02 First Law

NOTES

Class ppt notes

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Unit 2

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Q1 — State and explain the First Law of Thermodynamics for a closed system undergoing a cyclic process. 8M

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Q2 — Define the following terms: 8M

1. Joule’s Experiment
2. Energy in State
3. Energy in Transition

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Q3 — Explain the following terms: 8M

1. Point function
2. Path function
3. Enthalpy
4. Specific heat at constant pressure

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Q4a — Explain about PMM-I. Why is such a machine considered impossible according to the First Law of Thermodynamics? 4M

Q4b — During a certain process, the specific heat capacity of a system is given by $C=(0.4+0.004T)\text{kJ/kg°C}$. Find the heat transferred and mean specific heat of gas when temperature changes from $25°C$ to $125°C$. Mass of system is $5\text{kg}$. 4M

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Q5 — Derive the steady-flow energy equation along with its assumptions. 8M

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Q6 — Discuss the applications of steady-flow energy equation in devices such as nozzles, diffusers, turbines, compressors, and throttling along with its assumptions. 8M

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Q7a — A fluid at a pressure of $3\text{bar}$ and specific volume of $0.18{\text{m}}^3/\text{kg}$, contained in a cylinder behind a piston, expands reversibly to a pressure of $0.6\text{bar}$ according to a law $p=C{v}^2$ where $C$ is a constant. Calculate the work done by the fluid on the piston. 4M

Q7b — Discuss the limitations of the First Law of Thermodynamics. 4M

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Q8 — Air flows steadily at the rate of $0.5\text{kg/s}$ through an air compressor, entering at $7\text{m/s}$ velocity, $100\text{kPa}$ pressure, and $0.95{\text{m}}^3/\text{kg}$ volume, and leaving at $5\text{m/s}$, $700\text{kPa}$, and $0.19{\text{m}}^3/\text{kg}$. The internal energy of the air leaving is $90\text{kJ/kg}$ greater than that of the air entering. Cooling water in the compressor jackets absorbs heat from the air at the rate of $58\text{kW}$. 8M

• (a) Compute the rate of shaft work input to the air in kW.
• (b) Find the ratio of the inlet pipe diameter to outlet pipe diameter.