Boiler Experiment

Objective 1. To demonstrate the relationship between the pressure and temperature of saturated steam in equilibrium with water. 2. To determine the vapour pressure curve.

Introduction
Properties of a fluid can change when heat and work are applied to it. There’s an interchange between the fluid and its surroundings when heat and work are applied according to the study of thermodynamics. Substances such as gases and vapors are often referred as P-V-T substances.

Theory:
An ideal gas obeys the equation of state that the pressure, specific volume or density, and absolute temperature with mass of molecule and the gas constant, R.
PV = mRTM
Where, P = Absolute pressure V = Volume n = Amount of substance (moles) R = Ideal gas constant T = Absolute temperature (K)
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 8 bars. The experimental slope (dT/dP)SAT obtained is compared to the theoretical value determined through calculation from the steam table. Clausius-Clapeyron states:

(dT/dP)sat = Tvfg/ hfg
(dT/dP)sat = T(vf – vg)/hf -hg
Where, hf +hfg = hg hfg = hg - hf
(dT/dP)sat = 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 vapor hfg = latent heat of vaporization

Apparatus
I HE169 Marcet boiler The unit essentially consists of: a) Pressure transducer b) Temperature controller/Indicator c) Pressure indicator d) Control panel e) Bench f) Bourdon tube pressure gauge g) Temperature sensor h) Pressure relief valve i) Water inlet port & valve j) Heater

Procedure 1. The power supply is switched on 2. The boiler is initially filled with water and the valves at the level tube are then opened to check the water level. 3. Temperature controller is then set to 185oC, which is slightly above the expected boiling point of the water at 8 bar (abs). 4. Valve at the feed port is opened and the heater is turned on. 5. The temperature of the rising steam is then observed. 6. Steam is allowed to come out from the valve for 30 seconds and the valve is then closed. This is to ensure the air from the boiler is removed so that the accuracy of the experimental results will not be affected. 7. Temperature and the pressure of the steam is recorded when the boiler is heated until the steam pressure reaches 8 bar (abs).
Warning: Never open the valves when the boiler is heated as pressurized steam can cause severe injury 8. The heater is then turned off and the steam pressure and temperature droped.The boiler is then cooled down to room temperature 9. The steam temperature at different pressure readings when the boiler is heated and cooled is recorded. 10. Heater is switched off and the temperature of the boiler is allowed to drop.
Note: Do not open the valve at the water inlet port as it is highly pressurized at high temperature.

Results
Atmospheric pressure : ________1_____ bar
Atmospheric temperature : ________273_____ (0C)

Pressure, P (bar) | Temperature, T | Measured Slope, dT/dP | Calculated Slope, Tvg/hfg | absolute | Gauge | Increase(0C) | Decrease(0C) | Average Tavc (0C) | Average Tavc (K) | | | 1.0 | 0 | 100 | 100 | 100 | 373 | 0.75 | 0.2799 | 1.5 | 0.5 | 111.2 | 111.4 | 111.3 | 384.3 | 0.23 | 0.2002 | 2.0 | 1.0 | 120.1 | 120.3 | 120.3 | 393.2 | 0.202 | 0.1582 | 2.5 | 1.5 | 127.4 | 127.7 | 127.6 | 400.6 | 0.184 | 0.132 | 3.0 | 2.0 | 133.6 | 134.1 | 133.9 | 406.9 | 0.1695 | 0.1139 | 3.5 | 2.5 | 138.9 | 139.5 | 139.2 | 412.2 | 0.1568 | 0.1006 | 4.0 | 3.0 | 143.7 | 144.3 | 144 | 417 | 0.147 | 0.09039 | 4.5 | 3.5 | 148.0 | 148.6 | 148.3 | 421.3 | 0.138 | 0.08225 | 5.0 | 4.0 | 152.1 | 152.6 | 152.4 | 425.4 | 0.131 | 0.0756 | 5.5 | 4.5 | 155.9 | 156.2 | 156.1 | 429.1 | 0.124 | 0.07012 | 6.0 | 5.0 | 159.3 | 159.6 | 159.5 | 432.5 | 0.119 | 0.06544 | 6.5 | 5.5 | 162.5 | 162.7 | 162.6 | 435.6 | 0.114 | 0.06141 | 7.0 | 6.0 | 135.4 | 165.6 | 165.5 | 438.5 | 0.109 | 0.0579 | 7.5 | 6.5 | 168.2 | 168.4 | 168.3 | 441.3 | 0.105 | 0.05483 | 8.0 | 7.0 | 170.8 | 170.8 | 170.8 | 443.8 | 0.101 | 0.0521 |

Table 1: Data Collected and Calculated Results

Calculations Temperatureavg (oC) : Tinc +Tdec 2 Example : 100oC + 100oC 2
= 100oC Tempeatureavg (K) : Tavg +273oC
= 373K Measured slope(dT/dP) : [ ( 384.3 – 373) / (1.5-1)]/100 = 0.226 K/kPa

Calculated slope Tvg/hfg : 384.3K x hfg (vg/hfg from table A5) = 384.3K x 1.1594 / 2226.0
= 0.2002 K/kPa Gradient of graph : 435.6-400.6 6.5-2.5 = 8.75 K/bar

Discussion It is necessary to remove air form the boiler because this could affect the accuracy of the experimental results caused by the impurities in the air. Based on the graphs, the relationship between pressure and temperature is directly proportional however there is a small difference between the experimental slope and the theoretical slope. This is caused by several errors such as room temperature and pressure, the stability of materials. The temperature of the room temperature can affect the temperature of the boiler slightly, thus this can cause the readings obtain to not be accurate. Other than that, the materials use such as the valve might have a small leakage which can contribute to a certain level of an error. Thus, this factors might cause the readings obtain to not be very accurate. Conclusion Therefore, based on the 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 difference between them because of certain errors such as room temperature and the stability of materials.This experiment influences many industrial applications such as steam motor and also at water treatment plants. References 1. R.K Bansal 1983, A textbook of Fluid Mechanics and Hydraulic Machines,1st Edition, Laxmi Publications (P) Ltd, India. 2. Rama Durgaiah, 2002 Fluid Mechanics and Machinery, 1st Edition, New Age International (P) Ltd, India.

References: 1. R.K Bansal 1983, A textbook of Fluid Mechanics and Hydraulic Machines,1st Edition, Laxmi Publications (P) Ltd, India. 2. Rama Durgaiah, 2002 Fluid Mechanics and Machinery, 1st Edition, New Age International (P) Ltd, India.