Solar Air Heater Research Articles

Strategies for maintaining indoor temperature in rural residences in highland pastoral areas

Previous studies on improving indoor thermal environments focus on plain areas. However, the scattered rural residences in highland pastoral areas have special climatic conditions and living habits. This article presents an approach to utilize the abundant renewable energy in the local area to create an indoor thermal environment that residents need. A rural village in Qinghai province of China was taken as the target; we used field investigation and questionnaire survey to explore typical layout. Combined with local building codes, two envelope and two heating systems were proposed to achieve indoor thermal comfort. We also introduce building simulation models and field tests to discover four combinations’ energy-saving effects in maintaining indoor thermal comfort. The average energy-saving rate in the heating season of the four schemes is 89.31%, and the mean temperature is 16.64 °C. The results suggest the heating system has a more significant influence on energy consumption than the enclosure structure, which needs attention under the same budget situation. The solar air heating system has better indoor temperature maintenance effects than the carbon fiber floor heating system. Regarding construction, the prefabricated integrated enclosure structures improve thermal insulation performance significantly.

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

An Investigation into The Enhancement of Heat Transfer in Roughened Ducts of Solar Air Heaters

One of the most crucial tools for the process of transforming solar energy into thermal energy is a solar air heater. Thanks to its low cost and ease of installation, solar air heaters have quickly become one of the most popular and widely used methods of harvesting solar energy. Low convective heat transfer coefficient values between the absorber plate and the air significantly reduce the solar air heater's thermal efficiency. This is because absorber plates are used in solar air heaters. As a consequence, the absorber plate heats up, releasing a great deal of thermal energy into the surrounding space. This article presents the findings of a study that used computational fluid dynamics to investigate how heat is transferred in a solar air heater. The work for this project was done by the author (CFD). Researchers are now investigating the impact of the Re on the Nu. Commercial software known as ANSYS FLUENT 20 may be used to analyse and visualise the flow that happens across the duct of a solar air heater. This programme falls under the category of finite volume software. Using the programme helps get the job done.

Carbon nanotube-based photothermal membrane for efficient cold air heating and removal of particulate matter and airborne bacteria

Indoor heating results in high energy consumption and severe atmospheric pollution. Although the development of solar air heaters provides a sustainable route for indoor thermal comfort, such heaters still face challenges in terms of adequate heat exchange and filtering of atmospheric pollutants. Inspired by solar-driven interfacial evaporation, we propose a multifunctional carbon nanotube-based photothermal membrane for efficient cold air heating and purification via ventilation. Carbon nanotubes endow the membrane with high light absorption and thermal conversion capabilities, thereby sufficiently heating the approaching cold air. With the hierarchical structure formed by phase inversion, the thin upper skin of the composite membrane intercepts micropollutants via the size-sieving effect, whereas the finger-like pores and interpenetrating macrovoids inside the membrane ensure that the heated clear air passes through quickly. A proof-of-principle experiment indicated a cold airflow of 1 L/min across the membrane, yielding a temperature increase of ca. 37 °C as well as a PM 2.5 rejection always higher than 93%. Further antibacterial experiments demonstrated that the membrane effectively removed airborne bacteria. This multifunctional carbon nanotube-based photothermal membrane with specific microstructures not only improves the indoor living quality but also provides a sustainable development scheme to coordinate the relationship among energy utilization, building heating, and air purification.

Energy-efficient crumb rubber drying by heat recovery and solar air heating

Natural rubber is a key agro-industrial product in Asia, Africa, America, and Oceania, with widespread applications (e.g. tires, latex gloves, wet suits). The energy consumption of the traditional rubber drying process is very high and improvements should be investigated to both reduce the energy consumption, and reduce the cost of the rubber processing. The research investigated both heat recovery and solar air heating (SAH) to minimize the energy consumption of the drying process. A complete assessment of an industrial rubber drying plant in China demonstrated that a heat recovery can reduce the energy consumption by 16 to 44%. If moreover SAH is applied, further energy savings can be achieved. A pilot-scale SAH was tested. Its solar transfer efficiency was between 30% and 50%. Experimental data were theoretically validated, and used in a scale-up design strategy, resulting in an overall drying energy saving of 60 to 77%. The corresponding total investment and payback period are 300 and 420 k€ and 2 to 3.3 years respectively. The novel layout of the energy-efficient rubber dryer, and its energy performance are illustrated.

