Study on the effect of channel layout of flat-plate micro pulsating heat pipes under a local heating condition

Abstract

The rapid development of the performance of semiconductors requires high power, and it has led to a rise in heat flux. Thus, there has been a growing demand for heat spreaders for appropriate thermal management in electronics. Recently, a micro pulsating heat pipe (MPHP) has been getting a lot of attention because of its very simple structure and high thermal performance. Generally, in electronics, the heating area is restricted to small chip size, and it causes a local heating condition. Under a local heating condition, in case of a MPHP with a uniform channel layout, only a few channels are overlapped with the heating area, and the rest of them are thermally-isolated. A MPHP transfers heat from the evaporator to the condenser through the oscillating motion of the working fluid, which is derived from the pressure difference due to the phase change of the working fluid. Thus, the oscillating motion may not occur in the thermally-isolated channels. To overcome this limitation caused by the local heating condition, it is desirable to induce the active oscillating motion of the working fluid throughout all the channels. For this objective, in this study, two kinds of channel layouts, according to the size of the local heating area, are suggested. First, the channels of the MPHP are re-arranged that all the channels overlap the heating area, and it is called non-uniform channel layout. In the case of non-uniform channel layout, a non-uniform heating pattern occurs. Thus, the method, which can quantify the non-uniformity of the heating pattern, is proposed taking into account the characteristics of MPHPs, and the experiments are performed to verify the effectiveness of the quantified value. The results show that the thermal performance of the MPHPs with the non-uniform channel layouts is proportional to the effective dissimilarity, which is the proposed value in this study. However, when the heating area is excessively small, all the channels cannot be overlapped the heating area due to the fixed channel width. To overcome this limitation, the channel layout, which is designed based on the topology optimization method, is suggested. In the topology-optimized channel layout, the channels are merged so that all the channels overlap the heating section. To verify the effectiveness of the proposed method, the thermal performance of the MPHP with the topology-optimized channel layout is compared with that of various references. As the results, the thermal performance of the MPHP with the topology-optimized channel layout is up to two times higher than that of the MPHP with the uniform channel layout, and the active oscillating motion of the liquid slugs are observed in all the channels even under the excessively localized heating condition. In this study, the channel design methods of the MPHPs under local heating conditions are firstly suggested. The experimental results clearly show that the proposed methods can widen the applicable range of MPHPs by overcoming the limitation associated with localized heating conditions.