Cavity Receiver Research Articles

Comparative analysis of entropy generation and heat transfer in a tilted partially heated square enclosure using the finite difference method

PurposeIn recent times, there has been a growing interest in buoyancy-induced heat transfer within confined enclosures due to its frequent occurrence in heat transfer processes across diverse engineering disciplines, including electronic cooling, solar technologies, nuclear reactor systems, heat exchangers and energy storage systems. Moreover, the reduction of entropy generation holds significant importance in engineering applications, as it contributes to enhancing thermal system performance. This study, a numerical investigation, aims to analyze entropy generation and natural convection flow in an inclined square enclosure filled with Ag–MgO/water and Ag–TiO2/water hybrid nanofluids under the influence of a magnetic field. The enclosure features heated slits along its bottom and left walls. Following the Boussinesq approximation, the convective flow arises from a horizontal temperature difference between the partially heated walls and the cold right wall.Design/methodology/approachThe governing equations for laminar unsteady natural convection flow in a Newtonian, incompressible mixture is solved using a Marker-and-Cell-based finite difference method within a customized MATLAB code. The hybrid nanofluid’s effective thermal conductivity and viscosity are determined using spherical nanoparticle correlations.FindingsThe numerical investigations cover various parameters, including nanoparticle volume concentration, Hartmann number, Rayleigh number, heat source/sink effects and inclination angle. As the Hartmann and Rayleigh numbers increase, there is a significant enhancement in entropy generation. The average Nusselt number experiences a substantial increase at extremely high values of the Rayleigh number and inclination.Practical implicationsThis numerical investigation explores advanced applications involving various combinations of influential parameters, different nanoparticles, enclosure inclinations and improved designs. The goal is to control fluid flow and enhance heat transfer rates to meet the demands of the Fourth Industrial Revolution.Originality/valueIn a 90° tilted enclosure, the addition of 5% hybrid nanoparticles to the base fluid resulted in a 17.139% increase in the heat transfer rate for Ag–MgO nanoparticles and a 16.4185% increase for Ag–TiO2 nanoparticles compared to the base fluid. It is observed that a 5% nanoparticle volume fraction results in an increased heat transfer rate, influenced by variations in both the Darcy and Rayleigh numbers. The study demonstrates that the Ag–MgO hybrid nanofluid exhibits superior heat transfer and fluid transport performance compared to the Ag–TiO2 hybrid nanofluid. The simulations pertain to the use of hybrid magnetic nanofluids in fuel cells, solar cavity receivers and the processing of electromagnetic nanomaterials in enclosed environments.

Improvement in the photothermal conversion performance of a solar cavity receiver with concave spherical windows

Photothermal conversion parameters are key indicators for measuring the operational performance of solar cavity receivers. By utilizing the redistributive ability of a functional surface in an optical concave lens to transmit solar radiation, previous studies have shown that installing a concave spherical quartz window at the front end of a solar cavity receiver can homogenize the flux distribution on the receiver wall. On this basis, research has been conducted on the impact of solar cavity receivers with concave spherical windows on their photothermal conversion performance. Based on the finite volume method, a coupling model for photothermal conversion in the receiver is established to calculate the heat transfer efficiency and temperature distribution of the receiver for different windows. The results indicate that, compared with a receiver with a flat quartz window, a receiver with a concave spherical quartz window can significantly reduce the peak temperature and peak temperature gradient of the spiral tube in the receiver, effectively improving the temperature distribution of the tube. When DNI = 1000 W/m2, the flow velocity at the inlet is 2.5 m/s, and the temperature at the inlet is 650 K. The receiver with a concave spherical quartz window has a reduced temperature peak from 868.09 K to 834.23 K and a temperature gradient from 2.46 K/mm to 1.27 K/mm relative to the receiver with a flat quartz window. This study provides ideas for the design of cavity receivers and improves their photothermal conversion performance.

