A three-dimensional numerical study was carried out to investigate effects of fin angle

fin length

and tube wall temperature in natural convection on heat transfer enhancement for a longitudinal externally-finned tube placed vertically in a closed space.The numerical results show that the heat transfer rate per unit mass increases with fin length.The maximum heat transfer rate per unit mass occurs when the fin angle is about 60° for all the fin angles investigated.With increasing tube wall temperature

the maximum ratio of the natural convection occurs in the temperature range studied.In order to consider the effect of fin angle on heat transfer enhancement

the dimensionless factor d/H is introduced.The natural convection heat transfer criterion of longitudinal externally-finned tube in vertical is fitted based on 65 computational cases and the mean error is 3.53% between the criterion and simulations.