Heat transfer utilizing vascular composites and field induced forces

A system includes a matrix material to remove heat from an object. The matrix material includes a plurality of vascular structures. Each of the vascular structures are filled with a fluid. At least one transducer generates field-induced forces into the fluid within the vascular structures of the matrix material. At least one controller pulses the transducer to generate the field-induced forces into the fluid within the vascular structures. The field-induced forces generate fluid flow within the vascular structures to remove the heat from the object.

TECHNICAL FIELD

This disclosure relates to heat transfer systems, and more particularly to a matrix material embedded with fluid filled channels that are excited via field induced forces to remove heat from an object.

BACKGROUND

Heat transfer relates to the exchange of thermal energy between physical systems. The rate of heat transfer is dependent on the temperatures of the systems and the properties of the intervening medium through which the heat is transferred. The direction of heat transfer is from a region of high temperature to another region of lower temperature, where heat transfer changes the internal energy of the systems from which and to which the energy is transferred. Thermal equilibrium is reached when all involved bodies and the surroundings reach the same temperature. Heat transfer systems have many applications with respect cooling vehicles such as aircraft or land vehicles. In one specific example, it is desirable for aircraft systems to be able to reduce the respective infrared (IR) heat signature and to therefore increase the stealth of the system. Current aircraft do not have an IR signature management system. Traditional heat dissipation techniques involve the use of pumps which have high maintenance requirements. These technologies are difficult to impossible to retrofit onto existing aircraft as they require modification of the airframe itself (e.g., cutting holes into the aircraft skin). Furthermore, in order to place a cooling pump or other heat transfer device on/in the aircraft, some other subsystem must be removed because there is no available usable space within modern aircraft. Thus, any new modification to the system must be certified which is costly and may take years.

SUMMARY

This disclosure relates to a matrix material that includes fluid-filled vascular structures that are excited via field induced forces to remove heat from a structure. In one aspect, a system includes a matrix material to remove heat from an object. The matrix material includes a plurality of vascular structures. Each of the vascular structures are filled with a fluid. At least one transducer generates field-induced forces into the fluid within the vascular structures of the matrix material. At least one controller pulses the transducer to generate the field-induced forces into the fluid within the vascular structures. The field-induced forces generate fluid flow within the vascular structures to remove the heat from the object.

In another aspect, an apparatus includes a matrix material to remove heat from an object. A plurality of vascular structures are embedded in the matrix material. Each of the vascular structures are filled with a fluid. A plurality of particles with higher heat capacity than the fluid are embedded in the fluid to facilitate the removal of heat from the object based on movement of the particles. The movement of particles within the fluid are in response to field-induced forces applied to the vascular structures.

In yet another aspect, a method includes pulsing at least one transducer to generate field-induced forces into vascular structures of a matrix material. The method includes moving a fluid within the vascular structures in response to the field-induced forces. The method includes applying the matrix material to an object. The method includes removing heat from the object based on movement of the particles within the vascular structures of the matrix material in response to the field-induced forces.

DETAILED DESCRIPTION

This disclosure relates to a matrix material that includes fluid-filled vascular structures that are excited via field-induced forces to remove heat from an object. A system and method facilitate transferring heat from an area of high heat on an object (e.g., air or land vehicle) to a cool surface of the object utilizing a vascular composite material to remove heat from the object. Such material can also be referred to as a matrix material that can include embedded transducers that spans the hot and cold areas of the respective object. The transducers apply field-induced forces to the material to move fluids within the material to cause heat convection flow from the object. The matrix material can include embedded channels filled with fluid and particles to facilitate heat removal from the object. The matrix material can have a series of ultrasonic transducers and a controller attached to it to circulate fluids and particles within the respective channels to facilitate convection flow. The fields induced by the transducers apply a force on the particles within the channels to circulate both fluids and particles through a respective channel. If the channel is circular for example, the transducers can circulate fluids within a vascular composite structure of the material to cool and redistribute cooling fluids on a given surface of the vehicle. The matrix material and system can support many heat removal applications such as for aircraft skin cooling, for example. By reducing the heat on the respective aircraft, its respective heat signature can be reduced thus increasing the overall stealth of the aircraft. The convection flow provided can be sufficient to reduce the overall infrared (IR) signature of the aircraft, thus making it difficult to detect with Infrared search and track (IRST) sensors. The ability to be stealthy in IR can support intelligence gathering for airborne and space vehicles, for example. Moreover, the matrix material and system can be installed as an aftermarket addition with little alteration to the original vehicle which mitigates costly retesting and recertification of the original vehicle after installation.

