Jawaharlal Nehru Technological University Hyderabad B.Tech III AERODYNAMICS – II Previous Question Paper (September - 2021 - R13)

Enthalpy (H) is a thermodynamic property defined as the sum of the internal energy (U) and the product of pressure (P) and volume (V), expressed as H = U + PV. It represents the total heat content of a system.

For an ideal gas, the internal energy (u) is a function of temperature only, as defined by the kinetic theory of gases where intermolecular forces are neglected. Since the equation of state for an ideal gas is Pv = RT, the enthalpy per unit mass (h) becomes h = u + RT. Because both u and the product RT depend solely on temperature (T), the enthalpy of an ideal gas is strictly a function of temperature. This implies that for any process involving an ideal gas, the change in enthalpy is independent of the pressure or volume changes and depends only on the temperature difference.

The First Law of Thermodynamics for a closed system states that energy cannot be created or destroyed, only transformed. It establishes the principle of conservation of energy, asserting that the net heat transfer (Q) to a system and the net work done (W) by the system result in a change in the internal energy (ΔU) of the system.

The mathematical expression is:

In this equation:

• Q is the net heat added to the system.
• W is the net work done by the system.
• ΔU is the change in internal energy of the system.

For a closed system, mass remains constant, and energy crosses the boundary only in the form of heat or work. If the system undergoes a cyclic process where the final state equals the initial state, the net change in internal energy is zero, meaning the net heat transfer equals the net work done.