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Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour.
The integration of a flux over an area gives the volumetric flow rate. The SI unit is cubic metres per second (m 3 /s). Another unit used is standard cubic centimetres per minute (SCCM). In US customary units and imperial units, volumetric flow rate is often expressed as cubic feet per second (ft 3 /s) or gallons per minute (either US or ...
Mass flow rate is defined by the limit [3] [4] ˙ = =, i.e., the flow of mass m through a surface per unit time t. The overdot on the m is Newton's notation for a time derivative . Since mass is a scalar quantity, the mass flow rate (the time derivative of mass) is also a scalar quantity.
Standard cubic centimeters per minute (SCCM) is a unit used to quantify the flow rate of a fluid. 1 SCCM is identical to 1 cm³ STP /min. Another expression of it would be Nml/min. These standard conditions vary according to different regulatory bodies.
The standard liter per minute (SLM or SLPM) is a unit of (molar or) mass flow rate of a gas at standard conditions for temperature and pressure (STP), which is most commonly practiced in the United States, whereas European practice revolves around the normal litre per minute (NLPM). [1]
In describing the units of a rate, the word "per" is used to separate the units of the two measurements used to calculate the rate; for example, a heart rate is expressed as "beats per minute". Rates that have a non-time divisor or denominator include exchange rates, literacy rates, and electric field (in volts per meter).
It is expressed in units of distance across the workpiece surface per unit of time, typically surface feet per minute (sfm) or meters per minute (m/min). [1] Feed rate (also often styled as a solid compound, feedrate, or called simply feed) is the relative velocity at which the cutter is advanced along the workpiece; its vector is perpendicular ...
This gives the lower of the average rate at 12 breaths per minute. Average resting respiratory rates by age are: [11] [self-published source] [12] birth to 6 weeks: 30–40 breaths per minute; 6 months: 25–40 breaths per minute; 3 years: 20–30 breaths per minute; 6 years: 18–25 breaths per minute; 10 years: 17–23 breaths per minute