Investigation of the entropy production rate of ferrosoferric oxide/water nanofluid in outward corrugated pipes using a two-phase mixture model

Abstract

This study investigates the turbulent entropy production rate of ferrosoferric oxide/water (Fe3O4/H2O) nanofluid flowing through outward corrugated pipes of different profiles (circular, triangular, and trapezoidal). Both the multi-phase mixture model and the k−ω turbulent model were adopted for simulating the turbulent ferrofluid flow. The effects of Reynolds number (between 5.0 × 103 and 3.0 × 104) and nanoparticle concentration (0.0–3.0%) on viscous entropy production rates (due to mean and turbulent velocity gradients) and thermal entropy production rates (due to mean and turbulent temperature gradient) were examined parametrically. The results show that trapezoidally corrugated pipes tend to have the best heat transfer performance, but also the worst hydraulic performance, where they increase the pressure drop and the average Nusselt number by 2.92 and 1.66 folds, respectively, for a 2.0% nanoparticles’ concentration at Reynolds number of 3.0 × 104. Increasing the concentration of nanoparticles from 0.0 to 3.0% has the same effect, where the two quantities increase by 1.31 and 1.07, respectively, for a triangularly corrugated pipe at a Reynolds number of 1.5×104. The mean temperature gradient contributes most to the thermal entropy production rate, compared to the turbulent temperature gradient. However, the opposite is the case for the viscous entropy production rate. Furthermore, the presence of corrugation was found to increase the viscous entropy production rate but reduce the thermal entropy production rate. The normalized thermal and viscous entropy production rates (referencing a smooth pipe) in circularly, triangularly, and trapezoidally corrugated pipes are {0.81, 0.75}, {0.56,3.38}, and {3.29,3.45}, respectively. It is also noticed that the Bejan number decreases as the Reynolds number increases by 51.4, 81.4, 82.2, and 87.6% for smooth, circularly corrugated, triangularly corrugated, and trapezoidally corrugated pipes, respectively.