marcet boiler

Lab 1

[DATE]niall buckleyA00224937

ContentsIntroduction:..........................................................................................................................................1

Methodology:........................................................................................................................................2

Results:..................................................................................................................................................3

Results:..................................................................................................................................................4

...............................................................................................................................................................5

Discussion:.............................................................................................................................................6

Conclusion:............................................................................................................................................6

References:............................................................................................................................................7

1

Introduction:

A Marcet Boiler is a bench top unit with a built in heating system used to demonstrate the

relationship between pressure and temperature of a system in equilibrium with water. The

boiler is fitted with a pressure gauge and a temperature gauge which are used to take readings

of both for this experiment. The readings in our case will be taken at 0.5bar increments. We

will then be able to plot a graph of pressure over temperature for both experimental and

reference values.

Steam has been used as a source of power since the 1700’s where it was used in industry

and on the railways to provide drive for the engines. Back then it was inefficient as the

boilers were not very good and much of the fuel was wasted in providing power or drive.

Steam is created by adding heat or energy to a system under pressure, this energy separates

the water molecules from one another and changing the water from a liquid phase to a vapour

phase. Initially the steam is wet steam due to the fact that there are still water droplets

contained in the vapour the more it is heated the less droplets it contains and then it becomes

superheated steam which is a dry gas.

The purpose of this experiment is to investigate the relationship between the pressure and

temperature of saturated steam in equilibrium with water at pressures from 0 to 10 bar and to

use the recorded data to plot a graph of dT/dP and compare it to values obtained by

calculations from the steam table.

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Methodology:

Before we started the experiment with the Marcet boiler (Figure 1) we opened the top of the

boiler as well as the tap on the side. Then we filled the boiler until the water began to flow

from the tap. The filler was then tightened and we waited for the water to stop flowing from

the tap at this point the tap was put into the closed position and we were ready to start the

experiment.

The power supply was then turned on and the system allowed to heat up to 110°C. Once

this was done the pressure release valve was opened for approximately 20 seconds in order to

expel any air trapped in the system. The temperature was then recorded at zero pressure and

zero time and the stop watch was started. The pressure was then allowed to build up in .5 bar

increments where time, pressure and temperature readings were recorded. This was done up

to 10 bar. Once 10 bar had been reached the power was switched off and readings were again

taken of time, pressure and temperature until the boiler had reached a pressure of 4 bar. At

this point we could draw up a table for both sets of results and plot a graph of

temperature/absolute pressure.

Figure 1

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Results:

Gauge Pressure (bar)

Time (sec.)

Temperature (°C)

Temperature K

Average Temperature (K)

Reference Temperature

Reference Temperature

Slope Slope Calculated

1 0 110 383.15 99.6 372.15 1.5 250 121 394.15 111.4 384.55 2 400 128 401.15 120.2 393.35 2.5 520 133 406.15 127.4 400.55 3 630 138 411.15 133.5 406.65 3.5 730 142 415.15 138.9 412.05 4 810 146 419.15 143.6 416.75 4.5 890 149 422.15 420.65 147.9 421.05 5 960 152 425.15 423.65 151.8 424.95 0.06 0.0765.5 1030 155 428.15 427.15 155.5 428.65 0.07 0.076 1105 158 431.15 430.65 158.8 431.95 0.07 0.0656.5 1175 161 434.15 433.65 162.1 435.25 0.06 0.0617 1230 163 436.15 436.65 165 438.15 0.06 0.067.5 1290 165 438.15 439.15 167.9 441.05 0.06 0.0558 1360 167 440.15 441.15 170.4 443.55 0.04 0.058.5 1420 171 444.15 443.15 173 446.15 0.04 0.0489 1475 173 446.15 446.15 175.4 448.55 0.05 0.0479.5 1535 175 448.15 447.65 177.8 450.95 0.04 0.04610 1590 177 450.15 449.65 179.9 453.05 0.04 0.044

Figure 2 Table 1

Results:

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Figure 3 Table 2

Gauge Pressure (bar)

Time (sec.)

Temperature (°C)

Temperature K

9.5 34 178 451.159 60 176 449.15

8.5 91 175 448.158 171 173 446.15

7.5 200 171 444.157 252 169 442.15

6.5 333 166 439.156 452 163 436.15

5.5 604 160 433.155 768 156 429.15

4.5 909 152 425.154 1106 149 422.15

350 370 390 410 430 450 4700

2

4

6

8

10

12

Pressure/Temperature

Experimental ValueReference

Temperature (K)

Pres

sure

(bar

)

Figure 4 Graph 1

4 5 6 7 8 9 10 110

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

dT/dP

ExperimentalCalculated

Pressure (bar)

Slop

e

Figure 5 Graph 2

5

Figure 6 Steam Table (1)

6

Discussion:

As we can see from the graphs in figure 4 and 5 the experimental values are slightly off as compared with the reference values, this may be due to not enough air being drained from the system at the start of the experiment. It could also be as a result of inaccuracy in the readings for the temperatures at the corresponding pressure values. The thermometer was an analogue one which made readings difficult due to the fact that they had to be interrupted by the reader. The Marcet Boiler itself may also have been defective as there could have been a leak in it which would also have thrown the results off. Impurities in the tap water could also have contributed to inaccuracy’s in the readings.

The results show us that as more energy is put into the system more steam is created and pressure builds up and although the experimental results are off compared with the reference values the graph in figure 4 shows us a similar curve which proves the theory.

Conclusion:

The purpose of this experiment was to show the relationship between temperature and pressure in a closed system and then to plot graphs of the results as compared with reference values taken from a steam table. As the results show the curves in both graphs (figure 4 and 5) differ from the reference values however the relationship between temperature and pressure in a system was demonstrated although there were inaccuracy’s.

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References:

1. A.I.T. Moodle. [Online] 08 10 2015. [Cited: 08 10 2015.] http://www.ait.ie/.

2. Engineers Edge. Engineers Edge. [Online] LLc, 2000. [Cited: 08 10 2015.] http://www.engineersedge.com.

3. Al, Shahda Mazin Abduijabbar. Slideshare. slashdocs. [Online] 2015. [Cited: 08 10 2015.] www.slashdocs.com.

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