Numerical solution of a problem of rough surfaces interaction in power plants

Аuthors

Ezhov A. D.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

e-mail: ezzhov@gmail.com

Abstract

The design of modern power plants contains a significant number of coupling structural components of various shapes and geometries, made of materials differing in mechanical and heat-transfer properties. Most important task while creating a reliable power plant consists in correct calculation of thermal contact resistance occurring due to non-ideal contact of mating parts, and, as consequence, retraction and extension of heat flow lines to contact spots, as well as higher temperature gradient within the contact zone. All these factors reduce heat-conducting ability of the contact and cause different thermal expansion of the adjoining parts, leading to relative shifts, deflection and warpage of the parts.

The surface roughness is considered to be one of the key factors in solving thermal contact problems. Analysis of the literature on modeling and forecasting of contact thermal resistance shows that in practically all the works contain some analytical simplifications and assumptions concerning surface microrelief. In particular, irregularities were modeled as a variety of geometric shapes. The behavior of one pair of interacting irregularities was extrapolated to describe the behavior of a pair of interacting surfaces coated with irregularities. But if one takes into consideration the time when the suggestions of the CCC definition (60-70) were put forward, then we can say that the simulation of three-dimensional models was not carried out due to insufficient computer resources.

Despite this, there have been many achievements in the field of metrology and methods of numerical analysis.The optical measurement of surface features at the micro and macro level and the surface condition data storing in a digital form became possible. The numerical and finite-element modeling of contact problems with complex geometry, boundary conditions and material properties setting appeared.

Generally, to evaluate the temperature difference losses, the contact thermal resistance is introduced by different empirical formulas. But their diversity, incompletely given conditions of obtaining experimental data on which basis these relationships were obtained cast doubts on the correctness of the selection of a particular equation. While the differences in the absolute values of contact thermal resistance for the same conditions make it difficult to use them.

On the assumption of the formed problem, analysis of contact pairs of different materials was performed, and comparison was made with the known calculation dependencies.

Analysis of the known calculation dependencies to determine the CCC showed that the results obtained by rather accurate modeling of the ongoing process and analytical solutions differ, but they also have a number of matches. Nevertheless, the presented algorithm for calculating the CCC provides rather accurate values of temperature fields for almost all pairs of materials with minimal costs of the experiment. The use of this approach in engineering analysis allows reducing significantly the time of further testing and refinement of the product.

Keywords:

surface roughness modeling, contact thermal resistance

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