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mechanical engineering

Questions and Answers of Mechanical Engineering

Outdoor air (cp = 1.005 kJ/kg·°C) is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. Air enters the heat exchanger at 101 kPa and 30°C at a rate
Steam is to be condensed on the shell side of a heat exchanger at 120°F. Cooling water enters the tubes at 60°F at a rate of 115.3 lbm/s and leaves at 73°F. Assuming the heat exchanger to be well
Air enters a compressor at ambient conditions of 100 kPa and 20°C at a rate of 4.5 m3/s with a low velocity, and exits at 900 kPa, 60°C, and 80 m/s. The compressor is cooled by cooling water that
A hot-water stream at 160°F enters an adiabatic mixing chamber with a mass flow rate of 4 lbm/s, where it is mixed with a stream of cold water at 70°F. If the mixture leaves the chamber at 110°F,
Liquid water at 20°C is heated in a chamber by mixing it with saturated steam. Liquid water enters the chamber at the steam pressure at a rate of 4.6 kg/s and the saturated steam enters at a rate of
A refrigerator has a second-law efficiency of 28 percent, and heat is removed from the refrigerated space at a rate of 800 Btu/min. If the space is maintained at 25°F while the surrounding air
Refrigerant-134a is expanded adiabatically in an expansion valve from 700 kPa and 25°C to 160 kPa. For environment conditions of 100 kPa and 20°C, determine (a) The work potential of R-134a at the
Steam enters an adiabatic nozzle at 3.5 MPa and 300°C with a low velocity and leaves at 1.6 MPa and 250°C at a rate of 0.4 kg/s. If the ambient state is 100 kPa and 18°C, determine (a) The exit
Steam is condensed in a closed system at a constant pressure of 75 kPa from a saturated vapor to a saturated liquid by rejecting heat to a thermal energy reservoir at 37°C. Determine the second-law
Refrigerant-134a is converted from a saturated liquid to a saturated vapor in a closed system using a reversible constant pressure process by transferring heat from a heat reservoir at 6°C. From
An adiabatic heat exchanger is to cool ethylene glycol (cp = 2.56 kJ/kg ∙ °C) flowing at a rate of 2 kg/s from 80 to 40°C by water (cp = 4.18 kJ/kg ∙ °C) that enters at 20°C and leaves at
A well-insulated, thin-walled, counter-flow heat exchanger is to be used to cool oil (cp = 2.20 kJ/kg ˆ™°C) from 150 to 40°C at a rate of 2 kg/s by water (cp = 4.18 kJ/kg ˆ™ °C) that enters
Hot exhaust gases leaving an internal combustion engine at 4008C and 150 kPa at a rate of 0.8 kg/s is to be used to produce saturated steam at 2008C in an insulated heat exchanger. Water enters the
A crater lake has a base area of 20,000 m2, and the water it contains is 12 m deep. The ground surrounding the crater is nearly flat and is 140 m below the base of the lake. Determine the maximum
The inner and outer surfaces of a 5-m = 6-m brick wall of thickness 30 cm are maintained at temperatures of 20°C and 5°C, respectively, and the rate of heat transfer through the wall is 900
A 1000-W iron is left on the ironing board with its base exposed to the air at 20°C. If the temperature of the base of the iron is 150°C, determine the rate of exergy destruction for this process
A 30-cm-long, 1500-W electric resistance heating element whose diameter is 1.2 cm is immersed in 70 kg of water initially at 20°C. Assuming the water container is wellinsulated, determine how
An adiabatic steam nozzle has steam entering at 300 kPa, 150°C, and 45 m/s, and leaving as a saturated vapor at 150 kPa. Calculate the actual and maximum outlet velocity. Take T0 = 25°C.
A steam turbine is equipped to bleed 6 percent of the inlet steam for feed water heating. It is operated with 500 psia and 600°F steam at the inlet, a bleed pressure of 100 psia, and an exhaust
What are the air-standard assumptions?
Define the following terms related to reciprocating engines: stroke, bore, top dead center, and clearance volume.
Rework Prob. 9-99 when the compressor isentropic efficiency is 87 percent and the turbine isentropic efficiency is 93 percent.Prob. 9-99A gas turbine for an automobile is designed with a regenerator.
