Measuring Properties of Saturated Water PDF

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Thermo Lab 2...

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Experiment 2: Measuring Properties of Saturated Water

Experiment 2: Measuring Properties of Saturated Water MAAE 2400 F (L8) February 24,2021

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Experiment 2: Measuring Properties of Saturated Water

Table of Contents Objective:....................................................................................................................................................3 Test Procedure:............................................................................................................................................3 Engineering Schematic:...............................................................................................................................4 Data Tables:.................................................................................................................................................4 Calculations, Graphs, and Results:...............................................................................................................5 Discussion Questions:..................................................................................................................................9 Error Analysis:............................................................................................................................................10 Conclusion:................................................................................................................................................11 Appendix:.................................................................................................................................................. 11 References:................................................................................................................................................12

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Experiment 2: Measuring Properties of Saturated Water

Objective: There are three objectives to be satisfied in this lab experiment. First is to analyze the physical behavior of water within the vapor dome as it transitions between liquid and vapor phases and just as boiling begins. Second is to develop and understanding of the relationship between pressure and temperature of saturated water. Third is to understand how to use a throttling calorimeter to determine the quality of a mixture.

Test Procedure: 1. Turn on the heater and set the power control to maximum. Immediately start recording time. 2. Continually observe the water within the boiler through the sight glass as it begins to boil (this will take about 20 minutes). Take notice of its behavior such as bubbles forming at the heater, evaporation at the surface, and condensation of bubbles on the sight glass. 3. After five minutes, record the resistance of the temperature sensor (Rm1), the gauge pressure (Pg1), and any observations on the appearance of the water. 4. Repeat step 3 every five minutes until a working pressure of 7 bar is reached. 5. When the working pressure reaches 7 bar, switch the heater power to minimum and open the throttling calorimeter isolation valve to bleed off a sample of water. This will cause pressure to drop. 6. Monitor the resistance of the temperature sensor and record the value for state point two as Rm2 when it stops changing rapidly. 7. Record values for Pg1, Rm1 and Rm2 when the Bourdon gauge indicates a gauge pressure of 4 bar. 8. When the Bourdon gauge shows a pressure of 1.5 bar, close the calorimeter isolation valve and turn off the heater.

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Experiment 2: Measuring Properties of Saturated Water

Engineering Schematic:

Data Tables:

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Experiment 2: Measuring Properties of Saturated Water

Calculations, Graphs, and Results: 1. For each row of your first data sheet, determine the temperature T1 and absolute pressure P1 at state point 1 using the procedures described in section 7. To find temperature: m∗¿=109.7 Ω at t=5 mins R¿ c∗¿=? R¿ From Appendix A: Rm 1=109 Ω

Rm 2=110 Ω

Rc 1=107.78 Ω

Rc 2=108.68 Ω

m∗¿−Rm 1 R¿ ¿ Rc 2−Rc 1 c∗¿= ¿ Rm 2 − Rm 1 R¿ c∗¿=

108.68Ω−107.78 Ω ( 109.7 Ω−109Ω )+107.78 Ω 110 Ω−109Ω R¿

c∗¿=108.41 Ω R¿ T ¿ =? From Appendix B: Rc 1=107.79 Ω

Rc 2=108.57 Ω

o

o

T 1 =20 C

T 1 =22 C

c∗¿−R c1 R¿ ¿ T 2−T 1 T ¿= ¿ Rc 2 − Rc 1 o

T ¿=

o

22 C−20 C ( 108.41 Ω−107.79 Ω ) +20 o C 108.57 Ω−107.79 Ω

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Experiment 2: Measuring Properties of Saturated Water

T ¿ =21.59 o C The same procedure was followed for each measured resistance. To find pressure: Patm=100.02 kPa Pg 1=15 kPa

P1=Patm+ P g 1 P1=100.02 kPa +15 kPa

P1=115.02 kPa All values for temperature and pressure are listed in Table 1 below. Table 1: Elapsed Time (min) 5 10 15 20 25

Temperature T1 (C) 21.59 22.52 63.16 96.83 149.76

Pressure P1 (kPa) 115.02 197.02 483.02 631.02 756.02

2. Plot each pair of T1 and p1 points found for the warmup phase (step 1) on the P-T diagram (phase diagram).

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Experiment 2: Measuring Properties of Saturated Water

3. Determine the temperature (T1) and absolute pressure (P1) at state point 1 and the temperature at state point 2 (T2) using the procedures described in Section 7 for the first row of your second data sheet (ie that corresponding to a nominal gauge pressure of 7 bar). As explained in Section 1, state point 2 is at atmospheric pressure. The same procedure as shown in question 1 was used to determine temperature and pressure. All temperature and pressure values are displayed in Table 2 Table 2: Nominal Pressure (bar)

Temperature T1 (C)

Absolute pressure Pabs

Temperature T2 (C) P a g e 7 | 13

Experiment 2: Measuring Properties of Saturated Water

7 4

(kPa) 756.02 500.02

156.01 148.26

95.91 102.43

4. Determine the enthalpy at state 2 (h2) using data from Table A-4 of Moran et al. (2014). Interpolate, as necessary. Enthalpy at 7bar nominal pressure: o o o T 1 =100 C T 2 =120 C T ¿ =102.43 C h1=2676.2 kJ /kg h2=¿ 2716.6kJ/kg h¿ =? h¿ =

h¿ =

h2−h1 T 2− T 1

(T ¿−T 1 ) +h 1

2716.6 kJ /kg−2676.2 kJ /kg (102.43−100 )+2676.2 kJ /kg 120−100

h¿ =2681.1 kJ /kg

Enthalpy at 4bar nominal pressure: Note: the recorded temperature from the lab experiment was found to be 95.91 degrees Celsius. This temperature is below the lowest temperature given on table A-4. Since we know that the water at state point 2 is saturated steam, it was decided to use the enthalpy at saturation temperature of 99.63 degrees Celsius. h¿ =2675.5 kJ /kg

