Thermo Final Nadar

For a refrigeration cycle, what must be true?

(Q_out)net = (W_in)net

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

False

In an actual gas-turbine cycle, when does compressor work occur?

During process 1→2a

In an actual gas-turbine cycle, when does turbine work occur?

During process 3→4a

How do you calculate heat rejected in an actual gas-turbine cycle?

(Q_out)=h4a−h1

How do you calculate heat added in an actual gas-turbine cycle?

(Q_in)=h3−h2a

What is process 4→1 in the Carnot cycle?

Adiabatic compression.

What is process 2→3 in the Carnot cycle?

Adiabatic expansion.

What happens to entropy during process 2→3 of the Carnot cycle?

ΔS=0

How do you find h2 in the Rankine cycle?

h2=h1+(v_f,1)(P2−P1)

True or False: If the COP of a heat pump is 2.5, the COP of the refrigerator is 3.5.

False - COPHP=COPR+1

True or False: The Stirling cycle, like the Carnot cycle, has regeneration.

False

What happens during throttling?

Internal energy decreases as specific volume increases.

What is the pressure ratio for a Brayton cycle?

r_p=P1/P2

True or False: An actual power cycle is more efficient than an ideal power cycle because it has more irreversibilities.

False

What is the purpose of regeneration?

It increases the temperature of heat addition and decreases the temperature of heat rejection.

True or False: For an isentropic cycle, thermal efficiency increases as the area under the curve on a T−− s diagram increases.

True

True or False: During Rankine-cycle reheat, the pressure during process 4→5 is the same as during process 2→3

False

True or False: A higher back-work ratio means higher net work output and higher cycle efficiency.

False

True or False: The actual steam cycle has a higher efficiency than the simple Rankine cycle.

False

What is the energy balance for a cascade refrigeration cycle?

m˙_A(h5−h8)=m˙_B(h2−h3) - Be careful because cycles A and B may be switched.

Why is the Carnot cycle not practical for refrigeration?

The compressor cannot handle a liquid-vapor mixture.

What is the purpose of refrigeration according to the notes?

To store energy temporarily so that it can be reused in the cycle.

True or False: In a Diesel cycle, the compression ratio before combustion is between P_3 and P_4

False

True or False: In an ideal vapor-compression refrigeration cycle, states 3 and 4 have the same enthalpy.

True h_3 = h_4

In a combined gas-vapor power cycle, what does the following represent?

m˙(h8−h9) / t

What is the purpose of cascading?

To increase overall efficiency.

What conditions describe a conceivable cycle?

ΔU=0

S_gen >= 0

ΔS = 0

All items listed.

True or False: Carnot efficiency is different from Ericsson-cycle efficiency.

False

True or False: For a steam Rankine cycle, thermal efficiency increases as the area enclosed on the T− s diagram increases.

True

True or False: Otto-cycle efficiency and compression ratio are linearly related.

False

What happens to Otto-cycle efficiency when the compression ratio increases?

Thermal efficiency increases, but the relationship is not linear.

True or False: During process 1→2 of a refrigeration cycle, compression raises the refrigerant temperature above the surroundings.

True