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engineering
mechanical engineering
Questions and Answers of
Mechanical Engineering
Water flows steadily through an insulated nozzle. The following data is supplied: Inlet: p = 200 kPa, V = 10 m/s, z = 2 m; Exit: p = 100 kPa, z = 0. (a) Determine the exit velocity. Assume density of
Water flowing steadily through a 2 cm diameter pipe at 30 m/s goes through an expansion joint to flow through a 4 cm diameter pipe. Assuming the internal energy remains constant, determine (a) The
An adiabatic work producing device works at steady state with the working fluid entering through a single inlet and leaving through a single exit. Derive an expression for the work output in terms of
A pump is a device that raises the pressure of a liquid at the expense of external work. (a) Determine the pumping power necessary to raise the pressure of liquid water from 10 kPa to 2000 kPa at a
An adiabatic pump working at steady state raises the pressure of water from 100 kPa to 1 MPa, while the specific internal energy (u) remains constant. If the exit is 10 m above the inlet and the flow
Steam flows steadily through a single-flow device with a flow rate of 10 kg/s. It enters with an enthalpy of 3698 kJ/kg and a velocity of 30 m/s. At the exit, the corresponding values are 3368 kJ/kg
Steam enters an adiabatic turbine with a mass flow rate of 5 kg/s at 3 MPa, 600oC and 80 m/s. It exits the turbine at 40oC, 30 m/s and a quality of 0.9. Assuming steady-state operation, determine the
A gas enters an adiabatic work consuming device at 300 K, 20 m/s, and leaves at 500 K, 40 m/s. (a) If the mass flow rate is 5 kg/s, determine the rate of work transfer. Neglect change in potential
An electric bulb consumes 500 W of electricity. After it is turned on, the bulb becomes warmer and starts losing heat to the surroundings at a rate of 5t (t in seconds) watts until the heat loss
A refrigerant is compressed by an adiabatic compressor operating at steady state to raise the pressure from 200 kPa to 750 kPa. The following data are supplied for the inlet and exit ports. Inlet: v
Two flows of equal mass flow rate, one at state-1 and another at state- 2 enter an adiabatic mixing chamber and leave through a single port at state-3. Obtain an expression for the velocity and
Air at 500 kPa, 30oC from a supply line is used to fill an adiabatic tank. At a particular moment during the filling process, the tank contains 0.2 kg of air at 200 kPa and 50oC. If the mass flow
An insulated tank is being filled with a gas through a single inlet. At a given instant, the mass flow rate is measured as 0.5 kg/s and the enthalpy h as 400 kJ/kg. Neglecting ke and pe, determine
Saturated steam at 200 kPa, which has a specific enthalpy (h) of 2707 kJ/kg is expelled from a pressure cooker at a rate of 0.1 kg/s. Determine the rate of heat transfer necessary to maintain a
Suppose the specific internal energy in kJ/kg of the solid in problem 2-2-1 [NX] is related to its temperature through u = 0.5T, where T is the temperature of the solid in Kelvin, determine the rate
A cup of coffee is heated in a microwave oven. If the mass of coffee (modeled as liquid water) is 0.2 kg and the rate of heat transfer is 0.1 kW. (a) Determine the rate of change of internal energy
At a given instant a closed system is loosing 0.1 kW of heat to the outside atmosphere. A battery inside the system keeps it warm by powering a 0.1 kW internal heating lamp. A shaft transfers 0.1 kW
A semi-truck of mass 20,000 lb accelerates from 0 to 75 m/h (1 m/h = 0.447 m/s) in 10 seconds. (a) What is the change in kinetic energy of the truck in 10 seconds? (b) If PE and U of the truck can be
An insulated tank contains 50 kg of water, which is stirred by a paddle wheel at 300 rpm while transmitting a torque of 0.1 kN-m. At the same time, an electric resistance heater inside the tank
Heat is transferred from a TER at 1500 K to a TER at 300 K at a rate of 10 kW. Determine the rates at which entropy (a) Leaves the TER at higher temperature. (b) Enters the TER at lower
A 10 m3 insulated rigid tank contains 30 kg of wet steam with a quality of 0.9. An internal electric heater is turned on, which consumes electric power at a rate of 10 kW. After the heater is on for
One kg of air is trapped in a rigid chamber of volume 0.2 m3 at 300 K. Because of electric work transfer, the temperature of air increases at a rate of 1oC/s. Using the IG system state daemon,
A rigid cylindrical tank stores 100 kg of a substance at 500 kPa and 500 K while the outside temperature is 300 K. A paddle wheel stirs the system transferring shaft work at a rate of 0.5 kW. At the
A 1 cm diameter insulated pipe carries a steady flow of water at a velocity of 30 m/s. The temperature increases from 300 K at the inlet to 301 K at the exit due to friction. If the specific entropy
Liquid water (density 997 kg/m3) flows steadily through a pipe with a volume flow rate of 30,000 L/min. Due to viscous friction, the pressure drops from 500 kPa at the inlet to 150 kPa at the exit.
