MARCET BOILER1.0 ABSTRACT

In order to determine the relationship between pressure and temperature of saturated

steam in equilibrium with water and demonstrate of the vapor pressure curve, this

experiment was designed. For the study of thermodynamics, the research concerning

the system that can be observed and measured is important. By measuring both

pressure and temperature, it was obvious to find out the graph (dT/dP) was almost

same with the slope obtained from the calculated one which was Tvfg/hfg. In this

experiment, the ideal gas equation will be applied and the calculation according to the

steam table will be needed too.

2.0 OBJECTIVE

2.1 To determine the relationship between pressure and temperature of saturated

steam in equilibrium with water.

2.2 To demonstrate of the vapor pressure curve.

3.0 INTRODUCTION

To complete and get results in this experiment, the measurement of pressure and

temperature is not enough. It is also important to apply the ideal gas equation and

make the calculation based on steam table correctly. Derived from the kinetic theory,

an ideal gas is consisted by three state variables: absolute pressure (P), volume (V),

and absolute temperature (T). And it is ideal gas law that can determine the

relationship between them. The equation which includes both P, V and T can be

presented as PV = nRT. Where, P = Absolute pressure; V = Volume; n = Amount of

substances (moles); R = Ideal gas constant; T = Absolute temperature (K). When it

comes to calculation which is based on the steam tables, the formular should be

Tvfg/hfg = T (vf - vg)/(hf - hg). And hf + hfg = hg, hence, T (vf - vg)/hfg = Tvg/hfg.

As vg >> vf, in which, vf =specific volume of saturated liquid; vg = specific volume

of saturated vapor; hf = enthalpy of saturated liquid; hg = enthalpy of saturated liquid;

hfg = latent heat of vaporization.

As is shown in the Figure 3.1, the Marcet Boiler is the unit where the whole process

take place. It has been developed for investigating the relationship between the

pressure and temperature of saturated steam,

Figure 3.1

4.0 APPARATUS

Figure 4.1

1 Pressure transducer 6 Bourdon tube pressure gauge

2 Temperature controller / indicator 7 Temperature sensor

3 Pressure indicator 8 Pressure relief valve

4 Control panel 9 Water inlet port and valve

5 Bench 10 Heater

Table 4.2

5.0 EXPERIMENTAL METHODS

A. General start-up procedures

1. A quick inspection was performed to ensure that the unit is in proper

operating condition.

2. The unit was connected to the nearest power supply.

3. The valves was opened at the feed port and the level sight tube.

4. The boiler was filled with distilled water through the feed port and made

sure that the water level was at about the half of the boiler’s height. Then,

the valves were closed at the level sight tube.

5. The power supply switch was turned on.

6. The experiment was ready to carried on.

B. General shut-down procedures

1. The heater was switched off to allow the boiler temperature to drop. (Note:

Do not open the valve at the water inlet port as it is highly pressurized at

high temperature).

2. Both main switch and main power supply were turned off .

3. Retained the water next use.

C. Experiment: The fundamental Pressure – Temperature Relationship of

saturated steam in equilibrium.

1. Performed the general start-up procedures.

2. If the boiler is initially filled with water, open the valves at the level side

tube to check the water level. Poured in additional distilled water if

necessary. Then, closed the valves.

3. The temperature controller was set to 170.7˚C which was slightly above

the expected boiling point of the water at 8.0 bar (abs).

4. The valve was opened at feed port and the heater was turned on.

(Important: Always make sure that the valves at the level sight tube are

closed before turning on the heater as the sight tube is not designed to

withstand high pressure and temperature.)

5. Observed the steam temperature rise as the water boils.

6. Steam was allowed to come out from the valve for about 30 seconds, and

then closed the valve. This step was important to remove air from the

boiler as the accuracy of the experimental result will be significantly

affected when air is present.

7. The steam temperature and pressure were recorded when the boiler was

heated until the steam pressure reaches 10.0 bars (abs). ( Never open the

valve when the boiler is heated as pressurized steam can cause severe

injury.)

8. Then, the heater was turned off and the steam temperature and pressure

began to drop. The boiler was allowed to cool down to room temperature.

