9) Thermal contact resistance
Due to the absence of atmosphere in satellite orbits, the heat transfer mechanisms on a
satellite are, exclusively, conduction and radiation. Conduction is the main heat transfer
mechanism. Since the satellite has a large number of devices attached on a metallic structure,
it is necessary to predict precisely the heat conduction paths through the various interfaces
and devices. Such interfaces result in the thermal contact resistance. Thermal contact
resistance occurs due to the microscopic rugosity of the contacting surfaces. When two
non-flat surfaces are brought into contact, only a few discrete asperities actually touch each
other, which results in a large void space between the contacting surfaces.
Such void spaces make heat transfer difficult. The heat flow must come around empty spaces and
cross the interface through the discrete asperity contact points, as shown in the illustration
below. In a macroscopic view, such phenomena can be observed through a sudden temperature drop
in the contact area. The study of thermal contact resistance has the objective of controlling
surfaces, materials, and contact pressures so that heat transfer across the interface is within
acceptable levels.
One of the most important parameters that affect the thermal contact resistance is the interface
pressure distribution. If it is uniform, the problem is relatively straightforward. However, if
it is not uniform, like in bolted joints, the task is more complex. The existing theory on rough
solids in contact is not capable of predicting the pressure distribuition accuratelly. In this
case, LABTUCAL is developing an experimental study on teh contact pressure distribution using
pressure sensitive films. The film is placed between the contacting surfaces. After unloading,
a color densidty distribution appears on the film, whcih is proportional to the pressure
distribution. The color density is then correlated to the pressure distribution using the
Weibull distribution.
Publications:
PEREIRA, E.; MANTELLI, M. B. H.; MILANEZ, F.; FLETCHER, L. Statistical Model for Pressure Distribution of a Bolted Joint. In: 40th Thermophysics Conference, Seattle, Washington, June 23-26, 2008.
MILANEZ, F. H.; YOVANOVICH, M. M.; MANTELLI, M. B. H. Thermal Contact Conductance at Low Contact Pressures. Journal of Thermophysics and Heat Transfer, v. 18, n. 1,p. 37-44, 2004.
MILANEZ, F. H.; YOVANOVICH, M. M.; CULHAM, J R. Effect of Surface Asperity Truncation on Thermal Contact Conductance. IEEE Transactions on Components and Packaging Technologies, New York, v. 26, n. 1, p. 48-54, 2003.
MILANEZ, F. H.; CULHAM, J R; YOVANOVICH, M. M. Experimental Study on Thermal Contact Conductance of Bead Blasted SS 304 at Light Loads. Journal of Thermophysics and Heat Transfer, Reston, Virginia, USA, 2003.
MILANEZ, F. H.; YOVANOVICH, M. M.; CULHAM, J R. Comparisons between Plastic Contact Hardness Models and Experiments. 41th AIAA Aerospace Sciences Meeting and Exhibit, 2003, Reno, NV. 2003.
MILANEZ, F. H.; YOVANOVICH, M. M; MANTELLI, M. B H. Thermal Contact Conductance at Low Contact Pressures. 36th AIAA Thermopsysics Conference, Orlando, 2003.
MILANEZ, F. H.; MANTELLI, M. B. H. Theoretical and Experimental Studies of a Bi-metallic Heat Switch for Space Applications. International Journal of Heat and Mass Transfer. ELSEVIER, p. 4573-4586, 2003.