Thermo-hydraulic performance investigation of double pass solar air heater integrated with PCM-based thermal energy storage

The solar air heater (SAH) is one of the ways to utilize solar energy for the purpose of drying, greenhouse heating and air conditioning. However, the SAHs are unable to deliver reliable thermo-hydraulic performance as a result of the intermittent nature of solar energy and the low convective heat transfer coefficient. Thus, in the present study, a three-dimensional numerical investigation is performed to study the thermo-hydraulic performance of the double pass solar air heater (DPSAH) having semi-cylindrical PCM tubes and perforated baffles as roughness geometry. The parameters selected for this study include baffle height ratio (eb/H) from 0.4 and 0.8, tube radius ratio (rt/H) from 0.2 and 0.5, and Reynolds numbers (Re) from 3000 and 13,000. Experimental validation has been conducted to verify the numerical results, and it has been found to be well-validated with mean absolute errors of 6.5 % and 1.2 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number (Nur) is found to be 200.08 at Re of 13,000, while the maximum friction factor (fr) is measured to be 0.6290 at Re of 3000, which corresponds to eb/H of 0.8 and rt/H of 0.3. The maximum heat transfer enhancement (Nur/Nus) in comparison to the smooth duct is found to be 5.08 times with a maximum friction factor increment (fr/fs) of 65.80 times, which corresponds to eb/H of 0.8, Re of 13,000 and rt/H of 0.3. The maximum thermo-hydraulic performance parameter (THPP) is observed to be 1.83 at Re of 13,000, rt/H of 0.2 and eb/H of 0.4. This study contributes to the design and optimisation of SAHs by incorporating thermal energy storage and roughness geometries.

Optimized solar food dryer with varied air heater designs

The use of solar energy for drying is considered one of the most environmentally friendly ways to reduce dependence on fossil fuels. The purpose of this experimental study is to determine how absorption plate design affects the evaporation rate of a solar food dryer in Baghdad, Iraq. Tests were performed on four different absorbent panel models. This dryer design consists of a section for heating solar air and one for preserving food. There is insulation at the back of the dining cabinet, which is made of wood. As food samples, orange slices were selected. Except for the absorb plate design, all four models have identical measurements. Matte black aluminum absorbent plate is featured on the Model-1. Both Models 2 and 3 have perforated cylindrical fins arranged uniformly and vertically in Model 2 and horizontally in Model 3. Model 4 uses horizontal fins and an absorber plate coated with 15 % silicon content. A fruit cabinet holds sliced fruit in five movable mesh trays. According to experimental results, the shape of the absorbent plate directly affects the temperature of the outlet air, which in turn affects the rate at which water is evaporated from fruit slices and the overall drying process. Model-1 solar air heaters could be improved by approximately 17 % by coating them with 15 % silicon. The efficiency of Models 2, 3, and 4 is increased by 20 %, 40 %, and 65 % by adding fins and tint over Model 1. Models 1, 2, 3, and 4 had moisture contents of 28 %, 25 %, 20 %, and 18 %, respectively, at 15 p.m. A solar dryer has been demonstrated to be suitable for successfully drying fruits and vegetables in Iraq's atmosphere through practical experiments.

