Collector Absorber Research Articles

Numerical analysis of heat transfer rate from absorber of a flat-plate type solar collector to the tube

Flat plate type solar collector is known as the simplest solar collector. However, its thermal efficiency is very low in comparison with other type of solar collector such as evacuated tube. The heat transfer mechanism in the flat plate type solar collector should be elaborated to improve thermal efficiency of a flat plate type solar collector. In this work, commercial code computational fluid dynamics is employed to explore heat transfer rate from the collector plate to the collector tube. The objectives are to explore the fluid flow characteristics in the solar collector and to estimate the useful heat transfer rate. The solar collector is modelled as a two-dimensional computational domain. The conservation mass, momentum equations and energy equations are developed and solved iteratively. Temperature and pressure distributions are plotted and velocity vector is presented. The results reveal that the heat transfer rate from the absorber plate is 28.955 Watt. The transfer rate from the air to the pipe is 24.06 Watt. On the other hand, heat loss to the atmosphere is 4.92 Watt.

Performance of factory made solar heating systems according to standard ISO 9459-5:2007

The utilization of solar energy based technologies has attracted increased interest in recent times in order to satisfy the energy demands in buildings. This research work presents a comparative analysis of the energy production and costs of factory made solar heating systems, Thermosiphon Solar Water Heaters Systems (TSWHS) and Forced-circulation Solar Water Heaters Systems (FSWHS), as a function of profile type (high and low) and collector absorber treatment (selective and black painting). We observe that the energy performance and the Levelized Cost of Energy (LCOE) is similar in TSWHS and FSWHS for load volumes below tank nominal volume, black painting absorbers and locations with high solar irradiation. In the case of load volumes greater than nominal, climates with low irradiation and collectors with selective absorbers, the differences in their energy performance can reach a 7% and the LCOE can increase up to 9%. The LCOE is lower for TSWHS systems for all the evaluated scenarios. We have also found that for cold climates, the FSWHS systems present higher net annual energy produced, however, for warm climates TSWHS systems present greater net annual energy production.

Effect of vacuum deterioration on thermal performance of coaxial evacuated tube solar collector considering single and two phase flow modelling: A numerical study

Boiling and condensation play an important role in heat transfer in evacuated tube solar collectors (ETC), especially for low flow rates. Another factor that influences the efficiency of an ETC is deterioration of vacuum inside the ETC. The present study investigates numerically the effect of deteriorating vacuum during single and two phase flows inside an ETC to analyze its thermal performance. A steady-state one-dimensional model is developed which can simulate the steady-state thermal performance of the Evacuated tube solar collector (ETC) with single and two-phase flows under saturation conditions considering effects of vacuum deterioration to simulate a more real-life situation of solar collectors. The rise in pressure inside the ETC has a significant effect on the suppression of boiling and condensation due to rise in overall heat loss coefficient. The radiative, convective and conductive heat loss coefficients from the collector are studied for gradual pressure rise inside the ETC. The two phase model also indicates that if boiling starts inside the ETC in a particular inlet flow condition, consideration of two phase flow along with the effect of vacuum deterioration shows significant deviation of efficiency and temperature profile from those of single phase flow models and predicts more accurate results. Inducing of two-phase heat transfer in ETC, with all the fluid condensing again within the collector tube, will result in improved efficiency for that range of mass flow rates. It also helps in maintaining uniform temperature and equal heat gain throughout the collector absorber plate. The efficiency of the collector for higher inlet temperatures is seen to be effected more significantly by vacuum deterioration than at lower inlet temperatures in single phase flows. However, in two phase flows for a fixed saturation temperature of the fluid, vacuum deterioration has negligible effect on the efficiency at higher inlet temperatures (Tfi ≥ 85 °C).

