrodes” and the Provisional Patent Application filed 18 Oct. 2002 bearing Ser. No. 60/419,649 and having the title, “Thin Film Micro-Evaporators with Slit-Type Restrictor” 

   GOVERNMENT SUPPORTED RESEARCH 
   No 
   BACKGROUND 
   Integrated circuits (IC) utilize micro-components such as transistors, capacitors and resistors that use and control electrical energy, frequently in digital form for controllers and computers. Larger macro sized solid state components are employed as power controllers such as switches, rectifiers, and alternators. Neither the micro nor the macro sized components or conductors are 100 percent efficient. Especially the micro-digital assemblies used in computers convert most of the electrical energy used in their computations into heat. 
   In the early versions of these integrated circuits having relatively few components per unit area, natural convection cooling proved adequate to limit the operating temperatures to safe values. As technology allowed packing more components into an integrated package the heat generated required motor driven fans mounted directly on the integrated circuit packages, thereby providing forced convection cooling, to control the package temperature. In order to accommodate higher and higher component densities and higher operating speeds requiring more and more power, more and more vigorous efforts have been made to remove heat effectively from the integrated circuit packages to keep the operating temperatures of the integrated circuit at safe levels. 
   These include more powerful fans, specialized venturis to direct the fan output onto the external surface of the integrated circuit package at higher velocities, plastic fins molded directly into the integrated circuit package and metal fins mounted on the package with heat conducting paste to better foster heat flow from the package to the fins to the fan forced air stream. All of these heat dissipation schemes have employed macro-cooling methods to cool micro components. 
   The increases in component density and accompanying heat dissipation rates have acted to raise operating temperatures of the IC packages to such levels that, with the best heat dissipating systems, their operating life can be endangered. To cope with this problem, temperature sensing thermistors have been placed in the micro-circuits to reduce their performance and thereby their heat dissipation and temperature under high ambient conditions or when the heat dissipating mechanisms lose efficacy, as when fouled with room dust. These mechanisms keep the computer operating but at reduced capability. This may be tolerable in household computing situations, but is intolerable in military or commercial systems where human lives and great fortunes can be endangered. 
   The current invention is directed to means for sharply improving the coefficients of heat transfer between the integrated circuit package and the coolant by improving the flow rate of cooling fluid dispersed over the IC package for evaporative cooling and to means for controlling cooling flow for temperature control. 
   PRIOR ART 
   U.S. Pat. No. 6,443,704 issued 3 Sep. 2002 describes a micro-array of substantially parallel electrodes applied to a hot surface for the purpose of moving a volatile cooling fluid along the electrodes.  FIGS. 9 and 10  disclose one set of alternating electrodes formed with linearly varying width over the electrode length. The operation of the array relating to these figures is described at col. 6 lines 63–68 and col. 7 lines Ines 1–29. From the text it is clear that no slit or restrictor for restricting or limiting or controlling flow is shown or suggested. Further, Darabi not only teaches no means for allowing operation of the hot surface in horizontal or near horizontal positions but limits operation of his device to angles between vertical and 75 degrees off-vertical. (Col 6, lines 51–61) by contrast with the current invention which allows operation in any position. 
   OBJECTS AND ADVANTAGES 
   An object of the invention is to provide low cost, easily applied means for circulating, without moving parts, a volatile cooling fluid in heat transfer relation to a heated surface requiring cooling, whereby the liquid is evaporated. 
   A further object is to provide an array of interleaved micro-electrodes each having an electrical charge opposite the charge on its neighbors. 
   A further object is to position the array on the heated surface for the purpose of receiving liquid at a receiving or inlet end and moving the liquid from the receiving or inlet end over the length of the microelectrodes thereby covering the remainder of the array with a thin film of liquid, whereby the liquid in the film is evaporated over the area covered by the array, thereby cooling the heated surface. 
   A further object is to provide a reservoir of volatile liquid separate from the heated surface. 
   A further object is to provide a flow communication between the liquid reservoir and the array on the heated surface. 
   A further object is to provide that the flow communication is a slit-type flow restrictor for limiting liquid flow between the liquid reservoir and the array of microelectrodes on the heated surface. 
   A further object is to provide such a flow restrictor and array where a portion of inlet end of the array is positioned within the slit. 
   A further objective is to size the slit so that flow occurs only under the driving force of the electrically energized array partly positioned therein. 
   A further object is to position the receiving end of the array within the slit-restrictor 
   A further objective is to provide an interleaved array having parallel electrodes. 
