Numerical study on convective flow boiling of nanoliquid inside a pipe filling with aluminum metal foam by two-phase model

Abstract

This study tries to employ the computational fluid dynamics (CFD) approach to investigate the influence of the simultaneous use of the metal foam (porous media) and the water-based nanofluid on the boiling flow regime. For this purpose, boiling flow heat transfer of water-based copper nanofluid inside of both simple pipe and aluminum metal foam pipe is simulated using the Eulerian two-phase CFD model. The nanofluid is supposed to flow inside the pipe with the mass flux of 1927 kg/m2s and the subcooled temperature of 10oc at atmospheric working pressure. The pipe is also under a constant wall heat flux (50–110 KW/m2). Different copper nanoparticle volume fractions (i.e., 0.5, 1, and 1.5%) are considered for this investigation. The porosity and pore density of the metal foam are 0.8 and 10 pore per inch (PPI) respectively. The heat transfer parameters of boiling flow including the wall temperature, the vapor volume fraction on the wall, the onset of the nucleate boiling (ONB), the local heat transfer coefficient, and the mean diameter of the vapor bubble are considered in this study. All heat transfer coefficients predicted by the CFD are compared with the Chen correlation. As far as the authors know, for the first time, the boiling flow of nanofluid-based water inside a metal foam pipe was simulated by the two-phase model of Eulerian. The results reveal that for the metal foam pipe, after happening of the ONB, the wall temperatures suddenly jump over the saturated temperature and the critical heat flux (CHF) happens. But no such sudden increase of the wall temperature is seen along the simple pipe before and after the ONB. Besides, the convective heat transfer coefficient in the metal foam pipe before the beginning of the boiling is more than double the boiling flow in the simple pipe. Although in metal foam pipe, once the boiling happened, the heat transfer coefficient was degraded by 50%, this value is still 25% more than the heat transfer coefficient of the boiling flow in the simple pipe. The results of this study could be practically used for boiling heat transfer analysis of heat exchangers filled by porous media and nanofluid.