Heat Transfer in Laminar Solid-Fluid Suspension Flow
Sohn, Chang Wook
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https://hdl.handle.net/2142/67023
Description
Title
Heat Transfer in Laminar Solid-Fluid Suspension Flow
Author(s)
Sohn, Chang Wook
Issue Date
1980
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
This thesis consists of two parts. In the first part of the thesis, effective thermal conductivities of neutrally buoyant, concentrated polyethylene suspensions in silicone oil and kerosene mixture, and polystyrene suspensions in silicone oil and Freon 113 mixture were measured in a rotating Couette flow apparatus. Contrary to the case of single phase fluid, effective thermal conductivity was observed to be shear dependent when the particle Peclet numbers (defined by Pe(,d) (TBOND) ed('2)/(alpha)(,f), where e is the external shear rate, d the particle diameter, and (alpha)(,f) the thermal diffusivity of fluid) are high. Measured particle volume fractions were (phi) = 0.15 and 0.30 for the suspensions of polyethylene beads (2.9 mm in diameter), and (phi) = 0.15 for the suspensions of polystyrene beads (0.3 mm in diameter). The case for (phi) = 0 (single phase liquid mixture only) was also measured in various shear rates to show the independence of thermal conductivity of single phase fluid on shear rates. The dependence of conductivity on particle Peclet number appeared to approach a power-law relationship for the range of high Peclet numbers (Pe(,d) > 300). The data showed an asymptotic relationship k(,e) (PROPORTIONAL) Pe(,d)('1/2).
In the second part of the thesis, generalized theoretical results for heat transfer in pipe flow of fluid with shear dependent thermal conductivity are presented. The analysis was based on a two parameter representation of the thermal conductivity-shear rate dependence, in accordance with experimental observations from the experimental studies. When the results are expressed in terms of Nusselt numbers based on the thermal conductivity at the wall, corresponding to the wall shear rate, they are found to be independent of k(,w)/k(,o) (ratio of conductivity at the wall to the unenhanced conductivity), and k(,w)/k(,o) greater than two. Thus for all cases when significant enhancement in conductivity is present the heat transfer results can be represented in two curves, one for uniform wall temperature and the other for uniform wall heat flux. The obtained solutions are applicable to a thermally developing region as well as a fully developed flow, with uniform wall temperature and heat flux boundary conditions. The significant increase in Nusselt number (heat transfer), for all the cases studied, implies a potential augmentation in heat transfer by employing a suspension as a heat transfer medium.
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