Numerical simulation of a solar water disinfection system based on a small-scale linear Fresnel reflector

Abstract

This paper describes the details of the design of a solar water disinfection system based on a small-scale linear Fresnel reflector. The proposed system consists of a small-scale linear Fresnel reflector, a filtering system, two disinfection units, a heat exchanger, a compressed air system and the control system. A detailed mathematical model has been developed and solved through an iterative procedure. The system has been studied under different operating conditions, such as beam solar irradiance (the beam solar irradiance on a horizontal surface, corresponding to solar noon, varies from 325 to 798 W m⁻², for winter solstice and summer solstice, respectively), ambient temperature (the ambient temperature varies between 19 and 29 °C at the summer solstice and from 8 to 16 °C at the winter solstice), thermal fluid flow rate (2200 L h⁻¹, 2400 L h⁻¹, 2600 L h⁻¹, and 2800 L h⁻¹) and water temperature at the outlet of the filtered water tank (8 °C, 12 °C, 16 °C, and 20 °C). The performance of the system has been studied as a function of the temperature of the thermal fluid of the small-scale linear Fresnel reflector, the water temperature of the disinfection unit, the filling and emptying of inertia tanks, clean water productivity and the daily cumulative productivity of clean water. Numerical simulations reveal that the maximum values of cumulative daily productivity of clean water were 357.14 (L m⁻² day⁻¹) at 100 (°C) and 198.41 (L m⁻² day⁻¹) at 100 (°C) for summer solstice and winter solstice, respectively, in Almeria (Spain), for a thermal fluid flow rate of 2400 L h⁻¹. Values much higher than those obtained by other systems. The inclusion of a heat exchanger in this system significantly increases its productivity. Small-scale linear Fresnel reflector thermal fluid temperature, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity decreased with increasing thermal fluid flow rate above 2400 L h⁻¹. On the other hand, the water temperature at the outlet of the filtered water tank between 8 and 20 °C has a negligible influence on the small-scale linear Fresnel reflector thermal fluid temperature values, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity. It is concluded that the proposed solar system offers an energy efficient and environmentally friendly water treatment method.