Parabolic Trough Solar Receiver Research Articles

A detailed 1D model of a parabolic trough solar receiver with a double-validation approach

This study proposes a detailed Parabolic Trough Collector (PTC) 1D model offering precise optical and thermal analysis. Our motivations were accuracy while ensuring fast and inexpensive computation. The proposed model differs from existing models by considering a more extensive set of possible optical and thermal losses, which to our knowledge have not previously been grouped together in a single model. Testing of the model based on experiments carried out by Sandia National Laboratories showed near-similar accuracy to much more complex models, with a mean standard deviation of 0.891% and 5.99 W/m2 for thermal efficiency and thermal losses respectively. These tests were carried out using two types of selective coating: cermet and black chrome, with two operating modes, namely vacuum and pressure annulus. To expand its scope of validity, the developed model was also tested using data from a selection of PTCs of commercial lengths (70, 106, 143, and 150 m) under real operating conditions. Additional validation of the model was carried out with available results from different heat transfer fluids (HTF), including two nanofluids. We highlighted that the deviation from the results of the various PTCs, although very satisfying in general, becomes more critical with increasing length and temperature, reaching a maximum outlet temperature deviation of around 2.14 °C. On the other hand, when switching from water to the nanofluid Water/CuO (5 %), the results show an increase in outlet fluid temperature from 325.91 to 334.73 °C. Experimental validation was also carried out using a 25 kW PTC test loop located at Ben Guerir. The average relative error perceived between simulation results and experimental measurements is estimated at 0.99 % for the steady-state test (based on the HTF temperature at the PTC outlet). An additional validation based on the external temperature of the glass envelope was also considered. This approach, which is rarely used in the literature, showed a relative error of around 4.39 % between simulations and experimental data, which remains within the uncertainty range of the thermal camera used.

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.

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.

Numerical comparative study on fully-developed mixed laminar convection in two different physical models of parabolic trough solar receiver tube

In this work, a numerical study is presented on the effect of the buoyancy force induced by a non-uniform heat flux NUHF on a laminar air flow in the solar absorber of a parabolic trough collector PTC. The temperature and velocity distributions as well as the development of Nusselt number “Nu” and friction factor “f” were analysed for two physical models of PTC. The study is carried out with a Reynolds number of 2200, a Grashof number covering the range 1x106-6x106 and an angle of inclination of the cylinder of α = 0˚ (horizontal). Calculating the values of "Nu" and "f" showed larger values in the Jeter-PTC case (ϕrim =90֯, GC=20) than in the LS2-PTC (ϕrim=70֯, GC=22.7) case. We deduce that the hydrodynamic and thermal characteristics in the case of mixed convection are affected by the physical model of the chosen PTC.

A hybrid parabolic trough solar collector system integrated with photovoltaics

It is challenging to reduce the massive radiation heat loss from the parabolic trough solar receiver and enhance the solar utilization efficiency of the parabolic trough collector (PTC) system. On the basis of the negative thermal-flux phenomenon discovered in the PTC system, a novel PTC system integrated with photovoltaic (PTC-PV) panels is proposed in this study to effectively enhance the thermal performance and solar utilization efficiency of the PTC system. Four modes of the hybrid PTC-PV system are put forward for catching the optimum configuration. The mathematical models of the hybrid PTC-PV system in terms of photothermal and photoelectrical conversions are established. Additionally, a test rig of the hybrid system is built, and the experiments are carried out in an indoor laboratory with a solar simulator. Comparisons between the experimental and simulated results show that the model has an excellent prediction ability. Furthermore, a 12 m-length PTC-PV system using molten salt as heat transfer fluid is studied to validate its thermal, exergy, and overall performance. The results show that the hybrid PTC-PV system exhibits dramatic superiority in overall performance over the PTC prototype system. The heat loss of the solar receiver in the hybrid PTC-PV system is significantly reduced by 44.0 %, and the photoelectrical efficiency of the PV panel in the PTC-PV system is drastically enhanced by 118.3 % compared to that installed on the ground. Moreover, the overall and exergy efficiencies of the PTC-PV system can be improved by 14.3 and 13.7 %, respectively, at the inlet fluid temperature of 580 °C.

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%.

