A correlation for heat transfer during laminar natural convection in an enclosure containing uniform mixture of air and hydrogen

In this paper, a correlation for heat transfer due to laminar natural convection in a rectangular enclosure containing a uniform mixture of hydrogen and air with vertical walls at different temperatures is proposed. This correlation is in terms of Nusselt and Rayleigh numbers evaluated by taking properties of air alone. Mixture properties, viz., density, viscosity, specific heat capacity and thermal conductivity are not needed in this correlation. A modification factor which is based on the mole fraction of hydrogen in the mixture accounts for the differences in heat exchange due to differences in the properties of mixture and pure air. Thus, this correlation is easier to use for a dilute mixture of hydrogen and air as compared to the conventional correlations that are based on mixture properties which may be cumbersome to evaluate. Further, the results highlight that heat transfer correlations for a mixture of gases can be expressed in terms non-dimensional numbers for dominant gas and a correction factor for the gas mixing with it. An in-house code HDS (Hydrogen Distribution Simulator), which has well validated modules for calculation of mixture properties, has been used to carry out numerical study and establish this heat transfer correlation.