Thermo Unit 8: Entropy Continued

In steady-flow processes, the energy change within the control volume does what?

Is 0, constant energy

Compressors are for…

Increasing pressure in GASES

Pumps are for

increasing pressure for LIQUIDS

Isentropic Eff for Turbines eqn

n= (h1-h2a) / (h1 -h2s)

Isentropic Eff for Turbines

Actual turbine work/ Isentropic work

Energy balance eqn for turbine:

(m*1*h1)= W* out + (m*2 *h2a)

Isentropic eff for compressors

Isentropic compressor work input/ actual compressor work input

Isentropic eff for compressors eqn

nC= (h2s-h1) / (h2a- h1)

Isentropic eff for pump eqn

nP= v(P2-P1) / (h2a- h1) where v is constant specific volume cause its a liquid

Adiabatic compressor energy balance eqn

m*h1+ Win= m*h2a

Isentropic eff for nozzles

Actual KE at nozzle exit/ Isentropic KE at nozzle exit= V2a²/V2s²

Isentropic eff for nozzles eqn

nN= (h1- h2a) / (h1-h2a)

Energy balance for a nozzle if the inlet velocity is relatively small compared to exit?

h1= h2a + (V2a² /2)

Isentropic Process of Ideal Gas with constant specific volume?

T2s/ T1= (P2s/P1)^ (k-1)/k

Entropy Transfer by work?

No entropy transfer accompanies work as it crosses the system boundary, but entropy may be generated within the system as work is dissipated into a less useful form of energy (ie, friction)

The Entropy change of a closed system….

is equal to the net entropy transfer through the system boundary by heat transfers and the net entropy generated.

Water condensing in a frictionless piston?

Internally reversible isothermal process because a) the boundary temp is the same as internal temp and b) no temperature change associated with the phase change.

Throttling valve is a constant _____ process?

Enthalpy

1 m²/s² =

1 j/kg so 1/1000 kj/kg