FUND OF ENG THERMODYN(LLF)+WILEYPLUS
9th Edition
ISBN: 9781119391777
Author: MORAN
Publisher: WILEY
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10. Carnot cycle thermal efficiency is increased by reducing lower(sink) temperature
11. A system with higher exergy has more capacity to do work than a system with lower exergy.
12. A diffuser has low pressure at inlet and high pressure at outlet
13. Carnot efficiency equation can also be used to find efficiency of conversion of electrical
and/or magnetic energy to work.
14. Quality factor of 0.75 indicates supersaturated vapor
15. Law of conservation of Mass and energy applied to Nozzles and Diffusers indicates that
under ideal conditions, the change in kinetic energy of the fluid results in a complimentary
change in enthalpy of the fluid
Steady-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)
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
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Similar questions
- 7.58 Figure PZ.58 shows a gas turbine power plant using air as the working fluid. The accompanying table gives steady-state operating data. Air can be modeled as an ideal gas. Stray heat transfer and the effects of motion and gravity can be ignored Let To 290 K, po = 100 kPa. Determine, each in kJ per kg of air flowing, (a) the net power developed, (b) the net exergy increase of the air passing through the heat exchanger, (eg- e), and (c) a full exergy accounting based on the exergy supplied to the plant found in part (b). Comment. State p(kPa) T(K) h(kJ/kg) s° (kJ/kg K) 1100 290 290.16 1.6680 500 505 508.17 2 2.2297 3 500 875 904.99 2.8170 4 100 635 643.93 2.4688 a o is the variable appearing in Eq. 6.20a and Table A-22. Heat exchanger Compressor Turbine FIGURE P7.58arrow_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_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
- Determine the change in exergy in kJ for each of the following processes in the system with 1 kg of steam at 20 bar and 240 °C initially. a) In case the system is heated to double its volume at constant pressure. b) In case of expansion by doubling the system volume isothermally. dead state; T0=20 °C, P0=1 bararrow_forwardFigure PZ55 and the accompanying table provide the schematic and steady-state operating data for a flash 7.55 chamber fitted with an inlet valve that produces saturated vapor and saturated liquid streams from a single entering stream of liquid water. Stray heat transfer and the effects of motion and gravity are negligible. Determine (a) the mass flow rate, in Ib/s, for each of the streams exiting the flash chamber and (b) the total rate of exergy destruction, in Btu/s. Let To = 77°F, Po =1 atm State Condition T(°F) p(lbf/in.°) h(Btu/lb) s(Btu/lb R) liquid 300 80 269.7 1 0.4372 1.6996 30 1164.3 2 sat. vapor 3 sat. liquid 218.9 0.3682 30 2 Saturated vapor P2=30 lbf/in.2 Flash chamber Valve =100 lb/s T 300°F P=80 lbf/in.2 Saturated liquid,A+ P3=30 lbf/in.2 3 FIGURE P7.55arrow_forward7.36 At steady state, hot gaseous products of combustion from a gas turbine cool from 3000°F to 250°F as they flow through a pipe. Owing to negligible fluid friction, the flow occurs at nearly constant pressure. Applying the ideal gas model with ₂ = 0.3 Btu/lb/ºR, determine the exergy transfer accompanying heat transfer from the gas, in Btu per lb of gas flowing. Let T. = 80°F and ignore the effects of motion and gravity. -568.43arrow_forward
- At 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_forwardExergy flow associated with a fluid stream when the fluid properties are variable can be determined by.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
- A 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_forwardAt 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_forward1. Water and air are used as working fluids in a counter-flow heat exchanger operating at steady state. Water enters as a saturated vapor at 300 kPa with a mass flow rate of 10 kg/s and exiting as saturated liquid. Air enters in a separate stream at 0°C, 100 kPa and exits at 37°C. Pressure changes and the heat transfer between the heat exchanger and its surroundings are negligible. Determine the rate of exergy destruction in the heat exchanger.arrow_forward
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