92 ENGINEERING THERMODYNAMICS

Dharm

\M-therm/th3-2.p65

At 1.1 bar. From steam tables,
hf = 428.8 kJ/kg ; hfg = 2250.8 kJ/kg
∴ ms [(428.8 + 0.95 × 2250.8) – 1 × 4.18 × 40]
= (90 + 5.25) [1 × 4.18 × (40 – 25)]
ms [2567.06 – 167.20] = 95.25 × 62.7
i.e., 2399.86ms = 5972.17
∴ ms = 2.488 kg
Hence, mass of steam condensed = 2.488 kg. (Ans.)

3.18.2. Throttling calorimeter

The dryness fraction of wet steam can be determined by using a throttling calorimeter

which is illustrated diagrammatically in Fig. 3.15.

Fig. 3.15. Throttling calorimeter.
The steam to be sampled is taken from the pipe by means of suitable positioned and dimen-
sioned sampling tube. It passes into an insulated container and is throttled through an orifice to
atmospheric pressure. Here the temperature is taken and the steam ideally should have about
5.5 K of superheat.
The throttling process is shown on h-s diagram in Fig. 3.16 by the line 1-2. If steam initially
wet is throttled through a sufficiently large pressure drop, then the steam at state 2 will become
superheated. State 2 can then be defined by the measured pressure and temperature. The enthalpy,
h 2 can then be found and hence
h 2 = h 1 = ()hxhf 11 + 1 fg at p 1
[where hh h cT T 2 =+ +f 22 fg pssu()]p 22 −s

∴ x

hh

h

f

(^1) fg
(^21)
1

−
...(3.20)