FIG. 1illustrates an example of a system100that employs a matrix material110to remove heat from an object. The matrix material110includes a plurality of vascular structures shown as VS1though VS M, with M being a positive integer. Each of the vascular structures in the matrix material110are filled with a fluid. At least one transducer, shown as transducer1though N, with N being a positive integer, injects field-induced forces into the fluid within the vascular structures of the matrix material110. At least one controller120pulses the transducers1-N to generate the field-induced forces into the fluid within the vascular structures VS1though VS M. The field-induced forces move the fluid within the vascular structures in the matrix material110to remove heat from the object. In this system example, the object is not shown, however the matrix material110can be applied to the object (e.g., as an overly material on the object) to remove heat from the object as the fluid is moved in the vascular structures in response to the field-induced forces

In one example, the controller120can operate in open-loop mode and apply a predetermined pattern of pulses to the transducer1-N to generate the field-induced forces. The pulses include a pulse frequency and a pulse duty cycle. As used herein, the pulse frequency refers to the number of times a pulse is repeated over a given time period whereas duty cycle refers to the amount of on time with respect to off time of the respective pulse from the controller120. A subset of transducers may be pulsed on at a given frequency and duty cycle whereas another subset may be pulsed off during the on time pulsing of the other subset. The controller120can operate from a memory (not shown) (e.g., memory or register circuit of CMOS transistor devices) to generate the pulses described herein. The controller120can include a processor (e.g., processor circuit, application specific integrated circuit ASIC)) executes instructions (e.g., logic configured in memory, gate array, or registers) from the memory. The processor140can be a central processing unit (CPU), field programmable gate array (FPGA), ASIC, or a set of logic circuits that can be defined via a hardware description language such as VHDL. The instructions can be executed out of firmware, random access memory, and/or executed as configured logic circuits such as via registers, flip/flops, and/or state machines configured in a gate array, for example.

In another example, the controller120can operate in closed-loop mode where it receives temperature feedback130from the object to control a pulse frequency or a pulse duty cycle applied to the transducer1-N. The pulse frequency can be varied in frequency based on a given size of the vascular structures. For example, if the vascular structures VS1though VS M are in the 1 to 10 micron diameter, the respective excitation frequencies applied to the structures can be in the megahertz range. For smaller diameter structures (e.g., carbon nano tubes), higher frequencies can be applied and for larger diameter structures (e.g., several microns), lower frequencies can be applied (e.g., kilohertz range).

The objects described herein can be a vehicle in one example that includes at least one of an aircraft or a land vehicle, where the matrix material110is applied to a portion of the vehicle to remove heat from the vehicle. In another example, the object can be an interior structure such as a printed circuit board (PCB) where the matrix material wraps or is applied to the PCB to remove heat therefrom. In yet another example, the object can be a device such as an infrared camera where the matrix material is applied to all or portions of the camera to remove heat therefrom. Such cameras can be deployed on other objects such as aircraft to gather data during a given aircraft mission. By cooling the camera (or other sensor/device) in this manner, the performance of the camera is maintained versus traditional cooling methods but in a smaller SWAP (size weight and power) form factor.

The vascular structures VS1though VS M can be cylindrical (e.g., tubes) or cubic structures that are filled with the fluid. For example, the vascular structures VS1though VS M can be circular tubes or linear ducts that are filled with the fluid (See e.g.,FIG. 2). The fluid in the vascular structures can be at least one of deionized water, Anhydrous Ammonia, Propylene, Betaine, Ethylene Glycol, Diethylene Glycol, Propylene Glycol, Liquid Nitrogen, Liquid Oxygen and Freon, for example. To increase the heat removal efficiency of the fluid, particles can be embedded within the fluid. The embedded particles can include at least one of aluminum and copper, for example. The matrix material110can be fabricated from at least one of a carbon, an epoxy, and a polymer, for example.