An ultra-high-temperature cavity receiver with a simple flat absorber for safe and efficient solar-thermal conversion

Improving the operating temperature to >1573 K is promising to enhance the generating efficiency of solar thermal power. However, such extremely ultra-high temperature inevitably brings severe challenges to solar-thermal conversion. Therefore, a cavity receiver with a simple flat absorber was designed and optimized in this study. Firstly, the receiver cavity was designed to be made of machinable insulation material, and its crucial absorbing surface was a flat absorber assembled from individual tungsten panels to simplify the structure. Then, an optical-thermal-mechanical model was established to identify the suggested configuration. It was found the partially coated receiver with a 130-mm-depth cavity and a down-in flow pattern can operate safely and efficiently under ultra-high temperatures, which was regarded as the optimized design. Finally, the performance of the optimized receiver was evaluated when the mass flow rate was within 22.0–32.0 g·s−1 and the inlet temperature was within 623∼873 K. The results indicated the highest outlet temperature reached 1579.2 K with receiver efficiency ranging from 69.9%–80.8%. Additionally, the maximum thermal losses from the glass and the insulation reached 860.2 W and 365.9 W, respectively, pointing out the crucial adiabatic directions for ultra-high-temperature receivers. The obtained results can offer promising insights to ultra-high-temperature solar receivers.

Design and Construction of a 700kWth High-Temperature Sodium Receiver

The Australian Solar Thermal Research Institute (ASTRI) has been developing technologies designed to collect and store solar energy at high-temperature to drive a new high-efficiency power block based on the supercritical CO2 Brayton cycle. ASTRI is pursuing two alternative pathways: one based on the use of liquid sodium as a heat transfer fluid, and the other based on the use of solid particles. The current work describes ASTRI’s progress towards design and construction of a 700kWth prototype sodium receiver suited to this type of system, which will be installed and tested on Solar Field 2 at the CSIRO Energy Centre in Newcastle, Australia. The receiver is a cavity receiver with a circular aperture oriented at a tilt down towards the centre of the heliostat field. Inside the cavity are ten vertical tube banks in a semi-circular arrangement, with sodium flowing from the centre to the outside in a serpentine manner. Optical and thermal modelling at design point predicts aperture interception efficiency of 95.3%, receiver efficiency of 90.9% and thus a combined interception and receiver efficiency of 86.6%. Conservative flux limits are set based on the tube material’s (Alloy 625) time independent tensile strength, which is dominated by creep for the sodium temperatures considered. In the event of incident, the receiver is designed to drain and a door closes over the aperture to limit smoke egress. Insulation is SiO2-CaO-MgO blanket, and all pipes are heat traced. Fabrication of the receiver was completed in July 2022 and first on-sun testing is expected in September 2023.

Simulated Performance Analysis of a Hybrid Water-Cooled Photovoltaic/Parabolic Dish Concentrator Coupled with Conical Cavity Receiver

The present research discloses a novel hybrid water-cooled Photovoltaic/Parabolic Dish Concentrator coupled with conical cavity receiver and spectral beam splitter (PV/PDC-CCR-BSF). In effect, a compact co-generating solar-concentrating PV system involving a subsequent optical interface has been fully developed and numerically tested. The optical performance of the proposed hybrid solar-concentrating system was modeled and assessed using the RT 3D-4R method while the thermal yield of the system was examined using the Finite Element Method. In addition to that, different configurations of serpentine-shape embedded water-cooling pipes (rectangle, semicircle, semi-ellipse and triangle) have been tested and optimized for maximum heat collection and minimum operating cell temperature. The performance of all the tested serpentine-shape embedded water-cooling pipes was evaluated with respect to conventional serpentine-shape water-cooling pipes. The outcomes indicated that the triangular cross-section outperforms other shapes in terms of heat dissipation capabilities, with about −446 W and maximum useful thermal power in the medium of the heat transfer fluid of 11.834 kW.