Energy, exergy, environmental, and economic (4E’s) analysis of a solar driven humidification-dehumidification desalination system: An experimental investigation

A solar-driven humidification-dehumidification (SDH-DH) desalination system has shown to be a highly efficient and viable solution to meet the freshwater needs of a community. However, the solar air heater based on flat plate collector, imposes constraints on their efficiency. The current work focuses on the development of an SDH-DH desalination system. This system is comprised of a solar air heater that utilizes a double-ends open evacuated tube collector, a humidifier equipped with cellulose pad packing material, and a dehumidifier based on a direct evaporative cooler. The current SDH-DH desalination system is operated in two modes, namely open loop and closed loop, at four distinct process air flow rates. The system's performance indices are evaluated based on energy, exergy, environmental and economic analysis. The solar air heater is capable of generating hot air at an approximate average temperature of 100 °C, while maintaining an airflow rate of 150 kg/h. This enhances the efficiency of the humidifier, resulting in a freshwater production rate of about 2.43 L/m2/day at a cost of 0.027 $/L. Moreover, the use of an evaporative cooler-based dehumidifier effectively mitigates the issue of fouling that arises during the condensation process. The system achieved the maximum mean energy efficiency of 25.39 % and exergy efficiency of 4.59 % in a closed loop configuration, with an air flow rate of 150 kg/h. The total CO2 reduction amounts to 119.08 tons during the designated duration.

Exploring the performance of an indirect solar dryer by combining three augmentation approaches (trapezoidal absorber, shot blasting, and pebble stone)

The shelf life of food products can be increased by reducing their moisture content with the aid of solar dryers. However, the poor efficiency of solar collectors increases the time and energy required for drying the food crops. Hence, the present work aims to overcome the above bottleneck by employing corrugated shot-blasted absorbers in solar air heaters and comparing their performance with flat plate solar air heaters. Subsequently, the drying kinetics of bitter gourd and tapioca cassava were subject to experimental investigation using indirect solar dryers in their natural mode, aiming to assess the dryers' overall performance. The experiments revealed that the average thermal efficiencies of the SAHs equipped with flat plate absorber plates and corrugation with shot-blasted absorber plate treatment displayed variations ranging from 39.05 to 53.12 % while maintaining a constant MFR of 0.02 kg/s. The average exergy efficiency of the FPAP is 1.103 % and the CSB absorber plate is 1.755 % with a constant flow rate of 0.02 kg/s. The research findings indicate that the CSBAP (surface-improved SAH) demonstrates a higher heat-absorbing capacity when compared to the FPAP SAH. The utilization of the CSBAP design along with the incorporation of pebble stone results in a greater ability to efficiently absorb and retain heat when compared to the traditional FPAP design with a shot-blasted surface. The inclusion of pebble stones in the drying process, as observed in Case II for Tapioca cassava, led to a remarkable improvement in drying efficiency by approximately 36 % when compared to Case I. Furthermore, the drying efficiency for bitter gourd in Case IV experienced a notable improvement of around 30 % when pebble stones were integrated into the drying process, in contrast to Case III. Eventually, the experimental results specified that the carbon credits accrued for the CO2 mitigated by the FPAP and CSBAP systems in the natural convection mode were calculated to be approximately 226.48 and 308.11 Rate $/year, respectively. These alterations synergistically contribute to enhancing the SAH's effectiveness and effectively utilizing solar heat directly contributes to reducing greenhouse gas emissions and, subsequently, the carbon footprint.

Thermal performance estimation of a v-corrugated solar air heater using ann techniques

A solar air heater (SAH) is a unique form of solar thermal collector that utilizes solar energy emitted from the sun to produce heated air. Various experimental and theoretical investigations have been undertaken to improve the poor thermal performance of SAHs. The difficulties related to these studies drew attention toward a reliable soft computing technique exemplified by the Artificial Neural Network (ANN) technique. The current work applied actual meteorological data from Miskolc City, Hungary, to an ANN model with the structure of a Multi-layer Perceptron (MLP) to forecast the energy performance of a V-corrugated solar-powered air heater. Seven input parameters and one output parameter make up the ANN structure, with a single hidden layer. For the purpose of selecting the most effective network for predicting output parameters, ten neurons have been assessed. The suggested ANN model was trained with 336 data sets using the Levenberg-Marquardt (LM) learning technique. The comparison of anticipated and real thermal performance values shows a very good agreement. The statistical error analysis showed that the optimal ANN model structure of 7-8-1 can reliably and accurately predict SAH’s thermal performance and thus it can save both time and cost.

