Mechanical Engineering

Which one of the following is the extensive property of thermodynamic system?

Ice kept in a well-insulated thermosflask is an example of which system?

Measurement of temperature is based on which law of thermodynamics?

A closed system receives 60 kJ heat but its internal energy decreases by 30 kJ. Then the work done by the system is

A reversible engine operates between temperature 900 K and $ T_{2} $ $(T_{2} < 900 \text{ K})$ and another reversible engine between $ T_{2} $ and 400 K $(T_{2}> 400 \text{ K})$ in series. The value of $ T_{2} $ if work outputs of both the engines are equal is

For real thermodynamics cycle, which one of the following is correct?

The specific volume of water when heated from $ 0^{\circ}C $

A four-stroke petrol engine theoretically operates on

On psychometric chart, the constant wet bulb temperature lines coincide with

One ton of refrigeration in kW is equivalent to

If a gas of volume 6000 cm³ and at pressure of 100 kPa is compressed quasistatically according to $ pV^{2} = \text{constant} $ until the volume becomes 2000 cm³, determine the final pressure and the work transfer.

unavailabile question

A turbine operates under steady flow conditions, receiving steam at the following State: Pressure 1.2 MPa, temperature $ 188^{\circ}C $, enthalpy $ 2785 \text{ kJ/kg} $, velocity $ 333 \text{ m/s} $ and elevation 3 m. The steam leaves the turbine at the following state: Pressure 20 kPa, enthalpy $ 2512 \text{ kJ/kg} $, velocity $ 100 \text{ m/s} $ and elevation 0 m. Heat is lost to the surroundings at the rate of $ 0.20 \text{ kJ/s} $. If the rate of steam flow through the turbine is $ 0.42 \text{ kg/s} $, what is the power output of the turbine in kW?

Prove the equivalence of Clausius statement to the Kelvin Planck statement with schematic diagram.

Two reversible heat engines A and B are arranged in series, A rejecting heat directly to B. Engine A receives 200 kJ at a temperature of $ 421^{\circ}C $ from a hot source, while engine B is in communication with a cold sink at a temperature of $ 44^{\circ}C $. If work output of A is twice that of B, find
(i) The intermediate temperature between A and B.
(ii) The efficiency of each engine.
(iii) The heat rejected to the cold sink.

Derive an expression for the efficiency of a Carnot cycle. What is the difficulty in constructing an engine working on Carnot cycle.

With the help of net sketch, differentiate between the working of Otto and Diesel cycle.

What do you understand by exergy and energy? In a steam generator, water is evaporated at $ 260^{\circ}C $, while the combustion gas $ (c_{p}=1.08 \text{ kJ/kg K}) $ is cooled from $ 1300^{\circ}C $ to $ 320^{\circ}C $. The surroundings are at $ 30^{\circ}C $. Determine the loss in available energy due to the above heat transfer per kg of water evaporated (Latent heat of vaporization of water at $ 260^{\circ}C = 1662.5 \text{ kJ/kg} $).

A rigid closed tank of volume contains 5 kg of wet steam at a pressure of 200 kPa. The tank is heated until the steam becomes dry saturated. Determine the final pressure and the heat transfer to the tank.

(i) Write down the van der Waal's equation of state. How does it differ from the ideal gas equation?
(ii) Write three Maxwell's equations.

A geothermal plant utilizes steam produced by natural means underground. Steam wells are drilled to tap this steam supply which is available at 4.5 bar and $ 175^{\circ}C $. The steam leaves the turbine at 100 mm Hg absolute pressure. The turbine isentropic efficiency is 0.75. Calculate the efficiency of the plant. If the unit produces 12.5 MW, what is the steam flow rate? Use steam table for required data.

A Brayton cycle operates with air entering the compressor at 1 bar and $ 25^{\circ}C $. The pressure ratio across the compressor is 3 to 1, and the maximum temperature in the cycle is $ 650^{\circ}C $. Determine the compressor work, turbine work, thermal efficiency and work ratio of the cycle.

