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Normal cubic meters per hour (often abbreviated NCMH) is a measure of flow rate, commonly used in the Natural Gas industry. It is equal to one cubic meter under "normal" conditions, defined as 0°C and 1 atmosphere (101.3 kPa). This should not be confused with standard cubic meters per hour (SCMH) or standard cubic feet per hour, which are defined in the gas industry at 60°F and 1 atmosphere. These units may be converted as 1.000 NCMH = 1.056 SCMH = 37.31 SCFH.

Whenever you see a unit of time -- usually the second, s, but occasionally the minute or hour -- in the denominator of fractional units, we are dealing with a rate. Meters per hour, for example, implies a rate of speed or velocity, which is the change in displacement (distance) per unit time. The question, however, is about cubic meters per hour. We still have a rate here, but it's not a rate of speed, because the numerator -- the top number -- is not meters but cubic meters. So, a brief discussion of cubic meters -- or, if you prefer, meters cubed, m3 -- is in order first. A cubic meter is a unit of volume. Think of it as the amount of space occupied by a cube measuring one (linear) meter on each edge. A cubic meter is equal to about 1,000 liters or 264.2 gallons [US]. So one cubic meter per hour (m3/hr) is a rate of volume. In other words, it's a flow rate. More familiar units of measure for flow rate are gallons per minute or liters per second. Both of those imply a quantity of something per unit time. But cubic meters per hour is also a legitimate unit of measure for flow rate. Let me give you an example. Let's say you have a backyard swimming pool that contains 13,250 gallons of water (about the size of round pool with a 24-foot diameter. That's equivalent to about 50 cubic meters. If you fill that pool with a garden hose in ten hours, you know that the flow rate of the hose is five cubic meters per hour. That's a pretty substantial flow rate for a garden hose! (The hose is delivering more than a gallon of water every three seconds. That's a lot but not out of the realm of possibility.) A "normal" cubic meter refers to the conditions of measurement. As this is a flowrate, the volume of a given mass of gas fluctuates with temperature and pressure (PV=nRT ring a bell?). Normal is a set of conditions at which the volume stated. In other words, since the volume varies with these conditions, if we want to talk about flow, we have to pick conditions first. Normal are simply a set to which we all agree upon. Unfortunately, it depends on whom is agreeing on the term. Different industries have picked different "normal conditions." In the case of natural gas, 60°F and 14.73 psia. This is different for STP (Standard Temperature and Pressure) which are often termed 25°C and 1 atm. Again, you have to know which industry took the number to know which standard is being applied (though it generally only makes subtle differences as these are all very similar conditions).

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16y ago

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