Numerical investigation of thermohydraulic performance of air to water double-pipe heat exchanger with helical fins

In this work, the thermohydraulic performance of a proposed design of an air-to-water double pipe heat exchanger with helical fins on the annulus gas side, is numerically studied. Three-dimensional computational fluid dynamics (CFD) simulations are performed, using the FLUENT software in order to investigate the gas side fluid flow, turbulence, heat transfer, and power consumption for different configurations of the heat exchanger. CFD performance analysis is conducted under turbulent flow conditions for configurations with helical fin spacings in the range of 0.05-0.2 m. The numerical model is first verified against experimental data available in the literature, for a double-pipe heat exchanger with longitudinal fins. Then, longitudinal fins are considered as a reference configuration and a comparative analysis of the thermohydraulic performances of the different helical fin configurations and the reference configuration is conducted. The flow field characteristics of the helical fin configurations are clearly demonstrated and discussed. Key design parameters such as the heat transfer coefficient, pressure drop, and thermal performance enhancement factor are evaluated to predict the overall performance of the heat exchangers. Results show that the use of helical fins significantly enhances the heat transfer rate for the same unit weight, but it also increases the pressure drop. The overall compactness and performance of the heat exchanger improve through the use of helical fins, and within the scope of the present investigation, the helical fin configuration with a fin spacing of 0.1 m provides the optimal thermohydraulic performance. Therefore, the present study helps to reveal and expand the potential of helical fins in providing an enhanced overall performance of this type of heat exchanger as well as in limiting its material cost for design engineers and manufacturers. (C) 2017 Elsevier Ltd. All rights reserved.