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Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger.Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12π.As the varying radius of curvature became a dominant flow parameter,three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field.From the analysis,centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer.The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube.Even then,friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number.Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.