Heat Transfer Enhancement of the Absorber Tube in a Parabolic Trough Solar Collector through the Insertion of Novel Cylindrical Turbulators

This study includes an experimental and numerical analysis of the performances of a parabolic trough collector(PTC)with and without cylindrical turbulators.The PTC is designed with dimensions of 2.00 m in length and 1.00 m in width.The related reflector is made of lined sheets of aluminum,and the tubes are made of stainless steel used for the absorption of heat.They have an outer diameter of 0.051 m and a wall thickness of 0.002 m.Water,used as a heat transfer fluid(HTF),flows through the absorber tube at a mass flow rate of 0.7 kg/s.The dimensions of cylindrical turbulators are 0.04 m in length and 0.047 m in diameter.Simulations are performed using the ANSYS Fluent 2020 R2 software.The PTC performance is evaluated by comparing the experimental and numerical outcomes,namely,the outlet temperature,useful heat,and thermal efficiency for a modified tube(MT)(tube with novel cylindrical turbulators)and a plain tube(PT)(tube without novel cylindrical turbulators).According to the results,the experimental outlet temperatures recorded 63.2°C and 50.5°C for the MT and PT,respectively.The heat gain reaches 1137.5 Win the MT and 685.8 Win the PT.Compared to the PT collector,the PTC exhibited a(1.64 times)higher efficiency.

Improving Heat Transfer in Parabolic Trough Solar Collectors by Magnetic Nanofluids

A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.

Investigative Review of Design Techniques of Parabolic Trough Solar Collectors

Parabolic trough solar collectors(PTCs)are among the most cost-efficient solar thermal technologies.They have several applications,such as feed heaters,boilers,steam generators,and electricity generators.A PTC is a concentrated solar power system that uses parabolic reflectors to focus sunlight onto a tube filled with heattransfer fluid.PTCs performance can be investigated using optical and thermal mathematical models.These models calculate the amount of energy entering the receiver,the amount of usable collected energy,and the amount of heat loss due to convection and radiation.There are several methods and configurations that have been developed so far;however,it is usually difficult for a designer to choose the appropriate method or configuration for his application.The present work investigates different PTC configurations and methods of solution,compares their efficiency and accuracy,summarizes their key behaviors and trends,and improves the available methods by maximizing the positives and minimizing the negatives among them.We investigated three methods and seven configurations.The findings suggest that optimizing the collector structure,tracking system,and reflector can lead to high PTC performance and reduced capital costs.After investigating and comparing the recent mathematical models,the study identified a clear deficiency in estimating the output temperature.Three PTC’s solution methods are investigated,and a novel method is developed to give more accurate estimations of the output temperature.

Design and Development of a Parabolic Trough Solar Air Heater for a Greenhouse Dryer

Design and Development of a Parabolic Trough Solar Air Heater (PTSAH) for a Greenhouse Dryer (GD) was done to improve the dryer’s performance. The materials used for the fabrication of the PTSAH included galvanized sheets covered with aluminium foil, an absorber tube made of GI pipe painted matt black to increase heat absorbance at the focal line, mild steel square tubes, shutter plywood, and an axial fan to push air through the absorber tube. Key geometrical parameters used for the design of the PTSAH were a rim angle of 98 degrees, focal length of 0.2608 m, height of 0.3451 m, length of 2 m, and an aperture width of 1.2 m. The PTSAH’s total aperture surface area was 2.4 m2, while its absorber tube surface area was 0.1587 m2. The PTSAH was experimentally tested to establish its thermal performance. It was found that the ambient air recorded an average value of 31.1˚C and that the air heater could increase the air temperature by 45.6˚C above ambient with a thermal efficiency of 5.3%. It can, therefore, be concluded that the PTSAH can significantly improve the performance of a GD by supplying the GD with air at a higher temperature than ambient.

Investigation and simulation of parabolic trough collector with the presence of hybrid nanofluid in the finned receiver tube

The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiver tube increase the turbulent fluid flow.In pursuance of uniform distribution of heat transfer,various fin shapes such as square-shape,circle-shape,triangle-shape,and combined square-circle shapes were inserted,examined,and compared.A study of the temperature differences and fluid flow is meaningful for this project therefore finite volume method was used to investigate heat transfer.Also,hybrid Nano-Fluid AL_(2)O_(3-)CuO,TiO_(2-)Cu,and AgMgO were applied to increase thermal diffusivity.When the combined square-circle-shaped fin was inserted,the thermal peak of fluid flow in the receiver tube was lower than the other studied fin shapes by almost 1%.Besides,the hybrid nano-fluid Ag-MgO Syltherm-oil-800 has lower thermal waste in comparison to others by more than 3%.

