JNTU
JNTU B.Tech II THERMAL SCIENCE Previous Question Paper (August/September - 2022 - R18)
Answer any five questions
All questions carry equal marks
Main
What is a thermodynamic system? What is the difference between a closed system and an open system? Give few examples for closed and open systems.
Answer
A thermodynamic system is a defined quantity of matter or a region in space chosen for study, separated from the rest of the universe by a real or imaginary boundary. Everything external to the system is referred to as the surroundings.
The difference between closed and open systems lies in the exchange of mass:
- A closed system (control mass) involves a fixed amount of mass; mass cannot cross the system boundary, but energy in the form of heat or work can.
- An open system (control volume) allows both mass and energy to cross the system boundary.
Examples:
- Closed system: A piston-cylinder device with sealed valves or a rigid tank containing a gas.
- Open system: A turbine, compressor, nozzle, or a heat exchanger where fluid flows through the device.
Write the differences between system and control volume.
Answer
The distinction between a system and a control volume is based on the focus of the analysis:
| Feature | System (Control Mass) | Control Volume |
|---|---|---|
| Mass | Fixed quantity of matter. | Fixed region in space. |
| Boundary | The boundary moves with the mass. | The boundary is fixed (control surface). |
| Mass Transfer | No mass crosses the boundary. | Mass can enter and leave. |
| Analysis | Lagrangian approach (tracking particles). | Eulerian approach (observing flow at a point). |
| Application | Useful for solid mechanics or batch processes. | Useful for fluid flow and steady-flow devices. |
Differentiate between intensive and extensive properties. Give examples in each case.
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What is Quasi static process?
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Explain Joule's experiment for determining the mechanical equivalent of heat.
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A Piston and cylinder machine contains a fluid system which passes through a complete cycle of four processes. During a cycle, the sum of all heat transfers is 170 kJ. The system completes 100 cycles per min. Complete the following table showing the method for each item and compute the net rate of work output in KW.
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In a steady flow apparatus, 135 kJ of work is done by each kg of fluid. The specific volume of the fluid, pressure, and velocity at the inlet are 0.37 m3/kg, 600 kPa, and 16 m/s. The inlet is 32 m above the floor, and the discharge pipe is at floor level. The discharge conditions are 0.62 m3/kg, 100 kPa, and 270 m/s. The total heat loss between the inlet and discharge is 9 kJ/kg of fluid. In flowing through this apparatus, does the specific internal energy increase or decrease, and by how much?
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Which is the more effective way to increase the efficiency of a Carnot engine: to increase T1, keeping T2 constant; or to decrease T2, keeping T1 constant?
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A fluid undergoes a reversible adiabatic compression from 0.5 MPa, 0.2 m3 to 0.05 m3 according to the law, pv1.3 = constant. Determine the change in enthalpy, internal energy and entropy, and the heat transfer and work transfer during the process.
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A refrigeration plant for a food store operates as a reversed Carnot heat engine cycle. The store is to be maintained at a temperature of -5°C and the heat transfer from the store to the cycle is at the rate of 5 kW. If heat is transferred from the cycle to the atmosphere at a temperature of 25°C, calculate the power require to drive the plant.
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Derive the thermal efficiency of air standard diesel cycle.
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In an air standard Diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the temperature is 15°C and the pressure is 0.1 MPa. Heat is added until the temperature at the end of the constant pressure process is 1480°C. Calculate: (i) the cut-off ratio, (ii) the heat supplied per kg of air, (iii) the cycle efficiency, and (iv) the m.e.p.
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Explain the working of four stroke SI engine with a neat sketches.
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Write differentiate between battery ignition system and magneto ignition system.
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