Parabolic Trough Collector Research Articles

OPTIMIZATION OF THERMO-FLOW IN A SOLAR FOOD DEHYDRATOR USING COMPUTATIONAL TECHNIQUES

A solar food dehydrator converts solar energy into heat required to remove moisture from food. This study involved development of an optimized design for a solar dehydrator using computational techniques. A computer-aided design of six (6) different configurations of the dehydrator was developed, and a remotely-installed heat capture device was modelled and analysed using MATLAB. The results show that the Parabolic Trough Collector (PTC) could be used in effectively transferring heat remotely to a dehydrator. The temperature of air leaving the heat exchanger increases in proportion to the increase in the temperature of the heating fluid entering the heat exchanger. Computational Fluid Dynamics (CFD) in Ansys Fluent was employed to aid in the study of airflow and temperature distribution. The hot air was simulated at 2 m/s and 350 K inlet conditions. The CFD simulation results showed significant variations in the air velocity distribution and temperature for different configurations of the dehydrator. The back inflow - front outflow configuration provided the most uniform distribution of heated air in the drying chamber, with minimal variation on each tray. This uniformity was also observed in the distribution of static temperature. The back inflow – side outflow configuration showed a similar performance in flow and temperature distribution. However, the bottom inflow – top outflow and bottom inflow – front outflow configurations showed uneven velocity and temperature distribution inside the drying chamber. Supply of airflow across the trays horizontally provides best airflow and temperature distribution in solar dehydrators and thus highly recommended.

Pinch and exergy assessment of an innovative hydrogen and methane purification process configuration based on solar renewable energy

Energy recovery from waste sources and developing new high-performance systems are essential to minimize energy consumption. A novel purification structure is developed to produce hydrogen and liquid natural gas (LNG) using exhaust gases from various industries, mixed refrigeration system, organic Rankine cycle (ORC), and solar energy sources. Solar parabolic trough collectors are used to supply energy in the low-temperature ORC. The proposed system produces 1.922 kg/s hydrogen with purity of 94.25 mol% and 1.777 kg/s LNG as the main product by consuming 10.56 kg/s crude hydrogen feed gas. The LNG and pure hydrogen specific power consumption (SPC) are 0.4111 and 0.3803 kWh/kg, respectively. The SPC of the sum of both products is obtained at 0.1975 kWh/kg. The methane and hydrogen recovery factors are 94.80% and 98%, respectively, indicating maximum methane and hydrogen absorption of the crude hydrogen feed gas. The exergy analysis indicates that the total exergy destruction of the integrated system is calculated at 5561 kW, and its exergy efficiency is obtained as 28.56%. The heat exchanger networks for the HE1, HE2, HE3, HE4, and HE6 multi-stream heat exchangers are extracted through the pinch strategy. The multi-stream heat exchangers have 8, 13, 6, 8, and 2 simple heat exchangers. The outcome results obtained from the parametric study is a 25.88% increase in the production rate of the main products (LNG and pure hydrogen). In addition, when the ratio of LNG to fuel gas increases by 48.08%, the ratio of main product to by-product increases from 54 to 62 mol%. By performing parametric analysis, it can be concluded that increasing the hydrogen content of the crude feed improves the performance of the system.

Challenges, limitations, and applications of nanofluids in solar thermal collectors-a comprehensive review.

The daily increase in the demand for energy consumption is partly caused by the global population explosion and advancements in technology. Humanity relies on energy to fulfil its daily routines, such as electricity for lighting, heating, cooling, and running electronic devices. There are continuous attempts by researchers and industry experts to optimize and enhance the efficiency of various sustainable energy generation devices. Solar collectors play a critical role in the renewable energy sector, which is vital in helping the world achieve a clean, green, and sustainable environment. Over the last two decades, researchers have made significant efforts to explore various techniques for enhancing the effectiveness of solar thermal collectors. Their effort has been centered around improving the fluid thermal properties, which act as the heat transfer medium in solar collectors. The discovery of nanofluids will help resolve some of the challenges associated with conventional fluid used in solar collectors. Enhancement through nanofluids is influenced by several factors, which include nanoparticle types, nanoparticle concentration, base fluid, and the purpose of its application. This review provides a technical summary of the application of nanofluids in the two main types of collectors: non-concentrating and concentrated thermal collectors. Findings from this study showed that TiO2 + Cu hybrid nanofluids with a mass fraction of 0.03 augment heat transfer coefficient by 21% in parabolic trough collectors. The merits of employing nanofluids as heat transfer fluids in solar collectors are examined, while also outlining the obstacles and areas where further research is needed.

