Flow boiling heat transfer and two-phase flow in microgravity

Flow boiling heat transfer can provide high heat transfer rates due to latent heat transportation. Its possible use is therefore potentially important to reduce size and weight of cooling systems in space platforms and satellites. A comprehensive knowledge is also important for the safe operation of existing single-phase systems in case of accidental increase of heat generation rate. For space applications and appropriate design of components accommodating flow boiling heat transfer, it is important to understand the influence of microgravity conditions on forced convective boiling heat transfer. The number of existing researches on flow boiling in reduced gravity is very small due to large heat loads required and reduced available room in a 0-g apparatus for experiments, as well as complexity of the experimental facility for microgravity environment. This lecture will summarize the results of the few research carried out on flow boiling heat transfer in microgravity, discussing flow pattern, heat transfer coefficient, critical heat flux, with a particular emphasis to the recent experiments carried out at ENEA. The experiments were carried out at low gravity during the ESA (European Space Agency) parabolic flights campaign of November 2013. The paper will show the analysis of differences between flow patterns and vapour bubble parameters at normal and at zero gravity.