Thermo-Hydraulic Investigation of Nanofluid as a Coolant in VVER-440 Fuel Rod Bundle

The main purpose of this study is to perform numerical simulation of nanofluids as the coolant in VVER-440 fuel rod bundle. The fuel rod bundle contains 60 fuel rods with length of 960 mm and 4 spacer grids. In VVER-440 fuel rod bundle the coolant fluid (water) is in high pressure and temperature condition. In the present Thermo-hydraulic simulation, water-AL2O3 nanofluids containing various volume fractions of AL2O3 nanoparticles are investigated. Calculations performed for Reynolds number of 125000 to 203000, nanoparticles fraction of 0 to 0.05 and nanoparticles diameter of 20 to 100 nm. In this literature, the effects of diameter and volume fraction of nanoparticles on thermo-hydraulic parameters are studied. To perform correct calculation, different grid qualities of fuel rod bundle are studied and results are compared with reference results. Empirical studies show that as the temperature rises, the effect of nanoparticles on enhancing thermal conductivity intensifies. So it can be said that as the VVER-440 fuel rod bundle works in high temperature condition, using the nanofluids in this rod bundle can be effective. Results of our numerical study showed that by using nanofluids as coolant fluid the heat transfer coefficient increases significantly and heat transfer enhancement raises with increase in volume fraction of nanoparticle

Analytical approach for solving two-dimensional laminar viscous flow between slowly expanding and contracting walls

In this article, an analysis has been performed to study the two dimensional viscous flow between slowly expanding and contracting walls with weak permeability. The governing equations for the base fluid of this problem are described by dimensionless parameters wall dilation rate (α) and permeation Reynolds number (Re). The nonlinear differential equation is solved using two different analytically approaches by Homotopy Analysis Method (HAM) and Homotopy Perturbation Method (HPM). Then, the results are compared with numerical solution by fourth order Runge–Kutta–Fehlberg technique. Furthermore, the effects of dimensionless parameters on the velocity distributions are investigated in this research. As an important outcome, it is observed that, great agreement was found between the obtained results from the analytical and the numerical models

Variational iteration method for flow of non-Newtonian fluid on a moving belt and in a collector

In this paper, the thin film of a non-Newtonian fluid namely, a Sisko fluid on a vertical moving belt and this fluid in a collector is investigated. Sisko fluid’s behavior is expressed by non-linear equation. At the first problem, we consider a container having a non-Newtonian fluid in it. A wide moving belt passes through this container and moves vertically upward with constant velocity. The graphical representation of the velocity v against the horizontal distance x shows that the velocity increases as the non-Newtonian effect increases. Physics of the second problem includes a moving flat plate with constant velocity. The flat plate is cooled with a kind of oil through which its properties follow the Sisko fluid model. We obtain the velocity gradient with difference values of b and k coefficient, in Collector. By the use of velocity gradient, the pressure gradient can be predicted. Predicting the pressure can help to analyze the extra stresses in the collector. The variational iteration method (VIM) is used to solve this non-linear equation analytically. Comparison of the result obtained by the present method with numerical solution shows the accuracy, reliable and fast convergence of this method for nonlinear problems