A self validating digital coriolis mass flow meter an overview
A detailed analysis may reveal other significant issues. The measurement of gasoline was given as an example of the inferred mass flow measurement (using volumetric units). (New York Times, September 24, 2001, Empowered II Smart Energy Management, A clean car is an efficient car, page 7). This volume is then compensated for the actual temperature to indicate the volume of the gasoline as if it were a certain temperature.
While this is perhaps more information than one would like to know about the subject, this discussion clearly illustrates the need to understand the process ? Comments resulted in Part 3.1 that addressed some issues associated with retail gasoline measurements. The compensated volume is an implied mass measurement.
Volumetric flow is expressed in units that reflect a volume per unit time.
Thinking locally, one might conclude that it is more economical to purchase gasoline during the wee hours of the morning when the temperature is coldest. Gasoline pumps compensate for density variation that occurs due to temperature, and in doing so, they measure the amount (mass) of gasoline dispensed.
The answer would seem to be to purchase a flowmeter. Having discovered that there are two types of flow rates (volumetric and mass), it should not be a surprise that some flowmeters measure mass (W) while other flowmeters measure volume (Q). Repeating the equations from Part 1 (for convenience), it can be seen that, assuming A is constant, Q can be determined by measuring the average fluid velocity v. The most common of these measurements measure the velocity head (1/2 rho v x v) to infer the volumetric flow.
With fluid flow defined as the amount of fluid that travels past a given location, this would seem to be straightforward ? However, consider the following equation describing the flow of a fluid in a pipe. a pound is assumed to be a mass unit.) Note that W is a mass per unit time, so W is commonly denoted as the ? Further, assuming that rho is constant, W can be determined from Q. Notice that these flowmeters do NOT measure volume, do NOT measure mass, and do NOT measure velocity ?
A number of e-mails questioning this assertion and further investigation resulted in the interesting discovery that retail gasoline flowmeters are not temperature-compensated in the United States, but are temperaturecompensated in Canada.
In other words, either the measured volume (in the US) or the measured temperature-corrected volume (in Canada) is used to infer mass. Air temperature differences between hot and cold climates are large.