Review of various solar cavity receivers of parabolic dish concentrators with design aspects and heat loss analysis

Review of various solar cavity receivers of parabolic dish concentrators with design aspects and heat loss analysis

Numerical investigation to optimize the modified cavity receiver for enhancement of thermal performance of solar parabolic dish collector system

The concentrated parabolic dish collector (PDC) systems are widely utilized for the purpose of generating high-temperature heat by receiving and converting solar energy efficiently into thermal energy. Cavity receivers including spiral coils have a common use in PDC system for optimal thermal performance. Therefore, to enhance the thermal performance of a PDC system, the present study investigates different cavity receiver configurations, such as cylinder and conical shaped receivers with flat and spherical absorber surface as well as the effect of spiral coil arrangement. To identify the most optimal spirally coiled cavity receiver, the comparison is conducted based on outlet temperature, heat exchange rate, thermal efficiency, effectiveness, and thermal performance capability (TPC). The investigations were conducted using the ANSYS Fluent CFD simulation software package. The SolTrace software package was utilized to compute the maximum heat flux incident on the absorber surface of the receiver, and peak heat flux data was used as input parameter at the absorber surface of the receiver. Furthermore, to select the suitable working fluid in PDC system, different heat transfer fluids, such as Syltherm 800, Xceltherm 600, ParathermHR™ and water, respectively were studied. From the thermal analysis of various proposed receiver geometries, the receiver with conical shape and spherical absorber surface is more efficient over other configurations. It provides 50 % higher heat transfer rate thancylindrical receiver with flat absorber surface. Moreover, receiver's thermal performance could modestly be improved by modifying the spiral coil pitch (variable pitch). In terms of pumping power consumption, readily availability, low viscosity, and high specific heat, water is suggested as working fluid for receiver of PDC system.

Optical and thermal investigation of hyperbolic cavity receiver with secondary reflector for solar parabolic dish collector

A hyperbolic-shaped cavity-type receiver with a second stage reflection for a 40 m2 solar parabolic dish concentrator (PDC) is presented in this paper,along with optical and thermal modeling. The receiver geometry and the secondary reflector complete the hyperbolic geometrical shape of the present receiver. This study aims to estimate heat losses owing to natural convection and radiation under influential parameters associated with solar parabolic dish system. Optical modeling has been performed with verified model using ASAP® 2013 V1R1. The optical simulations have been carried out for varying receiver height (h1), height of the secondary (h2) and diameter-to-total height ratios (d/h) of 0.5, 1, and 1.5 while keeping the diameter of the plane aperture of the receiver (d) constant. The optimum receiver geometry has been selected based on the performance in terms of optical efficiency. The maximum efficiency found is 91.72% for h1 = 0.75 m and d/h = 0.5 for the mounting distance of 4.21 m. The optimized shape is further studied to determine how the receiver absorptivity and the secondary reflector's reflectivity affect the optical performance. The absorptivity and reflectivity range from 0.86 to 0.94. Obtained optimum receiver geometry from the optical investigation is further analyzed to estimate the heat transfer rate. The thermal modeling is performed for 0°, 30°, 60°, and 90° orientations of the receiver in ANSYS Fluent 2020 R1. A comprehensive comparison among the available models has been reported and validated with well-established experimental data. This work has developed free convective Nusselt number correlation. It can be a valuable addition to the existing literature.

Energy and exergy studies on the receiver models with materials and heat transfer fluids.

This work focuses on meeting the growing demand in solar energy conversion for small-scale applications. In this regard, experimental and CFD research has been done to examine the thermal performance (energy and exergy efficiencies) of a dish collector (reflector and receiver) system with different receiver models. In this work, receivers with uniform absorber cavity areas having cylindrical and hemispherical shapes were modeled for length-to-diameter ratios (L/D) of 1.5, 1, and 0.75. The modeled receivers having coil tube configurations concerning the geometrical shape of the models were tested with two different materials of aluminum and copper. The performance of the receiver models was compared by experimental and CFD methods for the average solar direct normal irradiations of 860 W/m2 by the dish reflector area of almost 12 m2. The supplied average heat flux by the dish reflector was 7kW/m2 at the absorbing area of the cavity receivers. The energy and exergy efficiencies from the experimental and CFD analyses on the models were determined based on the cavity surface temperature distribution of receiver walls, and heat gain for different mass flow rates by the heat transfer fluid water. The receiver with copper material and L/D ratio of 0.75 has been found as the optimized one among all other models with the maximum obtained energy and exergy efficiencies of 73.64 and 7.31% when water is used as the heat transfer fluid. The performance of the optimized receiver model was also validated with a few other heat transfer fluids such as SiC + water nanofluid and therminol VP1.

