Geometry
Multifunctional heat exchanger / reactor (MHER): High-Efficiency Vortex (HEV) Trapezoidal vortex generators inserted in a circular tube
Pressure gradient Counter-rotating vortex pairs (CVP) Kelvin-Helmholtz instability Periodic transient “hairpin” vortices
Enhanced transfer phenomena by artificially generated vorticity in turbulent flows
5thEuropean Postgraduate Fluid Dynamics Conference, Göttingen, Germany, 9-12 August 2011
Objectives
Experimental study of the effect of longitudinal vorticity on heat transfer characterized by the Nusselt number
Quantify the transfer enhancement and compare different heat exchanger geometries
Evaluate friction losses and energetic costs Validate numerical results
Akram GHANEM*, Charbel HABCHI, Thierry LEMENAND, Dominique DELLA VALLE, Hassan PEERHOSSAINI
Thermofluids, Complex Flows and Energy Research Group, Laboratoire de Thermocinétique de Nantes, CNRS UMR 6607, Nantes University, Nantes, France
Experimental study
Imposed constant wall heat flux (12000 W/m2) Reynolds number ranges between 2000 and 15000
Temperature measured at different longitudinal positions Local heat flux measured by two series of superposed thermocouples
“Agilent “ data acquisition chain and “BenchLink Data Logger”
post-treatment software
Re
2160 4530 6390 8670 10460 12860 14920
hexperimental[Wm-2K-1]
1192 1781 2076 2300 2549 2682 3023
Local Nusselt number, Nu vs. zRelative intensification of heat transfer (with respect to plain tube), vs. Re
Results - Intensification of convective heat transfer
χ Global Nusselt number, Nugvs. Re
Conclusions and Perspectives
Longitudinal vorticity produced in the HEV multifunctional heat exchanger / reactor is the principal factor of heat and mass transfer enhancement.
The experimental study validates the results of previous numerical simulations and proves the capacity of the HEV to intensify convective transfer phenomena between 200% and 800% relative to the empty pipe flow.
A thorough and more profound study necessitates some modifications on the experimental setup in order to increase the inlet - outlet temperature gradient and reduce errors and measurement uncertainties Increase of heating power and thermal conductivity of the medium surrounding the exchanger.
Introduction
Longitudinal vortices enhance heat and mass transfer phenomena
Development of three-dimensional turbulent boundary layers,
Reduction of the laminar sublayer thickness near the wall,
Intensification of radial transfer in the flow cross section
http://www.uni-marburg.de/fb13/epfdc5
e p
(T -T ) e ϕ = λ
(p m) h
T T
=
ϕ
− hD
N u= κ
-0.25
f =0.079Re Gnielinski, plain tube:
Colburn factor, j vs. Re Friction factor, f vs. Re
Convective heat transfer coefficient, h
1 3
j = Nu RePr
0 1 2 2 3
( f 8)(Re-1000)Pr Nu =1+12.7( f 8) (Pr -1)
g 0
0
Nu - Nu
= Nu χ
