Collector Absorber Research Articles

Cold solar: PVT heat exchanger designs for heat pump integration

There has been an increase in solar photovoltaic/thermal (PVT) research in recent years, however, relatively little research has been dedicated to the design of PVT collectors as part of a heat pump system. This study aims to identify cost-effective design strategies for a PVT collector absorber to be integrated into a ground source heat pump (GSHP) circuit and enhance heat capture from the ambient air. The effect of geometry, material selection, fins, and forced convection on the overall U-value and thermal performance coefficients of the collector, are evaluated under steady state conditions using numerical modelling tool COMSOL Multiphysics. An annual mean fluid temperature profile is derived from a PVT + GSHP system simulation to calculate the annual thermal energy output, energy-to-mass and energy-to-cost ratios of the absorbers. Results show that the addition of fins and forced convection have the greatest influence on collector thermal performance, while material selection has a negligible impact. The corrugated, polycarbonate absorber with 10 mm fins, generates 55 % more thermal energy (1,464kWhth/m2-yr) than the reference metallic sheet and tube collector at an energy-to-cost ratio 1/10th the reference, suggesting good market potential. An exergy analysis reveals that thermal exergy contributes 20 % to 50 % of the total exergy output, highlighting that low-temperature PVT designs exhibiting a smaller thermal share relative to electrical exergy compared to their higher temperature counterparts. This work’s novelty and contribution comes from PVT design specifically for GSHP integration, examined at component and system levels, from both technical and economic perspectives.

Weaknesses of steady state analysis when used for selecting solar air heaters

The paper highlights the constrains faced by the user when choosing the most appropriate solar collector from a set of collectors belonging to the same category. Two basic kinds of one porous and one non-porous with single flow/pass flat solar air heaters were tested. The collectors have the same size but different internal shapes and absorber materials. The two collectors were tested and a shading procedure was implemented in order to emphasize several aspects related to the thermal inertia of the collectors. Comparison has been made between the efficiency values obtained experimentally. The shade test shows a faster decrease of the outlet air temperature for V-porous absorber collector in comparison with the U-corrugated absorber collector i.e. 6 °C and –3.5 °C respectively in a time interval of 74 s. Exposing the collectors on a fresh heating cycle under a low stability radiative regime (450–750 W/m2) one observe that 60% of the first 180 s the corrugated collector outperforms the porous collector; after that interval of time the porous collector becomes more effective. The low thermal inertia of the solar air collectors yields high variation of the thermal efficiency in days with low stability of the radiative regime. In such days, using measured series of solar irradiance data with long sampling period between two successive measurements does not allow a proper choice of the most appropriate solar collector type.

Future Parabolic Trough Collector Absorber Coating Development and Service Lifetime Estimation

This work presents a study on the optical and mechanical degradation of parabolic trough collector absorber coatings produced through the spray coating application technique of in-house developed paint. The main aim of this investigation is to prepare, cure, load, and analyze the absorber coating on the substrate under conditions that mimic the on-field thermal properties. This research incorporates predicted isothermal and cyclic loads for parabolic trough systems as stresses. Biweekly inspections of loaded, identical samples monitored the degradation process. We further used the cascade of data from optical, oxide-thickening, crack length, and pull-off force measurements in mathematical modelling to predict the service life of the parabolic trough collector. The results collected and used in modelling suggested that cyclic load in combination with iso-thermal load is responsible for coating fatigue, influencing the solar absorber optical values and resulting in lower energy transformation efficiency. Finally, easy-to-apply coatings made out of spinel-structured black pigment and durable binder could serve as a low-cost absorber coating replacement for a new generation of parabolic trough collectors, making it possible to harvest solar energy to provide medium-temperature heat to decarbonize future food, tobacco, and paint production industrial processes.