Development and enhancement in drying performance of a novel portable greenhouse solar dryer

The increasing demand for drying technology for agriculture and food products has gained significant attention due to population explosion and inadequate resources available. The present study focuses on the concept of enhancing the drying performance of portable greenhouse solar dryer. The experimental investigations for evaluating the dryer performance were carried out while drying out onion slices. The experimentation was carried out in 4 different modes to demonstrate the effect of various modifications implemented to improve the dryer performance. The active greenhouse solar dryer (AGHSD) is the first working mode which comprises of the conventional drying system with active mode of removing moisture. The second working mode uses recirculating fans along with exhaust fans (AGHSD@circulating fans). In the third working mode an Evacuated Tube-type solar Air Heater was added to along with previous modification (AGHSD@circulating fans + ETAH). The last working mode adds an air flow distribution system to the incoming pre heated air from the Evacuated Tube-type solar Air Heater (AGHSD@circulating fans + ETAH + air flow system). Various performance characteristics like moisture ratio, heat utilization factor, coefficient of energy, heat gain and thermal efficiency of the dryer are used to analyze the changes in the drying performance. AGHSD@circulating fans + ETAH + air flow system reduced the moisture ratio in the onion slices to 5.32% from 95% in one day, compared to 19.99% for AGHSD and 46% for open sun drying. The heat utilization factor and coefficient of energy for AGHSD@circulating fans + ETAH + air flow system and AGHSD@circulating fans + ETAH improve by 10% and 15% respectively as compared to AGHSD. AGHSD@circulating fans + ETAH + air flow system shows improved heat gain of 29.53% and shows the best drying rate for the developed drying system. The thermal efficiency of AGHSD@circulating fans + ETAH + air flow system is around 60% while for AGHSD is around 41% which is higher than the thermal efficiency of 20% for sundried samples.

Performance prediction of single-pass and multi-pass low-cost solar air heater

This study introduces a mathematical model and experimental evaluation of solar air heating utilising an absorber surface constructed from low-cost upcycled materials. The research presents a solar air heater prototype, suitable for applications such as space heating and agricultural drying. The solar heating system was modelled using upcycled beverage aluminium cans, considering both single and multi-pass flow configurations. Performance in terms of useful heat was determined through both mathematical model simulations and experimental methods. The multi-pass system demonstrated superior performance, delivering increased usable heat at elevated temperatures compared to the single-pass system. A comparative analysis and validation were conducted between numerical investigations with natural and forced convection on the five-pass solar air heater and experimental test outcomes. This research highlights the potential of utilising waste materials to develop cost-effective, solar heating solutions, contributing to energy management and waste reduction strategies. The findings can be explored for future explorations into sustainable and renewable energy solutions, particularly beneficial in regions with constrained economic resources.

Exploring the thermal performance of a solar air heater with a V-corrugated and shot-blasted absorber plate comprising nano-enhanced phase change materials

This research aims to carry out an experimental investigation into the performance of a solar air heater using phase change materials in combination with V-corrugated absorber plates and shot blasting. This shot blasting approach is applied to interrupt the boundary layer thickness of the absorber plate material it will increase the absorbance of the material. This study incorporates the analysis of four distinct absorber plates namely (i) V-Corrugated Plate (ii) V-Corrugated with shot blasting, incorporating PCM (iii) V-Corrugated with shot blasting, including NEPCM (0.6 %) (iv) V-Corrugated with shot blasting, including NEPCM (0.9 %). In this study, Paraffin wax was selected as the base PCM, and MWCNT dispersed into base PCM with different weight fractions. The nano-enhanced phase change material with a concentration of 0.9 wt% examined that the latent heat of melting and solidification experienced a significant augmentation. This enhancement resulted in a maximum increase of 12.5 % for melting and 8.2 % solidification was attained at 0.9 % of MWCNTs compared with paraffin wax. The average exergy efficiencies of V-corrugated plate attains an efficiency of 1.023 %, V-corrugated with PCM records 1.357 %, V-corrugated with 0.6 % NEPCM attains 1.698 %, and V-corrugated with 0.9 % NEPCM attains the highest efficiency at 2.167 %. The significant enhancement in exergy efficiency observed in NEPCM configurations with volume fractions of 0.6 % and 0.9 % is primarily attributed to two key factors namely enhanced thermal conductivity and improved heat transfer properties. The maximum sustainability index for the V-corrugated design with 0.9 % NEPCM falls within the range of 1.014 to 1.037. The average “Nu” value of 27.5 was achieved under the conditions of a mass flow rate of 0.02 kg/s and the addition of 0.9 % MWCNTs dispersed in paraffin wax.

