T-junction experiments to investigate thermal-mixing pipe flow with combined measurement techniques

Abstract

In context with thermal fatigue of T-junction pipelines caused by thermal mixing of flows, experiments are carried out at the Fluid-Structure-Interaction (FSI) test facility at the University of Stuttgart with a horizontal T-junction, in which a cold water flow (20° C) in the branch pipe (DN40) and a hot water flow (max. 280° C) in the main pipe (DN80) are mixed at pressure up to 75 bar. The focus of present investigation is on the flow mixing behavior close to the T-junction with presence of a weld root model inside the pipe, which is representing a typical pipeline weld connection with internal circumferential weld root.In this work, the experimental investigation is performed with multiple measurement techniques. Temperature measurement in the mixing region and inlet flow is performed with micro-thermocouple technique. The Near-Wall LED Induced Fluorescence (NW-LED-IF) method is applied to investigate the influence of the rimmed weld root in the mixing region. Due to the operation safety, the experiments are performed with 30 bar. The experiments are conducted with different flow temperatures in the main pipe line of 150 °C, 120 °C and 90 °C. The experiments are performed with periodical and continuous mixing processes. This paper presents the results of the experiments with two different measurement techniques. Fatigue assessment for the piping materials in the mixing region is discussed according to the thermocouple measurements. The impact of the rimmed weld root on the nearby flow field is shown in the NW-LED-IF measurement. The results show mixing behavior in the T-junction can be changed with temperature difference in the inlet flow and the rimmed weld root can increase the possibility of thermal fatigue damage significantly.