Application of impermeable screens to stabilize the flow in the angle control valve

• Дата: 2016
• Автори: Бабаев, А. И., Голощапов, В. Н.
• Формат: Стаття
• Мова: Russian
• Опубліковано: Інститут енергетичних машин і систем ім. А. М. Підгорного Національної академії наук України 2016
• Теми: control valve; impermeable screen; steam turbine
• Онлайн доступ: https://journals.uran.ua/jme/article/view/86779
• Назва журналу: Energy Technologies & Resource Saving

Formation of vortex flow in the control valve is determined not only the transition to a separated flow of the valve channel formed by the valve seat and the plug, but the conditions of steam supply to it. Most modern designs of control valves has a one lateral inlet of steam. Therefore, when steam moves along the annular section of the steam chest, cross section of the channel is unchanged and mass flow is decreased. For this reason, a diffuser effect occurs in the stream. As a result, non-uniform velocity field is formed, promoting the formation of separated flow in the inlet section of the valve channel. The main goal of the present work was to investigate the possibility of improving the gas-dynamic characteristics of the control valve by installing an impermeable screen at the entrance to the steam chest. The object of investigation was adopted design of the control valve of the high pressure cylinder of turbine 200 MW. To investigate the effect of the installation of the impermeable screen to gas-dynamic flow characteristics has been developed a new design of the protective glass. The proposed glass, unlike to the original, has an impermeable sector, located opposite to the inlet, and the additional force racks located on the remainder of the circular sector. As a result, the calculation of three-dimensional flow in the valve is determined that the installation of the screen with length α = 30–60 ° leads to an increase in the efficiency of gas-dynamic of control valve. To skip the established steam consumption at nominal mode at the valve without the screen relative pressure drop was 3,3%, with the screen – 2,1–2,4%. This reduction in pressure drop is observed in the investigated range in all modes. Analysis of the results showed a large loss of energy in the original model of the valve caused, first of all, flow separation in the valve channel. This flow separation from the surface of the valve seat profile observed in all investigated modes. The formation reverse flow negative impact on the reducing ability of the diffuser. In the variant of the control valve with the screen design provides greater uniformity of flow in the inlet of the valve channel. When steam stream around the screen is its redistributed. As a result, in the throat cross section of the saddle there is a more uniform velocity field and there is no separating  jet in the streamlined wall. With these conditions it is possible to significantly increase reducing the ability of the diffuser. In conclusion, the work points out that the installation of impermeable screen with length of 30 ° ...60 ° with forcer racks leads to increased gas-dynamic efficiency of control valve due to the formation of the more uniform flow at the inlet of the valve channel. The increase losses, when the steam flows around the screen and power racks, compensated by a significant increase in regenerative ability of the diffuser. As a result, energy loss ratio in the diffuser and pressure drop desired of the model for the control valve are reduced by 50%. The most effective is a screen length of α = 40 °.