Computational fluid dynamics (cfd) analysis of the core of motel facility

Abstract

The aim of this thesis is to perform Computational Fluid Dynamics (CFD) analysis of the core of the Modular Test Loop (MOTEL) facility designed and built in Lappeenranta–Lahti University of Technology LUT using the simulation software ANSYS Fluent. Even though the power distribution in the core of the MOTEL facility is five-stepped cosine, for this study flat and cosine power distributions are also simulated to compare different parameters e.g., temperature, density, velocity with the existing five-stepped cosine power distribution. Two meshes were created for demonstrating the effect of mesh density. Two vertical planes are created in the middle of the modelled geometry to take temperature and velocity contours and analyse the way they change while flowing from inlet to outlet. Four lines are created adjacent to the four instrumentation rod walls and velocity, temperature and turbulence kinetic energy profiles are analysed along those lines. Better heat transfer is observed for cosine power distribution as the difference between the average and highest temperature is the least. The line adjacent to the instrumentation rod 1, which is near the centre of the core, shows least fluctuation in temperature, velocity, and turbulence kinetic energy profiles. When simulating the case for 990kW power and five-stepped cosine power distribution with both Shear Stress Transport (SST) and standard k-ϵ model, there were some differences between the result. This is due to the limitation of standard k-ϵ model in simulating near-wall boundary and capturing the transitions in natural circulations flows.