The steam temperatures was recorded at different pressure readings when

the boiler was heated and cooled.

6.0 RESULTS

Pressure, P

(bar)

Temperature, T

(˚C)

Measured

slope,

dT/dP

Calculated

slope,

Gauge AbsoluteIncrease

(˚C)

Decrease

(˚C)

Average

Tavc(˚C)

Average

Tavc (K)

0.0 1.0 100.0 99.2 99.6 372.6 0.037 0.279

0.5 1.5 111.5 111.1 111.3 384.3 0.234 0.199

1.0 2.0 120.3 120.3 120.3 393.3 0.180 0.158

1.5 2.5 127.5 127.7 127.6 400.6 0.146 0.132

2.0 3.0 133.7 133.8 133.75 406.75 0.123 0.114

2.5 3.5 139.0 139.3 139.15 412.15 0.108 0.100

3.0 4.0 143.7 144.1 143.9 416.9 0.095 0.090

3.5 4.5 148.1 148.4 148.25 421.25 0.087 0.082

4.0 5.0 152.1 152.3 152.2 425.2 0.079 0.075

4.5 5.5 155.8 155.9 155.85 428.85 0.073 0.071

5.0 6.0 159.2 159.3 159.25 432.25 0.068 0.0647

5.5 6.5 162.4 162.4 162.4 435.4 0.063 0.061

6.0 7.0 165.3 165.5 165.4 438.4 0.060 0.057

6.5 7.5 168.1 168.3 168.2 441.2 0.056 0.054

7.0 8.0 170.7 171 170.85 443.85 0.053 0.052

Table 6.1

Pressure

(abs) bar

1.5 2.0 2.5 3.0 3.5 4.0 4.5

Error 15.0 12.2 9.6 7.3 7.4 5.2 5.7

percentage(%)

Table 6.2

Pressure

(abs) bar

5.0 5.5 6.0 6.5 7.0 7.5 8.0

Error

percentage(%)5.0 2.7 4.9 3.2 5 3.6 1.9

Table 6.3

6.1 Sample Calculation

Take the calculation when the absolute pressure is 7.0 bar as an example.

dT = 438.4K - 435.4K = 3K

dP = 7.0 - 6.5 = 0.5 bar = 50 kpa

dT/dP = 3/50 = 0.06

According to steam table;

When the pressure is 7.0 bar, T = 483.4 K; vg = 0.2729m3/kg; hfg = 2066.3 kJ/kg

Tvg/hfg = 483.4×0.2729÷2066.3 = 0.057

error percentage = |((measured – calculated) /measured)| × 100% = |((0.057 – 0.060)

/0.057)| × 100% = 5%

6.2 Graphs

Graph 6.1

Graph 6.2

7.0 DISCUSSION

From this experiment, the relationship between pressure and temperature of saturated

steam in equilibrium with water was figured out which is directly proportional.

Although there did exist some deviation between experimental slope and theoretical

one. According to the Table 6.2 and Table 6.3, the error percentage was between

1.9% to 15%. Also in this experiment, it is necessary to remove the air from the

boiler, because this may affect the accuracy of the experimental results.

When it comes to errors in this laboratory, there were four main reasons caused the

error. They were reading accuracy, room temperature and pressure, the stability of

materials respectively. And when the liquid absorbed enough heat energy, it will

change to vapour form. As the steam is not allowed to exit, it will cause an increase in

pressure and thus causing the temperature to increase. There are many applications of

this theorem in industrial area. For example, power plant, gasifier and water boiler.

8.0 CONCLUSION

By doing this experiment, the the relationship between pressure and temperature of

saturated steam in equilibrium with water was determined and the demonstrate of the

vapor pressure curve was made. It is directly proportional between pressure and

temperature. And because of the certain errors existed in this laboratory, the error

percentage was between 1.9% to 15% which can validate this experiment.

9.0 REFERENCE

[1] Conor, J. (2012), Marcet Boiler Lab Report, [online], Available:

http://zh.scribd.com/doc/51634867/Marcet-Boiler-Lab-Report.

[2] Mardhiah, A (2010), Marcet Boiler lab report, [online],

Available:http://zh.scribd.com/doc/159694163/Marcet-Boiler-lab-report