The throttle device in application of measuring flow in thermal power plants
Single-phase fluid flow measurement by throttling device is widely used in coal-fired power plant, it has a good accuracy, small investment, and used widely, such as the standardization of assembly feature. For standard throttling device in power plant common fluid flow measurement, the application of analysis of standard throttling devices supporting the design of the instrument to measure flow condition in application characteristics and the selection of installation and concrete problems, including measurement data compensation can contact cisco measurement and control technology co., LTD., henan concrete solution. Introduces the principle of the standard throttle device measuring flow under below:
Throttling device in the coal-fired power plant on the use of measuring flow applications. For now, with the national standard throttle device requirements need not be the world to carry on the design and manufacturing flow calibration, choose convenient is differential pressure type throttling device measuring flow of the system.
Measuring principle: in the have a steady flow state of a straight pipe before and after adding an orifice plate is less than in straight pipe diameter of throttle, flow through the throttle parts occur after a sudden contraction, part of the internal energy is transformed into kinetic energy, causes the average flow velocity increases, the static pressure decrease. The throttle device produces a square value of the static pressure difference before and after and flow through the throttle device has the certain function relation. By using the principle of flow continuity and cuny's equation calculation formula of traffic flow can be concluded that the throttle device. The following is a common calculation formula of volume flow:
The actual flow through the throttle device and the ratio of the principle of flow; Epsilon fluid expansion system for liquid general approximate 1, epsilon in the throttle device using the above formula to determine the parameter after calibration. Generally USES experiment method is given a series of experimental data for calculation. In a given throttle device diameter ratio, epsilon depends on the differential pressure, static pressure and quotient index such as k, may refer to the following formula:
D work under the condition of the throttle device upstream flow diameter pipe m; D work under the conditions of flow diameter of orifice throttling device or m; The static pressure difference before and after Pa Δ P throttling devices. Beta throttling device aperture ratio, beta = d/d; Rho (1 kg / ㎎ 3 be work flow density. Mass flow calculation formula:Qm=Qvρ
The standard throttle device basic requirements:
Standard throttle device measuring flow by throttling device commonly (throttling, measuring tube, straight pipe, the flow regulator, pressure piping), and differential pressure measuring instrument, signal processing instrument, etc. Main measuring medium for saturated water in thermal power plants, the superheated steam, condensate gas and other clean single-phase fluid, the more general situation, the flow measurement by standard throttle device can be satisfied. Because of the throttle device of standard nozzle or length to diameter of nozzle flow resistance is small, wear resistance, good product pollution resistance and deformation resistance, its application has become increasingly widespread. Nozzle is lower high Reynolds number, flow coefficient as the determination of orifice plate stability of these shortcomings can be through the flow calculation software for dynamic modification.
The design of the flow measurement by standard throttling device
1, fluid must be full of circular tube and throttling device, the flow of fluid through the measuring section before must be maintain stability of subsonic, or the state of only slowly changing over time, the fluid must be uniform single-phase fluid, or can be considered a single phase fluid. Generally refers to the dry steam of steam. Sometimes because of steam flow, heat and humidity increases, is no longer a pure single-phase fluid. This phenomenon can be through the steam humidity compensation, and there is no more standard usage.
2, to facilitate the measurement and calculation, should know the density and viscosity of fluid in the work condition.
3, take pressure method USES the Angle joint take pressure, flange taps, D and D / 2 take pressure, throttle with orifice, nozzle, and venturi tube throttling device, each should be used within the prescribed measuring throttle device.
The throttle device design calculation, the fluid in the pipe does not change with time and change is slow. Without phase change, the flow through the throttle device may occur if the phase change, can be used to increase orifice diameter reduced differential pressure method of eliminating phase change. General liquid according to the calculated, isothermal change gas according to the adiabatic change to calculate.