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LPH 105 W15 15.5-7

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by

Richard Datwyler

on 18 July 2016

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Transcript of LPH 105 W15 15.5-7

Engines & refrigerators
Efficiency
Entropy
Entropy
If 1.00 mL of water at 0 C is frozen and cooled to -8.0 C by being in contact with a great deal of ice at -8.0 C, estimate the total change in entropy of the process.
37.8 J/K
A 2.8 kg piece of aluminum at 28.5 C is placed in 1.0 kg of water in a Styrofoam container at 20 C. Estimate the net change in entropy of the system.
.645 J/K
30.0 kg of water at 44.0 C is mixed with 15.0 kg of water at 20.0 C. Estimate the change in entropy.
128 J/K
at position 1, P=400 KPa, T=300 K
at position 3, P=100 KPa, V=4000 cm^3, T=300 K
Find P,V,T everywhere.
Fill out the engine table
what is the efficiency of this engine?
V_1 = 1000 cm^3
V_2 = 1000 cm^3 , P_2 = 1007.9 kPa
T_3 = 755.95 C
0 911.9 911.9 J
911.9 0 -911.9 J
-554.5 -554.5 0 J
357.4 357.4 0 J
39.2 %
If these temps are the reservoir temperatures, what is the ideal efficiency?
What percent of the ideal efficiency is this engine running?
60.3 %
65 % of ideal
at position 1, P=100 KPa
at position 2, P=400 kPa, V=1000 cm^3 , T=400 K
at position 3, P=100 KPa, V=4000 cm^3 T=400 K
Find P,V,T everywhere.
Fill out the engine table
what is the efficiency of this engine?
V_1 = 2297 cm^3 T_1 =229.7 K
-255.4 0 255.4 J
554.5 554.5 0 J
-170.2 -425.6 -255.4 J
128.9 128.9 0 J
23.2 %
A diesel engine runs with two adiabatic and an isochoric and isobaric process. Starting at 25 C 1 atm and 1050 cm^3 compresses to about 70 cm^3. It also absorbs about 1000 J in the burning of the fuel. (it is usually diatomic, but we'll pretend monatomic)
Find n , P,V,T for this engine
Fill in the engine energy chart
What is the efficiency.
n=.0429
101300 Pa, .00105 m^3, 298 K
9242000 Pa, .00007 m^3, 1812.5 K
9242000 Pa, .0001132 m^3, 2931.4 K
226000 Pa, .00105 m^3, 664.8 K
1
2
3
4
-810 0 810 J
400 1000 600 J
1213 0 -1213 J
0 197 - 197 J
803 803 0 J
80.3 %
S =
Q
T
"Can we go over the difference between effeciency and COP?"
"I am still struggling with how a refrigerator works."
"My only question is about Adiabatic processes. I'm not understand them in relation to a PV diagram."
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