A simplified opto-thermal assessment and economic study of parabolic dish solar concentrator pondering on the receiver position induced uncertainties
01 Jun 2023-Thermal science and engineering progress-Vol. 42, pp 101920-101920
TL;DR: In this article , the authors investigated the opto-thermal and economic assessment of low-cost solar parabolic dish concentrators (PDC), focusing on the receiver position-induced uncertainties.
Abstract: This paper investigates the opto-thermal and economic assessment of low-cost solar parabolic dish concentrators (PDC), focusing on the receiver position-induced uncertainties. An optical model of the proposed PDC system is developed in Tonatiuh optical simulation tool. The optical analysis is conducted by the Monte Carlo Ray Tracing method for different vertical and horizontal positions of the PDC’s receiver. In addition, An experimental test rig based on a locally manufactured PDC with a low-cost reflecting surface made of aluminum reflector foil is developed to achieve the purpose of this work. A cavity receiver made of a cylindrical-cone brass tube is used and tested under different positions of the focal point of the PDC. The impact of the uncertainties on the performance of the proposed PDC is experimentally estimated. A relatively simple mathematical model is utilized to evaluate the thermal and exergy performance for the different positions of the cavity receiver. The results showed that the proposed PDC could generate hot water at temperatures 77°C, 64°C, and 55°C for the three focal point positions, respectively. The collector efficiency of the PDC-cavity receiver system in the receiver position 1, 2, and 3 were 70.2%, 53.2%, and 24 % while the average values of exergy efficiency for the PDC at the receiver positions were 4.7%, 2.3%, and 0.93% respectively. This clearly shows the effect of the receiver positions on the performance of the parabolic dish solar concentrator and justifies the requirement of appropriate positioning of the receiver for the parabolic dishes.
07 Jul 2009
TL;DR: In this paper, an attempt has been made to design a new type portable thermoelectric solar still (PTSS), which is used to improve the temperature difference between evaporating and condensing zones.
Abstract: In this study, an attempt has been made to design a new type portable thermoelectric solar still (PTSS). In the PTSS, a thermoelectric module is used to improve the temperature difference between evaporating and condensing zones. Also, a heat-pipe cooling device is used to cool down the hot side of the thermoelectric cooler. To evaluate the performance of the PTSS, the equipment was tested under the climatic condition of Semnan (35° 33′ N, 53° 23′ E), Iran. The experiments were carried out in 5 days. The measurement of solar intensity, wind velocity, ambient temperature, water production, and temperature of other components, for example, thermoelectric module, water, walls and heatpipe was done in the same manner for each day. The results showed that ambient temperature and solar radiation have a direct effect on still performance but there is a reduction in water productivity by increasing the wind speed. The results also showed that temperature of thermoelectric device was lower than that of walls which indicated on the higher production of water.
TL;DR: In this paper, the first and second law efficiencies for a stainless steel closed-tube open rectangular cavity solar receiver were determined for a small-scale solar thermal Brayton cycle using a micro-turbine with low compressor pressure ratios.
Abstract: The first law and second law efficiencies are determined for a stainless steel closed-tube open rectangular cavity solar receiver. It is to be used in a small-scale solar thermal Brayton cycle using a micro-turbine with low compressor pressure ratios. There are many different variables at play to model the air temperature increase of the air running through such a receiver. These variables include concentrator shape, concentrator diameter, concentrator rim angle, concentrator reflectivity, concentrator optical error, solar tracking error, receiver aperture area, receiver material, effect of wind, receiver tube diameter, inlet temperature and mass flow rate through the receiver. All these variables are considered in this paper. The Brayton cycle requires very high receiver surface temperatures in order to be successful. These high temperatures, however, have many disadvantages in terms of heat loss from the receiver, especially radiation heat loss. With the help of ray-tracing software, SolTrace, and receiver modelling techniques, an optimum receiver-to-concentrator-area ratio of A ′ ≈ 0.0035 was found for a concentrator with 45° rim angle, 10 mrad optical error and 1° tracking error. A method to determine the temperature profile and net heat transfer rate along the length of the receiver tube is presented. Receiver efficiencies are shown in terms of mass flow rate, receiver tube diameter, pressure drop, maximum receiver surface temperature and inlet temperature of the working fluid. For a 4.8 m diameter parabolic dish, the larger the receiver tube diameter and the smaller the mass flow rate through the receiver, the higher the receiver surface temperature and the less efficient the collector becomes. However, the smaller the receiver tube diameter, the higher the pressure drop through the tube and the smaller the second law efficiency. It was found that the receiver with larger tube diameter would perform better in a solar thermal Brayton cycle. An overall solar-to-heat efficiency of between 45% and 70% is attainable for the solar collector using the open-cavity receiver.
TL;DR: In this article, the authors analyzed the optical efficiency of three different geometries: cylindrical, conical and spherical, of a cavity receiver, with the objective of analysing their behavior using an advanced ray tracing method.
Abstract: Concentrated Solar Power (CSP) can be used as an efficient low cost energy conversion system to produce different types of energy, such as electricity, through the use of concentrated parabolic dish systems. In the study of CSP, most of the researchers focus on the heat losses and their relationships to the receivers' geometries. The present study concentrates on the optical efficiency as well as the flux distribution of the three different geometries: cylindrical, conical and spherical, of a cavity receiver, with the objective of analysing their behaviour using an advanced ray tracing method. The results of this study have shown that there is a connection between the flux distribution on the internal surfaces of the cavities and their optical efficiency. Moreover, the conical shape receiver received, as well as absorbed, a higher amount of reflected flux energy than the other shapes. The optical efficiency reached 75.3%, 70.1% and 71.5% for the conical, spherical and cylindrical shapes respectively at surface absorptivity of 85%. Also, the focal point location depends on the shape of the cavity receiver and its absorptivity. Thereby, there is an optimum distance for each design depending on these two factors. The results of the simulated work are validated using the experimental work found in the literature.
TL;DR: In this paper, a low-cost solar collector with a dish reflector and spiral absorber was investigated experimentally and numerically with a developed thermal model in the Engineering Equation Solver (EES).
Abstract: A low cost solar collector with a dish reflector and spiral absorber is examined in this work. This collector is investigated experimentally and numerically with a developed thermal model in the Engineering Equation Solver (EES). Numerical simulations are performed by the commercial software OptisWorks. The solar ray distribution inside these receiver geometries, including the helical coil used for the heat transfer fluid, was determined using this tool. The final results show that the thermal performance is about 34%, due to the high rate of thermal losses. After validating the numerical model, it is used for investigating the collector for various operating conditions. Three working fluids (Water, Therminol VP-1 and Air) are compared energetically and exergetically for various combinations of volumetric flow rates and operational temperature levels. The results proved that water is the most appropriate working fluid, among those investigated, as it is able to efficiently work at low temperature levels, while the thermal oil is the best at higher temperature values, according to thermal analysis. The exergetic analysis showed that air is the best choice in low temperatures and thermal oil in greater temperatures. Finally, an open receiver of a conical cavity shape with a helical tube was optically investigated, as a second strategy for enhancing the optical performance of the receiver. The results show that an average flux value of about 2.6 × 10 5 W/m 2 was absorbed by the helical conical shape with an aperture area of 0.01606 m 2 .