JJF 1004-2004Metrological Terms and Their Definitions for Flow Rate (English PDF)

1 General term (1)

2 Measuring instruments and methods (6)

3 Flow standard device (16)

4 Letter symbols (17)

Appendix A Chinese Index (19)

Appendix B English Index (27)

Terms and definitions of flow measurement

1 General term

1.1 flowrate

The amount of fluid flowing through a section is called flow. Flow is a collective term for instantaneous flow and cumulative flow. during one period the amount of internal fluid flowing through a certain cross section is called cumulative flow, also called total. When the time is short, the fluid flows through a certain section the quantity is called instantaneous flow, and in the case of no misunderstanding, instantaneous flow can also be referred to as flow. Volume meter for flow when it is displayed, it is called volume flow, and when it is expressed by mass, it is called mass flow.

1.2 Pipeflow, ductflow the fluid fills the flow of the pipe.

1.3 Open Channel Flow the liquid has a free surface flow in the open channel.

1.4 flowmeter

Apparatus for measuring flow. It usually consists of a primary device and a secondary device.

Note. High accuracy and good stability. The flowmeter that can be used as a comparison standard for other flowmeters is called standard flowmeter.

1.5 Flowmeter error characteristic curve (errorperformancecurveofflowmeter) the curve showing the relationship between the flow rate and the error of the flowmeter is a function of other quantities that are measured and affect the measurement error.

1.6 metertube

In all aspects, it meets the technical requirements in the standard, and a specially processed section of pipeline equipped with a flow measurement device.

1.7 Primary device

A device that generates a flow signal. Depending on the principle used, the primary device can be inside or outside the pipeline.

Note. For electromagnetic flowmeters, a primary device includes. a measuring tube, one or more pairs of radially opposed signals Electrode and an electromagnet that generates a magnetic field in the measuring tube. For differential pressure flowmeters, the primary device includes a measuring tube, Throttling device and pressure taking hole. For ultrasonic flowmeters, the primary device includes a measuring tube and an ultrasonic transducer.

1.8 secondary device A device that receives a signal from a primary device and displays, records, converts, and/or transmits the signal to obtain a flow value.

1.9 output signal

Is the output of the secondary device. This signal is a function of flow.

1.10 calibration factor of the primary device the quotient of the flow rate and the corresponding signal value sent by the primary device under the specified reference conditions.

1.11 maximum flow-rate Maximum flow to meet metering performance requirements.

1.12 minimum flow-rate Minimum flow to meet metering performance requirements.

1.13 flow-raterange

The range defined by the maximum flow and the minimum flow meets the measurement performance requirements within this range.

1.14 transitional flow-rate the flow value between the maximum flow and the minimum flow, it divides the flow range into two areas, namely "high area" and "low area".

1.15 nominal flow-rate at the nominal flow rate, the flow meter should be able to meet the measurement performance requirements during continuous operation and intermittent operation.

Note. For water meters, the nominal flow is called common flow.

1.16 fullscale flow-rate Corresponds to the maximum output signal flow.

1.17 pressureloss

Unrecoverable pressure drop due to the presence of a primary device in the pipeline.

1.18 working conditions the characteristic value of the physical property of the measured fluid flowing through the device and meeting the specifications of the primary device.

1.19 working temperature the temperature of the measured fluid flowing through a primary device and meeting the primary device specifications.

1.20 working pressure the absolute static pressure of the measured fluid flowing through a primary device and meeting the primary device specifications.

1.21 installation conditions Physical environment that allows the use of flow meters (or flow measurement devices).

Note. The physical environment includes external conditions, fluid status, numerical range of fluid physical properties, and geometric configuration of pipelines and their corresponding accessories.

1.22 straight length Pipe sections installed upstream and downstream of the flowmeter to achieve a certain level of flow field. Its axis is straight and the area and shape of the internal cross-section is constant, the cross-sectional shape is usually circular or rectangular, but it can also be circular or any other Has a regular shape.

1.23 Pipe wall pressure tap [wal (pressure) tapping] the edge of the circular hole in the pipe wall is flush with the inner surface of the pipe. The pressure taking hole is used to measure the static pressure of the fluid in the pipeline.

