Flat Plate Solar Air Heater Research Articles

Experimental analysis of a solar air heater using waste mild steel chips as a sensible heat storage material.

Heat storage materials improve the utility of solar air heaters (SAHs) after sunset. This study investigates an improved solar air heater (SAH) performance with baffles and waste mild steel chips as sensible heat storage (SHS) materials. Comparative experimental natural convection heat transfer studies were performed with four different improved air heater setups under similar solar radiation conditions. These setups consist of a flat collector plate (I), a baffled plate collector (II), a flat plate collector with SHS (III) and a baffled plate collector with SHS (IV) respectively. Setups I, II, III and IV were obtained by modifying the same air heater enclosure and each experiment was replicated for three similar sunny days. During the periods, the solar radiation varied in the range of 556-934 W/m2. The maximum thermal efficiencies found for setups I, II, III and IV were 18.76%, 22.40%, 27.21% and 28.22% respectively under natural convection. The highest average useful energy rate was produced by setup IV, followed by setups III, II and I. After sunset, setups III and IV were able to deliver warm air for an extended period of 1h, 18min and 1h, 42min, respectively. It was found that setups III and IV had sensible thermal energy storage reserves of 0.38kJ and 0.53kJ, respectively. The storage efficiencies found for setups III and IV were 60.25% and 70.89%, respectively. Among the four setups, setup IV boasts the most economical energy cost at 1.39 ₹/kWh and having the least payback period of 1year 4months. As a result, the employment of baffles and waste mild steel chips as SHS in a flat plate SAH not only presents a method for harvesting waste for efficient heat retention, but it also effectively uses solar energy for beneficial uses.

Numerical and experimental investigation of heat transfer of longitudinal fin with varying pitch length in flat plate solar air heater

Solar energy is a promising clean energy alternative, and consequently, the novel and innovative applications of solar energy in day-to-day life are expected to rise in the near future. The reason for limited applications of solar air heaters is their low thermal efficiency. This is due to inadequate heat transfer from the absorber plate to the air (working fluid). It has done various experiments with different pitch lengths and recorded the efficiencies corresponding to various pitch lengths. Numerical and Experimental Investigation of heat transfer of longitudinal fin with varying number of pitch length (1–5) in a flat plate solar air heater to improve the rate of heat transmission, thin and lengthy fins have been put underneath the absorber plate. The fin was intended to be square. The investigation included two different fluid masses at rates of 0.0252 and 0.10 kg/s with two distinct Reynolds numbers, 627.46 and 26585.55. The goal of the present study is to get an understanding of the effects of variations in air flow rate on the outlet temperature, heat transfer through the solar collector's thickness, and overall thermal efficiency. It has done a CFD simulation on Ansys to verify the experimental results with the simulation results.

A simple graphical method for sizing flat‐plate solar air heaters based on transversal and longitudinal aspect ratios

AbstractSolar air heaters (SAHs) are widely used for drying vegetables and fruits or for domestic heating. Certain sizing parameters are necessary to obtain the right dimensions for the required air temperature, flow rate, and thus useful thermal energy. The well‐known Hottel–Whillier–Bliss equation was used and made dimensionless by applying the collector longitudinal and transversal aspect ratios (rl and rt) of a double‐glazed flat plate solar air heater (DG‐FPSAH). The steady‐state equations are solved to determine the average temperatures. Thereafter, one could calculate the overall loss heat coefficient and efficiency factor, obtained analytically. A Matlab code was developed to estimate primarily unknown temperatures, useful energy, and the Nusselt number. An iterative numerical method is used until convergence occurs. The inlet cross‐sectional area and air flow velocity are defined as input data. The proposed sizing method depends on the output temperature required by the customer. This temperature can be determined from the plotted curves of the dimensionless ratios. Hence, the SAH‐needed dimensions are determined graphically depending on the functional requirements for construction planning, such as technology choice, work breakdown, and budgeting. In the present case study, based on the input parameters, an airflow rate of 1.2 kg/s entering a DG‐FPSAH with an output temperature of 41.5°C yields the dimensions of Lin = 3.824 m, Win = 2.735 m, and Hin = 0.1825, specifying the collector length, width, and air duct height. The gathered energy and thermohydraulic efficiency are: Qu = 7.91 kW, ηcol = 0.752, respectively.

