Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II THERMAL SCIENCE Previous Question Paper (September - 2021 - R13)
Answer any five questions. All questions carry equal marks.
Main
How do the terms energy content and energy transfer differ from each other? Explain.
Answer
Energy content refers to the total internal energy stored within a system at a specific state, representing a property of the system that depends on its thermodynamic state variables like temperature, pressure, and mass. It is a point function, meaning its change depends only on the initial and final states, not the path taken.
Energy transfer refers to the movement of energy across the boundaries of a system, typically occurring in the form of heat or work. Unlike energy content, energy transfer is a path function; it depends on the process or the specific manner in which the system transitions from one state to another. While energy content is a state property, energy transfer is a transient phenomenon that occurs only during a process.
Classify the following into open system or closed system, giving reasons:
i) Radiator of car ii) Thermos flask iii) Water pump iv) Pressure cooker.
Answer
- Radiator of car: Open system. It allows both mass (coolant) and energy (heat) to cross its boundaries, as the coolant circulates through the radiator to dissipate heat to the surroundings.
- Thermos flask: Closed system (ideally). It is designed to prevent mass transfer and minimize heat transfer, keeping the contents isolated from the surroundings.
- Water pump: Open system. It involves the continuous flow of mass (water) through the device, while simultaneously transferring mechanical work energy to the fluid.
- Pressure cooker: Closed system. During the cooking process, the mass of the food and water remains trapped inside the sealed vessel, while energy is transferred across the boundary in the form of heat from the burner.
State the first law of Thermodynamics for a closed system undergoing a change of state.
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A mass of 8 kg gas expands within a flexible container so that the p-v relationship is of the form
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State and explain the Kelvin - Planck Statement of second law of thermodynamics.
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An engine is to be designed to produce 0.735 kW by taking continuously 6000 kJ/h from heat source which is at 505 K. The heat sink is atmosphere i.e., sink temperature is atmospheric. Calculate the efficiency of carnot cycle. The atmospheric temperature varies from 38°C in summer and 0°C in winter.
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An Otto cycle is conducted as follows. Air at 100 kPa and 20°C is compressed reversibly and adiabatically. The air is then heated at constant volume to 1500°C. The air then expands reversibly and adiabatically back to the original volume, and is cooled at constant volume back to the original pressure and temperature. The volume compression ratio is 8. Calculate the:
a) thermal efficiency
b) heat input per kg of air
c) network output per kg of air.
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Compare the P – V diagrams of two stroke and four stroke engines.
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Discuss the need for lubrication in I.C. engines, and explain the types of lubrication systems used in I.C. engines.
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What are the requirements of cooling system in I C engine? Compare the advantages and disadvantages of Air cooling system over Water cooling system.
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Name the various fuels used in I.C. engines and the type of ignition with each one of them.
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Write the steady flow energy equation for a single stream entering and a single stream leaving a control volume, and explain the various terms in it.
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What do you understand by Path function and Point function? Show that work is a path function and not a property.
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Write short notes on:
a) Limitations of the first law of thermodynamics
b) Perpetual Motion Machine of the second kind
c) Carnot cycle.
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