Life cycle cost analysis of new FRP based solar parabolic trough collector hot water generation system

Parabolic trough collectors （PTCs） are employed for a variety of applications including steam generation and hot water generation. This paper deals with the experimental results and an economic analysis of a new fibre reinforced plastic （FRP） based solar PTC with an embedded electronic controlled tracking system designed and developed for hot water generation in a restaurant in Madurai, India. The new collector performance has been tested according to ASHRAE Standard 93 （1986）. The performance of a new PTC hot water generation system with a well mixed hot water storage tank is investigated by a series of extensive tests over ten months period. The average maximum storage tank water temperature observed was 74.91℃, when no energy is withdrawn from the tank to the load during the collection period. The total cost of the new economic FRP based solar PTC for hot water generation with an embedded electronic controlled tracking system is Rs. 25000 （US$ 573） only. In the present work, life cycle savings （LCS） method is employed for a detailed economic analysis of the PTC system. A computer program is used as a tool for the economic analysis. The present worth of life cycle solar savings is evaluated for the new solar PTC hot water generation system that replaces an existing electric water heating system in the restaurant and attains a value of Rs. 23171.66 after 15 years, which is a significant saving. The LCS method and the MATLAB computer simulation program presented in this paper can be used to estimate the LCS of other renewable energy systems.

Design and Analysis of Parabolic Trough Solar Water Heating System

Renewable energy technology is one of the prospective sources which can meet the energy demand and can contribute to achieve sustainable development goals.Concentrated collectors are widely used in solar thermal power generation and water heating system also.It is very popular due to its high thermal efficiency,simple construction requirements and low manufacturing cost.This paper is concerned with an experimental study of parabolic trough collector for water heating technology.It focuses on the performance of concentrating solar collector by changing the reflector materials(aluminum sheet,aluminum foil and mirror film).In Bangladesh,it is possible to use low cost solar concentrating technologies for domestic as well as industrial process heat applications.The line focusing parabolic trough collectors have been designed,developed and evaluated its performance by collecting solar radiation,inlet and outlet water temperature,flow rate,efficiency etc.

Modelling of Solar Thermal Power Plant Using Parabolic Trough Collector

The target of the National Solar Mission is to build up India as a worldwide pioneer in solar energy generation. Solar power can be transmitted through grid either from solar photovoltaic or solar thermal technology. As compared to solar photovoltaic, solar thermal installations are less studied, especially regarding energy estimation and performance analysis. For estimating the potential of CSP plants, it is planned to simulate a power plant. We have marginally modified the design of 1 MW operational power plant installed at Gurgaon using Parabolic Trough Collector (PTC) technology. The results are compared with the expected output of Gurgaon power plant and also 50 MW power plant at Rajasthan. Our results have closely matched with a small deviation of 3.1% and 3.6% for Gurgaon and Rajasthan plants, respectively. Our developed model is also validated with 18 different solar power plants in different parts of the world by slightly modifying the parameters according to the plant capacity without changing major changes to the plant design. Difference between our results and the expected energy generation varied from 0.4% to 13.7% with an average deviation of 6.8%. As our results show less than 10% deviation as compared to the actual generation, an attempt has been made here to estimate the potential for the entire nation. For this modelling has been carried out for every grid station of 0.25° × 0.25° interval in India. Our results show that annual solar thermal power plant of 1 MWe capacity potential varies from 900 to 2700 MWh. We have also compared our results with previous studies and discussed.

Study of a Parabolic Trough Adequate for the CERER Site （Dakar-Senegal）

This study presents the modeling of a parabolic trough solar collector. The main objective is to show the influences of the parabolic trough sensor effective efficiency （concentrator optical efflciencies of transmission, reflection, geometrical and the receiver absorption coefficient）, of its length, of the mass flow rate on temperatures distributions of the heat fluid and the receiver and on thermal global efficiency （solar conversion efficiency into energy usable）. The atmospheric parameters are those of Senegal in April. A prototype existing in the CERER （Center of Studies and Research on Renewable Energies） （Dakar-Senegal） is given as example of application.

