marcet boiler

STUDENT NAME MD ATIQUR RAHMAN FAISAL

STUDENT ID SCM-012154

COURSE BACHELOR IN MECHANICAL ENGINEERING

LECTURER DR. THAM

SUBMISSION DATE 7th May 2012

SUBJECT THERMODYNAMICS (EAT 106)

Marcet Boiler Experiment

Title : Marcet Boiler Experiment

Introduction : Thermodynamics is a part of physics, which deals with work energy and power of a system. Thermodynamics mainly works with large-scale system,

which can be measured by experiment study of liquid or gas or the properties of fluid is also a part of thermodynamics.

Abstract : The experiment is going to be carried out to demonstrate the relationship between the pressure and temperature of saturated steam in equilibrium.

Marcet boiler is going to be used as apparatus.

The Marcet boiler filled with water is to be healed first, until a certain absolute pressure reached. Then the heater will be turned off and will be

allowed to cool down to its initial temperature. The increasing and decreasing temperature will be recorded for further use and calculation of the experiment.

Objective : Demonstrating the relationship between pressure and temperature of a saturated steam in equilibrium with water and determining the pressure

vapor curve.

Theory : As we know about ideal gas law and how they behave. The ideal gas equation states that, relates the pressure, specific volume or density and

absolute temperature with the mass of molecule and gas constant “R”.

PV=mRTM

= PV=nRT

Where,

P= absolute pressure.

V=volume.

n= amount of substance in moles. Where, n= m(massof t he substance)

M (molar mass)

R= ideal gas constant.

T= absolute temperature in Kelvin.

In real life, real gas never exactly follows or obeys the equation. If a few changes are allowed on the ideal gas equation of state, then it can be applied

on the properties of real gas.

When energy increases within water, the water molecules with the water gets excited and try to escape from the water in the form of steam. It’s easier

for the molecules to escape, if the pressure is low.

MD Atiqur Rahman Faisal


The temperature at which the equilibrium state is reached (boiling point) at a given pressure is called saturated temperature, and the pressure where

saturated equilibrium occurs at given temperature is called saturated pressure.

Marcet boiler is used to investigate the relationship between the pressure and the temperature of saturated steam in equilibrium with water at all

temperature levels between the atmospheric pressure and 8 bars.

The measured value of the slope of the graph [ dTdP ]SAT

obtained from the practical

result can be compared with corresponding values calculated from the data in steam tables.

Clausius-clapeyron states:

[ dTdP ]SAT

= Tv fgh fg

[ dTdP ]SAT

= T (v f−v g)

(h¿¿ f−hg)¿

Where,

h f+h fg=hg

h fg=hg−h f

as,

vg≫v f

( dTdP )SAT

=T(v¿¿ f−vg)

h fg=Tvgh fg

¿

In which,

v f → specific volume of saturated liquid.

vg → specific volume of saturated vapor.

h fg → latent heat vaporization.

h f → enthalpy of saturated liquid.

hg → enthalpy of saturated vapor.



Apparatus : The unit consists of a stainless steel pressure vessel fitted with high-pressure immersion electric heater. The unit also comes with a safety relief

valve, temperature and pressure measuring devices. Water feed port is installed to allow water charging. The unit also includes temperature and pressure transducer, so that it is easy to read the respective valves on the digital indicator. The water heater is

protected from burnout by setting the maximum operating temperature with temperature controller.



Figure: Marcet Boiler

Procedure :

1. A quick inspection is performed before starting the experiment to ensure the units is in proper operating condition.

2. The Marcet boiler is connected to the nearest power supply.3. The valves at the feedport are now opened.4. The boiler is filled with distilled water at about half of boiler’s height

through the feedport.5. The valve at the level sight tube is then closed.6. The power supply is then turned on, to start the experiment.

Precaution :

1. The temperature controller is set to 185.0oc, that is slightly above the expected boiling point of water at 10bars (abs).

2. The valve at the feed port was opened while the heater was turned on.

3. The valve at the level sight tube are made sure to be closed before turning on the heater as the sight tube is not designed to withstand high pressure and temperature.

