Interface Thermal Contact Resistance Problem in Space Vehicles

Abstract

This paper defines and analyzes the thermal contact resistance problem as applied to unpressurized satellites and components. Pertinent experimental results are reviewed, and results of experimental work carried out by the authors are presented. A guarded hot plate thermal conductivity apparatus was operated in a chamber held at a pressure of 10 ~4 to 10 ~6 mm Hg absolute to determine the effects of surface finish, flatness, and contact conductance between aluminum-aluminum and magnesium-magnesium plates. Surface finishes from 6 to 65 Min. (rms) and contact pressures up to 35 psi, as well as heat transfer promoting shim materials, were considered. The test apparatus and procedure also are described.T HE PRESENT trend in the design of space vehicles and long life communication satellites is toward higher and higher power density to conserve vehicle size and weight. A great deal of progress has been made in the development of electronic and other equipment and its associated power system. However, with the higher power output, the inevitable inefficiency products in such equipment, which manifest themselves in the form of heat, have to be accepted. Therefore, in order to keep internal vehicle temperatures within acceptable limits, adequate heat flow paths from the heat sources within the vehicle to the vehicle skin, which is the last link with the ultimate heat sink, must be provided.In attaining the high reliability required of long life satellites, vehicle temperature control is one of the most important design problems. This in turn requires a relatively thorough analysis of all heat flow paths, which depends on a knowledge of the thermal contact resistance at relatively low average contact pressures for structural components between the heatsource and the vehicle skin. Furthermore, just to know the contact resistance for bare joints is not sufficient for a reliable design; how to increase or reduce these contact resistances to control the operating temperatures of critical components must also be known.In spite of this need for knowledge of the thermal contact resistance in such heat flow paths--which can consist of several The modes of heat transfer to be considered are: 1) solid conduction through the true contact area; 2) gaseous, molecular, or other conduction through the interstitial fluid or filler; and 3) thermal radiation. The thermal contact conductance is defined aswhere Ti and T 2 are the temperatures of the bounding surfaces of the contact gap (2). Similarly, the contact resistance, as this effect is sometimes called, is T t -T t £lc = T -where R c 1 1/R. + 1/R f + 1/Rr [lb][2] L Numbers in parentheses indicate References at end of paper. Fig. 1 Representative view of a metal to metal contact FEBRUARY 1962 237 Downloaded by UNIVERSITY OF OKLAHOMA on February 5, 2015 | http://arc.aiaa.org |

A numerical solution for lageos thermal thrust: The rapid-spin case

“…Fried and Costello (1962, Figure 9) show that the resulting contact conductance between aluminum surfaces in vacuum would be at least 310Wm -2 K -l. We estimate that the contact conductance is greater than this by a factor of at least 5 when one or both of the interface materials is the more deformable KEL-F plastic. (Evidence for its deformability is the flexure of the disassembled mounting rings under finger pressure.)…”

“…Fried and Costello (1962) give an excellent review of contact conductance in a vacuum, and its dependence on contact pressure. The contact conductance term arises because at low contact pressures, the two surfaces at a joint touch in only a few microscopic high spots, so the joint offers high resistance to heat flow.…”

Review of thermal conductance models for joints incorporating enhancement materials

“…Wire screens can be used to reduce or enhance the thermal performance of the joint. Fried and Costello 24 showed in some of their experiments that copper wire screens reduced the thermal contact conductance, whereas in other investigations, wire screens were shown to act as a means of thermal insulation for surfaces in contact. Gyorog 25 also con rmed the insulation performance of stainless steel and titaniumwire mesh screens.…”