Performance Enhancement of Parabolic Trough Collector by Using Homogenizer and Spiral

In conventional parabolic trough collectors(PTCs),sunlight is concentrated at the bottom of the absorber tube,resulting in a significant circumferential temperature gradient across the absorber tube,heat loss and thermal deformation,which affects the safety and thermal performance of PTCs.In this study,a new receiver with homogenizer and spiral(RHS) is proposed,achieving the optical and thermal synergy to ameliorate the thermal deformation of the absorber tube and enhance thermal efficiency.A plane structure homogenizer is designed to improve uniformity of the concentrated solar flux of absorber tube through second reflection.In combination with the spiral,it improves the optical-thermal efficiency of the PTC by enhancing heat exchange between the fluid and the backlight side of the absorber tube.The performance of the collector is numerically studied by building a three-dimensional coupled light-thermal-structure model.The results show that the thermal deformation of the RHS is reduced by more than 96% and the optical-thermal efficiency is improved by 1.2%-0.63% compared with conventional receivers(CRs) under the same inlet temperature conditions.The proposed receiver is validated to be effective in reducing thermal deformation and improving optical-thermal efficiency.

Design and performance investigation of modified dual reflector parabolic trough collector with double planar mirrors

In a typical parabolic trough collector(PTC), sunlight is concentrated at the bottom of the absorber tube. This concentrated solar flux leads to uneven heat distribution, resulting in high local temperatures and significant thermal stress on the absorber tube.These limitations have restricted the application of PTCs in solar thermochemistry and other fields and have impacted their safe operation. In this study, a new PTC with dual planar mirrors(DPMS) is proposed to homogenize the circumferential solar flux distribution of the absorber tube. A design method and single-objective optimization of the new PTC with a DPMS are proposed,and an uncertainty analysis of the operational and structural parameters is performed. A coupled light-heat-structure numerical model was developed to study the heat transfer performance and structural mechanical properties. The thermodynamic properties of the PTC with DPMS under different boundary conditions were analyzed. The results show that the circumferential temperature difference of the new PTC is within 2.6 K, and the circumferential thermal deformation is within 0.9 mm under typical working conditions(the inlet velocity of the heat transfer fluid is 3 m/s, inlet temperature is 573.15 K, and the direct normal irradiance is 1000 W/m^(2)). Compared with conventional PTCs, the circumferential temperature difference is reduced by 74%–90%, and the maximum thermal deformation along the y-axis is reduced by more than 95% under all working conditions(1–5 m/s, 373.5–675.15 K, 200–1000 W/m^(2)). The new PTC maintains the uniformity of the circumferential solar flux distribution for different operating parameters(sun incident angle of 0°–3°) and installation errors(±3 mm), is suitable for solar energy applications in various fields, and has the potential for large-scale applications.

Exploring the influence of optical and thermal parameters on the effectiveness of parabolic trough collector receiver units

This study investigates the optimization of physical parameters in a parabolic trough collector receiver unit to improve its thermal and optical performance.The parameters include the transmissivity,reflectivity,absorptivity,emissivity and thermal conductivity of the outer cover and absorber pipe.This study utilizes a novel experimental design and a simulation model that accounts for the infrared reflectivity inside the receiver.The simulation results were validated by the experimental data,with a maximum deviation of 8%.The study analyses the effects of varying the physical parameters on the heat transfer fluid temperature,total plant efficiency,temperature profiles,temperature gradients and thermal stress.The study finds that increasing the reflectivity and decreasing the emissivity of the outer cover and the absorber pipe significantly enhance the performance,with maximum increases of 25.8%and 26.5%in total efficiency,respectively.The study also finds that increasing the thermal conductivity of the absorber pipe reduces the temperature gradients and thermal stress,with maximum decreases of 42.2%and 29%,respectively.This study provides valuable insights for optimizing the receiver design and operation in solar-thermal systems.

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

Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which can provide different grades of thermal energy with two heat transfer fluids(oil and water),is designed to improve thermal efficiency.In this FPTR-IT,an inner tube and straight fins are employed to respectively lessen heat loss at upper and lower parts of the absorber.Based on the design,a numerical model is developed to investigate its performance.Comparisons with other PTRs indicate that the FPTR-IT can combine the advantages of PTR with inner tube and finned PTR and obtain the best performance.Moreover,performance evaluation under broad ranges of direct normal irradiances(300–1000 W/m^(2)),flow rates(50–250 L/min)and inlet temperatures(400–600 K)of oil as well as flow rates(3.6–10 L/min)and inlet temperatures(298.15–318.15 K)of water is investigated.Compared with conventional PTR,heat loss is reduced by 20.7%–63.2%and total efficiency is improved by 0.03%–4.27%.Furthermore,the proportions of heat gains for water and oil are located in 8.3%–73.9%and-12.0%–64.3%,while their temperature gains are located in 11.6–37.9 K and-1.2–19.6 K,respectively.Thus,the proposed FPTR-IT may have a promising application prospect in remote arid areas or islands to provide different grades of heat for electricity and freshwater production.