Thermal analysis of five flat air solar collectors in Epinal (France) using modelling and simulation

ABSTRACT The purpose of this study is to investigate the effect of the position of the solar collector absorber and stagnant air relative to the airflow path on the thermodynamic properties of traversing air and the overall thermal performance of the collector. A numerical model was developed and validated using five different absorber design positions. Numerical results are validated using experimental data obtained from Epinal (France). The model was subsequently used to parametrically study the influence of these absorber positions on the density, temperature, velocity variations of the airflow through the collector and the thermal efficiency of each case scenario. The study showed the importance of stagnant air in solar collector thermal performance. Also, it showed that when one absorber is used, it is better to locate the absorber on the top of the airflow path than below the airflow path. Sandwiching the airflow path between double absorbers with the upper absorbers having stagnant air between it and the plexiglass cover and the down absorber having stagnant air between it and the bottom of the collector can produce a thermal efficiency of 31% which is 2% higher than the closest case and 13% higher than the worst-case design.

Performance evaluation and parameter optimization of tubular direct absorption solar collector with photothermal nanofluid

Photothermal nanofluids exhibit broad-spectrum absorption characteristics, rendering them highly promising for applications in direct absorption solar collector (DASC). A three-dimensional computational fluid dynamics (CFD) model is established to analyze the solar collection performance of a tubular DASC. Three distinct types of nanofluids used in direct solar absorption collector have been investigated, employing the Rayleigh scattering method to compute their optical parameters. The non-gray discrete ordinates radiation method is employed to solve radiation heat transfer within the glass wall and nanofluid. The findings reveal that graphite nanofluids exhibit the most favorable thermal performance among the tested nanofluids. The impact of different operating parameters, such as mass fraction and flow rate, on the thermal performance of the tubular DASC is elucidated through thermal and exergy efficiency analyses. The results indicate that thermal performance experiences only marginal changes when the mass fraction exceeds 50 ppm. Thermal efficiency increases with higher mass flow rates, while exergy efficiency displays an inverse relationship. This research contributes valuable insights that can guide the selection of suitable working mediums and the optimization of operational parameters for DASC system.

Cross-sectional temperature field of a solar collector’s absorber in the case of annular pipe

In households, solar collectors are finding ever increasing use for hot water preparation. Although the design of solar collectors is relatively simple, the authors over many years concentrate attention on modelling the cross-sectional temperature field of the solar collector’s absorber [1-7]. In solving the cross-sectional temperature field for an annular pipe [1], the periodical cross-sectional domain is divided into three sub-domains where the first sub-domain is the plate between pipes, the second – a pipe’s wall, and the third – the liquid; as a result, the temperature field expressions have been obtained for all the three sub-domains. In works [2, 3] the temperature fields obtained were simplified. To define its variations in time, the temperature field was found by solving the Laplace equation under non-stationary time-dependent conditions [4]. The obtained results evidence that the non stationary conditions might not be taken into account in long- lasting sunny weather, while such non-stationarity changes considerably the temperature field when it is short-term (e.g. in cloudy weather). The temperature has also been found for a square-pipe absorber [7] as more technological in design. In the present work, the final temperature field model is proposed for the absorber of a round-pipe collector. As distinguished from [1], in this work the temperature of liquid is assumed to be constant over the entire pipe cross-section. Such an assumption significantly simplifies the calculation while not changing the physical essence.

Experimental and numerical analysis of the thermal performance of pebble solar thermal collector

In this work, pebbles of higher specific heat than the conventional absorber materials like aluminium or copper are proposed as a absorber in the solar flat plate collector. The proposed collector are integrated into the building design and constructed with masonry. Tests were conducted by varying the operating parameters which influence its performance, like the flow rate of the heat-absorbing medium, and the tilt of the collector using both coated and uncoated pebbles. The maximum temperature difference that could be measured for a conventional absorber was approximately 8 °C for a flow rate of 0.6 L/min. While for a coated and uncoated absorber, it was 7 °C and 5.5 °C respectively. This difference decreased with an increase in flow rates from 0.6 L/min to 1.2 L/min. For all the flow rates, it was observed that the average difference in efficiency between the coated and the conventional absorber collector is 5.82 %, while the difference between the coated and uncoated absorber collector is 15.68 %. Thus, it is very much evident that by replacing the conventional absorber with the proposed coated pebble absorber, the overall loss in efficiency is just 5.82 %, but the advantages are enormous. Along with the experimental study, numerical analysis was also carried out with CFD modeling. The numerical results agreed well with experimental results with the least error. Therefore, CFD simulation can be further used to optimize the design of the collector.

Numerical Analysis of Solar Collector Absorber Tubes with C- shaped Roughness for Enhanced Heat Transfer

Numerical Analysis of Solar Collector Absorber Tubes with C- shaped Roughness for Enhanced Heat Transfer

A Novel Design of Parabolic Trough Solar Collector's Absorber Tube

Abstract This paper proposes an investigation of a novel design of receiver absorber tube (circular-trapezoidal shaped) for PTC (Parabolic Trough Concentrator) system aiming at catching a part of the lost (reflected) solar rays due to effects related to the incidence angle deviation, and thus improving the PTC's thermal performance. Although they are always present in PTC, the effects of the deviation angle are often not considered in the literature. These effects are considered here in view of presenting a better and more useful focal area, the optimal circular-trapezoidal absorber tube shape being determined according to the maximal limit of the deviation angle that allows catching the maximum amount of solar rays. The corresponding model is established considering it as a two-dimensional problem and the derived deviation angle coefficient compared to that obtained for a traditional circular shaped tube. Moreover, the energy balance model is adapted to simulate the thermal efficiency of the considered tubes as a function of the deviation angle with some assumptions. The obtained results prove that from a deviation angle value of 0.1 degrees, the gain in efficiency becomes more significant; it can reach 5 % and even be higher for a deviation angle value of 0.5 degrees. Finally, Comsol Multiphysics software package was used to determine the pressure drops, temperature and velocity field distributions, considering a deviation angle value of 0.2 degrees. The results confirm that the proposed tube absorbs more heat than the traditional one.

Numerical simulation of nanofluid in central tube of solar collector by two‐phase mixture approach

AbstractIn this study, a new idea was proposed to enhance the direct absorption of radiation by the nanofluid by incorporating a central absorber copper tube. Copper oxide (CuO) nanoparticles were used as the nanofluid with mass percentages of 0.05%, 0.055%, and 0.01% by weight, mixed with an oil‐based fluid. The absorption coefficients were varied in the range of 10, 40, and 100. The performance of the collector was compared to experimental and numerical data from other literature. Based on the results, the presence of the central copper tube inside the absorber tube of the collector led to higher radiation absorption under the same conditions compared to the nanofluid alone. In the case of the highest nanofluid composition (0.055% by weight), the thermal efficiency increased by up to 7% compared to a standard direct absorption collector.For an absorption coefficient of 10, the proposed collector exhibited the largest difference in output temperature compared to the usual volumetric absorption collector (DATPSC), with a temperature difference of approximately 23 K. To obtain more accurate results, the fluid domain in the parabolic collector with the new configuration was numerically investigated using ANSYS software.

Investigation of stress and deflection in absorber of parabolic trough solar collector for direct steam generation

