Design and development of novel air-cooled heat exchangers for enhanced thermal-hydraulic performance

• Main Author: Ng, Swee Yong
• Other Authors: Leong Kai Choong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/149156
• Institution: Nanyang Technological University

This report outlines the investigation of novel fin designs on the heat exchangers’ thermal and hydraulic performances. In this report, two novel airfoil heat exchangers (Design 1 and Design 2) were designed in SolidWorks and their thermo-hydraulic performances were numerically studied using COMSOL simulations. In this report, we will be investigating the effects of different angles of attack (α) of the airfoil fins (0°, 10°, 20°) on the thermal and hydraulic performance of the airfoil heat exchanger. Experiments were also conducted in the wind tunnel to assess the thermo-hydraulic performance of the conventional heat exchanger. The thermo-hydraulic parameters evaluated were air-side heat transfer coefficient (h_a), pressure drop (ΔP), pressure drop per unit depth (ΔP/H), and pumping power per unit depth (W ̇/H). Different conclusions for the simulation and experimental results were drawn due to the large differences in numerical simulation setup and experimental setup. The simulation setup consists of eight airfoil fins and uses a k-epsilon (k−ϵ) model with various empirical coefficient constants while the experimental setup was done on a conventional heat exchanger. For the wind tunnel speed of 7.57 m/s and 16.39 m/s tested, the h_a for the conventional heat exchanger varies between 75.038 W/m2·K to 77.09 W/m2·K and 184.05 W/m2·K to 190.08 W/m2·K respectively. It is determined that at higher air velocity flow, the air-side temperature rise decreases and hence increases the uncertainty of h_a calculated. From an air velocity of 7.57 m/s to 16.39 m/s, it was determined that the air temperature rise decreases by 78.5%. On the other hand, preliminary investigations on Design 1 of the numerical simulations found that the 0α airfoil fins is the optimum angle of attack as it provides a higher air-side temperature rise and pressure drop characteristic compared to 10α and 20α. The air-side temperature rise for 0α is 4.80% and 5.11% higher as compared to 10α and 20α respectively. The pressure drop for 0α is 13.8% and 43.8% lesser as compared to 10 and 20α. From the above simulation results, it implied that the streamline profile of 0α airfoil fins improve flow by maintaining a low pressure drop while providing considerable amount of temperature rise. Further numerical investigations were then performed on Design 2 for airfoil fins of 0α at 5, 7 and 10 m/s. It is observed that as the flow velocity rises, the air-side temperature rise decreased, and pressure drop increased. For instance, from 5 m/s to 10 m/s, the air-side temperature rise decreases by 17.2% while pressure drop increases by 198.3% giving rise to a lower coefficient of performance (∆T/∆P). The simulation results suggested that to achieve a higher temperature rise and lower pressure drop, a lower air velocity should be employed.