Patent Application
20070119568
This invention relates generally to the field of cooling systems and, more particularly, to a system and method for enhanced boiling heat transfer using pin fins.
A variety of different types of structures can generate heat or thermal energy in operation. To prevent such structures from over heating, a variety of different types of cooling systems may be utilized to dissipate the thermal energy. To facilitate the dissipation of such thermal energy in such cooling systems, a variety of different types of coolants may be utilized.
According to one embodiment of the invention, a cooling system for a heat-generating structure comprises a channel having an inlet and an exit and a plurality of pin fins extending at least partially across the channel. The inlet is operable to receive a fluid coolant into the channel substantially in the form of a liquid. The exit is operable to dispense of the fluid coolant out of the channel at least partially in the form of a vapor. The plurality of pin fins are operable to receive thermal energy from the heat generating structure and transfer at least a portion of the thermal energy to the fluid coolant. The thermal energy from the heat-generating structure causes at least a portion of the fluid coolant substantially in the form of a liquid to boil and vaporize in the channel upon contact with the plurality of pin fins.
Certain embodiments of the invention may provide numerous technical advantages. For example, a technical advantage of one embodiment may include the capability to enhance heat transfer in a cross-flowing coolant stream. Other technical advantages of other embodiments may include the capability to utilize pin fin configurations to alter the heat transfer phenomenology and thereby enhance heat transfer.
Although specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.
For a more complete understanding of example embodiments of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
It should be understood at the outset that although example embodiments of the present invention are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or in existence. The present invention should in no way be limited to the example embodiments, drawings, and techniques illustrated below, including the embodiments and implementation illustrated and described herein. Additionally, the drawings are not necessarily drawn to scale.
In the transfer of a heat or thermal energy from a structure to a cross-flowing coolant stream, conventional heat transfer configurations utilize straight or wavy fin stock to enhance heat transfer. To further enhance heat transfer, such cross-flowing coolant streams can be replaced with either jet impingement or spray cooling. Although jet impingement and spray cooling offer improved performance, they are more complex and may not be able to be used due to packaging limitations. Accordingly, teaching of some embodiments of the invention recognize pin fins configurations that can be utilized in cross-flowing coolant streams to alter the heat transfer phenomenology and thereby enhance heat transfer.
The cooling system 10 of
The structure 12 may be arranged and designed to conduct heat or thermal energy to the channels 23, 24. To receive this thermal energy or heat, the channels 23, 24 may be disposed on an edge of the structure 12 or may extend through portions of the structure 12, for example, through a thermal plane of structure 12. In particular embodiments, the channels 23, 24 may extend up to the components of the structure 12, directly receiving thermal energy from the components. Although two channels 23, 24 are shown in the cooling system 10 of
In operation, a fluid coolant flows through each of the channels 23, 24. As discussed later, this fluid coolant may be a two-phase fluid coolant, which enters inlet conduits 25 of channels 23, 24 in liquid form. Absorption of heat from the structure 12 causes part or all of the liquid coolant to boil and vaporize such that some or all of the fluid coolant leaves the exit conduits 27 of channels 23, 24 in a vapor phase. To facilitate such absorption or transfer of thermal energy, the channels 23, 24 may be lined with pin fins or other similar devices which, among other things, increase surface contact between the fluid coolant and walls of the channels 23, 24. Further details of the pin fin embodiments are described below with reference to
The fluid coolant departs the exit conduits 27 and flows through the condenser heat exchanger 41, the expansion reservoir 42, a pump 46, and a respective one of two orifices 47 and 48, in order to again to reach the inlet conduits 25 of the channels 23, 24. The pump 46 may cause the fluid coolant to circulate around the loop shown in
The orifices 47 and 48 in particular embodiments may facilitate proper partitioning of the fluid coolant among the respective channels 23, 24, and may also help to create a large pressure drop between the output of the pump 46 and the channels 23, 24 in which the fluid coolant vaporizes. The orifices 47 and 48 may have the same size, or may have different sizes in order to partition the coolant in a proportional manner which facilitates a desired cooling profile.
A flow 56 of fluid (either gas or liquid) may be forced to flow through the condenser heat exchanger 41, for example by a fan (not shown) or other suitable device. In particular embodiments, the flow 56 of fluid may be ambient fluid. The condenser heat exchanger 41 transfers heat from the fluid coolant to the flow 56 of ambient fluid, thereby causing any portion of the fluid coolant which is in the vapor phase to condense back into a liquid phase. In particular embodiments, a liquid bypass 49 may be provided for liquid fluid coolant that either may have exited the channels 23, 24 or that may have condensed from vapor fluid coolant during travel to the condenser heat exchanger 41.
