Estimating an Efficiency of the High Pressure Discharge Nozzles of Steam Turbines

Анотація

Consideration was given to the influence of the expansion ratio and a relative volume of the axisymmetric collection chamber on the loss factors of the diffusion-free discharge nozzles of high pressure cylinders (DN HPC) with two parallel pipe bends connected to the collection chamber. Methods of the estimation of loss coefficients were suggested based on the data of experimental investigations of the models of discharge nozzles carried out using the static aerodynamic test bench with the turbine cascade simulator. It was proved that the simulator should be installed at relatively low volumes of the collection chamber. A dimensionless criterion was proposed to describe a relative volume of the collection chamber. It has been established that the net loss factor of diffusion-free DN HPC cannot be less than 1.5 due to the complicated helical flow in the collection chamber and high hydraulic losses caused by the entry of helical steam flow into the pipe bends (outlet pipes). To estimate the operation efficiency of DN HPC we offered to use the hydraulic loss coefficient that takes into account inhomogeneous flux flattening losses in the initial section of outlet pipes in addition to actual hydraulic losses.  Proceeding from common methodological standpoint, the research data obtained for DN HPC and cogeneration steam bleeding channels of the flow pass of steam turbines were compared. It has been established that when the steam leaves the cogeneration steam bleeding chamber through one or two pipe bends stagnation pressure losses are in the range of 0.4 to 0.8 of the dynamic pressure calculated using the average flow rate in pipe bends.