Laboratory of Thermodynamic

Experiment (1)
Marcet Boiler

Objective:
1. To study the relationship between the pressure and the temperature steam in
equilibrium with water.
2. To plot the curve of saturation pressure of the steam.
3. To record the temperature and the pressure of the saturated steam.

Introduction:
Thermodynamics is a branch of study of physics that deals with the
interchange of energies such as work and heat between a system and a surrounding
when the system undergoes a process which are either cooling or heating. The loss
or gain of energy of the system during a process has a direct impact on the
thermodynamics properties. Two of the most important thermodynamics properties
that are being investigated in this experiment are absolute pressure and temperature
that are both changes during the process in the system. The data from the
experiment will be compared with the theoretical value obtained from the steam
table.
For this experiment, we will be using SOLTEQ®Marcet Boiler (Model:
HE169) which is the bench top unit designed for the demonstration of the basic
principle in thermodynamics which is boiling. SOLTEQ®Marcet Boiler (Model:
HE169) are the most common device used for students in the laboratory for them
to have a better understanding the relationship between absolute pressure and
temperature of saturated steam in equilibrium with water.
 Theory:
While water boils in an open vessel at a temperature of 100°C, it does not
turn to steam in an enclosed vessel, such as a steam boiler, until a higher
temperature is reached.
The heat initially causes water molecules to evaporate, increasing the pressure in
the steam chamber and in the water itself. As steam pressure rises, the boiling point
temperature also increases because water molecules encounter increased resistance
as they attempt to move from the liquid to the gas phase. Consequently, each steam
pressure has a corresponding, precisely defined boiling point temperature.

Fig.1: Boiling point curve for water

 The use of Marcet Boiler is to investigate the relationship between saturated
pressure and the temperature of water between ranges of 0-14 bar. By using the
Marcet Boiler, we can observe that as the temperature of water increases, the
pressure also increases. Thus, the temperature of water is said to be directly
proportional with the pressure. Thermodynamics is a study related to energy and
entropy, which is also deal with heat and work. It is a set of theories that related to
macroscopic properties, visible with naked eye which we can measure the volume,
pressure and temperature. Ideal gas law is a law in which related to pressure,
temperature and also volume of an ideal gas. Ideal gas law is originally derived
experimentally measured from Charles’s Law and Boyle’s Law. Let P is pressure
of a gas, V is a volume it occupies and T is it temperature which is in Kelvin, K.
The ideal gas law state that
PV =nRT

Where,
P = Absolute pressure, kPa
V = Volume, m3
n = Amount of substance, moles
R = Ideal gas constant, KJ/Kg. K
T = Absolute temperature, K
 The measured value of the slope of a graph (dT/dP) SAT can be obtained from
the data of result from the experiment done and compare it with corresponding
values calculated from the steam tables. Clausius-Clapeyron states:

( dTdP )
SAT
=
T ∆v
∆h

( dTdP )
T v fg
=
SAT h fg

( dTdP )
SAT
=
T (v g−v f )
h g−h f

T ( v g −v f ) T v g
( dTdP )
SAT
=
hg−hf
=
hfg

 As v g ≫ v f ,
 vf ≈ 0 ,
 v fg=v g−v f →∴ v fg=v g

Where,
 vf = specific volume of saturated liquid
 vg = specific volume of saturated vapour
 hf = enthalpy of saturated liquid
 hg = enthalpy of saturated vapor
 h fg = latent heat of vaporization

v fg , h fg : from steam tables at known T , P

Apparatus & Material:

 1. Drain Valve 6. Temperature Sensor
2. Heater 7. Manometer
3. Overflow 8. Boiler with insulating jacket
4. Filler Opening 9. Temperature gauge
5. Safety Valve 10. Heater
11. Master Switch

An insulated steel vessel is filled with a specific amount of water and sealed
tightly to prevent any pressure loss. The water is heated using an electric heater
until it starts to boil.
To monitor the heating process and steam temperature, the system includes a
temperature sensor connected to an electronic unit with a digital display.
The steam pressure inside the boiler during the experiment is measured and
displayed using a mechanical pressure gauge (manometer).
For safety, a safety valve is installed to release excess pressure and prevent
overpressure inside the boiler.
 The experiment demonstrates how temperature and pressure are related in a
sealed boiling system.
 The insulation ensures that heat is retained efficiently, reducing energy loss.
  The system is designed to be safe and easy to use in laboratory settings.

Methodology:
The experiment follows a structured procedure to ensure accurate results and safe
operation. The methodology includes the following steps:
1. Preparation Phase
 Conduct a quick inspection to ensure the unit is in proper working condition.
 Connect the unit to a power source.
 Check if the boiler contains water. If not, fill it with distilled water up to half
of its height.
 Ensure all valves (V1, V2, V3) are properly adjusted before proceeding.
2. Heating Process
 Turn on the power supply and activate the heater.
 Monitor the water temperature using the temperature sensor and digital
display.
 Observe the pressure readings on the mechanical manometer as the water
starts to boil.
 Ensure safety protocols are followed to prevent overpressure buildup.

