Parabolic Trough Receiver Research Articles

Heat transfer enhancement of a parabolic trough solar collector using innovative receiver configurations combined with a hybrid nanofluid: CFD analysis

The present study investigates the thermal performance of three novel parabolic trough receiver configurations and compares the performance of two different heat transfer fluids: Syltherm800 and MWCTN-TiO2/Syltherm800 hybrid nanofluid. Numerical simulations were conducted using computational fluid dynamics in ANSYS Fluent software. The model was validated by comparing the numerical results with experimental results from Dudley's study. Simulations were performed for various inlet velocities and temperatures to evaluate parameters including the Nusselt number, friction coefficient, performance evaluation criterion, temperature gradient, and thermal efficiency. Among the three configurations, Configuration 3 demonstrated the highest thermal performance. The MWCTN-TiO2/Syltherm800 hybrid nanofluid exhibited better thermal performance compared to Syltherm800. The maximum variation in parameters comparing new configurations with the smooth receiver is: Nusselt number increased by 60 %, 55.1 %, and 149 %; thermal efficiency increased by 2.55 %, 1.86 %, and 5.12 %; friction factor increased by 2.7, 3.8, and 6.5 times; temperature gradient decreased by 29.67 %, 23.9 %, and 47.4 %, for configurations 1, 2, and 3, respectively. When comparing the MWCTN-TiO2/Syltherm800 hybrid nanofluid to Syltherm800: Nusselt number increased by 4.9 %, 3.6 %, 4.9 %, and 3.5 %; thermal efficiency increased by 2.7 %, 1.98 %, 2.5 %, and 2.56 %; friction factor increased by 8.48, 7.123, 11.62 and 9.88 times; temperature gradient decreased by 3.1 %, 6.8 %, 6.3 %, and 6.4 %, for the smooth receiver and configurations 1, 2, and 3, respectively. The findings highlight the potential of using tabulators and the MWCTN-TiO2/Syltherm800 hybrid nanofluid for improving thermal performance and reducing thermal stresses in parabolic trough receivers.

A comparative study on optical and thermal performance of parabolic trough concentrator using a bundle of absorber tubes

Reorganizing the larger diameter receiver tube into a bundle of smaller diameter receiver tubes in regions of high solar flux density can enhance the thermal performance of the solar parabolic trough collector. The data that really is presently available in the literatures are studied. The parabolic trough concentrator's optical performance and the solar parabolic trough receiver thermal performance is 66.4% and 74.8% respectively. It is concluded from the comparative study that the use of the original receiver bundle (copper tube selective coating), has been ascertained, improving convective heat transfer coefficient, bringing down receiver tube surface temperature and increasing thermal performance, but the expense of raising friction coefficient and pumping power.

Determination of Hydrogen Content in Getter Material from Parabolic Trough Receivers

In this study, a procedure for analyzing the hydrogen content of used getter material is described based on mass spectrometry coupled to thermal gravimetry. It is shown that hydrogen masses per getter mass in the range of 2 – 15 mg/g can be quantified. At least three differently strong hydrogen binding situations are found with the thermal desorption program applied so far. Up to 450 °C only traces of hydrogen can be desorbed from the getter material with the applied method and up to 99% is released on heating up to 800 °C.

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.

Analytical investigation of solar parabolic trough receiver with multiple twisted tapes using exergy and energy analysis

Exergy analysis is an important thermodynamic approach to studying the system's actual output, considering all losses. The present study is an analytical approach to calculating the thermal and exergetic efficiencies of the parabolic trough receiver using MATLAB R2018a simulation software. These efficiencies are evaluated considering temperature rise characteristics and parametric design factors. The influence of the solar air heater's thermal and exergy analysis-based mathematical model on all design parameters is examined. The receiver tube has multiple twisted tape inserts with three varying parameters, i.e., twist ratio (y/w) = 3 to 5, perforation ratio (dp/w) = 0.05 to 0.25, and winglet ratio (d/w) = 0.1 to 0.3. The twisted tape with y/w, dp/w, and d/w having values 3, 0.1, and 0.05 perform better regarding energy and exergy with values 84.27% and 4.28%, respectively. This thorough examination can prove to be highly effective and advantageous in generating the design model for the specified twisted tape parameter value without requiring extensive investment in actual experimentation while also furnishing an evaluation of the performance of the solar air heater design.