A gas turbine engine operates on the ideal Brayton cycle with regeneration, as shown in Fig. P9-99. Now the regenerator is rearranged so that the air streams of states 2 and 5 enter at one end of the
An ideal regenerator (T3 = T5) is added to a simple ideal Brayton cycle (see Fig. P9-99). Air enters the compressor of this cycle at 16 psia and 100°F; the pressure ratio is 11; and the maximum
The idea of using gas turbines to power automobiles was conceived in the 1930s, and considerable research was done in the 1940s and 1950s to develop automotive gas turbines by major automobile
An ideal Brayton cycle with regeneration has a pressure ratio of 10. Air enters the compressor at 300 K and the turbine at 1200 K. If the effectiveness of the regenerator is 100 percent, determine
Reconsider Problem 9-104. Using EES (or other) software, study the effects of varying the isentropic efficiencies for the compressor and turbine and regenerator effectiveness on net work done and the
Repeat Problem 9-104 using constant specific heats at room temperature.Problem 9-104An ideal Brayton cycle with regeneration has a pressure ratio of 10. Air enters the compressor at 300 K and the
A Brayton cycle with regeneration using air as the working fluid has a pressure ratio of 7. The minimum and maximum temperatures in the cycle are 310 and 1150 K. Assuming an isentropic efficiency of
A stationary gas-turbine power plant operates on an ideal regenerative Brayton cycle (ε = 100 percent) with air as the working fluid. Air enters the compressor at 95 kPa and 290 K and the turbine at
Air enters the compressor of a regenerative gas-turbine engine at 310 K and 100 kPa, where it is compressed to 900 kPa and 650 K. The regenerator has an effectiveness of 80 percent, and the air
What is the maximum possible thermal efficiency of a gas power cycle when using thermal energy reservoirs at 1100oF and 80oF?
Repeat Prob. 9-109 using constant specific heats at room temperature. Prob. 9-109 Air enters the compressor of a regenerative gas-turbine engine at 310 K and 100 kPa, where it is compressed to 900
Repeat Prob. 9-109 for a regenerator effectiveness of 70 percent. Prob. 9-109 Air enters the compressor of a regenerative gas-turbine engine at 310 K and 100 kPa, where it is compressed to 900 kPa
Develop an expression for the thermal efficiency of an ideal Brayton cycle with an ideal regenerator of effectiveness 100 percent. Use constant specific heats at room temperature.
For a specified pressure ratio, why does multistage compression with intercooling decrease the compressor work, and multistage expansion with reheating increase the turbine work?
A simple ideal Brayton cycle without regeneration is modified to incorporate multistage compression with intercooling and multistage expansion with reheating, without changing the pressure or
A simple ideal Brayton cycle is modified to incorporate multistage compression with intercooling, multistage expansion with reheating, and regeneration without changing the pressure limits of the
Consider a regenerative gas-turbine power plant with two stages of compression and two stages of expansion. The overall pressure ratio of the cycle is 9. The air enters each stage of the compressor
An air-standard cycle is executed within a closed piston-cylinder system and consists of three processes as follows: 1-2 V = constant heat addition from 100 kPa and 27oC to 700 kPa 2-3 Isothermal
Repeat Problem 9-119 using argon as the working fluid. Problem 9-119 Consider a regenerative gas-turbine power plant with two stages of compression and two stages of expansion. The overall pressure
Consider an ideal gas-turbine cycle with two stages of compression and two stages of expansion. The pressure ratio across each stage of the compressor and turbine is 3. The air enters each stage of
Repeat Problem 9-121, assuming an efficiency of 86 percent for each compressor stage and an efficiency of 90 percent for each turbine stage. Problem 9-121 Consider an ideal gas-turbine cycle with two
Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kPa and 17°C. This system uses a regenerator as well as reheating and intercooling. The pressure ratio
Repeat Prob. 9-123 for the case of three stages of compression with intercooling and three stages with expansion with reheating.Prob. 9-123Air enters a gas turbine with two stages of compression and
How much would the thermal efficiency of the cycle in Prob. 9-124 change if the temperature of the cold-air stream leaving the regenerator is 80°C lower than the temperature of the hot-air stream
What is propulsive efficiency? How is it determined?
A turbojet is flying with a velocity of 900 ft/s at an altitude of 20,000 ft, where the ambient conditions are 7 psia and 10°F. The pressure ratio across the compressor is 13, and the temperature at
Repeat Problem 9-129E accounting for the variation of specific heats with temperature. Problem 9-129E A turbojet is flying with a velocity of 900 ft/s at an altitude of 20,000 ft, where the ambient
A turbofan engine operating on an aircraft flying at 200 m/s at an altitude where the air is at 50 kPa and -20°C, is to produce 50,000 N of thrust. The inlet diameter of this engine is 2.5 m; the
A pure jet engine propels an aircraft at 240 m/s through air at 45 kPa and -13°C. The inlet diameter of this engine is 1.6 m, the compressor pressure ratio is 13, and the temperature at the turbine
A turbojet aircraft is flying with a velocity of 280 m/s at an altitude of 9150 m, where the ambient conditions are 32 kPa and -32°C. The pressure ratio across the compressor is 12, and the
Repeat Prob. 9-133 using a compressor efficiency of 80 percent and a turbine efficiency of 85 percent. Prob. 9-133 A turbojet aircraft is flying with a velocity of 280 m/s at an altitude of 9150 m,
Consider an aircraft powered by a turbojet engine that has a pressure ratio of 9. The aircraft is stationary on the ground, held in position by its brakes. The ambient air is at 7°C and 95 kPa and
Reconsider Prob. 9-135. In the problem statement, replace the inlet mass flow rate by an inlet volume flow rate of 18.1 m3/s. Using EES (or other) software, investigate the effect of compressor inlet
Air at 7°C enters a turbojet engine at a rate of 16 kg/s and at a velocity of 300 m/s (relative to the engine). Air is heated in the combustion chamber at a rate 15,000 kJ/s and it leaves the engine
Determine the total exergy destruction associated with the Otto cycle described in Problem 9-33, assuming a source temperature of 2000 K and a sink temperature of 300 K. Also, determine the energy at
Determine the total exergy destruction associated with the Diesel cycle described in Problem 9-46, assuming a source temperature of 2000 K and a sink temperature of 300 K. Also, determine the energy
Using EES (or other) software, study the effect of varying the temperature after the constant-volume heat addition from 1500 K to 2500 K. Plot the net work output and thermal efficiency as a function
Determine the exergy destruction associated with the heat rejection process of the Diesel cycle described in Prob. 9-52E, assuming a source temperature of 3200 R and a sink temperature of 540 R.
Calculate the exergy destruction for each process of Stirling cycle of Prob. 9-74, in kJ/kg.
Calculate the exergy destruction associated with each of the processes of the Brayton cycle described in Prob. 9-83, assuming a source temperature of 1600 K and a sink temperature of 295 K.
Repeat Prob. 9-86 using exergy analysis.
Determine the total exergy destruction associated with the Brayton cycle described in Prob. 9-107, assuming a source temperature of 1500 K and a sink temperature of 290 K. Also, determine the energy
Reconsider Prob. 9-144. Using EES (or other) software, investigate the effect of varying the cycle pressure ratio from 6 to 14 on the total exergy destruction for the cycle and the energy of the
Determine the exergy destruction associated with each of the processes of the Brayton cycle described in Prob. 9-109, assuming a source temperature of 1260 K and a sink temperature of 300 K. Also,
Calculate the lost work potential for each process of Prob. 9-125. The temperature of the hot reservoir is the same as the maximum cycle temperature and the temperature of the cold reservoir is the
A gas-turbine power plant operates on the regenerative Brayton cycle between the pressure limits of 100 and 700 kPa. Air enters the compressor at 308C at a rate of 12.6 kg/s and leaves at 2608C. It
A four-cylinder, four-stroke, 1.8-liter modern, highspeed compression-ignition engine operates on the ideal dual cycle with a compression ratio of 16. The air is at 95 kPa and 708C at the beginning
A Carnot cycle is executed in a closed system and uses 0.0025 kg of air as the working fluid. The cycle efficiency is 60 percent, and the lowest temperature in the cycle is 300 K. The pressure at the
An air-standard cycle with variable coefficients is executed in a closed system and is composed of the following four processes: 1-2 V 5 constant heat addition from 100 kPa and 278C to 300 kPa 2-3 P
Repeat Problem 9-151 using constant specific heats at room temperature.
An Otto cycle with a compression ratio of 10.5 begins its compression at 90 kPa and 358C. The maximum cycle temperature is 10008C. Utilizing air-standard assumptions, determine the thermal efficiency
A Diesel cycle has a compression ratio of 20 and begins its compression at 13 psia and 458F. The maximum cycle temperature is I8008F. Utilizing air-standard assumptions, determine the thermal
A Brayton cycle with a pressure ratio of 12 operates with air entering the compressor at 13 psia and 208F, and the turbine at 10008F. Calculate the net specific work produced by this cycle treating
A four-stroke turbocharged V-16 diesel engine built by GE Transportation Systems to power fast trains produces 4400 hp at 1500 rpm. Determine the amount of work produced per cylinder per (a)
Consider a simple ideal Brayton cycle operating between the temperature limits of 300 and 1500 K. Using constant specific heats at room temperature, determine the pressure ratio for which the
A four-cylinder, four-stroke spark-ignition engine operates on the ideal Otto cycle with a compression ratio of 11 and a total displacement volume of 1.8 liter. The air is at 90 kPa and 508C at the
A four-cylinder spark-ignition engine has a compression ratio of 10.5, and each cylinder has a maximum volume of 0.4 L. At the beginning of the compression process, the air is at 98 kPa and 378C, and
Reconsider Prob. 9-159. Using EES (or other) software, study the effect of varying the compression ratio from 5 to 11 on the net work done and the efficiency of the cycle. Plot the P-v and T-s
A typical hydrocarbon fuel produces 43,000 kJ/kg of heat when used in a spark-ignition engine. Determine the compression ratio required for an ideal Otto cycle to use 0.039 grams of fuel to produce 1
An ideal dual cycle has a compression ratio of 14 and uses air as the working fluid. At the beginning of the compression process, air is at 14.7 psia and 1208F, and occupies a volume of 98 in3.
Consider an ideal Stirling cycle using air as the working fluid. Air is at 400 K and 200 kPa at the beginning of the isothermal compression process, and heat is supplied to air from a source at 1800
Consider a simple ideal Brayton cycle with air as the working fluid. The pressure ratio of the cycle is 6, and the minimum and maximum temperatures are 300 and 1300 K, respectively. Now the pressure
Repeat Prob. 9-164 using constant specific heats at room temperature.
Helium is used as the working fluid in a Brayton cycle with regeneration. The pressure ratio of the cycle is 8, the compressor inlet temperature is 300 K, and the turbine inlet temperature is 1800 K.
Consider an ideal gas-turbine cycle with one stage of compression and two stages of expansion and regeneration. The pressure ratio across each turbine stage is the same. The highpressure turbine
A gas-turbine plant operates on the regenerative Brayton cycle with two stages of reheating and two-stages of intercooling between the pressure limits of 100 and 1200 kPa. The working fluid is air.
Compare the thermal efficiency of a two-stage gas turbine with regeneration, reheating and intercooling to that of a three-stage gas turbine with the same equipment when All components operate
The specific impulse of an aircraft-propulsion system is the force produced per unit of thrust-producing mass flow rate. Consider a jet engine that operates in an environment at 10 psia and 308F and
Electricity and process heat requirements of a manufacturing facility are to be met by a cogeneration plant consisting of a gas turbine and a heat exchanger for steam production. The plant operates
A turbojet aircraft flies with a velocity of 1100 km/h at an altitude where the air temperature and pressure are 2358C and 40 kPa. Air leaves the diffuser at 50 kPa with a velocity of 15 m/s, and
An air standard cycle with constant specific heats is executed in a closed piston-cylinder system and is composed of the following three processes: 1-2 Constant volume heat addition 2-3 lsentropic
Consider the ideal regenerative Brayton cycle. Determine the pressure ratio that maximizes the thermal efficiency of the cycle and compare this value with the pressure ratio that maximizes the cycle
Using EES (or other) software, study the effect of variable specific heats on the thermal efficiency of the ideal Otto cycle using air as the working fluid. At the beginning of the compression
Using EES (or other) software, determine the effects of pressure ratio, maximum cycle temperature, and compressor and turbine efficiencies on the net work output per unit mass and the thermal
Repeat Problem 9-176 by considering the variation of specific heats of air with temperature.
Repeat Problem 9-176 using helium as the working fluid.
Using EES (or other) software, determine the effects of pressure ratio, maximum cycle temperature, regenerator effectiveness, and compressor and turbine efficiencies on the net work output per unit
An air standard Carnot cycle is executed in a closed system between the temperature limits of 350 and 1200 K. The pressures before and after the isothermal compression are 150 and 300 kPa,

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