1. Introduction: The first law of thermodynamics suggests that a closed system conserves energy even when the energy transfers form one form to another. The second law of thermodynamics suggests that in any transfer of energy, some energy will be lost to other processes such as friction or heat transfer. In this experiment, a steam motor and energy conversion test set shown in Figure 1 is studied. It uses a laboratory scale steam plant based on Ranking Cycle to help the students understand some of the principles of thermodynamics. It can also show the performance characteristics of steam motor, a boiler and a condenser.
Fig.1: Schematic view of the Rankine cycle and the present experiment’s cycle The water flow system in the cycle of the present experiment is shown in the Figure:
Fig.2: Water Flow System of the present cycle 1
2. Objectives:
To determine the performance of the steam plant cycle and analyze it in comparison with the ideal Ranking cycle. To be familiar of Willans Line Analysis. To be familiar of Specific Steam Consumption Analysis. To be familiar of steady Flow Analysis (Energy Balance).
3. Equipment:
Stop watch. User manual. TecQuipment's optional Versatile Data Acquisition System, VDAS. TD 1050, Steam Motor and Energy Conversion Test Set. Ideal for students to gain insight into the first and second laws of thermodynamics Introduces students to industry-standard methods of analyzing steam plant performance, including Rankine Cycle Analysis and using the Willans Line Uses a simple two-cylinder steam motor and an electrically-heated boiler for easy understanding of the main parts of a steam plant Self-contained in a mobile frame that includes all instruments needed for experiments Allows students to copy the Marcet Boiler Experiment to prove the pressuretemperature relationship for saturated steam.
4. The general Asembly: 1. Steam motor The main part of the motor splash lubricates itself from its sump. The motor has a totally enclosed crankcase, two cast iron trunk pistons and an overhead piston valce made of stainless steel. The over head piston is driven by an external connecting link from a vertical shaft, turned by a bevel gear at the crank shaft. The crankcase has a combined dipstick and filler, a breather and a drain plug. A displacement lubricator lubricates the over head piston. A guard around the motor protects the user from parts and hot surfaces. A cross sectional view of the the steam motor is shown in Figure 3.
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Fig.3: Cross sectional view of the steam motor. 2. The Pump and Boiler: An electric pump fills the boiler with water from reservior in the base of the frame. The water passes through non-return valve from the pump to the boiler. The steel boiler contains two electric immersion heater. They each include a thermal cutout that protects against overheating due to low water level. A spring loaded pressure relife valve protects against over pressure in the boiler. The top of the boiler has a steam valve or stop valve to regulate the steam flow from the boiler. A side view of the boiler including the steam valve is shown in Figure 4.
Fig.4: Side view of the boiler including the steam valve. 3. The Sight Gage: The sight gage on the end of the boiler allows the use to see the water level in the boiler. The gauge is a glass tube surrounded by a clear safety shield that helps protect against breakage. It has two valves for safety reasons, which the operator can also use
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to help bow down the sight gauage when checking the blockages. Side view of the sight gauge with the upper and lower valves are shown in Figure 5.
Fig.5: Side view of the sight gauge with the upper and lower valves. 4. The Condenser: The exhaust steam from the motor passes through the condenser which is a heat exchanger. Cooling water circulates through the heat exchanger cooling the steam. The steam condenses and drains out of a connection below the condenser to a measuring vessel or to the waste tank. The side view of the condenser is hown in Figure 6. When using the calorimeter for dryness fraction testing, the outlet steam of the calorimeter also passes through the condenser. The condenser cools this steam so only water passes down to the waste tank.
Condenser
Fig.6: The side view of the condenser.
