Nader Thermo Exam 3

For a refrigeration cycle, what must be true?

Correct:

(Qout)net = (Win)net

Incorrect:

(Qin)net = (Win)net

(Qout)net = delta(U)

(Qout)net = (Wout)net

True or False. The conversion of entropy applies to a car engine.

False

What is an isentropic process?

Adiabatic and internally reversible

What is considered a conceivable cycle?

A. deltaU = 0

B. Sgen >= 0

C. deltaS = 0

D. All items listed

D. All items listed

Qh/Ql = Th/Tl, work done = QL(Th/Tl - 1)

True

True or False. Carnot efficiency is different than the thermal efficiency of the Ericsson cycle.

False

For a Rankine cycle, thermal efficiency increases as the area under the curve.

True

What is q_in for this actual cycle?

h1-4a

Energy balance for cascade refrigeration cycle.

In the formula sheet

The compression ratio in a cylinder before combustion process such as the diesel cycle between P3 and P4.

False

Question asking about h3 and h4 are the same enthalpies?

True

The actual steam cycle has higher efficiency than the simple rankine cycle.

False

What happens in Process 2-3 of Carnot cycle?

a. delta(h) < 0

b. delta(s) = 0

c. delta(u) > 0

d. All of these

e. None

Correct Answer: B

Higher back ratio means higher net work output in the cycle, and higher efficiency in the cycle.

False

For the otto cycle, thermal efficiency and compression ratio are linearly related so when the compression ratio increases so does the thermal efficiency.

False, not linearlly related.

For a refrigeration cycle from step 1 --> 2, compression leads to the temperature rising above its surroundings.

True

During the rankine cycle reheat, the pressure at 4-5 is the same as 2-3?

False

For an isentropic cycle, the thermal efficiency increases as the area under the curve increases on a T-s diagram?

True

What is the purpose of regeneration?

Increases the temperature of heat addition and decreases the temperature of heat rejection.

COP of a heat pump is 2.5 so the COP of a refrigerator is 3.5.

False

Which of the following is true?

(turbine question)

Heat addition to a turbine increases efficiency.

Isentropic stands for constant entropy.

True

The Stirling Cycle, like the Carnot cycle, has regeneration.

False (Stirling does, Carnot doesn't)

The actual power cycle is more efficient than the ideal power cycle because of more irreversibilites in the actual power cycle.

False

The pressure ratio calculates which of the following?

P2/P1 for Brayton cycle

The ideal vapor refrigeration cycle, s3=s4.

False

What happens during throttling?

Internal Energy decreases, specific volume increases.

PV^n = C, if n is 0. What is it?

Isobaric

In an actual gas turbine cycle, when does the compressor work happen?

1-2a

In an actual gas turbine cycle, when does the turbine work happen?

3-4a

In an actual gas turbine cycle, how do you find (q)out?

h4a-h1

In an actual gas turbine cycle, how do you find (q)in?

h2a-h3

What's happening in 2-3 Carnot Cycle?

delta(s) = 0

What is the process from 2-3 of the Carnot Cycle?

Adiabatc expansion

What is the process from 4-1 of the Carnot Cycle?

Adiabatic compression