Describe with net schematic arrangement, working of a simple vapour compression cycle.

Define the terms 'unsaturated air' and 'relative humidity'.

With the help of suitable diagram, explain the psychrometric chart.

With help of a suitable diagram, explain the process of cooling and dehumidification.

Which one of the following is the extensive property of thermodynamic system?

Ice kept in a well-insulated thermosflask is an example of which system?

Measurement of temperature is based on which law of thermodynamics?

A closed system receives 60 kJ heat but its internal energy decreases by 30 kJ. Then the work done by the system is

A reversible engine operates between temperature 900 K and $ T_{2} $ $(T_{2} < 900 \text{ K})$ and another reversible engine between $ T_{2} $ and 400 K $(T_{2}> 400 \text{ K})$ in series. The value of $ T_{2} $ if work outputs of both the engines are equal is

For real thermodynamics cycle, which one of the following is correct?

The specific volume of water when heated from $ 0^{\circ}C $

A four-stroke petrol engine theoretically operates on

On psychometric chart, the constant wet bulb temperature lines coincide with

One ton of refrigeration in kW is equivalent to

If a gas of volume 6000 cm³ and at pressure of 100 kPa is compressed quasistatically according to $ pV^{2} = \text{constant} $ until the volume becomes 2000 cm³, determine the final pressure and the work transfer.

unavailabile question

A turbine operates under steady flow conditions, receiving steam at the following State: Pressure 1.2 MPa, temperature $ 188^{\circ}C $, enthalpy $ 2785 \text{ kJ/kg} $, velocity $ 333 \text{ m/s} $ and elevation 3 m. The steam leaves the turbine at the following state: Pressure 20 kPa, enthalpy $ 2512 \text{ kJ/kg} $, velocity $ 100 \text{ m/s} $ and elevation 0 m. Heat is lost to the surroundings at the rate of $ 0.20 \text{ kJ/s} $. If the rate of steam flow through the turbine is $ 0.42 \text{ kg/s} $, what is the power output of the turbine in kW?

Prove the equivalence of Clausius statement to the Kelvin Planck statement with schematic diagram.

Two reversible heat engines A and B are arranged in series, A rejecting heat directly to B. Engine A receives 200 kJ at a temperature of $ 421^{\circ}C $ from a hot source, while engine B is in communication with a cold sink at a temperature of $ 44^{\circ}C $. If work output of A is twice that of B, find
(i) The intermediate temperature between A and B.
(ii) The efficiency of each engine.
(iii) The heat rejected to the cold sink.

Derive an expression for the efficiency of a Carnot cycle. What is the difficulty in constructing an engine working on Carnot cycle.

With the help of net sketch, differentiate between the working of Otto and Diesel cycle.

What do you understand by exergy and energy? In a steam generator, water is evaporated at $ 260^{\circ}C $, while the combustion gas $ (c_{p}=1.08 \text{ kJ/kg K}) $ is cooled from $ 1300^{\circ}C $ to $ 320^{\circ}C $. The surroundings are at $ 30^{\circ}C $. Determine the loss in available energy due to the above heat transfer per kg of water evaporated (Latent heat of vaporization of water at $ 260^{\circ}C = 1662.5 \text{ kJ/kg} $).

A rigid closed tank of volume contains 5 kg of wet steam at a pressure of 200 kPa. The tank is heated until the steam becomes dry saturated. Determine the final pressure and the heat transfer to the tank.

(i) Write down the van der Waal's equation of state. How does it differ from the ideal gas equation?
(ii) Write three Maxwell's equations.

A geothermal plant utilizes steam produced by natural means underground. Steam wells are drilled to tap this steam supply which is available at 4.5 bar and $ 175^{\circ}C $. The steam leaves the turbine at 100 mm Hg absolute pressure. The turbine isentropic efficiency is 0.75. Calculate the efficiency of the plant. If the unit produces 12.5 MW, what is the steam flow rate? Use steam table for required data.

