文档介绍：风机根底讲义
Outline
Air fundamentals, volume, pressure & power
Fan and Air Systems
Fan testing & ratings
Fan performance re
Fan Velocity Pressure (VP)
The pressure corresponding to the fan outlet velocity
The kinetic energy per unit volume of flowing air
VP = total pressure (TP) - static pressure (SP)
VP = (V / 1096)2
= Density in lb./ft3
V = Velocity in FPM
if standard air:
VP = (V / 4005)2
Fan Power
Air Horsepower (AHP)
Assuming 100% efficiency, the horsepower required to move a given volume of air against given pressure
Static AHP = (CFM x SP) / 6356
Total AHP = (CFM x TP) / 6356
Brake Horsepower (BHP)
The actual horsepower a fan requires
BHP > AHP, because a fan is not 100% efficient
In addition to fan power input, BHP may include power absorbed by V-belt drives, accessories, etc.
Fan Efficiency
Static Efficiency (SE)
Ratio of fan power output to the fan power input
Uses SP, which does not include kinetic energy
SE = (CFM x SP) / (6356 x BHP)
Mechanical Efficiency (ME) or Total Efficiency
Ratio of total fan power output to the fan power input
Uses TP, which includes kinetic energy
ME = (CFM x TP) / (6356 x BHP)
Fan Testing and Rating
Fans are tested in setups that simulate installations
Four standard installation types:
Fan Testing and Rating
Fans are tested a given speed (RPM)
Volumetric flow rate (CFM) is measured at:
No resistance (wide open volume or free delivery),
Complete resistance (shut off), and
Everything in between
Complete Resistance
No Resistance
Fan Performance Curve
The test data is plotted, producing a “fan curve〞
Brake Horsepower
Static Pressure
Air Volume (CFM)
Fan Performance Curve - Example
Fan Testing and Rating
Not all fan sizes are tested for rating
By use of equations called “fan laws〞 test data is used to calculate performance of a larger fan that is geometrically similar (not smaller)
Not practical to test a fan at every speed
By use of “fan laws〞 it is possible to predict fan performance at various speeds