Experimental study on the performance of miniature heat pipes with woven-wire wick

The thermal density of electronic system has been increased continuously because high speed and high density are required for them. The heat dissipation of CPU for a notebook PC has been recently increased to be more than 10 W, but, on the other hand, the available packaging space has been decreased. Therefore, it has become inevitable to perform cooling by using miniature heat pipes (MHPs). In the present study, a new woven-wire-type wick for the MHP is developed, which has a large capillary limit and a high productivity. These MHPs with diameters of 3 mm or 4 mm are applicable to small-sized electronic parts such as CPU of a notebook PC. Because the operational characteristics of MHPs with the diameters of 3 mm or 4 mm are different from those of general medium-size heat pipes, performance tests have been conducted in order to review heat-transfer characteristics and effects of various factors on the performance of MHPs. The design factors under consideration are fill ratio of working fluid, length of heat pipe, length of evaporator and condenser, inclination angle of installation, number of wick strand and thermal load.

I. Introduction

The trend of high-speed/high-density packaging of electronic system has recently become a general phenomenon in the field of electronic industry. Out of many problems to be solved in the field of the thin-plate-type packaging such as notebook PC, cooling is known to be the one of the most critical one among EMI/EMC, interconnection, noise, vibration and so on [1]. For a conventional CPU of notebook PC prior to the pentium-grade CPU, the cooling had been performed by just attaching a heat sink or a small fan on the upper part of CPU (about 6 W of the heat dissipation). However, due to an increase of the heat dissipation per a CPU larger than 10 W and a limitedpackaging space of CPU for higher grade than Pentium-II CPU, the cooling with heat pipes has become inevitable [2]. In this reason, the MHPs with diameter of 3 mm to 4 mm have been applied to cool the CPU of notebook PC [3]–[5].