In recent years, water stress has become a global crisis due to climate and demographic changes and lifestyle changes. Freshwater production from the sea using various processes is known as the most important solution to deal with this crisis. Among these processes, the humidification-dehumidification process has been considered by the scientific community as a flexible and low-cost method. The present work has investigated the performance of vortex-humidification-dehumidification water desalination cycle. The existing system is a dehumidifier-dehumidifier type, in which a vortex tube has been added. According to the structure of the vortex tube, its hot air outlet has been used to increase the possibility of moisture absorption in the humidifier and its cold air outlet has been used to increase the amount of condensed water in the humidifier. According to the second law of thermodynamics, the performance of the cycle has been studied. In the analysis of multi-flow cycles with heat and mass transfer, the commercial software EES has been used to solve the equations. The fresh water output for specific conditions (sea level, air temperature 35 degrees Celsius and relative humidity 30 percent) is equal to 7.85 kg/h and the research results show that the Gained-Output-Ratio is equal to 1.189. It is shown that the use of the vortex tube and the consequent increase in air temperature at the inlet of the humidifier and the use of the second dehumidifier in the cycle increase the production of fresh water.

Solar humidification-dehumidification desalination is one of the most practical methods for water desalination in small scale for regions far from cities and with low population. The aim of this study is manufacturing and simulation of a solar humidification-dehumidification desalination system with capacity of 20 lit/day. This system consists of humidification and dehumidification units, solar air and water heaters. To this end, first this system is explained and modeled. Then, manufacturing process of solar air heaters and different parts of desalination system is investigated. After the manufacturing process of the desalination system, this system is experimentally tested and the effect of pertinent parameters, such as the temperature of inlet water and air to humidifier; inlet water temperature and flow rate to dehumidifier on the performance of the system and distillate product are investigated. The results show that the effect of water temperature on the fresh water produced is more than air temperature. Moreover, using the chilled water, which has a temperature in the range of water well temperature, in the dehumidifier inlet leads to an increase of 31 % in the fresh water produced. Also, the best water flow rate to the dehumidifier inlet is 0.12 kg/s. Finally, experimental and simulation results are compared with each other and good consistency is seen.

Packed columns are important parts of mass and heat transfer equipments, Nowadays, using packed columns is increasing due to lower pressure drop, higher capacity and mass transfer compared with tray columns.In this survey, parameters affecting column performance were measured, these include: liquid hold up and gas-phase mass transfer coefficient in a humidification column using random packing in towers with 0.1 m and 0.2 m diameters and 1m height. In these experiments, liquid and gas phase were water and air, respectively. Air velocity was between 1.32 to 3.92 (m3/hr) and liquid velocity was between 10 and 70 (m3/hr). In this paper, Nakajima model was used to predict the effective area. Experimental data of gas-phase mass transfer coefficient was compared with Zech, Shi, Grouff, Shulman, Billet and Onda models. Average relative errors were 7%, 15%, 29%, 21%, 45% and 195%, respectively. To predict mass transfer coefficients, Zech model was more accurate Also, by decreasing diameter of tower, gas-phase mass transfer coefficient (Kg.ae) increased.

The humidification-dehumidification system is one of the desalination technologies that can utilize non-fossil thermal sources and requires insignificant input energy. This system is usually suitable for rural areas and places far from the main sources of energy. The purpose of this study is to obtain the most suitable working conditions and dimensions of this system. In this research, thermodynamic modeling was first performed for a simple type of the system (water-heated); then, the effect of parameters on the system performance was investigated. Modeling was conducted through a numerical simulation; furthermore, the assumption of the saturation of exhaust air from the humidifier was also considered in the mentioned code. Afterward, a comparison was made between two different forms of the system, and the proper form was chosen for the rest of the research. Moreover, through heat transfer equations, the dimensions of the two main parts of the system, i. e., humidifier and dehumidifier, were calculated. Besides, multi-objective optimization was carried out for two objective functions, i. e., gained output ratio (GOR) and the system volume, to reduce the space occupied by the system and reach the desired efficiency simultaneously. The optimization was performed using a simulation program, and results were obtained for different weights in order to optimize each objective function. For instance, 379 liters of freshwater can be produced in a day with a total volume of 48 liters for the humidifier and the dehumidifier in the optimized system.

Purpose: Students are presented with a variety of case formulas to promote the development of clinical reasoning.Methods: 120 third-year medical students at our medical university were randomly assigned to 18 small groups. After each ICM (Introduction to clinical Medicine) course, they were given a paper case. A few days later small group sessions were formed and students asked tutors some questions to have more history and physical examination data and discussed and developed a differential diagnosis list. Then, all small groups met in a large group session for further discussion. After that, back to small groups, students ordered preclinical tests and they were given the results by tutor. At this stage, each group tried to further narrow the differential diagnosis list and to determine the most probable diagnosis. Finally, in the large group session a consensus diagnosis was reached after reflective observation. A questionnaire was used before and after intervention. The small group tutor rated student's abilities at the end of first day and last day.Results: The attitude of students about the positive effects of MPCD increased significantly from the first day to the last day (P<0.05). The progress checklist of the student's abilities showed a statistically significant improvement post intervention.Conclusion: Our study suggests that using MPCD method is an effective way to increase clinical reasoning skills of medical students.

In this research and for the first time, the performance of hybrid solar-gas turbine power plants modified with humidification-dehumidification (HD) desalination process was simulated with TRNSYS. The system included a 4. 6 MW gas turbine, solar tower and HD process with air heater and open cycle for water and air. The results showed that in the hybrid solar-gas turbine power plants, the solar power supplied about the 35-45% of required energy and the amount of fossil fuel consumption was reduced. Also, the emission of CO2 was declined for about 40%. The electric power and efficiency of hybrid system was slightly lower than gas turbine only due to the pressure losses in piping and receiver of solar system. The results of HD desalination indicated that the increase in the temperature and relative humidity of the inlet air increased the amount of fresh water production and increase in the temperature of inlet saline water declined its production. Moreover, the amount of fresh water production had an optimum value respect to the mass flow rate of air and with increasing the air flow, the amount of fresh water production increased and then decreased. In addition, if the mass flow rate ratio of saline water to dry air was equal to 1. 8, the gain output ratio (GOR) had a maximum value of 2. Variation of GOR in terms of returned air at different inlet air temperatures was explained.