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5. Brake Dynamometer with Digital Torque and Speed Display: The Brake Dynamometer (Figure 7) is a simple friction brake instrumentthat fits at the back of the steam motor. As you adjust any of the two controls of the dynamometer, they pull a cord against the dynamometer drum applying a load. A force sensor measyres the torque as you apply the load. Another sensor measures the motor speed. The product of torque and shaft speed gives the mechanical shaft power the steam motor absorbs from the steam flow Shaft power= Shaft speed (Rad/sec) X Shaft Torque (Nm)
Fig.7: Side view of the Brake Dynamometer 6. Heater Power: The electrical control cabient contains an isolator and indvidiual control switches with indicator lights for the two heater elements and the feed pump. A wattmeter on the bacl of the equibment measures electrical power input to the boiler. 7. Pressure Gauges: Two Bourdon gauges on the back panel of the equibment indicate boiler and motor inlet pressure. Behind each gauges is an electronic pressure sensor. The electronic pressure sensors and a low voltage signal from the wattmeter connect to a small electronic socket near to the left hand (engine inlet) pressure gauge. This socket is connected to the analogue inputs of the VDAS interfaceso that VDAS can record of the pressures and boiler electrical power. 8. Temperatures: Four thermocouples on the apparatus connect to a separate Digital Temeopeartre Display that fits on the instrument frame. The thermocouples meausre the temperature of 5
The boiler, T1 The calorimeter, T2 Cooling water inlet, T3 Cooling water outlet, T4 The VDAS shows the temperatures and has a digital output socket for connection to TecQuibment VDAS. 9. Cooling Water Flow Rate: A flowmeter under the boiler (Figure 8) measures the cooling flow water flow rate.
Fig.8: Side view of the Flowmeter. 10. Calorimeter and Dryness Fraction: A throttling calorimeter (Figure 9) allows the student to calculate the dryness fraction of the steam that leaves the boiler. The calorimeter has a valve that stays shut during normal tests, but you open it few seonds when doing dryness fraction tests.
Calori meter
Fig. 9: Calorimeter
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11. Water Flow System The water flow system in the cycle of the present experiment is shown in the Figure 10:
Fig.10: The Water Flow System of the present cycle 12. Condensate (Steam) Flow Rate: In this exepriment measuring cylinder and stop watch are provided to meausre the flow of condensate (steam flow) from the heat exchanger. The condensate runs down a flexuble pipe, so that you can direct it to the waste tank for most of the time, then direct it to the measuring vessel during experiments. The Temperature of the condesate is denoted by T5 and mass flow rate is denoted by m.
13. Versatile Data Acquistion System (VDAS): In this experiment, a versatile data acquistion system (VDAS) is used and to be connected with a suitable computer. The VDAS will Automatically log data from your tests Automatically calculate data fro you Save your time Reduce errors Create charts and tables of your data Export your data for processing in other software.
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5. Procedure: 1. Create a blacnk results table similar to Table 2. If you use VDAS, the software will create it automatically. Table 1. Blank result table Atmospheric Pressure: Ambient Temperature: Cooling water flow: Motor Motor Heater speed power Power (rev/min) (W) (W)
Condensate
Pressures Temperatures (kN/m2) (L/min) (oC) Boiler Motor T1 T2 T3 T4
2. 3. 4. 5.
If you have the optional VDAS, select TD1050 layout Note your local pressure and temperature for reference Direct the flexible condensate pipe into to the waste tank Unscrew the two motor bleed by 2 turn. This will help to prevent steam condesning in the engine cyliner, producing a hyrdaulic lock during up time. 6. Switch the heaters. When the boiler pressure has reached approximately 300 kN/m2, slowly open the boiler steam valve about one quarter turn until the motor inlet pressure reaches about 80 kN/m2. 7. Turn the motor starting control clock wise to start the motor. The starting control has a built-in-centrifugal clutch, so you need to turn it quickly at first to make it work correctly. 8. Use the steam valve to control the motor speek and run the motor two mintues (warm up time) at around 1000 revultion/mintue (rev/min). 9. Tighten the motor bleed screws. 10. Now use the steam valve to maintain a constant speed of 2000 rev/min (+,- 100 rev/min) while you use the dynamometer to load the motor in at least six equal steps (TecQuibment recommend steps of increasing torque of around 0.05 Nm). Continue loading the motor until it cannot maintain its speed. 11. Use the heaters to keep the boiler pressure at just 300 kN/m2 during the experiment (you may need to switch one heater off for a few seconds at a time with the lower steam flow). If the pressure relif valve opens, the pressure can drop down to 200 kN/m2 and may delay your experiment. 12. At each step record the boiler pressure and tempearture, motor inlet pressure, motor speed, motor power (on the dynamometer display), condeser cooling water temperatures and flow rates, and condensate flow rate. Alternatively use the VDAS to record the results. 13. Measure the condensate flow rate by directing the flexible pipe into the measuring cylinder and measure the amount of condesate collected over intervals of 60 seconds. This allows you to directly convert the flow into liters per minute. Use thermometer to measure the temperature of the condensate.