4. The rise of the steam temperature could be observed when the water boils.

5. The steam from the valve was allowed to come out for 30 seconds before the valve was closed (this step is very important to remove the air from the boiler as the accuracy of the experiment results would be significantly affected if air is present).

6. The steam temperature, gauze pressure at 1.00bar (abs) and time taken for steam to reach until 8.00bar (abs) is recorded.

7. After the experiment, the heater is allowed to cool down to room temperature.

8. The time taken for the heater or boiler to cool down is also recorded.9. All the readings of result are recorded and tabulated on a table.10. Graph is plotted at absolute temperature “T” against absolute

pressure “P”.11. The slope of the graph is measured using certain points.

12. Another graph[ dTdP ]SAT

vs. P, [Tv f gh fg ] vs. P, is plotted.

13. The graph plotted from experiment data is compared to that of the calculated data.



Obtained data :

Pressure, P(bar) Temperature, T Measured Slope. Calculated Slope. ErrorPercentage

Absolute Gauze (abs) Increase, 0C

Decrease, 0C

Average, 0C

Average, K

(dT) (dP) [ dTdP ]SAT

Tv fg h fg [Tv fghfg ] %

1.0 0 101 100.0 99.7 99.85 372.85 626.42

2256.8 0.28

1.5 0.5 150.03 111.2 111.3 111.25 384.25 20.3 98.06 0.20 447.65

2226.28 0.20 0

2.0 1.0 199.06 120.1 120.2 120.15 393.15 16.40 98.06 0.17 348.99

2190.82 0.16 5.88

2.5 1.5 248.09 127.4 127.9 127.65 400.65 13.70 98.06 0.14 287.35

2180.47 0.13 7.14

3.0 2.0 297.12 133.6 134.1 133.85 406.85 11.55 98.06 0.12 244.76

2162.46 0.11 8.33

3.5 2.5 346.65 138.9 139.5 139.20 412.20 10.15 98.06 0.10 214.43

2146.67 0.10 0

4.0 3.0 395.18 143.7 144.3 144.00 417.00 9.10 98.06 0.09 191.19

2132.22 0.09 0

4.5 3.5 444.21 148.0 148.6 148.30 421.30 8.35 98.06 0.08 173.03

2119.04 0.08 0

5.0 4.0 493.24 152.1 152.6 152.35 425.35 7.75 98.06 0.08 157.76

2106.37 0.08 0

5.5 4.5 542.27 155.9 156.2 156.05 429.05 7.10 98.06 0.07 145.06

2094.64 0.07 0

6.0 5.0 591.3 159.3 159.6 159.45 432.45 6.55 98.03 0.07 134.58

2083.76 0.07 0

6.5 5.5 640.3 162.5 162.7 162.60 435.60 6.05 98.06 0.06 125.84

2073.47 0.06 0

7.0 6.0 689.36 165.4 165.6 165.50 438.50 5.70 98.09 0.06 118.18

2063.92 0.06 0

7.5 6.5 738.39 168.2 168.4 168.30 441.30 5.30 98.10 0.05 111.52

2054.17 0.05 0

8.0 7.0 787.42 170.8 170.8 170.80 443.80 105.81

2046.06 0.05

Calculation :

Equation used

PV=mRTM

m→mass(grams)

M→molecular weight(grams/mol)



P→Pressure(Kpa)

V→volume(m3)

R→molar gas constant(J/mol K)

T→temperature(K)

Things to do :

Plotted graph, T vs P. Calculate gradient of graph.

Graph [ dTdP ]SAT

vs P, and [Tv f gh fg ] vs P.

Compare graph plotted from experiment data to that of calculated data.

