LAUSR

Abstract In this article, two-phase flow in a double-pipe porous heat exchanger and associated phase change processes has been numerically analysed to investigate the impacts of the relative permeabilities. The modified h-formulation along with the assumption of Local Thermal Equilibrium condition has been employed. Finite Volume Method (FVM) has been used to discretise the governing equations. The solutions of incomplete evaporation process have been validated with the experiments and they show an excellent agreement between them. The pertinent parameters have been systematically investigated to demonstrate the importance of the above mentioned influences on the complete evaporation process. It has been observed that the power index of the relative permeabilities for either liquid or vapour region has a significant effects on the beginning and ending of phase change operation, especially when the steam is formed inside the pipe. Comparison between results obtained with maximum and minimum values of the power index indicated that the latter value must be used while simulating the complete evaporation process, particularly for very low inlet Reynolds number and very high wall temperature. It is also evident that the operating conditions and geometric parameters of the heat exchanger have been substantially changed the location of the beginning and ending of the phase change process. On the other hand, the properties of porous media have only minor influence.