Optimizing Solar Parabolic Trough Receivers with External Fins: An Experimental Study on Enhancing Heat Transfer and Thermal Efficiency

Several researchers have shown that the heat transfer performance of solar parabolic trough (SPT) receivers may be improved by increasing their surface area or by adding internal fins to the tubes. Unfortunately, the manufacture of internally finned tubes involves complex processes, resulting in significant cost increases. On the other hand, the addition of external fins to tubes is more technically and economically feasible in a low-resource setting. This study investigates the potential benefits of integrating external fins on the receiver tubes of a low-cost SPT collector system. Experiments were conducted using an SPT system with a focal length of 300 mm and a collector length of 5.1 m, and they were positioned by an automated Sun tracking system. Tests were undertaken using both smooth and externally finned receiver tubes operating at five different water flow rates. The solar receiver with a finned tube was able to provide a maximum water temperature of 59.34 °C compared with that of 56.52 °C for a smooth tube at a flow rate of 0.5 L per minute. The externally finned absorber tube was also found to have a maximum efficiency of 18.20% at an average daily solar intensity of 834.61 W/m2, which is approximately 48% more efficient than the smooth tube. The calculations indicate that the experimental SPT system using finned tubes potentially avoids 0.2726 metric tons of CO2e per year, with finned tubes outperforming smooth tubes by up to 44%. The results show that using externally finned receiver tubes can significantly enhance the thermal performance of SPT collector systems.

Impact of installation error and tracking error on the thermal-mechanical properties of parabolic trough receivers

As the solar energy utilization technology for renewable clean energy, actual parabolic trough receivers are subject to tracking errors and absorber tube installation errors, and the bellows and Kovar ring under these errors have a significant impact on the receiver's safety. Based on the MCRT-FVM-FEM principles in this paper, a receiver's optical-thermal-stress mathematical model is modeled and the thermal-stress performance and safety of the receiver's key components under two errors are evaluated. The correlation between the bellows and Kovar ring's performance and the two errors is analyzed. The results demonstrate that the lower tracking errors and larger installation errors markedly increment the absorber's deformation and have a negative impact on the receiver safety. Bellows and Kovar ring's asymmetrical temperature distribution causes variable swell and uneven stress under tracking and installation errors. Temperature gradient variation of bellows is more sensitive under errors than Kovar rings. Kovar ring's compressive stress rises substantially as the Y-directional installation error varied from −15 mm to 15 mm compared to other errors. With tracking errors exceeding 8 mrad, bellows' tensile stress and Kovar ring's compressive stress diminish under installation error. Thus, larger tracking errors significantly reduce the threat to the receiver when installation errors exist.

Performance analyses of a novel finned parabolic trough receiver with inner tube for solar cascade heat collection

Performance analyses of a novel finned parabolic trough receiver with inner tube for solar cascade heat collection

Thermal-mechanical performance analysis of parabolic trough receivers under various optical errors based on coupled optical-thermal-stress model

As green and sustainable technology, the parabolic trough receiver's thermal-mechanical performance is widely concerned because of the optical errors in all practical systems. The coupled MCRT-FVM-FEM approach was employed to construct the receiver's optical-thermal-stress model. The receiver's safety and thermal-mechanical performance is thoroughly analyzed using the model to illustrate the coupling effects of tracking error (σt), slope error (σs), and installation error (σx and σy). Bellows and Kovar ring's deformation and thermal stresses under multi-error are investigated for the first time. Bellows and Kovar rings' variable expansion and uneven axial stresses are brought on by the uneven heat flux distribution and absorber's heat transfer. While bellows and Kovar ring enhance absorber's deformation and stress. Optical errors mainly affect the bellow's axial tensile stress and the Kovar ring's axial compressive stress. Tracking and installation errors have less impact on receiver safety when σs exceeds 4 mrad. However, they enhance the risk of receiver failure when σs is sufficiently small (<4 mrad). Positive σy leads to receiver's maximum deformation (23.57 mm), significantly increasing the Kovar ring's maximum compressive stress and threatening the receiver's safety. Therefore, the impact of bellows and Kovar ring on receiver safety should be considered when simulating actual operation.

