CFD Study for Steam Flows Downstream From Turbine Bypass Pipe Flow

Abstract

The main goal of this study is to investigate the evaporation process of a coolant (water droplets) which is injected through spray nozzles mounted on a steam turbine bypass pipeline in a co-generator system. The study includes several important factors: (1) the effects of four elbows on the flow pattern and evaporation process of the water particles, (2) heat transfer that affects the steam temperature and also the evaporation rates, and (3) the effects of inserting a perforated plate on the flow pattern and evaporation process. The first goal of this study is to investigate whether or not the existence of elbows in the pipeline will enhance the evaporation process of water droplets. Two effects have been observed so far. One is that the generation of turbulence increases in the core of the elbow which results in a higher heat transfer rate between particles and steam and the other is that particles are forced to impinge onto the outer side of the pipe wall in the elbow due to the centrifugal inertia force of the flow in the curvature path. The second goal is to carefully study the heat transfer effects of three different modes; i.e., the heat exchange between the steam and the water particles, the heat transfer of flow to the wall due to turbulence convection, and the conjugate heat transfer by means of heat conduction through the pipe wall and insulation materials. The last goal of the research is to investigate the effect of the insertion of a perforated plate downstream from the cooling water spray nozzles. A detailed analysis was conducted by microscopically modeling the flow through each hole of the perforated plate. Modeling of the high-pressure turbulent steam flow was based on a non-staggered finite volume method in three-dimensional, turbulent, compressible, two-phase dispersed flow formulations. The investigation of the structure of liquid spray jets during the transition into the gaseous phase was accomplished by developing a physical model of a particle tracking technique to investigate evaporation processes of the liquid droplets in a highly turbulent flow. Computations were performed by separating the entire pipeline system into four sections, each of which was generated in a three-dimensional grid system for more efficient computations by maintaining a sufficiently large number of meshes for each section. Flow calculations were made in each region separately by patching the end conditions from one pipe to the inlet conditions of the next one. Through this research, numerous data have been acquired and analyzed for heat transfer mechanisms of the cooling water droplets in the pipeline system. The results of the computations were verified by comparing them with theoretical models, and were shown to be quite reliable.