Techno-economic analysis of hybrid solar thermal systems with flat plate and parabolic trough collectors in industrial applications

Hybrid configurations that combine two different solar thermal collector technologies are considered to improve the economic competitiveness of solar systems in district heating applications. However, the performance of these systems in the industrial sector has been scarcely studied. This study evaluates the energetic and economic potential of hybrid systems with flat plate and parabolic trough collectors under different industrial process temperatures and radiation levels. To enable this evaluation, a hybrid field sizing methodology was developed. The results showed that the hybrid system could achieve high solar fractions with a lower levelized cost of heat than parabolic trough collector individual systems and smaller solar field areas than flat plate collector individual systems. Furthermore, the hybrid system with approximately 50% flat plate collectors reached monthly solar fractions up to 91% higher than the individual flat plate collector alternative. The seasonal performance demonstrates that the hybrid configuration could have great potential for applications with higher demand in the summer months, such as solar cooling with absorption chillers and solar water desalination for crop irrigation. This study contributes to the understanding of the potential of hybrid systems in the industrial sector and presents tools and insights for future research of hybrid solar thermal configurations.

Control of Solar Energy Systems

This review deals with the control of parabolic trough collector (PTC) solar power plants. After a brief introduction, we present a description of PTC plants. We then provide a short literature review and describe some of our experiences. We also describe new control trends in PTC plants. Recent research has focused on (a) new control methods using mobile sensors mounted on drones and unmanned ground vehicles as an integral part of the control systems; (b) spatially distributed solar irradiance estimation methods using a variable fleet of sensors mounted on drones and unmanned ground vehicles; (c) strategies to achieve thermal balance in large-scale fields; (d) new model predictive control algorithms using mobile solar sensor estimates and predictions for safer and more efficient plant operation, which allow the effective integration of solar energy and combine coalitional and artificial intelligence techniques; and (e) fault detection and diagnosis methods to ensure safe operation.

An upscaled model for heat transport in a parabolic trough collector

Parabolic trough collectors are important devices of practical use that profit from solar radiation. Currently, modeling this type of systems is mostly performed using direct numerical simulations where the governing equations at the microscale are solved in time and space, which demands considerable computational time. An alternative is to systematically reduce the number of degrees of freedom by developing upscaled models. The main finding of this work is that an upscaled model is a reliable approach to study heat transfer in the receiver tube of a parabolic trough collector. The model was derived using the volume averaging method, by capturing the essential microscale information in a cross-sectional averaging process. The model consists on a partial differential equation that accounts for the (axial) spatio-temporal changes of the average temperature and it is written in terms of four effective-medium coefficients that are predicted from the solution of two ancillary closure problems. The functionality of these coefficients with the Biot number was adjusted using a fractional function, which are the second main finding of this work. In addition, the model was validated by comparisons with direct numerical simulations (DNS). The model derived here is shown to perform adequately (i.e., with a relative error with respect to DNS smaller than 5%) under the desirable operating conditions of the system and this constitutes the third main finding of this work.

Optimization of gaseous working fluid and internally finned absorber tube for enhancing the thermal performance of parabolic trough solar collector

