Solar Heat Collector Research Articles

Drying of the orange slices, and energetic analysis of the drying chamber alimented by a solar air collector for extraction of the water from an orange slice

This study is focused on the extraction of water from sliced oranges through the process of solar drying, while also integrating an energy analysis of the drying chamber, which is powered by a solar air collector for the water extraction process. The experimental investigation encompasses various parameters, including the dimensions of the drying chamber, the solar collector, and the geometry of the orange slices (with a diameter D of 80 mm and thicknesses of ep = 3 mm and 5 mm). The results present the moisture ratio of the orange slices over the drying time and mass flow rate, with three different values (0.019, 0.024, and 0.033 kg/s). Throughout the experiments, the distance between the product support and the drying chamber's heat source was maintained at 140 mm. The report provides an energetic analysis that encompasses the enthalpy of the product, water, vapor, drying chamber, solar collector, and latent heat, all contributing to the control of the drying system. The effects of different mass flow rates (0.019, 0.024, and 0.033 kg/s) on the drying process are also examined in this study, with a focus on the important effects on the moisture ratio and drying velocity. Ultimately, the findings demonstrate that the mass flow rate plays a crucial role in determining the outlet temperature of the solar collector and the inlet temperature of the drying chamber, thereby affecting the kinetics of the drying process and the resulting moisture ratio.

Energy, exergy and economic investigation of novel hybrid dryer, indirect solar dryer and traditional shade drying

By integrating a secondary energy source into solar dryers, more moisture can be removed from food products in the same time period. For this purpose, tomato slices of different thicknesses (7 mm, 15 mm and quarter size) were dried to see the drying, energy, exergy and economic performance of an innovative hybrid dryer consisting of an indirect solar dryer and geothermal heat exchanger unit. The hybrid dryer’s performance was compared simultaneously with indirect solar dryer and traditional shade drying. The analyzes were evaluated according to the feeding of drying air from the solar air collector and geothermal heat exchanger unit. Compared to the other two dryers, the hybrid dryer dried the 7 mm, 15 mm and quarter size samples in the earliest time, with an average of 1380, 2476.3 and 2397.3 min, respectively. The average highest specific moisture extraction rate (0.87 kg/kWh) and dryer efficiency (45.25 %) and the lowest specific energy consumption (4.75 kWh/kg) for hybrid dryer were obtained for the 15 mm. The highest exergy efficiency for the solar air collector and drying chamber of the hybrid dryer was determined at 7 mm with 3.08 % and 38.9 %, respectively. The lowest payback period for the hybrid dryer was found to be 0.37 years for 7 mm. The results showed that the hybrid dryer was superior to the other two dryers by drying continuously day and night. Hybrid dryer can create a successful commercial ecosystem as an important drying alternative for locations where geothermal energy is available.

Analysis of the heat collection performance of a capillary solar heat collection wall structure

Solar thermal utilization in high-rise buildings is often constrained by the limited surface area of the rooftop. A novel façade-integrated capillary solar heat collection wall structure was proposed in this study, which involves embedding capillary tubes that circulate water within the cement mortar material, facilitating the integration of solar thermal collector and the exterior walls. To validate the feasibility of this new type of heat collection structure, experiments were conducted to investigate the impact of water flow rates on the heat collection performance of the proposed capillary solar heat collection wall structure under indoor solar simulator conditions, and outdoor field testing were conducted to assess its heat collection performance during winter, spring, and summer in Nanjing city. The experimental results revealed that, at water flow velocities of 0.05 m/s, 0.10 m/s, 0.15 m/s, and 0.20 m/s, the system's heat collection reached 4721 kJ, 4833 kJ, 4872 kJ, and 5326 kJ, respectively, showing a consistent increase with higher flow velocities in the capillary tube. The heat collection efficiency also increased gradually with flow velocity, but the rate of increase was relatively slow. The instantaneous heat collection efficiency decreased gradually as the experiment progressed, with a relatively small value of 47 % at a flow rate of 0.05 m/s. Data fitting revealed a linear relationship between the instantaneous collector efficiency and the normalized temperature difference at water flow velocities of 0.05 m/s and 0.1 m/s, and a quadratic exponential relationship at water flow velocities of 0.15 m/s and 0.2 m/s. During winter, spring, and summer in Nanjing city, the effective heat collection efficiency reached 45.8 %, 40.4 %, and 39.5 %, respectively, demonstrating that the capillary solar heat collection wall structure has significant potential in subtropical regions like Nanjing.