Manufacture of absorber fins for solar collector using incremental sheet forming

This article sets out to present a new manufacturing process applied to create absorber fins for solar collectors. Using Incremental Sheet Forming, a flexible process that can be performed at a CNC production center, it is possible to make prototypes of absorber fins with collector riser fittings, which also enables the development of new fin designs using different materials in a wide range of thicknesses. This article analyzes parameters of the Two Point Incremental Forming process, with a partial die for solar collector absorber fin manufacturing using a 1mm thick aluminum AA1200-H14 in order to determine the influence of the step down and the tool's rotation speed on the sheet's formability, being thus able to determine the most appropriate combination of these parameters to obtain a process with the greatest quality and productivity. A series of 16 experiments was proposed to manufacture a small absorber fin comparing the rotation speed values of S = 50, 200, 400, and 800rpm, with step down values of Δz=2, 1, 0.5, and 0.2mm. The feed rate value was kept at F=250mm/min, and each experiment was performed until the first crack occurred in the sheet. In this study, it was possible to indicate the feasibility of the process under more efficient parameters for manufacturing absorber fins using the step down of 2mm and the rotation speed of 50rpm.

Exergy and thermal assessment of a Novel system utilizing flat plate collector with the application of nanofluid in porous media at a constant magnetic field

A Novel system is introduced which utilizes Fe3O4/Water nanofluid in porous media at a constant magnetic field in a Flat Plate Collector (FPC) absorber tubes. The Fe3O4/Water nanofluid was used in 1% and 2% weight concentration flowing inside porous media with 0.8 porosity at constant magnetic fields of 200 and 400 G. The Novel system is studied by exergy and thermal analysis means and is compared to a Rival system which is a regular FPC that uses water as working fluid and porous foam inside its tubes. A new evaluation approach has been adopted which assesses the thermal effectiveness, exergy, and energy efficiencies in a variety of working conditions. Furthermore, a novel parameter, which is regarded as Feasibility Indicator Parameter (FIP), is introduced which represents the performance of the solar collector. The results reveal that the Novel system average Nusselt number is 1.36 times the average Nusselt number of the Rival system. Moreover, the overall heat loss coefficient is reduced to 3.149 W/m2K in comparison to 3.4 W/m2K in the Rival FPC. Additionally, the thermal efficiency of the Novel system has been demonstrated to rise to 83.97% compared with 83.63% efficiency in the Rival system. The absorbed heat flux, feasibility factor or Performance Evaluation Criterion (PEC), and the heat transfer coefficient enhancement of the Novel system are 1.015, 1.32, and 1.52 concerning the Rival system, respectively. Furthermore, the novel assessing parameter, FIP value is higher than unity for the Novel system with 200 G constant magnetic field and 1% and 2% wt nanoparticle. However, the required pumping power in the Novel system increases considerably. Hence, the relative exergy efficiency of the Novel system to the Rival system is below the value one. Although the Rival FPC system has a higher exergy efficiency than the Novel system, however, the Novel system provides better thermal performance and higher PEC and FIP than the Rival system. Thus, it can be used wherever the availability of space and higher thermal efficiency are crucial.

Blended morphologies of plasmonic nanofluids for direct absorption applications

Direct absorption solar collectors were introduced to overcome the limitations of conventional surface absorber collectors. The advances in nanotechnology accompanied with phenomenological discoveries at the nanoscale have allowed the appearance of plasmonic nanofluids, which utilize localized surface plasmon resonance phenomenon that multiplies the extinction efficiency of the plasmonic nanoparticle several times at the resonance wavelength. Silver nanoparticles exhibit a high intensity of the localized surface plasmon, which can be fine-tuned within the broadband 350–1200 nm by tailoring their shape, size and aspect ratio. In this paper, we have numerically investigated the effects of silver nanoparticles' morphology on the localized surface plasmon resonance and on the extinction peaks. Numerical results allow determining the effective morphologies at every band of the solar spectrum. Thus, nanofluids composed of blended Ag nano-morphologies were designed, which can expand the absorbance over the entire solar spectrum. By means of the radiative transfer equation, we found that blended plasmonic nanofluids have the potential to raise the efficiency of the direct solar collector to more than 85% at a very low concentration below 0.001 wt%. Utilization of the blended plasmonic nanofluids are not limited to solar thermal and concentrated solar power applications, but also can be extended into the optical filters in PV/thermal applications.

