Numerical and Experimental Study of Heat Transfer Characteristics with Centrally Cleared Two Twisted Tapes

Abstract

One of the key ways to enhance the heat transfer is use of twisted tape inserts. But along with the heat transfer it also increases pressure drop which results in increase in pumping power. So optimized tape design is required to achieve optimum cost. To get improved heat transfer coefficient with reasonable pressure drop two twisted tapes with center clearance is proposed. Effect of addition of two twisted tapes inside a tube at constant heat flux condition is reported in this paper. Results obtained for single twisted tape insert and two twisted tape inserts are compared analytically as well as numerically. Air is used as a test fluid. Study is carried out in turbulent region. Results are compared at Reynolds number 45,000 for no twisted tape, one twisted tape and two tapes. Results for two twisted tapes with twist ratios 3, 4, 5 are compared at Reynolds number 45,000. Heat transfer coefficient is improved as compared to plain tube and single tape by 2.2% to 10.1%. Optimum results are obtained at twist ratio 5.