Numerical Study of the Solar Energy-Powered Embedded Pipe Envelope System

This study introduces a Solar Energy-Powered Embedded Pipe Envelope System (SEPES) designed to enhance indoor thermal comfort and reduce heating loads during the heating season. To achieve this objective, a dynamic simulation model coupling a SEPES and building thermal environment was established under the TRNSYS environment. Based on the model, a case analysis was conducted to investigate the operational characteristics of the system during the heating season in a rural building in Beijing. The results indicate that, on the coldest heating day, the system can elevate the indoor temperature by 14.5 °C, reducing the daily heat load from 76.3 kWh to 20.3 kWh, achieving a remarkable energy savings of 73.4%. Additionally, due to the utilization of lower solar heat collection temperatures, the energy efficiency of the system reaches 26.9%. Throughout the entire heating season, the SEPES system enhances the natural indoor temperature by 13.3 °C to 16.6 °C, demonstrating significant effectiveness. Moreover, regional adaptability analysis indicates that the SEPES achieves energy savings ranging from 43.9% to 66% during the heating season in cold regions and regions with hot summers and cold winters in China. Overall, the SEPES is most suitable for climates characterized by both low temperatures and abundant solar radiation in order to achieve optimal performance.

Radiation-convective heat transfer and performance analysis of a parallel-plates duct direct absorption solar heat collection system

Solar photo-thermal conversion and solar heat collection are hot topics today. However, which solar collection mode is the best? The question has puzzled scholars for many years. In this study, a direct absorption solar heat collection (DASC) duct system was investigated. Carbon quantum dots (CQDs) were selected as the heat absorption medium. Different absorption modes were clarified. It is found that the ratio of the radiation penetration depth of nanofluids to duct depth (duct penetration ratio, α) plays a key role in the duct heat transfer and system performance. Totally three solar heat collection modes can be classified depending on the value of α: volume absorption (partial volume 0<α<1 or whole volume α = 1), surface absorption (upper α → 0 or bottom α → ∞) and hybrid absorption for α > 1. Of them, the whole volume absorption has the best performance when α = 1, while the hybrid performs the best when the penetration ratio is not unity. Surprisingly, a higher fluid absorption coefficient does not necessarily lead to a higher photo-thermal performance. The extreme high fluid absorption coefficients (upper surface mode) are inferior to extreme low absorption coefficients (bottom surface mode). Of the different modes, the total Nusselt numbers in the whole volume absorption mode are 2–3 times higher than those in the bottom surface absorption mode. For solar heat collection, convective heat collection is better than standstill collection, and a certain flow velocity should be ensured to have a satisfactory efficiency. The findings were experimentally verified.

Energetic and exergetic study of a flat plate collector based solar water heater - investigation of the absorber size

Small sized absorber in a flat plate solar collector is beneficial in terms of cost and minimum heat losses. However, its detailed thermal performance compared to standard size collector is still not fully understood. There is a paucity of research to appreciate thermal performance of solar water heating collector with consideration of a small absorber size (below 1m2) and a standard absorber size (2 m2). The present study attempts to investigate the energy and exergy efficiencies of flat plate solar water heating collector with two absorber plate areas (2 m2 and 0.74 m2) to enumerate size of the absorber required for improved first and second law thermal efficiencies of the collector. The efficiencies of these two collector designs are experimentally compared with the help of a test facility available in the site for given operating temperatures and rate of flow. The combined experimental uncertainty due to the measuring instruments and the measured parameters is also ascertained. The obtained results highlight the significance of the larger absorber size (2m2) for higher thermal efficiency, and lower absorber size (0.74m2) for higher exergetic efficiency. The highest thermal efficiency obtained is 77.38% for larger absorber size, and the highest exergy efficiency of 13.21% is obtained for lower absorber size collector. It is demonstrated that larger and lower absorber size of the collector have higher thermal efficiency and higher exergy efficiency, respectively, than some of the published works.

