Flow Instability of a Liquid Through a Small-Scale Channel During a Flow Evaporation

Finite volume analysis of two-dimensional model has been performed to study of the influence of heat flux and mass flux on two phase heat transfer through microchannel during water flow boiling. The channel dimensions were (5×5××50) m3. The inlet boundary conditions were (1.63, 3.32, 4.9, 6.65, 8.16) . The supplied heat fluxes were 24.8 , 33.2 , 46.13 , 51 and 69  for nucleate boiling while 33.3 , 50 , 66.7 , 83.3 , and 100  for dryout condition. The inlet temperature was 30oC. It was shown that the highest heat transfer coefficient occurs at beginning of onset of nucleate boiling (ONB) after that the it will drop due the changing of the flow patterns. According to supplied heat flux, the patterns were bubble flow, dispersed bubbles, churn flow, annular flow, and then dry out condition occurs. For the mass flux 1.63kg/  the highest heat transfer coefficient was 9.5 kW/  while for the mass flux 8.16 kg/  the highest heat transfer coefficient was 20kW/ . For the mass flux 1.63kg/  the highest value of vapour quality was 0.09  while for the mass flux 8.16 kg/  the highest value was 0.15. There is a sharp pressure drop when starts to nucleate and the highest value occurs at dryout condition. This study gave an understanding of the heat exchange flow behaviour during water boiling through a single microchannel.