Dr Hajar Moghadas,
Volume 4, Issue 2 (11-2023)
Abstract
Solar energy conversion systems have been developed to convert solar energy into thermal energy, functioning at both small domestic and large industrial scales. The efficiency and performance of these systems depend on several factors, including the design of the parabolic light concentrator, the heat-absorbing tube, the detector system, and the surrounding environmental conditions. Numerous studies have explored how geometric parameters, surface coatings, and the optical and thermal properties of various components impact system performance, as well as the type of heat transfer fluid used. Optimizing these parameters can improve performance and significantly lower construction costs in relation to the useful thermal output. The incorporation of heat-absorbing salts allows for energy storage during periods without sunlight, enabling a continuous cycle of electricity production. The durability of the materials used in the system’s components is crucial for assessing the economic feasibility of these devices in practical applications. Given its impressive capability to produce clean energy across different scales, this system presents a viable long-term alternative to fossil fuels, particularly in regions with high solar radiation, such as Iran.
Hajar Moghadas, Karim Tabatabai,
Volume 4, Issue 2 (11-2023)
Abstract
The H-type cap is one of the most widely used chimney caps in heating and industrial systems. Despite its extensive application, no specific standard has yet been established for determining the optimal dimensions of this type of cap. In the present study, the effect of the H-cap and its geometric dimensions on the performance of a chimney with a diameter of 20 cm and a height of 3 m is investigated. To generate a buoyancy-driven flow of hot air, a heat source with a constant temperature of 1800 K was placed at the bottom section of the chimney. The flow is driven solely by buoyancy forces resulting from the elevated temperature of the air surrounding the heat source, which, together with the chimney draft, induces a turbulent upward flow. This turbulent flow is modeled using the standard k-ε turbulence model. Simulations were carried out for the chimney without a cap, as well as for chimneys equipped with H-caps having various diameters and brim lengths (ranging from 15 to 25 cm). The average velocity and total pressure at the chimney inlet were evaluated for all cases. The results indicate that adding an H-cap with a diameter and brim of 20 cm reduces the average velocity by approximately 2.6%. This reduction is attributed to energy losses caused by the presence of the cap along the flow path. A cap with a diameter of 15 cm and a brim of 20 cm results in a significant reduction of 26% in velocity, whereas a cap with a diameter of 25 cm and a brim of 20 cm increases the velocity by 7%. The maximum velocity was observed for the cap with both diameter and brim equal to 25 cm, while the minimum velocity corresponded to the cap with a diameter of 15 cm and a brim of 20 cm. The findings also demonstrate that, among the various geometrical parameters, the cap diameter has a more dominant influence on chimney draft performance. Furthermore, the optimal performance is achieved when the diameter and brim of the cap are equal. These results are of considerable importance for optimal design, safety improvement, and energy efficiency enhancement.