Advances in solar thermal harvesting technology based on surface solar absorption collectors: A review

This study presents a critical review of the major research and development work that has advanced surface solar absorption technology and also discusses the applications of this technology in the last 15 years. In a surface solar absorption collector (SSAC), solar radiation is first absorbed on the surface of the collector and then transferred to the circulating fluid. This article reviews a wide range of studies on different SSAC systems with the aim of identifying research gaps to prepare this technology for commercial availability. Moreover, qualitative and quantitative research information on non-concentrating and concentrating SSACs was collected and evaluated in the context of a performance-based assessment, environmental issues, and sustainability concerns. The performance of these collectors mainly relies on the receiver design and thermal storage tanks with different heat transfer fluids. For high concentration collectors, there is an urgent need for new heat transfer and storage fluids to withstand elevated temperatures to minimize the flow instability. A review of the literature suggests that ongoing high quality research on this technology, especially on medium and high concentration collectors, will soon overcome the existing problems bringing this technology into temperature ranges that will make it commercially available. Finally, the scientific challenges and opportunities relevant to this technology are also discussed.

Experimental and numerical study on a freeze protection system for flat-plate solar collectors with silicone peroxide tubes

The freeze protection is essential in the majority of solar thermal installations to prevent breakage of solar thermal collectors. Therefore, there are different methods of protection against freezing of flat plate solar thermal collectors, all of them with certain limitations. This paper shows a novel freeze protection mechanism in the solar thermal collector by using flexible silicone peroxide tubes inside the absorber of the solar collector. We demonstrate, in a theoretical and experimental way, that the increase of volume and pressure produced inside a solar collector during freezing process can be absorbed using a flexible silicone peroxide tubes under all exposure conditions. The parameters that optimize the geometric configuration of the solution proposed have been calculated. A collector prototype with silicones peroxide has experimentally complied with the Standard ISO 9806:20 13, including freeze resistance test, without any significantly influence on its efficiency or pressure drop. Therefore, the solution proposed presents an inexpensive, effective, reliable and maintenance-free freeze protection system for flat plate solar collectors.

Structural analysis of absorber tube used in parabolic trough solar collector and effect of materials on its bending: A computational study

The maximum deflection of a Parabolic Trough Solar Collector (PTSC) absorber tube is a result of the circumferential non-uniformity in temperature distribution and self-weight. This non-uniformity in temperature is a factor of incoming solar flux distribution as well as material property of the absorber tube. The present work focuses on structural analysis of absorber tube used in PTSC and the effects of variations of material. Multiphysics platform, namely thermal-fluid analysis and structural analysis has been made in this regard. The computational investigation has been carried out on Schott PTR70 2008 receiver and Therminol VP1 as the Heat Transfer Fluid (HTF). Evacuated annular space along with specular and non-grey nature of glass cover which is semi-transparent to the input flux has been modeled to obtain better accuracy in results. The materials investigated are steel, copper, aluminum and various laminated composites like bimetallic (Cu-Fe) and tetra-layered laminate (Cu-Al-SiC-Fe), which are subjected to different mass flow rate of HTF at the absorber tube inlet with constant heat flux on the absorber tube outer surface. It is found that the change in the material of the absorber tube has a negligible effect on the amount of heat transferred to the HTF, but it has a significant effect on the bending due to thermal expansion as well as due to self-weight. Steel absorber tube is generally used, but its lower thermal conductivity results in poor circumferential temperature distributions. Copper has better thermal characteristics, but higher self-weight and lower mechanical strength compared to steel. So a combined effect of these properties is utilized in bimetallic tube, which results in a decrease in maximum deflection by 7–15% as compared to steel. As the self-weight of the absorber tube plays a vital role in deflection, therefore a tetra-layered laminate absorber tube having lower weight and improved temperature distribution results in a decrease in maximum deflection by 45–49% as compared to steel.

