Transitional flow inside enhanced tubes for fully developed and developing flow with different types of inlet disturbances: Part II-heat transfer

Due to efficiency demands, augmented tubes are often used in heat exchangers with the result that many heat exchangers operate in the transitional region of flow. Due to the paucity of data, however, no data exists for enhanced tubes in this region. This article, being the second of a two-part paper (Part I investigating adiabatic flow), presents experimental heat transfer and diabatic friction factor data for four horizontal enhanced tubes for fully developed and developing flow in the transition region with four different types of inlet geometries. Smooth tube data was used for comparison. It was found that, unlike results obtained for adiabatic flow in Part I, inlet disturbances had no effect on the critical Reynolds numbers, with transition occurring at a Reynolds number of approximately 2000 and ending at 3000. Correlations were developed to predict the heat transfer and friction factors for a wide range of flow regimes, from laminar to turbulent flow. The correlations predicted the heat transfer data on average with a mean absolute error of 9.5%, predicting 85% of the data to within 15%. The friction factor correlations predicted the data with a mean absolute error of 5.5%, predicting 96% of the data to within 20%.