An electric water heater works by passing electricity through an electrical resistance placed inside the flow of liquid water as shown in the accompanying animation. The specific internal energy and
An open system with only one inlet and one exit operates at steady state. Mass enters the system at a flow rate of 5 kg/s with the following properties: h = 3484 kJ/kg, s = 8.0871 kJ/kg-K and V = 20
Steam flows steadily through a work-producing, adiabatic, single-flow device with a flow rate of 7 kg/s. At the inlet h = 3589 kJ/kg, s = 7.945 kJ/kg-K, and at the exit h = 2610 kJ/kg, s = 8.042
The following information are supplied at the inlet and exit of an adiabatic nozzle operating at steady state: Inlet: V = 30 m/s, h = 976.2 kJ/kg, s = 6.149 kJ/kg-K; Exit: h = 825.5 kJ/kg.
A refrigerant flows steadily through an insulated tube, its entropy increases from 0.2718 kJ/kg-K at the inlet to 0.3075 kJ/kg-K at the exit. If the mass flow rate of the refrigerant is 0.2 kg/s and
A wall separates a hot reservoir at 1000 K from a cold reservoir at 300 K. The temperature difference between the two reservoirs drive a heat transfer at the rate of 500 kW. If the wall maintains
A resistance heater operates inside a tank consuming 0.5 kW of electricity. Due to heat transfer to the ambient atmosphere at 300 K, the tank is maintained at a steady state. The surface temperature
Heat is conducted through a slab of thickness 2 cm. The temperature varies linearly from 500 K on the left face to 300 K on the right face. If the rate of heat transfer is 2 kW, determine the rate of
A 30 kg aluminum block cools down from its initial temperature of 500 K to the atmospheric temperature of 300 K. Determine the total amount of entropy transfer from the system's universe. Assume the
Water is heated in a boiler from a source at 1800 K. If the heat transfer rate is 20 kW, (a) Determine the rate of entropy transfer into the boiler's universe. (b) Discuss the consequences of
An insulated tank contains 50 kg of water at 30oC, which is stirred by a paddle wheel at 300 rpm while transmitting a torque of 0.2 kNm. Determine (a) The rate of change of temperature (dT/dt) (b)
A rigid insulated tank contains 1 kg of air at 300 K and 100 kPa. A 1 kW internal heater is turned on. Determine the rate of (a) Entropy transfer into the tank. (b) The rate of change of total
A rigid tank contains 10 kg of air at 500 K and 100 kPa while the surroundings is at 300 K. A 2 kW internal heater keeps the gas hot by compensating the heat losses. At steady state, determine the
A tank contains 50 kg of water, which is stirred by a paddle wheel at 300 rpm while transmitting a torque of 0.2 kNm. After the tank achieves steady state, determine (a) The rate of heat
A gearbox (a closed steady system that converts low-torque shaft power to high-torque shaft power) consumes 100 kW of shaft work Due to lack of proper lubrication, the frictional losses amounts to 5
A closed steady system receives 1000 kW of heat from a reservoir at 1000 K and 2000 kW of heat from a reservoir at 2000 K. Heat is rejected to the two reservoirs at 300 K and 3000 K,
A tank contains 1 kg of air at 500 K and 500 kPa. A 1 kW internal heater operates inside the tank at steady state to make up for the heat lost to the atmosphere which is at 300 K. Determine (a) The
A rigid tank contains 1 kg of air initially at 300 K and 100 kPa. A 1 kW internal heater is turned on. After the tank achieves steady state, determine (a) The rate of heat transfer. (b) The rate of
A closed chamber containing a gas is at steady state. The shaft transfers power at a rate of 2 kW to the paddle wheel and the electric lamp consumes electricity at a rate of 500 W. Using an energy
A copper block receives heat from two different sources: 5 kW from a source at 1500 K and 3 kW from a source at 1000 K. It loses heat to atmosphere at 300 K. Assuming the block to be at steady state,
An electric bulb consumes 500 W of electricity at steady state. The outer surface of the bulb is warmer than the surrounding atmosphere by 75oC. If the atmospheric temperature is 300 K, determine (a)
An electric heater consumes 2 kW of electricity at steady state to keep a house at 27oC. The outside temperature is -10oC. Taking the heater inside the house as the system, determine (a) The maximum
An electric adaptor for a notebook computer (converting 110 volts to 19 volts) operates 10oC warmer than the surroundings, which is at 20. If the output current is measured at 3 amps and heat is lost
At steady state, the input shaft of a gearbox rotates at 2000 rpm while transmitting a torque of 0.2 kN-m. Due to friction, 1 kW of power is dissipated into heat and the rest is delivered to the
A steam power plant produces 500 MW of electricity with an overall thermal efficiency of 35%. Determine (a) The rate at which heat is supplied to the boiler. (b) The waste heat that is rejected by