The tubular absorber of a parabolic trough solar collector (PTSC) experiences deflection and thermal stress during the operation due to the adverse circumferential and longitudinal thermal gradient in the direct steam generation (DSG) process. This study presents the coupled three-dimensional thermal–structural analysis of the absorber tube by combining heat transfer and static structural analyses using ANSYS Fluent 2021R1 software. The receiver of the LS-3 solar collector unit with a length of 4.06 m is considered as a computational domain with mass flow rates of 0.4 kg/s and 0.6 kg/s, an operating pressure of 100 bar, and the direct normal irradiance (DNI) of 750 W/m2. The deformation and stress analyses have been performed for preheating, evaporation, and superheating stages of the DSG process at solar noon. Under the subjected boundary conditions, the circumferential thermal gradient at the middle of the absorber in preheating, evaporation, and superheating sections are 27 K, 13 K, and 31 K, respectively. The maximum and minimum deflections observed in the absorber tube are 17.6 mm and 7.6 mm, respectively. The maximum and minimum normal stress along the axial direction on top of the absorber are 26.0 MPa and 12.6 MPa, respectively. It is observed that normal stresses along the axial direction is maximum at the mid of the absorber. The maximum thermal strains observed in preheating, evaporation, and superheating sections are 4.6 mm/m, 5.2 mm/m, and 5.6 mm/m, respectively.

Investigation of parabolic trough collector receiver with U-pipe exchanger using a numerical approach: Towards temperature non-uniformity optimization

In this work, a numerical study of the heat flux and temperature distribution for a parabolic trough collector absorber with an internal U-pipe tube exchanger is carried out using SolTrace and ANSYS Fluent software. The effect of solar flux and temperature non-uniformity on the system performance related to the focal distance is investigated. It was noticed that the highest circumferential temperature gap of about 105 °C occurs at the medium of the absorber (0.9 m). Moreover, for the focal distances of 0.18 m, 0.19 m, and 0.2 m, the outlet water temperatures are increased to 328.8, 329.01 and 328.89 K, respectively. For these distances, the highest thermal efficiencies of about 69, 70 and 71%, respectively, are reported. Furthermore, the promising proposed approach to investigate the receiver performance combines simulation results and correlations between variables. Indeed, a strong negative correlation of −0.65 between thermal efficiency and focal distance is noticed. Thus, thermal efficiency correlates positively with maximum temperature gap, inlet–outlet temperature gap, flow rate, and outlet temperature in decreasing order with correlation coefficients of 0.64, 0.59, 0.38, and 0.32, respectively. Additionally, the simulation study emphasizes the importance of relating optimum temperature uniformity and thermal efficiency for optimizing the system performance.

Thermal Analysis of Novel Pebble Absorber Based Solar Thermal Collector

The fluid flow rate of the heat absorbing medium plays a crucial role in the performance of the collector. Studies were carried out with varying fluid flow rates of 0.01 kg/s, 0.013 kg/sec and 0.016 kg/sec respectively for different days from 8:00 hour to 18:00 hour. The input parameters considered for the computational modeling are i) Solar radiation (I) ii) Ambient temperature (Ta) iii) Inlet water temperature (Ti) and iv) Mass flow rate (mf). Experiments carried out using coated and uncoated pebbles as absorber along with a conventional flat plate collector. The efficiency of the solar thermal collector increases with flow rate and incident radiation. The coated pebble absorber collector is more efficient than the uncoated pebble absorber collector and less efficient than the conventional metal absorber collector at above mentioned flow rates. The total average efficiency of coated absorber collector was 67.036%, 51.35% for the uncoated absorber collector and 72.857% for the conventional copper absorber collector.

Experimental assessment of novel designed solar hot water storage collector incorporating an array of partitioned ducts absorber

A Novel design of a solar water collector consisting of an array of adjacent partitioned ducts representing the collector absorber is investigated experimentally. Each duct is divided into two flow passages by a partitioned plate made from insulation material. The heated water flows over the partitioned plate to the storage tank, while the cold water flows from the storage tank to the duct down the portioned plate. The designed partitioned ducts solar collector (PDSC) performance is compared to conventional flat plate solar water collectors (FPSC) with the same dimensions and materials. The study is performed under hot weather conditions of upper Egypt for collectors’ tilt angles of; 17°, 27°, and 37°. The findings reveal that PDSC has higher storage water temperature, energy storage, energy efficiency, and lower energy losses. The PDSC has average daily efficiencies of 57.5%, 55.2%, and 47.5%, with enhancement percentages of 31.2%, 32.4%, and 38.6%, relative to the FPSC, at the studied tilt angles, respectively. The PDSC has average exergy efficiencies of 4.47%, 3.71%, and 2.89%, with enhancement percentages of 36.3%, 36.5%, and 41% relative to the FPSC, at the studied tilt angles, respectively. The maximum required thermosyphon heads of the PDSC are 0.8, 0.7, and 0.1, and the corresponding values of the FPSC are 1.7, 1.65, and 0.9 mm at the studied tilt angles, respectively.