1.24 drainholes

Holes for discharging undesired solid particles or fluids with a density greater than the fluid being measured in the pipeline.

1.25 ventholes

Holes for venting undesired gases in pipes.

1.26 swirling flow

Flow with axial and peripheral velocity components.

1.27 pulsating flow of mean constant flow-rate Although the flow in the measurement section is a function of time, when averaged over a sufficiently long time interval, it has A constant average flow.

Note. There are two types of periodic pulsating flow and random pulsating flow.

1.28 turbulentflow

Compared with viscous force, inertial force plays a major role in flow, also called turbulence.

Note. Turbulence is the flow in which the irregular (random) velocity fluctuations in time and space are superimposed on the average flow.

1.29 laminarflow

Compared with inertial forces, viscous forces play a major role in the flow.

Note. Laminar flow is the layered movement of the fluid particles, and no mixed flow occurs between the stratospheres.

1.30 steady flow

Speed, pressure, and temperature do not change over time, and do not affect the flow of measurement accuracy, also known as steady flow.

Note. The observed steady flow is actually that its speed, pressure, and temperature will all have small changes around the average, but not Affects the flow of measurement uncertainty.

1.31 unstable flow

Flows in which one or more parameters of velocity, pressure, density, and temperature fluctuate over time, also known as unsteady flows.

Note. The time interval considered should be long enough to exclude the random component of the turbulence itself.

1.32 multiphase flow Two or more fluids of different phases flow together. It is also called two-phase flow when only two-phase fluid flows together.

1.33 critical flow

The fluid flows through the throat of the throttle, and the ratio of the absolute pressure of the downstream to the upstream is less than the critical value. Critical flow upstream when the fluid state (pressure, temperature, and velocity distribution) is constant, the mass flow rate remains constant.

1.34 velocity distribution the distribution pattern of the axial component of the fluid velocity over the cross section of the pipe.

1.35 Fully developed velocity distribution (fulydevelopedvelocitydistribution) Velocity distribution that does not change from one cross-section to another in the flow direction. it it usually forms at the end of a long enough straight pipe section.

1.36 regular velocity distribution Very similar to the fully developed velocity distribution, accurate flow measurement can be performed.

1.37 flowprofile

Graphical representation of velocity distribution.

1.38 mean axial fluid velocity the ratio of the instantaneous volume flow (the integral of the axial component of the local fluid velocity over the pipe section) to the cross-sectional area.

1.39 hydraulic diameter Quotient of four times the wet cross-sectional area and wet circumferential length.

Note. For circular pipes filled with fluid, the hydraulic diameter is equal to the inside diameter of the pipe.

1.40 hydraulic radius Equal to the quotient of wet cross-sectional area and wet circumferential length.

1.41 Static Pressure A pressure value measured in a fluid without being affected by the flow rate.

1.42 absolute static pressure of the fluid the static pressure of the measured fluid relative to a complete vacuum.

1.43 gauge pressure

The difference between the absolute static pressure of a fluid and the atmospheric pressure at the measurement site at the same time.

1.44 dynamic pressure

1.44.1 Dynamic Pressure Offluid Element for elementary stream bundles in a pipeline, the kinetic energy of the fluid is all isentropically converted into pressure energy which produces a pressure higher than the static pressure force. For incompressible fluids, the dynamic pressure of the fluid element is Note. The meaning of each letter symbol in the formula is shown in Table 1, the same applies hereinafter.

1.44.2 Mean dynamic pressure in cross-section the ratio of the power of a fluid flowing through a section to the volumetric flow in the form of kinetic energy. For incompressible fluids, the the average dynamic pressure is the sum of the gauge pressure and the dynamic pressure.

Note. For stationary unit fluid, the gauge pressure and total pressure have the same value.

1.46 stagnation pressure A pressure characterizing an energy state in which the kinetic energy of a fluid is fully converted into pressure energy. Its value is equal to the sum of absolute static pressure and dynamic pressure.

Note. For static unit flow, absolute static pressure and stagnation pressure have the same value.