Development of friction model for offset strip fin with separated viscous and inertial resistances

To predict the flow resistance of a compact heat exchanger with an offset strip fin, a large number of correlations have been developed and these correlations have been well used in the engineering field. Recently, three-dimensional computational analysis has been frequently used for the design and verification of heat exchangers. To improve the accuracy of three-dimensional numerical analysis and reduce the resources used for the analysis, the fins of compact heat exchangers are assumed to be a porous medium generally. To predict the flow resistance of an offset strip fin assumed to be a porous medium, the resistance must be separated into viscous and inertial resistances. However, the correlations developed so far for the offset strip fin have not been able to distinguish between these resistance types. In this paper, we propose a new friction model that can represent the flow resistance of an offset strip fin as the sum of the viscous and inertial resistances. The new friction correlation model has a maximum error of 10 % compared to existing correlation models. In addition, using the new friction model, the permeability and the Ergun constant for offset strip fins are defined as functions of offset strip fin parameters. Therefore, when predicting the flow resistance of a compact heat exchanger with an offset strip fin using three-dimensional numerical analysis, viscous and inertial resistances can be defined without additional calculations or tests for a porous medium approach.