JNTU B.Tech IV BASIC MECHANICAL ENGINEERING Previous Question Paper (July/August - 2022 - R18)

The first law of thermodynamics, based on the principle of conservation of energy, states that energy can neither be created nor destroyed, only transformed. For a thermodynamic process occurring between two states, the net heat transfer (Q) and net work transfer (W) are related to the change in internal energy (ΔU) of the system.

In this equation, Q is the heat added to the system, W is the work done by the system, and ΔU is the change in internal energy. For a cyclic process where the initial and final states are identical, the change in internal energy is zero, resulting in Q = W, meaning the net heat transferred is equal to the net work performed.

The Carnot cycle is a theoretical ideal cycle consisting of two reversible isothermal processes and two reversible adiabatic processes. It is physically impossible to construct a real engine operating on this cycle due to several practical constraints:

1. Reversibility: Real processes are inherently irreversible due to friction, turbulence, and unrestrained expansion, whereas the Carnot cycle assumes perfect reversibility.
2. Isothermal Heat Transfer: Maintaining a constant temperature during heat addition and rejection requires extremely slow processes, which would result in zero power output.
3. Adiabatic Processes: Achieving perfectly adiabatic conditions (zero heat transfer) without any heat leakage is impossible in practical engineering.
4. Heat Transfer Rates: The cycle requires infinite time for heat transfer to occur reversibly, making the power output negligible for any practical application.