Natural convection heat transfer from an array of horizontal rectangular fins on a vertical flat plate in non-Newtonian power-law fluids has been studied. The underlying physical principles affecting heat transfer were studied using comprehensive solutions obtained from numerical investigations. Heat transfer to the power-law fluid was found to depend on the fluid rheology (power-law index) and significantly on the geometric parameters (interfin spacing, fin length) as well. The dependence was quantified using the Nusselt number (Nu) and fin effectiveness (Q/Q0). The present study shows that compared to a fin analyzed in isolation, the spatial arrangement of multiple fins relative to one another in an array does have a significant effect on the flow field around subsequent fins in power-law fluids. Therefore, the average heat transfer coefficient of the natural convection system is affected significantly. The variation of Nu with the dimensionless fin length (l/L), dimensionless interfin spacing (S/L), and fluid power-law index (n) was plotted. The dependence was found to be counter intuitive to expectations based on studies for natural convection from vertical flat plates to power-law fluids. In the present study involving fins, shear-thinning fluids (n < 1) show a decrease in heat transfer and shear-thickening fluids (n > 1) show an enhancement in heat transfer for higher l/L values. The results of the study may be useful in the design of natural convection systems that employ power-law fluids to enhance or control heat transfer.

References

References
1.
Chhabra
,
R. P.
, and
Richardson
,
J. F.
,
2008
,
Non-Newtonian Flow and Applied Rheology: Engineering Applications
,
Butterworth-Heinemann
,
Oxford, UK
.
2.
Bird
,
R. B.
,
Armstrong
,
R. C.
, and
Hassager
,
O.
,
1987
,
Dynamics of Polymeric Liquids, Volume 1: Fluid Mechanics
,
Wiley
,
New York
.
3.
Acrivos
,
A.
,
1960
, “
A Theoretical Analysis of Laminar Natural Convection Heat Transfer to Non-Newtonian Fluids
,”
AIChE J.
,
6
(
4
), pp.
584
590
.
4.
Reilly
,
I. G.
,
Tien
,
C.
, and
Adelman
,
M.
,
1965
, “
Experimental Study of Natural Convective Heat Transfer From a Vertical Plate in a Non-Newtonian Fluid
,”
Can. J. Chem. Eng.
,
43
(
4
), pp.
157
160
.
5.
Gray
,
D. D.
, and
Giorgini
,
A.
,
1976
, “
The Validity of the Boussinesq Approximation for Liquids and Gases
,”
Int. J. Heat Mass Transfer
,
19
(
5
), pp.
545
551
.
6.
ANSYS
, 2010, “
Ansys 13.0 Help
,” ANSYS,
Canonsburg, PA
.
7.
Tu
,
J.
,
Yeoh
,
G. H.
, and
Liu
,
C.
,
2012
,
Computational Fluid Dynamics: A Practical Approach
,
Butterworth-Heinemann
,
Oxford, UK
.
8.
Irvine
,
T. F.
, Jr., and
Capobianchi
,
M.
, 2005, “
Non-Newtonian Fluids—Heat Transfer
,”
The CRC Handbook of Mechanical Engineering
, 2nd ed., F. Kreith and Y. Goswami, eds., CRC Press, Boca Raton, FL, pp. 4–269.
9.
Leung
,
C. W.
,
Probert
,
S. D.
, and
Shilston
,
M. J.
,
1985
, “
Heat Exchanger Design: Optimal Uniform Separation Between Rectangular Fins Protruding From a Vertical Rectangular Base
,”
Appl. Energy
,
19
(
4
), pp.
287
299
.
10.
Senapati
,
J. R.
,
Dash
,
S. K.
, and
Roy
,
S.
,
2017
, “
Numerical Investigation of Natural Convection Heat Transfer From Vertical Cylinder With Annular Fins
,”
Int. J. Therm. Sci.
,
111
, pp.
146
159
.
You do not currently have access to this content.