Flow Boiling Heat Transfer and Pressure Drops of R1234ze(E) in a Silicon Micro-pin Fin Evaporator

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 cm(2) containing 66 rows of cylindrical in-line micro-pin fins with diameter, height, and pitch of, respectively, 50 mu m, 100 mu m, and 91.7 mu m. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m(2) s to 1750 kg/m(2) s and heat fluxes ranging from 20 W/cm(2) to 44 W/cm(2). The effects of saturation temperature on the heat transfer are investigated by testing three different outlet saturation temperatures: 25 degrees C, 30 degrees C, and 35 degrees 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/m(2) K, whilst in two-phase flow it goes up to 30 kW/m(2) K.