Numerical study on performance of double-fluid parabolic trough solar collector occupied with hybrid non-Newtonian nanofluids: Investigation of effects of helical absorber tube using deep learning

Influences of a helical absorber tube on the thermal performances of a double-fluid parabolic trough solar collector (PTSC) occupied by non-Newtonian nanofluid are investigated numerically. The problem geometry includes a double-fluid parabolic trough solar receiver with high insulation and a non-circular adsorbent tube. The finite volume method, SIMPLE algorithm, and k-ε model were used for numerical solutions. The result showed that the double-fluid solar receiver was equipped with a helical absorber tube filled with nanofluid with a volume fraction of 4% and nanoparticles diameter of 50nm flowing in the absorber tube, and an annulus glass cover is introduced as the optimal model in this paper. For single-flow PTSC, the value of ηmax nanofluid- and water-based PTSCs are 47.5% and 43.1%, respectively, at a flow velocity of Re=5000. In double-flow PTSC, the value of ηmax at 1 and 4 vol.% is 56.5% and 58.2%, respectively, at the flow velocity of Re=5000. Finally, a deep learning method is employed to examine the parameters affecting the efficiency, including the concentration and diameter of nanoparticles and Re number. The results indicate the ANN has acceptable performance in prediction of the efficiency of the double-fluid parabolic trough solar collector occupied by non-Newtonian nanofluid.

A review study on the performance enhancement of solar parabolic trough receiver by various passive techniques

This is a new era where the world’s energy consumption is so high and is likely to increase over 60% of current consumption by the year 2030. Therefore, renewable energy should be used most frequently. The most preferred alternative to fossil fuels is solar energy but converting solar energy into usable form is the most challenging part. The conversion to thermal energy is the one option. In the area of solar thermal power generation, a solar parabolic trough (SPT) collector is an effective method. Also, the use of passive methods to enhance the thermal performance of these parabolic trough receivers is currently the researcher’s interest This review study is focused on different types of geometrical modification (Artificial roughness) used to enhance the thermal performance of SPT receivers. Based on the extensive study it has been found that conical strip insert is a very broad field for research as it can enhance the thermal performance up to 5–10 times. Also there are parameters associated with the conical strips like shape, pitch, angle of twist, slant angle, geometry angle, etc. which can contribute to better performance when used in SPT receiver.

Experimental investigation on a solar parabolic trough receiver tube enhanced by toroidal rings

The experimental investigation with the incorporation of toroidal rings in an absorber tube of a lab-scale solar parabolic trough collector is carried out in the present study. Five different cases of the absorber tube including the reference smooth absorber tube and the absorber incorporated with 2, 4, 6 and 8 mm thick toroidal rings are investigated. The influence of performance parameters like thermal efficiency, heat loss, thermal enhancement index and so on with different absorber tube configurations are evaluated, compared and illustrated to determine the best case. The outcomes indicate that the absorber tube with 6 and 8 mm thick toroidal rings are the best cases, with the 8 mm case exhibiting a higher exergy efficiency in the range of 38.57%-24.64%. The thermal efficiency for the best absorber cases is found to be 69.43% and 70.34% with the pressure drop being 1.67 and 0.93 kPa, respectively. Also, the cost of heat gain produced with the efficient absorber case is seen to be ₹ 3.43/kWh (US$ 0.045/kWh and € 0.040/kWh), which is nearly 15.51% lower than the reference case. Hence, the incorporation of toroidal rings could be effectively utilized in a large-scale solar thermal system for improved thermal performance.

Performance evaluation of solar parabolic trough receiver using multiple twisted tapes with circular perforation and delta winglet

A parabolic trough collector (PTC) is one of the concentrating types of a solar collector working in the medium range of temperature from 100–400 °C, for this reason, the efficiency of the solar parabolic trough is less than other types of concentrating solar collector (Point focusing types) in terms of solar to thermal energy conversion, the improvement in efficiency is achieved by various passive heat augmentation techniques in the receiver tube. One of the promising passive techniques is twisted tape inserts used in the receiver due to its simplicity in design and the various possibility of geometric modification. This paper deals with the performance evaluation of the solar parabolic trough receiver system by using passive techniques in the receiver. The testing of the receiver of PTC was done by using multiple perforated twisted tapes with winglets having different perforation ratios ([Formula: see text]) of 0.05, 0.15, 0.25, twist ratios ([Formula: see text]) of 3, 4, 5 and wing depth ratios ([Formula: see text]) of 0.1, 0.2 and 0.3. The number of twisted tapes was fixed at 4. The examination was conducted for Reynolds numbers ([Formula: see text]) varying from 3000–21,000 using air as working fluid. The outcome shows that the use of perforation and winglet in twisted tapes augment the Nusselt number as compared to that of smooth twisted tapes. The maximum thermohydraulic performance ([Formula: see text]) of 2.40 is received by using multiple twisted tapes with perforation and winglet having [Formula: see text] = 0.3, [Formula: see text] = 3, and [Formula: see text] = 0.05 at the Re = 21,000. The correlations for Nusselt number ([Formula: see text]) and friction factor ([Formula: see text]) are also developed with ± 8.5% and ± 8.3% accuracy, respectively.

