Modified Wilson Plots for Enhanced Heat Transfer Experiments: Current Status and Future Perspectives

Abstract

Heat transfer coefficients for enhanced tubes are typically measured indirectly using the “Wilson plot” method to first characterize the thermal performance of the one side (heating or cooling supply) and then to obtain the heat transfer data for the enhanced side based on the Wilson plot results. A brief history of the Wilson plot evolution and alternative methods to the Wilson plot, including the advantages and disadvantages, are discussed as applied for enhanced heat transfer. A slight modification to the Briggs and Young (1969) method is proposed so that the experimental errors can be propagated through the method, allowing us to estimate the error in the generated correlations. Furthermore, a new method based on unconstrained minimization is proposed as an alternative to the least-squares regression. As an example, both methods have been applied to two enhanced boiling tubes (the most recent generation) and heat transfer coefficients were compared against direct wall temperature based heat transfer coefficient measurements made on the same tubes for water flow with high-performance internal helical ribs. Both the unconstrained minimization method and the modified Briggs and Young (1969) method performed well and predicted the same heat transfer performance within experimental uncertainty for two databases taken on two different experimental facilities. Furthermore, if the presently modified Wilson plot method is utilized, and the form of the correlating equation is chosen judiciously and is only applied within the range of experimental conditions tested, the results garnered from the analysis can very adequately predict the local heat transfer performance.

Acknowledgments

This project has been supported financially by the LTCM Falling Film Research Club members: Carrier Corporation, the Trane Company, Wieland-Werke AG, and Wolverine Tube, Inc., which is gratefully acknowledged. Special acknowledgment is made to Wieland-Werke AG and Wolverine Tube, Inc., for providing the tube samples for the tests.