Marcet Boiler

ABSTRACT

This experiment was carried out to determine the relationship between the pressure and the temperature of saturated steam in equilibrium. Besides that this experiment was also done to demonstrate the vapor pressure curve. The marcet Boiler was used for this experiment. When the pressure increases, the temperature also increases. Therefore, the relationship of pressure and temperature is directly proportional. The derived formulae and the data were used to calculate the slope. The dT/dP measured was compared with the data in the steam table. Theoretically, the values measured should be almost the same with the predicted values. However, at certain points, the values are not the same. This may because of the errors made in the experiment

Table of Contents

Abstract..............................................................................................................2

Table of Contents..............................................................................................3

1.0 Introduction........................................................................................................4

2.0 Objectives..........................................................................................................5
.
3.0 Theory................................................................................................................5

4.0 Diagram and Description of Apparatus..............................................................7 4.1 Description and assembly 4.2 Experimental Capabilities 4.3 Overall Dimensions 4.4 General Requirements

5.0 Experimental Procedures..................................................................................9 5.1 General Start-up Procedure 5.2 General Shut-down Procedure 5.3 Experimental Procedure 6.0 Results and Discussion...................................................................................12

7.0 Sample calculations.........................................................................................15

8.0 Conclusions and Recommendations...............................................................15

9.0 References......................................................................................................16

11.0 Appendices......................................................................................................17

1.0 INTRODUCTION

The SOLTEQ® Marcet Boiler (Model: HE169) is a bench top unit designed for the demonstration of the basic principal in Thermodynamics studies which is the boiling phenomenon. Thermodynamics is defined as a study related to the transfer of heat and work between a system and its surrounding, undergoing a process causing any of the properties of the system change.
An ideal gas obeys the equation of state that relates the pressure, specific volume or density, and absolute temperature with mass of molecule and the gas constant, R.

However, real gas does not absolutely obey the equation of state. A few changes on the ideal gas equation of state allow its application in the properties of real gas.
When energy increases within water, the increasing of activities among the molecules enables the increase in the number of molecule escape from the surface until an equilibrium state is reached. The state of equilibrium depends on the pressure between the water surface and steam. At lower pressure, the molecules become easier leaving the water surface while less energy required in achieving the state of equilibrium (boiling point). The temperature where equilibrium occurs at a given pressure level is called saturated temperature.
The Marcet Boiler is used to investigate the relationship between the pressure and temperature of saturated steam in equilibrium with water at all temperature levels between the atmospheric pressure and 10 bars.

2.0 OBJECTIVES
The main goal of this experiment is to demonstrate the relationship between the pressure and temperature of saturated steam for water at all pressure levels between atmospheric pressure and 10 bars (150 lb/in2). Then, the experimental value for the slope of the graph (dT/dP)SAT is compared to the theoretical value found in the steam table.

3.0 THEORY

Marcet Boiler (Model: HE169) has been developed for investigating the relationship between the pressure and the temperature of saturated steam, in equilibrium with water, at all pressures between atmospheric and 10 bar (abs) (150 lb/in2).

Thermodynamics is a branch of physics, which deals with the energy, and work of a system. Thermodynamics deals only with the large-scale response of a system that we can observe and measure in experiments. Small-scale gas interactions are described by the kinetic theory of gasses, which is a compliment to thermodynamics.

An ideal gas can be characterized by three state variables: absolute pressure (P), volume (V), and absolute temperature (T). The realationship between them maybe deduced from kinetic theory and is called the Ideal Gas Law. The ideal gas law was originally determined empirically snd is simply.

PV = nRT

Where,
P = Absolute pressure
V = Volume n = Amount of substance (moles)
R = Ideal gas constant
T = Absolute temperature (K)

If a gas behaves exactly as the ideal gas laws would predict it to behave in terms of volume, pressures, moles, and temperature, then the gas is said to be an ideal gas. On the other hand, the gas deviates from Ideal Gas Behaviour, then the gas is said to be acting like a “real gas”.

When energy increases within water, the increasing of activities among the molecules enables the increase in the number of molecule escape from the surface until an equilibrium state is reached. The state of equilibrium depends on the pressure between the water surface and steam. At lower pressure, the molecules become easier leaving the water surface while less energy is required in achieving the state of equilibrium (boiling points). The temperature where equilibrium occurs at a given pressure level is called saturated temperature.

