Numerical investigation of complete evaporation process inside porous evaporator using staggered and non-staggered grid arrangements

Abstract

The complete evaporation process inside an asymmetrically heated porous channel, under steady-state condition, has been numerically investigated in this article, based on the modified enthalpy formulation along with the assumption of Local Thermal Non-Equilibrium (LTNE). The governing equations have been discretised using finite volume method on both staggered and non-staggered grid arrangements and solved iteratively in a SIMPLE-like manner. All simulations have been carried out by applying the proposed smoothing algorithm for the effective diffusion coefficient in order to avoid the non-physical jump in the predicted temperature distributions. The performance of staggered and non-staggered grid layouts have been compared only on orthogonal coordinates for various parameters and the results show that the accuracy and effectiveness of the non-staggered and staggered grid layouts are identical. Different models for the partitioning of the wall heat flux have no influence on the total evaporated volume fraction. Effects of various parameters on the temperature and liquid saturation distributions have been carefully investigated, which clearly indicate that imposed heat flux, Reynolds number, Darcy number and thermal conductivity of the solid phase strongly influence the initiation and termination of phase change process, whereas the porosity has only a minor impact. Therefore, operating conditions and properties of porous media are required to be properly designed in order to achieve the desired objective. In addition, the results obtained using the modified h- and H-formulations have been compared and excellent agreement have been observed. It has been found that the modified h-formulation requires considerably less computation time as compared to that for the H-formulation and hence the method is strongly recommended for the future use. Nevertheless, it should now be extended in order to accommodate the multi-dimensional complex geometries that require the employment of curvilinear coordinates using non-staggered grid layout.