Experimental and Numerical Investigation on Forced Convection in Circular Tubes With Nanofluids

Abstract

In this paper an experimental and numerical study to investigate the convective heat transfer characteristics of fully developed turbulent flow of a water–Al₂O₃ nanofluid in a circular tube is presented. The numerical simulations are accomplished on the experimental test section configuration. In the analysis, the fluid flow and the thermal field are assumed axial-symmetric, two-dimensional, and steady state. The single-phase model is employed to model the nanofluid mixture and the k-ϵ model is used to describe the turbulent fluid flow. Experimental and numerical results are carried out for different volumetric flow rates and nanoparticles concentration values. Heat transfer convective coefficients as a function of flow rates and Reynolds numbers are presented. The results indicate that the heat transfer coefficients increase for all nanofluids concentrations compared to pure water at increasing volumetric flow rate. Heat transfer coefficient increases are observed at assigned volumetric flow rate for nanofluid mixture with higher concentrations, whereas Nusselt numbers present lower values than the ones for pure water.

NOMENCLATURE

As	=	external area, m2
c	=	specific heat, J kg −1 K−1
D	=	tube diameter, m
h	=	heat transfer coefficient, W m−2 K−1
k	=	turbulent kinetic energy, m2 s−2
Nu	=	Nusselt number, Eq. (17)(17)
p	=	pressure, kPa
Q	=	heat transfer rate, W
Re	=	Reynolds number
T	=	temperature, °C
v	=	flow rate, m s−1
	=	volumetric flow rate, m3 h−1
V, v	=	time-averaged and fluctuating velocity component, m s−1
	=	velocity

Greek Symbols

ϵ	=	dissipation of turbulent kinetic energy, m2 s−3
φ	=	particle volume concentration
λ	=	thermal conductivity of the fluid, W m−1 K−1
μ	=	dynamic viscosity, kg m −1 s−1
ρ	=	density, kg m−3
τ	=	wall shear stress, Pa

Subscripts

b	=	bulk
bf	=	refers to base fluid
DB	=	Dittus–Boelter
exp	=	experimental
in	=	inlet
m	=	mixture
nf	=	refers to nanofluid property
p	=	refers to particle property
s	=	solid
t	=	turbulent

Additional information

Notes on contributors

Laura Colla

Laura Colla has been a researcher at the Construction Technologies Institute (ITC) in Padova of the Italian National Research Council (CNR) since 2014. She graduated in mechanical engineering in 2008 and received a Ph.D. in Ingegneria dell’Energia in 2014 at the University of Padova. Her activity is focused on theoretical and experimental research on nanofluids and new alternative refrigerants, in particular on their thermodynamic and thermophysical properties. She is the author of about 30 publications in international and national journals and conferences.

Laura Fedele

Laura Fedele graduated in chemical engineering in 1998 and received a Ph.D. in fisica tecnica in 2004 at the University of Padova. Since 1999 she has been working at the Construction Technologies Institute (ITC) in Padova (ex ITEF) of the National Research Council (CNR). She has been a CNR researcher since 2003. Her interests concern theoretical and experimental research on new alternative refrigerants and nanofluids, in particular on their thermodynamic and thermophysical properties. She is the author of about 90 publications in international and national journals and conferences.

Oronzio Manca

Oronzio Manca is a professor of mechanical engineering at Seconda Università degli Studi di Napoli (SUN). His main scientific activities are on active solar systems, passive solar systems, refrigerant fluids, natural and mixed convection in an open-ended cavity with and without porous media, conduction in solids irradiated by moving heat sources, combined radiative and conductive fields in multilayer thin films, analytical and numerical solutions in material processing, thermal control of electronic equipment and solar systems, and heat transfer augumentation by nanofluids. He is a member of the American Society of Mechanical Engineering and Unione Italiana di Termofluidodinamica (UIT). He is the author or coauthor of 410 papers, 115 in peer-reviewed journals, seven book chapters, and in conference proceedings. He is a co-author of the book Applied Diffusion Processes From Engineering to Finance and is an associate editor for the ASME Journal of Heat Transfer and Journal of Porous Media.

Lorenzo Marinelli

Lorenzo Marinelli is a Ph.D. student at the Seconda Università degli Studi di Napoli. His research activities are on enhanced heat transfer, particularly on heat transfer with nanofluids, thermophysical properties evaluation of nanofluids, convective heat transfer coefficients, and investigation on natural, mixed, and forced convection and radiation in channels with metal foams or ribs. He is the author or co-author of 25 scientific papers in international and national journals and conference proceedings.

Sergio Nardini

Sergio Nardini graduated from the Facoltà di Ingegneria Meccanica, Università degli Studi di Napoli Federico II, Napoli, Italy, in 1989. He obtained his Ph.D. in 1994. He is an associate professor at the Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università degli Studi di Napoli, Napoli, Italy. Some of his recent research activities include heat conduction, numerical and analytical evaluation, and analysis of linear and nonlinear problems in solids with moving or stationary heat sources such as laser and electron beams. His research activity on natural and mixed convection in open-ended cavities includes the following: experimental investigations on natural and mixed convection of air in inclined and horizontal channels with secondary motions, evaluation of correlations, and optimal geometrical configurations of vertical, inclined, and horizontal channels. He also carries out research on analysis of active and passive solar systems, heat transfer enhancement, numerical and experimental investigations on impinging jets, extended surfaces, and swirl flows in the presence of nanofluids. He is the author or co-author of 230 scientific papers (55 in peer-reviewed journals).