Conjugate-Based Numerical Analysis of Parabolic Trough Receiver Pipe With Temperature-Dependent Thermo-Physical Properties of Heat Transfer Fluid Under Laminar Flow Regime

Abstract In this article, the use of gas as a working fluid in the parabolic trough receiver (PTR) has been investigated numerically. The present study aims to determine which gas will work best as a heat transfer fluid (HTF) by analyzing the impact of several gases on the PTR’s performance. So, gases, such as carbon dioxide, helium, nitrogen, oxygen, hydrogen, methane, neon, and air, are considered in the present study, which flow through a thick-wall stainless steel pipe under a laminar flow regime. The temperature-dependent thermo-physical properties of the gas are considered. The finite difference method (FDM) with the harmonic mean technique is employed to solve this conjugate heat transfer problem. The current research findings are verified with those reported in the literature and are in excellent agreement. The grid-independent study is conducted to choose the optimal grid size. After that, the multi-objective function optimization technique and performance enhancement factor (PEF) is used to select the best suitable HTF, and it found that hydrogen gas is most appropriate based on these two criteria. Then, the influence of various parametric studies such as Reynolds number, solar flux, and receiver pipe thickness on the Nusselt number has been carried out. It is found that the Nusselt number increases with the Reynolds number while it decreases with solar flux and receiver pipe thickness. The significance of the current study may aid in choosing the appropriate gas as HTF in the parabolic trough solar collector (PTSC).

In-situ heat losses measurements of parabolic trough receiver tubes based on infrared camera and artificial intelligence

Thermal problems occurring in glass cover, getters, vacuum, expansion bellows, and HTF lead to significant thermal losses due to convection-conduction, which accelerates the absorber degradation and implies replacing immediately these tubes. The replacement of the absorbers tubes is very expensive and interrupts the normal production of concentrated solar power plants. Therefore, the maintenance of the absorber tubes is one of the most critical challenges. In this paper, the Heat Loss Out System (Heat LOS) is proposed for regular evaluation and monitoring of absorbers tubes to maintain their efficiency and reduce operation and maintenance costs through immediate intervention. The proposed system is based on the intelligent processing of photos and videos in real time taken by a robust infrared camera with exact GPS coordinates and implemented on a vehicle. The Heat LOS evaluates in real-time, precisely, and rapidly, the temperature distribution of the absorbers tubes without contacting the surface or interrupting the normal production. First, an analytical study is performed to determine the appropriate speed of the vehicle, which can reach up to and the distance between the camera and the absorber tube that meet a high accuracy of measurement and do not disturb it which should not exceed 5 m. In addition, several absorbers tubes installed in the Green Energy Park (GEP, Morocco) research center are tested and evaluated using the Heat Loss Out system. The results obtained show a promising performance of the proposed system up to an accuracy of 93% based on deep learning with the CNN method, which will be valid when compared to manual analysis. This solution was assembled on a vehicle to rapidly evaluate several tubes and goes through many loops.

Effect of Different Arrangements of V-Shaped Ribs on the Performance of an Optically Enhanced Parabolic Trough Solar Collector

Abstract In this article, a V-shaped ribbed tube is utilized to improve the thermal performance of a parabolic trough collector (PTC). Six different rib arrangements are employed, and a detailed analysis is presented. In addition, the effect of adopting a secondary reflector (SR) on the temperature distribution around both a smooth and a ribbed parabolic trough receiver (PTR) tube is conducted. A computational fluid dynamics model is employed to study the heat transfer and fluid flow characteristics inside the tube. Results show that V-shaped ribs are an effective tool to stir up the flow and increase the velocity gradient of the fluid near the inner surface of the tube. This helps increase the convective heat transfer rate and reduce the tube’s maximum circumferential temperature. Moreover, results from the study show that the secondary reflector contributes to a further decrease in the tube surface temperature and hence improves the overall thermal efficiency of the collector. The combination of a V-shaped ribbed PTR tube and a secondary reflector is thus shown to be beneficial for the PTC system, especially at high Reynolds numbers.

