Navid Sharifi

Comprehensive understanding of evaporation in porous channels is important for the design of modern heat exchangers and thermal systems such as heat pipes. This paper presents a numerical study of evaporation in a vertical porous channel. The volume of the fluid method was applied to capture the interface between phases. The multi‐dimensional limiter for explicit solution method, in which there are additional constraints based on the flux‐corrected transfer method, was used to solve the interface transfer equation. Pressure drop, Nusselt number, and the drying rate were considered as performance parameters. Comparing simulation results with experimental data showed that this new solver can precisely solve the thermal phase change in a porous medium. The influence of parameters effective on the drying process, such as porosity, permeability, the dynamic contact angle was investigated. Based on the results of the pressure profile in the final state, four different regions are visible. Because of the close fit of the wall temperature to the average cross‐sectional temperature, the Nusselt number increases sharply at transition points from the liquid to the vapor phase. By increasing the dynamic contact angle, the average drying rate in the channel is reduced.

Thermo-compressors are used instead of mechanical compression devices in many industries and play a main role in the process. Through the process of designing desalination systems, amount of exergy dissipation is a very important economical factor. Most of the exergy losses in multi-effect distillation systems with thermal vapor compression (multiple-effect desalination–TVC) occur in the thermo-compressor. The aim of this article is to investigate geometrical effects in thermo-compressors by numerical methods based on the second law of thermodynamics to obtain lower exergy loss and consequently, higher entrainment ratio. A lot of geometrical parameters such as converging and diverging angles in mixing section, diffuser, nozzle location and also its throat area ratio affect thermo-compressors’ performance. The modifications in the above-mentioned parameters were applied to a thermo-compressor established in a desalination unit in Kavian petrochemical company which is working with 15 barg of motive pressure. Numerical simulation of the base model has an accurate agreement with experimental data with about 1.3% discrepancy in maximum discharge pressure and just 6.7% in entrainment ratio. Results of the analysis indicate that thermo-compressor’s performance is sensitive to the mixing area converging angle. The other parameter which mostly affects the performance is the location of nozzle in thermo-compressor’s body.

Thermo-compressors are among the most important facilities in thermal desalination systems. Such devices are compressing and recycling the useless vapors and hence effectively enhancing the efficiency of desalination units. Since the connection between the evaporator box and suction surface is not perfectly symmetric, it is necessary to consider the effect of this curved path on pressure loss at the inlet boundary. In this study, a numerical procedure is developed to achieve reliable results in thermo-compressors through using CFD simulations. Two approaches are examined: axisymmetric and full three-dimensional method. The results are compared and the deviations of velocity, pressure and temperature are evaluated in both methods. The flow pattern in the steam collector is investigated afterwards. The distributions of velocity and pressure through this canal are illustrated and the critical point where pressure loss originates is revealed. In the meantime, the effect of this non-symmetric path on the flow is compared with the axisymmetric results. Finally, it is shown that the influence of the curved-shape inlet on flow properties is insignificant such that it can be neglected, because the flow swirl at the inlet is very negligible. Therefore, the axisymmetric model is capable of producing reliable results for thermo-compressors in a more advantageous way with a simpler mesh generation and reduced computational cost.