Experimental Investigation of Subcooled Flow Boiling in a Minichannel

Abstract

The present work presents experimental results of subcooled flow boiling heat transfer phenomena in minichannels. The experiments were conducted with high surface tension liquid (water), which clearly indicates that inertial effects are important for both momentum and thermal transport in minichannels. The test section is a horizontal AISI 316 stainless-steel minitube with internal diameter of 1.13 mm with uniform heated length of 250 mm and the tube is heated by AC electric current. The variation in wall temperature and pressure drop gives an indication of the different boiling regions along the axis of the horizontal tube. Based on sudden oscillations of the pressure drop and wall temperature, onset of nucleate boiling (ONB) is identified in the tube. During ONB, pressure drop and the fluctuations of fluid outlet temperature are observed near the exit of the test section. Predictive models for ONB were evaluated and Kandlikar's ONB model was found to agree well with the present data. Comparisons of experimental heat transfer coefficient in the subcooled boiling regime with the existing correlations are also presented.

NOMENCLATURE

A	=	area, m2
Bo	=	boiling number
Di	=	tube inner diameter, mm
Cp	=	specific heat, J kg−1 K−1
f	=	friction factor
G	=	mass flux, kg m−2 s−1
h	=	heat transfer coefficient, W m−2 K−1
hfg	=	latent heat of vaporization, J kg−1
h9	=	enthalpy at exit of the test section, J kg−1
k	=	thermal conductivity, W m−1 K−1
L	=	length of stainless steel tube, m
m	=	mass flow rate, kg s−1
Nu	=	Nusselt number
Q	=	heat transfer rate, W
q	=	heat flux, W m−2
Re	=	Reynolds number
T	=	temperature, °C
We	=	Weber number
x	=	thermodynamic quality
z	=	axial position along the axis of the test section, m

Greek Symbols

ρ	=	density, kg m−3
σ	=	surface tension, N m−1

subsript

c	=	cross section
cond	=	condenser
f	=	fluid
i	=	inlet
l	=	liquid
v	=	vapour
s	=	surface
sat	=	saturation
ONB	=	onset of nucleate boiling
w	=	wall

Additional information

Funding

The financial support provided in part by the Indian Space Research Organization (ISRO), India, is gratefully acknowledged.

Notes on contributors

Manoharan Aravinthan

Manoharan Aravinthan is a Ph.D. student at the Heat Transfer and Thermal Power Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, India. He received his master's degree in thermal power engineering from Annamalai University, India, in 2004 and a bachelor's degree in engineering from the University of Madras, India, in 2001. He is currently working on flow boiling heat transfer in minichannels.

Muniyandi Venkatesan

Muniyandi Venkatesan is a senior assistant professor in the School of Mechanical Engineering, SASTRA University, Thanjavur, India. He received his Ph.D. from the Indian Institute of Technology Madras, Chennai, India, in 2012. His research interests include two-phase flows and flow boiling in mini-/microchannels.

Sarit K. Das

Sarit K. Das is a professor in the Mechanical Engineering Department and the Dean of Academic Research at Indian Institute of Technology, Madras. He has published four books and more than 200 research papers. He is the editor-in-chief of International Journal of Micro-Nano Scale Transport and also an associate editor of Journal of Heat Transfer Engineering. His research interests include heat transfer in nanofluids, microfluidics, biological heat transfer, nanoparticle-mediated drug delivery in cancer cells, heat exchangers, boiling in mini-/microchannels, fuel cells, jet instabilities, heat transfer in porous media, and computational fluid dynamics. He is the recipient of the DAAD and Alexander von Humboldt Fellowship of Germany. He is a fellow of the Indian National Academy of Engineering and National Academy of Sciences, India. He has been awarded the Peabody Visiting Professorship at the Mechanical Engineering Department of Massachusetts Institute of Technology (Cambridge, MA), 2011.

Arcot R. Balakrishnan

Arcot R. Balakrishnan is a professor of chemical engineering at the Indian Institute of Technology Madras, India. He received his B.Tech. degree from the University of Madras in 1972. and M.A.Sc. and Ph.D. degrees from the University of Waterloo, Canada, in 1974 and 1977, respectively. He has published extensively. He is a fellow of the Indian National Academy of Engineering. The primary focus of his recent research work has been directed toward addressing the concerns of energy and the environment. This includes among other work energy storage, liquid desiccant dehumidification of air and gases, augmentation of boiling heat transfer using enhanced surfaces, boiling in mini-/microchannels, and boiling of multicomponent liquid mixtures. He is the editor of the International Journal of Heat and Mass Transfer and of the International Communications in Heat and Mass Transfer, and editor-in-chief of the Journal of Energy, Heat and Mass Transfer.