Numerical heat transfer and turbulent flow in a circular tube fitted with curvilinear converging rings

In this study; heat transfer,friction factor and thermal performance factor characteristics are numerically investigated in a plain tube inserted the curvilinear converging rings (ccrs). three different pitch ratios are considered as p/d = 1,2 and 3. the study is conducted in the range of reynolds number 5000 -20000. air is accepted as the working fluid (pr=0.7). the governing equations are solved using the simple algorithm and standard k-ε turbulence model with fluent 6.1.22 programme. to validate the applied numerical method,the results obtained from the plain tube with ccrs are compared with the empirical results presented in literature. the values of nusselt number,friction factor and thermal performance factor for the plain tube with ccrs are presented depending on reynolds number and pitch ratios studied. the thermal performance results for the studied cases are also compared with results given in previous studies related to the conical rings. consequently,the average nusselt number and friction factor for all the pitch ratios are found to be about 68- 109 % and 412-635 % over the plain tube at the same pumping power,respectively. the best enhancement of 7.5 % was obtained for re = 5000 and p/d = 1. the cases of p/d = 2 and 3 are thermodynamically advantageous only for re<10000. © 2013 tibtd printed in turkey.