Effective thermal conductivity of binary mixed materials with fissile components - an empirical approach

Abu Saleem, Rabie

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https://hdl.handle.net/2142/29763 Copy

Description

Title

Effective thermal conductivity of binary mixed materials with fissile components - an empirical approach

Author(s)

Abu Saleem, Rabie

Issue Date

2012-02-06T20:15:02Z

Director of Research (if dissertation) or Advisor (if thesis)

Uddin, Rizwan

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Thermal conductivity
• Mixed materials
• homogenization
• Empirical approach

Abstract

An empirical approach to determine the effective thermal conductivity of a binary mixed material with heat generation is presented. Analysis was carried out for a steady state problem with spherical geometry to develop an expression for the effective thermal conductivity for the spherical pebble fuel in a pebble bed reactor. The approach is based on two main concepts: a structural approximation and an empirical formulation. As for the structural approximation, the binary mixed material was assumed to be equivalent to a binary layered system of adjacent fuel and moderator layers oriented perpendicular to the direction of the heat flux. A model for heat transfer using an equivalent thermal conductivity in a binary mixture with no heat generation was developed. An assessment for this model was performed by comparing the effective thermal conductivity predicted by this model to some existing experimental data. Results from this evaluation showed good agreement between the experimental and the predicted values. It also showed that the less the difference between the thermal conductivities of the individual components, the better is the prediction for the effective thermal conductivity. Next, an empirical formulation was developed for an expression for the effective thermal conductivity of a binary layered system with heat generation. This empirical formulation was analyzed systematically by considering the parametric and conditional effects of the system on the overall effective thermal conductivity. Some parameters were found to have no effect on the final expression of the thermal conductivity. These are the heat generation rate and the boundary conditions. Other parameters were found to significantly influence the value of the effective thermal conductivity. These are the abundance of individual components in the mixture and their thermal conductivities. Evaluation of this model was performed by comparing the predicted values of the effective thermal conductivity and temperature profiles with benchmark values. Results from this comparison showed that the empirical expression for the effective thermal conductivity developed here gives a better approximation for the heat conduction process in the layered system compared to the simple volume weighted thermal conductivity, which gives an unsatisfactory result. The last step in the evaluation of the approach developed here was more comprehensive, in which the values predicted by the expression developed here for the effective thermal conductivity were compared to the values of effective thermal conductivity for the pebble fuel in a pebble bed reactor obtained using a correlation based on experimental data. This comparison showed satisfactory agreement between the two results with an average error of 18.41 percent.

Graduation Semester

2011-12

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http://hdl.handle.net/2142/29763

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Copyright 2011 Rabie Abu Saleem

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