The transducers1-N can generate acoustic energy (e.g., speaker below about 20 khz), ultrasonic energy (e.g., speaker above 20 khz), or generate electromagnetic energy (e.g., magnetic forces) to inject the field-induced forces into the fluid within the vascular structures of the matrix material110. The application of field-induced forces to initiate particle movement within the vascular structures VS1through VS M is based on a principle that a particle placed in a medium having a different impedance from itself will experience forces if a wave is set up in that medium. Such waves can be generated as standing waves within the vascular structures. A collection of particles can self-assemble into a shape governed by the geometry of the field applied to the vascular structures. Therefore, the placement of the accumulated particles (e.g., the shape of the structure being formed) can be tailored by externally controlling the field via the transducers1-N. Thus, no physical contact with the particles themselves is necessary to cause particle movement within the vascular structures. Particle-particle forces also play a role in successful shape formation. For particles that are small relative to the wavelength of the applied standing wave, the inter-particle forces can be derived from dipole-dipole interactions and thus have regions of both attraction and repulsion.

A particle having an impedance different from that of its host medium will experience forces from a wave setup in that medium, owing to gradients in energy density. That behavior can be understood by treating such particles as radiating dipoles and monopoles or a combination thereof. A small dielectric particle can be polarized if placed in an alternating electric field, such as that in a standing electromagnetic wave. If that particle is about one order of magnitude smaller than the wavelength (electrostatic limit, ∇×E=0, where ∇ is the del operator and E is the electric field), then the polarized dielectric can be represented as an equivalent electric dipole. Analogously, a small particle that is denser than its host medium can radiate as an acoustic dipole in the presence of an acoustic wave. As long as the size criterion is met, ka<<1, where k is the wave number and a is the particle diameter, the behavior of a single particle in a standing-wave field—whether acoustic or electromagnetic—is then described by treating the particle as an equivalent dipole. In acoustic fields, small particles may also radiate monopole fields in proportion to the contrast in compressibility between the particles and their host fluid medium. The expressions governing the force onto a single particle can be unified in both an acoustic and an electromagnetic field through a generalization of the variables.

When multiple particles are present, the interactions that are considered include not only the interaction of the dipole (e.g., polarized dielectric in electric fields and acoustic dipoles in alternating pressure fields) with the field, but also its interaction with the other particles through dipole-dipole interactions. Treating the particles and their response to the external field and to each other through dipole interactions reduces the problem to an analytical one, where a potential field is defined to represent the standing acoustic or electromagnetic wave, and acoustic or electromagnetic dipoles are used to represent the particles.

FIG. 2illustrates examples of vascular structures that can be embedded within a matrix material. In one example, a circular tube200can be provided as the vascular structures described herein. The tube200can be fluid filled and can have embedded particles in the fluid. When the field-induced forces are applied to the tube200, the particles move in a circular pattern around the tube. As the particles move, heat is transferred away from a given surface of an object that are in contact with the tube200. As used herein, the term tube can include cylindrical three-dimensional structures in one example. In another example, rather than a cylindrical shape, the tube200can include a cubic shape where a rectangular three-dimensional structure is provided in place of the cylindrical structure. Other examples include polygon structures such as pentagon, hexagon, and octagon structures.

In another example a tube210can include a linear tube that does not wrap around on itself like the tube200. In the linear example (e.g., linear duct), particles may accumulate at one end or another of the tube210. In such cases, excitation frequencies and patterns applied to the transducers may have to be alternated to cause a change in direction of the particles from one end of the tube210to another. In some cases, transducer pulse pattern alteration can be based on feedback received by the controller described above. For example, if temperature feedback indicates and increase in temperature, the controller can change its pulse pattern to the transducers to cause particles to flow in the opposite direction of the tube210. In yet another example, pulse patterns to the transducers can be alternated at a predetermined interval (e.g., every second change pattern to cause particles to migrate in the opposite direction).

FIG. 3illustrates an example of a controller and transducer configuration to cause particle movement within a vascular structure over different time periods. At a given time period shown as time step1, transducers T1through T5are excited by a controller310. It is noted that more or less than five transducers can be employed than shown in this example. In this example, transducers T1, T3, and T5are excited and transducers T2and T4are not excited to begin particle movement shown at320. In another excitation period shown as time step2, transducers T2and T4are excited while transducers T1, T2, and T3are turned off to cause particle movement shown at330. Substantially any excitation pattern can be applied. For instance, transducers could be turned on in pairs T1/T2on and T3/T4off during one time period where each pair is in turn alternated on and off in subsequent time periods.

