BAEN320HW4

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Texas A&M University *

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320

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Mechanical Engineering

Date

Feb 20, 2024

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pdf

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Uploaded by jjulianmurilloc

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 1/8 1. Award: 10 out of 10.00 points Score: 70/100 Points 70 % On a P - v diagram, what does the area under the process curve represent? pressure change during the process work done during the process volume change during the process It represents the boundary work for quasi-equilibrium process. References Multiple Choice Diﬃculty: Easy  ✓  

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 2/8 2. Award: 0 out of 10.00 points 3. Award: 10 out of 10.00 points A fixed mass of an ideal gas is heated from 50 to 80°C at a constant volume and again at a constant pressure. For which case do you think the energy required will be greater? The energy required will be greater for the case with a constant volume. The energy required will be greater for the case with a constant pressure. The energy required will be the same for both the cases. For the constant pressure case. This is because the heat transfer to an ideal gas is mc p Δ T at constant pressure and mc v Δ T at constant volume, and c p is always greater than c v . References Multiple Choice Diﬃculty: Easy Is the relation Δ u = mc v , avg Δ T restricted to constant-volume processes only? Yes No No, it can be used for any kind of process of an ideal gas. References Yes / No Diﬃculty: Easy      ✓ 

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 3/8 4. Award: 10 out of 10.00 points 5. Award: 10 out of 10.00 points Is the relation Δ h = mc p , avg Δ T restricted to constant-volume processes only? Yes No No, it can be used for any kind of process of an ideal gas. References Yes / No Diﬃculty: Easy The energy released during metabolism in humans is used to maintain the body temperature at 39ºC. True False The energy released during metabolism in humans is used to maintain the body temperature at 37ºC. References True / False Diﬃculty: Easy  ✓   ✓ 

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9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 4/8 6. Award: 10 out of 10.00 points A well-sealed room contains 60 kg of air at 200 kPa and 30°C. Now solar energy enters the room at an average rate of 0.8 kJ/s while a 120-W fan is turned on to circulate the air in the room. If heat transfer through the walls is negligible, the air temperature in the room in 30 min will be ____°C. 136.88 93.44 68.44 34.22 Solved by appropriate software. Solutions can be verified by copying-and-pasting the following lines on a blank software screen. (Similar problems and their solutions can be obtained easily by modifying numerical values). m=60 [kg] P1=200 [kPa] T1=30 [C] Qsol=0.8 [kJ/s] time=30*60 [s] Wfan=0.12 [kJ/s] R=0.287 [kJ/kg-K] cv=0.718 [kJ/kg-K] time*(Wfan+Qsol)=m*cv*(T2-T1) References Multiple Choice Diﬃculty: Easy   ✓  

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 5/8 7. Award: 10 out of 10.00 points A room contains 75 kg of air at 100 kPa and 15°C. The room has a 250-W refrigerator (the refrigerator consumes 250 W of electricity when running), a 120-W TV, a 1.8-kW electric resistance heater, and a 50- W fan. During a cold winter day, it is observed that the refrigerator, the TV, the fan, and the electric resistance heater are running continuously but the air temperature in the room remains constant. The rate of heat loss from the room that day is _____ kJ/h. 7632 6192 7560 7992 Solved by appropriate software. Solutions can be verified by copying-and-pasting the following lines on a blank software screen. (Similar problems and their solutions can be obtained easily by modifying numerical values.) m=75 [kg] P _1=100 [kPa] T_1=15 [C] time=30*60 [s] W_ref=0.250 [kJ/s] W_TV=0.120 [kJ/s] W_heater=1.8 [kJ/s] W_fan=0.05 [kJ/s] R=0.287 [kJ/kg-K] "Applying energy balance E_in-E_out=dE_system gives E_out=E_in since T=constant and dE=O" E_gain=W_ref+W_TV+W_heater+W_fan Q_loss=E_gain*Convert(kJ/s, kJ/h) References Multiple Choice Diﬃculty: Easy    ✓ 

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 6/8 8. Award: 0 out of 10.00 points A 2-kW electric resistance heater submerged in 3.5 kg of water is turned on and kept on for 10 min. During the process, 300 kJ of heat is lost from the water. The temperature rise of the water is _____ºC. 73.82 61.52 41.01 86.52 Solved by appropriate software. Solutions can be verified by copying-and-pasting the following lines on a blank software screen. (Similar problems and their solutions can be obtained easily by modifying numerical values.) m=3.5 [kg] Q_loss=300 [kJ] time=10*60 [s] W_e=2 [kJ/s] c=4.18 [kJ/kg-K] time*W_e-Q_loss = dU_system "from energy balance E_in-E_out=dE_system" dU_system=m*c*DEL TAT References Multiple Choice Diﬃculty: Easy     

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9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 7/8 9. Award: 10 out of 10.00 points 5 kg of liquid water initially at 12°C is to be heated to 95°C in a teapot equipped with an 800-W electric heating element inside. The specific heat of water can be taken to be 4.18 kJ/kg·°C, and the heat loss from the water during heating can be neglected. The time it takes to heat water to the desired temperature is ____ min. 63.2 20.1 53.1 36.1 Solved by appropriate software. Solutions can be verified by copying-and-pasting the following lines on a blank software screen. (Similar problems and their solutions can be obtained easily by modifying numerical values.) m=5 [kg] T1=12 [C] T2=95 [C] Q_loss=0 [kJ] W_e=0.8 [kJ/s] c=4.18 [kJ/kg-K] time*W_e-Q_loss = dU_system "time in minutes" "from energy balance E_in-E_out=dE_system" dU_system=m*c*(T2-T1) time min=time/60 References Multiple Choice Diﬃculty: Easy    ✓ 

9/27/23, 11:38 PM Assignment Print View https://ezto.mheducation.com/api/caa/activity/C15Print?jwt=eyJhbGciOiJSUzI1NiJ9.eyJlbnZpcm9ubWVudCI6InByb2QiLCJpc3MiOiJlenQiLCJwcmlud… 8/8 10. Award: 0 out of 10.00 points NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. An ideal gas has a gas constant R = 0.3 kJ/kg·K and a constant-volume specific heat c v = 0.7 kJ/kg·K. If the gas has a temperature change of 130°C, choose the correct answer for each of the following questions. References Section Break Diﬃculty: Easy The change in enthalpy, in kJ/kg, is _____. 130 91 39 insuﬃcient information to determine Solved by appropriate software. Solutions can be verified by copying-and-pasting the following lines on a blank software screen. (Similar problems and their solutions can be obtained easily by modifying numerical values.) R=0.3 [kJ/kg-K] c_v=0.7 [kJ/kg-K] DEL TAT=130 [K] c_p=R+c_v DEL T Ah=c_p*DEL TAT References Multiple Choice Diﬃculty: Easy     