The performance evaluation of the free-falling particle solar receiver with a novel zigzag mass-flow controlled particle release pattern

A free-falling particle receiver is a promising technology to be used in concentrating solar power plants. In this study, an optical-thermal coupled model is established by combining a Monte Carlo ray-tracing method with a finite volume method to simulate the energy transfer processes in a solar power tower system employing a cavity receiver. Using the developed model, a novel particle release pattern, zigzag mass-flow controlled pattern, is proposed and compared with three other patterns, straight-line, zigzag, and mass-flow controlled patterns. First, the effects of the amplitude of the zigzag particle release slots on the receiver performance are analyzed. Then, the variations of the solar energy entering the receiver at different times on the vernal equinox is studied. Moreover, a new particle release pattern, zigzag mass-flow controlled pattern, is proposed and evaluated. The results demonstrated that the thermal performance of the zigzag mass-flow controlled particle release pattern was found to be superior to the other three patterns, allowing an increase in the thermal efficiency of 2.90 %. This allows for achieving effective thermal performance improvements while employing cost-effective designs in the free-falling particle receiver.

Numerical investigation and comparison of tubular solar cavity receivers for simultaneous generation of superheated steam and hot air

Solar cavity receivers are a crucial technology to transform solar energy into easily usable thermal energy. Various cavity receiver structures employing helical absorber tubes were investigated to provide either superheated steam or hot air efficiently. However, few studies have focused on receivers that generate both hot fluids simultaneously. The simultanoues generation can lead to a more compact and cheaper system, and can be used for applications such as a high-temperature electrolysis to produce green hydrogen or syngas. In our study, three different tubular solar cavity receivers were proposed and numerically investigated. Each receiver consists of three different processes: (1) water evaporation, (2) superheating steam, and (3) heating air. The 1D-3D model developed in our previous study was used to investigate the various aspects such as lamp-to-thermal (solar simulator was used as a light source) and exergy efficiencies. The numerical results have proven that the receiver employing both cylindrical and conical helical tubes can obtain the highest lamp-to-thermal (67.0%) and exergy efficiencies (46.9%). A parameter study was also conducted based on the chosen optimal receiver. The obtained results can become a basis for further implementation, and especially the use in high-temperature electrolysis could become crucial in a future energy system.

Numerical study on the stress and thermal performance of a supercritical CO2 solar conical cavity receiver

Solar thermal power systems rely on high-temperature cavity receivers. Guaranteeing the effective and secure operation of a receiver involves researching the impacts of various geometric parameters and operating conditions on its thermal performance and mechanical qualities. To examine the impacts of diameter, curvature, and various operating conditions on the thermal and mechanical performance of a receiver, a coupled thermal–mechanical model was created and assessed. The findings showed that the spiral coiled tube's thermal stress distribution is very nonuniform. Thermal efficiency declines and maximum stress rises from 74.9 MPa to 171.87 MPa as the diameter increases from 10 mm to 30 mm. The thermal efficiency rises when the curvature goes from 1/190 to 1/130, but the stress rises as well. The outlet temperature drops by 73.46 K after 5 min of cloud cover; cloud cover and startup conditions will result in rapid variations in stress and temperature on the coiled tube wall, endangering the receiver's safe function and shortening its lifespan.

Experimental investigation of the thermal efficiency of a new cavity receiver design for concentrator solar technology

The most popular design for solar energy receivers that achieves great thermal performance is a cavity receiver. This study experimentally compared two novel shapes of cavity receivers: conical-cylindrical-conical (CCC) and double cylindrical, with conventional conical and cylindrical designs, to examine the effectiveness of solar energy receivers. The findings indicate that the CCC shape demonstrated a higher level of efficiency, as it performed better than all other shapes that were examined. Results emphasized the influence of radiation intensity on receiver efficiency, with all shapes exhibiting improved performance at higher intensities, maximizing at 1000 W/m2. Lower friction factors were desirable for minimizing heat losses and maximizing efficiency, resulting in values of 0.078, 0.09, 0.1, and 0.12 for CCC, conical, double cylindrical, and cylindrical shapes at a flow rate of 2 L/min, respectively. The temperature differences for CCC, conical, double cylindrical, and cylindrical shapes are computed as 6.4 °C, 5.7 °C, 5 °C, and 4.3 °C, respectively. The thermal efficiencies of the CCC, conical, double cylindrical, and cylindrical shapes are computed as 86.5 %, 81.5 %, 79.9 %, and 68.9 %, respectively, at a flow rate of 2 L/min.