If nine transducers were employed, transducers subsets of three could be alternatively turned on and off to cause particle movement in a given direction. In addition to controlling on and off times of the respective transducers, duty cycles can be controlled where instead of 50% on and 50% off times are employed, more or less on versus on time can be provided. For example, a first transducer subset may be turned on for 25% of a given time period and a second transducer subset may be turned on for 75% of the given time period. Also, the frequency of the alternating patterns can be changed in addition to individual excitation frequencies applied to each transducer that can be collectively and/or individually adjusted.

FIG. 4is an example of a matrix material being applied to an aircraft to remove heat from the aircraft. The matrix material can cover an entire object, cover a single portion of the object, or can be employed as separate materials and systems to affect heat removal from selected portions of the object. When multiple matrix material applications are applied to a given object, each application can have its own controller and transducer subset as described herein to control heat removal. In this example, a conventional aircraft400is shown that does not have the matrix material and control system described herein to remove heat from the aircraft. At410, an IR sensor output graph is shown that describes the respective heat signature for the aircraft. An IR sensor (not shown) can be pointed at the aircraft to detect the respective heat signature and generate the graph410.

An aircraft420includes a matrix material430and transducer/control system (not shown) to remove heat from the aircraft. An IR Sensor graph440shows a reduced heat signature for the aircraft420when utilizing the matrix material430. As noted previously, the matrix material430can be applied to any system or subsystem to remove heat. These can include land vehicles, isolated power systems, modules, and so forth where the matrix material430can be applied to remove heat. As will be shown with respect toFIG. 5below, more than one section of the aircraft can have matrix material and associated transducer/controller subsystems to remove heat from different portions of the aircraft.

FIG. 5illustrates an example of an aircraft500that employs multiple matrix materials and excitation components to remove heat from the aircraft. In this example, two matrix material overlays are installed at510and520. In other object examples, more than two areas of the object can have respective matrix material applications to remove heat from selected portions of the object. Each of the overlays510and520can be formed to fit a general area on the aircraft500to remove heat from the aircraft. The overlays510and520can include vascular structures that are filled with fluids having particles embedded therein. Each overlay510can520can be excited via a transducer set shown at530and540respectively. The transducer set at530can be controlled via controller550and the transducer set540can be controlled via controller560. In another example, a single controller could control all the transducers in the sets530and540. A single controller example is shown inFIG. 6controlling more transducers than shown inFIG. 5.

FIG. 6illustrates an example of a matrix material600that employs multiple vascular channels to facilitate heat flow from the material. In this example, four vascular channels are shown at610though640. Each channel610-640can be filled with fluids and particles as previously described which are excited via the filed-induced forces described herein. Although four channels (also referred to as vascular structures) are shown, more or less than four channels can be provided within the confines of a given matrix material600. A plurality of transducers such as shown at650can be provided to direct field-induced forces at the channels610-640. In this example, a single controller660is provided however as mentioned previously, multiple controllers can be provided which can control multiple transducer subsets to remove heat from all or portions of a given object.

In view of the foregoing structural and functional features described above, an example method will be better appreciated with reference toFIG. 7. While, for purposes of simplicity of explanation, the method is shown and described as executing serially, it is to be understood and appreciated that the method is not limited by the illustrated order, as parts of the method could occur in different orders and/or concurrently from that shown and described herein. Such method can be executed by various components configured in an IC or a controller, for example.

FIG. 7illustrates an example of a method700to remove heat from an object. At710, the method700includes pulsing at least one transducer to generate field-induced forces into vascular structures of a matrix material (e.g., via controller120ofFIG. 1). At720, the method700includes moving a fluid within the vascular structures in response to the field-induced forces (e.g., via the transducers1though N ofFIG. 1). At730, the method700includes applying the matrix material to an object. At740, the method700includes removing heat from the object based on movement of the particles within the vascular structures of the matrix material in response to the field-induced forces. Although not shown, the method700can also include applying a predetermined pattern of pulses to the transducer(s) to generate the field-induced forces. The pulses can include a pulse frequency and a pulse duty cycle. The method700can also include receiving temperature feedback from the object to control a pulse frequency or a pulse duty cycle applied to the at least one transducer. The pulse frequency can be varied in frequency based on a given size (e.g., diameter) of the vascular structures.