One-Dimensional Semimechanistic Model for Flow Boiling Pressure Drop in Small to Micro Passages

Abstract

Accurate predictions of two-phase pressure drop in small to micro-diameter passages are necessary for the design of compact and ultra-compact heat exchangers, which find wide application in process and refrigeration industries and in the cooling of electronics. A semimechanistic model of boiling two-phase pressure drop in the confined bubble regime is formulated, following the three-zone approach for heat transfer. The total pressure drop is calculated by time-averaging the pressure drops for single-phase liquid, elongated bubble with a thin liquid film, and single-phase vapor. The model results were compared with experimental data collected for a wide range of tube diameters (4.26, 2.88, 2.02, 1.1, and 0.52 mm) for R134a at pressures of 6–12 bar. In this model's present form, its predictions are close to those of the homogeneous flow model but it provides a platform for further development.

Acknowledgments

Dereje Shiferaw received his M.Sc. in sustainable energy engineering in 2004 from the Royal Institute of Technology (Sweden) and his Ph.D. from Brunel University (UK) in 2008. His graduate work at Royal Institute of Technology included film boiling of subcooled nanofluids for reactor safety applications, for which he received best thesis award from the Swedish Centre for Nuclear Research. His Ph.D. research involved flow boiling of refrigerants in small to micro tubes: an experimental and theoretical study of two-phase flow patterns, pressure drop, and heat transfer at macro and micro scales. He received the 2009 Ted Perry Memorial Award from the Institute of Refrigeration. His research interests include single-and two-phase flow heat transfer in microchannels and their applications, heat transfer enhancement technologies, application of nanofluids for cooling and quenching of extreme temperatures, and sustainable power generation and utilization.

Mohamed Mahmoud graduated in 1998 from the Mechanical Engineering Department, Faculty of Engineering, Zagazig University, Egypt. He has been a lecturer assistant in the Environmental Engineering Department in the same university since 1999. He received his M.Sc. in 2004 in the field of biomass combustion from Zagazig University. Currently, he is a Ph.D. student in the School of Engineering and Design, Brunel University (UK), where his studies include single- and two-phase flow heat transfer, pressure drop and flow visualization in mini-/micro-channels.

Tassos G. Karayiannis is a professor of thermal engineering in the School of Engineering and Design of Brunel University, where he is co-director of the Centre for Energy and Built Environment Research. He obtained a B.Sc. in mechanical engineering from City University (UK) in 1981 and a Ph.D. from the University of Western Ontario (Canada) in 1986. He has carried out research in single-phase heat transfer, enhanced heat transfer, and thermal systems. He has been involved with research in two-phase flow and heat transfer for about 20 years. He is a fellow of the Institution of Mechanical Engineers and the Institute of Energy.

David B. R. Kenning graduated in mechanical sciences from Cambridge University in 1957 and worked for the UK Atomic Energy Authority for three years before returning to Cambridge to start his career of research on multiphase flows and boiling heat transfer. He joined Oxford University in 1963 and was a University Lecturer in Engineering Science and Tutorial Fellow of Lincoln College from 1967 until his official retirement in 2003. He then joined the research group of Professor Tassos Karayiannis as a visiting professor, first at London South Bank University and now at Brunel University.