Modelling long term pressure and temperature oscillations in the flow boiling in microchannels

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Heat exchangers equipped with microchannels have many industrial applications. This is due to their capability for transfer of high heat fluxes. In flow boiling in microchannels three different flow regimes: steady bubbly/slug flow regime, bubbly/annular alternating flow and annular/mist alternating flow have been observed. In the present paper the model of heat and mass transfer in microchannels system has been proposed. Oscillations between quasi steady state of boiling in microchannels have been considered. Changes of two-phase flow in microchannels have been described by the relations between: heating surface temperature, vapour quality, liquid mass flux, pressure drop in microchannels and heat flux absorbed by boiling liquid. Simulation results indicate that shape of curve pressure-drop-versus-flow-rate is responsible for appearance or disappearance of heating surface temperature and pressure oscillations.