Investigation of optimal utilization of solar energy in electric vehicles: An economical and low carbon growth perspectives

Solar energy is an essential source of clean, renewable energy that has the potential to transform our energy system and reduce impact on the environment. But, only 3.6% of solar energy is effectively used around the globe for electricity generation. So, using solar energy to the maximum extent is essential to control air pollution and save the environment for future generations. This article discusses the operative use of solar energy and suggests measures for optimal solar energy utilization in electric vehicles (EVs). The water-based silicon dioxide (SiO2) and aluminum oxide (Al2O3) combination is considered due to the high refractive index of SiO2 and scratch resistance and durability of Al2O3. A theoretical model was established by considering the shape of the solar collector, temperature change, nano spray, and radiative heat. The modeled problem was computationally resolved using the bvp5c MATLAB scheme, and simultaneous results were explored for various outlines of solar collectors. It is found that the shape of the solar collector and nanospray/nanocoating play a significant role in the practical usage of solar energy. Using curved-shaped solar collectors with water-SiO2-Al2O3 nanocoating allows the solar collector to absorb more light. This helps to improve the effectiveness of solar collectors in running EVs, which can reduce carbon growth.

Modeling of Integrated Hollow-Fiber Solar-Powered VMD Modules for Desalination for a Better Understanding and Management of Heat Flows.

The direct integration of membrane distillation and solar energy collection in a single module is a promising technology for autonomous seawater desalination in remote regions; however, the modeling and design of such modules are challenging because of the coupling of the radial and longitudinal heat and mass transfers. In a previous study, we provided as a first modeling approach a hollow fiber solar collector vacuum membrane distillation (VMD) module, considering a constant temperature at the shell side and a pure water feed. Here, a full model is developed to describe the coupled effects of the solar collector and a hollow fiber VMD module operating in an outside/in mode with saline water. The model considers all the main phenomena (membrane distillation, temperature and concentration polarization, absorption of solar radiation and energy balances over the solar collector, radial and longitudinal heat and mass transfer, seawater properties, and more than 30 variables). Applied to simulate the behavior of a semi-industrial-scale module, it allows the influence of solar radiation on the performance/limits of the integrated module to be discussed based on the radial and longitudinal profiles and heat flows. The model can be used to identify key points in the module design to better utilize solar radiation and manage heat flows.

Numeric simulation and experimental validation for a Novel Trapezoidal Solar Collector

In a global warming context, the diversification of the energy matrix is essential for mitigation. Technologies and solar devices have begun to play an important role in this sense, being flat-plate solar collectors the most practical device. On the other hand, numerical modeling and experimental validation are important tools for improving the performance of these technologies. In this work, a trapezoidal solar air heating collector for food drying processes was modeled by using the Simusol open-access software, and experimental validation was performed. This particular shape presents a geometrical novelty since no other similar designs were found into the available literature, even in such application as food drying. Key parameters, such as air temperature, global efficiency, air mass flow, global heat loss coefficient, and useful heat, are determined and discussed. The proposed air collector numerically behaves as expected. The output air temperature reaches about 100 °C, while the peak heat gain is about 900 W, which makes the air heating collector suitable for drying applications. Due to natural convection is the main heat transferring mechanism, low air mass flows were obtained. For the case analyzed here, this last parameter ranges in 0.012–0.016 kg/s for the optimal thermal behavior.

Vapor compression air conditioning system with solar heat collector

THE RELEVANCE of the study lies in the fact that air conditioning systems in Iraq consume more than half of the electricity generation. During the summer, when temperatures rise, the demand for air conditioning increases, resulting in constant power outages. Consumers are starting to use local generation - diesel generators, which increase environmental pollution. THE PURPOSE. Consider the problems thermal energy from the sun is an ideal solution for reducing electricity consumption, increasing the performance of air conditioners, ensuring continuity of power supply and reducing pollution from diesel generators and power plants, as well as saving energy and reducing the consumption of fossil fuels. METHODS. When solving the problem, a comparison of options for standard and (hybrid using solar thermal energy) air conditioning systems was used. In a hybrid system, thermal energy enters the system from a solar collector built behind the compressor. Thermal parameters and level of electricity consumption were calculated. RESULTS. The article showed that a hybrid air conditioning system using solar thermal energy is more efficient than a traditional system, as it increases the cooling coefficient by (38.9 - 46.3%) and reduces electricity consumption by (56.89 - 66.66). %). CONCLUSION. The use of a hybrid air conditioning system in the climate of Baghdad city with a vapor compression air conditioning system reduced the electrical energy consumption of the compressor and increased the performance of the system, which will lead to increased reliability of power supply and eliminate the need to use local diesel generators.

