Parametric study of twisted tape insert on the heat transfer characteristics in a square tube under turbulent conditions

In the present study, the effect of inserting a twisted tape as a passive device for heat augmentation inside a square tube has been numerically studied under turbulent conditions. A twisted tape with constant pitch has been placed inside a square tube with negligible thickness and numerical simulation was done with Reynolds number (Re) of the fluid varying from 2,500 to 10,000. Heat transfer characteristics like Nusselt number and friction factor have been determined. Initially, the numerical results are validated by comparing with the empirical correlations for the bare tube under constant wall temperature boundary conditions. To study the parametric variation, simulation was conducted for different tape width ratios 0.4, 0.6 and 0.8. Thermo-Hydraulic Performance Index (THPI) was measured and was found to be higher for low Re and found to be reduced as Re increases. Similarly, as the width ratio increases, THPI reduces and optimum value obtained for a width ratio of 0.4. It was concluded that using a passive device like a twisted tape inside a square tube performs better than bare tube and also tape width has a significant influence on the thermohydraulic characteristics in a square heat exchanger.