A Brayton cycle operates with air entering the compressor at 1 bar and $ 25^{\circ}C $. The pressure ratio across the compressor is 3 to 1, and the maximum temperature in the cycle is $ 650^{\circ}C $. Determine the compressor work, turbine work, thermal efficiency and work ratio of the cycle.

Describe with net schematic arrangement, working of a simple vapour compression cycle.

Define the terms 'unsaturated air' and 'relative humidity'.

With the help of suitable diagram, explain the psychrometric chart.

With help of a suitable diagram, explain the process of cooling and dehumidification.

Extensive property of a system is one whose value

For reversible adiabatic process, the change in entropy is

If $ Q_{1} $ is the heat transfer between hot temperature source and machine, and $ Q_{2} $ between cold temperature source and machine, then for heat pump, COP will be equal to

Kelvin-Planck law deals with

For same compression ratio and for same heat added

Gas turbine cycle consists of

Tripple point temperature and pressure for water are

Select the correct relation.

The first law of thermodynamics gives $ dU = \delta Q - \delta W $ and the second law tells that $ dS > \frac{\delta Q}{T} $. In which of the way these two laws can be combined and written?

Air-standard efficiency of diesel cycle is a function of

(a) Perpetual motion machine of second kind
(b) Point and path functions
(c) Total energy of the system
(d) Psychrometry
(e) Pure substance
(f) Exergy destruction
(g) Refrigeration

A certain water heater operates under steady flow conditions receiving $ 4.2 \text{ kg/s} $ of water at $ 75^{\circ}C $ temperature, enthalpy $ 313\cdot93 \text{ kJ/kg} $. The water is heated by mixing with the steam which is supplied to the heater at temperature $ 100\cdot2^{\circ}C $ and enthalpy $ 2676 \text{ kJ/kg} $. The mixture leaves the heater as liquid water at temperature $ 100^{\circ}C $ and enthalpy $ 419 \text{ kJ/kg} $. How much steam must be supplied to the heater per hour?

In an air-standard diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the temperature is $ 15^{\circ}C $ and the pressure is 0.1 MPa. Heat is added until the temperature at the end of the constant pressure process is $ 1480^{\circ}C $. Calculate (i) the cut-off ratio, (ii) the heat supplied per kg of air, (iii) the cycle efficiency, and (iv) the mean effective pressure.

A gas flows steadily through a rotary compressor. The gas enters the compressor at a temperature of $ 16^{\circ}C $, a pressure of 100 kPa, and an enthalpy of $ 391\cdot2 \text{ kJ/kg} $. The gas leaves the compressor at a temperature of $ 245^{\circ}C $, a pressure of 0.6 MPa, and enthalpy of $ 534\cdot5 \text{ kJ/kg} $. There is no heat transfer to or from the gas as it flows through the compressor. Evaluate the external work done per unit mass of gas assuming the gas velocities at entry and exit to be negligible.

Evaluate the external work done per unit mass of gas when the gas velocity at entry is $ 80 \text{ m/s} $ and that at exit is $ 160 \text{ m/s} $.

Define 'reversibility' and 'irreversibility'. What are the various causes of irreversibility?

Derive an expression for entropy change in an irreversible process.

State Kelvin-Planck and Clausius statements for 2nd law of thermodynamics and show the equivalence between these statements.

A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship $ p = a + bV $, where a and b are constants. The initial and final pressures are 1000 kPa and 200 kPa respectively and the corresponding volumes are $ 0\cdot20 \text{ m}^{3} $ and $ 1\cdot20 \text{ m}^{3} $. The specific internal energy of the gas is given by the relation $ u = 1.5 pv - 85 \text{ kJ/kg} $, where p is in kPa and v is in $ \text{m}^{3}\text{/kg} $. Calculate the net transfer and maximum internal energy of the gas attained during expansion.