Numerical simulation of solar parabolic trough collector with viscous dissipation in slits of arc-plug insertion

This paper investigates the effect of slits within the arc-plug insert of the solar parabolic trough receiver (PTR). In order to predict the performance of the parabolic trough collector (PTC) with arc-plug slits within the absorber tube; two different variants of slits of 2 mm and 1 mm thicknesses are considered. Then, each of the variants of slits with different thicknesses are varied in terms of numbers of their occurrence in the arc-plug. The 2 mm thickness slits are varied in 5, 7, and 9 numbers with uniform space of separation between them in the arc-plug. While 1 mm thickness slits are varied from 11 to 13 in numbers and also maintaining uniform space of separation between them like in 2 mm thickness slits. The objective is to determine the effects of viscous dissipation within the slits of the arc-plug of PTR; and also, the optimized version of the slit with its numbers. It is found that 2 mm slits with 9 in numbers showed the highest value of thermal efficiency as compared to all other cases. The thermal efficiency (η) of the PTC with arc-plug slits are seen to be about 1.642 times of conventional PTC; whereas, 1.309 times of arc-plug without slits. Therefore, it is always beneficial to use slits within inserts of PTCs for its performance enhancement; but, the selection of slit’s thickness and its numbers plays a vital role in its application.

Heat transfer augmentation of parabolic trough solar collector receiver's tube using hybrid nanofluids and conical turbulators

BackgroundParabolic Trough Solar Collector (PTSC) is one of the most popular and an effective device that converts solar radiation into a heat or useful energy. However, it suffers from high temperature gradient and low thermal efficiency. The solution for this problem is to use new advanced coolants (hybrid nanofluids) in order to enhance PTSC's thermal efficiency. MethodsA numerical analysis on the thermo-hydraulic performance of a PTSC receiver's tube equipped with conical turbulators is presented. The Navier-Stokes equations are solved using Finite Volume Method (FVM) coupled with Monte Carlo Ray Tracing (MCRT) method. The flow and thermal characteristics as well as entropy generation of the PTSC's receiver tube are investigated for three hybrid nanofluids (Ag-SWCNT, Ag-MWCNT, and Ag-MgO) having a mixing ratio of (50:50) dispersed in Syltherm oil 800, Reynolds number (5000 to 100,000) and fluid inlet temperatures (400 to 650 K). Significant findingsThe conical turbulators effectively augmented the thermal performance by 233.4% utilising Ag-SWCNT/Syltherm oil instead of pure Syltherm oil. The performance evaluation criterion is found to be in the range of 0.9–1.82. The thermal and exergetic efficiencies increased by 11.5% and 18.2%, respectively. The maximum decrement in the entropy generation rate and entropy generation ratio are 42.7% and 33.7%.

A spectral self-regulating parabolic trough solar receiver integrated with vanadium dioxide-based thermochromic coating

A significant decrease in the solar-thermal conversion efficiency of parabolic trough collectors occurs at high operating temperatures, mainly due to the massive radiant heat loss from the parabolic trough solar receiver incurred in this case. In this paper, a novel parabolic trough solar receiver integrated with vanadium dioxide-based thermochromic coating is proposed to effectively reduce the radiant heat loss and improve the overall performance of solar receivers. The thermochromic layer, deposited on the glass envelope’s inner surface in the negative thermal-flux region, has a reversible transition from a monoclinic (M) phase to a rutile (R) phase at the critical temperature of 68 °C. The occurrence of the phase transition in the thermochromic coating induces beneficial self-regulation of the spectrum-selectivity characteristics of the glass envelope, i.e., transmittance, reflectance, and absorptance (emittance) of glass envelope to solar and infrared radiation, for enhancing the thermal performance of solar receivers. Comprehensive heat transfer models based on the finite volume and spectral radiant heat transfer methods are established in this study. It is validated the models can predict the thermal performance of the solar receivers with high accuracy. In this framework, the total heat loss, thermal efficiency, and exergy efficiency of parabolic trough collector systems integrated with the proposed novel solar receivers are investigated and analyzed. Besides, the effects of transmittance of thermochromic coating (M phase) and emittance of thermochromic coating (R phase), two key parameters, on the overall performance of proposed solar receivers are also studied. The results show that no matter under the M phase or R phase, the thermochromic coating can play unique advantages to improve the thermal performance of the proposed solar receivers. The heat loss and thermal efficiency of the proposed solar receivers are effectively reduced and enhanced by 18.2% and 4.8% at the absorber temperature of 600 °C and inlet fluid temperature of 580 °C, respectively.

