Entropic analysis of a double helical tube heat exchanger including circular depressions on both inner and outer tube

In this research, entropic analysis of a double helical tube heat exchanger including circular depressions on both inner tube and outer tube is provided. Experimentally validated 3D numerical simulation is employed to reach the aim of this study. Entropic characteristics of four cases are investigated and reported. In case “a” both inner tube and outer tube are smooth. In case “b”, circular depressions are created on only inner tube while in case “c” both tubes contain circular depression. Case “d” is the same as case “c” while the depression arrangement is different from case “c”. Dimensionless entropy generation and dimensionless Nu number are used to evaluate the proposed designs based on the first and second laws of thermodynamics. Moreover, heat transfer improvement (HTI) factor is adopted to consider the impacts of said two parameters simultaneously. Results demonstrate that, although creating circular depressions on both tubes significantly improves the heat transfer characteristics of the heat exchanger, it increases the entropy generation level of heat exchanger as well. Case “d” in which the location of any circular depression of the outer tube is placed between any two continuous depressions of the inner tube, gives the highest thermal performance and also entropy generation

Single solar chimney technology as a natural free ventilator; energy-environmental case study for Hong Kong

The importance of ventilation is highlighted through the recent COVID pandemic particularly in populated societies with crowded buildings. The application of single solar chimney ventilator with and without fin, at different tilt angles, is evaluated for Hong Kong climate using transient 3D validated numerical simulation in present research from energy and environmental viewpoints. The results show that the ventilation performance of the solar chimney ventilator is significantly enhanced by selecting an optimum value for the tilt angle of the chimney. Moreover, the maximum air mass flow rate increases from 0.06 to 0.14 kg/s by reducing the tilt angle from 80° to 20°. Energy saving performance of the solar chimney ventilator with tilt angle of 20° is around 144% higher than that of the solar chimney ventilator with the tilt angle of 80°. During the morning time (sunrise to noon), the highest performance is achieved under the tilt angle of 40°. From the environmental viewpoint, the solar chimney ventilator with the tilt angle of 20° and 40° can prevent 0.098 kg and 0.108 kg CO2 production through the morning. Prevention of the CO2 production through the afternoon is 0.209 kg and 0.151 kg for the mentioned tilt angles respectively