Saturated air at $ 2^{\circ}C $ is required to be supplied to a room where the temperature must be held at $ 20^{\circ}C $ with a relative humidity of 50%. The air is heated and then water at $ 10^{\circ}C $ is sprayed in to give the required humidity. Determine the temperature to which the air must be heated and the mass of spray water required per $ \text{m}^{3} $ of air at room conditions. Assume that the total pressure is constant at 1.013 bar and neglect the fan power. Use steam table for required data.

What are Helmholtz's and Gibbs' functions? Write four Maxwell's equations.

A turbo-compressor delivers $ 2\cdot33 \text{ m}^{3}\text{/s} $ of air at 0.276 MPa, $ 43^{\circ}C $ which is heated at this pressure to $ 430^{\circ}C $ and finally expanded in a turbine which delivers 1860 kW. During the expansion, there is a heat transfer of 0.09 MJ/s to the surroundings. Calculate the turbine exhaust temperature if changes in kinetic and potential energies are negligible.

A vessel of volume $ 0.04 \text{ m}^{3} $ contains a mixture of saturated water and saturated steam at a temperature of $ 250^{\circ}C $. The mass of the liquid present is 9 kg. Find the pressure, the mass, the specific volume, the enthalpy, the entropy, and the internal energy.
Given: At $ 250^{\circ}C $, $ P_{sat} = 3\cdot973 \text{ MPa} $, $ \nu_{f} = 0.0012512 \text{ m}^{3}\text{/kg} $, $ \nu_{g} = 0.05013 \text{ m}^{3}\text{/kg} $, $ h_{f} = 1085\cdot36 \text{ kJ/kg} $, $ h_{fg} = 1716\cdot2 \text{ kJ/kg} $, $ s_{f} = 2\cdot7927 \text{ kJ/kg K} $, $ s_{fg} = 3\cdot2802 \text{ kJ/kg K} $, $ u_{f} = 1080\cdot39 \text{ kJ/kg} $, $ u_{fg} = 1522 \text{ kJ/kg} $.

A gas turbine plant operates on the Brayton cycle between the temperatures $ 27^{\circ}C $ and $ 800^{\circ}C $.
(i) Find the pressure ratio at which the cycle efficiency approaches the Carnot cycle efficiency.
(ii) Find the pressure ratio at which the work done per kg of air is maximum.
(iii) Compare the efficiency at this pressure ratio with the Carnot efficiency for the given temperatures.

Extensive property of a system is one whose value

For reversible adiabatic process, the change in entropy is

If $ Q_{1} $ is the heat transfer between hot temperature source and machine, and $ Q_{2} $ between cold temperature source and machine, then for heat pump, COP will be equal to

Kelvin-Planck law deals with

For same compression ratio and for same heat added

Gas turbine cycle consists of

Tripple point temperature and pressure for water are

Select the correct relation.

The first law of thermodynamics gives $ dU = \delta Q - \delta W $ and the second law tells that $ dS > \frac{\delta Q}{T} $. In which of the way these two laws can be combined and written?

Air-standard efficiency of diesel cycle is a function of

(a) Perpetual motion machine of second kind
(b) Point and path functions
(c) Total energy of the system
(d) Psychrometry
(e) Pure substance
(f) Exergy destruction
(g) Refrigeration

A certain water heater operates under steady flow conditions receiving $ 4.2 \text{ kg/s} $ of water at $ 75^{\circ}C $ temperature, enthalpy $ 313\cdot93 \text{ kJ/kg} $. The water is heated by mixing with the steam which is supplied to the heater at temperature $ 100\cdot2^{\circ}C $ and enthalpy $ 2676 \text{ kJ/kg} $. The mixture leaves the heater as liquid water at temperature $ 100^{\circ}C $ and enthalpy $ 419 \text{ kJ/kg} $. How much steam must be supplied to the heater per hour?

In an air-standard diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the temperature is $ 15^{\circ}C $ and the pressure is 0.1 MPa. Heat is added until the temperature at the end of the constant pressure process is $ 1480^{\circ}C $. Calculate (i) the cut-off ratio, (ii) the heat supplied per kg of air, (iii) the cycle efficiency, and (iv) the mean effective pressure.

