measuring quality of steam

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