The liquid fluid coolant exiting the condenser heat exchanger 41 may be supplied to the expansion reservoir 42. Since fluids typically take up more volume in their vapor phase than in their liquid phase, the expansion reservoir 42 may be provided in order to take up the volume of liquid fluid coolant that is displaced when some or all of the coolant in the system changes from its liquid phase to its vapor phase. The amount of the fluid coolant which is in its vapor phase can vary over time, due in part to the fact that the amount of heat or thermal energy being produced by the structure 12 will vary over time, as the structure 12 system operates in various operational modes.
Turning now in more detail to the fluid coolant, one highly efficient technique for removing heat from a surface is to boil and vaporize a liquid which is in contact with a surface. As the liquid vaporizes in this process, it inherently absorbs heat to effectuate such vaporization. The amount of heat that can be absorbed per unit volume of a liquid is commonly known as the latent heat of vaporization of the liquid. The higher the latent heat of vaporization, the larger the amount of heat that can be absorbed per unit volume of liquid being vaporized.
The fluid coolant used in the embodiment of
Water boils at a temperature of approximately 100° C. at an atmospheric pressure of 14.7 pounds per square inch absolute (psia). In particular embodiments, the fluid coolant's boiling temperature may be reduced to between 55-65° C. by subjecting the fluid coolant to a subambient pressure of about 2-3 psia. Thus, in the cooling system 10 of
In particular embodiments, the fluid coolant flowing from the pump 46 to the orifices 47 and 48 may have a temperature of approximately 55° C. to 65° C. and a pressure of approximately 12 psia as referenced above. After passing through the orifices 47 and 48, the fluid coolant may still have a temperature of approximately 55° C. to 65° C., but may also have a lower pressure in the range about 2 psia to 3 psia. Due to this reduced pressure, some or all of the fluid coolant will boil or vaporize as it passes through and absorbs heat from the channels 23 and 24.
After exiting the exits ports 27 of the channels 23, 24, the subambient coolant vapor travels to the condenser heat exchanger 41 where heat or thermal energy can be transferred from the subambient fluid coolant to the flow 56 of fluid. The flow 56 of fluid in particular embodiments may have a temperature of less than 50° C. In other embodiments, the flow 56 may have a temperature of less than 40° C. As heat is removed from the fluid coolant, any portion of the fluid which is in its vapor phase will condense such that substantially all of the fluid coolant will be in liquid form when it exits the condenser heat exchanger 41. At this point, the fluid coolant may have a temperature of approximately 55° C. to 65° C. and a subambient pressure of approximately 2 psia to 3 psia. The fluid coolant may then flow to pump 46, which in particular embodiments 46 may increase the pressure of the fluid coolant to a value in the range of approximately 12 psia, as mentioned earlier. Prior to the pump 46, there may be a fluid connection to an expansion reservoir 42 which, when used in conjunction with the pressure controller 51, can control the pressure within the cooling loop.
It will be noted that the embodiment of
Although components of one embodiment of a cooling system 10 have been shown in
As briefly referenced above, teachings of some embodiments of the invention recognize that pin fins configurations, such as pin fin configurations 110A, 110B, can be utilized in cross-flowing coolant streams to alter the heat transfer phenomenology and thereby enhance heat transfer. By using pin fin configuration 110A, 110B, the cross flowing coolant creates jet-impingement-like flows of coolant that impact the surfaces of the plurality of pin fins 113, 115. As vapor is produced in the transfer of heat to the fluid coolant, the velocity of the coolant increases, which further increases the impacting velocity of the cross flowing coolant on the pin fins 113, 115. The effusing vapor also causes a near chaotic flow of vapor with embedded liquid coolant that impacts the pins fins 113, 115. That is, a situation is created where globs of liquid coolant (e.g., formed from the vaporization of other liquid coolant) are thrown against downstream pin fins 113, 115—creating a spray cooling-like quality. Accordingly, the pin fin configurations 110A, 110B allow a cross flowing coolant to be used while taking advantage of the attributes of jet impingement and spray cooling, which are provided by the chaotic cross flowing liquid impacting the pins.
The pin fins 113, 115 may be made of a variety of materials and may take on a variety of sizes and shapes. In this embodiment, the pin fins are made of a nickel plated copper and vary in size from 0.04 inches high to 0.1675 inches high. The pin fins 113, 115 are shown with a columnar shape. In other embodiments, the pin fins 113 may be made of other materials, may have heights less than 0.04 inches, may have heights greater than 0.1675 inches, and may have shapes other than columnar shapes. Additionally, in other embodiments the pin fins 113, 115 may be arranged in configurations other than inline or staggered configurations.
Although the present invention has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformation, and modifications as they fall within the scope of the appended claims.
