Natural convection in vertical tube with axial grooves

An experimental investigation on natural convection of air in axially grooved vertical channels is carried out. Generally axially grooved tubes have higher heat transfer in comparison with round tubes. Averaged and local Nusselt number for 4 different axially grooved tubes is experimentally investigated. The tube dimensions are selected in the range of short cylinders to see the effect of entrance region on heat transfer increment. Averaged Nusselt numbers is proposed in a range of Rayleigh number from 1.07 *10° to 2.81*10 . The comparison between grooved tubes and round tubes shows 4.76% increment in averaged Nusselt number which depends on dimension of slots and Rayleigh number. Uncertainty of Nusselt number is about 16.22% in this study.