Research on flow boiling heat transfer for vertical upward and downward flows along a minichannel with a smooth heated surface

The paper reports results for flow boiling heat transfer in a 1.7 mm deep minichannel vertically-oriented with upward and downward flow. The heated element for HFE-649 flowing upward or downward in a channel was a smooth plate. Infrared thermography allowed determining changes in temperature on the outer plate side. Two-phase flow structures were recorded through a glass pane at the other side of the channel being in contact with the fluid. Analysis of the results was performed on the basis of experimental series obtained for the same heat flux for upward and downward flows and two mass flow velocities. The results are presented as relationships between the heat transfer coefficient or the plate temperature and the channel length, boiling curves, and between the heat flux and the heat transfer coefficient and two-phase flow structure images. The impact of mass flow velocity on the heat transfer coefficient and two-phase flow structures for vertical upward and downward flows were discussed