   A further object is to provide an interleaved array having electrodes positioned in a radial pattern. 
   A further is to provide such an array having electrodes more closely spaced at the receiving or inlet end and more widely spaced at the other or periphery end. 
   A further object is to position a portion of the array having the more closely spaced electrodes within the slit-type restrictor. 
   A further object is to provide a non-alternating electrical charge having opposite polarities on adjacent electrodes. 
   A further object is to provide such means that require unusually small amounts of electrical power. 
   A further object is to provide such means employing micro-electrodes that can be applied to the heated surface itself. 
   A further object is to provide such means having radially positioned electrodes. 
   A further object is to provide such electrodes having connected ends and free ends and where the free ends have a rounded shape. 
   A further object is to provide such means having an integral condenser for rejecting heat from the vapor to a coolant thereby condensing the vapor to a liquid. 
   A further object is to provide such means that utilize fluid polarization or dielectrophoresis principles for moving the liquid coolant along the length of the electrodes. 
   A further object is to provide such means that require only direct current energization and do not require single or multi-phase alternating currents for electrode energization. 
   A further object is to provide means for sensing a condition of the assembly and for electrically adjusting the flow in response to the value of the condition to control the condition. 
   A further object is to provide such control means where the voltage across the microelectrodes is increased to increase flow to the evaporator and decreased to reduce flow to the evaporator. 
   A further object is to provide such circulating or pumping means for a fluid that evaporates on contact with the surface being cooled. 
   A further object is to provide such circulating means that includes means for applying an electric field directly to the surface being cooled, thereby improving the heat transfer coefficient between the cooling fluid and the surface. 
   A further object is to provide an active thin film evaporation and cooling process. 
   A further object is to deploy the pumping means over the surface to be cooled. 
   A further object is to provide such circulating means to a surface positioned at any angle to the horizontal. 
   A further object is to employ a closed circulating system for the fluid circulated including a condenser for removing heat from the vapor produced by the evaporating process. 
   A still further object is to employ a volatile liquid as the fluid circulated and to deploy an externally cooled condenser to condense vapor generated at the cooled surface to the liquid state for reuse at the cooled surface. 
   A further object is to provide gravity circulating means for returning the condensed vapor to the surface. 
   A further object is to employ the principle of micro-electro-mechanical systems or MEMS to achieve the above objects. 
   Other equally important objects and objectives will be noted as the detailed exposition of the construction and usage of the invention is perused in the text below. 
   ADVANTAGES 
   The evaporator of this invention provides high heat transfer coefficients through the application of thin liquid film directly to the heated surface by depositing electrodes directly to the heated surface thereby allowing the direct liquid delivery to the heat transfer surface. 
   The use of cooling by evaporation allows higher heat transfer coefficients both at the cooled surface using the electrodes of the invention and at the condenser where the heat is rejected to a cooling fluid. 
   The provision of a slit type restrictor between a liquid reservoir and the heated surface prevents an excess flow of liquid over the heated surface that can reduce the heat transfer coefficient. 
   The positioning of the inlet portion of the electrodes within the slit itself allows the slit dimensions to be small enough to ensure that flow does not occur without the electromotive action of the electrodes. 
   BRIEF SUMMARY OF THE INVENTION 
   A micro-evaporator surface having a slit-type inlet for entry of a cooling volatile liquid and an exit for discharge of vapor or a mixture of liquid and vapor. The surface has positioned thereon an array of electrodes of substantially uniform width. The array has an inlet end and an outlet end. The array and the heated surface are positioned within an enclosure. A liquid reservoir is provided with a supply of volatile liquid coolant. The reservoir is connected to the portion of the enclosure containing the array positioned on the heated surface. A restrictor in the form of a slit is positioned to provide limited flow communication between the reservoir and the heated surface bearing the array. An inlet portion of the array is positioned within the slit. Energization of the array with alternate polarity electrical charges applied to adjacent electrodes causes the inlet portion of the array to draw liquid coolant from within the slit and distribute the liquid coolant in a thin film over the area covered by the micro array, thereby providing very high heat transfer coefficients for evaporation of the liquid coolant to a vapor. Condenser means are provided to receiving the vapor, condensing the vapor to a liquid and returning the liquid to the liquid reservoir. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of a heat producing integrated circuit with its many connection points. 
       FIG. 2  is a side elevation of the device of  FIG. 1  showing a crossection of the heat producing integrated circuit assembly and the cooling device of the invention mounted in heat transfer relation to the integrated circuit assembly, with a baffle mounted to direct vapor flow. 
