JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III FUNDAMENTALS OF MECHANICAL ENGINEERING Previous Question Paper (September - 2021 - R16)

Heat transfer (Q) is the energy interaction across the boundary of a system due solely to a temperature difference. It is a path function and a transient phenomenon, occurring only when there is a thermal gradient. It is significant in determining the thermal efficiency of power cycles and the cooling or heating requirements of mechanical systems.

Work transfer (W) is defined as the energy interaction across the system boundary that can be completely converted into the raising of a weight in the surroundings. It is also a path function. In mechanical engineering, work transfer is the primary mechanism for energy conversion in engines, turbines, and compressors, representing the mechanical output or input of a system.

Internal energy (U) is a macroscopic property representing the sum of all microscopic forms of energy (kinetic and potential) of the molecules within a system. Unlike heat and work, it is a point function and a state property. It is significant because it accounts for the energy stored within a system, and changes in internal energy are essential for calculating energy balances in closed systems.

The First Law of Thermodynamics, also known as the Law of Conservation of Energy, states that energy can neither be created nor destroyed, only transformed from one form to another. For a closed system undergoing a thermodynamic cycle, the net heat transfer is equal to the net work transfer.

For a process occurring in a closed system, the law is expressed as:

Where:

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

This law implies that energy is a conserved property. If a system undergoes a change in state, the difference between the heat added and the work done by the system results in a change in the internal energy stored within the system. It serves as the fundamental basis for energy balance equations in all mechanical systems.