Experimental Investigation on Humidification - Dehumidification Water Desalination Technique Using Solar Energy

Abstract

Although water is one of the prime constituents on the earth and available in an abundant amount, nearly one-half of the people of the globe are suffering from shortage of freshwater that is increasing at a frightening rate most exclusively in growing nations where commercial water shortages prevail. So, the regions with ample saline water and solar radiation where freshwater is usually limited, the humidification-dehumidification (HDH) desalination systems have shown promising results for low quantum need of freshwater. A distinctive and uncomplicated Bubble Column Humidification- Thermoelectric Cooler based Dehumidification water desalination system has been introduced. The humidification-dehumidification water desalination system is an inexpensive solution and offers many attractive advantages over current desalination systems. The HDH system can be utilized to supply fresh water to the populations who have faced the freshwater scarcity that is harmful to their health and overall economies. The proposed desalination system has two main components namely Bubbler humidifier and thermoelectric cooler based dehumidifier. For air humidification, an innovative design of BC humidifier has been developed. A spiral tube with a number of holes on its circumference is fixed at the bottom of the humidifier chamber. The formation of bubbles of air in the evaporation chamber increases mass & energy exchange and surface contact area between heated water and air bubbles, which accelerate the air humidification process. A new design of thermoelectric cooler based dehumidifier has been proposed for the air dehumidification which is run by Direct current supply from solar photovoltaic. The humidified air is then passed through the cold section of TEC based dehumidifier. The humid air is cooled down well below the saturation temperature in the dehumidifier; as a result, dehumidification of the air takes place. The condensate droplets are separated by gravity and collected in a distillate water tank. The performance analysis of BC humidifier, TEC based dehumidifier and BC humidifier-TEC based dehumidifier HDH system has been presented in this work. In Bubbler humidifier, the Relative Humidity (RH) of air has obtained from 68% to 97% for different operational parameters. The maximum Relative Humidity of air has reported 97% for do = 1 mm, ma = 7 g/s, Tw = 60˚ C, Ta = 48˚ C, Z = 7 cm. In TEC based dehumidifier, the highest distillate of around 160 ml/hr has been achieved while having ma = 6 g/s, Ta = 55 ºC and RH = 85%. The daily distillate production achieved during the investigation of HDH system was in the range of 7 - 13 Liter/day for different operational parameters although the best experimental productivity of the system was reported 12.96 Liter/day for do = 2 mm, ma = 0.016 kg/sec, Tw = 60˚C, Ta = 27˚C and Z = 7 cm. The GOR of the HDH system was 0.8 for ma = 0.016 kg/sec. Also, the results of bubbler humidifier, TEC based dehumidifier, and HDH system indicate that the relative humidity and daily production is in proportion to the temperature of the air, the temperature of the water, water column height and mass flow rate of the air; whereas in inversely proportional to the bubble generation hole diameter. Also, in all the above three cases, the experimental results present a fine confirmation with results of proposed mathematical model. For calculating the cost of productivity and compensation period, an economic analysis of the HDH system has been executed. From the analysis, Yearly price per liter and the payback period of the HDH system are INR.5.1/L and 3.08 years respectively, which is a very promising value, considering the scope and possibilities of further cost diminishment due to mass production and industrial fabrication facilities. In the presented work, Genetic optimization of the HDH system has been performed to calculate the optimal value of the mass of freshwater, pressure loss, a diameter of the hole, the height of water column, the temperature of the air, a mass flow rate of air, temperature of water and payback period. It is found that the optimized mass of freshwater was 16.7934 L/day and the Payback period was 3.0076 years.