Effect of Chamfered Turbulators on Performance of Solar Air Heater - Numerical Study

This paper presents a numerical analysis of the thermal performance improvement in a flat plate solar air heater equipped with chamfered turbulators attached below the absorber plate for evaluating performance for Reynolds numbers ranging from 3,000 to 21,000. According to the research, chamfered turbulators caused the flow to become highly turbulent. This flow behaviour with flow separation around the turbulators positively affects performance. This paper attempts to explain the complex flow behaviour found during the analysis. The turbulator diameter varies in 1 mm increments from 3 to 7 mm at a constant longitudinal pitch of 200 mm. The number of turbulator rows in the transverse direction is kept constant at three. The chamfer is represented by the flow attack angle, which can be 30°, 45°, or 60° facing the direction of flow and opposing the direction of flow. The results showed that a 7mm diameter turbulator with a 30° chamfer angle placed against the flow of air yielded a considerably more significant thermal enhancement factor of 1.15 over the spectrum of flow Reynolds number studied

Assessment and enhancement of thermal performance for ring roughened finned jet impingement solar air heater for low-temperature applications

The current study investigates the synergetic impact of artificial roughness with fins and jet impingement on the performance of flat plate solar air heater. The impingement jet Solar Air Heater (SAH) achieves roughening through the incorporation of conical ring shapes, strategically placed between the straight fins of the absorber plate. The analytical work focuses on maximizing the thermal and effective thermal performance by considering the design parameters: ring thickness ratio (TR/DH) ranging from 0.07 to 0.13, ring diameter to thickness ratio (Do/TR) from 1.67 to 2.67, streamwise pitch to diameter ratio (X/Do) from 4.71 to 7.71, ring diameter ratio (Do/Db) from 1.30 to 2.30, and a number of fins (n) ranging from 4 to 7 based on spanwise pitch ratio (Y/Do) from 2.92 to 5.14. A MATLAB code is created to solve governing equations and validated by comparing results with existing literature. The results indicate that the new configuration of SAH is most effective up to the Reynolds number of 10850 and produces the maximum energy and thermo hydraulic efficiency is 81.4 % and 77.4 %, respectively. It enhances the thermo hydraulic performance by 15.1 % and 4.1 % compared with conventional single pass and parallel pass jet impingement SAH. The system has the capability to increase the air temperature per unit of supplied solar heat flux, is ranging between 0.006 and 0.038 Km2/W.

Investigation of the effect of dimensional and non-dimensional parameters on the performance of pitch-varied staggered arranged dimple solar air heaters

In this study, the efficacy of a single pass, single glazed, five different types of absorber plate incorporated solar air heater (SAH) was experimentally examined in outdoor test conditions on alternative days. The experiment was carried out for flat plate solar air heater (FPSAH) and staggered arranged dimple imprinted absorber plate solar air heater (SDPSAH) maintained at four different pitch ratios (Pt/Pl: 1.0, 1.11, 1.25, and 1.67) by varying the air mass flow rate (ma) from 0.01-0.05 kg/s (corresponding Re range: 1971.66–10466.45). The results show that the performance of both FPSAH and SDPSAH improves when the ma increases. For the tested range of ma, SDPSAH outperforms FPSAH regardless of pitch ratio. SDPSAH, with a pitch ratio of 1.25, on the other hand, has a greater air temperature difference, efficiencies, heat removal factor, collector efficiencies, and averaged Nusselt number (Nuavg) while having a lower global heat loss coefficient and top loss. The Nuavg of SDPSAH at a pitch ratio of 1.25 is 1.01–1.17, 1.16–1.24, 1.26–1.57, and 1.44–1.88 times higher than SDPSAH at pitch ratios 1.0, 1.11, 1.67, and FPSAH, respectively. The higher averaged friction factor (favg) of 0.0443 is attained for SDPSAH at a pitch ratio of 1.25 due to the presence of the largest number of dimples. The ηth and ηd of SDPSAH at a pitch ratio of 1.25 are 34.5 and 35.5 % higher than those of FPSAH. The global heat loss coefficient of SDPSAH at pitch ratios 1.11, 1.0, and 1.67 is 1.05–1.84, 1.09–2.15, and 1.11–2.92 times higher, respectively, than that of SDPSAH at a pitch ratio of 1.25.

