ASME MFC-21.1:2015 pdf free download Measurement of Gas Flow by Means of Capillary Tube Thermal Mass Flowmeters and Mass Flow Controllers
2.2 Definitions Specific to This Document
bypass: the laminar flow element in a capillary tube ther-mal mass flowmeter or mass flow controller. The fluidenters the flowmeter and flows through the bypass. Thiscreates a pressure drop that forces a small, but propor-tional,fraction of the total mass flow rate through anadjacent capillary sensor tube. The flow path throughthe bypass and capillary sensor tube are shown in
Fig. 3.5-1. See bypass ratio,capillary tube thermal massflowmmeter (MFM), laminar flowo elenent , and sensor tube.
bypass ratio: the ratio of the total mass flow rate in theprocess line to the mass flow rate measured by the sensortube.This ratio is constant (i.e., independent of all fluidproperties) in capillary tube thermal mass flowmetersand mass flow controllers. See bypass,process line, andsensor tube.
capillary tube: a tube with an internal diameter and fluidmass flow rate that are sufficiently small and with alength-to-diameter ratio that is sufficiently large that,over almost its entire length, the fluid flow is laminarand has a fully developed velocity distribution. See fullydeveloped velocity distribution (para.2.1), laminar floiw(para.2.1),laminar hydrodynannic entrg lengt,and sen-sor tube.
capillary tube thermnal mass floo controller (MFC): a capil-lary tube mass flowmeter (MFM) with an integral flow control valve mounted on the same flow body. The MFMportion of the instrument measures the mass flow rate of the fluid flowing in the process line, the electronicscompare this measurement with a set-point value, andthe control valve regulates the flow to equal the set-pointvalue. See capillary tube thermal mass flomneter (MFM),control valve, and electronics.
capillary tube thermal mass flozmeter (MFM): an MFM thatmeasures the mass flow rate in a process line by meansof a bypass and an adjacent capillary sensor tube. Seebypass, process line, and sensor tube.
control valve: a flow control valve mounted on the sameflow body as a capillary tube thermal mass flowmeter(MFM). See capillary tube thernal mass floww controller(MFC).
electronics: an electronic system providing the drive to,and transforming the signal from, the sensor tube togive the total mass flow rate output. It also provides outputs and corrections for other parameters,such asfluid temperatures. See sensor tube.
flowe calibration: the act of comparing the fluid mass flowrate measured by a flowmeter under test with that of aflow calibration standard in the same conduit. Also, theact of adjusting the output of the flowmeter under testto bring it to a desired value, within a specified tolerance,for a particular value measured by the standard. SeeMandatory Appendix I and calibration (para.2.1).
gas coroersion factor: a constant factor，often called aK-factor, that relates the flow calibration data found witha reference gas to another gas. The gas conversion factoris the ratio of the product of standard mass density timesthe coefficient of specific heat (p cp) of the reference gasto that same product for another gas (see section 7).SeeMandatory Appendix I, flow calibration, and reference gas.general purpose MFM or MFC: a capillary tube thermalMFM or MFC used for general purpose industrial andlaboratory applications (see para.3.2).
heat capacity: the thermodynamic property of a gas thatmeasures its ability to store thermal energy (enthalpy).See sensor tbe.
heat capacify rate: the product (qmcp) of the gas mass flowrate in the sensor tube times the coefficient of specificheat at constant pressure that is a primary componentof the heat capacity of the gas. The output of capillarytube thermal mass flowmeters and mass flow controllersis proportional to the heat capacity rate in the linearrange of the instruments. See heat capacify and sensor tibe.innstrement(s: specifically for this text, the term instru-ment(s) is defined as a capillary tube thermal mass flow-meter,mass flow controller, or both collectively.
intrinsic sensor oise: noise intrinsic to the sensor tubeitself, as distinguished from noise associated with theelectronics. See electronics and sensor tbe.
K-factor: see gas conzversion factor.
laminar flow eleent: the bypass in a capillary tube ther-mal mass flowmeter or mass flow controller that has afully developed laminar velocity distribution in its flowpassages.The ratio of the mass flow rate through thelaminar flow bypass to that of the sensor tube is a con-stant.See bypass, bypass ratio, fuly developed oelocity distri-bution (para.2.1),laminar flow (para. 2.1j, and sensor tabe.la miinar hydrodynamic enfry length: the length at theentrance of the sensor tube required for the velocitydistribution of its internal flow to have attained, withina certain percentage (usually 2%),a fully developedlaminar velocity distribution.See fully developed velocitydistribution (para. 2.1) and laminar florw (para. 2.1).
leak rate: the rate of leakage of
(a) the process gas in the instrument to the outsideenvironment
(b) outside air into the instrument, or
ASME MFC-21.1:2015 pdf free download
