A CFD BASED THERMO-HYDRAULIC PERFORMANCE ANALYSIS IN A TUBE FITTED WITH STEPPED CONICAL NOZZLE TURBULATORS

The paper presents a numerical analysis of heat transfer and friction characteristics in a stepped nozzle inserted tube. Nine different configurations are used for numerical analysis. In the first part of study, to certify the Nu (average Nusselt number) and the f (average friction factor), the computational fluid dynamics (CFD) models of tube with conical nozzle turbulators are validated with the experimental results available in the literature. In the present work, the turbulators are thoroughly inserted in the tube three different pitch ratios, with various Reynolds numbers ranging from 6000 to 22000, and also with three step numbers. The investigations were carried out with the RNG k-ε turbulence model in a CFD package program, after some different turbulence models were tried, and grid independency with three different grid models were analyzed, for the average Nusselt number, and the average friction factor. As a consequence, Nusselt number increases and friction factor decreases with increasing Reynolds number. The highest Nusselt number and friction factor is obtained for s/a=4, p/s=2 model. The overall enhancement ratio rises with decreasing spacing of the stepped conical nozzle and increasing step value. The ultimate overall enhancement of 11% was achieved for Re=6000 where the spacing and step ratios are 4, 2 respectively.