A heat engine receives heat from a source at 2000 K at a rate of 500 kW, and rejects the waste heat to a medium at 300 K. The net output from the engine is 300 kW. (a) Determine the maximum power
A Carnot heat engine with a thermal efficiency of 60% receives heat from a source at a rate of 3000 kJ/min, and rejects the waste heat to a medium at 300 K. Determine (a) The power that is generated
A heat engine operates between a reservoir at 2000 K and an ambient temperature of 300 K. It produces 10 MW of shaft power. If it has a thermal efficiency (ηth) of 40%, (a) Determine the rate of
A heat engine, operating between two reservoirs at 1500 K and 300 K, produces an output of 100 MW. If the thermal efficiency of the engine is measured at 50%, determine (a) The Carnot efficiency of
A heat engine receives heat from two reservoirs: 50 MW from a reservoir at 500 K and 100 MW from a reservoir at 1000 K. If it rejects 90 MW to atmosphere at 300 K, (a) Determine the thermal
A heat engine produces 1000 kW of power while receiving heat from two reservoirs: 1000 kW from a 1000 K source and 2000 kW from a 2000 K source. Heat is rejected to the atmosphere at 300 K.
A heat engine, operating between two reservoirs at 1500 K and 300 K, produces 150 kW of net power. If the rate of heat transfer from the hot reservoir to the engine is measured at 350 kW,
A solar-energy collector produces a maximum temperature of 100oC. The collected energy is used in a cyclic heat engine that operates in a 5oC environment. (a) What is the maximum thermal
The Ocean Thermal Energy Conversion (OTEC) system in Hawaii utilizes the surface water and deep water as thermal energy reservoirs. Assume the ocean temperature at the surface to be 20oC and at some
You have been hired by a venture capitalist to evaluate a concept engine proposed by an inventor, who claims that the engine consumes 100 MW at a temperature of 500 K, rejects 40 MW at a temperature
A utility company charges its residential customers 12 cents/kW.h for electricity and $1.20 per Therm for natural gas. Fed up with the high cost of electricity, a customer decides to generate his own
A heat engine produces 40 kW of power while consuming 40 kW of heat from a source at 1200 K, 50 kW of heat from a source at 1500 K, and rejecting the waste heat to atmosphere at 300 K. Determine (a)
Two reversible engines A and B are arranged in series with the waste heat of engine A used to drive engine B. Engine A receives 200 MJ from a hot source at a temperature of 420oC. Engine B is in
A Carnot heat engine receives heat from a TER at TTER through a heat exchanger where the heat transfer rate is proportional to the temperature difference as QH = A(TTER-TH). It rejects heat to a cold
Two Carnot engines operate in series. The first one receives heat from a TER at 2500 K and rejects the waste heat to another TER at a temperature T. The second engine receives this energy rejected by
A reversible heat engine operates in outer space. The only way heat can be rejected is by radiation, which is proportional to the fourth power of the temperature and the area of the radiating
A heat engine receives heat at a rate of 3000 kJ/min from a reservoir at 1000 K and rejects the waste heat to the atmosphere at 300 K. If the engine produces 20 kW of power, determine (a) The thermal
A household freezer operates in a kitchen at 25oC. Heat must be transferred from the cold space at a rate of 2.5 kW to maintain its temperature at - 25oC. What is the smallest (power) motor required
To keep a refrigerator in steady state at 2oC, heat has to be removed from it at a rate of 200 kJ/min. If the surrounding air is at 27oC, determine (a) The minimum power input to the
A Carnot refrigerator consumes 2 kW of power while operating in a room at 20oC. If the food compartment of the refrigerator is to be maintained at 3oC, determine the rate of heat removal in kJ/min
An actual refrigerator operates with a COP that is half the Carnot COP. It removes 10 kW of heat from a cold reservoir at 250 K and dumps the waste heat into the atmosphere at 300 K. (a) Determine
A sport utility vehicle with a thermal efficiency (ηth) of 20% produces 250 hp of engine output while traveling at a velocity of 80 mph. (a) Determine the rate of fuel consumption in kg/s if the
An inventor claims to have developed a refrigerator with a COP of 10 that maintains a cold space at -10oC, while operating in a 25oC kitchen. Is this claim plausible? (1:Yes; 0:No)
A refrigeration cycle removes heat at a rate of 250 kJ/min from a cold space maintained at -10oC while rejecting heat to the atmosphere at 25oC. If the power consumption rate is 0.75 kW, determine if
A refrigeration cycle removes heat at a rate of 250 kJ/min from a cold space maintained at -10oC while rejecting heat to the atmosphere at 25oC. If the power consumption rate is 1.5 kW, (a) Do a
