Optimization of Heat Sinks with Flow Bypass Using Entropy Generation Minimization

Mechanical Engineering;Heat Sinks;Optimization;Flow Bypass;Pressure Drop;Heat Transfer;Electronic Packages;Entropy Generation Minimization

Hossain, Md Rakib

University of Waterloo

关键词: Mechanical Engineering;    Heat Sinks;    Optimization;    Flow Bypass;    Pressure Drop;    Heat Transfer;    Electronic Packages;    Entropy Generation Minimization;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/896/1/mrhossai2006.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Forced air cooling of electronic packages is enhanced through the use of extendedsurfaces or heat sinks that reduce boundary resistance allowing heat generating devices to operate at lower temperatures, thereby improving reliability. Unfortunately, the clearance zones or bypass regions surrounding the heat sink,channel some of the cooling air mass away from the heat sink,making it difficult to accurately estimate thermal performance.The design of an ;;optimized;; heat sink requires a completeknowledge of all thermal resistances between the heat source andthe ambient air, therefore, it is imperative that the boundaryresistance is properly characterized, since it is typically thecontrolling resistance in the path. Existing models are difficultto incorporate into optimization routines because they do notprovide a means of predicting flow bypass based on information athand, such as heat sink geometry or approach velocity.

A procedure is presented that allows the simultaneous optimizationof heat sink design parameters based on a minimization of theentropy generation associated with thermal resistance and fluidpressure drop. All relevant design parameters such as geometricparameters of a heat sink, source and bypass configurations, heatdissipation, material properties and flow conditions can besimultaneously optimized to characterize a heat sink thatminimizes entropy generation and in turn results in a minimumoperating temperature of an electronic component.

An analytical model for predicting air flow and pressure dropacross the heat sink is developed by applying conservation of massand momentum over the bypass regions and in the flow channelsestablished between the fins of the heat sink. The model isapplicable for the entire laminar flow range and any type ofbypass (side, top or side and top both) or fully shroudedconfigurations. During the development of the model, the flow wasassumed to be steady, laminar, developing flow. The model is alsocorrelated to a simple equation within 8% confidence levelfor an easy implementation into the entropy generationminimization procedure. The influence of all the resistances toheat transfer associated with a heat sink are studied, and anorder of magnitude analysis is carried out to include only theinfluential resistances in the thermal resistance model. Spreadingand material resistances due to the geometry of the base plate,conduction and convection resistances associated with the fins ofthe heat sink and convection resistance of the wetted surfaces ofthe base plate are considered for the development of a thermalresistance model. The thermal resistance and pressure drop modelare shown to be in good agreement with the experimental data overa wide range of flow conditions, heat sink geometries, bypassconfigurations and power levels, typical of many applicationsfound in microelectronics and related fields. Data published inthe open literature are also used to show the flexibility of themodels to simulate a variety of applications.

The proposed thermal resistance and pressure drop model aresuccessfully used in the entropy generation minimization procedureto design a heat sink with bypass for optimum dimensions andperformance. A sensitivity analysis is also carried out to checkthe influence of bypass configurations, power levels, heat sinkmaterials and the coverage ratio on the optimum dimensions andperformance of a heat sink and it is found that any change inthese parameters results in a change in the optimized heat sinkdimensions and flow conditions associated with the application foroptimal heat sink performance.