       FIG. 3  is a crossection of  FIG. 2  showing the relationship of the components. 
       FIG. 4  is a crossection of the cooling assembly of the invention having an integral condenser and having a flow directing baffle positioned to facilitate return flow of condensed liquid to the reservoir during operating of the device in a horizontal position. 
       FIG. 5  (Section  4 A) is a very much enlarged view of the flow restricting slit and its relation to the first end of the array. 
       FIG. 6  shows an embodiment of the invention where the condensing surface is external of the enclosure and a condition sensor is positioned to sense outlet conditions from the evaporator and is connected to affect the voltage applied to the electrodes. 
       FIG. 7  (Section  2 A— 2 A) shows the relative position of the flow restricting slit with respect to the electrodes of a radial array of microelectrodes. 
       FIG. 8  (Section  2 A— 2 A) shows the relative relationship of the slit-type restrictor to the electrodes of a parallel array of microelectrodes. 
       FIG. 9  (Section  2 C— 2 C) shows the relation of both the slit-type restrictor and the flow directing baffles with respect to an array of microelectrodes. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Technical Background 
   Fabrication: 
   While a typical fabrication sequence is described, it is not intended that the described sequence be part of the invention and that any technology that applies microelectrodes will fulfill the requirements of the invention. 
   Typical fabrication begins with wafer or substrate pre-metalization cleaning. The substrate is typically quartz but sapphire or other similar material may be employed. After cleaning, 300 Å thickness Chromium and 2500 Å thickness Platinum (1 Å=10 E−10 m) is deposited using an e-beam evaporator. A 15,000 Å thick layer of photo resist is applied over the deposited metals followed by a soft bake at 100° C. Photolithography is employed to create the desired electrode pattern followed by a hard-bake at 120° C. While ion beam-milling can be employed, a variety of other etching techniques such as wet etching and deep reactive ion etching are available. Following the micro fabrication, the packaging is performed. 
   Cooling Fluid: 
   A cooling fluid suitable for use in this invention should be volatile and have low electrical conductivity. It should be highly subject to electrical polarization. It should have a saturated pressure at 100 C not far from atmospheric pressure in order to minimize costs of manufacturing an enclosure that would have to operate at higher pressures. Such a cooling fluid is a mixture of about 50 percent each of nonafluoroisobutylether and nonafluorobutylether. This fluid is offered by 3M Company located in St. Paul Minn. (1 800 364-3577) under the trade name HFE-7100 (liquid dielectric constant k=7.4). This fluid has a typical boiling point at atmospheric pressure of 60 C (˜140 F) and a viscosity of 0.23 CPS at 23 C (73.4 F). 
   Among other useable fluids are those having low electrical conductivity and dielectric constants in the range of 2 to 100. Examples of these are deionized (DI) water (k=78.5), HFC-134a (k=9.5), L-13791 (k=7.39) and methoxynonafluorobutane (C4F90CH3). 
   Principles of Operation: 
   It is well known that thin film evaporation of a volatile liquid on a heated surface-to-be-cooled produces the highest heat transfer coefficients and therefore the most effective cooling of the surface. Therefore a basic principle of the invention is provision of means for reliably securing the desired thin film regardless of the orientation of the surface. 
   While the following principles are believed to be those responsible for the thin film distribution of the liquid over the area of the array, these principles are not the essence of the invention. It should be understood that it is the specific arrangement for metering the volatile liquid into the microelectrode array that is of the essence of the invention as described herein and as detailed in the claims. 
   The application of non-alternating direct current voltages to microelectrodes having alternate positive and negative polarities provides an electric field that causes polarization pumping of the high dielectric volatile cooling liquid along the lengths of the electrodes, thereby covering the area over which the microelectrodes extend. The microelectrodes can be parallel or positioned in a splayed or radial arrangement. The polarization effect causes the liquid to cover the microelectrode area with a film thickness of the order of a micron. It is this extremely thin liquid film that evaporates with the highest heat transfer coefficient between itself and the heated surface. 
   The thin liquid layer is delivered over the heat transfer surface covered by the electrodes using dielectrophoresis force. This force is generated through the use of non-uniform electric fields generated by the electrode arrangement. The thin liquid layer moves along the lengths of the microelectrode pairs by dielectrophoresis force action upon the liquid dipoles. The liquid dipoles can either be permanent or formed in the nonuniform electric field. 
   A second force, electrostriction force, acts on the liquid-vapor interface thereby both holding the liquid securely against and in the immediate vicinity of the electrodes and resisting the dielectrophoresis forces. It is believed that these forces acting together produce both the liquid flow and the very thin film over the microelectrode area. 