A design method and numerical study for a new type parabolic trough solar collector with uniform solar flux distribution

The non-uniform concentrated solar flux distribution on the outer surface of the absorber tube can lead to large circumferential temperature difference and high local temperature of the absorber tube wall,which is one of the primary causes of parabolic trough solar receiver(PTR)failures.In this paper,a secondary reflector used as a homogenizing reflector(HR)in a conventional parabolic trough solar collector(PTSC)was recommended to homogenize the solar flux distribution and thus increase the reliability of the PTR.The design method of this new type PTSC with a HR was also proposed.Meanwhile,the concentrated solar flux distribution was calculated by adopting the Monte Carlo ray-trace(MCRT)method.Then,the coupled heat transfer process within the PTR was simulated by treating the solar flux calculated by the MCRT method as the heat flux boundary condition for the finite volume method model.The solar flux distribution on the outer surface of the absorber tube,the temperature field of the absorber tube wall,and the collector efficiency were analyzed in detail.It was revealed that the absorber tube could almost be heated uniformly in the PTSC with a HR.As a result,the circumferential temperature difference and the maximum temperature could be reduced significantly,while the efficiency tended to decrease slightly due to the inevitably increased optical loss.Under the conditions studied in this paper,although the collector efficiency decreased by about 4%,the circumferential temperature difference was reduced from about 25 to 3 K and the maximum temperature was reduced from667 to 661 K.

Heat Transfer Enhancement in a Parabolic Trough Solar Receiver using Longitudinal Fins and Nanofluids

In this paper,we present a three dimensional numerical investigation of heat transfer in a parabolic trough collector receiver with longitudinal fins using different kinds of nanofluid,with an operational temperature of 573 K and nanoparticle concentration of 1% in volume.The outer surface of the absorber receives a non-uniform heat flux,which is obtained by using the Monte Carlo ray tracing technique.The numerical results are contrasted with empirical results available in the open literature.A significant improvement of heat transfer is derived when the Reynolds number varies in the range 2.57×104≤ Re≤ 2.57×105,the tube-side Nusselt number increases from 1.3 to 1.8 times,also the metallic nanoparticles improve heat transfer greatly than other nanoparticles,combining both mechanisms provides better heat transfer and higher thermo-hydraulic performance.

Thermal analysis of a solar parabolic trough receiver tube with porous insert optimized by coupling genetic algorithm and CFD

In this paper, the heat transfer enhancement in a solar parabolic trough receiver tube with porous insert and non-uniform heat flux condition was investigated. A new optimization method, which couples genetic algorithm(GA) and computational fluid dynamics(CFD) based on Socket communication, was proposed to optimize the configuration of porous insert. After the acquisition of the optimal porous inserts, some performance evaluation criterions such as synergy angle, entransy dissipation and exergy loss were introduced to discuss the heat transfer performance of the enhanced receiver tubes(ERTs) with optimal and referenced porous inserts. The results showed that, for a large range of properties of porous insert(including porosity and thermal conductivity) and Reynolds number, the heat-transfer performance of ERT with porous insert optimized by GA is always higher than that of the referenced ERTs. Better heat-transfer performance can further improve the solar-to-thermal energy conversion efficiency and mechanical property of the solar parabolic trough receiver. When some porous materials with high thermal conductivity are adopted, ERT can simultaneously obtain perfect thermal and thermo-hydraulic performance by using the same optimized porous insert, which cannot be achieved by using the referenced porous insert. In the view of those introduced evaluation criterions, using the optimized porous insert can obtain better synergy performance and lesser irreversibility of heat transfer than using the referenced porous insert. Entransy dissipation per unit energy transferred and exergy loss rate have equivalent effects on the evaluation of irreversibility of heat transfer process. These evaluation criterions can be used as optimization goals for enhancing the comprehensive performance of the solar parabolic trough receiver.

