Simulation of complete liquid–vapour phase change process inside porous evaporator using local thermal non-equilibrium model

Simulation of liquid–vapour phase change process inside porous media using modified enthalpy formulation

“…Nevertheless, if required, particularly for multi-dimensional problems and for LTNE model, Eq. (8) may be employed in order to retrieve the massevelocities for the liquid and the vapour phases as [9,22]:…”

“…Possibly owing to the generality and the ease of numerical implementation, the H-formulation [12] is by far the most widely used method for the simulation of phase change process inside porous media [13e20]. Although this formulation [12] is applicable only under the assumption of Local Thermal Equilibrium (LTE) condition, it has been extended further in order to accommodate the more general Local Thermal Non-Equilibrium (LTNE) condition [11,21,22]. 3 An additional problem that is encountered while simulating the complete liquidevapour phase change process inside porous media is the occurrence of rapid, non-physical change in the predicted properties (e.g., temperature) over an extremely short distance 4 that results primarily due to the presence of discontinuities in the effective diffusion coefficient across the interfaces between the single and the two phase regions.…”

“…5 Such a remedy, however, does not perform equally well for cases where the pressure drop inside the porous medium is negligible owing to the extremely low mass flow rate 6 and hence the saturation temperature remains nearly the same in the entire two-phase region. Nevertheless, after critically analysing the reasons for the occurrence of "jumps" in the predicted properties, Alomar et al [22,27] suggested remedies using the smoothing of effective diffusion coefficient for both LTE [27] and LTNE [22] models and applied it successfully for the simulation of complete phase change process inside divergent porous evaporators [28].…”

“…Nevertheless, the formulation could be easily extended for multi-dimensional problems and even involving complex geometries that require the employment of curvilinear coordinates. In order to eliminate the occurrence of non-physical "jumps" in the predicted properties, however, the smoothing of effective diffusion coefficient has been used by suitably adopting the recommendations of Alomar et al [22,27] for Hformulation. The results obtained with the modified h-formulation have been compared with that predicted by the existing Hformulation [12,22,27] for different parametric variations.…”

“…The numerical method is fairly straightforward and hence is briefly discussed in section 4 for the sake of completeness along with the smoothing algorithm adopted for the present modification. The necessity for smoothing of effective diffusion coefficient and the results predicted by the modified h-formulation are presented and compared with that obtained with the H-formulation [12,22,27] in section 5. Finally, the conclusions and the final remarks are reported in section 6.…”