Metal rota high pressure air flow meters for lubrication oil, variable area type flow meters Pipe size DN15-100

Operation principle

The variable area, also called metal flowmeter's flow sensing element consists of a vertical tapered tube expanding from bottom to top and a float set moving up and down along the tapered tube axis. Working principle shown in Figure 1, the measured fluid from the bottom up through the conical tube 1 and the float 2 formed ring gap 3, the upper and lower ends of the float to produce differential pressure to form the floating force of the float when the lift is greater than the submerged fluid The weight of the float, the float will rise, the ring gap area increases, the annular gap at the immediate decline in fluid flow velocity, the float lower differential pressure decreases, the role of the buoy lift force also decreases until the lifting force is equal to immersed in the fluid In the float weight, the float will be stable at a certain height. The height of the float in the conical tube and the flow through the corresponding relationship.

The basic equation of volume flow Q is:

When the float is non-solid hollow structure (put the weight adjustment), then

Where α - instrument flow coefficient, due to float shape varies;

ε - gas expansion coefficient measured gas is gas, usually due to the small coefficient of this correction is ignored, and has been included in the flow coefficient through the calibration, such as liquid, then ε = 1;
△ F - Circulation area, m2;
g - local acceleration of gravity, m / s2;
Vf - float volume, if extended body should also include, m3;
ρf - float material density, kg / m3;
ρ - measured fluid density, such as gas is the density of the upstream cross-section of the float, kg / m3;
Ff - working area of ​​the float (maximum diameter) cross-sectional area, m2;
Gf - float quality, kg.
Circulation area and the relationship between the height of the float as shown in equation (3), when the structural design has been set, then d, β are constant. There is a quadratic term in h, we can not ignore this nonlinear relationship. Only when the cone angle is small, can we regard it as approximate linearity.
m2 (3)
Where d - maximum diameter of the float (ie, working diameter), m;
h - float from the cone diameter equal to the maximum diameter of the float rise height, m;
β - taper cone angle;
a, b - constant.

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Data sheet