exam 3 kill me

when does maximum work and efficiency occur?

in reversible processes

what devices are considered reversible?

carnot heat engines, refrigerators, heat pumps

does the efficiency or COP of a reversible heat engine operating between the same temperature limit depend on the working fluid?

NO

when two streams, one hot and the other cold, flow through a
heat exchanger, the primary irreversibility is the pressure drop
for the two streams

false, because heat transfer through a finite temperature difference is the cause of irreversability

an electric resistance heater and a heat pump consume the
same electricity to heat a given household in winter

false, less electricity is required for a heat pump (bc it has external heat transfer)

a reversible power cycle with a thermal efficiency of 100%
violates the first law of thermodynamics

false

a reversible power cycle with a thermal efficiency of 100%
violates the second law of thermodynamics

true

what is the carnot cycle?

adiabatic compression, isothermal expansion, adiabatic expansion, isothermal compression

what characteristics are satisfied by the carnot power cycle?

Qc/Qh = Tc/Th, Qcycle = Wcycle, nthermal = Wcycle/Qh

what is a reversed carnot cycle?

refrigeration cycle

what does the clasius inequality say?

entropy generation = 0 for reversibble cycle

does entropy generation depend on path?

no, thus it is a property

entropy change for incompressible substance

s2 - s1 = cln(T2/T1) (incompressible, constant specific heat)

entropy change for ideal gas

cpln(T2/T1) - Rln(P2/P1)

what causes irreversabilities?

friction, mixing, chemical reactions, expansion, compression

what gives optimum performance of practical devices?

isentropic processes

what is an internally reversible and adiabatic process?

isentropic (constant or none)

what is entropy balance for a closed system?

delta s = Qj/Tb + sgen (no entropy transfer)