Heat Transfer In Solar Air Heater Research Articles

Heat transfer and flow behavior in solar thermal collector equipped with obstacles

Solar energy, an inherently pure and abundant source of power, is integral to a myriad of daily activities. Among the various solar thermal systems, Solar Air Heaters (SAHs) are often esteemed for their economic viability and practical utility in heating spaces and drying the products.. However, sometimes the conventional SAHs are criticized for their poor performance and capability in heat transfer, making them not well organized in application. The introduction of a new method of improvement in the efficiency of heat transfer in SAHs using carefully designed obstacles with sharp corners is presented in this paper. The obstacles are conceptualized in a Triangular winglet configuration, type-based on the following: Type 1 (Single Triangular winglet), Type 2 (Dual Triangular winglet), Type 3 (Triple Triangular winglet), and Type 4 (Quadruple Triangular winglet). The setups' empirical configurations were processed for the SAH duct where the experiments were executed with a Reynolds number (Re) up to 2000 to 16,000. The obstacle parameters such as the relative transverse pitch (Pt/b), relative obstacle height (e/H), and the relative longitudinal pitch ratio (Pl/e) were clearly maintained at 4, 0.5, and 4, respectively. From the experiments, the Nusselt number was found to be significantly enhanced, up to 3.85 for the Type 3 obstacle configuration. The Thermohydraulic Performance Parameter (η) also showed a strong value for all obstacle configurations that eventually reaches a peak value of 2.29, hence presenting a comprehensive performance for heat transfer efficiency and hydraulic performance within the SAH system.

Parametric analysis of artificial rib roughness for the enhancement of thermohydraulic performance of solar air heater: A review

Solar air heaters (SAHs) convert incident solar radiation to thermal energy on an absorber plate. Smooth absorber plates have a low convective heat transfer rate in traditional ducts. Artificial rib roughness is applied to the bottom sides of the absorber plate in order to improve heat transfer in SAHs. However, when the rib roughness is employed over the absorber plate of the airflow side, it also increases the pressure loss due to friction. The purpose of this work is to provide researchers with a scientific perspective on the geometry, structure of ribs, flow directions, and laminar zone in order to maximize heat transfer and reduce friction. This review article discusses different roughness parameters, various artificial roughness geometries, and thermohydraulic performance. Nusselt number and friction factor correlations have also been incorporated in this review article which is developed by various scientists based on their respective experimental results for various roughness parameters. The paper also provides a thorough analysis of current research, summarises prior developments, and speculates on potential future routes for developing new heat transfer systems. Furthermore, this review paper will assist researchers and academics in developing a sound understanding of the effects of roughness on the absorber plate.

Enhancement of heat transfer in SAH with polygonal and trapezoidal shape of the rib using CFD

A numerical investigation was carried out in Solar Air Heater (SAH) by implementing an artificial rough absorber plate for higher thermal performances. A polygonal transfer rib, the forward and backward trapezoidal rough ribs were nominated for simulation analysis using ANSYS, Fluent version 13.0. The Renormalization k-ε model was selected to predict the augmentation of Nusselt number (Nu), friction factor (ƒ) characterization and Thermo Hydraulic Performances (THP) for a proposed rib by varying relative roughness pitch P/e = [3.33–20] and relative roughness height e/D = [0.03–0.09]. Dittus Boelter and Blasius correlation were used for validating the smooth surface of Nu and ƒ besides compared with the rough surface to ascertain augmentation of heat transfer. The investigation reported on the performance of Nu and ƒ of the proposed rib at a Reynolds number ranges from 3800 to 18,000. The result reveals that the polygonal rib shape with relative roughness pitch P/e = 3.33 has produced higher Nu and gradual reduction of ƒ at Reynolds number 18000. It was found that THP has achieved a maximum of 1.89 in P/e = 10 & e/D = 0.06 at Reynolds number 15000 in the backward trapezoidal rib.

Heat transfer in concentrated solar air-heaters filled with a porous medium with radiation effects: A perturbation solution

In this study, convection-radiation heat transfer in solar air-heater filled with a porous medium is investigated. The effects of porous media shape parameter (s), Forchheimer number (F) and radiation parameter (ζ) on the collector efficiency are discussed. Approximate analytical solutions for the dimensionless velocity, temperature, and Nusselt number are obtained using perturbation method. The radiation heat transfer has been modeled using the Rosseland approximation method. A discussion on the accuracy and limiting cases of the solution is represented and a good agreement has been found between the analytical solutions and previous works. The results showed that by increasing the radiation parameter, the efficiency of the collector was improved. Also, the collector heat removal factor enhances when the porous media shape parameter increases.

A study of heat transfer enhancement in a new solar air heater having circular type turbulators

In this study, the heat transfer, friction factor and thermal performance factor characteristics of a new solar air heaters (SAHs) with circular type turbulators having different relief angles and distances were performed. Effect of the pitch ratio (PR) and angle ratio (AR) were investigated to improve in heat transfer in SAHs in a range of between 3000 and 7500 Reynolds number under solar radiation heat flux. The experimental results obtained using various turbulators were compared with conventional plain tube. Nusselt numbers were increased with increasing Reynolds number whereas; it was decreased with increasing PR and AR. The friction factor and thermal performance factor was decreased with increasing Reynolds number, PR and AR. It was found that the turbulators arrangement with PR = 2 and AR = 0.125 shown the maximum heat transfer enhancement of 416%, friction factor of 511% than conventional plain tube and the thermal performance factor was obtained as ∼2.9. In addition, the empirical equations for heat transfer, friction factor and thermal performance factor were derived and compared with the experimental results. The predicted results indicated a good agreement with experimental results within 10% of error.