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14. At the end of the experiment and while the moto is still running use the calorimeter to measure the dryness fraction. To use it fully open the calorimeter valve to a small amount of steam to pass through for about 10 seconds (or until the calormeter temperature stabalize). Record the boiler steam pressure, temperature and calorimeter temperature.
Shut Down Process (Method 1): a. Switch off the heaters. b. Allow the motor to use up as much as the boiler steam as possible. c. Use gloves and carfully open the boiler drain valve a small amount, allowing the hot water to escape into cooling water reservior. d. Leave the steam valve open to let air into boiler e. Leave the cooling water running for about two minutes to cool the water reservior. f. Switch off the electrical and water supply and drain any water from the apparatus.
Shut Down Process (Method 2): a. b. c. d.
Switch the cooling water supply. Allow the boiler to cool down naturally (about two hours). Open the boiler drain valve and steam valve. Switch off the electrical supply and drain any water from the apparatus.
6. Results and Discussions: Atmospheric Pressure: 1 bar Ambient Temperature: 25 C Cooling water flow: 0.03 Kg/s Motor speed
Motor Heater power Power
(rev/min)
(W)
(W)
1530 1670 1650 1830 1850 2090
35 40 44 52 55 61
4920 4900 4900 4840 4950 5080
Condensate
Pressures (kN/m2)
(L/min) (oC) Boiler Motor 0.106 0.098 0.104 0.11 0.107 0.115
25 25 25 25 25 25
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296 294 291 287 281 292
151 162 163 164 180 196
Temperatures T1
T2
T3
T4
144.3 107.2 46 31.3 143.2 109 46.1 31.9 143.8 109.1 46.3 32.2 143.5 109 46.1 32.1 143 110 46.2 32.9 142 110.6 46.5 33.7
1. Willans Line:
Steam Used (per hour)
Engineers often produce a performance curve (or line) for steam engines and turbines, determined by the steam that passes through them (steam flow) and the power that they produce from the steam. This curve (or line) is the Willans line. It is usually linear and can therefore be easily extended down to the horizontal axis to give an approximate value for power losses in the engine or turbine, to help calculate effeciencies. These losses are usually caused by friction in the moving parts of the engine or turbine.
(Negative axis)
(Positive axis)
0
Power losses
Power Output
Willans Line Steam Flow Rate ( Kg/h)
9
-190
8 7 6 5 4 3 2 1 -170
-150
-130
-110
-90
-70
-50
-30
Powre Output ( Watt) Fig.11: The Willans Line 10
0 -10 -1
10
30
50
70
At first, the first reading has beed neglected, because of it irregular behavior. Then we see that the mechanical loss is 178 Watt.
2. Specific Steam Consumption (SSC): Another useful curve that engineers use is the specific steam consumption (S.S.C) curve. Specific steam consumption is the steam mass flow needed for a unit power output, usually expressed in units of kilogrammes per kilowatt hour (kg/kWh). Specific Steam Consumpton (kg/kWh) = Steam Flow (kg/h) / Power Output (KW) The minmum specific steam consumption gives a useful value that help engineers compare relative sizes of steam plants for example A steam locomotive has a minimum SSC of around 10 kg/kWh A modern steam power plant may have a minimum SSC of around 3 kg/kWh
(SSQ) kg/kWh
(SSC) Curve
Power Output (kW)
SSQ 200
SSQ( kg/kWh)
180 160 140 120 100 0.03
0.035
0.04
0.045
0.05
0.055
Power Output (kW) Fig.12: SSQ Curve 11
0.06
0.065
3. Steady Flow Analysis (Energy Balance) The notations of needed for performing the energy balance is given in table 3. And the thermodynamic system of the present cycle is shown in Figure 13.
