formation of steam

1. DEPARTMENT
OF
MECHANICAL ENGINEERING
GOVERNMENT POLYTECHNIC,
HOLENARASIPURA

2. A
Presentation on
“STEAM CALORIMETERS”
Course : 15ME52T- APPLIED THERMAL ENGG
Unit : 1-FORMATION OF STEAM
Class: 5th Sem Diploma in Mechanical Engg
Course Coordinator: MANJU R B
2

3. CONTENTS
STEAM CALORIMETERS
➢ Barrel Calorimeter
➢ Seperating Calorimeter
➢ Throttling Calorimeter
➢ Combined Seperating & Throttling Calorimeter
REFERENCES
3

4. 4
➢The dryness fraction of steam can be measured experimentally.
➢Calorimeters are used for measurement of dryness fraction of steam.
➢There are four methods of determining the dryness fraction of steam.
1. Bucket or barrel calorimeter
2. Throttling calorimeter
3. Separating calorimeter
4. Combined separating & throttling calorimeter
STEAM CALORIMETERS

5. 5
BARREL CALORIMETER
➢The Bucket/Barrel Calorimeter consists of a
copper vessel which contains cold water.
➢The copper vessel is insulated from the
surrounding so as to prevent any heat transfer
from or to the system.
➢The top of the vessel is covered with
wooden plate containing two holes.
➢In one of the hole a thermometer is inserted
to record the temperature and in another
hole, steam supply pipe is inserted as shown in
the below figure.
➢The whole assembly is placed on the
weighing bridge

6. 6
Contd….
➢In this calorimeter, steam from the main
pipe of boiler enters into the calorimeter
through nozzles.
➢The steam coming in contact with water gets
condensed and results in an increase in the
mass and temperature of water.
➢Temperatures of water before and after
condensation are recorded. Knowing the
quantities of steam and water, we can very
easily calculate the dryness fraction steam.

7. ➢ let, ms= weight of steam condensed
➢ mw = weight of cold water in barrel
➢ Cpw= sp. heat of water
➢ x= dryness fraction of steam
➢ hfg = latent heat of the steam at pressure of steam P,
➢ t1, =initial temperature of water before mixing steam
➢ t2 = final temperature of steam after mixing of steam
➢ tsat = saturation the temperature of steam at P.
➢ ms[ x hfg1+ Cpw( tsat-t2)]=mwCpw(t2-t1)
➢ Therefore, Heat lost by steam = Heat gained by cold water
=ms[ x hfg1+ Cpw( tsat-t2)]=mwCpw(t2-t1)
From this equation, we can find the dryness fraction of steam 7
Contd….

8. 8
SEPERATING CALORIMETER
➢It is a simple calorimeter, used for determining
the dryness fraction steam by separating the
moisture content from the wet steam.
➢It consists of two eccentric chambers, inner and
outer chambers. They communicate with the help
of opening at the top.
➢The wet steam to be tested enters the inner
chamber of separating calorimeter through a
sampling tube controlled by a valve.
➢ In the inner chamber of calorimeter, perforated
cups or baffles plates are arranged in such a
manner as to separate the moisture from the
steam.

9. 9
SEPERATING CALORIMETER
➢Hence, when steam enters the separating calorimeter, it undergoes a
sudden reversal of direction of motion when it strikes the baffles plates.
This causes the water particles which have greater inertia to separate
from the wet steam.
➢The water moves downwards and collected at the bottom portion of
the inner chamber.
➢The dry steam moves upwards and this steam is measured by
condensing it.
Let m= Mass of water collected in a particular time.
M= mass of dry steam passing in the same time
x = dryness fraction of wet steam
Therefore, x= Mass of Dry Steam / Mass of Wet Steam
X= M/(M+m)

10. 10
THROTTLING CALORIMETER
➢In this, the principle of constant enthalpy
expansion is adopted for the measurement of
moisture in the wet steam is as shown in the figure.
➢ In this calorimeter, steam from the main pipe of
boiler enters into the calorimeter through controlled
valves and moves into the well insulated expansion
chamber in which the temperature is measured.
➢During throttling, pressure of the steam decreases
and volume increases.
➢Neglecting the heat losses, total heat of the steam
before and after the throttling remains same.
➢Hence Steam becomes dry; therefore super heated
steam is obtained after throttling.

11. 11
THROTTLING CALORIMETER
In Enthalpy before throttling = (hf1+ x hfg1)
Where, P1 = absolute pressure of steam before throttling
hf1 = sensible heat of steam corresponding to P1
hfg1= latent heat of steam corresponding to P1and
x = dryness fraction of steam (at P1) entering the throttling unit.
Enthalpy after throttling (steam being superheated) = hg2+ Cp (tsup- tsat)
Where, P2 pressure of steam, after throttling
hg2 = enthalpy of 1 kg of dry saturated steam corresponding to P2
tsup = temperature of superheated steam after throttling
tsat= temperature of saturated steam corresponding to pressure P2
Cp = specific heat of superheated steam at constant pressure.
Enthalpy before throttling = Enthalpy after throttling = hf1+ x hfg1= hg2+ Cp (tsup- tsat)
hfg2+ Cp (tsup- tsat)- hf1
Dryness fraction, X = --------------------------------
hfg1

12. 12
COMBINED SEPERATING & THROTTLING CALORIMETER
➢Separating calorimeter gives approximate value because of incomplete separation of
moisture from wet steam where as throttling calorimeter can be used to find dryness
fraction, only if superheated is obtained after throttling.
➢Hence to overcome the limitations of these calorimeters and to obtain accurate results
combined separating and throttling calorimeter is used.
➢When steam sample enters the separating unit, most of the water vapours are
separated from the steam.
➢Then dry steam passes throttling unit where the steam is superheated without change
in enthalpy.

13. 13
COMBINED SEPERATING & THROTTLING CALORIMETER

14. References
1. Engineering Thermodynamics, P. K. Nag, Tata McGraw-Hill Publications
2. Engineering Thermodynamics, S.S. Khandare, Charotar Publication House
3. Thermal Engineering, P. L. Ballani, Khanna Publications
4. https://www.ohio.edu/mechanical/thermo/property_tab es/H2O/
5. https://www.engineeringtoolbox.com/saturated-steam-properties d273.html
6. http://www.uniklinger.com/ask-the-expert/steam-engineering-guideline/basic-
of-steam/properties-of-steam/
14