Thermal oscillations during flow boiling of hydrocarbon refrigerants in a microchannels array heat sink

Highlights: • Thermal oscillations for R600a, R290 and R1270 during flow boiling in a microchannels array. • Parametric effects of the signal behaviors for temperature and pressure transducers. • Analysis of signal amplitudes based on the equilibrium between inertial and boiling forces. • Refrigerant R1270 presents lower thermal oscillations for the same operational conditions than R600a and R290. -- Abstract: This paper presents an experimental investigation on thermal oscillations during flow boiling of the hydrocarbons R600a, R290 and R1270 in a microchannels array heat sink. The test section is composed of fifty microchannels manufactured in a copper block with each channel having a rectangular cross-section of 123 × 494 μm² and 15 mm in length. Experimental data were obtained for mass velocities of 165–823 kg/m² s, heat fluxes up to 400 kW/m², liquid subcooling at the inlet of the test section of 5, 10 and 15 °C and saturation temperatures of 21 and 25 °C. Fluctuations of the fluid temperature at the test section outlet and of the pressure at the heat sink inlet are presented and analyzed. The results reveal that the thermal oscillation amplitude increases with decreasing saturation temperature and increasing heat flux and liquid subcooling at the inlet of the test section. Propylene was found to present the lowest thermal oscillations. The analysis of thermal oscillations allows to identify potential conditions that allows to maximize the efficiency of the heat sink for microcooling applications.