1. No category

6.1 A system executes a power cycle while receiving 1000 kJ by heat transfer at a temperature of
500 K and discharging energy by heat transfer at a temperature of 300 K. There are no other heat
transfers. Applying Eq. 6.2, determineσcycle if the thermal efficiency is (a) 60%, (b) 40%, (c) 20%.
Identify the cases (if any) that are internally reversible or impossible.
6.2 A reversible power cycle R and an irreversible power cycle I operate between the same two
reservoirs. Each receives QH from the hot reservoir. The reversible cycle develops work WR, while the
irreversible cycle develops work WI. The reversible cycle discharges QC to the cold reservoir, while the
irreversible cycle discharges Q ’C.
(a) Evaluateσcycle for cycle I in terms of WI, WR, and temperature TC of the cold reservoir only.
(b) Demonstrate that WI ＜WR and Q ’C＞QC.
6.6 The system shown schematically in Fig. P6.6 undergoes a cycle while receiving energy at the
rate Q0 from the surroundings at temperature T0,
energy at the rate
from a source at temperature Ts, and delivering
at a use temperature Tu. There are no other energy transfers. For Ts ＞Tu ＞
T0, obtain an expression for the maximum theoretical value of
in terms of
and the
temperatures Ts, Tu, and T0.
6.8 A closed system consists of an ideal gas with constant specific heat ratio k.
(a) The gas undergoes a process in which temperature increases from T1 to T2. Show that the entropy
change for the process is greater if the change in state occurs at constant pressure than if it occurs at
constant volume. Sketch the processes on p–v and T–s coordinates.
(b) Using the results of (a), show on T–s coordinates that a line of constant specific volume
passing through a state has a greater slope than a line of constant pressure passing through that state.
(c) The gas undergoes a process in which pressure increases from p1 to p2. Show that the ratio of
the entropy change for an isothermal process to the entropy change for a constant-volume process is
(1 - k). Sketch the processes on p–v and T–s coordinates.
6.19 Using the appropriate table, determine the change in specific entropy between the specified
states, in kJ/kg K. Check the results using IT.
6.21 Employing the ideal gas model, determine the change in specific entropy between the indicated
states, in kJ/kg K. Solve three ways: Use the appropriate ideal gas table, IT, and a constant specific
heat value from Table A-20.
6.23 One kilogram of oxygen (O2) modeled as an ideal gas undergoes a process from 300 K, 2 bar to
1500 K, 1.5 bar. Determine the change in specific entropy, in kJ/kg K, using
(a) Equation 6.19 with
(b) Equation 6.21b with
from Table A-21.
from Table A-23.
(c) Equation 6.23 with cp at 900 K from Table A-20.
6.25 A quantity of liquid water undergoes a process from 80oC, 5 MPa to saturated liquid at 40oC.
Determine the change in specific entropy, in kJ/kg﹒K, using
(a) Tables A-2 and A-5.
(b) saturated liquid data only from Table A-2.
(c) the incompressible liquid model with a constant specific heat from Table A-19.
6.26 逻辑:推论和证明的思想过程 valid reasoning, Write out the logic of our textbook Ch1~Ch6 in
a A4 paper. Include a diagram with concepts and equations