Experimental investigation and visualization of flow boiling heat transfer in a vertical tube containing metal porous medium

In this study, flow boiling heat transfer in a vertical copper tube with internal diameter of 16 mm under constant heat flux conditions and at atmospheric pressure is experimentally investigated by using water as working fluid. To validate the results and to ensure the accuracy of the experimental loop, several experiments are performed in the single-phase mode, and the results are compared with the existing relationships for single-phase heat transfer, which indicates the validity of the test section. The experiments are carried out in both empty vertical tube and the vertical tube containing a metal foam. The two-phase tests are within the range of the slug flow regime which is visualized by a glass tube placed at the end of the test section. Heat transfer parameters such as Nusselt number and Convection heat transfer coefficient are measured in different mass flow rates and heat fluxes. The results of the experiments are also compared with the experimental data available for two-phase flow in the literature. The effects of porous material, heat flux and mass flux on heat transfer parameters are investigated. It was found that in low vapor qualities and in the range of mass fluxes (i.e. 38-53 kg/m2s), and heat fluxes (i.e. 23-36 kW/m2), the inserted metal foam leads to an improvement in the heat transfer coefficient from 1.5 to 1.82 times (compared to the empty tube). It was also found that despite the use of metal foam, the slug flow regime is remained in the pipe.