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Effects of polymer additives in the bulk of turbulent thermal convection

Published online by Cambridge University Press:  04 November 2015

Yi-Chao Xie ,
Shi-Di Huang ,
Denis Funfschilling ,
Xiao-Ming Li ,
Rui Ni  and
Ke-Qing Xia
Yi-Chao Xie
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Shi-Di Huang
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Denis Funfschilling
Affiliation:
LRGP, Lorraine University, CNRS, 1 rue Grandville B.P. 20451, F-54001 Nancy, France
Xiao-Ming Li
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Rui Ni
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Ke-Qing Xia*
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
*
†Email address for correspondence: kxia@phy.cuhk.edu.hk
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Abstract

We present experimental evidence that a minute amount of polymer additives can significantly enhance heat transport in the bulk region of turbulent thermal convection. The effects of polymer additives are found to be the enhancement of coherent heat fluxes and suppression of incoherent heat fluxes. The enhanced heat transport is associated with the increased coherency of thermal plumes, as a result of the suppression of small-scale turbulent fluctuations by polymers. The incoherent heat flux, arising from turbulent background fluctuations, makes no net contribution to heat transport. The fact that polymer additives can increase the coherency of thermal plumes is supported by the measurements of a number of local quantities, such as the extracted plume amplitude and width, the velocity autocorrelation functions and the velocity–temperature cross-correlation coefficient. The results from local measurements also suggest the existence of a threshold value for the polymer concentration, only above which significant modification of the plume coherent properties and enhancement of the local heat flux can be observed. Estimation of the plume emission rate suggests a stabilization of the thermal boundary layer by polymer additives.

JFM classification

Convection: Plumes/thermals Non-Newtonian Flows: Polymers
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 784 , 10 December 2015 , R3
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Copyright
© 2015 Cambridge University Press 

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Footnotes

‡

Present address: Department of Mechanical and Nuclear Engineering, Pennsylvania State University, State College, PA 16802-1412, USA.

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