Evaluation of the Energy Efficiency of a Solar Parabolic Collector Equipped with Phase Change Materials inside the Receiver Tube of a Desalination System

IntroductionWith increasing the world's population, the demand for supply water resources is also increasing. Nevertheless, climate change has severely impacted the accessibility of fresh water resources. Consequently, researchers have been focusing on producing drinkable water from seas and oceans. Iran, with its significant levels of solar radiation and access to open water from the north and south, is an ideal country for fresh water production. Using solar water desalination systems is a reliable and cost-effective solution for producing drinking water from salt water sources. The purpose of this research is to enhance the performance of the solar water desalination system by using the latent heat storage system and a solar tracking system. In this experimental setup for fresh water production, water was used as the working fluid, while a parabolic collector functioned as the source of thermal energy.Materials and MethodsThe solar water desalination system was designed and built on a laboratory scale at the University of Kurdistan, and then the necessary experiments were carried out. The flowing fluid (water) inside the spiral tube in the tank is pumped into the absorber tube of the parabolic collector. Inside the receiver tube, there is a spiral copper tube with a 7 cm pitch, which contains paraffin. The parabolic mirror reflects the sunlight onto the receiver tube, causing the working fluid, water, to heat up. The cooling process is achieved using a specific source located in the upper section of the distillation tank. In this case, the steam droplets in the tank hit the bottom surface of this cooling tank, which has the shape of an inverted funnel, leading to condensation. The study was conducted over four consecutive days, from 10:00 to 14:00, under identical conditions from August 24th to August 27th, 2022. It took place at the Renewable Energy Laboratory, University of Kurdistan in Sanandaj, Iran, and was conducted for three different volume flow rates of fluid: 1.9, 3.1, and 4.2 l.min-1 with phase change materials (PCM) and 4.2 l.min-1 without phase change materials (WOPCM); the pump’s maximum flow rate was 4.2 l.min-1. Variations of outlet temperature, thermal efficiency, desalination efficiency, and produced water were investigated under different conditions.Results and DiscussionThe results reveal that by decreasing the pitch of the spiral tube, there is an increase in the amount of heat captured, due to the increase in the Nusselt number. At the beginning of data collection, a significant amount of the energy that enters the receiver tube is absorbed by both the phase change material and the spiral tube inside the receiver and as a result, the initial air temperature is lowered. The highest temperature of salt water occurs when the fluid is flowing at a rate of 4.2 l.min-1, while the lowest temperature is observed at a flow rate of 1.9 l.min-1. With a flow rate of 4.2 l.min-1, the absorbent tube rapidly transfers the absorbed heat to the salt water chamber through the fluid. The input energy to the tank has increased from 1.53 to 2.83, 1.14 to 2.18, and 0.73 to 1.48 MJ for fluid flow rates of 4.2, 3.1, and 1.9 l.min-1, respectively. At a flow rate of 4.2 l.min-1, the thermal efficiency of the system without phase change materials (3.51%) is lower compared to the case with phase change materials (5.02%). Moreover, using a solar tracking mechanism increased the thermal efficiency of the collector by 9.86% compared to the system using a photocell sensor. Based on the water quality values, it can be stated that the level of dissolved solids in the water sample has been significantly decreased. This indicates that the water can be used for drinking.ConclusionIn this research, the process of thermal changes in a solar water desalination system using PCM was investigated. The obtained results demonstrate that the use of PCM improved the thermal efficiency of the collector and the water obtained from the current system is safe for consumption. Furthermore, by implementing a solar panel tracking system, the efficiency of the solar collector is improved.