3242 -- Measurement of Contact Resistance in Finned Tube Heat Exchangers PDF

Experiments were conducted to measure and evaluate contact resistance in mechanically finned tube heat exchangers with different expansion interferences, fin densities, and initial assembly clearances between the tube and fin collar. Five different test cores were tested in a vacuum environment. The measured contact resistances were compared using a thermal model, and the agreement with reported data is good. Higher contact conductances were predicted by the contact conductance model because the experimental contact conductances were based on full contact at the tube/fin interface. Test cores expanded by larger bullets or those with longer fin collars showed less contact resistances. The predicted contact pressure decreased with larger bullets. Estimation of the apparent contact area at the tube/fin interface was made by sectioning all test cores after the thermal experiments.