   The electrical potential needed to cause polarization of a preferred fluid depends, in part on the nature of the fluid and in part on the form and separation distance of the microelectrodes. While the breakdown potential for the vapor of the cooling fluid may be in the region of 1 kV/mm the very small electrode spacing requires an actual voltage in the range of 50 to 200 V. While a uniform, substantially non-varying DC voltage performs well, it is within the scope of this disclosure that the voltage may be caused to vary while maintaining the same relative polarity between the electrodes. The voltage variation may be in the form of an impressed sine wave, a square wave or some other format. Further, a variation having a defined frequency such as 20 Hertz (Hz) or 60 Hz or a much higher frequency such as 1000 Hz may be preferred. The voltage may also be varied in response to an external stimulus such as the outlet condition of vapor from the evaporator or the actual temperature of the surface to be cooled or the actual temperature of heat generating device itself. 
   DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1  is a front elevation of an Integrated Circuit assembly (IC) in package  20  formed in an enclosure  24  and having a multiplicity of electrically connecting pins  22  for providing power and information to the IC from a computer connected socket and for withdrawing from the IC information processed by it. In the process of performing its information or power processing function, heat is generated by the IC sealed within the enclosure  24 . It is this heat that the cooling device of the invention is intended to efficiently remove.  FIG. 1  displays sectioning lines  1 — 1  to indicate a side elevation. Since there are two embodiments of the construction, one is shown in  FIG. 2 , labeled section  1 — 1 ; the other is shown in  FIG. 4 , also labeled section  1 — 1 . While the term ‘elevation’ is employed to describe the orientation of this or other sections, the term elevation is not intended to suggest any particular physical position of the unit with respect to the horizontal. 
   Referring now to  FIG. 2 , which is section  1 — 1  of  FIG. 1 , we see the cooling system assembly  26  of the invention thermally connected to the outer hot surface  40  of the IC package  20  on the package side opposite its pins  22 . Typically the thermal connection is made by coating the surfaces to be thermally connected with a heat conducting grease and clamping or otherwise securing together (clamping means not shown) the IC  20  to be cooled and the cooling device  26 , thereby forming a mechanical and thermal interface  29 . 
   While the cooling unit  26  has a silicon substrate  28 , other materials may be employed for substrates including other ceramics and single crystal quartz. The primary substrate requirements are low electrical conductivity, rigidity and high thermal conductivity. Surface  27  of the substrate  28  of the cooling unit  26  is now the heated surface because of its thermal coupling with the IC package  20 . On heated surface  27  is positioned microelectrode array  31 . Array  31  comprises a multiplicity of substantially linear microelectrodes  42  and  44  each having an opposite electrical charge from its neighbors. While the electrodes  42 ,  44  in the electrode array are described and shown as being straight, they can also be positioned on a curved or cylindrical surface and the description should be understood to apply to each surface to which such an array could be applied whether flat, curved, cylindrical, convex or concave and whether the electrode pattern is parallel, splayed or some other pattern. The positively charged microelectrodes  44  are connected together in parallel by conductor  46  and supplied with their charge from external connector  34  connected to  46 . In like fashion the alternately positioned negatively charged microelectrodes  42  are connected together by conductor  48  that is supplied with its negative voltage by external connector  32 . The points where the external connectors traverse the enclosure  32 , of course, are sealed to prevent escape of cooling fluid or entry of contaminants. 
   An enclosure  30  is provided for containing and for channeling cooling liquid  36  over the microelectrodes. The enclosure  30  is bonded or otherwise sealed to the substrate  28 . Within enclosure  30  is positioned baffle  50  substantially coextensive with the area covered by the electrodes. While baffle  50  is shown substantially parallel with the surface  27  on which the micro electrodes are positioned, other baffle orientations are possible and one alternate orientation is shown and described in connection with  FIG. 4 . One end of the baffle is enlarged to form a planar portion  50 S one side of which is closely spaced from the surface  27  on which the microelectrodes are positioned, thereby forming a slit-like opening  52  through which there is restricted flow of volatile liquid  36 . While slit  52  is shown formed by an enlargement of baffle  50  it may be constructed in any suitable and convenient way, so long as the inlet portion of array  31  is positioned within the slit. The slit gap or distance DS of the extended baffle surface  50 S from the surface  27  of substrate  28  or microelectrode array  31  is generally between 10 and 150 microns depending on the viscosity and electrical characteristics of the liquid  36  used as volatile coolant. In the case of HFE-7100, a gap of 40 microns has been successful. 
