Stress Distribution and Stress Reduction in Copper/Brass Radiators

This paper presents quantitative information on stress in copper/brass radiators. Strain gages were used to measure the stresses in the unsupported tubes near the header, and to determine thermal stress resulting from uneven expansion of the tubes and the side support bar. Strain measurements were performed on plain and ribbed “turbulator” tubes. The compressive strength of various fin arrays was also measured. An analytical model was developed to predict the compressive strength of the fin array as a function of the fin geometry parameters. A finite element stress analysis model was used to predict the stress in the tubes and in the tube/header solder joint. The predicted values agree well with the measured stress. Mechanical design changes, intended to affect reduced stress, were evaluated using the finite element model. Reduction of the unsupported tube length near the header, and use of rounded tube ends are shown to provide a significant stress reduction in the tube/header solder joint. Use of turbulator tubes will reduce the tensile peeling stress on the fin/tube solder joint.