Patent Application
20100038056
The subject invention relates to methods for cooling heat sources such as radar arrays.
A variety of heat sinks with different fin configurations are used to cool heat sources such as electronic chips. See U.S. Pat. Nos. 6,508,301 and 6,519,955 incorporated herein by this reference. The technique used for many decades to air cool one or more heat dissipating components was to place an extruded aluminum heat sink containing straight fins onto the device. In the prior art, the heat fluxes were low enough that natural convection along with the increase in surface area due to the fins sufficiently cooled the components. As the thermal challenges increased, active cooling using a fan in conjunction with the fin heat sink was needed. Additional optimizations included changing the shape of the fins to maximize the effective thermal conductance (a product of surface area and heat transfer coefficient) from the fins to the surrounding air. Fin shapes and styles such as wavy fins, convoluted fins, lanced and offset fins, and serrated fins were engineered. Although these specialized fins typically resulted in an increase air side pressure drop, the corresponding thermal conductance also increased. One of the challenges is determining the optimum fin configuration (e.g., spacing, thickness, height, and the like).
The next generation of heat sinks used high thermal conductivity inserts such as copper in the base of the heat sink. The insert more efficiently spread the heat load over the entire base and therefore lowered the effective heat flux at the fins. The current state of the art in cooling uses a combination of these techniques to maximize the effective thermal conductants at an air flow and pressure drop suitable for today's state of the art fans.
In radar arrays, cooling of the numerous transmit/receive integrated microwave modules (TRIMMs) is usually effected by mounting the side rails of the TRIMM module to a cooling manifold rib carrying a coolant in the equipment rack housing the TRIMM modules. See U.S. patent application Ser. No. 11/716,864 filed Mar. 12, 2007 incorporated herein by this reference.
In an active electronically scanned array (AESA) radar, high power, high density electronics are packed into tight arrays with extremely limited space for thermal management. For such a radar system and other new radar systems, thermal management remains a concern.
It is therefore an object of this invention to provide a new heat exchanger.
It is a further object of this invention to provide such a heat exchanger which is compact.
It is a further object of this invention to provide a high performance heat exchanger.
It is a further object of this invention to provide a heat exchanger with improved thermal performance.
It is a further object of this invention to provide such a heat exchanger with a lower power draw.
It is a further object of this invention to provide such a heat exchanger with a greater thermal conductance.
It is a further object of this invention to provide such a heat exchanger which can be manufactured at a reasonable cost.
The subject invention results from the realization that a compact, high performance heat exchanger is effected in a design where a pumped refrigerant flows in both the base and the fins of the heat sink.
This invention features a novel high performance compact heat exchanger. A base plate includes evaporator channels for cooling a heat source adjacent the base plate. A condenser is connected to the base plate and includes fins with channels therein for the coolant. A pump delivers the coolant to the evaporator channels of the base plate after passing through the fins of the condenser.
A fan may be included for moving air over the fins of the condenser. Typically, the condenser is disposed between the fan and the base plate. In one preferred embodiment, the fins of the condenser are in a spiral configuration and comprise a continuous body with an orifice therein for the coolant. In another example, the fins comprise an array of individual conduits in a spiral configuration. The evaporator channels may comprise a continuous spiral groove formed inside the base plate. The evaporator channels in the base plate may be micro-channels within the base plate.
The heat exchanger may further include a synthetic jet ejector micro-array subsystem between the base plate and the condenser and configured to move air over the fins of the condenser.
A high performance compact heat exchanger in accordance with the subject invention includes a base plate with coolant evaporator channels cooling a heat source adjacent the base plate, a condenser with fins carrying the coolant therein for condensing the same; and means for moving air over the fins. The means for moving air over the fans may include a synthetic jet ejector micro-array subsystem between the base plate and the condenser and/or a fan disposed on the condenser.
The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
Condenser 30,
The result is an integrated pumped liquid refrigerant loop in both the base and the fins of the heat sink. The internal refrigerant loop enables complete optimization of the assembly as a whole. With a standard heat sink, the shape of the fins and the amount of the surface area provided by the fins is driven by the fin efficiency and the associated pressure loss at a particular flow rate. With forced convection cooling over the fins, the efficiency decreases as the air flow rate (and air velocity) over the fins is increased. Circulating a refrigerant within the heat sink in accordance with the subject invention takes advantage of the latent heat of vaporization of the refrigerant and results in an almost perfect (isothermal) heat sink from the entire base to the tips of all the fins. The fin efficiency for this design approaches unity since the temperature variation from the base to the tip of the fins is negligible. Pump 40 actively circulates the refrigerant inside the fins and it overcomes the inefficiencies seen in other heat sinks associated with conduction. The result is that the fins can be shaped so that they maximize thermal conductance on the air side of the heat sink using the most surface area and convection enhancements as possible while maintaining a fin efficiency approaching 100%. This new design results in a thermal conductance that is estimated to be approximately four times higher than that seen in the current state of the art designs and requires less than half of the power draw as well. The design includes a tremendous amount of surface area on both the internal refrigerant side and the external air side while maintaining the pressure drop on both sides to reasonable levels. One way this is accomplished is with the spiral-like shape of condenser 30 in combination with the low profile high efficiency evaporator base plate 20. This combination of attributes allows for the optimum design possible for any given set of parameters. The evaporator base plate 20, condenser 30, and pump 40 as well as optional fan 50 comprise an integral assembly minimizing the required volume, weight, and power draw, while maximizing the thermal performance using the standard refrigerant evaporation-condensation cycle. The power draw can further be reduced by incorporating a feed-back circuit which senses the internal pressure (which corresponds to the saturation temperature) and varies the speed of fan 50 accordingly.
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The result in any embodiment is a novel closed loop refrigerant cycle where coolant flows in both the base plate and the fins of the heat sink. Such a heat exchanger can be made very compact (e.g., 4″ wide by 4″ long by 1″ to 4″ tall depending on whether a fan is used). The novel heat exchanger of the subject invention can be used in conjunction with radar arrays and also in connection with other heat sources including electronic components and assemblies of any configuration. The result is a high performance heat exchanger with improved thermal performance and a lower power draw. The cooling channels in the evaporator base plate, the cooling channels in the fins of the condenser and the air side surface of the fins of the condenser might also include heat transfer enhancement features such as vortex winglets, fins or other means of disrupting the fluid boundary layer and/or increasing heat transfer surface area.
Although specific features of the invention are shown in some drawings and not in others, however, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
Other embodiments will occur to those skilled in the art and are within the following claims.
