When entering a new fan or blower to the database, we must define if the reference gas volume flow units are based on STP (101325 Pa at 15oC) or NTP (101325 Pa at 0oC) conditions (Figure 1). When we then model the specific blower/fan in a system, FluidFlow automatically corrects the blower/fan performance based on actual flowing air density and pressure conditions.
Figure 1: Blower Performance Curve Referenced to STP.
Details of the performance curve are shown in Figure 2 below.
Figure 2: Blower Performance Curve.
We have created a simple model with air as the fluid and the blower is the Radial Blower RB75 as shown above. Using a trial and error approach, we have adjusted the pressure and temperature conditions of the air at the system inlet (node 4) to arrive at a condition where we have a pressure of almost exactly 101325 Pa and 15oC (STP) at the inlet of the blower.
As we can see, the calculated actual duty flow rate is 736 m3/h. If we look at our original data entry for this fan above, we can see the curve has been defined at STP conditions which is almost identical to our actual operating scenario. Therefore, we can see that the duty flow calculated at STP conditions is 737 m3/h. The very slight difference can be attributed to the subtle difference in system pressure vs the specific 101325 Pa and 15oC condition.
If we were to adjust the actual flowing temperature or pressure conditions, we would get a different answer and the blower performance curve would be adjusted accordingly.