关键词: 微通道, 烧结, 纳米粒子, 浓度, 气液两相, 压降

Abstract:

Uniform and stable nanorefrigerant coolants of 0.05%-0.4% Al₂O₃/R141b (mass fraction) were prepared by ultrasonic vibration and used to investigate nanoparticle concentration on pressure drop of gas-liquid two-phase boiling flow of a nanorefrigerant in micro channels. A micro heat exchanger was fabricated by direct metal laser sintering (DMLS) with designed capacity of system pressure at 176 kPa and inlet temperature at 40℃. At conditions of heat flux 21.2-38.2 kW·m^-2 and mass flow rate 183.13-457.83 kg·m^-2·s^-1, the experimental results show that the nanoparticle concentration had significant impact on pressure drop of Al₂O₃/R141b nanoparticle coolant boiling flow in micro channels and the pressure drop decreased with the increase of nanoparticle concentration. After added Al₂O₃ nanoparticles to pure R141b coolant, pressure drop of the pure refrigerant in micro channels was reduced by 5.5%-32.6% depending on mass faction of nanoparticles. Scanning electron microscopy (SEM) and static contact angle measurement revealed that deposition of some Al₂O₃ nanoparticles on the microchannel surface increased surface wettability, which might lower pressure drop of Al₂O₃/R141b upon increase of nanoparticle concentration. Considered three classic pressure drop models and correlations of Qu-Mudawar's and Zhang's for gas-liquid two-phase boiling flow, a revised correlation was developed that 85% of the experimental data points on pressure drop were fallen within a ±15% range of model calculation. The revised correlation can effectively predict the experimental results under these conditions as supported by small MAE number of 11.7%, which was relative deviation between experimental results and revised model predictions.

Key words: microchannel, sintering, nanoparticle, concentration, gas-liquid two-phase, pressure drop