Unsteady characteristics of flow pattern and pressure drop of flow boiling in single straight microchannel under sudden heat flux increase

The high heat flux on the CPV (concentrator photovoltaic) cells may lead to heat dissipation difficulty and high temperature, which will result in the decrease in electricity efficiency or even damage of CPV cells. To tackle with this problem, microchannel cooling has attracted increasing attentions recently due to its much higher heat transfer performance. However, the significantly varying solar radiation intensity will cause the sudden variation of heat load on the CPV cells, which may further influence the flow boiling inside the microchannels. Therefore, in this study, the flow characteristics including the pressure drop and flow pattern of deionized water boiling in a single straight microchannel (D-H = 400 mu m) under sudden heat flux increase were experimentally investigated. The serious pressure drop variation and flow boiling instability properties after the sudden heat flux increase were observed. The study on the influential factors indicates that increasing the mass flux from 411.66 to 720.41 kg m(-2) s(-1) and lowering the inlet temperature from 55 to 45 degrees C helped weaken fluctuation intensity of pressure drop due to the lower vapor quality. Meanwhile, the detailed flow pattern encountering different levels of heat flux increase were observed using high speed camera, which indicates that much higher heat flux increase leaded to a more rapid bubble generating and phase change phenomenon.