Eulerian multiphase study of direct steam generation in parabolic trough with OpenFOAM

AbstractDirect steam generation (DSG) in parabolic trough solar collectors is a feasible option for economic improvement in solar thermal power generation. Three‐dimensional Eulerian two‐fluid simulations are performed under OpenFOAM to study the turbulent flow in the evaporation section of the parabolic trough receiver and investigate the phase change, and pressure drop of water as a heat transfer fluid. First, the model's validity has been tested by comparing the numerical results of a laboratory scale boiler with the available correlations and semi‐correlations of boiling flows from the literature. Simulations agreed well with Rouhani–Axelsson correlation for horizontal tubes, with a mean relative error of less than 7.1% for all studied cases. However, despite a mean relative error of less than 13.19% compared to the experimental data in the literature, the reported pressure drop factor remains valid; overprediction remains tolerable for most engineering applications. Second, the scaling effect on the mathematical model, from laboratory to commercial‐scale configuration, was tested with experimental data of the DISS test loop in Platforma Solar de Almeria, Spain. The Monte Carlo Ray Tracing method under the Tonatiuh package allowed for obtaining the nonuniform heat flux distribution. Due to the large size of the evaporation section in the DISS loop (eight collectors), each collector is considered independently in the simulations. Thus, simulations follow each other, taking the numerical results of each collector output as input data in the next collector and so on until the last. The numerical results showed an excellent agreement for the void fraction with 3.53% against the Rouhani–Axelsson correlation. Frictional pressure losses are within a 17.06% error of the Friedel correlation, in the range of previous work in the literature, and the heat loss is less than 4.69% error versus experimental correlation.

Numerical Investigation of Solar Flux Homogeneity and Intensity of a Parabolic Trough Receiver with Various Secondary Reflectors

Numerical Investigation of Solar Flux Homogeneity and Intensity of a Parabolic Trough Receiver with Various Secondary Reflectors

Heat Transfer Enhancement in a Receiver Tube of Solar Collector Using Various Materials and Nanofluids

The solar flux distribution on the Parabolic Trough Collector (PTC) absorber tube is extremely non-uniform, which causes non-uniform temperature distribution outside the absorber tube. Therefore, it generates high thermal stress which causes creep and fatigue damage. This presents a challenge to the efficiency and reliability of parabolic trough receivers. To override this problem, we have to homogenize the heat flux distribution and enhance the heat transfer in the receiver’s absorber tube to improve the performance of the PTC. In this work, 3D thermal and thermal stress analyses of PTC receiver performance were investigated with a combination of Monte Carlo Ray-Trace (MCRT), Computational Fluid Dynamics (CFD) analysis, and thermal stress analysis using the static structural module of ANSYS. At first, we studied the effect of the receiver tube material (aluminium, copper, and stainless steel) on heat transfer. The temperature gradients and the thermal stresses were compared. Second, we studied the effect of the addition of nanoparticles on the working Heat Transfer Fluid (HTF), employing an Al2O3-H2O based nanofluid at various volume concentrations. To improve the thermal performance of the PTC, a nanoparticle volume concentration ratio of 1%–6% is required. The results show that the temperature gradients and thermal stresses of stainless steel are significantly higher than those of aluminium and copper. From the standpoint of thermal stress, copper is recommended as the tube receiver material. Using Al2O3 in water as an HTF increases the average output temperature by 2%, 6%, and 10% under volume concentrations of 0%, 2%, and 6% respectively. The study concluded that the thermal efficiency increases from 3% to 14% for nanoparticle volume fractions ranging from 2% to 6%.

Effects of geometric configurations on the thermal-mechanical properties of parabolic trough receivers based on coupled optical-thermal-stress model

An optical-thermal-stress coupled analysis model of the Parabolic Trough Receiver (PTR) was built based on the Monte Carlo Ray Tracing method and Computational Fluid Dynamics. The temperature field and stress field of the PTR were studied by numerical simulation, and the absorber deformation and the Kovar ring failure were analyzed. Furthermore, the effects of the aperture width (W) and focal length (f) across the entire receiver temperature gradient and thermal stress field were studied. The results showed that the effect of width and focal length on the temperature field was mainly reflected in the change in the high-temperature distribution of the absorber. The maximum collector efficiency were 81.02% and 70.4% when W = 13 m and f = 1.84 m, respectively. The maximum deformation on the absorber reached 17.85 mm at W = 7 m. High deformation and high Von Mises stress were maintained with f from 3.5 m to 5.5 m. The trends of maximum temperature difference and average temperature on bellows, Kovar ring and glass tube were similar. The results also showed that width and focal length mainly affected the axial stress on Kovar rings and bellows.

