This study discussed the effect of ribbed fin, which was suggested by the authors, on the enhancement of heat transfer and flow characteristics of fluid in a solar air heater. The ribbed fin has a rectangular rib at the base and side surfaces of the fin. Thus, it can increase the heat transfer coefficient in the fluid field of a solar air heater as well as extend the heat transfer area. The simulation was performed with various Reynolds numbers, relative heights, and pitches of the rib. The presence of the rib enhances the heat transfer performance by 3.497 times over a smooth fin. However, the addition of the rib also increases pressure drop. Thus, the thermo-hydraulic performance, which considers both heat transfer enhancement and pressure drop increase, was also discussed. Furthermore, this study developed correlations for the Nusselt number and friction factor as a function of geometric condition of the rib and Reynolds number. The correlations accurately predicted the Nusselt number for the base and side surfaces of the fin and friction factor with mean absolute percent errors of 4.24%, 4.53%, and 7.33%, respectively.

Air-type photovoltaic/thermal (PV/T) collectors attached to ducts beneath the solar panels are devices that can recover heat while the panel cools. By contrast, water-type PV/T is easily used because the air of an air-type PV/T has a lower heat capacity than water. A number of studies have been conducted on the installation of ribs as a way to increase the heat recovery capacity of air through ducts. In this study, a protrusion with a non-uniform cross-section was selected to increase the contact area of the air side as well as to promote turbulence. A computational fluid dynamics (CFD) analysis was conducted to confirm the heat transfer performance and the characteristics of the pressure drop according to different shape conditions. As a result, the heat transfer performance was improved by 1.3-to 1.9-fold depending on the conditions of the protrusion installation. However, the pressure drops also increased from 2.534-to 4.685-fold. It is therefore necessary to identify those factors of the thermal hydraulic performance that consider both the heat transfer and pressure drop. As a result, the maximum heat-recoverable shape condition achieved the largest performance coefficient value of 1.24 when e/H = 0.16, P/e = 20, and W p /e = 5.

Approximately 40% of the domestic building load is used for heating and cooling, and fossil fuels are commonly used to produce heat. To lower the proportion of fossil fuels, policy subsidies for the use of new and renewable energy facilities are being activated. Among them, solar thermal systems can contribute to reducing the heating load of buildings, including hot water supply and space heating. The production of thermal energy in this solar thermal system takes place in a collector, and the heat collection system is generally categorized into an air-type solar collector, which can heat only air, and a water-type solar collector, which can heat only water. In contrast, a solar air-water heater is a collector that can heat air and water simultaneously and can be applied to both hot water supply and space heating, occupying the same area. This system can also improve solar energy utilization by retrieving waste heat at the top of the absorber plate. In this system, the increase in thermal efficiency of the air side results in an improvement in the total efficiency of the collector as well as the air heating performance. Furthermore, the performance of the solar air-water heater is affected by air and water mass flow rates. Thus, in this study, a novel type of solar air-water heater with a triangle obstacle was fabricated, and the thermal performance of this system was experimentally evaluated using various air and water mass flow rates when air and water were heated simultaneously. We observed that a higher air and water mass flow rate can lead to higher thermal performance of the suggested system.

The solar air-water heater is a combined system of air-type and water-type collectors and a composite collector that can produce hot water and heated air in one system. Although it can maximize heat acquisition by transferring some of the heat lost from the absorbent plate and pipe toward the air duct, the heat acquisition is low due to the low heat capacity. To address this problem, several studies have been conducted using turbulent promoters in ducts. In this study, to improve the air-side heat transfer performance of the solar air-water heater, perforated fins on the bottom side of the absorption plate were arranged in various arrangements. Thereafter, computational fluid dynamics (CFD) was performed according to the flow conditions, and the heat transfer performance and pressure drop characteristics were analyzed. Results indicated that the heat transfer performance improved by at least 1.24 times to a maximum of 2.21 times, and that the pressure drop was in the range of 4.10 ~ 7.38 times, confirming the thermal hydraulic performance parameter (THPP). In the case of the performance coefficient, when perforated fins were attached side by side to the pipe, the highest performance coefficient was 1.18.