With the rising population, environmental pollution, and social development, potable water is reducing and being contaminated day by day continually. Thus, several researchers have focused their studies on seas and oceans in order to get potable fresh water by desalination of their saltwater. Solar still of basin type is one of the available technologies to purify water because of free solar energy. The computational fluid dynamic CFD model of the solar still can significantly improve means for optimization of the solar still structure because it reduces the need for conducting large amount of experiments. Therefore, the main purpose of this study is presenting a multi-phase, three-dimensional CFD model, which predicts the performance of the solar still without using any experimental measurements, depending on the CFD solar radiation model. Simulated results are compared with experimental values of water and glass cover temperatures and yield of fresh water in climate conditions of Sheben El-Kom, Egypt (latitude 30.5° N and longitude 31.01° E). The simulation results were found to be in acceptable agreement with the experimental measured data. The results indicated that the daily simulated and experimental accumulated productivities of the single-slope solar still were found to be 1.982 and 1.785 L/m² at a water depth of 2 cm. In addition, the simulated and experimental daily efficiency were around 16.79% and 15.5%, respectively, for the tested water depth.

A step-by-step technique has been implemented in the analytical study of heat transfer and pressure gradient characteristics of refrigerants R-410A, R-407C, R-22, and R-134a used as cooling media in the condenser of a steam power plant. Refrigerants are optimized to replace water/air as coolant in the condenser of a steam power plant. Refrigerants have much lower temperatures and much higher heat transfer rates than water or air. The thermal resistances that affect heat transfer characteristics and surface condenser performance are included. The effect of inlet refrigerant temperature and mass flow rate are reported for the four refrigerants. Calculations are performed at two inlet refrigerant temperatures −21 °C and −30 °C and mass flow rate ranging from 92.905 to 132.905 kg/s. The results revealed that the overall heat transfer coefficient, heat transfer rate, and condensation rate increased with refrigerant mass flow rate, with higher values at lower inlet refrigerant temperatures. For a given refrigerant mass flow rate and inlet temperature, the analytical study indicated that R-410A has higher values of overall heat transfer coefficient, heat transfer rate and condensation rate than R-407C, R-22, and R-314a, respectively. Moreover, it is found that R-410A, at −30 °C and 132.905 kg/s, is superior in condensing all steam entering the condenser than the other refrigerants; this corresponds to higher exergy efficiency. The condenser pressure was observed to be slightly higher for R-410A than the other refrigerants.

It is proposed in the current paper to combine the steam plant with two refrigeration cycles and a cooling storage container. Throughout the time of a day, the steam plant is made to work at full power, where the excess power generated over the electric power demand is used to drive the compressors of the refrigeration cycles. The stored cooling is used for dissipating the heat absorbed by the cooling refrigerant in the steam condenser during the period of peak-loads, while the two refrigeration machines are stopped. In this way, the energy used for driving the refrigeration machine is saved so that the whole power generated by the steam plant is exported to the grid. Energy analyses of the proposed combined system has led to inferring that the net power of the steam plant during the period of exclusive direct cooling of the steam condenser (only the first refrigeration machine is running) is about 70–86% of the whole power generated by the steam plant when the coefficient of performance of the first refrigeration cycle lies in the range of 4–10. Also, it has been found that relatively small coefficients of performance of the first and second cycles, less than 6 and 1.5, respectively, result in low net power of the steam plant over the period of charging the cooling storage container (both refrigeration machines run in unison). In this case, the net plant power amounts to less than 26% of the total generated plant power when the time of storing the cooling is lower than double the time of the peak-loads. This necessitates increasing the storing time to assure reasonable available power to be exported to the grid. Economical analyses of the proposed system have showed that both the capital cost and energy charges are less for the proposed system than that of the steam plant without cooling storage for practically possible operating conditions.

In the current work, a simple and low energy consuming system is proposed for holding on the vacuum in the steam power plant system. The vacuum is created at the tip of an inverted U-pipe through which water flows by siphon effect due to the height difference in water surfaces of two tanks. This height difference and the elevation of the inverted U-pipe tip define the value of the vacuum to be grown. The U-pipe tip is connected to the discharge pipe of a compressor which draws a mixture of air, and water vapor from the steam condenser and raises their pressure a little higher than that of the inverted U-pipe tip. The mixture flows with the water down the inverted U-pipe till they depart the U-tube. A thermodynamic and fluid flow analysis is developed for predicting the performance of the proposed system. The results of this analysis show that the right selection of the mass flowrate ratio of water flowing in the inverted U-pipe to air and water vapor mixture sucked by the compressor from the steam plant condenser, in the range of 25,000, the height of the inverted U-pipe summit from the water level of the higher water tank greater than 9.2 m and the height difference of the water levels in the two water tanks small enough, in the range of 0.1 m saves the power of vacuum system by 80% less than that consumed when using compressor alone for venting the steam plant condenser.

An experimental and numerical study is presented in the current work for gas entrainment using an inverted vertical U-tube. Water flows vertically up in an inverted U-tube which creates a low-pressure region in the tube upper portion. This low-pressure region can be used to extract gases by connecting it to a branch pipe. The extracted gases considered in this work are a mixture of air and water vapor. The water vapor from the side branch pipe is mixed with the flowing water under the siphon effect. This results in a progressive water vapor condensation as the mixture proceeds towards the exit due to an increase in vapor partial pressure. The air is drawn by inertia to be released out at the tube lower exit of the inverted U-pipe. The current study deals with these complicated flow behaviors due to the mixing undergoing condensation. A test rig is designed for experimentally studying the behavior of water flow in an inverted U-tube where the air is mixed with the flowing water at the top region of this tube. The CFD computations are accomplished for a side gas mixture with volume fractions up to 0.7 with water vapor mass fractions in this mixture to be 0.1–0.5. The tested water mass flow rates in the main tube are 2, 4, 6, 8 kg/s to account for all possible flow mass ratios. The CFD computations are validated with water and air two phase flow with the measurements of both the experiments of the current research and the literature. The present results reveal that slightly raising the water mass flow rate at a constant side mixture mass ratio produces a reduced generated pressure in the upper tube part. This is attributed to extra water vapor condensation taking place rapidly by increasing the water flow rate in the tube upper part. Furthermore, the turbulence quantities begin to break down at a side mixture volume fraction of 0.55 with water and air mass flow rates of 2 kg/s and 0.002 kg/s, respectively. On the other side, raising the air mass flow rate at the higher values of water vapor and water mass flow rates breaks the generated vacuum pressure and turbulence due to entrainment. Moreover, this proposed framework can produce a lower static pressure, reaching 55.1 kPa, which makes it attractive for gas extraction. This new technique presents innovative usage with less consumable energy for extracting gases in engineering equipment.