The current study examined the effect of various types of longitudinal finned absorber tubes with the gaseous working fluid on the performance of the parabolic trough collector. Conventional heat transfer fluids, such as water, thermal oils, molten salts, etc., have been limited when the parabolic trough collector works at very high temperatures. Gas may be used as heat transfer fluid when this collector may operate at very high temperatures. However, the heat transfer coefficient of gas is smaller than the conventional heat transfer fluid. Therefore, fins may be used to improve the parabolic trough collector's thermal performance when gas is used as heat transfer fluid. Hence, selecting the best suitable gas as heat transfer fluid and the optimum fin structure is essential to improve this collector's thermal performance. In this context, the current study has considered seven different gases, namely air, carbon dioxide, helium, nitrogen, oxygen, methane, and neon, and six longitudinal finned absorber tubes with different profiles, namely, rectangular, triangular, trapezoidal, T-shaped, and Y-shaped to select the best suitable heat transfer fluid and optimum fin structure. The best suitable gas and optimum fin profile have been chosen based on specific criteria (multi-objective optimization technique or the performance enhancement factor index). This problem has been simulated using commercial software ANSYS Fluent 2020 R2. The experimental and numerical data discovered in the literature are used to validate the results of the current investigation and found in good accuracy between them. The methane gas is found to be the most suitable heat transfer fluid based on both criteria. Then, the effect of mass flow rate and inlet temperature of methane gas on the average friction factor and Nusselt number have been investigated. It is found that the average friction factor decreases with the mass flow rate for the given inlet temperature, while the opposite trend has been observed for the average Nusselt number. For the first time, the T-shaped and Y-shaped finned absorber tube has been proposed in the present study and compared with earlier fin profiles utilized by the researcher. It is found that the increment in thermal efficiency for T-shaped and Y-shaped finned absorber tubes with methane gas is 8.9338 % and 10.1360 %, respectively. In contrast, the increment in exergy efficiency for T-shaped and Y-shaped finned absorber tubes is 8.942 % and 11.622 %, respectively. There is a significant improvement in the thermal and exergy efficiency of the proposed model compared to the models considered in the literature (air flow through absorber tube with the rectangular fin profile). Furthermore, the highest average Nusselt number of 480.4651 is found for the T-shaped finned absorber tube than other examined cases. However, the friction factor is also high for these fin profiles. As a result, the value of the performance enhancement factor for this fin profile is reduced, and the maximum value of the performance enhancement factor is obtained for rectangular fin profiles. Generally, increasing fin height and width increases thermal performance and pressure loss. Therefore, six different dimensions of rectangular fin have been studied and compared with smooth tubes. It is found that the optimum fin dimension of the rectangular fin is a height of 5 mm and a width of 4 mm. The present results can be utilized for designing an internally finned absorber tube to improve the collector's thermal performance with gas as heat transfer fluid.

Influence of different circumferential heat flux distributions on flow boiling of R245fa in a circular horizontal tube

Direct steam (and vapour) generation in parabolic trough collectors remains practically untapped due to inherent multi-physics challenges. Such difficulties include an understanding of the effect the non-uniform solar flux has on the boiling flow within absorber tubes. For this purpose, steady-state flow boiling of R245fa was experimentally investigated in a 17.12 mm diameter horizontal stainless-steel tube, at a saturation temperature of 40 °C, and mass fluxes of 125 kg/m2s to300 kg/m2s. Various circumferential heat flux distributions were considered at the same total heat rate, including fully uniform heating, bottom half heating, top half heating, side half heating, and a representative parabolic trough collector heating profile. Locally applied heat fluxes ranged from 0.38 kW/m2 to 30.48 kW/m2. It was found that the transition between flow patterns were not affected by the heat flux distribution. A stochastic inverse model based on Bayesian inference was developed to resolve the heat transfer coefficients. The heating profile significantly altered the heat transfer performance in terms of the local and average heat transfer coefficients. Relative to uniform heating, the average heat transfer coefficients ranged between approximately a 144 % enhancement to a 40 % reduction, depending on the heat flux distribution, mass flux, and vapour quality. The parabolic trough collector heating profile had the best average heat transfer coefficient for most conditions, whereas uniform heating demonstrated superior heat transfer coefficients for highly convective dominant flow. Locally resolved heat transfer coefficients identified the dominance of nucleate boiling at the tube’s lower circumference. Existing predictive methods from literature were found unsuitable when applied at the local level. Further investigation is required to determine the relative dominance of convective and/or nucleate boiling at different circumferential positions.

Thermal and economic investigations of parabolic trough collector arrays with application in Brazil

Thermal and economic investigations of parabolic trough collector arrays with application in Brazil

Design of a Parabolic Trough Collector Solar Field for a Pilot CO2 Capture Plant from Natural Gas Combined Cycle Power Plant Flue Gas.

A parabolic trough collector solar field was designed to supply the heat needed to regenerate the CO2-rich monoethanolamine in a solar-assisted carbon capture system. Process design modeling was performed for 90% of the CO2 removal from 1% of the flue gas produced by a 255 MWe natural gas combined cycle power plant. Calculations with and without 24 h of thermal energy storage by increasing the solar collector size needed and providing a buffer vessel to store hot heat transfer fluid were performed. A dynamic analysis of the solar field using the hourly solar forecast was performed to investigate how heat transfer fluid mass flow changes during January and June to maintain the desired parabolic solar field outlet temperature needed for CO2 reboiler operation. The calculations provided here present an explicit method to calculate relevant solar field design parameters that can be scaled up and used in solar energy-assisted gas capture processes.

