Numerical design and heat transfer analysis of a non-Newtonian fluid flow for annulus with helical fins

Abstract

In this research, the flow and thermal characteristics of a non-Newtonian fluid flowing through a double pipe heat exchanger with helical fins around the inner tube were studied numerically. The non-Newtonian power law fluid is flowing in the laminar steady state through the annulus side. A 3D-CFD computational model has been conducted to determine the mean heat transfer coefficients and pressure lost in the annulus with constant temperature tube walls. A numerical analysis is performed for different values of Graetz number of (23 × 103 ≤ Gz ≤ 55 × 103) and fin pitch (25 mm ≤ p ≤ 100 mm). The model was validated for a smooth double pipe heat exchanger, and it's found a good agreement with empirical correlations. The use of helical fin established rotationally flow with vortex core, which enhances the heat transfer and pressure drop simultaneously. In addition, thermal performance was enhanced by the increase of fin pitch. By data reduction, valuable and applicable correlations for Nu and f are presented, which can be used in industrial designs of double pipe heat exchangers.