Effects of Injection Pipe Orientation on Mixing Behavior in Contributing to Thermal Fatigue in a T-junction of a Pipe

Abstract

Vincent Agbodemegbe, The thesis dealt with the temperature fluctuation in a T-junction with two fluid streams of different temperature. This phenomenon is of crucial importance in many engineering applications such as Nuclear Power Plants, because temperature fluctuation leads to thermal fatigue and subsequently might result in failure of structural material. In mixing areas of a Nuclear Power Plant where piping structure is exposed to unavoidable temperature differences in a bid to maintain plant operational capacity, the effects of the temperature difference on the piping structure at the mixing junctions cannot be neglected. Temperature fluctuation is tightly coupled with flow turbulence, which has attracted extensive attention and been investigated worldwide since several decades. The main target of this thesis is the investigation of the temperature fluctuation with the emphasis on the effect of the injection pipe orientation on the temperature fluctuation. The computational fluid dynamics (CFD) approach was applied using STAR CCM+ code. Due to the limitation in computing efforts, the RANS method was selected instead of LES or DNS method. Four inclination angles were selected. The mixing intensity and the size of the effective mixing zone were investigated. Smaller inclination angle (both injection pipes are perpendicular to each other, in case of zero degree inclination angle) led in one side to a larger turbulence intensity or mixing intensity, and subsequently to larger temperature fluctuation and on the other side the mixing zone is reduced. The simulated temperature fields are employed as thermal boundary conditions in heat transfer analyses of a pipe wall.

The findings gives useful data for the design of devices where attention needs to be paid to thermal fatigue.