Computational fluid dynamics (CFD) technique to study the effects of helical wire inserts on heat transfer and pressure drop in a double pipe heat exchanger

In this communication, the computational fluid dynamics (CFD) technique has been employed to study the influence of coiled wire inserts on the Nusselt number, friction coefficient and overall efficiency in double pipe heat-exchangers. For this purpose, some wire coil inserts fitted inside heat-exchangers were meshed and simulated at various Reynolds numbers by using the CFD softwares of Gambit and Fluent. To fulfill reliable and validated results, a big effort was made to generate structural hexahedral meshes over all of the heat-exchanger geometries. The validated models, then, made clear the object and the conditions which could exactly facilitate heat transfer throughout double pipe heat-exchangers. The outcome of this work indicates that taking the advantage of proper wire coils could improve the Nusselt values to 1.77 times. Following the numerical simulation, proper friction coefficient and Nusselt number correlations for various coiled wire inserts with different geometry arrangements under the laminar flow were proposed. Unlike the preceding relations, the correlations of this work are based on the occupied spaces where helical wires take up inside tubes; therefore, the two modified correlations can both be used for non-uniform helical wire insert geometries. (c) 2017 Elsevier Ltd. All rights reserved.