Performance analyses and heat transfer optimization of parabolic trough receiver with a novel single conical strip insert

Parabolic trough collectors are the crucial component of the concentrated solar power plant, which can meet heat demand and mitigate energy shortages. However, their operation suffers from defects of high local temperature and poor wall temperature uniformity. To alleviate this issue, an enhanced parabolic trough receiver (PTR) with a novel single conical strip insert is proposed and numerically investigated in detail. Furthermore, the effects of structural parameters of the conical strip on the enhanced PTR are investigated, and multi-objective optimization is conducted to determine the optimal parameters. Finally, the performance of the optimal enhanced PTR is evaluated under different operating conditions. The results show two symmetrical longitudinal vortices are formed in the absorber tube due to the guidance of the conical strip, which is beneficial to enhancing fluid mixing and heat transfer. Accordingly, the temperature uniformity of the absorber tube and the actual efficiency are effectively improved. Compared to the smooth PTR, the tube wall temperature is dropped by up to 168 K, and the actual efficiency is improved by 3.3% at most. Moreover, the entropy generation and exergy destruction are reduced by 22.2%–49.3% and 30.6%–45.9%, respectively. This research may guide designing the PTR for efficient and safe operation.

Improving overall heat transfer performance of parabolic trough solar receiver by helically convex absorber tube

The parabolic trough collector (PTC) system has been widely applied in concentrating solar power (CSP) technology. The absorber tube of PTC has a significant impact on the solar energy conversion efficiency. In order to improve the overall heat transfer performance of PTC system, the idea of using helically convex tube as a metal absorber tube of the parabolic trough receiver (PTR) is proposed. Combined with Monte Carlo ray tracing method, the Finite Volume Method is used to establish the numerical analysis model. The effects of structural parameters (p, h, and r) of helically convex absorber tube on the heat transfer and flow performance are studied. The results show that by designing the helically convex structure of tube, the heat transfer and flow properties of parabolic trough receiver can be effectively optimized. Compared with the traditional PTR, the overall heat transfer performance is improved by up to 34%.

Thermo-fluid modeling and thermodynamic analysis of low-temperature parabolic trough systems with multi-walled carbon nanotubes/water nanofluids

Numerical thermodynamic analysis for low-temperature parabolic trough receivers with Multi-walled carbon nanotubes/water (MWCNT/water) nanofluids as a heat transfer fluid is presented. Numerical modeling is carried out using developed in-house software and is based on a coupled 3D thermo-fluid mathematical model that combines Monte Carlo ray tracing method and finite volume method. Experimental thermophysical properties of the MWCNT/water nanofluids with 0.05%, 0.1%, and 0.3% nanoparticles volume fraction are approximated in the temperature range of 25 °C−70 °C. Created nonlinear mathematical model and numerical algorithm are validated through comparison with analytical and experimental data. It was discovered that the optimal correlation between MWCNT/water thermal conductivity and heat capacity plays a key role in the heat transfer enhancement and increased energy efficiency of the low-temperature parabolic trough collectors. Impact of the inner tube surface roughness and MWCNT/water viscosity on pressure drop inside tube receiver are studied. It was found that only the MWCNT/water nanofluid with 0.05% nanoparticles volume fraction at laminar flow regime in long tube receivers enhances convective heat transfer and guarantees temperature growth by 3% in comparison with pure water. MWCNT/water nanofluid with 0.05% nanoparticles volume fraction also increases energy and exergy efficiencies by 10% and has low pressure drops, and therefore is recommended as promising heat transfer fluid for different types of low-temperature parabolic trough collectors.

The Effect of Utilizing Pcms-Nanofluids on The Performance of the Parabolic Trough among Storage Medium

The present study relates to the investigation of a parabolic trough collector incorporated with a thermal storage tank containing rectangular boxes which stored stearic acid with 0.3vol% of CuO nanofluids acted as Phase-change Materials. The heat output of the parabolic trough's receivers and efficiency of the storage tank was determined by varying the flow rates of waste engine oil and water by 0.035, 0.045, and 0.065 kg/sec. The parabolic collector with a storage tank at 12-1 PM with a heat gain of 10441W for water and 13724W for waste engine oil at a flow rate of 0.035 kg/sec were observed. The waste oil result was 0.31 times greater than the water medium. Also, the PTC without a storage tank was 5.7 times lower at the same flow rate. The higher heat gain was achieved at a 0.035 kg/sec flow rate of the waste oil medium compared to flow rates of 0.045 and 0.065 kg/sec.