FUND OF ENG THERMODYN(LLF)+WILEYPLUS
9th Edition
ISBN: 9781119391777
Author: MORAN
Publisher: WILEY
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EXERGY TRANSFER BY HEAT, WORK, AND MASS
7.27 Figure P7.27 provides steady-state data for the outer wall of a dwelling on a day
when the indoor temperature is maintained at 25°C and the outdoor temperature is
35°C. The heat transfer rate through the wall is 1000 W. Determine, in W, the rate of
exergy destruction (a) within the wall, and (b) within the enlarged system shown on the
figure by the dashed line. Comment. Let T₂ = 35°C. 20.13, 33-56
Indoor
Boundary of
enlarged-
temperature=25°C
T=27C
T-3C
FIGURE PLAT
Outdoor
temperature=35°C
Determine the specific exergy of saturated water vapor at 137 °C, where To = 313K, Po = 101.3kPa. Assume the velocity and
elevation is zero with reference to the environment.
You must use following tables to solve this problem. (answer to 2 decimal)
Saturated water temperature table
Sat Liq.
Temp.,
Sat Liq. Sat Liq.
Sat Liq.
vf
uf
hf
sf
°C
m3/kg
kJ/kg
kJ/kg
kJ/kg.K
30
0.001004
125.73
125.74
0.4368
35
0.001006
146.63
146.64
0.5051
40
0.001008
167.53
167.53
0.5724
45
0.00101
188.43
188.44
0.6386
Saturated water temperature table
Temp.,
Sat. Vap.
Sat. Vap.
Sat. Vap.
Sat. Vap.
hg
kJ/kg
vg
ug
sg
°C
m3/kg
kJ/kg
kJ/kg.K
125
0.7508
2534.5
2713.5
7.0745
126
0.7358
2535.5
2714.8
7.0649
127
0.7208
2536.5
2716.1
7.0553
128
0.7058
2537.5
2717.4
7.0457
129
0.6908
2538.5
2718.7
7.0361
130
0.6758
2539.5
2720.0
7.0265
131
0.6608
2540.5
2721.4
7.0169
132
0.6458
2541.4
2722.7
7.0073
133
0.6308
2542.4
2724.0
6.9977
134
0.6158
2543.4
2725.3
6.9881
6.9785
135
0.6008
2544.4
2726.6
136
0.5858
2545.4
2727.9…
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Similar questions
- Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x, = 0.5 undergo the two different processes 7.33 described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300 K, Po =1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel. Answer b. The process is brought about by heat transfer from a thermal reservoir at 610 K. The temperature of the water at the location where the heat transfer occurs is 610 K Answerarrow_forwardAt a pressure of 1 bar, a temperature of 17 °C and a mass flow of 0.3 kg/s, air enters a stable insulated compressor and exits at 3 bar, 147 °C. Determine the power required by the compressor and the exergy destruction in kW. Express the exergy disappearance as a percentage according to the power required by the compressor. Changes in kinetic and potential energy will be neglected. dead state; T0=17 °C, P0=1 bararrow_forwardIf the specific exergy of a gas in a cylinder of an internal combustion engine modeled as air behaving like an ideal gas is 368.91 kJ / kg and the cylinder contains 2450 cm2 of gaseous combustion products. Åt what elevation in meters 3-kg mass does it have to be lifted from zero elevation with respect to the reference environment so that its exergy equals the exergy of the cylinder? Assume gravity as g = 9.81 m /s^2 NOTE: The density of dry air at a pressure of 7 bar and a temperature of 867 ° C is 2.1388 kg / m^3.arrow_forward
- At steady state, an electric pump motor develops power along its output shaft of 0.7 hp whiledrawing 6 amps at 100 V. The outer surface of the motor is at 150°F. Let T = 40°F.Determine: (a) the magnitude of the rate of heat transfer leaving the motor, in Btu/h.(b) the exergy flow with input power, exergy flow with output power, magnitude of exergy flowwith heat transfer leaving the motor, and exergy destruction, all in Btu/h.arrow_forwardA domestic water heater holds 189 L of water at 60°C, 1 atm. Determine the exergy of the hot water, in kJ. To what elevation, in m, would a 1000-kg mass have to be raised from zero elevation relative to the reference environment for its exergy to equal that of the hot water? Let To = 298 K, po = 1 atm, g = 9.81 m/s².arrow_forwardApply exergy balance to closed systems and control volumes.arrow_forward
- At steady state, an electric pump motor develops power along its output shaft of 0.7 hp whiledrawing 6 amps at 100 V. The outer surface of the motor is at 150°F. Let T = 40°F.Determine:(b) the exergy flow with input power, exergy flow with output power, magnitude of exergy flowwith heat transfer leaving the motor, and exergy destruction, all in Btu/h.arrow_forwardSteady-state operating data are shown in the figure below for an open feedwater heater. Heat transfer from the feedwater heater to its surroundings occurs at an average outer surface temperature of 50°C at a rate of 100 kW. Ignore the effects of motion and gravity and let To = 25°C, po = 1 bar. Determine (a) the ratio of the incoming mass flow rates, m/ṁ2. (b) the rate of exergy destruction, in kW. P2 = 1 bar Tz = 400°C 1 ṁy = 0.7 kg/s Pi = 1 bar T, = 40°C Feedwater heater X3 = 25% P3 = 1 bar Tp = 50°C %3D 2)arrow_forwardA balloon filled with helium at 20°C, 1 bar and a volume of 0.5 m³ is moving with a velocity of 15 m/s at an elevation of 0.5 km relative to an exergy reference environment for which To = 20°C, po = 1 bar. Using the ideal gas model with k = 1.67, determine the specific exergy of the helium, in kJ.arrow_forward
- A domestic water heater holds 189 L of water at 60°C, 1 atm. Determine the exergy of the hot water, in kJ. To what elevation, in m, would a 1000-kg mass have to be raised from zero elevation for its exergy to equal that of the hot water? Let T0 = 298 K, p0 = 1 atm, g = 9.81 m/s2 .arrow_forwardDefine the Mechanisms of exergy transfer.arrow_forwardUsing image below Evaluate the exergy X1 of the initial state 1 and answer the following question: • Is the useful work in the process 1 → 2 → DS smaller, equal, or greater than exergy X1? • Discuss your resultarrow_forward
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