Fig.13: The themodynamic System of the TD 1050
Sample calculations for steady flow analysis
Select a reading. For the boiler (steam and water) at T1= 143.5 C : Find from steam table at 143.5 C Enthalpy of the steam (hg) = 2735.11 kJ/kg Enthalpy of the water (hf) = 604.196 kJ/kg Enthalpy of the evaporation (hfg) = 2133.73 kJ/kg
For the Calorimeter at T2 = 109 C : Find from steam table at T2 Enthalpy of the steam (hg,c) = 2688.2 kJ/kg
Dryness factor (or Quality), x: x=
.
= 0.9767
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Heater input power, Q1: Electrical power reading at the selcted reading, Q1 = 4980 watt at T1 = 143.5 C.
Heat losses from boiler, Q2: Q1+mh0 = Q2 + mh1 here, h0=hw, h1= hg,c Q1+mh0 = Q2 + mh1 Q1+mhw = Q2 + mh1 , mass flow rate = 0.001794375 kg/s at T1 = 143.5 C. mhw = 0.001794375* 604.196 = 1.084 KW (1084 Watt ) mh1 = 0.001794375* 2688.2 = 4.8236 KW (4823.6 Watt) Q2 = Q1+mhw - mh1 = 4890 + 1084 - 4823.6= 1150.4 Watt
Heat transferred to the condenser cooling water, Q5: Q5 = mw * Cw * (T4-T3) = 0.03*4.18 * (46.1-32.1)= 1.7556 KW ( 1755.6 Watt) Where, mw= cooling water flow rate = 0.03 Cw= Specific heat of water = 4.18
Heat losses from engine and condenser (Q3 + Q4): It is diffcult to find Q3 and Q4 seperately, therefore the summation of Q3 and Q4 will be calculated simply from the energy balance equation Energy out = Energy in Q1+ mhw= Q2 + Q3 + Q4 + Q5 + W1 + mh3 Q3 + Q4= Q1+ mhw – Q2 - Q5 - W1 - mh3 = 4980 + 1084 – 1150.4 - 1755.6 - 178 (0.00179*104.8*1000) = 2702.4 watt
Engine power, W1: From the power output display = 52
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Thermal effeciency based on the engine power, W1: ηth = W1/ {Q1+ [m/(hw-h3)]}= 1.04%
Actual engine power, W1+ W2: Actual Power = W1+ W2 = 52 + 178 = 230 W1= Power output display From the display W2= Power losses from Willans Line
Thermal effeciency based on the actual power, W1+ W2: ηth = (W1+ W2)/ {Q1+ [m/(hw-h3)]} = 4.7%
Q1= 4980 Q2= 1150.4 Q3+Q4 = 2702.4 Q5= 1755.6 mh1= 4823.6
Mh3= 187 W1= 52 W2=178 mhw= 1084
Power(Watt)
Energy Balance For Steam Plant 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Boiler
Boiler
Engine
Fig.14: Energy Balance For Steam Plant
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Condenser
7. Conclusions: Mechanical Losses: The Willans Line shows an approximate 178 W of mechanical losses for the steam motor rested by TecOuipment on a motor that had been run for several hours. As men one in the theory sec on, this be very approximate.
Specific Steam Consump on: The specific steam consump on curve shows that specific steam consump on decreases as power increases, giving a minimum specific stearn consump on of approximately 140 kg/kWh. This is high due to the small size of the motor. Again, a new motor may give lower steam consump on (around 95 kg/KWh).
References 1. User manual. 2. www.tecquipment.com( last access 28 Apr)
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Appendix:
Experiments parameters:
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Table 3 Notations of the energy quantities needed for the steady flow analysis
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