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Principle of Variable Flow Meter(Rotameter)
- Principle of Rotameter ( Float Type) 1.
- As shown in the figure, the area (float type) flow meter has a conical cylinder (tapered tube) with the upper end larger than the lower end, having a float inside. The float moves up and down according to the flow, and the reading taken when it balances indicates the flow rate.
1. Figure
2.
The symbols and units are determined as follows:
Vf: Volume of float [cm3]
ρf: Density of float [g/cm3]
af: Maximum cross-section of float [cm2]
P1: Pressure directly under float [Pa]
P2: Pressure directly above float [Pa]
ρ: Flow density [g/cm3]
U1: Flow velocity directly under float [cm/sec]
U2: Flow velocity in float clearance [cm/sec]
A1: Cross section directly under float [cm2]
A2: Cross section of float clearance [cm2]
Q: Flow rate [cm3/sec]
g: Gravitational acceleration
Vf: Volume of float [cm3]
ρf: Density of float [g/cm3]
af: Maximum cross-section of float [cm2]
P1: Pressure directly under float [Pa]
P2: Pressure directly above float [Pa]
ρ: Flow density [g/cm3]
U1: Flow velocity directly under float [cm/sec]
U2: Flow velocity in float clearance [cm/sec]
A1: Cross section directly under float [cm2]
A2: Cross section of float clearance [cm2]
Q: Flow rate [cm3/sec]
g: Gravitational acceleration
3.
The force that pushes up the float is af (P1–P2).
Subtracting the buoyancy, the gravitation of the float is Vf (ρf–ρ) g.The balance equation is:
Subtracting the buoyancy, the gravitation of the float is Vf (ρf–ρ) g.The balance equation is:
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