EXPERIMENT-1
Pressure-Temperature Relationship for Steam
OBJECT:
The objective of this experiment is to determine the relationship between
saturation pressure and saturation temperature of the wet steam.
APPARATUS:
Pressure-temperature apparatus with pressure gauge and thermometer.
Valve
Steam
Inlet
Thermometer
(Steam
Temperature)
Pressure Gage
(Steam Pressure)
Valve
Steam
Exit
THEORY:
In order to determine the relationship between the saturation temperature and pressure of
wet steam it is necessary to obtain a number of corresponding values of the two variables
and to plot a graph.
PROCEDURE:
1. Connect the unit to the steam supply and open the stop valve on the inlet side.
2. Throttle the outlet from the cylinder to the desired pressure and allow a period of
time to elapse to obtain steady state conditions.
3. Record the steam temperature and pressure.
4. Adjust the steam pressure using the throttle valve, and allow sufficient time to
elapse to obtain steady state condition.
5. Record the steam pressure and temperature.
6. Repeat this procedure until the maximum pressure is reached.
7. Take a further set of readings with reducing pressure allowing time at each stage
to reach steady state conditions.
RESULTS AND CALCULATIONS:
Plot graphs of temperature (y-axis) against absolute pressure (x-axis) for
a)
Pressure increasing
b)
Pressure decreasing
c)
Steam table values for the range of pressure used
Absolute pressure
=
Atmospheric pressure =
PRESSURE (bar)
Increasing
Gauge
Atmospheric pressure + Gauge pressure
1 bar
Decreasing
Absolute Gauge
Steam
Table
Absolute Absolute
CONCLUSION AND DISCUSION:
TEMPERATURE oC
Increasin Decreasing Steam
g
Table
oC
oC
oC
EXPERIMENT-2
Separating and Throttling Calorimeter
OBJECT:
The objective of this experiment is to determine the dryness fraction of wet steam.
APPARATUS:
Ward steam bench
a)
b)
c)
d)
Steam boiler plant (unit 1).
Separating and throttling calorimeter (unit 3)
Measuring
Beaker
Separating
Calorimeter
Steam Pressure
Gauge
Throttling
Calorimeter
Thermometer
Throttle valve
Steam Inlet
Thermometer
Manometer
Separated Water
M1
Cooling Water
Out
Condenser
Cooling Water
In
Condensate
M2
Figure1. Schematic diagram for the separating and throttling Calorimeters.
THEORY:
The separating calorimeter is a vessel used initially to separate some of the
moisture from the steam, to ensure superheat conditions after throttling. The steam is
made to change direction suddenly; the moisture droplets, being heavier than the vapor,
drop out of suspension and are collected at the bottom of the vessel.
The throttling calorimeter is a vessel with a needle valve fitted on the inlet side.
The steam is throttled through the needle valve and exhausted to the condenser. Suppose
M kg of wet steam with a dryness fraction of x (state A) enters the separating calorimeter.
The vapor part will have a mass of xM kg and the liquid part will have a mass of (1-x)M
kg. In the separating calorimeter part of the liquid, say M1 kg will be separated from the
wet steam. Hence the dryness fraction of the wet steam will increase to x1 (state B)
which will pass through the throttling process valve. After the throttling process the
steam in the throttling calorimeter will be in superheated state (state C).
T
P1
A B
●
T1
●
P2
●
T2
C
S
Figure2. T-S diagram of the separating and throttling calorimeter.
From the steady flow energy equation;
Q – W = hC - hB
Since throttling takes place over a very small distance, the heat transfer is negligible, i.e.,
Q = 0. Then the steady flow energy equation for the throttling process becomes,
hC = hB
Hence, enthalpy after throttling = enthalpy before throttling
hC = hf1 + x1 hfg1
If the pressure of the steam before throttling, the pressure and temperature of the steam
after throttling, are known the value of x1 can be calculated using steam tables.
Dryness Fraction =
Mass of dry steam
Mass of mixture
Therefore,
X=
x1 M2
M1  M 2
Where, M2 is the mass of condensate.
PROCEDURE:
1. Start the boiler and supply steam to the separating and throttling calorimeter unit.
2. Start the cooling water flow through the condenser.
3. Open steam valve and allow the steam to flow through the calorimeters to warm
through the steam.
4. Open the throttle valve and adjust to give a pressure at exhaust of about 5cm Hg
measured on the manometer.
5. Drain the separating calorimeter.
6. Start the test and take readings at 2-3 minutes intervals.
7. When a reasonable quantity of condensate is collected measure the quantity of
separated water and the quantity of condensate.
RESULTS AND CALCULATIONS:
Using the average values, obtain the specific enthalpy of steam at (state C) hence
calculate the dryness fraction of incoming steam. Also calculate the specific enthalpy of
incoming steam.
Reading #
TABLE OF OBSERVATIONS
1
2
Steam pressure in main P1 (bars)
Steam pressure after throttling P2 (bars)
Temperature of main T1 (oC)
Temperature after throttling T2 (oC)
Quantity of Separated water M1 (kg)
Quantity of condensate M2 (Kg)
Atmospheric pressure Pa (bars)
3
4
5
6
Ave.
EXPERIMENT-3
INDEX OF COMPRESSION
OBJECT:
To determine the poly tropic index of compression, ‘n’, for air, from the poly
tropic expression PVn = C.
APPARATUS:
Reciprocating two-stage, air compressor/Dobbie-McInnes spring and piston
indicator/Indicator cards/Fortin barometer.
PROCEDURE:
1. With the compressor running and using the Dobbie McInnes indicator, mark the
atmospheric pressure line on the indicator card.
2. Produce a P-V indicator diagram by opening the pressure valve to the indicator
and operating the indicator marker in the usual manner.
3. Remove the indicator card and establish the pressure and volume datum axes.
This is carried out as follows:
Y
Compression
Pc (mm)
Atmospheric Pressure Line
X (mm)
Y (mm)
x- Represents the stroke of the piston.
y- Represents the clearance of the piston.
X
clearance volume
y
=
x
swept volume
Therefore, for a constant diameter:
and since x is measure on the diagram and the clearance and swept volumes may be
obtained from the compressor handbook ‘y’ is calculated, and for distance Pc we have:
Pc =
Barometric pressure
spring cons tan t
mm
Compressor information required;
Bore of cylinder
Stroke of piston
Clearance volume
Spring constant
4-
=
=
=
=
66.7mm
63.5mm
2.35 x 10-5 m3
2.5mm/bar
Measure the co-ordinates of at least eight points on the compression curve on the
indicator, diagram, take logarithms and tabulate.
P
V
Log P
Log V
It is not necessary to convert the measured ordinates to pressure or volume.
5Produce a graph of log P vs. Log V. This should be a straight line. The slope of
this line will give values of the index ‘n’
i.e. from PVn
= constant. (C)
Or
Log P +n log V
= log C
Log P
= -n log V + log C
Which is a linear relationship.
CONCLUSION
(i)
(ii)
(iii)
Summarize your results
Explain the significance of n = 1 and n =  = 1.4 for air.
From the knowledge of (ii) above, estimate the probable value for ‘n’ during this
test and comment on the experimental value obtained.