The measured value of the slope of the graph (dT/dP) SAT obtained from the practical results can be compared with corresponding values calculated from the data in steam tables. Clausius-Clapeyron states:

and hf + hfg = hg hfg = hg - hf 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 vapor hfg = latent heat of vaporization

4.0 DIAGRAM AND DESCRIPTION OF APPARATUS

The unit consists of a stainless steel pressure vessel fitted with high pressure immersion electrical heater. The unit also comes together with a safety relief valve, temperature and pressure measuring devices. Water feed port is installed to allow water charging.

The unit comes with temperature and pressure transducers so that students will be able to read the respective values on the digital indicators easily. The water heater is protected from burnout by setting the maximum operating temperature with a temperature controller.

4.1 Description and Assembly
The SOLTEQ® Marcet Boiler (Model: HE169) consists of mainly the following items:

a) Pressure Vessel
Capacity : 3 Liters
Material : Stainless Steel 304
Design Pressure : 30 bar
Operating Pressure : 10 bar
Certification : DOSH certified

b) Pressure Gauge
Type : Bourdon Tube
Range : 0-20 bar (g)

c) Pressure Transducer
Wetted Material : Stainless Steel
Case Materiam : Stainless Steel
Range : 0-16 bar (abs)

d) Electrical Heater
Power : 2000W
Type : Immersion Type
Safety : High temp-cut-off by means of a temperature

e) Temperature Sensor
Type : RTD (Class A)
Range : 0-200°C

f) Safety Features
Pressure Relief Valve (Set at 15 bar), Temoerature Controller (Set at 185.0°C)

4.2 Experimental Capabilities a) Demonstration of relationship between the pressure and temperature of saturated steam in equilibrium with water b) Demonstration of the vapour pressure curve

4.3 Overall Dimensions
Height : 1.15 m Width : 1.00 m Depth : 0.60 m

4.4 General Requirements
Electrical : 240VAC/1-phs/50Hz Water Supply : Distilled Water

5.0 EXPERIMENTAL PROCEDURES

5.1 General Start-up Procedures 1. A quick inspection is performed to ensure that the unit is in proper operating condition. 2. The unit is connected to the nearest power supply. 3. The valves at the feed port and the level sight tube (V1, V2 & V3) is opened. 4. The boiler is filled with distilled water through the feed port until the half of the boiler’s height. Then, the valves, V1 & V2 at the level sight tube is closed. 5. The power supply switch is turned on. 6. The experiment is now ready to be carried on.
5.2 General Shut-down Procedures 1. The heater is switched off and the boiler temperature is allowed to drop until room temperature.

Note:
Do not open the valve at the water inlet as it is highly pressurized at high temperature.

2. The main switch and the main power supply is switched off. 3. The water is retained for the next user. 4. The upper part of the level sight tube, V3 is drained and then the V1 and V2 is opened to drain off the water.

5.3 Experimental Procedure

1. The general start-up procedures as described in Section 5.1 is performed. 2. Since the boiler is initially filled with water, the valves at the level side tube (V2 & V3) is opened to check the water level. 3. The temperature controller is set to 185.0 °C which is slightly above the expected boiling point of the water at 10.0 bar (abs). 4. The vent valve, V3 is opened and the heater is 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. The steam temperature rise is observed as the water boils. 6. The steam is allowed to come out from the valve, V3 for about 30 seconds, and then the valve is closed. This step is important to remove air from the boiler as the accuracy of the experimental results will be significantly affected when air is present. 7. The steam temperature and pressure is recorded when the boiler is heated until the steam pressure reached 10.0 bar (abs).
Warning!
Never open the valve when the boiler is heated as pressurized steam can cause severe injury.

8. Then, The heater is turned off and the steam temperature and pressure will begin to drop. The steam temperature is recorded when the boiler is cooled until the steam pressure reaches atmospheric pressure. 9. The boiler is allowed to cool down to room temperature. 10. The steam temperatures at different pressure readings is recorded when the boiler is heated and cooled.

