Flow Analysis in a Steam Turbine Control Valve With Through-Flow Valve Chamber

Abstract

A nuclear power plant also includes a secondary cycle, which main component is a steam turbine. The steam turbine processes the thermal and pressure energy of steam and converts it into mechanical energy. Reliable and safe operation of the steam turbine, thus of the entire block, is ensured by valves. The flow in a pair of control valves, where the steam flows through the valve chamber past the first valve to the second valve, is investigated in this paper. The experimentally determined flow characteristics of both valves were evaluated and results were generalized. The experiments were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in Novy Knin where a wind tunnel for high speeds could be used. Data of the distribution of pressures in selected places were evaluated. The energy loss in the valves was compared with the loss in a separate diffuser with varying degrees of expansion. The influence of a valve strainer, which is a part situated upstream of the control valve cone, was also investigated. It was found out in which case and where there is a significant disturbance of the velocity flow field. The first valve in the chamber is more sensitive to pressure losses in contrast to the second valve which is comparable to an ideal design of the diffuser, which indicates that this part of the valve assembly is optimal. Regarding the strainers, it was found out that the strainer helps to balance the velocity ratios at the inlet to the valve which has a positive effect on reducing the total energy pressure loss. As a result, the loss in the first valve can be significantly reduced which helps to increase the efficiency of the whole turbine.