Experimental Investigation on Thermal Performance of Solar Air Heater using Nano-PCM

Herein, the performance of a solar air heater (SAH) is experimentally investigated, utilising an array of tubes as the absorbent part. The study evaluates the impact of incorporating Al2O3-paraffin wax as a non-PCM storage medium in comparison to a traditional flat-plate solar air heater, specifically under Najaf-Iraq climate conditions. The SAH is positioned at an inclination of 32.1 degrees with respect to the horizon, allowing it to align optimally with the solar direction. The results reveal notable differences in thermal performance characteristics among the various models. The highest thermal efficiency values are observed for distinct configurations: the proposed model achieves about 55.2%, the wax-supported model reaches 55.9%, and the nano-PCM-reinforced model attains 57.7%, while the traditional model lags at 48.2%. Furthermore, an analysis of different air mass flow rates highlights a crucial finding. Specifically, an air mass flow rate of 0.01 kg/s results in a higher temperature exiting from the system compared to a flow rate of 0.02 kg/s. This is attributed to the extended interaction time between the passing air and the absorbing surface, facilitating enhanced heat exchange. Consequently, the system's thermal efficiency experiences an increase. The study underscores the superior thermal performance and efficiency of the tube array nano-PCM collector type under Najaf city-Iraq climate conditions.

Impact of corrugated duct and heat storage element on the performance of a low-cost solar air heater under forced air circulation: an experimental study.

The need to address global warming issues and international policies has placed a greater emphasis on the development of solar energy utilization systems. Intensive study is necessary to expand solar energy applications, as solar energy potential varies widely. This study investigates the thermal and thermohydraulic performance of a modified flat plate solar air heater (FSAH) to assess the effects of using corrugated aluminium duct and sand heat storage elements (HSE) in various combinations. The different arrangements selected for the experimental investigation are the FSAH, FSAH with corrugated aluminium duct (FSAH-C), FSAH with a sand heat storage element (FSAH-S), and FSAH with a combined use of corrugated aluminium duct and a sand heat storage element (FSAH-CS). The materials used for fabrication are low-cost and readily available in the study area. The results indicate that the sand bed enhanced the thermal performance by acting as the thermal heat storage medium, which could also supply heat for a short duration after non-sunny hours, and the corrugated aluminium duct enhanced the surface area and allowed the air to pass twice inside the SAH. We observed that the SAHs with sensible heat storage had a higher top loss compared to the FSAH-S configuration. The average thermal efficiency of the FSAH-CS configuration was 59.17%, which is 8.81%, 5.72%, and 10.95% higher than FSAH-S, FSAH-C, and FSAH, respectively. Furthermore, this configuration achieved an exit temperature of 64.5°C. The proposed system has a thermohydraulic efficiency of 59.14%, which is not significantly different from the average thermal efficiency. Therefore, the suggested system verifies its ability to function without requiring substantial external power.

