Method and apparatus for absorbing thermal energy

Abstract

The subject invention pertains to a method and apparatus for storing thermal energy. The subject thermal energy storage apparatus can function as a heat absorber in a cooling system. A cooling system can incorporate a cooling cycle that utilizes thermal energy storage and has two coolant loops. The primary cooling loop acquires the waste heat from a heat source, such as an electronic device, by heat transfer to the primary coolant via, for example, a sensible heat process (where sensible heat is heat absorbed or transmitted by a substance during a change in temperature which is not accompanied by a change of state) or by evaporating the primary coolant through a latent heat phase change process. The waste heat absorbed by the primary coolant is transferred to the host material of the heat absorber. The subject invention uses a high thermal conductivity host material to house a lower thermal conductivity phase change material, in order to achieve a thermal energy absorber that has a high effective thermal conductivity. In a specific embodiment, the high thermal conductivity host material has voids within the structure that can be filled by the phase change material. The increased surface area of phase change material in thermal contact with the host material per volume of phase change material allows the thermal energy to be stored or released quickly, because of the enhanced effective thermal conductivity.

1 . A method for absorbing thermal energy from a heat source, comprising:
 absorbing thermal energy from a heat source via a heat exchanger; so as to transfer thermal energy from the heat source to a primary coolant, wherein the heat exchanger is an evaporative heat exchanger, wherein thermal energy transferred to the primary coolant from the heat source vaporizes at least a portion of the primary coolant;   transporting the primary coolant from the heat exchanger to a heat absorber so as to transfer thermal energy from the primary coolant to the heat absorber; and   removing thermal energy from the heat absorber.   
     
     
         2 . The method according to  claim 1 , wherein dissipating thermal energy from the heat absorber comprises:
 transferring thermal energy from the heat absorber to a secondary coolant; and   removing heat from the secondary coolant.   
     
     
         3 . The method according to  claim 1 , wherein absorbing thermal energy from a heat source via heat exchanger comprises absorbing thermal energy from a heat source at a first rate of thermal energy transfer during a first period of time, wherein dissipating thermal energy from the heat absorber comprises dissipating thermal energy from the heat absorber at a second rate during a second period of time, wherein the first rate of thermal energy transfer is higher than the second rate of thermal energy transfer, and the first period of time is shorter than the second period of time. 
     
     
         4 . The method according to  claim 3 , wherein the second period of time is at least 2 times as long as the first period of time. 
     
     
         5 . The method according to  claim 3 , wherein the second period of time is at least 5 times as long as the first period of time. 
     
     
         6 . The method according to  claim 3 , wherein the second period of time is at least 10 times as long as the first period of time. 
     
     
         7 . The method according to  claim 3 , wherein the second period of time is at least 20 times as long as the first period of time. 
     
     
         8 . The method according to  claim 3 , wherein the second period of time is at least 50 times as long as the first period of time. 
     
     
         9 . The method according to  claim 3 , wherein the second period of time is at least 100 times as long as the first period of time. 
     
     
         10 . The method according to  claim 1 , wherein the heat source comprises a laser. 
     
     
         11 . The method according to  claim 1 , wherein the evaporative heat exchanger is a spray cooling heat exchanger. 
     
     
         12 . The method according to  claim 1 , wherein transporting the primary coolant from the heat exchanger to a heat absorber comprises transporting the primary coolant from the heat exchanger to a heat absorber comprising a phase change material. 
     
     
         13 . The method according to  claim 12 , wherein transfer of thermal energy from the primary coolant to the heat absorber melts at least a portion of the phase change material. 
     
     
         14 . The method according to  claim 12 , wherein the heat absorber comprises a host material having voids that are filled with the phase change material such that the phase change material is in thermal contact with the host material. 
     
     
         15 . The method according to  claim 14 , wherein the phase material comprises a paraffin. 
     
     
         16 . The method according to  claim 14 , wherein the heat absorber comprises primary coolant tubing embedded in the heat absorber, wherein the primary coolant tubing is in thermal contact with at least a portion of the host material, wherein the primary coolant travels through the primary coolant tubing, wherein thermal energy is transferred from the primary coolant to the phase change material through the primary coolant tubing. 
     
     
         17 . The method according to  claim 14 , wherein the host material has a total porosity in the range from about 0.6 to about 0.75. 
     
     
         18 . The method according to  claim 14 , wherein the host material has an open porosity in the range from about 0.8 to about 1.0. 
     
     
         19 . The method according to  claim 14 , wherein the host material has an average pore size in the range from about 300 microns to about 400 microns. 
     
     
         20 . The method according to  claim 14 , wherein the host material filled with the phase change material has an effective thermal conductivity in the range from about 100 W/m-k to about 500 W/m-k.