Evaluation On Heat Transfer Performance Of Fabric Heat Sink By Finite Element Modeling

In terms of the limitation of the commercial heat sinks in the manufacture and conformability, the woven fabric heat sink similar to pin-fin heat sinks has been designed. However, it is lack of an understanding of the heat transfer performance of this kind of woven fabric heat sink. Nowadays, the finite element method has been generally developed to determine heat transfer of in-line and staggered pin-fin heat sinks used in electronic packaging applications. In this study, this method is used to evaluate the heat transfer performance of fabric heat sink.Considering the heat transfer performance of the fabric heat sink is determined by their working conditions and the structural parameters such as pin fin diameter, pin-fin spacing, this study will evaluate their effect on the heat transferring performance. The details are followed.(1)To analyze the heat transfer performance of fabric heat sinks, 3D graphics software is adopted to reconstruct the fabric heat sink on the basis of the woven fabric sink sample.The geometrical structure of woven fabric heat sink is determined by the interlaced thin metal wires with different diameter, weft and warp twist. The method reconstructed a three-dimensional model of the heat sink is different from the traditional heat sink. The geometrical model is reconstructed by sampling three-dimensional coordinates along the yarn pathway of fabric heat sink through the two-dimensional plane. And then, the twists are added by adjusting the yarn structure of fabric heat sink.(2) To evaluate and compare the heat transfer properties of the fabric pin-fin heat sink and pin fin heat sink, their heat transfer performance was predicted by a finite element method. The results showed that in the condition of natural convection the heat transfer performance of pin fin heat sink was better than the performance of fabric heat sink. However, the heat transfer of fabric heat sink performs better than pin fin heat sink under the forced convection condition.Effective method is a method by which the maximum surface area is obtained and the minimum volume material is needed. Based on effective methods and the structural geometry of fabric and pin fin heat sink, the different geometric models were designed. And the finite element analysis is used to predict the heat transfer performance of the fabric heat sink. Firstly, the heat transfer performance of fabric heat sink was searched under the condition of natural convection. The results showed that in the condition of natural convection the heat transfer performance of pin fin heat sink was better than the performance of fabric heat sink. Secondly, the heat transfer performance of fabric heat sink was analyzed under the condition of force convection. It is observed that in the condition of natural convection the heat transfer performance of pin fin heat sink was less than the performance of fabric heat sink. Finally, by the heat transfer theory and the predicted temperature contours as well as temperature profiles, it could found that the pin fin of the fabric heat sink has high density which will crimp flow. Besides, the power of the natural convection is weak, so that the heat flow cannot be taken from heat sink and the heat transfer performance of the fabric heat sink is poor. However, the flow volume and velocity provided by fans in the condition of forced convection could be controlled manually, so it could provide a strong wind to facilitate the air interchange. In this way, the advantages of large specific surface area of pin-fin heat sink are shown. Therefore, in the condition of force convection the heat transfer performance of pin fin heat sink was less than the performance of fabric heat sink.(3) To parametrically predict the heat transfer performance of the fabric pin-fin heat sink, effect of the fin length, fin diameter, fin space and the location of outlet on the thermal-structure response of the pin fin was investigated under forced convection. The results showed that under a fixed vertical distance between the outlet and the pin fin tip, the heat transfer performance of heat sink was improved with an increase of pin fin length,but the improved amplitude has decreased. The fabric heat sink has an optimal spacing and pin fin density.Since the heat transfer performance of fabric heat sink was better than the performance of pin fin heat sink under force convection. Therefore, a finite element model of fabric heat sink was built to explore the effect of the fin length, fin diameter, fin space and the location of outlet on the thermal-structure response of the fabric heat sink. The parametric simulation showed that under fixed outlet position the heat transfer performance of heat sink is improved with an increase of pin fin length,but the improving amplitude decreased. When the outlet of the pin fin tip distance is constant, the heat transfer performance of heat sink improves with the increase of pin fin length, whereas it will decrease with the increase of pin fin length over a certain value.Meanwhile, the thermal equilibrium time decreased with an increase of pin-fin spacing, and the heat transfer performance decreases after an increase. The heat transfer performance of fabric heat sink is improved when the radius was in the range of 0.075 mm ~ 0.2mm.In summary, the heat transfer performance of the fabric heat sink is less than that of pin-fin heat sink under the natural convection, and the difference become more obvious with the increasing size of the heat sink. However, the heat transfer performance of the fabric heat sink is better than that of pin-fin heat sink under the forced convection. When the outlet position is fixed, the heat transfer performance of fabric heat sink improves with an increase of pin fin length,but the improving amplitude has decreased. When the outlet of the pin fin tip distance is fixed, the heat transfer performance of heat sink has a parabolic relationship with pin fin length. Of course, besides the heat sink itself, the assembling conditions in practice affect the heat transfer performance of heat sink. Therefore, to fully determine the heat transfer performance of fabric heat sink, it needs to analysis the assembly process and the working condition.