3. Data Collection
 Record temperature and pressure readings at various intervals.
 Analyze the relationship between steam pressure and temperature.
 Ensure all measurements are taken accurately for precise results.
4. Shutdown Procedure
 Turn off the heater and allow the boiler to cool down to room temperature.
  Once cooled, switch off the main power supply.
 Drain the water, if necessary, by following the proper valve operation steps.
 Clean and inspect the unit for future use.
This methodology ensures the experiment runs smoothly, providing reliable data
on the relationship between temperature and pressure in a sealed system.

 Experimental Procedure:

 The boiler was filled with clean water through the filler plug.
 Fit the enclosed section of tubing to the overflow and open the valve (3).
 Fit the enclosed section of tubing to the drain (1) and close the valve.
 Switch on the unit at the master switch.
 Switch on the heater at the heater switch and heat up the boiler.
 Log the boiler pressure and temperature values in increments of
approximately 0.5 bar.
 Enter the measured values in the data table.
 Compare your own measurements with the values from literature.
Discussion

⚠ Warning: Never open the valve when a boiler is heated as pressurized steam
can cause severe injury.

( )
SAT SAT SAT SAT SAT
T exp (℃) T exp (° K ) Pexp gauge ¿ Pexp |(Kpa)| dT
dP exp

112 385.15 0.5 151.325 ///

121 394.15 1 201.325 0.18
127 400.15 1.5 251.325 0.12
133.2 406.35 2 301.325 0.124
143 416.15 3 401.325 0.098
150.5 423.65 4 501.325 0.075
157.5 430.65 5 601.325 0.07
163.4 436.55 6 701.325 0.059
169 442.15 7 801.325 0.056
173.6 446.75 8 901.325 0.046
178.1 451.25 9 1001.325 0.045
 182.2 455.35 10 1101.325 0.041

Results and Analysis:

 Table 1: Experiment Value

( )
SAT SAT SAT SAT SAT
T theo (℃) T theo (° K ) Ptheo ¿ Ptheo ( KPa) dT
dP theo

99.6 372.75 1 100 0.279645

120 393.15 2 200 0.158117
133.5 406.65 3 300 0.113821
143.6 416.75 4 400 0.090283
151.8 424.95 5 500 0.07552
158.8 431.95 6 600 0.06532
165 438.15 7 700 0.057826
170.4 443.55 8 800 0.052043
175.4 448.55 9 900 0.047461
179.9 453.05 10 1000 0.043709
184.1 457.25 11 1100 0.040558
188 461.15 12 1200 0.037895
 Table 2: Theoretical Value
 Table 3: Percentage Error
 ( )
SAT
dT %Error PSAT
% Error dP theo∧exp

theo∧exp

1 0.51325
0.138397 0.006625
0.05429 0.16225
0.373462 0.24669
0.297673 0.19735
0.148189 0.16446
0.210518 0.14096
0.133667 0.12334
0.179915 0.10964
0.052423 0.09868
0.10952 0.0897
0.081934 0.08223

1200

1000
f(x) = 13.5636711873454 x − 5175.01067521415
R² = 0.96383389368749

800

600
𝐓𝐒𝐀𝐓 exp (° 𝐊)

400

200

0
380 390 400 410 420 430 440 450 460

P𝐒𝐀𝐓 exp Abs(𝐊Pa)

Calculation:
  1 bar = 100 Kpa
 Assume Patm = 1 atm = 101.325 Kpa
 Pabs = Pgauge + Patm
 T (° K )=T (℃)+273.15

 ( )
dT
dP exp
=
(T 2−T 1)
P2−P1

( dTdP )
T vg
 theo
=
hfg

 %Error=
(( ) ( ) )
dT
dP exp
−
dT
dP theo

( dTdP ) theo

Discussion:
In this experiment, Marcet Boiler was used to study the relationship between
absolute pressure and temperature when heating water in a closed system. One
crucial step before starting the experiment was to ensure that air was removed from
the boiler, as the presence of air could affect the results by altering the actual
pressure within the system.
Based on the collected data, the percentage error was positive in all cases,
meaning that the experimental values were consistently lower than the
theoretical values. This discrepancy can be attributed to several factors, including:
1. Heat loss: Although the boiler operates as a closed system, some heat may
be lost to the surroundings, leading to lower actual pressure compared to
theoretical values.
2. Reading errors: Mistakes in reading the pressure or temperature gauges
could impact the accuracy of the recorded data.
3. Laboratory conditions: Room temperature and atmospheric pressure may
have influenced the experiment, especially at the initial heating stages.
4. Calculation accuracy: Errors in unit conversions or data analysis could
contribute to the observed deviations.

Conclusion:
Since all experimental values were lower than the theoretical ones, heat loss and
measurement inaccuracies are the most likely reasons for this variation. To
improve accuracy in future experiments, it is recommended to calibrate the
instruments before use, minimize external environmental effects, and ensure
precision in data calculations.

Appendix: