Fundamentals of Thermo
The ratio of a working fluid's vapor content to its total mass is called what?
Quality
What does the energy balance at steady state reduce down to for a throttle?
h_in = h_out; P_2 < P_1
Which statement of the 2nd law requires a thermodynamic cycle producing a net amount of work to exchange heat with two thermal reservoirs?
The Kelvin-Planck Statement
The state when a system is in equilibrium with the environment
Dead state
What is the purpose of reheat.
To reheat a portion of the exiting gas to gain more work
What parameter quantifies the deviation of a gas from ideal behavior?
Compressibility factor
The work associated with the flow of a fluid at the inlets and exits of a control volume
Flow Work
What two things carry entropy across a system boundary
Mass and heat
True or false, can the exergy of a system be completely destroyed?
True, if a system were permitted to undergo a spontaneous change to the dead state with no provision to obtain work
Why is an expansion valve preferred over a turbine in a vapor compression cycle?
While a turbine could theoretically recover some work during the expansion process, the amount of work recovered in a typical refrigeration or air-conditioning system is relatively small and may not justify the added complexity
In what conditions does a gas behave ideally
At high temperatures and low pressures
At S.S an ideal gas undergoes an isothermal process through a turbine, with kinetic and potential energy changes neglected. What is the expression of the first law for this system?
Q = W
In a closed insulated system, can mechanical work increase the system’s entropy?
Yes, because work can be irreversible and generate entropy
True or false, 1 kJ of heat carries the same amount of exergy into a system as 1 kJ of work?
False
Multiple stages of reheat and intercoolers leads Brayton cycle to transform into what type of cycle.
Ericsson cycle
What is the polytropic index for an adiabatic process
n = k
Steady flow devices that result in a drop in working fluid pressure from inlet to exit are?
(a) Nozzle, pump, throttling device
(b) Diffuser, turbine, throttling device
(c) Nozzle, turbine, throttling device
(d) Diffuser, pump, throttling device
(c) Nozzle, turbine, throttling device
When placed outside and exposed to the atmosphere, an ice cube melts, forming a thin film of liquid on the ground. Overnight, the liquid freezes, returning to the initial temperature of the ice cube. The water making up the cube undergoes
(a) a thermodynamic cycle
(b) a reversible process
(c) an irreversible process
(d) none of the above
(c) an irreversible process
True or false a system of multiple components can be at dead state pressure and temperature and still have the potential to produce work.
True, the system may still contain chemical exergy by virtue of its components’ concentration differences relative to the dead state.
What is the equation for reversible work in an open system
W = integral(vdp)
What are the ratios of a gas's temperature to its critical temperature and pressure to its critical pressure called?
Reduced temperature and reduced pressure
In an ideal throttling device, why is there no change in enthalpy for the throttle even though the pressure decreases?
The temperature for internal energy increases or another way of saying it is the PV energy is thermalized
Can a process still be isentropic if it’s undergoing irreversible work and heat transfer?
Yes, heat transfer out of the system can hypothetically offset the irreversible work’s entropy generation!
True or false, the 2nd law efficiency of a heat engine is the same as its Carnot efficiency
False
In a hypothetical Brayton cycle what happens to the net work produced by the cycle as the efficiency approaches 100%
(a)Approaches 0
(b)Approaches infinity
(c)Approaches a constant
Approaches 0