Dynamic response characteristics and economic analyses of two solar-assisted multi-generation systems

Efficient use of solar energy can alleviate the depletion of fossil energy and global warming. In this paper, two solar-aided combined cooling, heating and power systems are proposed and dynamically modeled. The main difference between the two systems is whether the solar energy is stored. A rotor speed-temperature-fuel control system is established, which is suitable for both systems. A control system for solar heat collection process is developed. Energy, exergy and techno-economic analyses are carried out to evaluate the thermodynamic and economic performances. The dynamic responses under direct normal irradiation perturbation and load perturbation are also investigated. The result shows that compared with the system without energy storage, the system with energy storage has higher primary energy utilization rate, exergy efficiency and fuel saving rate, but the economic performance is poorer. The rotor speed-temperature-fuel control system can guarantee a short equilibrium time and a small overshoot for power generation process. When electrical load disturbance occurs, the stabilization times of the output power, cooling energy supply and thermal energy supply are 30 s, 675 s and 770 s, respectively. Under the regulation of the solar heat collection control system, the maximum overshoot of the outlet thermal oil temperature of the parabolic trough solar collector is 2.6 % with a stabilization time of 83 s when the direct normal irradiation step disturbance occurs.

Performance analysis and optimization of a solar assisted heat pump-driven vacuum membrane distillation system for liquid desiccant regeneration

Liquid desiccant air-conditioning (LDAC) system is one of the excellent alternatives to conventional vapor compression refrigeration system due to its great energy-saving potential. However, regeneration of diluted liquid desiccant is the main energy-consuming process, and its performance plays a significant role in LDAC system. Recently vacuum membrane distillation (VMD) is becoming an emerging and promising separation process rely on the advantage of high permeate flux and low energy losses. The interest of usage solar energy techniques for feed solution heating in VMD systems is regarded as a sustainable path for membrane distillation process. In this work, a solar-driven VMD system incorporating a vapor-compression heat pump for liquid desiccant regeneration is introduced. An adapted solar/heat pump hybrid heating strategy has been devised to establish a connection between the heat-demanding process and the solar thermal supply. A comprehensive multicriteria assessment of energy, exergy, and environmental evaluation is conducted, and the influences of crucial parameters on both key components and system performance are evaluated to ensure a systematic examination. Results show that both the COP and STEC decrease obviously with the growth of the inlet solution temperature, whereas SEEC is improved abviously from 410.6 kW·h/m3 to 566.1 kW·h/m3 due to the effect of heat pump. The exergy analysis indicates that exergy losses in solar collector and stratified heat storage tank accounted for over 80 % of the total exergy losses. Additionally, single-objective optimization and multi-objective optimization are employed to explore the optimum operating conditions of key componets and whole system. Results show the ideal optimal solution can be obtained with a COP of 19.92 and a SEEC of 142.89 kW·h/m3 when the weights of COP and SEEC are taken as [0.5, 0.5].

