Flow boiling heat transfer and pressure drops of R1234ze(E) in a silicon micro-pin fin evaporator

Abstract

The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height and pitch of respectively 50 μm, 100 μm and 91.7 μm. At the entrance of the heated area an extra row of micro-pin fins with a larger diameter of 100 μm acts as inlet restrictions to avoid flow instabilities. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2s to 1750 kg/m2s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2 while maintaining a constant outlet saturation temperature of 35 °C. In order to assess the thermal-hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2K, whilst in two-phase flow it goes up to 30 kW/m2K.