5. Determine the enthalpy of saturated liquid (hf,1) and of saturated vapour (hv,1) corresponding to the pressure measured at state point 1 (P1) using data from Table A-3 of Moran et al. (2014). Interpolate as necessary. Using Table A-3 at p=7.56bar: p¿ =7.56 ¯¿ hf ¿ =? g∗¿=? h¿

p1=7 ¿¯

p2=8 ¿¯ hf 1=697.22 kJ / kg

h g 1=2763.5 kJ /kg

hf 2=721.11 kJ /kg h g 2=2769.1 kJ / kg

Through interpolation: f ∗¿=710.6 kJ /kg h¿

g∗¿=2766.6 kJ /kg h¿ P a g e 8 | 13

Experiment 2: Measuring Properties of Saturated Water

From table A-3 at p=5.00bar: f ∗¿=640.23 kJ /kg h¿

g∗¿=2748.7 kJ /kg h¿

6. Write an expression for determining the enthalpy at state point 1 (h1) using the unknown quality (x1) and the values of hf,1 and hv,1 determined in Step 5. h= hf +x ( hg− hf ) x=

(h− hf ) (h g−h f )

7. Substitute the properties determined in Steps 4 through 6 into the 1st law energy balance of the throttling calorimeter you prepared prior to the lab. Rearrange as necessary to solve for x1. At 7.56bar: At 5.00bar: x=

(h− hf ) (h g−h f )

x=

(h− hf ) (h g−h f )

x=

(2681.1 −710.6) (2766.6−710.6)

x=

(2675.5 −640.23) (2748.7−640.23)

x=¿ 95.84%

x=96.53%

8. Locate state points 1 and 2 on the T-v diagram your prepared prior to the lab.

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Experiment 2: Measuring Properties of Saturated Water

Discussion Questions: 1. Describe the behaviour observed as the water was heated. Was there a sudden change in behaviour, or were the transitions gradual? At what pressure and temperature did these changes occur? Did the bubbles that were formed on the heating elements collapse before reaching the surface? Explain why. As the water was heated, its behaviour gradually changed from calm, to violent bubbles, back to calm. The water began with no bubbles, and gradually began to bubble as the temperature increased until it reached its boiling point after about 15 minutes at a pressure of about 383kPa. At this point, the surface was moving violently with many large bubbles rising to the surface. As the temperature increased further, the surface gradually calmed until it was flat, and bubbles became smaller, and began to collapse before reaching the surface. The bubbles collapsed before reaching the surface due to the increased pressure and temperature causing the bubbles to no longer overcome the buoyant force of the water.

2. State point 1 should be located within the vapour dome, as explained in Section 1. Consequently, all of your data points plotted in Step 2 of Section 6 should lie on the

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Experiment 2: Measuring Properties of Saturated Water

saturated liquid-vapour line of your P-T diagram. Comment on your results and explain any discrepancies. State point one and two both fall within the vapor dome. Unfortunately, the points displayed on the P-T diagram did not line up well with the curve. This may have been due to the lack of insulation on the apparatus causing large heat loss which may have skewed the data. (this is explained further in the error analysis section). 3. Contrast the values you obtained for the quality at state 1 (x1) at the two pressures, and explain the reasons for this difference. The quality of vapor at a pressure of 7.56bar was 95.84% while the quality at a pressure of 5.00bar was 96.53%. 4. As the apparatus cools back down to room temperature, what will happen to the

pressure inside the apparatus? Will all the water condense into liquid? Explain why or why not. As the apparatus cools down to room temperature, the pressure will slowly decrease and return to atmospheric pressure as the water condenses. Vapor in the apparatus will begin to condense as the temperature decreases but not all at once because the apparatus will remain in the vapor dome state for some time. Over time, as the apparatus reaches room temperature and atmospheric pressure, all the vapor should condense back to water when it reaches the saturated water state.

Error Analysis: There are two main sources of error when performing this lab. Firstly, is the measuring device used to record several different measurements. The device is only capable of displaying one value at a time, which means that there is a slight discrepancy in time when recording the values. i.e. the values that are meant to be recorded at each time stamp are all slightly off. One potential solution for this issue is to use separate measurement tools which would all display their own specific measurements, allowing them to be recorded at the same time without needing to toggle the display. Alternatively, using a device that displays all the values at once could work as well. Secondly, the apparatus loses a significant amount of heat because it is made of metal with little to no insulation. This heat loss skews the data because the temperature in the fluid is no longer accurate or constant. A simple solution for this problem would be to improve the insulation of the apparatus.

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Experiment 2: Measuring Properties of Saturated Water

Conclusion: The purpose of the lab was to understand the behavior of water through changing the temperature and analyzing the pressure. It was seen that water changes gradually from completely calm, to bubbles and violent surface movement, then back down to small bubbles that do not pierce the surface again as temperature is increased. The quality of steam was found to be 95.84% at a pressure of 7.56bar, and 96.53% at a pressure of 5bar. Overall, the data made sense, but strayed from the p-T diagram quite a lot.

Appendix:

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Experiment 2: Measuring Properties of Saturated Water

References: MAAE2400 Thermodynamics and Heat Transfer Laboratory Instructions (Modified Version for Online Classes), January 2021

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