Impact of vapour bubble movement on the process of two-phase heat transfer phenomena over hybrid elliptical tubes

Abstract

The use of modified surface to improve the performance of two-phase heat exchanger in terms of pressure drop and heat transfer rate is one of the current need of industries. In light of this, the current analysis compares the diabatic two-phase heat transfer performance of hybrid elliptical tubes with that of traditional circular tubes at atmospheric pressure using distilled water as a quiescent test fluid. For the purpose of this investigation, a circular tube made of AISI 304 with a diameter of 25 mm and a heating length of 130 mm is used. In order to maintain the same surface area and heating length as a circular tube, the hybrid elliptical tubes are fabricated with varying aspect ratios of 1.17, 1.31, and 1.47. The heat flux varies between 14.87 and 94.82 kW/m2. For two orientation angles, i.e. 0ᵒ and 90ᵒ, the heat transfer performance of hybrid elliptical tubes are investigated. The analysis of results confirmed that both the tubes exhibit boiling characteristics. However, hybrid elliptical tubes outperform circular tubes in terms of heat transfer rate. It is also found that the hybrid elliptical tube with 0ᵒ orientation resulted in higher heat transfer coefficient about 20.61%, 36.74% and 20.69% than that of 90ᵒ orientation for aspect ratio of 1.17, 1.31 and 1.47 respectively. Regardless of orientation angle, the hybrid elliptical tube with aspect ratio of 1.31 demonstrated the highest heat transfer coefficient of all aspect ratios. Also, a non-dimensional correlation is developed which is found to predict the heat transfer coefficient of circular as we as hybrid elliptical tubes within an error band of ±12%.