A gas flows steadily through a rotary compressor. The gas enters the compressor at a temperature of $ 16^{\circ}C $, a pressure of 100 kPa, and an enthalpy of $ 391\cdot2 \text{ kJ/kg} $. The gas leaves the compressor at a temperature of $ 245^{\circ}C $, a pressure of 0.6 MPa, and enthalpy of $ 534\cdot5 \text{ kJ/kg} $. There is no heat transfer to or from the gas as it flows through the compressor. Evaluate the external work done per unit mass of gas assuming the gas velocities at entry and exit to be negligible.

Evaluate the external work done per unit mass of gas when the gas velocity at entry is $ 80 \text{ m/s} $ and that at exit is $ 160 \text{ m/s} $.

Define 'reversibility' and 'irreversibility'. What are the various causes of irreversibility?

Derive an expression for entropy change in an irreversible process.

State Kelvin-Planck and Clausius statements for 2nd law of thermodynamics and show the equivalence between these statements.

A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship $ p = a + bV $, where a and b are constants. The initial and final pressures are 1000 kPa and 200 kPa respectively and the corresponding volumes are $ 0\cdot20 \text{ m}^{3} $ and $ 1\cdot20 \text{ m}^{3} $. The specific internal energy of the gas is given by the relation $ u = 1.5 pv - 85 \text{ kJ/kg} $, where p is in kPa and v is in $ \text{m}^{3}\text{/kg} $. Calculate the net transfer and maximum internal energy of the gas attained during expansion.

Saturated air at $ 2^{\circ}C $ is required to be supplied to a room where the temperature must be held at $ 20^{\circ}C $ with a relative humidity of 50%. The air is heated and then water at $ 10^{\circ}C $ is sprayed in to give the required humidity. Determine the temperature to which the air must be heated and the mass of spray water required per $ \text{m}^{3} $ of air at room conditions. Assume that the total pressure is constant at 1.013 bar and neglect the fan power. Use steam table for required data.

What are Helmholtz's and Gibbs' functions? Write four Maxwell's equations.

A turbo-compressor delivers $ 2\cdot33 \text{ m}^{3}\text{/s} $ of air at 0.276 MPa, $ 43^{\circ}C $ which is heated at this pressure to $ 430^{\circ}C $ and finally expanded in a turbine which delivers 1860 kW. During the expansion, there is a heat transfer of 0.09 MJ/s to the surroundings. Calculate the turbine exhaust temperature if changes in kinetic and potential energies are negligible.

A vessel of volume $ 0.04 \text{ m}^{3} $ contains a mixture of saturated water and saturated steam at a temperature of $ 250^{\circ}C $. The mass of the liquid present is 9 kg. Find the pressure, the mass, the specific volume, the enthalpy, the entropy, and the internal energy.
Given: At $ 250^{\circ}C $, $ P_{sat} = 3\cdot973 \text{ MPa} $, $ \nu_{f} = 0.0012512 \text{ m}^{3}\text{/kg} $, $ \nu_{g} = 0.05013 \text{ m}^{3}\text{/kg} $, $ h_{f} = 1085\cdot36 \text{ kJ/kg} $, $ h_{fg} = 1716\cdot2 \text{ kJ/kg} $, $ s_{f} = 2\cdot7927 \text{ kJ/kg K} $, $ s_{fg} = 3\cdot2802 \text{ kJ/kg K} $, $ u_{f} = 1080\cdot39 \text{ kJ/kg} $, $ u_{fg} = 1522 \text{ kJ/kg} $.

A gas turbine plant operates on the Brayton cycle between the temperatures $ 27^{\circ}C $ and $ 800^{\circ}C $.
(i) Find the pressure ratio at which the cycle efficiency approaches the Carnot cycle efficiency.
(ii) Find the pressure ratio at which the work done per kg of air is maximum.
(iii) Compare the efficiency at this pressure ratio with the Carnot efficiency for the given temperatures.