Equation 1 shows the relationship between temperature rise and airflow, where q is the amount of heat absorbed by the air (W), w is the mass flow of air (kg/s), Cp is the specific heat of air (J/kg • K) and ΔT is the temperature rise of the air (°C). Once the maximum permissible temperature within the enclosure is known and the amount of heat generated is derived (based on the cumulative power/heat dissipated by the components) it is possible to calculate the amount of airflow required. Since mass flow (w) = air flow (Q) x density (ρ), substituting and solving for Q, Equation 1 can be rewritten to get Equation 2 (where Q is the airflow in CMM (m³/min), q is the amount of heat to be dissipated (W) and ρ is the density of air (kg/m3)). Substituting constants for Cp and ρ at 26°C, a general equation for calculating airflow can be derived, as shown in Equation 3. This calculated airflow figure can now be compared against the specification for a fan.