Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
1/7 1 2 7 July 2008 3 July 2008
COURSE DESCRIPTION COURSE TITLE: THERMODYNAMICS LABORATORY TOPIC: MARCET BOILER, CLAUSIUS-CLAPEYRON CLAUSIUS-CLAPEYRON EQUATION
1 .0 OBJECTIVE
To investigate the relation between saturated temperature and pressure during phase change for water 2 .0 EXPERIMENTAL EQUIPMENT
Marcet boiler equipped with manometer, thermometer, feed water port, control and safety features – safety valve and discharge valve and energy source – heater from 240V, 13A source 3 .0 THEORY
Water can exist in solid, liquid, and vapor/gas phase. Heat has to be added to the water in the solid form (ice) to change its state from solid to liquid phase (water). Adding more heat into water at a constant pressure will result in temperature rise. At 100 o C, water starts boiling, and again, the phase change process begins and but its temperature remains constant. The heat can be from any source, combustion, electrical heating etc.. Prepared by: Panel of Thermo-Fluid T hermo-Fluid
Approved by: Head of Plant & Automotive Engineering Department
Signature:
Signature:
Name: Penyelaras Makmal Termodinamik
Name: Dr. Ahmad Jais bin Alimin
Date:
Date:
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
2/7 1 2 7 July 2008 3 July 2008
After all liquid has changed into the vapor phase, the temperature rises, and the water now will be in a single phase - vapor phase. The heat added from the liquid state to boiling, the phase change and the result of adding more heat can seen from the phase diagram in Figure 1.
Figure 1: (a) T-v diagram & (b) p-v diagram of water,
In this experiment, water is heated up under a constant volume. During the phase-change process, the pressure and the temperature are dependent properties, and there is a definite relation between them. The characteristic of the relation is shown in Figure 2:
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
3/7 1 2 7 July 2008 3 July 2008
Figure 2: Characteristic curve of water
3.1 Clausius-Clapeyron equation
The relationship between the temperature of a liquid and its vapor pressure is not a straight line. The vapor pressure of water, for example, increases significantly more rapidly than the temperature of the system. This behaviour can be explained with the Clausius-Clapeyron equation which defines the slope of the vapor pressure curve:
dp / dT = h fg / Tv g where,
dp / dT = the slope of the coexistence curve
h fg
= latent heat enthalpy
T
= temperature
vg
= specific volume of saturated vapor.
(3.1)
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
4/7 1 2 7 July 2008 3 July 2008
Assuming that is,
vg = RT / p and replacing
vg
(3.2)
in equation (3.1) with equation (3.2).
If the corresponding temperature and pressure is known at two points, the enthalpy of vaporization can also be determined from this equation. ln p / p0 = h fg / R 1 / T 0
1 / T
(3.3)
where R is a gas constant for water R = 0.4615 kJ/kg. Index “ o” refers to the critical point of water. This equation also will let us figure out the vapor pressure of a liquid at any temperature if we know the enthalpy of vaporization. 4.0 EXPERIMENTAL PROCEDURES
a. Fill up the boiler with water to the marked level (until the water drips through the opened discharge valve). b. Open the discharge valve and heat up the water (see Figure 3). c. Close back the valve when you notice steam starts to come out from the boiler. This is to ensure that there is no more air trap inside the water. d. Record the temperature reading for each 0.5 bar increment of pressure until it reaches 6 bar (gauge pressure). e. Stop the heating process. f.
Record again the temperature reading when pressure drops. Measurement should be taken at every decreasing of 0.5 bar.
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
5/7 1 2 7 July 2008 3 July 2008
5.0 ANALYSIS AND DISCUSSION
a. Complete Table 1 by calculating the Δp / ΔT and dp/dT from Equation 3.1 for each measurement. For the dp/dT calculation, use steam table and make interpolation where necessary. b. Plot Δp / ΔT versus dp/dT . Compare the deviation between both values and state what is your explanation about this difference.
6.0 QUESTIONS
a. Although water is made up of two gaseous molecules hydrogen and oxygen, it can be considered as a pure substance, why? b. What is the difference between latent heat and sensible heat? c. The system comprising of water-steam in the boiler can be considered as a c losed or open system? State proper arguments.
7.0 CONCLUSION
Conclude your findings in this experiment
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
6/7 1 2 7 July 2008 3 July 2008
Table 1: Data sheet for water steam
Measured Data
Pressure (bar)
Gauge Abs. pressure pressure 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Calculated Values
Temperature
(oC )
( K)
Difference
Δp (bar)
ΔT (oC)
From experiment
From Equation 3.1
Slope
Slope
Δp / ΔT
dp/dT
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
Figure 3: Marcet Boiler
7/7 1 2 7 July 2008 3 July 2008
