Experimental and numerical investigations were carried out to study heat transfer and friction in flow through spirally fluted tubes. The experimental program consisted of flow visualization, isothermal pressure drop and heat transfer tests in all the hydrodynamic regimes. The test matrix consisted of fourteen fluted tubes in order to achieve a broad range of variation in flute geometry. A numerical model was also developed to predict friction and heat transfer in spirally fluted tubes.;Flow patterns and transitions between flow regimes were identified with the help of flow visualization tests. The flow inside the fluted tube was found to be rotational and the rotational angle of the core flow depended on the flute parameters and Reynolds number. Friction factor enhancements were typically found between 1 and 3 in all the flow regimes. Friction factor were correlated in two regimes that took into consideration the observed trends in friction factor. The laminar friction correlation (100 ;The numerical model divided the flow domain into two regions. The flutes were modeled as a porous substrate with directional dependent permeabilities. This enabled modeling the swirl component in the fluted tube. The properties of the porous substrate such as its thickness, porosity and ratio of the direction dependent permeabilities were obtained from the geometry of the fluted tube. Experimental data from three of the tubes tested were used to propose a relationship between the permeability of the porous substrate and the flute parameters, particularly the flute spacing. The governing equations were discretized using the Finite Element Method. The model was verified and applied to other tubes in the test matrix. Excellent agreement was found between the numerical predictions and the experimental data.
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