According to "220V AC Cooling Fan" differential thermal design flow based on differential thermal design flow, need to know the characteristics of forced convection heat sink and fan. Forced convection feature means that the thermal resistance of the heat sink radiator to the air and through the relationship between the pressure difference after the radiator and air traffic; "220V AC Cooling Fan" forced convection feature means that the relationship between fan air flow and air pressure difference . Intersection of the fan and radiator air flow and air pressure difference curve is the flow of air through the radiator (see Figure 10-8). In this air flow to the radiator air resistance ask, can be read directly from the curve "220V AC Cooling Fan" radiator air flow and thermal resistance.