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2014 | Book

Introduction Read chapter Read first chapter

Thermal Contact Conductance

Author: Chakravarti V. Madhusudana

Publisher: Springer International Publishing

Book Series : Mechanical Engineering Series

Part of: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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About this book

The work covers both theoretical and practical aspects of thermal contact conductance. The theoretical discussion focuses on heat transfer through spots, joints, and surfaces, as well as the role of interstitial materials (both planned and inadvertent). The practical discussion includes formulae and data that can be used in designing heat-transfer equipment for a variety of joints, including special geometries and configurations. All of the material has been updated to reflect the latest advances in the field.

Table of Contents

Frontmatter
Chapter 1. Introduction
Abstract
Microscopic and macroscopic irregularities are present in all practical solid surfaces. Surface roughness is a measure of the microscopic irregularity, whereas the macroscopic errors of form include flatness deviations, waviness and, for cylindrical surfaces, out-of-roundness.
C. V. Madhusudana
Chapter 2. Thermal Constriction Resistance
Abstract
It was seen that the contact interface consists of a number of discrete and small actual contact spots separated by relatively large gaps. These gaps may be evacuated or filled with a conducting medium such as gas. In the first case, all of the heat is constrained to flow through the actual contact spots. If the gaps are filled with a conducting medium, however, some of the heat flow lines are allowed to pass through the gaps, that is, they are less constrained and thus the constriction is alleviated to some extent.
C. V. Madhusudana
Chapter 3. Solid Spot Thermal Conductance of a Joint
Abstract
A real joint consists of a numerous contact spots and each spot is associated with two resistances—constriction and spreading—in series. The thermal contact conductance (or resistance) is a combination of individual conductances (or resistances) of all of the spots in the joint. In this chapter, the number and the average size of contact spots a given pair of surfaces in contact are established by statistical analysis of the contacting surfaces. These are then related to the mechanical properties of the contacting materials by deformation analyses. The thermal, the surface and the deformation analyses are then combined to obtain a relationship between the conductance the contact pressure. This chapter also includes brief discussions of macroscopic errors of form eccentric contacts the thermal boundary resistance.
C. V. Madhusudana
Chapter 4. Gap Conductance at the Interface
Abstract
At low contact pressures (of the order of 10−4 H or less), it can be shown that the heat transfer across a joint occurs mainly through the gas gap (Madhusudana 1993). Boeschoten and van der Held (1957) also observed that the heat transfer was predominantly through the gas gap for “low [up to several kg/(sq cm)]” contact pressure. Lang (1962) pointed out that convection heat transfer is usually negligible for gap widths of up to about 6 mm (corresponding to a Grashof number of about 2000 for air at atmospheric pressure and a temperature of 300 K). Since the mean separation between contacting solid surfaces is some three orders of magnitude smaller than this dimension, it is clear that convection cannot be the mode of heat transfer across the gap. We conclude that the heat transfer across the gas-filled voids, interspersed between the actual contact spots, is principally by conduction, as already noted.
C. V. Madhusudana
Chapter 5. Experimental Aspects
Abstract
Thermal conductance of joints may be determined experimentally in several ways. However, by far the most common method uses the axial heat flow apparatus, based on the method described in ASTM E1225–09 in which the two cylinders of similar or dissimilar materials are placed end to end as illustrated in Fig. 1.​2 (Chap.​ 1). There have been other apparatus built for specific needs, for example, to determine the contact conductance in duplex tubes when the heat flow is radial; in periodic contacts and in manufacturing processes. Also used frequently are transient heat flow measurements to establish thermal contact properties. The relative merits of steady state and transient methods are also discussed in this chapter.
C. V. Madhusudana
Chapter 6. Special Configurations and Processes
Abstract
In this chapter we will consider configurations other than simple plane joints and unique characteristics associated with them. In particular we will discuss in some detail contact conductance in bolted joints and cylindrical joints. This chapter also includes brief discussions on the role of thermal contact conductance in periodic contacts and in sliding friction.
C. V. Madhusudana
Chapter 7. Control of Thermal Contact Conductance Using Interstitial Materials and Coatings
Abstract
As noted in Chapter 1, the actual solid-to-solid contact area, in most mechanical joints, is only a small fraction of the apparent area. The voids between the actual contact spots are usually occupied by some conducting substance such as air. Other interstitial materials may be deliberately introduced to control, that is, either to enhance or to lessen, the TCC: examples include foils, powders, wire screens and epoxies. To enhance the conductance the bare metal surfaces may also be coated with metals of higher thermal conductivity by electroplating or vacuum deposition. Greases and other lubricants also provide alternative means of enhancing the TCC.
C. V. Madhusudana
Chapter 8. Major Applications
Abstract
In this chapter some major applications in which contact conductance plays a significant role will be discussed in detail. These applications include finned tube heat exchangers, a variety of manufacturing processes and heat transfer in stationary packed beds. The topics are chosen on the basis of their contemporary interest, practical significance and extensive information available in each category.
C. V. Madhusudana
Chapter 9. Additional Topics
Abstract
In this chapter are included several areas where thermal contact conductance is important, but each area does not fit into any of the categories of previous chapters. The topics included are, contact heat transfer at low temperatures, heat transfer across stacks of laminations, effect of oxide films, specific materials including non-metallic materials. The effect of heat flow direction on the joint conductance is also considered to see under what conditions rectification can exist. The effect of loading cycles on a joint is reviewed to determine the extent of hysteresis and its practical application.
C. V. Madhusudana
Chapter 10. Concluding Remarks
Abstract
Having discussed the influence of various parameters, surface configurations and types of thermal and mechanical loading, it is now possible to review the means by which the TCC (or TCR) can be controlled to suit a given practical application. The first section of the present chapter summarizes the possible methods of control; for more specific details, reference may be made to the relevant sections in the earlier chapters.
C. V. Madhusudana
Erratum to: Control of Thermal Contact Conductance Using Interstitial Materials and Coatings
C. V. Madhusudana
Backmatter
Metadata
Title
Thermal Contact Conductance
Author
Chakravarti V. Madhusudana
Copyright Year
2014
Electronic ISBN
978-3-319-01276-6
Print ISBN
978-3-319-01275-9
DOI
https://doi.org/10.1007/978-3-319-01276-6

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