Numerical prediction of turbulent flow and heat transfer in helically coiled pipes

Computational results were obtained for turbulent flow and heat transfer in curved pipes, representative of helically coiled heat exchangers. Following a grid refinement study, grid independent predictions from alternative turbulence models (k-ɛ, SST k-ω and RSM-ω) were compared with DNS results and experimental pressure drop and heat transfer data. Using the SST k-ω and RSM-ω models, pressure drop results were in excellent agreement with literature data and the Ito correlation. For heat transfer, the literature is not comparably complete or accurate, but a satisfactory agreement was obtained in the range of available data. Unsatisfactory results, both for pressure drop and heat transfer, were given by the k-ɛ model with wall functions. Following the validation study, the RSM-ω model was used to compute friction coefficients and Nusselt numbers in the range Re = 1.4·104-8·104, Pr = 0.7-5.6 and δ (coil curvature) = 3·10−3-0.3. Power-law correlations were found unsuitable to fit the Re-, Pr- and δ-dependence of the Nusselt number, while the use of a properly formulated momentum-heat transfer analogy collapsed all results with high accuracy.