**Centrifugal fans** are important ventilation equipment for production enterprises. There are many parameters to refer to when selecting models, including flow rate, pressure, efficiency, etc. The pressure mainly refers to the total pressure, static pressure and dynamic pressure of the fan. What does the flow mean?

## 1.the definition of centrifugal fan flow

The flow rate of the centrifugal fan refers to the volume of gas flowing through the fan per unit time, also known as the air volume. It is often expressed by Q, and the commonly used units are m³/s (seconds), m³/min (minutes), and m³/h (hours). Sometimes “mass flow” is also used, that is, the mass of gas flowing through the fan per unit time, but at this time, the gas density (ρ) at the inlet of the centrifugal fan needs to be considered, and the gas density is related to the gas composition, local atmospheric pressure, gas temperature, The inlet pressure is closely related, so it needs to be converted to get the gas flow of the centrifugal fan that is customary.

## 2. Flow conversion of centrifugal fan

The flow of the centrifugal fan is usually expressed by the result of converting the outlet flow into its intake flow state. It is usually expressed by volume flow (Qv) and mass flow (Qm). The relationship between the two is:

**Qm=ρQv**

In industrial applications, the use of volume flow (Qv) is more common, so when the gas mass flow (Qm) is known, the calculation formula of volume flow (Qv) is:

**Qv=Qm/ρ(gas volume=gas mass/gas density)**

**ρ=P/R/T**

In the formula:

**R** is the gas constant, usually calculated as 287;

**T** is the gas temperature, usually calculated as 273+t (℃).

## 3. The relationship between centrifugal fan flow and environmental factors

In the actual use process, the volume flow (Qv) of the centrifugal fan will change with the changes of many factors, such as temperature, pressure, altitude, etc. The conversion relationship between the volume flow (Qv) of the centrifugal fan and the temperature and pressure is as follows:

In the formula:

**P1** and **P2** represent the pressure of the gas;

**T1** and **T2** represent the relationship between the thermodynamic temperature of the gas (the thermodynamic temperature T(k) and the Celsius temperature t(℃), the relationship is:

**T(k)=273.15+t(℃)**

In summary, the flow conversion between the actual working condition and the standard working condition of the gas is as follows:

The standard working conditions in the above formula refer to: the temperature is 0°C (273.15K) and the pressure is 101.325 kPa (1 standard atmosphere, 760mm Hg).