An innovative renewable energy–based tri-generation system for electricity, LNG regasification and hydrogen production

Waste incineration is a potent technique, that deals with the waste generated in a sustainable way to properly manage and reduce the generated waste and produce useful energy simultaneously. However, the waste-to-electrical efficiency of incineration plants is less (20–22) % because of the high moisture content of waste and flue gas heat losses. In the present study, a tri-generation system consisting of a solar parabolic trough collector integrated with a waste-to-energy plant, a liquefied natural gas (LNG), and a hydrogen production system is proposed and thermodynamically investigated. Parabolic trough collectors serve as a secondary heating source to the steam coming out of the incineration boiler. The useful heat collected by the parabolic trough solar field is provided to the fluid exiting the incineration boiler and entering into the steam turbine to improve the steam condition, while LNG is vaporized by the energy of exhaust flue gas and produces power for the PEM electrolyzer. Waste-to-energy incineration facility is capable of operating with a feed rate of 350 tons/day, producing 6.3 MW of power at an inlet temperature of 400 °C of the turbine. However, the net power produced is increased to 7.72 MW with increase in turbine inlet temperature to 515 °C. Results of the study conclude that the energetic and the exergetic efficiencies of the incineration plant are found to be 27.93 % and 26.51 %, respectively. In addition, both the first and second law efficiencies are observed as 21.51 % and 25.74 %, respectively, while the rate of hydrogen production is 7.72 kg/h. The cumulative exergy destruction rate of the system is 29.3 MW and the WtE boiler shares the maximum portion (58.14 %) of the exergy destruction.

Thermal performance enhancement in a solar parabolic trough collector with optimized secondary optics

Thermal performance enhancement in a solar parabolic trough collector with optimized secondary optics

Thermal performance analysis of eccentric double-selective-coated parabolic trough receivers with flat upper surface

The Parabolic trough collector (PTC) system combined with molten salt energy storage system has gathered increasing attention owing to its advantages of high operating temperature and stable power output. However, the substantial heat loss experienced by parabolic through receivers (PTR) under high temperatures imposes limitations on the thermal efficiency and power generation potential of the PTC system. In this study, a novel eccentric double-selective-coated parabolic trough receiver is proposed. The upper surface of the receiver is flattened to further reduce radiation heat loss. Various distances from collector focus are explored to determine the most suitable opening angle of secondary selective coating, ensuring the highest thermal efficiency. The results show that, although the eccentricity causes partial optical loss, the reduced upper surface area and the resultant larger secondary coating opening angle contribute to a significant reduction in heat loss and an improved thermal efficiency of the novel receiver. The thermal efficiency of the new absorber can be improved by up to 20.59 % (under direct normal irradiance of 600W/m2 and a receiver surface temperature of 600 °C). Furthermore, the higher the emissivity and the lower the absorptivity of the solar selective coating, the better the performance of the novel absorber tube.

Experimental Investigation of a Small-Scale Parabolic Trough Concentrated Solar Power ‎Systems

Large-scale systems have a lower levelized cost of electricity than small-scale concentrated solar power systems. Thus, the purpose of the present study is to evaluate the potential of using standalone small-‎scale ‎concentrated ‎solar power collectors in order to generate process ‎heat ‎at ‎a ‎moderate ‎temperature, which directly utilizes thermal energy without the need to generate electricity. ‎A ‎parabolic trough ‎collector (3.6m2) ‎was ‎designed ‎and ‎manufactured, including a dual-axis solar tracking system with and without an insulating function. An ‎insulating ‎cavity ‎was incorporated to ‎minimize the heat ‎losses collected by the absorbed ‎tube. ‎The experiments ‎were ‎carried out during a time of high winds and unfavorable weather ‎in ‎Sabratha City. The findings of the experiments demonstrated that the produced temperature and the collected heat energy progressively increase until they reach their maximum value, and then gradually decrease. The maximum water ‎temperature ‎was 96ºC at ‎a ‎flow rate ‎of ‎‎0.5L/min, and ‎the highest amount of ‎heat energy was 550W/m². ‎Wind speed showed an important impact on the produced temperature; therefore, various comparative experiments were carried out in the same climate condition; ‎the experiment with the insulating function ‎presented the least heat loss, and it takes a higher edge of 11% in terms of efficiency. ‎In addition, the water temperature rose to 120°C where steam was generated at a zero flow rate, while the oil ‎reached 194ºC. In addition, a mathematical model was also implemented to theoretically study energy balance; with little expected discrepancy, its predictions and the experimental results agreed. In conclusion, the results presented reasonable markers of interest despite the poor environmental conditions during the experiments.‎

Techno-economic analyses of solar thermal process heat integration at South African beverage producers

