Analysis of numerical and grey relation method of the effect of helical tape insert density on the hydrothermal performance

Abstract

In this study, the hydrothermal performance of the Double pipe heat exchangers(DPHEs) with a continuous and variable helical tape insert(HTI) conducted on the outer surface of the inner pipe was numerically investigated by using the generated three-dimensional(3D) computational fluid dynamics(CFD) models. The numerical analyzes were performed under variable pitch ratios (0.167≤λ≤0.500), annulus side Prandtl number(Pr) (5.9≤Pran≤7.8) and Reynolds numbers(Re) (4200≤Rean≤16000) conditions. The numerical model was first validated for the conventional equal HTI DPHE model by comparison with experimental data obtained from the literature and empirical correlations. The validated model was then used to determine the effects of the variable HTI on the outer surface of the inner pipe. The relationship between the Nusselt number(Nu) and Darcy friction factor(f) was examined by using Grey Relation Analysis(GRA) method. The using of the denser HTIs on the tube side inlet region increases Nu about 9% compared with the conventional model. The f values of the models with variable HTI densities were calculated as higher than the Equal model under all Re conditions. The obtained results from the GRA method, conventional Equal model can be used for low Re, but the Inlet model can be preferred for 14000 and above Re conditions.