Absorber Thickness Effect on The Effectiveness of Solar Collectors to Production Hot Air For Drying

One way to increase the drying rate using a solar collector is to increase the air temperature of the collector and the time of circulation of hot air delivered to the drying chamber. The optimization of heat absorber by utilizing solar energy has been shown to be strongly influence by fluid flow characteristics in the collector channel. This study examined the sharp turning channel on the air passage of a solar collector. Collector size used was 305 cm x 80 cm and had 10 sharp turning channel baffles. Solar radiation absorbent material used in this collector test is iron sand with three thickness variations, namely 3, 6, and 9 cm. The measurement results show that the air temperature that can be produced by the collector with a thickness of 3 cm absorber reaches 85 degree Celsius with an effective drying time of 8 hours and the final air temperature testing on the collector out side still reaches about 40 degree Celsius at air temperature of 32 degree Celsius. At a thickness of 6 cm absorber, the air temperature inside the collector was about 83 degrees and the duration of 10 hours of drying time, with the collector-out air temperature around 39 degree Celsius at the air temperature of 30 degree Celsius. In contrast to the 9 cm thickness of the absorber, the drying air temperature was only 81 degree Celsius and the drying time was 12 hours and the final air temperature measurement was 40 degree Celsius at the ambient temperature was 27 degree Celsius. This result can be seen as the effect of thick collector absorber on solar thermal energy that can also be absorbed by absorber solar collector.

Colloidal plasmonic structures for harvesting solar radiation

Abstract Direct Solar Absorption Collectors explore the thermo-optical properties of fluids to convert solar radiation into thermal energy. Colloids of metallic nanoparticles have shown a great potential to convert solar radiation into thermal energy efficiently, because of the matching between the absorption peak of the localized surface plasmon resonance and the solar radiation spectrum. Recently, multilayered metallic nano structures have been broadly studied for Thermo-optical applications due to the possibility to tune the plasmon resonance next to the near infrared region. In this work, using a full-wave field numerical model, we study the solar absorption of metallic nanofluids composed of Solid structures (Sphere, Cube, Tetrahedral, Octahedral), Silica-based structures (Shell and Multilayered) and its elliptical versions. Although a large part of the metallic material is replaced for SiO2 in the nanofluid composition of NanoShell (NS) and Multilayered (ML) structures, the values of solar radiation absorber coefficients are larger than the obtained with solid particles. Also, the quantity of metal is just 18% (NS) and 53% (ML) of the material necessary to fabricate colloids of solid particles. For the elliptical structures, the values of solar radiation absorber condition are larger than the obtained with spherical structures.

Experimental investigation of thermal performance and entropy generation of a flat-plate solar collector filled with porous media

The aim of the present experimental investigation is to examine the effect of metal foams asa passive thermal developer on the performance of water based flat plate solar collectors. Two similar wetted absorber collectors have been fabricated, the first is fully filled porous channel and the other one is empty channel. The thermal performance of the collectors is calculated based on ASHRAE standard and is compared with each other. The volume flow rate varies from 0.5 to 1.5lit/min. Results demonstrate that the porous media has a considerable effect on the characteristic curves, especially in the low flow rate. The maximum improvement of the absorbed energy parameter is 18.5%, which occurs in Reynolds number of 237 (i.e., 0.5lit/min). Moreover, porous media causes a usual pressure loss that increases nonlinearly with rising of the Reynolds number. For taking both the Nusselt number and pressure drop into account, an overall performance definition has been applied. Calculations show that the collector overall performance decreases with increasing the Reynolds number. The entropy generation analysis reveals that the portion of heat transfer irreversibility is more dominant in both collectors. Despite the greater pressure drop in porous channel, it doesn’t have considerable effect on the entropy generation.

