ENGR 224 - Thermodynamics at GRCC

Welcome to the Thermodynamics course at Green River Community College in Auburn, WA, USA.

Feel free to post any general questions about the course as comments on this blog entry.

I have created a blog entry for each chapter we will cover in this course. If you think your question applies to a specific chapter, then please post your question as a comment on the appropriate blog entry.

I have created a blog entry for each of the 7 HW assignments in the course. If you have a question about a problem in the HW, please post it as a comment on the appropriate blog entry. Be sure to state which problem number your question refers to !

You can post your questions using your Google ID or a crazy fake name or your real name or you can post anonymously. Whatever makes you happy. Just don't hesitate to ASK !

Remember...
"It's not a miracle, mother, it's thermodynamics !"
- Harrison Ford in Mosquito Coast

ENGR 224 - HW #1

This HW covers CB chapters 1 & 3 or LT chapters 1 & 2.

The homework consists of 15 problems for a total of 71 pts.

Please begin your question with the problem number you are asking about.

Cengel & Boles: Ch 1: 7E(3pts), 11E(4pts), 37E(2pts), 41E(3pts), 78(6pts)

WB-1 (4pts) , WB-2 (5pts)

Cengel & Boles: Ch 3: 26(4pts), 29E(4pts), 37E(5pts), 53(6pts), 66(4pts),
83(6pts) - Assume that the air in the tire behaves as an ideal gas, but then check the validity of this assumption.

WB-3 (10pts) , WB-4 (5pts)

HW 7B-16 - Isentropic Compression of High Quality Steam - 5 pts

Steam is compressed isentropically to a final pressure of 5 MPa. The steam is initially at 25oC and has a quality of 91%. How much work does this process require, in kJ/kg, if the process takes place in... (a) A closed system? (b) An open system ? (c) Explain why the answers to parts (a) and (b) are not the same.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B16

HW 7B-15 - Heat and Work in an Isothermal Expansion of Steam - 5 pts

Saturated water vapor is contained in a piston-and-cylinder device that is positioned in a constant-temperature bath at 250oC. The 5.7 kg of steam inside the cylinder expands reversibly and isothermally to a final pressure of 1.2 MPa. Determine the heat transferred between the constant-temperature bath and the water inside the cylinder as well as the work done by the H2O inside the cylinder during this process.

For hints and answers visit: http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B15

HW 7B-14 - Reversible Compression of Steam in a Piston-and-Cylinder Device - 4 pts

Superheated steam is reversibly compressed from 200 kPa to 1.4 MPa in a well-insulated piston-and-cylinder device. The cylinder initially contains 0.175 m3 of steam at 250°C. Determine the final temperature of the steam and the work done on the steam during this process.

For hints and answers visit: http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B14

HW 7B-13 - Minimum Power Required for Adiabatic Compression of R-134a - 4 pts

An adiabatic compressor is used to increase the pressure from 105 kPa to 1.25 MPa in a stream of R-134a with a volumetric flow rate of 1800 L/min. Determine the minimum power that must be supplied to the compressor.

For hints and answers visit: http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B13

HW 7B-12 - Reversible Expansion of R-134a in a Piston-and-Cylinder Device - 4 pts

The refrigerant R-134a expands reversibly from 2 MPa to 500 kPa in an insulated piston-and-cylinder device. The cylinder initially contains 15 L of R-134a with a quality of 1.0. Determine the final temperature of the R-134a in the cylinder and the work done during this process.

For hints and answers visit: http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B12

HW 7B-11 - Entropy Change and Boundary Work for the Isobaric Expansion of Water - 10 pts

Electrical work is done by an electrical resistance heater on H2O contained in an insulated piston-and-cylinder device. The cylinder initially contains 2.4 L of saturated liquid water at a pressure of 500 kPa. Assuming the piston moves freely, determine the total entropy change of the H2O during a process in which 1875 kJ of heat is transferred into the water. What is the boundary work for this process?