Analytical and Numerical Models of a New Hybrid System of Earth Air Tunnel Integrated Solar Air Heater With Sensible Storage

Abstract A novel combination of an earth air tunnel (EAT) and a sensible thermal storage-aided solar air heater has been proposed when the sensible storage medium is taken to be rocks filled within the air flow passage. Both time-dependent and steady-state models are reported. The former describes the exact thermal performance of the system for a two-month wintertime for the city of Baghdad, Iraq. The latter describes average performance of the system. The implicit finite difference method and method of separation of variables have been used to solve the pertinent equations in the respective models. Acceptable level of accuracy was obtained between the steady-state numerical and analytical solutions as well as between the numerical and the published data. It is revealed that preheating by a sufficiently long EAT module improves the effective power as well as the output temperature from the rock bed solar air heater by about 35% and 9% respectively for the present set of parameters considered. It is also observed that for the present set of parameters considered, the temperature gradients in the direction normal to air flow in the solar air heater are insignificant and may be ignored. A parametric study is also carried out that assesses the impact of system parameters on the quality as well as quantity of the energy extracted from the system. This work is hence the first to couple an EAT with a sensible thermal storage equipped solar air heater and may pave the way for future studies.

Thermal Performance Improvement of a Spiral Channel Solar Air Heater: Numerical and Experimental Investigation in the Desert Climate of Gabes Region

Abstract This study focuses on improving the thermal performance of a solar air heater (SAH) using a single-pass spiral-shaped ducts. The SAH is designed and tested under prevailing weather conditions of Gabes, Tunisia (33°52.8876′ N,10°5.892′ E). The experimental measurements are carried out over 4 days. Similarly, a computational fluid dynamics (CFD) model was developed to study the fluid flow and the heat transfer inside the SAH using the commercial software ansys fluent 2021 R1”. The discrete ordinate (DO) radiation model and the k-ω shear stress transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow in the SAH, respectively. The numerical model is validated against experimental data, and the average error does not exceed 3.6%. To improve the heat transfer phenomena, the ratio of horizontal baffle spacing “d” to vertical baffle spacing “p” (d/p) is numerically investigated. Moreover, the highest air outlet temperature during the test days reached 81.1 °C under a mass flowrate of 0.0077 kg/s. The maximum efficiencies are 57%, 54%, 49%, and 46% for the configurations d/p = 1.5, d/p = 2, d/p = 1, and d/p = 0.5 under a mass flowrate of 0.02 kg/s, respectively. The SAH design with d/p = 1.5 is about 4–10% more efficient than the standard design with d/p = 1 under a mass flowrate ranging from 0.0077 kg/s to 0.025 kg/s.