   An essential feature of the invention shown in  FIG. 2 , but shown more clearly in  FIGS. 4 through 9 , is the positioning of gap  52  such that it overlays and includes an inlet portion of the microelectrode array  31  comprising alternating positive and negatively charged electrodes  42  and  44 . The gap must be selected by trial with the particular liquid and unit orientation employed such that the capillary forces prevent free flow of liquid through the slit  52  when there is no electrical charge applied to the microelectrodes. Then, when the proper non-alternating DC charges of opposite polarity are applied to adjacent microelectrodes, the polarization or electrophoresis forces generate the required flow by withdrawing liquid  36  from between the faces of slit  52  and distributing that liquid in a thin film over the microelectrode areas. 
   The vapor  59  resulting from the evaporation of the liquid over the microelectrode area flows from the evaporator volume  51  in a vapor stream through the baffle end clearance  54  to condensing volume  55 . There the vapor  59  is exposed to cool external surface  38  where the vapor condenses to a liquid  36 . The liquid  36  flows by gravity into reservoir  57  forming a pool of liquid  36 . The reservoir is positioned to supply liquid to slit  52  from which the liquid  36  flows into evaporator section  51  as a thin film. The flow of liquid  36  through the slit  52  is under control of the voltage applied to the alternating positive and negatively charged microelectrodes  42  and  44  ( FIG. 6 ). 
     FIG. 2  displays three section lines: Section line  2 A— 2 A, shown in  FIG. 7 , is parallel to the microelectrode surface and cuts through baffle section  50 S but not the baffle  50  itself. Section  2 C— 2 C, shown in  FIG. 9 , is parallel to the microelectrode surface but does not cut any part of the baffle  50  or  50 S. Section  2 B— 2 B, shown in  FIG. 3 , looks from the central part of  FIG. 2  toward the slit  52 . 
   Referring now to  FIG. 3  which is the section  2 B— 2 B of  FIG. 2  and may be considered either a top view or an end view, there is again shown the integrated circuit  20  unit containing heat generating IC  21  with its connection pins  22 . It is the IC that generates the heat to be removed by the device  26  of the invention. The IC is mounted on substrate  24  which presents its hot face  40  to be cooled. The cooling package  26  has its substrate  28  mounted in heat transfer relation to the hot face  40  of the IC package, thereby forming the heat exchange interface  29 . The microelectrode array  31  of the invention are mounted on substrate  28 . An enclosure  30  is provided to contain the cooling fluid. Within the container is mounted baffle  50  to guide the flow of vapor  59  from the evaporating volume  51  where it is formed, to the condensing volume  55  where it is exposed to cooled condensing surface  38  that condenses the vapor to liquid for recycling through the process. 
   Referring now to  FIG. 4 , there is shown again section  1 — 1  from  FIG. 1 . In this embodiment of the invention the IC and its face  40  to be cooled are intentionally shown in a horizontal position. In this figure the elements are substantially the same as shown in  FIG. 2  with the exception that the condenser side face of baffle  50  has been pitched at an angle  61  from the plane of the array to provide for gravity flow of liquid condensed by condensing surface  38 . In this embodiment vapor formed in evaporating volume  51  flows to condensing volume  55  where it is exposed to cool surface  38  and condenses flowing down the inclined surface  50 C of baffle or directing means  50 , back to reservoir  57 , thereby forming a pool of liquid  36  for recycling through the cooling process. 
   While the entire baffle  50  is shown pitched to provide the drainage angle, in other embodiments the baffle side  50 E facing the evaporator volume may be horizontal to provide uniform spacing from the microelectrodes and only the upper baffle surface  50 C facing the condenser volume is pitched, thereby forming a wedge-shaped baffle that is not shown. 
     FIG. 5  is a greatly enlarged section  4 A shown in  FIG. 4 . There, one end of baffle  50  is shown with its enlarged portion  50 S. The enlarged portion forms slit gap  52  having a spacing dimension from surface  27  of substrate  28  in the range of 10 to 150 microns, depending on the orientation of the structure and the nature and viscosity of the fluid. The length L of the slit is typically about 10 percent of the overall dimension of the array measured in the direction of flow. Reservoir  57  is shown partly filled with liquid  36  and, with no electrical charge applied, the meniscus  63  is positioned within the slit, indicating that, with no electrical potential applied, little to no flow occurs. The portion of the array of microelectrodes Es lies within the slit, enabling the array to pump liquid out of reservoir  57  into the evaporating zone  51  covered by the array of microelectrodes when it is electrically energized. The portion of the array laying within the slit is defined as “the inlet end,” even if that portion of the array is midway between its two ends, because that portion is the “inlet portion” that induces and meters flow to the evaporating zone. 