Techno-economic assessment of performance-enhanced parabolic trough receiver in concentrated solar power plants

Solar-to-thermal conversion efficiency of the parabolic trough collector significantly degrades at high operating temperatures, which exerts seriously negative effects on the development of parabolic trough collectors. To solve this knotty problem, based on the theory of the negative thermal-flux region, a novel parabolic trough solar receiver with a radiation shield was proposed, manufactured, and tested. In this framework, the proposed solar receiver is employed in the concentrated solar power plants using solar salt as the heat transfer fluid to analyze its feasibility in real solar power plants. In this study, the mathematical models of heat collection and economic assessment are established, and the simulation results yield a good agreement with the experimental data. The techno-economic performances of the solar power plants installing the proposed solar receivers in three typical areas under different installed capacities and thermal storage capacities are comprehensively investigated. The results demonstrate that the proposed solar receiver has a great potential for significant enhancement of the techno-economic performance of the solar power plant. The solar power plant with the proposed solar receivers located in Dunhuang can effectively improve the annual net electrical energy production by 9.77%, reduce the levelized cost of energy by 8.67%.

A review on passive methods for thermal performance enhancement in parabolic trough solar collectors

SummaryAmong the diverse renewable energy sources available, solar energy harnessing has become very common in most countries. Various collectors were developed, built and checked to work in various temperature ranges. The parabolic trough solar collector is found to be the most common among the other collectors in applications such as the distribution of process heat and the production of steam. The heat collector part known as receiver tube is one of the key practical devices of parabolic trough solar collector. Numerous research studies have centered on receiver tube to raise its thermal potential. The usage of passive techniques such as provision of inserts in the receiver tube and geometrical changes of receiver tube are efficient strategies for increasing thermal performance. Detailed review of the numerical and experimental studies conducted on heat transfer enhancement strategies that rely on the use of inserts with the use of different working fluids in a parabolic trough solar collector's receiver tube is described in this article. Additionally heat transfer enhancement due to geometrical modification of receiver tube is also presented. Further, on the basis of literature survey, a comparison among various strategies is outlined. These studies show that future work in this area, that is, usage of passive techniques in parabolic trough solar collector will offer further growth.

Thermal-hydraulic and thermodynamic performance of parabolic trough solar receiver partially filled with gradient metal foam

With the aim to improve overall thermal-hydraulic and thermodynamic performance of parabolic trough solar receiver (PTR), a new configuration with partial insertion of gradient metal foam (GMF) is proposed. The effects of GMF with pore density gradient or porosity gradient on turbulent forced convection heat transfer, flow resistance, entropy generation rate and exergetic efficiency of PTR tube are numerically analyzed. The distribution of non-uniform heat flux on receiver tube wall is calculated by Monte Carlo Ray-Trace Method, and the local thermal non-equilibrium model is used, which considers the temperature difference between metal skeleton and fluid. The numerical method is validated by experimental data. The results show that GMF enhances the heat transfer of PTR tube, with Nusselt number being increased by 43.7%–812.6%; brings the increase of flow resistance, with friction factor being 4.2 to 16.7 times of empty tube; improves the overall thermal-hydraulic performance with performance evaluation criteria ranging from 1.5–3.6. The GMF causes maximum reduction of total entropy generation rate and maximum enhancement of exergetic efficiency to be 92.6% and 24.4%, respectively. The PTR tube partially filled with GMF can obtain higher thermal-hydraulic and thermodynamic performance than that with uniform metal foam.

A coupled optical-thermal-fluid-mechanical analysis of parabolic trough solar receivers using supercritical CO2 as heat transfer fluid

Supercritical CO2 (S-CO2) is an attractive heat transfer fluid (HTF) candidate for application in parabolic trough receivers (PTRs). The thermal and mechanical performances are of serious concern for the PTR using S-CO2 as HTF which suffers from the rigorous conditions of high operating pressure and non-uniform solar flux distribution. The present study develops an integrated numerical model for the optical-thermal-fluid-mechanical analysis of PTRs by coupling Monte Carlo ray-tracing method, finite volume method, and finite element method. It is found that the non-uniform solar flux distribution can induce significant secondary flow of S-CO2 which improves the synergy of the velocity vector and the temperature gradient in the fluid, benefiting the convective heat transfer. However, both of the high operating pressure and the non-uniform solar flux distribution can induce remarkable mechanical stress in PTR, and the superposition of the operating pressure and the solar flux distribution aggravates the mechanical stress. It should be noticed that the operating pressure has no contribution to the axial stress component, while the radial stress component induced by the non-uniform solar flux distribution can be neglected. Flattening the solar flux distribution by adding a secondary reflector is recommended as an effective approach to reducing the thermal stress, and the maximum thermal stress can be reduced from 50 MPa to 10 MPa under the conditions studied in this paper.