An Experimental and Computational Investigation on Fluid Flow and Thermal Performance of a Rhombus Passage Solar Air Heater of Various Configurations

An Experimental and Computational Investigation on Fluid Flow and Thermal Performance of a Rhombus Passage Solar Air Heater of Various Configurations

Review on different techniques used to enhance the thermal performance of solar air heater

Energy is the key driver of life. It is required for the growth, exaltation, modernization, and financial development of any country. The world is turning away from fossil fuels in favor of renewable energy sources in order to meet the rising demand for energy and protect the environment from pollution. Solar energy is becoming a significant source of energy among these new energy sources. The primary solar energy-using appliances are solar air heaters. However, the creation of a laminar sub-layer on the absorbing plate is the cause of its poor thermal efficiency, which is a cause for concern. This paper describes various techniques through which the efficiency of solar air heaters (SAH) is enhanced by disturbing the laminar sub-layer. This study is concentrated on four techniques artificial roughness, jet impingement, piezo-electric fan, and phase change material (PCM), which are explained in four sections. The first section gives a detailed description of artificial rib roughness, turbulators, and protrusions. The second section reviews the use of jet impingement in SAH. The third section introduces a new technique; a piezo-electric fan and describes its mechanism, working parameters, and possibilities for its use in SAH through the previous studies. The fourth section reviews the use of PCM material in SAH by the previous studies. The maximum thermal hydraulic performance factor (THPP) for non-circular ribs, ribs with a rectangular cross section, ribs with an equilateral cross section, and jet impinged SAH, respectively, has been observed to be 1.44–1.29, 2.19, 2.11, and 3.66.

Energetic performance evaluation of a corrugated channel solar air heater: Experimental investigation, mathematical modeling, and solution procedure

AbstractThe cost of manufacturing and electricity consumption are key considerations in encouraging the adoption of solar air heaters (SAH) in sunny and low‐income areas. These parameters can have a significant impact on promoting the use of these devices. In this study, solar air heating was designed with the objective of achieving the highest possible efficiency/cost ratio. It is a corrugated channel SAH whose structure is equipped with two barriers perforated with a sufficient number of holes for a good airflow distribution. A new model was developed to evaluate the qualitative parameters that describe the thermos‐energetic behavior of a heating system. These parameters were measured using experimental data obtained under real operating conditions. The thermal model assumes a uniform temperature for the glass, absorber, and insulation of the collector, while the temperature of the circulating air is assumed to vary linearly along the collector. To ensure that these assumptions were valid, the collector was cut into a number of 0.1 m sections in the direction of flow. By comparing the numerical results with the experimental data, the model was validated and then used to calculate the temperature profiles of the different elements of the collector, as well as to estimate the impact of certain operational parameters on its thermal performance. Relative percentage error values, between the numerical and the experimental results, of 1.7517%, 1.0750%, 0.8577%, 2.2371%, and 2.3637% for absorber plate temperature, outlet airflow temperature, useful power, thermal, and effective efficiencies, respectively, are recorded.

Preliminary study of a dual channel solar photocatalytic ventilation wall system for year-round air purification and building energy savings

With the aim of meeting the weak adaptability to different seasons and low solar energy utilization efficiency for solar ventilation wall system. In the present work, a novel dual-channel solar photocatalytic ventilation wall (DSPVW) integrated with a photovoltaic (PV) panel and phase change materials (PCM) has been numerically proposed and simulated in winter and summer in subtropical climate zone. A range of performance indicators, such as outlet temperature, air heating gain, and clean air delivery rate (CADR), is evaluated. Furthermore, a comparative analysis is performed to assess the energy and exergy characteristics, distribution, comfortable temperature range percentage (CTRP), energy consumption and savings rate of three different systems: typical solar photocatalytic ventilation wall (SPVW), dual-channel solar photocatalytic ventilation wall (DSPVW), and DSPVW-PV/PCM. Results show that melting temperature of 313.15 K and 323.15 K respectively shows a good performance in winter and summer. The rate of temperature change and peak temperature to the outlet air slow down and decrease with the increase of PCM thickness, resulting in a cooling effect of 1.27 % and 2.83 % in winter and summer. In addition, the simulations with small channels exhibit poor thermal performance but better air purification effect, reaching total CADR as high as 69.46 m3 and 67.33 m3 respectively in winter and summer. Meanwhile, the energy consumption and energy saving rate of the DSPVW-PV/PCM is −3.09 kW and 75.7 %, respectively, compared to the SPVW system. This study could contribute to the widespread adoption and application of solar ventilation walls in regions with hot summers and warm winters.