Electric field combined nanofluid to enhance photothermal efficiency of the direct absorption solar collector

Compared with conventional surface absorption collectors, nanofluid-based direct absorption solar collectors (DASC) have superior optical absorption performance and photothermal conversion efficiency. However, problems such as nanoparticles deposition and large temperature difference inside the collector still limit the development of DASC systems. To solve these problems, this paper firstly proposed to apply the electric field to manipulate the motion of nanoparticles to make the upper and lower nanofluids to exchange heat in the DASC system. The Al2O3-thermal oil nanofluids with the concentration of 0.01–0.3% are prepared, and the transmittance of the nanofluids and photothermal conversion as well as mechanism are performed and analyzed. The results show that the electric field can reduce the temperature difference inside the collector and improve the photothermal conversion efficiency of the DASC system. The temperature rise and photothermal conversion efficiency of 0.2 vol% Al2O3 nanofluid at voltage of 10 kV are 62.11 °C and 87.85%, which are 19.24% and 14.17% larger than those without electric field respectively. Under the action of electric field, the resuspension of deposited nanoparticles and heat transfer between upper and lower nanoparticles work together to improve the photothermal conversion efficiency of DASC system.

Numerical investigation of an enhanced PTC absorber tube using cylindrical inserts

AbstractThe main purpose of this study is to investigate numerically the thermal performance of a parabolic trough solar collector's absorber tube that contains a novel kind of inserts with the objective to improve the heat transfer between the heat transfer fluid and the absorber tube. In the first part of this paper, the diameter and the length of the cylindrical inserts are investigated based on finite volume method and Monte Carlo ray tracing method for Reynolds number ranges from 2.36 × 104 to 7.09 × 104. In the second part, the eccentricity of the cylindrical inserts is investigated under the same operating conditions. The Therminol®VP1 is the HTF that is used in this investigation's intermediate fluid. The numerical simulation indicates that the perturbators enhance the thermal behavior of the receiver and reduces the absorber tube's temperature difference.

An absorber of parabolic trough collector for hydrogen production in a solid oxide fuel cell

Sustainable energy development is a globally attractive and indispensable research area. An effective design process and good sustainable sources are crucial for meeting the objective. This investigation utilizes solar energy by utilizing an effectively designed the integration of two-parabolic trough collector (PTC) with an area of 2.8 m2 to operate Rankine cycle-based fuel cell for hydrogen production. The heat transfer rate is optimized for maximum net energy production to operate the solid oxide fuel cell (SOFC) to maximize the hydrogen production by experimenting with the solar heating system with 3 different heat transfer fluid (HTF) flow rates such as 0.12 kg/s, 0.27 kg/s, and 0.38 kg/s. The experimental outcomes at each flow rate setting were analyzed in such a way that solar radiation received, inlet and outlet temperatures of HTF with respect to clock time, Useful heat gain and Thermal efficiency of solar heating system with respect to solar radiation received and rate of Hydrogen production (kg/s) and Net power output (kW) by sustainable solar power generation arrangement were analyzed with respect to solar radiation received. The results recommended that the flow rate of 0.38 kg/s recorded the highest thermal efficiency 82%, for the heat gain of 27589 kW. Increasing the flow velocity of HTF improves both the solar collector's efficiency and the electrical energy for the fuel cell. As a result, more solar energy is falling on the absorber and enhances the rate of hydrogen production. A preliminary cost analysis was conducted for the PTC system integrated with the hydrogen production system to determine the electric cost based on the solar advisor model (SAM). A black coating material was used to absorb more solar radiation from the PTC.