CFD modeling of a tubular three-pass solar air heater with phase change material: Investigating heat transfer enhancement and energy efficiency

The present study introduces a novel solar air heater design featuring a tubular surface with three passes arranged in a counter-flow configuration, aimed at improving compactness and enhancing heat transfer characteristics. The research involved the development and validation of a computational fluid dynamics (CFD) model, which was utilized to accurately depict the distribution of solar flux through the system components by comparing the model results with experimental data. The study involved conducting a comparative analysis between the tubular three-pass solar air heater with phase change material (TTPSAH_PCM) and conventional flat plate solar air heaters (FPSAH) to ascertain the superior design characteristics. A thorough investigation was carried out, encompassing evaluations of energy, exergy, outlet temperature, convection heat transfer coefficient, and useful heat gain. The findings indicate that the TTPSAH_PCM outperforms alternative geometries. For instance, when operating at a mass flow rate of 0.006 kg/s, the TTPSAH_PCM demonstrates substantial enhancements in several key metrics, including an 11.4 % increase in the system's daily thermal efficiency, a 17 % improvement in exergy efficiency, and a 4 % rise in outlet air temperature. The convection heat transfer coefficient of TTPSAH_PCM exhibited a 155.6 % increase compared to the FPSAH type. Moreover, the system being investigated demonstrates an 8.5 % rise in useful heat gain. The results underscore the enhanced efficacy of the TTPSAH_PCM system in contrast to alternative solar air heater arrangements, and its applicability for both drying operations and indoor heating applications.

Differential exergy investigation and environ-economic assessment of a dimpled plate and flat plate solar air heater under turbulent conditions

The current investigation explores the performance of a spherical dimple solar air heater (D-SAH) within the framework of the Second Law of Thermodynamics under turbulent conditions. This analysis considers component-wise exergy potential losses, their differentials, and the overall exergy efficiency (ηEx). Given the inherently entropic nature of turbulent flow, an evaluation is conducted to determine the limiting mass flow rate (MFR). To ensure long-term adaptability and a comprehensive understanding of the designed solar air heater (SAH), various matrices, including economic, environmental, environ-economic, exergo-economic, and energy, are assessed across four service life scenarios. The obtained results are benchmarked against those of a flat plate solar air heater (F-SAH). Exergetic analysis is conducted for six different MFRs on different days, revealing absorption losses as the most influential exergy losses. D-SAH incurs 3.99% higher absorption losses, leading to a lower ηEx. The design is deemed suitable for MFR 0.028 kg/s. The impact of higher Reynolds number (Re) and the temperature rise parameter (TRP) results in a decrease in ηEx for both SAHs. Specifically, D-SAH shows a 71% reduction in ηEx as Re increases from 5684 to 10352. However, D-SAH exhibits promising performance in terms of CO2 mitigation and carbon credits earned, surpassing F-SAH by 27.89% to 23.38%. Furthermore, these performance metrics increase by 50% when extending the service life from 20 years to 30 years. Statistical correlation and the coefficient of determination authenticate these findings.

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.

Numerical Simulation of the Thermal Performance of a Tubular Solar Air Heater

In this work, a flat-plate solar air heater (FSAH) and a tubular solar air heater (TSAH) were designed and tested numerically. The work investigates the effect of increasing the contact area between the flowing air and the absorber surface of each heater and predicts the expected results before the fabrication of the experimental rig. Three-dimensional two models were designed and simulated by the ANSYS-FLUENT 16 Program. The solar irradiation and ambient air temperature were measured experimentally on December 1st 2022, at the weather conditions of Baghdad City- Iraq, at three air mass flow rates, 0.012 kg/s, 0.032 kg/s, and 0.052 kg/s. The numerical results showed the advantage in the thermal performance of the TSAH in comparison to the FSAH, represented by better air temperature difference, better heat transfer from the absorber to air, and better thermal efficiency. The TSAH has a higher thermal efficiency than the FSAH by 7 %, 19 % °C, and 22 % at 0.012 kg/s, 0.032 kg/s, and 0.052 kg/s, respectively. The improvement of the thermal characteristics of the TSAH can be referred to as the increment in the heat transfer contact area between the absorber and the flowing air.

Experimental study of heat transfer and frictional characteristics of impinging jet solar air heater with wire-mesh attached to the absorber plate

This study revolves around improving the thermal performance of impinging jet solar air heater (IJSAH) by using wire mesh of three different sizes. The wire mesh sizes were 0.5×0.5, 1.5×1.5, and 3×3 inches with nozzle diameter (Dj) equal to 3 and 6 mm and Reynolds number (Re) ranging from 4913 to 13103. The variation of Nusselt number (Nu), friction factor (f), thermo-hydraulic performance parameter (THPP), and effective efficiency (ηeff) were evaluated for varying Re. Maximum Nu was developed for case 3 and equalled 109.86, which was 7.3 % and 246 % higher than a smooth IJSAH and flat plate solar air heater (FPSAH), respectively. The minimum friction factor attained equated to 0.0314 for case 2 at Re = 13103. Maximum THPP attained by the setup equalled 1.78 for case 4, having Dj = 6 mm. The THPP attained by case 4 across the range of Re was on an average 9.15 % higher when compared to smooth IJSAH with Dj = 3 mm. Additionally, the system achieved maximum ηeff of 0.53695 at Re = 4913 for case 4. Finally, it was recommended to use a wire mesh having a mesh size equal to 1.5×1.5 inch with Dj = 6 mm for optimum performance.

CFD Simulations and Experimental Investigation of a Flat-Plate Solar Air Heater at Different Positions of Inlet and Outlet

In this study, the effects of the positions of inlet and outlet in a single-flow flat plate rectangular box active solar air heater due to convective heat transfer were designed, constructed, theoretically investigated using CFD fluid flow (fluent) software, and experimentally examined. The internal dimensions of the solar air heater are length and width of 100 cm and 50 cm, respectively, and the air gap between absorber plate and glazing glass is 9 cm. The solar air heaters are constructed with 18 mm thickness plywood, 4 mm thickness glazing glass, and 1 mm thickness aluminium sheet metal. Except for the glazing glass, other construction materials are painted black to absorb solar radiation. The positions of the inlet and outlet depend on the fraction of the width of the solar air heater. Based on the three-day average outlet temperature of the solar air heaters, solar air heater B has the highest average outlet temperature compared with other active solar air heaters and ambient air temperatures. Based on the three-day average outlet temperature of solar air heaters and ambient air temperatures, the active solar air heater B outlet temperature is 33.83 percent greater than the ambient air average temperature. The average outlet temperature of the air in passive solar air heaters increased by 17% and 4.43% compared to ambient air and active solar air heaters outlet air temperatures, respectively, due to the speed of the air in the solar air heater. The uncertainty of the instruments to measure the temperature of the air is ± 0.289°C, and the uncertainty of the solar air heater is ± 0.462°C. A higher average air outlet temperature was achieved in March at a tilt angle of 12° at a latitude of 8.89°. The negative tilt angle in May at a latitude of 8.89° indicates the south-facing orientation of solar air heaters is better. The passive solar air heater and ambient air temperature have a higher air temperature fluctuation than the active solar air collector.

Combined effect of solar intensity and air mass flow rate on inline spherical dimple based solar air heater during summer season

