Performance assessment of a shell and helically coiled tube heat exchanger with variable orientations utilizing different nanofluids

Abstract

In the present study, the effect of the inclination angle (ɵ) of a shell and helically coiled tube heat exchanger (SHCT-HE) on its performance utilizing based water, Al2O3/water, and SiO2/water nanofluids is investigated experimentally. The hot based water as well as nanofluids with volume concentrations (ϕ) of 0.1 vol%, 0.2 vol%, and 0.3 vol% flow through the coiled tube with a coil Reynolds number (Rec) varied from 6000 to 15000. The inclination angle is measured from the horizontal axis of the SHCT-HE as 0°, 30°, 60°, and 90°. The results indicate that increasing the inclination angle enhances the coil Nusselt number (Nuc) and the effectiveness of SHCT-HE (ε); while, it decreases the coil pressure drop (ΔPc). Where, at coil Reynolds number of 15000, changing the orientation of the SHCT-HE from the horizontal to the vertical orientation improves the coil Nusselt number by 11%, 8.3%, and 7.5% for based water, Al2O3/water, and SiO2/water nanofluids with 0.1 vol%, respectively. Furthermore, at vertical orientation of heat exchanger and coil Reynolds number of 6000, utilizing Al2O3/water nanofluid with 0.1 vol% intensifies significantly the coil Nusselt number and the effectiveness than those for the based water by 35.7% and 35.5%, respectively. In addition, increasing the inclination angle up to 30° keeping the performance evaluation criterion (PEC) almost constant and more elevating into the vertical orientation decreases the PEC. Using multiple regression analysis, empirical correlations are proposed to estimate the coil Nusselt number (Nuc) for based water, Al2O3/water, and SiO2/water nanofluids as a function of Rec,θ,andϕ.