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[en] Highlights: • The theoretical and experimental study on a solar air heaters with different configurations were performed. • Design and analysis of experiment was used to analyze the data from experiment. • Agreement between theoretical and empirical results, verified the exactness of the experimental design. • The highest efficiency was obtained from double pass solar collector with quarter perforated 10D cover. - Abstract: An experimental investigation was performed on a solar air heater with different configurations. The configurations included testing the single- and double-pass solar collectors with normal and perforated covers and with wire mesh layers instead of an absorber plate. Design and analysis of experiment was used to develop a model for the tested solar air heater and IBM’s Statistical Package for the Social Sciences software was used to analyze the model. Strong agreement was found between the results obtained from the theoretical and experimental investigations. Both methods suggested the same configuration for attaining the highest thermal efficiency from the system, i.e., a double-pass solar collector with a quarter-perforated cover with 3-cm hole-to-hole spacing and a mass flow rate of 0.032 kg/s
[en] A mathematical model for computing the thermal performance of an air heater with a truncated compound parabolic concentrator having a flat one-sided absorber is presented. A computer code that employs an iterative solution procedure is constructed to solve the governing energy equations and to estimate the performance parameters of the collector. The effects of the air mass flow rate, the wind speed and the collector length on the thermal performance of the present air heater are investigated. Predictions for the performance of the solar heater also exhibit reasonable agreement, with experimental data with an average error of 7%
[en] Solar air heaters (SAH) are becoming increasingly popular in the food industry, agriculture, and especially in the building sector. The paper presents results of the assessment of the environmental effects resulting from the application of these devices for preheating ventilation air. In the first step it was determined energy efficiency of typical solar air heater based on results of experiments performed under the operating conditions. In the next step the potential annual energy savings for typical houses and potential reduction of the greenhouse gases (GHG) emissions were calculated. Keywords: solar air heaters, ventilation air preheating, greenhouse gases, energy saving
[en] In order to obtain the best performance of the solar air heaters, it is necessary to find optimum performance conditions. The aim of this research paper is to achieve optimum conditions, by comparing single and double pass solar air heaters. Also, a brief review study of various related research works of all scenarios for a single and double pass and packed bed (including particle technologies) solar air heaters was carried out to observe the challenges of the mentioned systems. Energy modeling and simulation with EES and MATLAB open source code software indicated significant results in efficiency. According to the obtained results, it can be explained that double pass duct not necessarily always increases the overall system energy efficiency. Results of this work indicate, higher ambient air temperature (inlet air temperature) and lower solar irradiation can increase overall energy efficiency of solar double pass systems. More precisely at solar irradiation of 916 W/m2 and inlet air temperature of 302 οK, the system achieves the targeted optimum value in energy efficiency, approximately 90%, which is considerably more than the 65% as an average value.
[en] Highlights: • Effect of perforation shapes of blocks on heat transfer has been investigated. • A new parameter, circularity which represents perforation shape is proposed. • Effect of angle of attack of V-blocks on heat transfer has been investigated. • Nusselt number and friction factor correlations have been developed. - Abstract: The effect of non-circular perforation holes in term of circularity of V-shaped blockages attached to one heated wall of a rectangular duct of solar air heater. Five different hole shapes ranging from circular to square to rectangular in the circularity range of 1–0.6 have been used with varying relative pitch of 4–12, relative blockage height of 0.4–1.0, open area ratio of 5–25% and angle of attack of 30–75° and Reynolds number of flow was varied between 2000 and 20,000. It has been found that there exists an optimum non-circular shape of perforation holes that yields maximum value of Nusselt number; a perfectly circular hole performs substantially inferior as compared to a non-circular hole of considerable non-circularity (ψ = 0.69). An improvement of Nusselt number value in the ratio of 1.13 has been found when circular perforation holes are replaced by rectangular holes of circularity of 0.69. Correlations of Nusselt number as well of friction factor are established in term of Reynolds number and geometrical parameters of blockages which can be used to predict the values of Nusselt number and friction factor with considerably good accuracy
[en] Highlights: • An experimental investigation on the different absorber surface of the four collectors was made up. • The comparisons including efficiencies and pressure drop were made among them. • The performance factor, PF, is obtained by considering both heat transfer enhancement and the pressure loss. - Abstract: The aim of this work is to provide a remedy for the low thermo-physical properties of air using different absorber surface of air heater. An experimental investigation on the absorber surface of the collector whose shape was made up to provide better heat transfer surfaces was presented. In the study four types of air solar collectors: sinusoidal corrugated plate, protrusion plate, sinusoidal corrugated and protrusion plate and a base flat-plate collector are presented. The results of the experiments were evaluated at the same time of the days with the same radiation. The efficiencies were determined for the collectors and comparisons were made among them. The present data showed that heat transfer coefficient and pressure drop and the performance factor PF increase with shape of absorbers surface.
[en] Highlights: • Nu and f of perforated V-blocks in solar air heater are investigated. • There exist an optimum value of e/H, P/e and β for maximum Nu and f are found. • Better thermo hydraulic performance is achieved for perforated V-blocks. - Abstract: In this work, the effect of geometrical parameters of the V-shaped perforated blocks on heat transfer and flow characteristics of rectangular duct, has been investigated experimentally. The experimental investigation encompassed the geometrical parameter namely, relative blockage height (e/H) of 0.4–1.0, relative pitch ratio (P/e) of 4–12 and open area ratio (β) of 5–25% at a fixed angle of attack (α) of 60°. The effect of V-shaped perforated blockages has been investigated for the range of Reynolds number from 2000 to 20,000. The maximum enhancement in Nusselt and friction factor has been found to be 6.76 and 28.84 times to that of smooth duct, respectively. Thermohydraulic performance of V-shaped perforated blockages is also compared to that of V-shaped solid blockages for same geometrical parameters
[en] In this study, thermo-economic optimization of single-pass SAHs (solar air heaters) with obstacles of arcuate shape has been carried out. The research is conducted in order to compare the exergy efficiency of three different types of flat plate SAHs. Also, using NSGA-II (non-dominated sorting genetic algorithm) influencing factors were optimized. The SAHs were two different arcuate obstacles (type II and type III), and the other one had no obstacles (type I). All heater types with single and double glass cover were evaluated. The results showed that the heater with double glass cover and the obstacles (type III) had the highest function in both economic and exergetic aspects. Based on the NSGA-II results, collector with flow rate, area and the outlet temperature of 0.017 kg s−1, 2.6 m2 and 78 °C, respectively, had the best performance.
[en] The Computational fluid dynamics (CFD) based analysis is carried out to investigate the thermal and hydraulic performance of circular rib roughened triangular passage Solar air heater (SAH). The circular ribs were provided over the absorber plate. The roughness parameter such as relative roughness pitch (P/e) and relative roughness height (e/D) varies from 4 to 20 and 0.015 to 0.06 (in four sets), respectively, the Reynolds number (Re) varies from 4000 to 18000. The flow governing equations were solved using commercial ANSYS (Fluent) software. The predicted Nusselt number (Nu) and friction factor (f) are validated with the available experimental results. The thermal and hydraulic performance of roughened duct is estimated in the form of Nusselt number and friction factor, respectively. The Thermohydraulic performance parameter (TPP) is also evaluated depending on the friction factor (f) and Nusselt number (Nu) values for SAH. The maximum Thermohydraulic performance parameter (TPP) is observed at Reynolds number of 15000 in case of relative roughness pitch (P/e) and relative roughness height (e/D) value of 12 and 0.06, respectively