{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

TEST_3_F95

TEST_3_F95 - ME 326 THERMODYNAMICS I Test 3 Dec 1 1995 1(33...

This preview shows pages 1–2. Sign up to view the full content.

ME 326: THERMODYNAMICS I Test 3, Dec. 1, 1995 1) (33%) An inventor brings you a heat engine that she claims takes thermal energy from a solar collector at 227°C at a rate of 300 kW, converts 200 kW to mechanical power and rejects the rest to a cooling pond at 27°C. a) What is the thermal efficiency of this heat engine if it operates as claimed? b) Does this heat engine violate the first law of thermodynamics? c) Does this heat engine violate the second law of thermodynamics? (Provide some mathematical justification for your answers.) SOLUTION: a) h=W net /Q h =200/300=0.67 or 67% b) Write First Law around complete cycle: W net =Q h -Q c or Q c = Q h - W net =300-200 = 100 kW; As long as rejected rate of heat transfer is 100 kW, the device obeys the First Law . c) Can 1) Check whether efficiency of real device (0.67 from part a) is less than the ideal (Carnot) efficiency = 1 - (T c /T h ) =1-(27+273)/(227+273) =1 - (300/500) = 1 - 0.6 = 0.4. It’s not, so violates Second Law. or 2) Check whether (Q h /T h )-(Q c /T c )=0 (Eq. 5.207a for a cycle); If not, violates Second Law. In this case, (300/500)-(100/300)=0.6-0.333 =+0.267,not = 0, so violates Second Law if it obeys

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern