Investigation of hydrothermal performance and irreversibility production rate of ferrosoferric oxide/water nanofluid in corrugated-converging pipes with varying geometry parameters

In this study, hydrothermal performance and irreversibility production rate in ferrosoferric oxide (Fe₃O₄)/water nanofluid flowing in corrugated-converging pipes (CCPs) in turbulent flow regime have been examined. The ferrosoferric oxide (Fe₃O₄)/water nanofluid is modeled using discrete phase and $k-\omega$ turbulent models in Ansys Fluent. The impact of various factors on the Poiseuille number $\left(fRe\right)$, average Nusselt number $\left(Nu\right)$, performance evaluation criterion $\left(PEC\right)$, and irreversibility production rate are thoroughly examined. These factors include corrugation profiles (rectangular, trapezoidal, and spherical), Reynolds number $\left(5.0\times {10}^3\le Re\le 3.0\times {10}^4\right)$, normalized amplitude of corrugation ($0.025\le \frac{e}{D}\le 0.035)$, normalized width of corrugation ($0.2\le \frac{w}{D}\le 0.4)$, convergence diameter ratio (1.0 ≤ DR ≤ 2.0), and nanoparticles concentration (0.0 % ≤ VR ≤ 2.0 %). The findings revealed that the $Nu$ in CCPs is higher than that of smooth pipes, albeit at the expense of increased $fRe$. For instance, at $Re={10}^4$, $VR=1\%,DR=2.0,\frac{e}{D}=0.025,and\frac{w}{D}=0.4$, the values of $Nu$ and $fRe$ for rectangular, trapezoidal, and spherical CCPs and smooth straight pipe, which serves as the reference pipe (RP), are {156.96, 153.34, 137.00, and 103.35} and {13938.44, 11335.35, 7537.07, and 551.71}, respectively. In addition, it was found that, when compared to RP, the average volumetric entropy production rate due to the temperature gradient $⟨S_{th}^{‴}⟩$ in modified pipes was lower. Furthermore, an increase in certain geometric parameters (DR and $\frac{e}{D}$) increased $Nu$, $fRe$, and the viscous volume-average entropy production rate $⟨S_{visc}^{‴}⟩$. However, the opposite was observed for $\frac{w}{D}$. Thus, from an energy-saving perspective, CCPs can be suggested as a promising heat transfer enhancement method, especially the trapezoidal CCP.