Experimental Investigation of Metal Foam Effect on Subcooled Flow Boiling Heat Transfer between Two Vertical Annulus Tube

The subcooled flow boiling happens when the bulk flow temperature and the interface temperature are lower and higher, respectively than the saturated temperature corresponding to the flow pressure. One way to increase the heat transfer mechanism is to use high porosity metal foams in the ducts, which have a high surface area to volume ratio that increases the heat transfer surface area and the heat transfer coefficient of the duct. In the current study, an experimental apparatus was constructed, and subcooled flow boiling in an annulus tube was investigated. The annulus tube is in the vertical direction, and the internal and external diameters are 50.7 and 70.6mm, respectively. The operating pressure was 1atm, and the working fluid was water. The metal foam used is nickel with 10ppi and a porosity of 95%. In this investigation, heat flux and mass flow rate effectiveness on the heat transfer coefficient are considered. The experiments were performed in the mass flow rate range of 0.012kg/s to 0.0286kg/s in which the flow consists of both forced convection and flow boiling. The mass flow reduction causes the heat transfer coefficient increment to 30% in subcooled boiling regions. The use of porous media also increases the subcooled flow boiling heat transfer coefficient up to 30%.