Entropy Generation of Two-Phase Flow Boiling in Elliptical U-Bend Tube Heat Exchanger

Abstract

In this research paper, the entropy generation was used as a criterion to measure the quality level of energy transfer for two-phase flow boiling of R134a in the elliptical U-bend tube. The eccentricities of the elliptical cross-section ranging from 0 to 0.904, were constrained to the same hydraulic diameter of 8 mm. The input parameters utilized in the numerical computations were mass velocities of 100 and 200 kg/m² s for the inlet vapor qualities of 0.1 and 0.2 and a constant uniform heat flux of 10 kW/m² imposed on the outer surface of the tube. The calculations were performed using the volume of fluid multiphase model coupled with the phase change model. The findings demonstrated that when the eccentricity of the U-bend tube increases, the quality of energy transfer in the heat exchanger improves as entropy generation reduces. The numerical calculations were validated and found to be consistent with what has been published in the open literature. The results of this paper are important for the development of heat exchangers for air conditioners and refrigerators.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The International scholarship and NRF funding received from the University of Cape Town are acknowledged and appreciated. High Performance Computing facilities provided by the University of Cape Town is also acknowledged.

Notes on contributors

Tanimu Jatau

Tanimu Jatau is a Ph.D. candidate in the Department of Mechanical Engineering, University of Cape Town South Africa. He is currently working on heat transfer and two-phase flow pattern development in U-bend tube heat exchangers using computational fluid dynamics code. He received his B.Eng. in Mechanical Engineering in 2010 from Ahmadu Bello University Zaria, Nigeria, and his M.Sc. in Mechanical Engineering in 2017 from the University of Cape Town South Africa.

Tunde Bello-Ochende

Tunde Bello-Ochende is a Professor of Mechanical Engineering at the University of Cape Town, South Africa. His research focuses on the theoretical and numerical optimization of heat transfer devices from macro to micro scales. These include compact heat exchanger, micro-channel heat sink, and heat transfer augmentation using micro-fins. His recent works are in the areas of sustainable/renewable energy (solar, geothermal and fuel cells), Sterling engines, two-phase flow, and energy management in building envelopes. He is the author and coauthor of over 150 papers in referred journals and conference proceedings. He has graduated over 35 postgraduate students (masters and PhD). He is a B-rated researcher from the National Research Foundation South Africa. He is a member of several editorial board, among them is the International Communication Heat and Mass Transfer and Frontiers in Energy. He is a registered professional engineer of the Engineering Council of South Africa (ECSA). He is also a member of America Society of Mechanical Engineer (ASME). He received his Bachelor’s, master’s degree from the University of Ilorin, Nigeria (1995, 1999) and doctorate from Duke University, USA (2005), all in Mechanical Engineering.