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Edition 1 Revision No. 2 Effective Date 7 July 2008

Document Title

LABORATORY EXPERIMENT

Amendment Date 3 July 2008

COURSE DESCRIPTION COURSE TITLE: THERMODYNAMICS LABORATORY TOPIC: MARCET BOILER, 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 oC, 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 Signature: Name: Penyelaras Makmal Termodinamik Date:

Approved by: Head of Plant & Automotive Engineering Department Signature: Name: Dr. Ahmad Jais bin Alimin Date:

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Edition 1 Revision No. 2 Effective Date 7 July 2008

Document Title

LABORATORY EXPERIMENT

Amendment Date 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:

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LABORATORY EXPERIMENT

Amendment Date 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:

gfg Tvh=dTdp // (3.1)

where, dp / dT = the slope of the coexistence curve

fgh = latent heat enthalpy

T = temperature

vg = specific volume of saturated vapor.

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Edition 1 Revision No. 2 Effective Date 7 July 2008

Document Title

LABORATORY EXPERIMENT

Amendment Date 3 July 2008

Assuming that is,

vg= RT / p (3.2)

and replacing vg 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.

TTRh=pp fg //// 11 00 ln (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.

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Edition 1 Revision No. 2 Effective Date 7 July 2008

Document Title

LABORATORY EXPERIMENT

Amendment Date 3 July 2008 5.0 ANALYSIS AND DISCUSSION

a. Complete Table 1 by calculating the ΔTΔp / 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 ΔTΔp / 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 closed or open

system? State proper arguments.

7.0 CONCLUSION

Conclude your findings in this experiment

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Document Title

LABORATORY EXPERIMENT

Amendment Date 3 July 2008

Table 1: Data sheet for water steam

Measured Data Calculated Values

From experiment

From Equation 3.1

Pressure (bar) Temperature Difference Slope

Slope

Gauge pressure

Abs. pressure (oC ) ( K) Δp

(bar) ΔT (oC) ΔTΔp /

dp/dT

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

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Document Title

LABORATORY EXPERIMENT

Amendment Date 3 July 2008

Figure 3: Marcet Boiler