An Experimental and Numerical Investigation of Turbulent Variable Fluid Property Heat Transfer and Fluid Flow in Enhanced Tubes

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The proposed research will investigate both experimentally and numerically turbulent heat transfer and pressure drop in internally-finned tubes when there are large variable fluid property effects. The internally-finned tube geometry is ideal to test modeling capabilities because they are industrially relevant, have much surface area, have complex hydrodynamics due to the geometry, are amenable to numerical modeling, and are experimentally testable in a lab over a wide range of geometric and operating conditions. Ten internally-finned tubes are available for testing the experimental investigation; these tubes cover a wide range of geometric parameters. The tube will be tested in both heating and cooling over a range of wall-to-bulk temperature differences. The working fluids will be water, ethylene glycol, and mineral oil. In the numerical modeling, primary emphasis will be placed on development of appropriate near-wall modeling and accommodation of variable fluid properties. A newly developed anisotropic turbulence model, called the vorticity flux model, will be extended for use in this project and applied to both axially and spirally finned tubes where anisotropic turbulence is important. The numerical model will be validated by comparison against detailed local and overall data from the literature, and new overall data from this investigation. The validated model will fully describe the governing mechanisms for heat transfer and pressure drop in this geometry (particularly the effects of fin geometry and helix angle). It also will provide guidance on the incorporation of variable fluid properties in numerical models and with enhanced heat transfer techniques and suggest appropriate methods for the development of physically-based correlations for Nusselt numbers and friction factors.