بررسی تجربی عملکرد آب‌شیرین‌کن خورشیدی به روش رطوبت‌زنی- رطوبت‌زدایی با استفاده از سیکل بستۀ آب‌وهوا

در این پژوهش، عملکرد آب‌شیرین‌کن خورشیدی رطوبت‌زنیرطوبت‌زدایی با استفاده از سیکل بستۀ آب‌وهوا در شهرستان اهواز مورد بررسی قرار گرفت. این آب‌شیرین‌کن شامل کلکتور، چگالندۀ هوا ‌خنک، مخزن‌های آب‌ شور و شیرین، دمندۀ هوا و پمپ آب است. ارزیابی این سامانه در سه سطح سرعت هوا (3 ، 4 و 5 متر بر ثانیه) و در سه سطح دبی پمپ (2، 4 و 6 لیتر بر دقیقه) انجام شد. نتایج نشان داد که کمینۀ بازده تبخیر‌کننده در روز به‌طور میانگین حدود 56% بود که در سرعت هوا 3 متر بر ثانیه و دبی آب 2 لیتر بر دقیقه به دست آمد و همچنین بیشینۀ‌ بازده تبخیر‌کننده در روز حدود 79‌% بود که در سرعت هوا 5 متر بر ثانیه و دبی آب 6 لیتر بر دقیقه به دست آمد. همچنین بیشینۀ میانگین روزانۀ کارایی چگالنده حدود 21.52‌% بود که در سرعت هوای خروجی 3 متر بر ثانیه و دبی آب عبوری 6 لیتر بر دقیقه به دست آمد. کمینۀ مقدار آب شیرین به‌دست‌آمده مربوط به سرعت هوا 5 متر بر ثانیه و دبی 2 لیتر بر دقیقه و بیشینۀ مقدار آن برای سرعت هوا 3 متر بر ثانیه و دبی 6 لیتر بر دقیقه به دست آمد.

Experimental Investigation of a Solar Desalination Performance Based on Humidification-dehumidification Technique with Air and Water Closed Cycle

Extended AbstractIntroduction: Population growth and the increase in industrial activities have led to a water shortage that has become a significant threat to sustainable development. Saline water desalination is one of the most dominant approaches to access new drinkable water sources. In 2015, around 400 million people throughout the world used desalinated water, and it is estimated that more than 14% of the world population will have to use desalinated water by 2025. Water desalination plants consume a large amount of energy which dominantly comes from fossil fuels. The economic and environmental concerns of fossil fuels have caused a growing interest in the use of renewable energies as an alternative to fossil fuel resources. Humidification and dehumidification (HDH) of the flowing air, which can be easily adopted by solar collectors, is a suitable technique for saline water desalination at low temperature. ,. A review of literature indicates that the performance of a solar HDH desalination system with closed air and water cycles in Ahvaz rsquo;s conditions has not been investigated so far. Therefore, the present study was aimed to develop an experimental investigation of such a water desalination system at different air velocities and saline water flow rates. Material and Methods: A schematic of the designed solar HDH desalination system is shown in Fig. 1. The system comprised a solar evaporator, condenser, air blower, tanks of saline and fresh water, and a saline water pump. The system #39;s experimental investigation was conducted at three levels of saline water flow rates (2, 4, and 6 L/min) and three air velocity levels (3, 4, and 5 m/s). In each test, these features were measured: relative humidity at the outlets of the evaporator and condenser; the temperature of the evaporator and condenser air outlets; ambient temperature, air velocity through the condenser; and the solar radiation intensity on the solar evaporator. The solar HDH system #39;s performance parameters, including the efficiency of the evaporator, the useful thermal gain of the solar evaporator, evaporation rate, and effectiveness of the condenser were calculated using equations 14 respectively. Results and Discussion: Variations of ambient conditions, including temperature, relative humidity, and solar radiation intensity during the test period are shown in Fig. s 810. It can be observed that the ambient temperature changed from 34 to 39 oC; the relative humidity values ranged between 10 and 29%; and the maximum solar radiation intensity was around 1030 W/m2. The results of the analysis of variance of the effect of the water flow rate and the air velocity on the evaporator efficiency are given in table 1. Clearly, from Fig. 11, increasing the air velocity caused an increase in the evaporator efficiency. This was mainly due to the higher convective heat transfer coefficient of the air at the higher velocities, which enhanced the mass transfer coefficient and the moisture evaporation rate. Also, raising the water flow rate improved the evaporator efficiency. Since the saline water had a free flow over the solar evaporator, it covered a broader evaporator surface area at higher flow rates. In other words, the surface area of water evaporation increased with increasing the water flow rate. The maximum amount of daily water evaporation was around 7.5 L, which was achieved at the water flow rate of 6 L/min, and the air velocity of 5 m/s. The effect of the different operating conditions on the condenser effectiveness is illustrated in table 3 and Fig. 14. The results showed that the effectiveness values decreased with increasing the air velocity because of a decrease in the residence time of the humid air inside the condenser. Since raising the water flow rate increased the evaporation rate and increased the humidity accumulation in the moving air through the condenser, it improved the effectiveness values. Variations of the condenser effectiveness during the day (Fig. 15) indicated that effectiveness values decreased with the ambient temperature increase. Conclusion: The results of the experimental investigation of the designed solar HDH desalination system can be summarized as follow:a) The maximum evaporator efficiency (around 79%) was observed at the air velocity of 5 m/s and the water flow rate of 6 L/min.b) The highest value of the condenser effectiveness was around 21.52%, which was achieved at the air velocity of the 3 m/s and the water flow rate of 6 L/min.c) The maximum freshwater productivity of the solar HDH desalination system was around 1.4 L/day.