http://www.fsid.cvut.cz/en/u12110/tem/flow/rotameter.pdf
1
Determination of an Rotameter Static features
Rotameter is designated for flow measurement by speed method. It consist by conic vertical
tube, in which is the float raised by measured liquid or gas. The pressure difference on the float
is constant and it is equal to float weight multiplayed by the float cross section, while the flow
space around the float changes with raising of the float. In stable state, position of the float
depends only on the gas or liquid features and measured float.
Task: measure dependency of float lifting on flow, h=f(QR), for known specific weight R.
From this dependency calculate and draw to common graph the user (functional) characteristics
for following gases and standard environment condition (standard atmospheric pressure and the
zero degree centigrade temperature):
air
Qo = f(h) for o
chlorine Cl2
QCl2 = f(h) for Cl2
ammoniac NH3
QNH3 = f(h) for NH3
Used equipment:
 reducer with supply air pressure setting
 manometer for measure static pressure before rotameter
 gas meter - integrating instrument of amount of gas (volume, the V), which was passed
through
 verified rotameter (with specific and marked tube and float)
 stop watches, thermometer
Connecting scheme
pN QR pSR hVt-
pressure of the pressured air supply
air flow (main measured magnitude)
pressure before the rotameter. Main pressure loss is on gas meter.
float position (height)
air volume, which is passed through (from the start of using this instrument in our
laboratory)
surrounding temperature (from which the thermodynamic temperature (in K) and then the
specific weight is calculated). For this calculation, atmospheric pressure should be
measured as well.
stop watchers
2
http://www.fsid.cvut.cz/en/u12110/tem/flow/rotameter.pdf
Comments
Measure in ten points in all settable range of flow, not for zero. The volume of air by gas meter
measure for at least two minutes for each float position. Avoid unstable behaviour of float (must
be smoothly rotated).
Used equation
Air specific density equation
 R  3,484 
p1R
T1
[kg.m-3, kPa, K] ; p1R = psR + pbo
In the gas meter, consider half of the pressure measured by manometer.
Conversion of flow for other gases with regard to specific weight:
Qo  QR
R
o
, Q Cl 2  Q R
R
 Cl 2
, Q NH3  Q R
R
 NH3
Specific weight for standard conditions, i.e.
po=101325 Pa, To = 273,15 K ( = 0 oC) is:
 air
o = 1,293 kg.m-3
 chlorine Cl2
Cl2 = 3,22 kg.m-3
 ammoniac NH3
NH3 = 0,771 kg.m-3
calculating the pressure from length of a column form inclined manometer:
pSR = e . N . g . l
(e - inclined manometer conversion, in our case e=1, filling - distilled water)
Table of measured and calculated values:
h
psR
V1
[mm]
[mmH2O] [m3]
V2

V=V1-V2
QR
Q0
QCl2
QNH3
[m3]
[s]
[m3]
[m3.s-1]
[m3.s-1]
[m3.s-1]
[m3.s-1]