Numerical investigation on heat transfer performance and flow characteristics in enhanced tube with dimples and protrusions

In the present investigation, a new design of enhanced tube aiming to improve heat transfer by employing dimples and protrusions was put forward. The special enhanced tube with dimples and protrusions is obtained by extruded the conventional plain tube. The objective is to present details of flow field characteristics and heat transfer mechanisms for the ETDP, then effects of protrusion depth, pitch and radius on thermal-hydraulic performance also being discussed. The operating Reynolds number ranged from 5000 to 30,000 and the validated realizable k-ε turbulence model was employed on the numerical simulations. The local streamlines, velocity contour, temperature contour and Nusselt number were presented to illustrate the heat transfer enhancement mechanisms. From this investigation, it is found that the varying geometric parameters of ETDP play an important role in thermal-hydraulic characterises. The main findings are that the ETDP have an advantage for augmented heat transfer rate and PEC compared with the plain tube, due to improved flow mixing, interrupted the boundary layer, formed periodic jet flows and swirl flows induced by dimples and protrusions. The Nusselt number and friction factor increase and PEC decrease with an increasing protrusion depth. Among the investigated different protrusion pitch, it is found that the friction factor first decrease and then increase with the increase of protrusion pitch. For varying the protrusion radius, the ETDP with R = 3 mm have the largest PEC at the most Re. Under operating condition and geometric parameters considered, the ETDP with D = 3 mm, P = 30 mm and R = 4 mm offers the largest PEC value of about 1.65.