0 100 200 300 400 500 600 700 800 900320

340

360

380

400

420

440

460

f(x) = 0.0964792521872739 x + 374.093261702656R² = 0.953046700747467

T vs P

T vs PLinear (T vs P)

Gradient = 0.0965



0 100 200 300 400 500 600 700 800 9000

0.05

0.1

0.15

0.2

0.25

0.3

(dT/dP)sat vs P(Tvfg/hfg) vs P

Sample calculation:

Taking the values of fourth row,

h fg Calculation,

For the temperature 127.650C (from the saturated water- Temperature table)

(130−127.65)(130−125)

=(2173.7−h fg)

(2173.7−2188.1)

(2.35)(5)

=(2173.7−h fg)

(−14.4)

−33.84=10868.5−5hfg

5h fg=10868.5+33.84



h fg=10902.34

5

h fg=2180.47

vg Calcultion,

For the temperature 127.650C (from the saturated water- Temperature table)

(130−127.65)(130−125)

=(0.66808−vg)

(0.66808−0.77012)

2.45

=(0.66808−vg)(−0.10204)

(−0.244896 )=(3.3404−5vg)

5v g=(3.3404+0.244896)

vg=(3.3404+0.244896)

(5)

vg=0.7170592

Tvg Calculation,

Tvg=(400.65 )× (0.7170592 )

Tvg=287.35

[Tvgh fg ] Calculation,

[Tvgh fg ]= (287.35)(2180.47)

=0.13(2decimal places)

Calculating the value of P(abs) at the temperature 120.150C,

P¿¿

P¿¿

P¿¿

Calculating the values of P(abs) at the temperature 133.850C,



P¿¿

P¿¿

P¿¿

Calculating the value of dP

dP=297.12−199.06=98.06Kpa

Calculating the value of T(K) at 120.150C

T (K )=T 0C+273

T (K )=120.15+273=393.15K

Calculating the value of dT

dT=400.65−393.15=13.70K

Calculating the value of [ dTdP ]SAT

[ dTdP ]SAT

=(13.70)(98.06)

=0.14(2decimal places)

Calculating the difference between [ dTdP ]SAT

and [Tvgh fg ], error percentage.

Error%=(Measured Slope )−(Calculated Slope)

(Measured Slope)×100%

Error%=(0.14 )−(0.13)

(0.14)×100%=7.14%

Discussion : Marcet boiler was made by Nathan Chamberlain, Boston, USA, in the year 1850. He made this boiler for measuring the vapor pressure of saturated liquid. Later this Marcet boiler was used to study the evaporation filtration of water.

Pressure and temperature are two fundamental quantities of materials in thermodynamics. These two factors have relation directly proportional to each other.

When a container contains saturated liquid and are heated to it’s boiling temperature, the liquid will be changing it’s state from liquid to steam. If the steam are not allowed to escape from the container, their internal pressure will increase.



Because, when the liquid becomes gas by heating, the internal molecular energy will increase and the atoms will be more excited. All the excited atoms will hit each other and split with more speed or velocities. As their mass remains constant, so their forces on each other will increases. And when their forces on them increases, and are not allowed to occupy more area, they exerts pressure on the container, which gradually increases with temperature. Hence it is calculated and proved from the graph, that temperature is directly proportional to the pressure.

The error percentage should not cross or exceed 10%, as the experiment was done in enclosed surface and no volume of experimenting samples are allowed to escape from the system. That is done in closed system.

It is important to remove gas at the beginning to avoid the flaws of reading due to pressure difference.

Marcet boiler is being used as water boiler, gasifier, powerplant, cooking utensils, steam plant industries, etc.

Conclusion : From the experiment, it is found from the graph and calculation, temperature of a saturated steam is directly proportional to the pressure in equilibrium with water.

The percentage error on the experiment for first two values were found higher than those third value and onward. This happened due to take improper reading from the pressure gauze and some technical fault. The rest of the result for percentage error are found “O” zero percent, which is also not practically possible. This happened due to taking the two figure after decimal, which reduce the contrast of the reading.

Disgracing some negligible faults, this experiment can be consider successful, to improve the result of the experiment, it should be carried out at room temperature switching off all the air-conditions, and also by repeating the experiment and taking the average value. If some insulation were kept on the Marcet boiler to reduce heat loss, the experiment could be more accurate.