Effects of partly-filled encapsulated phase change material on the performance enhancement of solar thermochemical reactor

Solar thermochemical reaction is an efficient way for hydrogen production. Due to cloud transients, solar thermochemical reactor endures low chemical conversion efficiency and deactivation of catalyst. To mitigate adverse effect of solar radiation fluctuation, in present paper, a solar thermochemical reactor design partly filled with encapsulated phase change material (EPCM) is proposed. Firstly, a two-dimensional dynamic model of solar parabolic trough receiver reactors (SPTRR) partly filled with EPCM is established and validated against experimental data. Then, the steady-state performance of SPTRR under steady solar insolation is explored numerically, and the findings motivated us to create a novel multi-part filling pattern of EPCM designed to avoid high-temperature deactivation of catalyst. Furthermore, SPTRR’s thermal and chemical behaviors under unsteady condition of solar radiation are analyzed. Finally, an optimal cascaded EPCM (regarding thermal properties) design is selected for the best overall dynamic performance of SPTRR. The results show that under the steady solar radiation, filled with EPCM in multi-part filling pattern, SPTRR can keep high methanol conversion efficiency (0.926) with large filling proportion (0.52) of EPCM, less usage of catalyst (reduced by 48% compared to all-catalyst case) and safe operation. And under the unsteady solar radiation, compared to SPTRR fully packed with catalyst, the delay response time and vibration amplitude of SPTRR with EPCM in 4-part filling pattern can be extended by 63.2% and damped by 48.7%, respectively. The comprehensive unsteady performance indicator of SPTRR with the optimal cascaded EPCM is 23.2% higher than that with non-cascaded EPCM.

Optimization strategies and verifications of negative thermal-flux region occurring in parabolic trough solar receiver

Prospects for parabolic trough collector are growing as the market increasingly values concentrated solar-thermal utilization. Parabolic trough solar receivers, the key components of parabolic trough collector system, seriously suffer degradation of photothermal conversion performance at high operating temperature due to considerable emissive heat loss, which exerts significantly negative influence on the overall performance and development of parabolic trough collector and subsequent thermal utilization systems. This study examines the spectral emissive heat loss and circumferential heat transfer characteristics around the parabolic trough solar receiver. In this framework, a new concept is proposed, i.e. the negative thermal-flux region in which negative net heat gain occurs, accordingly enlightening and giving birth to new optimization strategies for reducing emissive heat loss of the parabolic trough receiver. A novel parabolic trough receiver with an inner radiation shield in the negative thermal-flux region is designed, manufactured and comprehensively tested. The results show a validity of the existence of the negative thermal-flux region and great potential of new optimization methods to achieve breakthrough enhancement of heat-collecting performance in parabolic trough collector system. Compared with the prototype solar receiver, the heat loss of proposed solar receiver is effectively reduced by 28.1% at absorber temperature of 600 °C, the heat-collecting and exergetic efficiencies are significantly enhanced by 12.9 and 17.6% at the solar irradiance of 600 W/m2 and inlet temperature of 550 °C.

Design and exergy evaluation of a novel parabolic trough solar-nuclear combined system

A novel solar-nuclear combined (SNC) system is proposed for both electricity production and sea water desalination. A parabolic trough solar thermal system and a small modular reactor (SMR) based on pressurized water reactor technology are coupled in this system. By using the Ebsilon code, the operation behavior and exergy evaluations of the SNC system are launched under both the design point and varying solar irradiance conditions. The results demonstrate that the output electric power and electric efficiency of the SNC system are 258.4 MW and 35.2% when the solar irradiance is 900.0 W·m−2. The output electric power, incremental electric power and electric efficiency of the SNC system all increase as the solar irradiance increases. The maximum exergy loss occurs in the parabolic trough solar receiver. The exergy efficiency of the parabolic trough solar receiver is 51.7% when the DNI increases to 1000.0 W·m−2.