Integration of a Solar Parabolic Dish Collector with a Small-Scale Multi-Stage Flash Desalination Unit: Experimental Evaluation, Exergy and Economic Analyses

In this study, a small-scale two-stage multi-stage flash (MSF) desalination unit equipped with a vacuum pump and a solar parabolic collector (PDC) with a conical cavity receiver were integrated. To eliminate the need for heat exchangers, a water circulation circuit was designed in a way that the saline feedwater could directly flow through the receiver of the PDC. The system’s performance was examined during six days in July 2020, from 10:00 a.m. to 3:00 p.m., under two distinct scenarios of the MSF desalination operation under the vacuum (−10 kPa) and atmospheric pressure by considering three saline feedwater water flow rates of 0.7, 1 and 1.3 L/min. Furthermore, the performance of the solar PDC-MSF desalination plant was evaluated by conducting energy and exergy analyses. The results indicated that the intensity of solar radiation, which directly affects the top brine temperature (TBT), and the values of the saline feedwater flow rate have the most impact on productivity. The maximum productivity of 3.22 L per 5 h in a day was obtained when the temperature and saline feedwater flow rate were 94.25 °C (at the maximum solar radiation of 1015.3 W/m2) and 0.7 L/min, respectively, and the MSF was under vacuum pressure. Additionally, it was found that increasing the feedwater flow rate from 0.7 to 1.3 L/min reduces distillate production by 76.4% while applying the vacuum improves the productivity by about 34% at feedwater flow rate of 0.7 L/min. The exergy efficiency of the MSF unit was obtained as 0.07% with the highest share of exergy destruction in stages. The quality parameters of the produced distillate including pH, TDS, EC and DO were measured, ensuring they lie within the standard range for drinking water. Moreover, the cost of freshwater produced by the MSF plant varied from 37 US$/m3 to 1.5 US$/m3 when the treatment capacity increased to 8000 L/day.

Comparative Study of Modified Conical Cavity Receiver With Other Receivers for Solar Paraboloidal Dish Collector System

Solar Parabolic Dish Concentrators are one of the most efficient solar power conversion technologies. The cavity receivers are most common type, used for reducing the heat losses from the receiver. In this paper a novel cavity receiver is proposed and the objective is to compare the novel modified conical cavity receiver with the existing cavity receivers such as cylindrical, conical and modified cavity receivers. The cavity receivers are designed for the parabolic dish of 4m diameter which is installed at National Institute of Technology Puducherry, India. Ray tracing analysis is carried out to determine the size of the receiver. The analysis was carried out for various orientations of the receivers from 0° to 90° with a step size of 15° and also for the cavity temperatures: 300℃, 400℃, 500℃, 600℃ and 700℃. Based on the results obtained the modified conical cavity receiver is found to be the best design in terms of minimum heat losses compared to other receivers. The next best choices are found to be modified cavity, conical cavity and cylindrical cavity receiver. The whole analysis is conducted with a developed model in COMSOL Multiphysics.

Estimation of convective heat losses from conical cavity receiver of solar parabolic dish collector under wind conditions and receiver orientations

The parabolic dish collector is one of the recognized concentrated solar power systems based on point focusing, which provides high-temperature heat, high concentration ratio, and low heat loss. This system consists of a parabolic reflector and a cavity receiver situated in the focus line. In this work, the conical cavity receiver with an aperture diameter of 0.5 m is considered for a 100 m2 parabolic reflector having a focal to diameter ratio of 0.48. Due to the complexity of flow and temperature profile, the estimation of convective heat loss is a difficult task in a cavity receiver. More heat losses are associated with high temperature obtained in the cavity receiver of the parabolic dish collector. Due to diverse wind effect, the convective heat losses ramp up, which significantly influences the thermal performance of the concentrating power system. The present work aims to investigate the heat losses due to convection from the conical cavity receiver. The numerical investigation was performed using ANSYS Fluent 20R1 to calculate the convective heat losses from the conical cavity receiver of varying diameter to height ratio for varying wind speed, receiver orientation in head-on, and back-on wind flow directions. The considered influential parameters are varying from 0.5 to 1.5 for diameter to height ratio (d/h), 0° to 90° for receiver orientation (γ), 0 to 10 m/s for wind speed (V). The heat losses are highest at 60° and 75° receiver orientation for d/h = 0.5 and d/h = 1-1.5, respectively, at high wind speed in head-on condition, whereas in back-on wind condition, 30° receiver orientation has more heat losses among all the d/h values at high wind speed. The heat loss at 90° receiver orientation is low for 4-10 m/s. The trends of heat loss curve at receiver orientations for given wind conditions are similar for velocity more than 2 m/s. The result reveals that the considered influential parameters have a remarkable effect on convective heat losses from the cavity receiver.