Fan Definition

Published on January 2017 | Categories: Documents | Downloads: 32 | Comments: 0 | Views: 202
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Definitions
Static pressure (SP) the pressure resulting from the gas density and its degree of compression and independant of the gas velocity the pressure resulting from the velocity of a gas and its air density VP = ½ ρV² the sum of the static pressure and the velocity pressure TP = SP + VP the difference between the average total pressure at the fan outlet (2) and the average total pressure at the fan inlet (1) FTP = TP2 - TP1 = SP2 + VP2 - SP1 - VP1 1 Fan static pressure (FSP) the difference between the fan total pressure and the velocity pressure at the outlet (2) FSP = FTP - VP2 = SP2 - SP1 - VP1 the difference between the static pressure at the fan outlet (2) and the static pressure at the inlet (1) SPR = SP2 - SP1 the minimum power required to move a specified rate of gas against a specified resistance then it is product of the flow (inlet and outlet conditions) and the fan total pressure Qin = flow (T1, SP1) Qout = flow (T2, SP2) Q = (Qin + Qout) / 2 Po = Q x FTP the power delivered to the fan shaft also known as fan shaft power the power delivered at the fan motor output (the shaft) also the fan input power divided by the fan drive efficiency Pmo = Ps / ηD the power delivered at the fan motor input (electrical power) also the fan output power divider by the motor efficiency Pe = Pmo / ηM then Ps = µM x µD x Pe Fan total efficiency (ηt) the ratio of the fan output power to fan input power also known as fan mechanical efficiency ηt = Po / Ps the product of mechanical efficiency and the ratio of fan static air in air out Po Ps Pmo ηD ηM Power source Pe

Velocity pressure (VP)

Total pressure (TP)

Fan total pressure (FTP)

2

Static pressure rise (SPR)

Fan output power (Po) or aeraulic power or air power

ηt

Fan input power (Ps)

Fan motor output power (Pmo)

Fan

Drive

Motor

Fan motor input power (Pe)

Fan static efficiency (ηs)

pressure to fan total pressure ηs = ηt x FSP / FTP Fan performance curve or fan pressure curve A curve showing the relationship between the gas flow rate delivered by a fan and the pressure generated at the different flow rates A curve showing the power of a fan at different flow rates
fan peak pressure operating point fan power curve

18 16

120 100 80

Fan power curve System resistance curve

14

Fan pressure

A curve showing how the resistance to flow through a system (pressure drop) changes with the flow rate. Typically, for turbulent flow, the curve follows the following relationship (parabola): ∆P = k ρ Q² The intersection of the fan pressure curve and the system resistance curve. The fan will operate at that point. The maximum pressure the fan can deliver. The fan should always operate on the right side of the peak pressure point

12 10 8 6 4 2 0 0

system resistance curve

Power

fan pressure curve

60 40 20 0 40000

Operating point

Fan peak pressure

10000

20000 Flow rate

30000

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