MURANG’A UNIVERSITY OF TECHNOLOGY
SCHOOL OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
BSC ELECTRICAL AND ELECTRONICS ENGINEERING
NAME: ONESMUS WAMBUA
REG NO: EN201/0203/2020
UNIT: THERMODYNAMICS
UNIT CODE: EES 202
A LAB REPORT ON STEAM THROTTLING CALORIMETER
STEAM THROTTLING CALORIMETER
Objectives
To determine the quality of steam
Introduction
A significant reduction in pressure can be achieved by simply introducing a restriction into a
line through which a gas or liquid flows, as shown in figure 1. In throttling type steam quality
measuring device, steam is discharged tangentially into a small vessel through a nozzle to be
expanded to low pressure superheated steam. For control volume enclosing such a device, the
mass and energy rate balances reduce at steady state
to,
m1 = m2
m1(h1 + V21/2) – m2(h2 + V22/2)
where,
h = specific enthalpy (KJ/kg)
m = mass flow rate (kg/s)
v = velocity (m/s)
Figure 1
suffices 1 and 2 denotes inlet and exit, respectively.
There is usually no significant heat transfer with the surroundings and the change in potential
energy from inlet to exit is negligible. With this idealization, the mass and energy rate
balances combine to give,
h1 + v21/2 = h2 + V22/2
In most cases, the change in the specific kinetic energy of the gas or liquid between the inlet
and exit can be neglected with this further simplification, equation (5) reduces to,
h1 = h2
Thus, the enthalpy of two-phase liquid-vapour mixture, h2, is deduced from h-s chart, (see
figure 2), by pressure and temperature of superheated vapour at the exit 2
Now
h1 = hf1 + x(hg1- hf1)
But from equation (6) h1 = h2, therefore, equation (6) and (7),
X = ( h2 -hf1)/ (hg1 – hf1)
Where,
hf1 = specific enthalpy of saturated liquid deduced from h-s chart using the boiler outlet
pressure (KJ/kg)
hg1 = specific enthalpy of saturated vapour deduced from h-s chart using the boiler outlet
pressure (KJ/kg)
h2 = specific enthalpy of superheated vapour deduced from h-s chart at the pressure and
temperature of expanded vapour from the
throttling process (KJ/kg)
X = steam quality or dryness
Figure 2 Figure 3
Procedure
• We recorded boiler pre-start and start check list at the beginning of the manual
• We recorded the ambient temperature and the barometric pressure.
• After the boiler had reached a pressure of around 5.5 kg/cm2G, we set valve SV1 and
SV2 to fully open. We recorded the boiler outlet pressure p1, boiler outlet steam
temperature t1, pressure in superheated chamber p2, and temperature in superheated
chamber t2 in table 1 below. We repeated this after every 2 minutes for various boiler
outlet pressures.
Boiler Boiler Pressure in Temperature hf1 hg1 h2 x
outlet outlet superheated in
steam steam chamber superheated
pressure, temperature chamber
p1 t1 p2 t2
Kg/cm2G 0
C Kg/cm2G 0
c kJ/kg kJ/kg kJ/kg
6.1 131.2 0.35 78.3 676.0 2755.5 2682.5 0.9649
5.2 132.3 0.30 84.1 646.5 2749.3 2682.5 0.9682
5.7 134.4 0.35 101.3 664.7 2754.0 2687.5 0.9682
6.0 134.2 0.35 104.4 670.4 2755.5 2687.5 0.9674
6.5 134.7 0.40 104.1 696.8 2759.5 2687.5 0.9651
5.6 133.1 0.35 105.8 658.8 2752.5 2687.5 0.9692
DISCUSSION
The dryness fraction at each instant of time was calculated using the formula below and
inserted in the table
X = (h2 -hf1)/ (hg1 – hf1)
X = (2682.5- 676.0)/ (2755.5- 676.0)
= 0.9649
X= (2682.5- 646.5)/ (2749.3- 646.5)
=0.9682
X = (2687.5- 664.7)/ (2754.0- 664.7)
=0.9682
X= (2682.5- 670.4)/ (2755.5- 670.4)
=0.9674
X = (2687.5- 696.8)/ (2759.5- 696.8)
=0.9651
X = (2687.5- 658.8.0)/ (2752.5- 658.8)
=0.9692
Average dryness fraction
X = (0.9649+ 0.9682+ 0.9682+ 0.9674+ 0.9651+ 0.9692)/6
= 0.9672
Dryness fraction (x) = 0.9672
In the boiler outlet, there was a significant change in pressure while we recorded temperature
showed slight changes.
In the superheated chamber there were changes in temperature whereas the pressure almost
remained constant.
The quality of steam was found was found to be on average 0.9672
This represents the amount of dry vapour per unit mass and from the results we obtained high
dryness fractions thus the steam had low moisture content. The maximum amount of dryness
fraction that can be obtained is 1. This shows that the practical was accurate with minimal
errors.
There was a deviation of 0.3283 which represents an error of 3.28%.
For a steam power plant, a high dryness fraction is preferred as it increases the life span of
the turbine as steam with a lot of moisture content causes corrosion of the turbine blades.
RECOMMENDATION
A generator should be put in place in order to be able to continue with the experiment even
when power is out.
CONCLUSION
The quality of steam was determined from the dryness fraction to be high, as the average
dryness fraction is 0.9672.
REFERENCES
Lord, John (1923) Capital and Steam Power, P S King & Son Ltd: London
Turbine Technologies, Ltd., Steam Turbine Equipment, 2002.