Experimental and economic analysis of concrete absorber collector solar water heater with use of dimpled tube

Abstract To increase the usage of solar water heaters in India, a low-cost solar collector made of concrete is experimentally investigated in Pune. The concrete slab consisting metal fibers is placed in a wooden box, with immersed serpentine copper tube and provided with glazing on top. With an objective of improving the efficiency of the collector, a heat transfer augmentation technique (dimple) is fabricated on water carrying serpentine tube. Testing is carried out in rainy, winter and summer seasons for different water flow rates to understand the working of collector throughout the year. Testing results show that average water temperature collected per day is 59 °C–69 °C. Further, to find the exact effect of dimples on outlet water temperature, two completely identical concrete plate collectors–one with a dimpled tube and other with a smooth tube, are designed, fabricated and tested simultaneously. The effect of dimples is observed up to 2.5 °C. Also, a detailed economic analysis and environmental benefits of concrete collector solar water heater for India are investigated in this paper.

Analysis of solar water heater with parabolic dish concentrator and conical absorber

This research focuses on developing novel technique for a solar water heating system. The novel solar system comprises a parabolic dish concentrator, conical absorber and water heater. In this system, the conical absorber tube directly absorbs solar radiation from the sun and the parabolic dish concentrator reflects the solar radiations towards the conical absorber tube from all directions, therefore both radiations would significantly improve the thermal collector efficiency. The working fluid water is stored at the bottom of the absorber tubes. The absorber tubes get heated and increases the temperature of the working fluid inside of the absorber tube and causes the working fluid to partially evaporate. The partially vaporized working fluid moves in the upward direction due to buoyancy effect and enters the heat exchanger. When fresh water passes through the heat exchanger, temperature of the vapour decreases through heat exchange. This leads to condensation of the vapour and forms liquid phase. The working fluid returns to the bottom of the collector absorber tube by gravity. Hence, this will continue as a cyclic process inside the system. The proposed investigation shows an improvement of collector efficiency, enhanced heat transfer and a quality water heating system.

Nanofluid Types, Their Synthesis, Properties and Incorporation in Direct Solar Thermal Collectors: A Review.

The global demand for energy is increasing and the detrimental consequences of rising greenhouse gas emissions, global warming and environmental degradation present major challenges. Solar energy offers a clean and viable renewable energy source with the potential to alleviate the detrimental consequences normally associated with fossil fuel-based energy generation. However, there are two inherent problems associated with conventional solar thermal energy conversion systems. The first involves low thermal conductivity values of heat transfer fluids, and the second involves the poor optical properties of many absorbers and their coating. Hence, there is an imperative need to improve both thermal and optical properties of current solar conversion systems. Direct solar thermal absorption collectors incorporating a nanofluid offers the opportunity to achieve significant improvements in both optical and thermal performance. Since nanofluids offer much greater heat absorbing and heat transfer properties compared to traditional working fluids. The review summarizes current research in this innovative field. It discusses direct solar absorber collectors and methods for improving their performance. This is followed by a discussion of the various types of nanofluids available and the synthesis techniques used to manufacture them. In closing, a brief discussion of nanofluid property modelling is also presented.