6.0 RESULTS AND DISCUSSION Pressure, P (bar) | Temperature, T (°C) | Measured Slope, dT/dP | Calculated Slope, Tvg/hfg | Absolute | Increase(°C) | Decrease(°C) | AverageTavc (°C) | AverageTavc (K) | | | 1.0 | 105.0 | 103.9 | 104.5 | 377.5 | | 0.28 | 1.5 | 114.8 | 116.1 | 115.5 | 388.5 | 0.217 | 0.20 | 2.0 | 123.8 | 125.2 | 124.5 | 397.5 | 0.179 | 0.16 | 2.5 | 131.9 | 132.6 | 132.3 | 405.3 | 0.153 | 0.13 | 3.0 | 137.8 | 138.9 | 138.4 | 411.4 | 0.120 | 0.12 | 3.5 | 143.6 | 144.2 | 143.9 | 416.9 | 0.120 | 0.10 | 4.0 | 147.9 | 149.1 | 148.5 | 421.5 | 0.091 | 0.09 | 4.5 | 152.3 | 153.4 | 152.9 | 425.9 | 0.086 | 0.08 | 5.0 | 156.7 | 157.2 | 157.0 | 430.0 | 0.081 | 0.08 | 5.5 | 160.0 | 160.9 | 160.5 | 433.5 | 0.069 | 0.07 | 6.0 | 163.4 | 164.3 | 163.9 | 436.9 | 0.067 | 0.07 | 6.5 | 166.6 | 167.4 | 167.0 | 440.0 | 0.062 | 0.06 | 7.0 | 169.5 | 170.4 | 170.0 | 443.0 | 0.058 | 0.06 | 7.5 | 172.4 | 173.2 | 172.8 | 445.8 | 0.056 | 0.06 | 8.0 | 175.1 | 175.9 | 175.5 | 448.5 | 0.053 | 0.05 | 8.5 | 177.6 | 178.4 | 178.0 | 451.0 | 0.049 | 0.05 | 9.0 | 180.0 | 180.9 | 180.5 | 453.5 | 0.048 | 0.05 | 9.5 | 182.4 | 183.3 | 182.9 | 455.9 | 0.047 | 0.05 | 10.0 | 184.7 | 184.7 | 184.7 | 457.7 | 0.037 | 0.04 |

Discussion:

1. Why is it necessary to remove air from the boiler at the beginning of the experiment?
It is necessary to remove air from the boiler because the present of air will affect the accuracy of the experimental results. 2. Compare the graph plotted from experiment data to that of calculated data. 3. Discuss any discrepancy and sources of error of the experiment. 4. Discuss the liquid and vapour behaviour observed through the experiment. 5. Discuss 4 applications of boiler in industries

7.0 SAMPLE CALCULATIONS

Calculating the value of dt/dp

1 atm = 1 bar = 101.325 kPa

1.5 bar 101.325 x 1.5 = 151.987 kPa 1

dp = 151.987 – 101.325 = 50.662 kPa

dt = 388.45 – 377.45 = 11

dt/dp = 11÷50.662=0.217

Calculating the value of Tvfg/hfg

Tvfg = 377.45 ×1.694=639.4

hfg = 2258 (Taken from saturated steam table)

Tvfg/hfg = 639.4 ÷2258=0.283

Calculating the value of the difference between (dt/dp) & (Tvfg/hfg) percentage error

Error %= (Calculated value – Measured value) x 100% = (0.283-0.217) x 100% = 6.6%

(ӿThe data sample calculation above is taken from table at Pressure equal to 1 bar)

8.0 CONCLUSIONS AND RECOMMENDATIONS

Conclusion

In this experiment, the relationship between pressure and temperature is found to be directly proportional. When compared to the theoretical slope, the experimental slope shows a small deviation between them because of certain errors. The percentage of error is around 6.6% which can validate this experiment.

Recommendation

The pressure and temperature readings should be taken more so that the graph is more accurately plotted and the error range could be reduced.

9.0 REFERENCES (1) MD Atiqur Rahman Faisal (2008). Marcet Boiler Experiment. Retrieved January 28, 2013 from http://www.scribd.com/doc/93324504/Marcet-Boiler. (2) John Cornor. (2009). Abstract of Marcet Boiler. Retrieved January 27, 2013 from http://www.scribd.com/doc/51634867/Marcet-Boiler-Lab-Report. (3) Admin of Marcet Boiler Analysis. (2009). Marcet boiler. Retrieved January 28, 2013 from MEHB 471: Heat Transfer & Applied Thermodynamics Lab - Unitenwww.uniten.edu.my/.../Lab%207%20-%20Marcet%20Boiler.doc)

11.0 APPENDICES