Experimental Test Setup of an Airwall to Reduce the Convective Heat Loss in Solar Thermal Cavity Receivers

An experimental setup is presented which allows to experimentally determine the thermal heat losses from a heated solar cavity receiver with an airwall. The setup is a ‘near-full-scale’ replica of a receiver, which ensures that the characteristic fluid dynamic numbers are in a range relevant for practical industrial applications. The executed tests show that – at ideal configuration – the airwall can reduce the overall thermal losses by 7±2%. The reduction of the convective losses amounts to 32±11%, which is in line with the known predictions from CFD simulations.

Numerical analysis of wind-induced convective heat losses in large-scale open volumetric cavity receivers and the evaluation of countermeasures

This study investigates the wind influence on the operation of an open volumetric cavity receiver (OVR) designed with a tower height of approximately 200m and a total thermal power of 240MWth. The receiver design incorporates an air return system where parts of the air are returned between the OVR modules after the heat exchange, while the remainder is recirculated externally from below the receiver. When operating such a scaled-up OVR, ambient wind becomes a relevant parameter in terms of convective losses and the air return ratio, which must be maintained at a high level to ensure economic viability. In this study, ambient wind and the receiver flow are modelled by CFD simulations with the RANS approach. In addition to the evaluation under windless conditions, the simulations in this study cover lateral wind at 4 and 8ms wind speed. The simulations show the vulnerability of externally returned air as it is significantly influenced by lateral wind. As a countermeasure, wind-adjusted external return air distributions are investigated, which show the potential to reduce convective heat losses due to incomplete air return. In addition, the application of aerowindows is investigated, which has limited potential due to the size of the receiver aperture. The results highlight the importance of the design of the external air return system and suggest a controllable return air system that can be adapted to the current wind situation.

Multi-objective optimizations of solar receiver based on deep learning strategy in different application scenarios

Efficient and secure operation of solar receivers is key to the development of concentrated solar power (CSP). Its precise and quick optimization is essential for receiver to achieve optimum thermal performance and safety across diverse application scenarios. In this study, we propose a hybrid model based on numerical simulation and deep learning to achieve this target. The hybrid model accounting for conduction, convection and radiation shows a small relative error (<2%) in over 96 % cases. We apply the model to two different application scenarios considering multiple performance objectives simultaneously and demonstrate that it can identify optimal structure parameters and heliostat scale for each inlet flow rate of the receiver. In combination with gas turbines, maximum efficiencies of 48.9 %, 53.2 %, and 56.8 % are achieved for flow rates of 0.5, 0.75, and 1 kg/s, respectively. When integrated into heating systems, the receiver achieves a maximum thermal efficiency of 89.8 % with a heliostat field scale of 5.76 MW. Furthermore, for the operation optimization, the proposed aiming strategy results in a 76 ℃ reduction in maximum tube wall temperature compared to the conventional aiming strategy. Our approach not only provides an advanced solution for rapid cavity receiver design and operation optimization but also has the potential for extension to other structures.

Numerical and experimental analysis on convective heat losses from a fully open cylindrical cascaded cavity receiver

A cavity receiver finds substantial application to improve the thermal performance of a solar parabolic dish collector. However, its limited surface area shortens the scope of utilization and bars thermal efficiency. This research has intercepted such problems by including a cascaded cavity receiver, which offers more surface area and high-temperature distributions, representing more heat absorption and utilization to convert into thermal energy. The crucial design of a cascaded receiver consists of two concentric steel cylinders with different heights attached at one end. The design is tested theoretically with the help of CFD analysis, and the heat loss results are compared with the traditional cavity receiver. Furthermore, according to design, an experimental set-up is fabricated, and experimentations are conducted in off-flux mode using an electric heater. The Pyromark coatings minimize radiation losses and implement the working conditions in the lab testing scenario. The convective heat losses estimated reduction of 4.3 % at 0°–24.8 % at 90° due to the application of coatings in the normal cavity and 3.4 % at 0°–16.4 % at 90° due to the application of coatings in the cascaded cavity. Also, the cascaded cavity receiver minimizes 6.98 %–13.93 % convective heat losses compared to traditional cavity receivers.

