Validated heattransfer and pressuredrop prediction methods based on the discreteelement method. Phase 2: Twodimensional rib roughness
Abstract
Surface roughness is a commonly used approach for enhancing the rate of heat transfer of surfaces, such as in heatexchanger tubes. Because the improved thermal performance of roughened surfaces is at the expense of increased flow resistance (increased pressure drop or friction factor), accurate prediction techniques for determining the friction factors and Nusselt numbers for roughened surfaces are required if such features are to be considered as design options. This report presents the results of the second phase of a research program sponsored by Argonne National Laboratory to validate models for the prediction of friction factors and Nusselt numbers for fully developed turbulent flow in enhanced heatexchanger tubes. The first phase was concerned with validating a roughness model for turbulent flow in tubes internally roughened with threedimensional distributed roughness elements, such as sandgrains, spheres, hemispheres, and cones. The second phase is concerned with devising and validating methods for the prediction of friction factors and Nusselt numbers for turbulent flow in tubes internally roughened with repeated, twodimensional ribs aligned perpendicular to the flow. The ribs are spaced sufficiently far apart that the leewardside separated flow reattaches to the wall before again separating in order to negotiate the next rib. This heattransfer enhancement mechanism is called the separation and reattachment mechanism, after Rabas (1989). This work is limited to rectangular rib shapes.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 May 1993
 Bibcode:
 1993STIN...9426763J
 Keywords:

 Flow Resistance;
 Friction Factor;
 Heat Exchangers;
 Heat Transfer;
 Nusselt Number;
 Surface Roughness;
 Turbulent Flow;
 Pipes (Tubes);
 Prediction Analysis Techniques;
 Ribs (Supports);
 Separated Flow;
 Temperature Effects;
 Fluid Mechanics and Heat Transfer