Minimum superheat imposed by equations of state in modelling the phase transition

Abstract

The boiling phenomenon has been studied extensively by using the pseudopotential lattice Boltzmann method (LBM) based on an equation of state (EOS) due to the algorithm simplicity. However, all reported studies have shown that a large superheat is either used to simulate the boiling or observed if a fixed heat flux is used. In the current study, insights into the large superheat required to initiate the phase transition in numerical simulations based on an EOS are obtained by theoretical analyses of the heating process, which show that density decrease is coupled with temperature increase through the adopted EOS at an almost constant pressure. Significant temperature increase from the saturation temperature is required to make the coupled density decrease large enough before having phase transition. The theoretically predicted minimum superheat is validated by the LBM simulation based on the Peng-Robinson EOS. A solution to reduce the minimum superheat is provided and verified by using a piecewise linear EOS in both theoretical analysis and LBM simulations. The conclusions are also valid for other simulation methods based on different EOS.