Design Parameters of Parabolic Solar Water Heater with Inbuilt Automatic Solar Tracking System

Abstract: This paper 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.

Investigation into the effect of twisted tape on the thermo-hydraulic performance and entropy generation of turbulent flow of mono and hybrid magnetic nanofluids inside a parabolic solar collector absorber tube by applying two-phase analysis

This research study examines the impact of applying a twisted tape on thermo-hydraulic performance as well as entropy generation related to the turbulent flow of mono and hybrid magnetic nanofluids inside a parabolic solar collector (PSC) absorber tube. In this study, two-phase water/multi-walled carbon nanotubes (MWCNTs) nanofluid and two-phase water/MWCNT-iron oxide nanofluid having the 1% volume fraction (VF) are applied as the working fluid. To model two-phase flow, the mixture model standard k-ε turbulence model and QUICK algorithm are utilized. This research study is implemented for diverse Reynolds numbers of 6000 to 24000 and some twisted tape's pitch ratios including 0.25, 0.50, and 0.75. In addition, the standard k-ε turbulence model is then applied for modeling the turbulent flow. The obtained results obtained by the numerical study demonstrate that using the twisted tape in solar collectors could improve thermo-hydraulic performance in comparison to the solar collector with no particular twisted tape. Also, the considered HT related to the collector having twisted tape is more than that without twisted tape in all cases, i.e., thermo-hydraulic performance coefficient is always greater than 1. The results reveal that using magnetic hybrid nanofluid leads to better thermal performance than mono nanofluid. Finally, the entropy generation is reduced with the Reynolds number as well as the pitch ratio of the twisted tape. The highest value in PEC surge was about 27% owing to using of magnetic hybrid nanofluid, while for simple nanofluid, it was 22%. According to this case, the use of magnetic hybrid nanofluid is recommended.

PECULIARITIES OF THE PV-MD PHOTOMODULE STRUCTURE FORMATION DURING THE ELECTRICAL ENERGY AND DISTILLATE PRODUCTION

The operating conditions of the photomodule are largely determined by the thermal regime, which affects the efficiency of electricity generation. The use of a forced cooling system in the photomodule with the implementation of the salt water distillation process allows you to control the thermal regime and obtain an additional product in the form of fresh water. The choice of the method of controlling the cooling process and the mode of its implementation makes it possible to achieve a rational combination of electrical and technological productivity of the photomodule. In this paper, analytical studies of the formation of the temperature field of the absorber of the hybrid solar collector (PV-MD) during cooling due to the evaporation of the heat carrier and recovery of the heat of the formed steam were carried out. The research method makes it possible to analyze the characteristics of the PV-MD collector, namely, the heating temperature of the absorber and coolant, as well as the performance of the distillate system, depending on the structure of the module and its operating conditions. The aim of the work is to develop a method for calculating the thermal performance characteristics of the hybrid solar collector in the conditions of a cascade method of heat and mass transfer of salt solution and distillate and to identify the rational architecture of the device. A complex mathematical model of local analysis of heat and mass exchange processes of a hybrid solar collector for real solar and climatic conditions is used. The analysis of heat and mass transfer in variant conditions showed that the degree of uniformity of the absorber temperature field, which depends on the efficiency of electricity production, when applying the PV-MD method is the same as for the PVT method. Cascade recovery of thermal energy using the PV-MD method for collectors of typical sizes is limited in efficiency to two stages. The generalized dependences for determining the technological productivity of the two-stage PV-MD collector in terms of distillate and absorber temperature when the external operating conditions of the collector change, which can be used to evaluate the efficiency of converting solar energy into a technological product, have been obtained.