Control of two-phase heat transfer and condensation loss in turbine blade cascade by injection water droplets

Abstract

The last few stages of a condensing steam turbine of fossil fuel power units and most stages of steam turbine in nuclear power units operate under wet steam conditions and the condensation phenomena as well as two-phase flow are crucial for efficiency of turbine stages. In this work, the water spray injection ahead of the vanes was used to control the two-phase heat transfer. Five cases of droplets injection with constant radius were considered to study the problem comprehensively. The results show that the injection of the droplets affects flow conditions and two-phase structure. These parameters can also be controlled by increasing or decreasing the number of injected droplets. The conclusions are that with the increase of the number of injected droplets the heat transfer process at the blade cascade inlet increases, whereas at the vicinity of the oblique shock the heat transfer weakens. When the radius and number of injected droplets are 57 nm and 2.5×10151/kg, respectively, the overall heat transfer and the condensation loss are reduced by about 40% and 25%, respectively. The conclusions from this work can provide scientific references for wetness loss control in steam turbine.