Comprehensive Review of Line-Focus Concentrating Solar Thermal Technologies: Parabolic Trough Collector (PTC) vs Linear Fresnel Reflector (LFR)

In the present review,parabolic trough collector(PTC)and linear Fresnel reflector(LFR)are comprehensively and comparatively reviewed in terms of historical background,technological features,recent advancement,economic analysis and application areas.It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal(CST)technologies,they are now standing at different stages of development and facing their individual opportunities and challenges.For PTC,the development is commercially mature with steady and reliable performance;therefore,extension of application is the main future demand.For LFR,the development is still in rapid progress to commercial maturity,yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs.The question,which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies,becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.

Characteristics of the transient thermal load and deformation of the evacuated receiver in solar parabolic trough collector

As a core element in solar parabolic trough collector, the evaluated receiver often runs under severe thermal conditions. Worse still, the transient thermal load is more likely to cause structural deformation and damage. This work develops an efficient transient multi-level multi-dimensional(M2) analysis method to address photo-thermal-elastic problems, thereby estimating transient thermal load and deformation for the receiver:(i) one-dimensional(1-D) thermo-hydraulic model is adopted to determine the transient thermo-hydraulic state,(ii) 3-D finite volume method(FVM) model for the receiver tube is established to obtain the real-time temperature distribution,(iii) 3-D finite element method(FEM) model is employed to make thermoelastic analysis. Based on this M2 method, the typical transient cases are conducted in cold-start, disturbed-operation and regulatedprocess. Three indicators(average temperature of the wall(ATW), radial temperature difference(RTD), circumferential temperature difference(CTD)) are defined for overall analysis of the receiver thermal load. It is found that in the transient process,receivers face response delay and endure significant thermal load fluctuation. The response time for a single HCE(heat collecting element) under lower mass flow rate(1.5 kg s-1) could sustain 280 s. During the cold-start stage(DNI=200 W m-2 to 800 W m-2), the maximum value of CTD in receiver is as high as 11.67℃, corresponding to a maximum deflection of 1.05 cm.When the mass flow rate decreases sharply by 80%, the CTD reaches 33.04℃, causing a 2.06-cm deflection. It should be pointed out that in the cold-start stage and the lower mass flow rate operation for solar parabolic trough collector, alleviating the transient thermal load and deformation is of importance for safely and efficiently running evaluated receiver.

Selective Absorber Coatings and Technological Advancements in Performance Enhancement for Parabolic Trough Solar Collector

Parabolic trough solar collector systems are the most advanced concentrating solar power technology for large-scale power generation purposes. The current work reviews various selective coating materials and their characteristics for different designs in concentrating solar power. Solar selective absorbing coatings collect solar radiation and convert it to heat. To promote higher efficiency and lower energy costs at higher temperatures requires, this study aims to analyse the fundamental chemistry and thermal stability of some key coatings currently being used and even under investigation to find reasons for differences, information gaps and potential for improvement in results. In recent years, several novel and useful solar absorber coatings have been developed. However, qualification test methods such as corrosion resistance, thermal stability testing and prediction of service life, which have essential technical value for large-scale solar absorbers, are lacking. Coatings are used to enhance the performance of reflectors and absorbers in terms of quality, efficiency, maintenance and cost. Differentiated coatings are required as there are no uniformly perfect materials in various applications, working conditions and material variations. Much more knowledge of the physical and chemical properties and durability of the coatings is required, which will help prevent failures that could not be discovered previously.

Potential of performance improvement of concentrated solar power plants by optimizing the parabolic trough receiver

This paper proposes a comprehensive thermodynamic and economic model to predict and compare the performance of concentrated solar power plants with traditional and novel receivers with different configurations involving operating temperatures and locations.The simulation results reveal that power plants with novel receivers exhibit a superior thermodynamic and economic performance compared with traditional receivers.The annual electricity productions of power plants with novel receivers in Phoenix,Sevilla,and Tuotuohe are 8.5%,10.5%,and 14.4%higher than those with traditional receivers at the outlet temperature of 550℃.The levelized cost of electricity of power plants with double-selectivecoated receivers can be decreased by 6.9%,8.5%,and 11.6%.In Phoenix,the optimal operating temperature of the power plants is improved from 500℃to 560℃by employing a novel receiver.Furthermore,the sensitivity analysis of the receiver heat loss,solar absorption,and freeze protection temperature is also conducted to analyze the general rule of influence of the receiver performance on power plants performance.Solar absorption has a positive contribution to annual electricity productions,whereas heat loss and freeze protection temperature have a negative effect on electricity outputs.The results indicate that the novel receiver coupled with low melting temperature molten salt is the best configuration for improving the overall performance of the power plants.