Thermodynamics Homework 11 – due Friday November 15th You may complete this assignment individually, or with anyone in your assigned group. Please include both

your team number and the ME-ID’s of all students who contributed to it. Your team number will only be

used to return the assignment to you in your file folder.

1. An adiabatic piston-cylinder device contains air at 300 K. The air supports 5 large bricks that weigh 40 kg each. The

diameter of the piston is 10 cm. Atmospheric pressure is 100 kPa.

When all 5 bricks are removed & replaced at once:

The temperature drops from 300 K to 239 K when the bricks are removed and then increases to 409 K when the

bricks are returned. The gas did 44 kJ/kg of work when the bricks were removed.

Each brick removed individually

The temperature drops from 300 K to 217 K if all five bricks are removed individually and then increases to 322 K

once the bricks are replaced. The gas did a total of 59 kJ/kg of work when the bricks were removed.

Bricks broken up and removed in small pieces (isentropic).

When the bricks are removed in small pieces the temperature dropped from 300 K to 210 K and returns to 300 K

when the pieces are returned (the process is reversible). The gas did 65 kJ/kg of work.

Discussion

The temperature drops increase from removing all 5 bricks at once, removing them one at a time, and removing

them in pieces because the process becomes more reversible (more work is done). Similarly, the final temperature is

highest when all five bricks are returned at once compared to replacing them one at a time and returning them in

pieces. Finally, the most amount of work is done when the bricks are removed in small pieces.

2. An eight-cylinder, four-stroke car engine draws in air at 30 psia and 100°F. The cylinders have a bore of 4 in and a

stroke of 4.5 in. The enclosed volume in each cylinder is 8 times larger when it is at BDC versus TDC. The flame

temperature is 4800 °F. Assuming it runs on an ideal Otto cycle, how much power will this engine produce when it is

running at 6,000 rpm? Note that if you use the "air" parameter in EES, it is a more accurate calculation because the

specific heat varies with temperature, which is more realistic. Either assuming a constant specific heat for air or

using EES is fine for these problems.

Compression from 1 to 2 is reversible and adiabatic (isentropic):

(100+459.67)*8^0.4=1,285.784

Expansion from 3 to 4 is isentropic:(4800+459.67)*(1/8)^0.4=2289.4043

0.171*((4800+459.67) - 1286 - 2290 + (100+459.67))=383.6111

(30*8*pi/4*(4/12)^2*(4.5/12)) / (0.3704*(100+459.67)) = 0.0378867083949543

6000/60 * 1/2 * 384 * 0.038 * 1.41 = 1028.736