For hints and answers visit: http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B11

HW 7B-10 - Isobaric Condensation of R-134a - 5 pts

The refrigerant R-134a is cooled in a piston-and-cylinder device from 190°F to 75°F. The piston moves freely and the initial pressure is 200 psia. Determine the specific entropy change of the refrigerant, the work per lbm and heat transfer per lbm during this process.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B10

HW 7B-9 - Expansion of Water into a Vacuum - 5 pts

A rigid tank is divided into two equal parts by a wall. One part of the tank contains 0.74 kg of water at 100 kPa and 25°C. The other part is a perfect vacuum. The wall is now removed and the water expands to fill the entire tank. A thermocouple indicates that the final equilibrium temperature of the H2O in the tank is 50oC. Determine the entropy change of water and the total heat transfer to the system during this process.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B9

HW 7B-8 - Vaporization of Water in a Rigid Tank - 5 pts

An electric resistance heater is used to heat the contents of an insulated rigid tank that holds 23.1 kg of H2O. Initially, the pressure in the tank is 150 kPa and 44% of the mass inside the tank is saturated liquid and the remaining 56% is saturated vapor. Power is applied to the heater until all of the H2O in the tank is saturated vapor. Determine the entropy change of the H2O and the total of heat transfer during this process.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B8

HW 7B-7 - Isentropic Expansion of R-134a - 4 pts

7-38E R-134a expands reversibly and adiabatically in a piston-and-cylinder device from 80 psia and 120°F to 5 psia. If the cylinder contains 17.4 lbm of R-134a, what are the total work done by the system during this process and final temperature of the R-134a ?

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B7

HW 7B-6 - Isentropic Compression of Water Vapor - 3 pts

An isentropic compressor takes in H2O at 105 kPa and delivers it at 450 kPa. If the temperature of the feed is 180°C, determine the temperature and specific enthalpy of the H2O at the compressor outlet.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B6

HW 7B-5 - Entropy Change for an Isobaric Heating Process - 4 pts

A piston-and-cylinder device holds 9.7 lbm of water at 250 psia in a volume of 3.6 ft3. Heat is added to the water until the temperature reaches 425oF. During this process, the pressure in the cylinder remains constant because the piston moves freely. Determine the change in the entropy on the water in Btu/oR.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B5

HW 7B-4 - Power Output of an Isentropic Turbine - 4pts

An isentropic turbine produces shaft work as R-134a at 275 psia and 225°F expands through the turbine and exits at 35°F. Assuming the turbine is adiabatic, determine the power output of the turbine per lbm of R-134a.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B4

HW 7B-3 - Entropy Changes Associated with the Evaporator of a Refrigerator - 4 pts

A refrigerator using R-134a as the refrigerant removes 200 kJ of heat from its refrigerated space. This heat is absorbed by a mixture of saturated liquid and saturated vapor that enters the evaporator at a pressure of 175 kPa. The R-134a leaves the evaporator as a saturated vapor. Determine...
a.) ... the entropy change of the R-134a,
b.) ... the entropy change of the refrigerated space assuming its temperature remains constant at -10°C,
c.) ... the entropy change of the universe for this process.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P7B3

HW 7B-2: Rate of Entropy Increase for a Heat Transfer Process

LearnThermo.com Homework Problem 7B-2

A hot reservoir at 944 K transfers heat to a cold reservoir at 298 K. If the rate of heat transfer is 25 kW,determine the rate at which the entropy of the two reservoirs combined changes (in kW/K) and determine if the second law is satisfied.

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P2

HW 7B-1: Entropy Change for a Heat Transfer Process

LearnThermo.com Homework Problem 7B-1

Calculate the entropy change of each reservoir when 1000 kJ of heat is transferred directly from a hot reservoir at 1000 K to a cold reservoir at 400 K. Calculate the entropy change of the universe for this process. Does this process violate the principle of increasing entropy?

For hints and answers visit:
http://www.LearnThermo.com/T1-tutorial/ch07/lesson-B/pg20.php#P1