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INVESTIGATION OF TURBULENT FORCED CONVECTION IN HELICALLY GROOVED TUBES

DOI: 10.1615/ICHMT.2012.CHT-12.340
pages 559-574

Zoltan Hernadi
Budapest University of Technology and Economics

Lorand Romvari
Furukawa Electric Institute of Technology, Budapest, Hungary

Gergely Kristof
Dept. of Fluid Mechanics, Budapest University of Technology and Economics, Hungary

Gabor Varga
Dept. of Physics, Budapest University of Technology and Economics, Hungary

Abstract

Tubes with helically grooved inner surfaces are widely used in heat exchangers of refrigerators and air conditioners for their heat transfer performance and relatively low pressure drop compared to other heat transfer enhancement techniques. Although there are great databases of measurement data for some groove geometries, the empirical correlations based on these databases are often inaccurate for new groove patterns. Since manufacturing tubes with future groove geometries is too expensive, an accurate numerical model for the performance of non-existing groove geometries is of great importance. A CFD model based on wall-resolved Large Eddy Simulation of turbulent flow with heat transfer is proposed. Forced convection is considered as a single-phase incompressible flow with uniform outside wall heat flux. High temperature variations are beyond the scope of this investigation, therefore thermophysical parameters are assumed to be constants. In the simulation, fully developed conditions are assumed, therefore the describing equations are solved for streamwise periodic variables with consistent source terms in the heat and momentum transport equations. Geometry specification and meshing are carried out with own developed software utilizing parametric description of helically grooved tubes. Simulation results developed in OpenFOAM for Re = 6000 to 10000 are presented for smooth pipe and helically grooved tubes. The simulation methodology is validated by comparing the results with literature data for smooth pipes and with in-house measurements for helically grooved tubes. Difference from literature data is within 5% for friction factors and Nusselt numbers of smooth pipes. Difference from measured data is within 15% for the friction factors and 7% for the Nusselt numbers for helically grooved tubes. The proposed model is concluded to be accurately predictive.

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