Optimization of geometrical parameters of the heat receiver of a solar air heating collector

The article presents the optimization of the radiant surface of the solar air heating collector (SAH). As a radiation-receiving surface of the SAH, a surface is used, which is a system of metal drainage shavings and a V-shaped surface. Based on the study of the heat transfer process, an effective scheme of heat removal from the radiation-receiving surface of the SAH is presented. When optimizing the radiation-sensing surface of the SAH, the process of radiation-sensing of the surface, which depends on the geometric shape of the chips, is taken as the target function of the maximum. A formula is proposed for calculating the determination of the transmitted amount of the radiant flux of the sun to the unit of the frontal surface through the shape of the metal shavings from the value of the opening step angle in different thicknesses of the metal shavings. It has been confirmed that the solar radiant flux passing to the unit of the frontal surface through the metal chip shape reaches its maximum value in the following cases: when the chips are 0,002 m thick, they have an optimal angle φ = 58°, the transmitted energy of the radiant flux through the chip shape is E = 31%; with a chip thickness of 0,0005 m, the optimal angle is φ = 42°, the transmitted energy of the radiant flux through the chip shape is E = 41%; with a thickness of 0,001 m, the optimal angle is φ = 50°, the transmitted energy of the radiant flux through the chip shape is.

The influence of artificial turbulization on the efficiency of heat exchange in the channels of solar air heating collectors

The influence of artificial turbulization on the efficiency of heat exchange in the channels of solar air heating collectors

Performance and economic considerations in augmentation of solar still efficiency using solar heat collector coupling

The literature on the integration of solar heaters with solar stills has sparked considerable debate regarding whether this combination genuinely enhances distillation efficiency. This paper seeks to shed light on this question by examining the daily freshwater yields and thermal efficiencies of four distinct still-heater configurations, each having a total of one-square-meter solar energy collecting area, over several days. These measurements are then compared with the yields and efficiencies of a one-square-meter simple standalone solar still obtained on the same days. The findings reveal that, despite standalone solar stills demonstrating efficiencies ranging from 35% to 45% on days with total daily solar radiation exceeding 6 kW/m2, none of the four still-heater configurations achieved comparable efficiencies on days with solar radiations below approximately 6.7 kW/m2. Notably, the efficiencies of the standalone still were consistently higher than those of all four configurations on days with solar radiation below 6.7 kW/m2. Furthermore, economic analysis indicates that standalone solar stills are more cost-effective to construct than still-heater systems with equivalent solar radiation collecting areas.

Application analysis based on solar grid-connected photovoltaic power generation and intermittent energy storage system

Solar photovoltaic power generation as a building electrical professional in the energy use of important technical means, through the realisation of photovoltaic conversion, can be a large amount of light energy transmission to the building application, once the electrical energy surplus is too much, but also can be transmitted to the power grid use. Based on this, the article takes the solar photovoltaic power generation system as the basis, comprehensively analyses the operation principle and basic characteristics of solar photovoltaic power generation, summarizes the main influencing factors of grid-connected solar photovoltaic power generation, as well as the impact of grid-connected solar photovoltaic power generation on the grid, and researches on applying automation technology to solar photovoltaic power generation, such as photovoltaic buildings, DC inverters, reactive power compensation, etc., so as to comprehensively improve the grid-connected solar photovoltaic power generation efficiency and provide a constant source of energy for buildings. Solar thermal power generation technology is another kind of solar power generation technology besides photovoltaic power generation. It is a renewable energy generation method that integrates solar thermal conversion power generation, large-scale heat storage and the characteristics of power grid synchronmachine. According to the influence of different intermittent heat load fluctuation characteristics on the design of solar heat collection and heat storage system, the design method of heat collection and heat storage of intermittent solar heating system is established. The operation characteristics of solar energy system in three typical intermittent heating modes are compared and analyzed. It provides the design method and operation optimization strategy for the efficient utilization of solar heating system.

Thermal performance of a solar heat collection and storage wall with night insulation in winter: A numerical study

The application of phase change material (PCM) in Trombe walls (TW) can improve all-day indoor thermal comfort. However, the heat loss via the glass is relatively large, resulting in low thermal efficiency at night. This paper designs a double glass and a thermal insulation curtain used to increase the thermal efficiency of a TW with PCM at night. In addition, a mathematical model based on the implicit difference method was established to study the thermal efficiency and heat loss of the proposed wall in Beijing. The findings indicate that the thermal efficiency at night is improved by 16.23 % compared to a traditional TW, while heat loss at night drops by 7.75 %. The heat gain at night first increased and then decreased with the augment of phase change temperature. As the latent heat or thermal conductivity of PCM increases, the heat gain declines during the day and increases during the night. The most suitable thickness of PCM is 0.02 m. The farther the insulation curtain is from the inner glass, the greater the heat loss and the smaller the indoor heat gain at night. And the later the opening time of the air vents during the day, the smaller the heat gain during the day and the greater the heat loss. But the resulting increase in nighttime heat gain is not significant. This study can offer design suggestions for enhancing indoor thermal comfort and nighttime insulation performance.

