Flow DetectorsSTEAM FLOW DETECTIONSince steam is considered to be a gas, changes in pressure and temperature greatly affect itsdensity. Equations 4-5 and 4-6 list the fundamental relationship for volumetric flow and massflow.(4-5)and(4-6)mVrwhere= volumetric flowK = constant relating to the ratio of pipe to orificeh = differential pressurer = density= mass flowmIt is possible to substitute for density in the relationship using Equation 4-7.(4-7)rpmRqwherer = densityp = upstream pressurem = molecular weight of the gasq = absolute temperatureR = gas constantBy substituting for density, the values are used by the electronic circuit to calculate the densityautomatically. Since steam temperature is relatively constant in most steam systems, upstreampressure is the only variable in the above equation that changes as the system operates. If theother variables are hardwired, measuring the system pressure is all that is required for theelectronics to calculate the fluid’s density.Rev. 0 Page 13 IC-04
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