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A heat engine using a diatomic gas follows the cycle shown in FIGURE P21.56. Its temperature at point 1is 20C.

a. Determine Ws,Q, and 螖贰thfor each of the three processes in this cycle. Display your results in a table.

b. What is the thermal efficiency of this heat engine?

c. What is the power output of the engine if it runs at 500rpm?

Short Answer

Expert verified

a. Table for the process is ,

b. The heat engine thermal efficiency is 46%.

c. The power output of the engine is12.5W.

Step by step solution

01

Calculation for heat,energy and work (part a)

a.

The area beneath the surface can be used to determine the work in the first procedure.

It is going to be

Ws=3010-6cm3(1.5-0.5)atm1052

=1.5J

The pressure was tripled and the volume was quadrupled in this procedure. This translates to a twelve-fold increase in temperature.

As a result, the temperature differential is eleven times greater than before. The change in internal energy can be calculated as follows:

螖贰th=nCv螖罢

=p1V1RT1Cv11T1

role="math" localid="1650265225764" =5104W110-5m31120.8C8.314

=13.75J

So,

Q=螖贰th+Ws

role="math" localid="1650265242221" =13.75J+1.5J

=15.25J

Isochoric cooling is the second procedure, in which the pressure lowers by a third.

As a result, the temperature decreases by the same factor, resulting in an eight-fold change in temperature.

This means that the heat applied to the gas will be more intense.

Q=p1V1nRT1Cv-8T1

role="math" localid="1650265302070" =5104W110-5m(-8)20.8C8.314

=-10J

The change in internal energy will be the same because the work in the isochoric process is zero.

02

Results in table part(a) solution

a.

In the third process we go isobarically from a temperature of four times is,

Q=p1V1nRT1Cp-4T1

=5104W110-5m(-4)29C8.314

=-7J

On the other hand, the work done on the other side can be represented by the rectangle under the graph. We can locate it right away.

Ws=-0.51053010-6J

=-3J

The change in internal energy is ,

螖贰th=3-7=-1J

03

Calculation for thermal efficiency (part b)

b.

From the table,

The total heat input is 3.25J.

The work done is1.5J.

The efficiency is,

role="math" localid="1650266315662" =1.5J3.25J

=46%

04

Calculation for power output (part c)

c.

work is 1.5Jdone.

Engine performs 500cycles per minute,.

Power is,

role="math" localid="1650266459838" P=1.5J500cyles/min60

=12.5W

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Most popular questions from this chapter

Engineers testing the efficiency of an electric generator gradually vary the temperature of the hot steam used to power it while leaving the temperature of the cooling water at a constant 20C. They find that the generator鈥檚 efficiency increases at a rate 3.510-4K-1at steam temperatures near 300C. What is the ratio of the generator鈥檚 efficiency to the efficiency of a Carnot engine?

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