An Evaluation of a Pressure Expansion Method for the Manufacturing of Copper Tube Heat Exchangers

The need for energy efficient, low cost, and reduced material solutions are encouraging HVAC&R engineers to explore new heat exchanger designs, including those using small diameter tubes and tubes with internal enhancements. Such developments thus require review and consideration for new and/or improved heat exchanger manufacturing techniques. Experimental and analytical study of a pressure expansion approach as compared to the more conventional mechanical expansion process was conducted to evaluate the impact of manufacturing method on heat exchanger performance. This included visual inspection and comparison of heat exchangers manufactured using pressure expansion and mechanical expansion, physical testing of heat exchanger strength and construction, measurement of heat exchanger dimensions, and physical testing of heat transfer performance. Multiple heat exchangers were constructed and evaluated using both the mechanical and pressure expansion methods. Consistency between coils was maintained in order to isolate the manufacturing method, to the extent possible, for comparison purposes. Visual inspection of compared coils and past research suggest that pressure expansion improves the contact between the expanded tube and the fin, providing the potential to improve heat transfer performance. Visual inspection also suggests that pressure expansion produces less deformation of any internal tube enhancements, maximizing the potential to improve heat transfer performance from the use of such tubes. Physical measurements of the tube expansion diameter throughout the construction of a heat exchanger expanded using the pressure expansion process proved that the pressure expansion method delivers a more consistent tube diameter. Air-side testing using water as refrigerant also confirmed that overall heat transfer performance for pressure expanded coils is, at minimum, consistent with that for mechanically expanded coils.