For continuous measurements, we need a system of continually filling and emptying buckets to divide the flow without letting it out of the pipe. The volume divided by the time gives the flow rate. The stopwatch is started when the flow starts and stopped when the bucket reaches its limit. Mechanical flowmeters Ī positive displacement meter may be compared to a bucket and a stopwatch. The properties of the primary flow element, and the fidelity of the practical installation to the assumptions made in calibration, are critical factors in the accuracy of the flow measurement. Generally, the physical property generated by the primary flow element is more convenient to measure than the flow itself. A vortex meter primary flow element produces a series of oscillations of pressure. For example, an orifice plate produces a pressure drop that is a function of the square of the volume rate of flow through the orifice. In oceanography a common unit to measure volume transport (volume of water transported by a current for example) is a sverdrup (Sv) equivalent to 10 6 m 3/s.Ī primary flow element is a device inserted into the flowing fluid that produces a physical property that can be accurately related to flow. or imperial) per minute, liters per second, liters per m 2 per hour, bushels per minute or, when describing river flows, cumecs (cubic meters per second) or acre-feet per day. Gas mass flow rate can be directly measured, independent of pressure and temperature effects, with ultrasonic flow meters, thermal mass flowmeters, Coriolis mass flowmeters, or mass flow controllers.įurther information on the Sage Prism flowmeter from: Sage Metering Liquid įor liquids, various units are used depending upon the application and industry, but might include gallons (U.S. References will be made to "actual" flow rate through a meter and "standard" or "base" flow rate through a meter with units such as acm/h (actual cubic meters per hour), sm 3/sec (standard cubic meters per second), kscm/h (thousand standard cubic meters per hour), LFM (linear feet per minute), or MMSCFD (million standard cubic feet per day). A volume of gas under one set of pressure and temperature conditions is not equivalent to the same gas under different conditions. Gases are compressible and change volume when placed under pressure, are heated or are cooled. In engineering contexts, the volumetric flow rate is usually given the symbol Q. Energy flow rate is usually derived from mass or volumetric flow rate by the use of a flow computer. The energy flow rate is the volumetric flow rate multiplied by the energy content per unit volume or mass flow rate multiplied by the energy content per unit mass. When gases or liquids are transferred for their energy content, as in the sale of natural gas, the flow rate may also be expressed in terms of energy flow, such as gigajoule per hour or BTU per day. This is not the case for gases, the densities of which depend greatly upon pressure, temperature and to a lesser extent, composition. The density of a liquid is almost independent of conditions. These measurements are related by the material's density. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope.īoth gas and liquid flow can be measured in physical quantities of kind volumetric flow rate or mass flow rates, with respective SI units such as cubic meters per second or kilograms per second, respectively. Flow may be measured by measuring the velocity of fluid over a known area. Positive-displacement flowmeters, which accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow.įlow measurement methods other than positive-displacement flowmeters rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow.Obstruction type (differential pressure or variable area).The common types of flowmeters with industrial applications are listed below: Flow can be measured using devices called flowmeters in various ways. Flow measurement is the quantification of bulk fluid movement.
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