Measurement of Quality of Steam
For pure substances –in-dependant properties such as pressure and temperature are needed (if pressure is known, temperature can be found)
We need specific volume, enthalpy or quality of mixture(liquid & vapour)
For measuring specific volume of mixture (quality) calorimeters are used.
a) Separating Calorimeter
b) Throttling Calorimeter
c) Separating & Throttling Calorimeter
d) Barrel Calorimeter
e) Electric Calorimeter
a) Separating Calorimeter:
Fig
X = M/ (M+m)
M=Mass of dry steam read from gauge of condenser
M=Mass of water separated in specified time interval
x= Dryness fraction or quality of steam
b) Throttling Calorimeter
Fig
x1= (h-hf1)/ hfg1
Let P1 = Initial Pressure
x1 = Dryness Fraction
hf1 = Enthalpy of water at P1
hfg1 = Enthalpy of vaporization
Cps = Sp heat of superheated steam after throttling..kJ/ kg
Tsat = Saturation temp at P2
During throttling process, the enthalpy remains constant.
Enthalpy of steam at P1 before throttling= Enthalpy of steam at P2 after throttling
hf1 + x1 hfg1 = hg2 + Cp (T2-Tsat)
x1 hfg1= hg2 + Cp (T2-Tsat) - hf1
x1= hg2 + Cp (T2-Tsat) - hf1/ hfg1
= h- hf1/ hfg1
h = sp enthalpy at state 2 from superheat read from table