Experimental investigation was done in this study to compare the effectiveness of flat and inline spherical dimple engraved absorber plates solar air heater (SAH). During the summer, a SAH with a single glass cover, one pass, and two different types of absorber plates was evaluated on alternating days by taking readings from 9.30 a.m to 2.00p.m at an interval of 30 min. In order to conduct the investigation, the air mass flow rate (Ma) was raised from 0.0098 kg/s to 0.0520 kg/s (corresponding Re: 1861–10218) while solar intensities varied throughout the days. By increasing the Ma, various parameters were measured and different thermal characteristics were examined, such as the convective heat transfer coefficient, the blower’s power consumption, extracted power, effective power, efficiency, the heat gain factor, the heat loss factor, the SAH-efficiency factor, the averaged Nusselt number (Nu), and the averaged friction factor (f). The investigation reveals that with an increase in Ma, both flat and dimpled roughened SAH exhibit an increase in convective heat transfer coefficient, extracted power, instantaneous efficiency, heat gain factor, heat loss factor, and SAH-efficiency factor. However, the enhancement rate of inline dimple plate-solar air heater (IDP-SAH) due to engraved dimples is always higher than the flat plate-solar air heater (FP-SAH). Up to a particular Ma, both types of SAH have higher effective efficiencies. Thereafter effective efficiency decreases due to a significant increase in required pumping power. Comparing IDP-SAH to FP-SAH, the averaged Nu and the averaged f of IDP-SAH is 83.42% and 176.51% greater, respectively. In addition, the effective efficiency of IDP-SAH is 31.24% higher than the FP-SAH. The friction factor (f) starts to decline as the Ma increases. Even though the IDP-SAH and FP-SAH performance analyses were conducted on different days during the summer, IDP-SAH outperformed FP-SAH. The indentation of dimple on absorber plate helps in increasing surface area as well as helps in changing flow structure which is responsible for augmentation of heat transfer rate.

Thermal Performance Evaluation for Two Designs of Flat-Plate Solar Air Heater: An Experimental and CFD Investigations

The main objective of this research was to create two different configurations of a flat-plate solar air heater, namely, Conventional-Case A and Modified-Case B, and develop a three-dimensional computational fluid dynamics (CFD) model using ANSYS R15.0. The purpose of the CFD model was to simulate the heat transfer behavior of the proposed solar air heaters under unsteady conditions. The RNG k-ε turbulence model was employed for this CFD study. The experiments were conducted on sunny days, under the same conditions as the Egyptian climate. The results of the experiments show that the simulated CFD model and the measured outlet airflow temperatures, relative humidity, and velocities of the two tested solar air heaters were compared. The developed model made very satisfactory predictions. Moreover, the deviations between the average CFD outlet air temperatures and the experimental results were 7% and 7.8% for Case B and Case A, respectively. The CFD-simulated average relative humidity was reduced by 31.6% when using Case B compared with Case A, and it was reduced by 28.8% when comparing the experimental data to Case B. Additionally, the average CFD thermal efficiencies obtained for Case B and Case A were 28.7% and 21.6%, respectively, while the average experimental thermal efficiencies for the cases were 26.4% and 18.2%, respectively. The proposed model can be used to design and simulate other solar air heater designs.

Numerical evaluation of air gap effect on double-glazed solar air heater performance

Double glazing is one of the effective ways to improve the thermal performance of flat-plate solar air heaters. In this regard, by considering this type of heat exchanger, the free convection flow between two glass covers and the forced convection flow inside the main air channel were analyzed in the present study. The exact implementation of this idea was numerically investigated using COMSOL Multiphysics commercial software. Due to the occurrence of Bénard convective flows in the space between two glasses, the air gap thickness must be optimized so that the positive effect of the presence of the air layer as a suitable thermal insulation is not affected by this phenomenon and does not lead to thermal dissipation. By choosing air gaps of 1 cm to 5 cm and sun radiative heat fluxes of 600, 800, and 1000 W/m2, it was found that the higher rate of heat transfer from the absorber plate into laminar forced convection airflow took place in the air heater with 3 cm air gap. Under the solar irradiation of 1000 W/m2, computations indicated the values of 11.2 K, 9.7 K, and 8.8 K for air temperature increase along the air heaters with the air gap thicknesses of 3 cm, 5 cm, and 1 cm, respectively. Comparisons between the present numerical findings and experimental data reported in the literature revealed an excellent consistency.

Optimizing Device Performance of Multi-Pass Flat-Plate Solar Air Heaters on Various Recycling Configurations

Various external-recycle configurations of multi-pass flat-plate solar air collectors were studied theoretically to examine the optimal thermal performance under the same working dimension and operation conditions. An absorber plate and insulation sheet were implemented horizontally and vertically, respectively, into an open rectangular conduit to conduct a recycling four-pass operation, which the device lengthens the air flow channel and increases the air mass flow rate within the collector, and thus, a more heat transfer efficiency is obtained. Four recycling types with different external-recycle patterns were introduced and expected to augment the heat transfer rate due to the turbulent convective intensity through four subchannels in the present study. Coupling energy balances into one-dimensional modeling equations were derived by making the energy-flow diagram within a finite element, which the longitudinal temperature distributions for each subchannel were obtained. The theoretical predictions show that the improved four-pass device is accomplished due to the multiple heating pathways over and under the absorber plate, from which the turbulence intensity augmentation results in the heat transfer rate as compared to that in the device without inserting the absorber plate and insulation sheet (say a downward-type single-pass solar air collector). The theoretical results also show that the external-recycle configuration (say Type C in the present study) acts as an optimal collector thermal efficiency and leading to a beneficial design in multi-pass solar air collectors for improving heat-transfer rate and increasing resident time under the same operation conditions. Theoretical predictions show a higher heat-transfer efficiency for the present recycling configurations up to a maximum 115% device enhancement in comparison to that of a single-pass device. Examination of implementing the absorber plate and insulation sheet on the heat-transfer efficiency enhancement as well as the hydraulic dissipated power increment were also delineated, and deliberated the suitable external-recycle configuration with respect to an economic consideration.

The Experimental Investigation of Double -Pass Solar Air Heater with V-Corrugated Plate, Phase -Change Material and Baffles Under Recycling Operation

The current paper presents an experimental work that had been implemented to observe the performance of an improved solar air heater and compared it with that of a conventional double-pass flat plate solar air heater. Improvements that have been added include the use of a V-shaped corrugated plate at an angle of 60 degrees, the addition of wood baffles in the lower pass and the use of phase-changing materials PCM as well as air recycling conditions. The heater was designed and tested under the weather conditions prevailing in the Duhok Governorate (latitude 36° 52' 1.52" N and longitude 42° 59' 18.42" E) in the Kurdistan Region of Iraq. The phase-changing material PCM is paraffin wax. The gathered results showed that the improvements that were added to the solar air heater significantly improved the performance at different mass flow values (0.037, 0.057, 0.077 kg/sec). For example, the maximum values of useful heat transfer at mass flow rates (0.037, 0.057, and 0.077kg/s) are 1.68, 1.86, and 2.34 kW, respectively, and the daily efficiency for improving and conventional heater value at mass flow rate 0.037kg/s for 15,16, and 17 of February on 2022 was (84% and 45%), (86% and 46%), and (91% and 60%), respectively.

Experimental Evaluation of Thermohydraulic Performance of Tubular Solar Air Heater

The thermohydraulic performance of a new design solar air heater (SAH) design was examined experimentally in this paper as a trial to improve the flat-plate SAH’s efficiency. A flat-plate solar air heater (FPSAH) and a jacketed tubular solar air heater (JTSAH) having similar dimensions were constructed to compare their thermal performance efficiencies. A band of Aluminum jacketed tubes were arranged side by side in parallel to the airflow direction to form the absorber of a jacketed tubular solar air heater (JTSAH). The experiments were accomplished at three mass flow rates (MFR)s: 0.011 kg/s. 0.033 kg/s, and 0.055 kg/s. Results revealed that the maximum temperature difference was obtained from JTSAH at 38°C in comparison to 32°C from the FPSAH at MFR of 0.011 kg/s. The thermal losses from the upper glass cover of the JTSAH were less than the same losses at the FPSAH due to the reduced absorber and glass temperatures of the JTSAH. The gained power was higher at the JTSAH than the FPSAH. At the JTSAH, at 0.055 kg/s MFR, the maximum average thermal efficiency obtained was 81%, and the maximum average thermos-hydraulic efficiency obtained was 75.61 %. It is noted that increasing the MFR increases the thermal efficiency, also, its optimum value rises the thermos-hydraulic efficiency to a specific optimum point. The pressure drop increases with the MFR and JTSAH compared to the FPSAH