Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II THERMODYNAMICS AND KINETICS Previous Question Paper (August/September - 2022 - R16)
Answer any five questions. All questions carry equal marks.
Main
Distinguish between reversible process and cyclic process.
Answer
A reversible process is an idealized process that occurs infinitely slowly, such that the system and its surroundings can be restored to their original states without leaving any net effect on the universe. It involves no dissipative effects like friction, turbulence, or unrestrained expansion, and the system remains in quasi-equilibrium throughout. In contrast, a cyclic process is a sequence of processes that begins and ends at the same state, meaning the net change in any state property (such as internal energy, enthalpy, or entropy) over the cycle is exactly zero. While a reversible process focuses on the path and the ability to reverse the direction of change, a cyclic process focuses on the return to the initial state, regardless of whether the individual steps within the cycle were reversible or irreversible.
Write the causes of irreversibility.
Answer
Irreversibility in thermodynamic processes arises due to the presence of dissipative effects that prevent a system from returning to its initial state without external intervention. The primary causes include:
- Friction: Mechanical friction between moving parts or fluid viscosity leads to the conversion of useful work into heat, which cannot be fully recovered.
- Unrestrained Expansion: When a gas expands into a vacuum or against a pressure lower than its internal pressure, it does not perform useful work, and the process cannot be reversed without external work.
- Heat Transfer across a Finite Temperature Difference: Heat flow from a high-temperature source to a low-temperature sink is inherently irreversible; it requires a temperature gradient, and the entropy of the universe increases.
- Mixing of Different Substances: The spontaneous mixing of two different gases or fluids is an irreversible process due to the increase in entropy associated with the loss of concentration gradients.
- Chemical Reactions: Spontaneous chemical reactions that occur rapidly and are not in chemical equilibrium are irreversible.
- Electrical Resistance: The flow of current through a resistor generates heat (Joule heating), which is a dissipative process that cannot be reversed to recover the electrical energy.
Discuss about Macroscopic and Microscopic viewpoints.
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Define the following terms:
i) Thermodynamics ii) open system iii) closed system iv) isolated system.
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Derive an expression for the First Law of thermodynamics applied to a closed system?
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A fluid at a pressure of 3 bar and with specific volume of 0.18 m3/kg contained in a cylinder behind a piston expands reversibly to a pressure of 0.6 bar according to a law pv3 = c, where c is a constant. Calculate the work done by the fluid on the piston.
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What is a PMM1? Why is it impossible?
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I) A gas undergoes a thermodynamic cycle consisting of the following processes:
i) Process 1–2: Constant pressure p = 1.4 bar, V1 = 0.028 m3, W12 = 10.5 kJ
ii) Process 2–3: Compression with pV = constant, U3 = U2
iii) Process 3–1: Constant volume, U1 – U3 = – 26.4 kJ.
II) There are no significant changes in KE and PE.
i) Sketch the cycle on a p–V diagram
ii) Calculate the network for the cycle in kJ
iii) Calculate the heat transfer for process 1–2.
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A reversible heat engine operates between two reservoirs at temperatures of 600°C and 40°C. The engine drives a reversible refrigerator which operates between reservoirs at temperatures of 40°C and -20°C. The heat transfer to the engine is 2000 kJ and the network output of the combined engine-refrigerator plant is 360 kJ. Evaluate the heat transfer to the refrigerant and the net heat transfer to the reservoir at 40°C.
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Explain about heat engine and heat pump?
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Explain Carnot cycle. Write its specialties?
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Two Carnot engines A and B are operated in series. The first one A receives heat at 900 K and reject to a reservoir at temperature T K. The second engine B receives the heat rejected by the first engine and in turn rejects to a sink at 400 K, calculate the temperature T when:
(i) The efficiencies of the two engines are equal
(ii) The work output of the two engines are equal?
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Write the Maxwell’s equations and derive the first and second Tds equations.
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Define fugacity coefficient. Discuss any two methods to evaluate fugacity coefficient in details.
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Define the following terms:
i) Order of a reaction. ii) Molecularity of a reaction. iii) Is it possible for a reaction to have identical values for molecularity and order?
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What is first order reaction? Give examples of first order reaction?
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What is the special characteristic of a zero order reaction?
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