Numerical study on Nusselt number of moving phase interface during wax melting in tube using lattice Boltzman method

Abstract

Paraffin melting is widely applied to the fields of PCM energy storage, gathering and transportation pipe-line paraffin removal, etc. Natural-convection is the main heat transfer mode during paraffin melting, and Rayleigh number is an important factor affecting the change of natural-convection intensity. Nusselt number variation can reflect the influence of natural-convection on heat transfer. The conventional Nusselt number of hot wall surface reflects only the convective heat transfer intensity of the fixed wall, while it does not take into account that the phase change interface has the characteristics of moving in the phase change process. A double distribution model of paraffin phase transformation in circular tube based on lattice Boltzmann method is established in this paper. The influence of Rayleigh number on the temperature field and flow field of wax in circular tube is analyzed. The heat transfer process is reflected by Nusselt number of moving phase interface. The relation between Nusselt number of moving interface and Nusselt number of hot wall surface is also presented. The results show that the Nusselt number of moving phase interface can reflect the complex non-linear characteristics of natural-convection and describe the phase change heat transfer process of wax more accurately. Calculation formula of Nusselt number of moving phase interface and hot wall during wax phase change is proposed. Increasing Rayleigh number can quicken the melting of wax to meet the actual engineering requirements.