In this paper a vertical downward flow map and a vertical upward flow map are presented. A comparison of the two flow maps shows that significant differences exist between the two directions of flow. The experimental work was performed with an air-water flow in a 11/2-in inside diameter transparent tube.

The present work examines theoretically the influence of surface coatings on the temperatures produced by friction due to sliding contact. A generalized thermal model is developed which incorporates three-dimensional, transient heat transfer between layered media with thermal coupling at multiple, interacting contact patches. A solution technique based on a variation of the boundary element method is developed and utilized. The method allows for the solution of the distribution of frictional heat and the resulting temperature rise in an accurate yet numerically efficient manner. Results are presented showing the influence of film thickness, thermal properties, velocity, and contact area on the division of heat and surface temperature rise. The results show that a film with thermal properties different than those of the substrate can have a pronounced effect on the predicted temperature rise.

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It is possible but quite challenging to include thermoelastic effects. As the materials heat up, the original contacting areas should change which in turn should influence surface temperature. More realistic thermomechanical modeling would make a large impact and we plan on developing this in our future research. 2. Temperature dependent properties can be included with the boundary element method using a technique called "dual reciprocity." 3. Some of the computational issues, including the effect of mesh size and time step, have been examined in the paper by Vick and Golan (1991). The numerical evaluation of the influence coefficients and the sensitivity of the solution to these influence coefficients was also examined. However, a direct comparison to other methods, particularly the finite element method, has not been performed and would be useful. The authors with to thank Professor Floquet for raising points on three extremely relevant issues concerning the paper.

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