   Referring now to  FIG. 6 , there is shown the heat producing IC assembly  20  with an attached cooling assembly  26 R provided with remote condenser  82 . The cooling assembly  26 R has enclosure  30  and substrate  28  positioned in heat transfer relationship to the IC  20 . Positioned on surface  27  of substrate  28  is an array of microelectrodes  31  having positive connection  34  and negative connection  32 . The array  31  extends into slit-type restrictor  52  thereby enabling flow when the array  31  is energized, the slit  52  having been sized to prevent flow when not energized. Reservoir  57  is partly filled with liquid  36 , ready to be pumped to the evaporator surface covered by microelectrodes  31 . 
   The liquid delivered to heated surface  27  by the array  31  is evaporated to a vapor  59  which flows to remote condenser  82  via vapor outlet  79  and conduit  80 . Liquid  36  generated in condenser  82  by condensation of vapor  59  flows back to reservoir  57  via condenser outlet conduit  84  and liquid inlet  81 . The liquid  36  accumulates as a liquid pool in said reservoir. 
   Within vapor outlet  79  is sensor  65  having communication to power supply  67  via conduit  73 . Conduit  73  is an electrical conductor when the sensor is a temperature sensor or a capillary tube where the sensor is s pressure sensor. However, the exact ways that the sensor communicates with the power supply is not of the essence. The sensor may also be clamped or otherwise thermally or pressure connected to sense conditions of vapor  59 . Sensor  65  is a temperature sensor. In other applications sensor  65  is a superheat sensor and in still others sensor  65  is a pressure sensor. The purpose of the sensor is to supply information to electrical power supply  67  upon which power supply  67  will increase or decrease the voltage applied to connections  32  and  34  of the array  31  via its conductors  69  and  71 . 
   One objective of the sensor is to sense the presence of a greater quantity of liquid than can be evaporated by the available heat input responding thereby reducing the voltage applied to the connections  32 ,  34 . Another objective is to protect the enclosure from excessive internal pressure that can arise on failure of the condenser cooling arrangement. 
   While the feedback control for the array power supply is shown in connection with  FIG. 6 , it must be understood that the feedback arrangement to control the voltage applied to the array is applicable to all shown constructions. In this construction, the flow of liquid over the microelectrode array and therefore the cooling effect generated is totally under electrical control. Such control can provide improved performance and prevent IC damage under unexpected circumstances. 
     FIGS. 7 and 8  (both section  2 A— 2 A) are provided to illustrate that the arrangement of the microelectrodes in the array  31  used in conjunction with the slit-type restrictor of the invention can have a number or patterns.  FIG. 7  shows array  31  having a radial or splayed pattern.  FIG. 8  shows array  31  having a parallel pattern. Other configurations are possible. Examination of  FIG. 2 , the source of the section, shows that the section line traverses only portion  50 S of baffle  50 . The microelectrodes within the slit area are hidden (dashed) and designated as Es. Reservoir  57  is shown on both, positioned to supply liquid to the slit. In both the array of  FIG. 7  and the array of  FIG. 8  there is shown external voltage connections  32  and  34 ; negative connectors  48  supplying potential to microelectrodes  42  connected to connection  32  and positive connectors  46  connected to external connection  34  and supplying potential to microelectrodes  44 . 
     FIG. 9  is section  2 C— 2 C where the section line is positioned between baffle  50  and the enclosure  30 . There the liquid  36  residing within reservoir  57  can be seen along with the end of baffle  50  and the vapor flow passage  54 . 
   While all embodiments of the invention have presented the advanced flow control construction in the context of evaporator as heat receiver and condenser as heat dissipator, the essence of the invention is the ability of the advanced construction taught herein to control flow and other applications utilizing these concepts are intended to be covered and included within the thrust and spirit of the appended claims. 
   From the foregoing description, it can be seen that the present invention comprises an advanced method for cooling integrated and other compact heat producing devices by controlling flow of the cooling medium to an evaporator. It will be appreciated by those skilled in the art that changes could be made to the embodiments described in the foregoing description without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment or embodiments disclosed, but is intended to cover all modifications and elements thereof and their equivalents which are within the scope and spirit of the invention as described above and claimed.