Heat Transfer in Boiling of a Moving Liquid in a Microchannel

Boiling of a moving liquid in channels whose transverse dimension is smaller than the capillary constant is characterized by the determining influence of capillary forces and of the constraint effects on the flow regime and heat transfer. In the present work, we have studied experimentally heat transfer in boiling of R318C and R21 coolants in an annular and rectangular channels with a clearance of 0.9 and 1.6 x 6.3 mm, respectively, in the range of mass velocities from 10 to 800 kg/m(2).sec, at heat fluxes of up to 90 kW/m(2), as well as heat transfer in boiling of water in a microchannel measuring 0.6 x 2 mm. The experiments were carried out at initial subcooling and at a fixed initial vapor content at the channel inlet. For R318C coolant and water under the conditions considered, the bubble boiling makes a determining contribution to the general heat transfer, whereas for the R21 coolant the boiling and forced convection make a commensurable contribution. The data on the structure of flow and local heat transfer coefficients, also in the regime of burnout heat transfer, the distribution of heat transfer coefficient over the perimeter of the rectangular channel, the space and time dispersions of the local heat transfer coefficient were obtained.