South Africa's industrial sector relies primarily on coal and gas to meet process heat requirements (700–750 petajoules per annum). Much of this energy is used to fire steam boilers operated at less than 200 °C. This study determines the viability of solar thermal technologies as a replacement for fossil fuels for the supply of steam in large beverage facilities in South Africa. The Gauteng and Western Cape provinces are considered, which account for two-thirds of South Africa's beverage production. The sizing of collector fields and potential solar fractions are determined using typical ready-to-drink beverage packaging hall energy requirements. The cost of heat from parabolic trough collector systems is modelled using quasi-dynamic simulations in Polysun, and heat storage configurations are optimised. This study demonstrates that solar thermal projects would be viable alternatives to heavy fuel oil, diesel, gas, and even coal - should the cost of coal remain above US$250 /tonne (2020 real-term values). Transition to solar thermal energy for process heat in this sector is thus strongly recommended.

Optical efficiency of parabolic troughs with a secondary flat reflector; effects of non-ideal primary mirrors

Secondary flat receivers enhance concentration of parabolic trough collectors with cylindrical receivers. An increase of 70 % was possible for commercial primary mirrors while allowing the optical efficiency to be less sensitive to misalignments. Including the secondary flat reflector close to a parabolic-trough receiver may, however, reduce the optical efficiency of the trough due to the shadow projected. In this work ray-tracing simulations were conducted to compare the optical efficiency and the misalignment sensitivity of the standard absorber and its secondary flat reflector variation. In some cases, the required dimensions for the secondary flat reflector would make it a non-realistic solution due to the impossibility of encapsulating it within a glass cover. To overcome this issue, a truncated version of the secondary mirror is proposed and evaluated. A truncated secondary flat reflector will decrease the deleterious effects of the shading, enhancing concentration further but changing the tolerance to misalignments of the troughs. Analysis of two benchmark primary mirrors shows a worst-case scenario of optical efficiency reductions less than 3.5 and 2 %, with concentration increases of 20 and 80 % respectively. The reduction on absorber size offsets the lower optical efficiency by the reduction of radiation losses, especially for high-temperature applications.

An experimental study on parabolic trough collector in simulated conditions by metal-halide solar radiation simulator

An experimental study on parabolic trough collector in simulated conditions by metal-halide solar radiation simulator

Insulator roof, acentric absorber tube and nanofluid effect on parabolic trough collector efficiency via two-phase flow simulation

Insulator roof, acentric absorber tube and nanofluid effect on parabolic trough collector efficiency via two-phase flow simulation

Thermodynamic analysis of absorption refrigeration systems with nanofluid for using in sport buildings

In the present study, a novel refrigeration cycle that works based on the absorption refrigeration cycle and uses solar energy to supply energy to sports buildings is presented. For collecting the solar energy, a parabolic trough collector is used, and for enhancement of the heat transfer to the working fluid, synthesis-based nanofluid containing SiO2 nanoparticles are used. The investigation of the fluid flow inside the absorber tube shows that the convection heat transfer coefficient is increased as a result of increasing the volume fraction of the nanoparticles in the nanofluid. In addition, using the nanofluid in the heat exchanger inside the generator increases the heat transfer to the solution inside the generator and the coefficient of performance of the absorption cycle. The benefits of this research are the analytical investigation of the new combined absorption–ejection refrigeration cycle, which can provide a good understanding of the effect of different parameters on the system performance, and the investigation of using nanofluid in the absorber tube of a trough parabolic collector in solar systems.

Solar thermal reactor model for pyrolysis of waste plastic

ABSTRACT The ability to convert waste plastic into combustible liquids and gases using solar energy could help transform the problem of disposal of non-recyclable plastic into a valuable and environmentally responsible source of fuel. The purpose of this study is to propose a practical model for a compound parabolic trough solar thermal reactor for pyrolysis of waste plastic. The model integrates predictions of energy available from solar radiation (at a given location, time of day and time of year) with parabolic trough collector orientation and efficiency, a transient energy balance for an evacuated tube reactor and pyrolysis kinetics of waste plastic. The experimental setup used to test the model includes a pyranometer, a commercial solar collector consisting of a 60 cm long evacuated tube with a compound parabolic reflector and multi-channel data loggers to collect temperature, humidity and radiation data. The solar radiation sub-model was found to be in excellent agreement with clear-sky irradiance data collected using the pyranometer. Predictions of reactor temperature and reaction rate were found to be sensitive to the concentrator aperture area, solar irradiance, type of plastic (Arrhenius kinetics) and radiation properties of the evacuated tube reactor but relatively insensitive to humidity, wind velocity and terrestrial irradiance. The model shows that even on a small scale, favourable conditions for pyrolysis of waste plastic can be achieved within a solar reactor.