Diffusion Foundations and Materials Applications Vol. 39

Abstract: Heat exchangers are widely recognized as eco-friendly devices that transfer heat between two or more fluids without mixing. Double Pipe Heat Exchangers (DPHE) are used in many industrial applications such as power generation, chemical processing, HVAC, and renewable energy systems. Traditional DPHEs are simple and reliable, however, they often face limitations in heat transfer. Improving the thermal performance of DPHE can significantly enhance the operational efficiency of thermal energy systems. This study presents a novel fin arrangement to the traditional DPHE using different diamond-shaped fins to improve its thermal performance. The thermal and hydraulic properties of DPHE with different diamond-shaped fin configurations are investigated using CFD analysis. The optimization process is carried out using the Response Surface Method (RSM) for optimal diamond-shaped fin design. The results indicate that novel diamond-shaped fins improve thermal performance, particularly at high mass flow rates. The thermal enhancement factor (TEF), overall heat transfer coefficient, and pressure drop are used to evaluate the thermal performance of DPHE. The diamond-shaped fins exhibit a 55% increase in overall heat transfer coefficient compared to conventional DPHE. The TEF for diamond-shaped fin configurations is higher than 1 with a maximum value of 1.63 for DPHE-HF45 depicting a 63% increase in thermal enhancement. The optimization results show that the optimal fin design achieves a desirability of 81.3%, with a pressure drop of 870.726 Pa and an overall heat transfer coefficient of 2199.85 W/m²K at a mass flow rate of 2.711 lit/min.

Abstract: Waste heat utilization is a critical aspect of enhancing energy efficiency and sustainability in various systems. This study investigates the recovery of waste heat using a heat exchanger installed at the outlet of a small-sized engine, demonstrating significant temperature control capabilities. The introduction of hot air from the heat exchanger effectively increased the ambient room temperature from 20 °C to 48 °C within 90 minutes. The heat exchanger's effectiveness improved with higher initial exhaust gas temperatures, as demonstrated across three test cases. In Case I, the room temperature rose to 33 °C with an initial exhaust temperature of 61 °C. Cases II and III showed further increases to 43 °C and 45.7 °C, respectively, corresponding to higher exhaust temperatures of 77 °C and 84 °C. A notable achievement was the consistent improvement in heat exchanger performance, evidenced by increased outlet temperatures and decreased exhaust temperatures, indicating efficient heat transfer. The effectiveness of the device improved from 0.31 to 0.55, highlighting its potential for energy-efficient ambient temperature regulation. However, the study also identified certain limitations. The temperature rise plateaued after 90 minutes, suggesting a limit to the heat exchanger’s capacity due to its size. Additionally, the minimal temperature difference between 60 and 90 minutes in Case III indicated that the engine had reached its peak efficiency, thereby limiting further heat recovery.

Abstract: Drying is the fundamental process for preserving agricultural products and food items, requiring a significant amount of energy. There are quality issues associated with the conventional drying processes and methods. The conventional drying methods are prone to the inclusion of impurities and surface damage, and their drying rates are very slow. In this research, a Concentrated Direct Forced Convection Solar Dryer (CDFCSD) dryer, having two DC brushless fans to regulate the air, was used to dry the test specimens, and the results were compared with the performance of a Direct Natural Convection Solar Dryer (DNCSD). The apple samples were selected as the test product. The drying process involves slicing the apples and placing them into the dryer. The apples were weighed before and after each drying mode, and moisture removal was evaluated and compared. The results show that moisture content removal was 58.15% in the Concentrated Direct Forced Convection Solar Dryer (CDFCSD) and 51.85% by the Direct Natural Convection Solar Dryer (DNCSD). 6.3% more moisture was removed using CDFCSD as compared to DNCSD, which shows a better effective moisture extraction rate using CDFCSD.

Abstract: Latent Heat Thermal Energy Storage (LHTES) systems are increasingly recognised as effective solutions for mitigating the intermittency of solar thermal energy. This study presents a comprehensive numerical investigation into the effect of fin geometry on the thermal performance of LHTES units designed for solar applications. Five configurations were examined: a baseline unit and four enhanced designs incorporating longitudinal, V-shaped, T-shaped, and triangular fins. The triangular fin geometry was further optimised by varying the number of fin patterns—two to five—across the heat transfer surface. All configurations employed paraffin wax (RT82) as the phase change material (PCM), thermally enhanced with copper particles to improve thermal conductivity. A high-fidelity 3D model was developed in ANSYS Fluent to simulate the melting process within a triplex-tube heat exchanger under natural convection conditions. The results revealed a strong dependence of melting performance on fin geometry. Notably, the five-pattern triangular fin configuration achieved the shortest melting time (78 minutes), representing an 82% reduction compared to the baseline. These findings underscore the critical role of fin optimisation in improving heat transfer and overall efficiency of LHTES systems.