Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels

Abstract

In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R245fa, R600a, R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure is considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of non-isothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects the bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the non-adiabatic effect is clearly pronounced.