Dynamic characteristics of a novel liquid air energy storage system coupled with solar heat and waste heat recovery

Liquid air energy storage (LAES) is a promising energy storage technology for its high energy storage density, free from geographical conditions and small impacts on the environment. In this paper, a novel LAES system coupled with solar heat and absorption chillers (LAES-S-A) is proposed and dynamically modeled. A power-speed control system is established for this system. Two operating control strategies are developed for the solar heat collection process. The transient characteristics of the novel system during the start-up, load-up process and encountering different disturbances are investigated. Besides, the dynamic responses when the waste heat is used for producing heating energy are also studied. The results indicate that the power-speed control system can guarantee a very short equilibrium time and a very small overshoot. The energy efficiency of the LAES-S-A system is 65.84 %, while that is 75.32 % when the waste heat is used for producing heating supply. When a disturbance occurs, the equilibrium times of the absorption chiller, air turbines and heating device are 1500 s, 40 s and 38 s, respectively. Compared with the absorption chiller, the heating device can better cooperate with the air turbines. The results can provide a reference for future studies.

Characterization and performance investigation of UiO-66 for low-grade thermochemical adsorption heat storage

Thermochemical energy storage can improve low-grade energy utilization efficiency, thereby reducing buildings' operating energy consumption. However, common thermochemical thermal storage materials have poor stability and low energy storage density. To this end, it put forward to use UiO-66 as a novel low-grade thermal energy storage material. It was synthesized and characterized, and its thermal conductivity, optimal activation temperature and time, adsorption kinetics and thermal energy storage density were also comprehensively studied. The results showed that the thermal conductivity of UiO-66 was 0.282 W/(m·K) at 30 °C. The optimal activation temperature and time for UiO-66 were 100 °C and 1.5 h taking into account the balance between the high water uptake and energy saving. The water uptake of UiO-66 at 30 °C and 80% RH reached 0.410 g/g, 2.1 times that of Zeolite 13X. The adsorption behavior of water vapour in UiO-66 was accurately described by the pseudo-second-order kinetic model. The thermal energy storage density of UiO-66 was 818 kJ/kg, which was 1.6 times higher than that of Zeolite 13X (515 kJ/kg), demonstrating excellent thermal storage performance. To sum up, the research results showed that UiO-66 had application potential in low-grade thermal energy storage fields such as heat from solar collector and industrial waste heat.

Building energy-saving potential of a dual-functional solar heating and radiative cooling system

Space heating and cooling devices that rely on renewable resources are in demand amid energy crises in parts of the world. However, common renewable space heating and cooling devices are mono-functional. For regions with heating and cooling seasons, using two mono-functional devices might double the installation and maintenance costs, and prolong the payback period. This study proposed a dual-functional renewable heating and cooling device by utilising solar power and nocturnal radiative cooling. The device is a modified solar heating (SH) collector that optimises the nocturnal radiative cooling (RC) to become an SHRC collector. Investigation of the SHRC collector’s performance and energy-saving potential of a building-integrated SHRC collector was conducted using CFD and EnergyPlus. Analysis of the SHRC collector’s performance in various environmental conditions shows that the SHRC collector can reach 42 % thermal efficiency at zero-reduced temperature and > 50 W/m2 of net cooling power. Also, studies on the optimal air duct and air gap height reveal that a 1 cm air duct and 4 cm air gap as the best options for the SHRC collector design. Simulations of the building-integrated SHRC with a collector area of 9.43 m2 for a typical 100 m2 house building demonstrate the multi-seasonal advantage of the SHRC collector, with at least 1.5 kWh more daily savings than the SH and RC collectors in typical winter and summer days. Furthermore, the simulations estimate the annual combined heating and cooling energy savings by the SHRC collector around 32.7 % in Madrid, 25.5 % in Tokyo, and 14.0 % in Isfahan.