In a cryogenic experiment a container is maintained at -120oC, although it gains 200 W due to heat transfer from the surroundings. What is the minimum power of a motor that is needed for a heat pump
An air-conditioning system maintains a house at a temperature of 20oC while the outside temperature is 40oC. If the cooling load on this house is 10 tons, determine(a) The minimum power
An air-conditioning system is required to transfer heat from a house at a rate of 800 kJ/min to maintain its temperature at 20oC.(a) If the COP of the system is 3.7, determine the power required for
A solar-powered refrigeration system receives heat from a solar collector at TH, rejects heat to the atmosphere at T0 and extracts heat from a cold space at TC. The three heat transfer rates are
Assume TH = 425 K, T0 = 298 K, TC = 250 K and Q⋅C = 20 kW in the above system of problem 2-5-36[GX]. (a) Determine the maximum COP of the system. (b) If the collector captures 0.2 kW/m2, determine
A refrigerator with a COP of 2.0 extracts heat from a cold chamber at 0oC at a rate of 400 kJ/min. If the atmospheric temperature is 20oC, determine (a) The power drawn by the refrigerator. (b) The
On a cold night a house is losing heat at a rate of 15 kW. A reversible heat pump maintains the house at 20oC while the outside temperature is 0oC. (a) Determine the heating cost for the night (8
A truck engine consumes diesel at a rate of 30 L/h and delivers 65 kW of power to the wheels. If the fuel has a heating value of 43.5 MJ/kg and a density of 800 kg/m3, determine (a) The thermal
On a cold night a house is losing heat at a rate of 80,000 Btu/h. A reversible heat pump maintains the house at 70oF, while the outside temperature is 30oF. Determine (a) The heating cost for the
A house is maintained at a temperature of 20oC by a heat pump pumping heat from the atmosphere. Heat transfer rate through the wall and roof is estimated at 0.6 kW per unit temperature difference
A house is maintained at a temperature TH by a heat pump that is powered by an electric motor. The outside air at TC is used as the low-temperature TER. Heat loss from the house to the surroundings
A house is maintained at steady state (closed system) at 300 K while the outside temperature is 275 K. The heat loss (Q⋅C) is measured at 2 kW. Two approaches are being considered: (A) electrical
A house is maintained at a temperature of 25oC by a reversible heat pump powered by an electric motor. The outside air at 10oC is used as the low-temperature TER. Determine the percent saving in
A house is heated and maintained at 25oC by a heat pump. Determine the maximum possible COP if heat is extracted from the outside atmosphere at(a) 10oC,(b) 0oC,(c) -10oC.(d) -40oC.(e) Based on these
A Carnot heat engine receives heat at 800 K and rejects the waste heat to the surroundings at 300 K. The output from the heat engine is used to drive a Carnot refrigerator that removes heat from the
A reversible heat engine is used to drive a reversible heat pump. The power cycle takes in Q1 heat units at T1 and rejects Q2 heat units at T2. The heat pump extracts Q4 from a heat sink at T4 and
A heat engine with a thermal efficiency (ηth) of 35% is used to drive a refrigerator having a COP of 4. (a) What is the heat input to the engine for each MJ removed from the cold region by the
A heat engine operates between two TERs at 1000oC and 20oC respectively. Two-thirds of the work output is used to drive a heat pump that removes heat from the cold surroundings at 0oC and transfers
Determine the rate of coal consumption by a thermal power plant with a power output of 350 MW in tons/hr. The thermal efficiency (ηth) of the plant is 35% and the heating value of the coal is 30
A heat engine is used to drive a heat pump. The waste heat from the heat engine and the heat transfer from the heat pump are used to heat the water circulating through the radiator of a building. The
A furnace delivers heat at a rate of Q⋅H1 at TH1. Instead of directly using this for room heating, it is used to drive a heat engine that rejects the waste heat to atmosphere at T0. The heat engine
A heat pump is used for heating a house in the winter and cooling it in the summer by reversing the flow of the refrigerant. The interior temperature should be 20oC in the winter and 25oC in the
In 2003 the United States generated 3.88 trillion kWh of electricity, 51% of which came from coal-fired power plants. (a) Assuming an average thermal efficiency of 34% and the heating value of coal
Determine the fuel cost per kWh of electricity produced by a heat engine with a thermal efficiency of 40% if it uses diesel as the source of heat. The following data is supplied for diesel: price =
A gas turbine with a thermal efficiency (ηth) of 21% develops a power output of 8 MW. Determine (a) The fuel consumption rate in kg/min if the heating value of the fuel is 50 MJ/kg. (b) If the
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