Marcet Boiler Experiment. 2h4o3p

MARCET BOILER Aim: To attain the relation between temperature and pressure of saturated steam in equilibrium. Introduction: The SOLETEQ Marcet boiler (model: HE169) is a bench top unit designed for the demonstration of the thermodynamics studies which is the boiling phenomenon. Students will be able to study the relationship between the pressure and temperature of saturated steam in equilibrium with water. The saturation pressure curve can be determined at the pressure within 10 bar (150lb/in2). The unit is made of 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. It is also installed with temperature and pressure transducers so that students are able to read the respective values in the digital indicators easily. The water heater is protected from the burnout by setting the maximum operating temperature with temperature controller. The figure below shows the unit construction of the boiler

Figure: unit construction for marcet bolier (model HE: 169) 1. Pressure transducer

2. Temperature controller/ indicator 3. pressure indicator 4. control 5. bench 6. bourdon tube pressure gauge 7. temperature sensor 8. pressure relief valve 9. water inlet port 10. heater The boiler consists mainly of the pressure vessel with a capacity of three litres made of stainless steel 304, with a design pressure of 30 bar and an operating pressure of 10 bar, certified by the DOSH. The pressure gauge is a bourdon type that ranges from 0-20 bar (g). The pressure transducer is also made of stainless steel with a pressure range of 0-16 bar. The heater is an immersion type heater that has a power capacity of 2000W and a high temperature cut-off by means of temperature controller. The temperature sensor is a RTD (class A) rated that ranges from 0-2000 C. it is also equipped with a pressure relief valve (set at 15 bar), temperature controller (set at 185.00C). Apparatus and requirement: 1. Marcet boiler 2. Electrical supply 3. Water supply Summary of theory: Marcet boiler (Model: HE169) has been develeloped for the investigating the relationship betwwen the pressure and temperature of saturated steam, in equilibrium with water, at all pressures between atmosphere and 10 bar (abs) (150lb/in2). Thermodynamics is a Branch of physics, which deals with the ebergy, and work of a system. Thermodynamics deals 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 gases, which is a compliment to thermodynamics. An ideal gas can be characterised by three state variable: absolute pressure (P), volume(V), and absolute temperature (T). the relationship between them may be deduced from kinetic theory and is called ideal gas law. The ideal gas law was originally determined empirically and is simply. PV=nRT Where P = Absolute pressure V = Volume n = amount of substance (moles) R = ideal gas constant T =Absolute temperature If gas behaves exactly as the ideal gas laws would predict it to behave in of volum, pressure, moles and temperature, then the gas is said to be an ideal gas. On the other hand, the gas deviates from ideal gas behaviour, 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 is reached. The state of equilibrium depends on the pressure between the water surface and the steam. At lower pressure, the molecules became easier leaving the 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 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 the steam tables. Clausius-Clapeyron states:

(

)

(

)

Add hf + hg = hg Hence, hfg = hg - hf (

)

As vg >> vf In which, Vf =specific volume of saturated liquid Vg = specific volume of saturated vapour hf = enthalpy of saturated liquid hg =enthalpy of saturated vapour hfg = latent heat of vaporization Installation and commissioning: The boiler is installed on a firm level work surface, with asingle phase work electrical supply. 1. The boiler is connected to the input power supply plug to a nearest single-phase electrical supply of 230VAC/50hz. 2. The reset button to earth leakage circuit breaker is then pushed inside the control after the main power supply is switched on. 3. The valves at the feed port V1, V2, & V3 and level sight tube are open. 4. The boiler filled with distilled water through the feed port and made sure the water level is at about half the boiler’s height. Then V1&V2 are closed, and V3 left at an open position. 5. The power switch then turned and indicators light up.

6. Temperature and pressure readings are taken to be at room temperature and at zero respectively. 7. The heater is then turned on and the temperature raise is observed and so the steam temperature as the water boils. At 1000C the valve v1 is left open for about 30 seconds for the steam to exit. 8. The reading of pressure is observed to be raising as the temperature raises. 9. The water is allowed to heat up up until a pressure of 9 bar and leakage is checked for around the boiler. 10. The boiler is allowed to cool down and with no leakage the commissioning is complete.

PROCEDURE: Start Procedure: 1. On performing a quick inspection to ensure that the unit is in proper operating condition, its connected to the nearest power supply. 2. Valves V1, V2 &V3 and level sight are open and the boiler filled with distilled water through the feed port and made sure that water level is at half the boiler’s height. The valves V1 & V2 are then closed at the level sight. 3. Power supply is then turned on and experiment started. Shutdown procedure: 1. The heater is turned off and allowed to cool to room temperature, upon which the power supply is turned off. 2. The valves V3 is open first opened then V1 & V2 are opened to drain off the water.

Experimental procedure:

Start up procedures are performed. And since the boiler was initially filled with water, the valves at the level side tube (V2 & V3) are checked for water level. The temperature controller is set to 18500C which is above the boiling point of water of 9 bar, then the valve V3 is opened and heater turned on. As the water boils, the steam temperature level is observed, upon reaching 1000C, the valve V3 is openned for 30 seconds to remove air from the boiler and excess pressure present. The steam temperature is then recorded from here on until it reaches 9 bars. Upon reaching the 9 bar, the heater is turned off and the readings of the reductions are read, this is done until the temperature returns to 1000C. The boiler is the left to cool and the recorded readings are used to determine the relationship between temperature and pressure of saturated steam. Calculations: (

)

Table of results: Pressure P

Temperature Temperature

Specific

Latent heat

(Bar)

T

volume Vg

of

T (K)

0

3

( C)

(m /kg)

vaporization hfg kJ/kg

0.1

101.9

374.9

0.2

105.5

378.5

0.3

107.3

380.3

0.4

109.6

382.6

0.5

111.4

384.4

0.6

113.5

386.5

0.7

115.3

388.3

0.8

117.1

390.1

0.9

118.7

391.7

1.0

120.8

393.8

1.2

123.1

396.1

1.4

126.1

399.1

1.6

128.8

401.8

1.8

131.1

404.1

2.0

133.4

406.4

2.5

138.8

411.8

3.0

143.8

416.8

3.5

147.5

420.5

4.0

151.5

424.5

4.5

154.9

427.9

5.0

158.3

431.3

5.5

161.2

434.2

6.0

164.5

437.5

6.5

167.2

440.2

7.0

169.3

442.3

7.5

172.3

445.3

8.0

174.7

447.7

8.5

176.9

449.9

9.0

179.15

452.15

Graph of ( )

versus P and

Graph of T against p.

versus P

SAFETY AND PRECAUTIONS: 1. The unit must be operated under the supervision of trained professional. 2. All operating instructions supplied with the unit must be carefully read and understood before attempting to operate the unit. 3. Do not open the valves on the level sight tube when the vessel is in operation. The sight tube is not designed to withstand pressure and high temperatures. 4. Always check and rectify leaks. 5. Always make sure the boiler vessel is filled with sufficient water to cober the heater elemt. Water level of the boiler’s height is sufficient to cover the heating element. 6. Do not touch the hot components of the unit. Be extremely carefull when handling liquid at high temperatures. References: Yunus A. Cengal & Michael A. Boles, “thermodynamics – An Engineering Approach”, 3rd edition, McGraw hill, 2002.