Experimental investigation of a novel design of cavity receiver for a parabolic dish collector humidification-dehumidification desalination system

In this study, a desalination cycle using a humidification-dehumidification method equipped with a parabolic dish collector has been experimentally designed and tested under the climatic conditions of Semnan City. A novel geometry of cylindrical-conical for parabolic dish collector’s cavity receiver was selected and used in this desalination system. For the experimental tests, four water samples were selected from the non-conventional brackish water sources in Semnan province. The performance of the desalination cycle was investigated for four days in the maximum period from 9:00 a.m. to 3:00 p.m. According to the results obtained from the tests, the maximum thermal efficiency of the collector with the cylindrical-conical cavity receiver for the test with water sample with electrical conductivity of 21,500 µS/cm was obtained as 45.49%. The highest water production rate was 0.966 l/day for a water sample with an electrical conductivity of 13,810 µS/cm. The average hourly water production rate for the saltiest water has reached the highest value, equivalent to 147.67 cm3/h. It was also found that there is an increasing trend of water production with an increase in the salinity of brackish water. The maximum hourly exergy efficiency of the system was 14.04% for a water sample with an electrical conductivity of 21,500 µS/cm. An increase in hourly exergy efficiency was observed with the increase in water salinity.

Response surface methodology for characterization of wind effect on combined convective loss from a bicylindrical cavity receiver

To assess the combined convective loss of a bicylindrical cavity receiver, an investigation was conducted using response surface methodology under varying wind directions, speeds, and cavity tilt angles. The study revealed that wind direction has a more substantial influence on the combined Nusselt number than cavity tilt angle. For all wind speeds and cavity tilt angles, the head-on wind direction results in a higher combined convective loss compared to back-on and side-on wind directions. Wind speed significantly affects the combined Nusselt number at higher cavity tilt angles for the back-on and side-on winds, with the effect diminishing at lower tilt angles. Increasing the tilt angle of the cavity leads to a greater change in the combined Nusselt number as wind speed increases. A quadratic model was developed to predict the combined Nusselt number, which achieves reasonable agreement between the predicted and experimental values, with a deviation of up to 12.5%.

Experimental performance and economic analysis of finned solar receiver for parabolic dish solar collector

The solar receiver is a vital component of concentrated solar collectors that absorbs solar radiation and converts it into heat. One of the challenges the research community faces is minimizing heat loss from the receiver at higher temperatures to maximize the thermal performance of parabolic dish collectors and achieve the system's cost-effectiveness. Cavity receivers have a complex design that makes them more challenging to manufacture and entails higher costs for improved thermal performance. Implementing innovative receiver designs is essential to maximize the absorption of solar radiation and minimize heat losses. In this experimental study, a cost-effective solar receiver was fabricated with fins to study heat transfer. The solar receiver is examined using water as heat transfer fluid with three flow rates of 0.097 kg/s, 0.125 kg/s, and 0.152 kg/s. The residence time of water is increased by adopting integrated fin receiver designs. The provision of fins in the solar receiver enhances heat transfer by increasing the turbulence in the fluid flow and results in higher thermal efficiency. The average energy and exergy efficiencies are 67.81 % and 8.93 %, respectively, with a 0.152 kg/s flow rate. At the highest water flow rate (0.152 kg/s) considered in this study, a lesser heat loss of about 3776.2 W occurred due to the effective heat transfer. The cost metrics, like levelized cost of electricity, net present value, and the payback period, are about 0.21 $/kWh, 923 $, and 3.38 years, respectively, at 0.152 kg/s flow rate. The proposed solar receiver produces optimal thermo-economic performance and lower initial investment for steam generation than other receiver designs. The current experimental study's findings could benefit the entire solar industry by presenting an effective solar receiver design for solar collectors.