Optimization of thermal performance of the parabolic trough solar collector systems based on GA-BP neural network model

ABSTRACTThe aim of this paper is to optimize the thermal performance (system output energy, thermal efficiency, and heat loss of cavity absorber) of parabolic trough solar collector (PTC) systems in order to improve its thermal performance, based on the genetic algorithm-back propagation (GA-BP) neural network model. There are a number of undefined problems, fuzzy or incomplete information and a complex thermal performance of the PTC systems. Therefore, the thermal performance prediction of the PTC systems based on GA-BP neural network model was developed. Subsequently, the metrics performances have been adopted to comprehensively understand the algorithm and evaluate the prediction accuracy. Results revealed that the GA-BP neural network model can be successfully used to predict the complex nonlinear relationship between the input variables and thermal performance of the PTC systems. The cosine effect has a great influence on the thermal performance; thereby the geometrical structure of the PTC systems was optimized. It was found that the optimized geometrical structure was beneficial to improve the thermal performance of the PTC system. In conclusion, the GA-BP neural network model has higher prediction accuracy than the other algorithm and it can be feasible and reliable.

Low-temperature solar-plate-assisted heat pump: A developed design for domestic applications in cold climate

Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature.

Evaluation of thermal characteristics of a flat plate solar collector with a back mounted air channel

Flat plate solar collectors for domestic hot water systems are known to experience problems under stagnation conditions, when the heat transfer fluid is at rest in the absorber flow passages. The solar collector absorber plate may reach temperatures approximately 170°C or more especially when power supply fails or periods when there is minimal energy demand. This paper evaluates the thermal characteristics of an commercial Enerworks Residential Collector integrated with a back mounted air channel under stagnation conditions which is the continuation of previous investigations of current authors both experimentally and numerically to optimize the performance of the collector during both operation and stagnation. Air flow and thermal conditions in the inclined air channel of the solar collector were simulated using the validated numerical model adopting the Reynolds Averaged Navier-Stokes (RANS) modeling approach with SST-k-ω turbulence model. The radiation exchange between the surfaces of the air channel was modeled using the Discrete Ordinate radiation Model. The numerical results for velocity contours, turbulence intensity, temperature distribution, heat transfer coefficient and averaged Nusselt numbers were obtained. A correlation of averaged Nusselt numbers with modified Rayleigh numbers was developed. From the results obtained it was concluded that the incorporation of a passive air cooling channel at the back of flat plate solar collectors with a suitable control valve at the outlet opening could be helpful in reducing the maximum temperature arrived under stagnation conditions approximately from approximately 170°C to 120°C and will prolong the life of solar collectors.

Preparation and characterization of nanographite- and CuO-based absorber and performance evaluation of solar air-heating collector

Nanostructured absorbers and novel collectors are to be developed so as to reap the enhanced thermal performance of solar thermal gadgets. In this connection, the nanographite- and CuO-coated solar absorber was developed, and it was characterized through XRD, SEM, and EDAX. In addition novel collector with nanostructured and baffle-arranged absorber was developed, and it was tested. It was found that the maximum temperature attained on sample absorber (1 m × 2 m) was 48.5 °C in outdoor conditions. It was also found that the grains in the coating were in nanosizes with spherical structure. The results of thermal analyses revealed that the maximum temperature enhancement of the working fluid was 59.4 °C, and the maximum thermal performance of the collector was 68%. On the basis of the present research outcomes, it could be concluded that nanostructured and baffle-arranged solar absorbers would be used in solar collectors for reaping enhanced thermal performances.

Experimental Investigation on the Effect of Partially Metal Foam inside the Absorber of Parabolic Trough Solar Collector

In the present work the efficiency of a solar parabolic trough has been investigated experimentality. parabolic trough solar collector constitute a proven source of thermal energy for industrial process heat and power genaration. The impact of using the partially porous media in the absorber on the efficiency of PTC (parabolic trough collector) has been investigated. The porosity of copper foam is 0.9 and the pore density is 30 PPI (pores per inch). The experiments were performed in different volume flow rates from 0.5 to 1.5 Lit/min and the standard of ASHRAE 93 was used to test the solar collector’s performance. Results illustrate that using metal foam in the absorber has a positive impact on the collector efficiency and increases the pressure drop in the absorber. When absorber filled with metal foam the overall loss coefficient UL decreases 45% and it causes to increase efficiency because less energy is lost.