CAPE PENINSULA UNIVERSITY OF TECHONOLOGY DEPARTMENT OF MECHENICAL ENGINEERING THERMODYNAMICS 2 LAB

1. Cape Peninsula University of Technology
Bellville Campus
Department of Mechanical Engineering
THERMODYNAMICS LABORATORY
THE DRYNESS FRACTION OF THE STEAM
By L.Nyandu………….
Subject: APT200S
Lecturer: S Makhomo
Evaluation Criteria
Introduction: (Aim for each lab, Background, List of the
apparatus, Procedure etc)
10%
Result: (Calculations, Correct method, etc) 55%
Explanations (did you explain what you are doing rather than
put formulas.)
10%
Discussion: (Discussion of the results, do they make sense?
Any possible errors,
etc)
10%
Conclusion and Recommendations: (Did we achieve our aims?
What do we need to
do to improve our
results)
5%
Presentation, layout and neatness: (Cover page, Typed/ print
neat, report format,
etc)
10%
Total 100%
Date of submission: 5/08/2014
LAB 1: THE DRYNESS FRACTIONOF THE STEAM
The aim of this experiment is to determine the dryness fraction of wet steam.

2. 1. Apparatus
 Steam boiler plant.
 Combined Separating and throttling calorimeter.
 Measuring beaker
 Thermometer
Figure 1: The figure above shows the apparatus for conducting the dryness fraction lab.
2. Theoreticalbackground
If we have steam that is nearly dry, we make use of a throttling calorimeter. This
calorimeter is operated by first opening the valve opening the stop valve fully so that the
steam is not partially throttled as it passes though the valve. The steam then passes
through the apparatus for a while to allow the pressure and temperature to stabilize. If
the pressure is very close to the atmospheric pressure, the saturation temperature
should be around 100 degrees Celsius. It may be assumed that the steam is to be
superheated if the temperature somewhere above 100 degrees Celsius. When the
conditions are steady, the gauge pressure before throttling is read from the pressure
gauge. After throttling, the temperature and the gauge pressure are read from the
thermometer and a manometer respectively. The baric pressure is also needed.
Suppose M kg of wet steam with a dryness fraction of x enters the separating
calorimeter. The vapor part will have a mass of x M kg and the liquid part will have a
mass of M kg. In the separating calorimeter part of the liquid, say1 kg will be separated
Condenser
Separating
Calorimeter
Throttling
calorimeter
Separated water
Scale
Measuring
beaker

3. from the wet steam. Hence the dryness fraction of the wet steam will increase to x1
which will pass through the throttling process valve. After the throttling process the
steam in the throttling calorimeter will be in superheated state.
3. Procedure
 Start the boiler and supply steam to the separating and throttling calorimeter unit.
 Start the cooling water flow through the condenser.
 Open steam valve and allow the steam to flow through the calorimeters to warm
through the steam.
 Open the throttle valve and adjust to give a pressure at exhaust of about 5cm Hg
measured on the manometer
 Drain the separating calorimeter.
 Start the test and take readings at 2-3 minutes intervals.
 When a reasonable quantity of condensate is collected measure the quantity of
separated water and the quantity of condensate.
4. Results
Determine the Absolute Pressure:
𝑃 𝑎𝑏𝑠 = 𝑃𝑔 + 𝑃 𝑎𝑡𝑚
=740 + 101
= 841.33 𝐾𝑃𝑎
∴ 𝑃1= 841.33 KPa and 𝑃2= 30 KPa
∴ 𝑇1= 112.5 ℃ and 𝑇2= 69.06 ℃
The above written values were calculated using interpolation method and values
from the steam tables.
Separating calorimeter only (xo):
M 𝑺 = 2500m𝑙

4. = 2,5𝑙
= 2,5𝑘𝑔
M 𝒘 = 400m𝑙
= 0,4𝑙
= 0,4 𝑘𝑔
𝑋1 =
Ms
Ms + Mw
=
2,5
2,5+0.4
= 0.862
Throttling calorimeter only x1
ℎ2 = ℎsup @ 30 𝐾𝑃𝑎,151℃ ( 𝑢𝑠𝑖𝑛𝑔 𝑑𝑜𝑢𝑏𝑙𝑒 𝑖𝑛𝑡𝑒𝑟𝑝𝑜𝑙𝑎𝑡𝑖𝑜𝑛)
= 2783,54 𝐾𝐽/𝑘𝑔
ℎ 𝑓 𝑎𝑛𝑑 ℎ 𝑓𝑔 @ 𝑃1 (Using interpolation)
ℎ 𝑓 @ 𝑝1 = 730.027 𝐾𝐽/𝐾𝑔
ℎ 𝑓𝑔 @ 𝑝1 = 2040,309 𝐾𝐽/𝐾𝑔
ℎ 𝑠𝑢𝑝 = ℎ 𝑓 + 𝑋2 . ℎ 𝑓𝑔
𝑋2 =
ℎ 𝑠𝑢𝑝−ℎ 𝑓 @ 𝑝1
ℎ 𝑓𝑔 @ 𝑝1
𝑋2 =
2783,54−730,027
2040,309
∴ 𝑋2 = 1.0064 This means it lies outside the dome to the superheated region.
∴ 𝑋0 = 𝑋1 × 𝑋2
= 0,862 × 1,0064
= 0,867
∴ 𝑋0 ≈ 0,87
Readings taken from experiment:
Reading Units
Volume of Steam (Vs) 0.0025 m3

5. Volume of Water (Vw ) 0.0004 m3
Pressure before throttling (P1) 840 kPa
Pressure After throttling (P2) 30 kPa
Temperature of steam before throttling (t1) 112,5 oC
Temperature of steam After throttling (t2) 69,06 oC
Figure 2: The table above shows the experimental readings that were recorded for the
dryness faction lab conducted.
5. Discussion
Based on the results of the readings we obtained when conducting the experiment in
the lab, it can be said that using the readings that were recorded in the lab, the dryness
fraction of the steam could be found in regards with the use of the theoretical equations
from the thermodynamics textbook. From the results obtained, the dryness fraction is
0.862 at x0 this showed us that at that point in time the steam is 87% dry and 13% wet.
We got 1.0064 at x1 so that showed us that the steam is superheated because it is
greater than 1 at that point so the combined separating and throttling calorimeter’s
dryness faction was found by using the equation where both x0 and x1 were multiplied to
get 0.87. This shows that the state of the steam is still wet because the value of the
dryness fraction of steam is less than 1.
6. Conclusion
It can be concluded that the experiment was successful and the dryness fraction of the
steam was found using the readings found to be 0.95 which then showed us that the
steam state is considered wet.
7. Recommendations
Maintenance in the laboratory apparatus for the dryness fraction lab conduction should
be done before students are allowed to go and do the experiments. This is due to
varying data or reading that student get when conducting the labs as that would make
lecturers to mark the laboratory work easier. That could also constitute to the
improvement on the efficiency of the set of apparatus as seen above calibration.
8. BIBLIOGRAPHY
J.A. Leach. 2007. “Engineering thermodynamics’. Chapter 8: Juta publishers, Cape
town, South Africa.