Nonadiabatic

In thermodynamics and physics, 'nonadiabatic' describes a process or system where heat transfer occurs, or where energy exchange beyond purely mechanical work (like compression or expansion) is present. It signifies a departure from the ideal adiabatic condition, in which no heat enters or leaves a system. This often involves changes in temperature, and the process may not be reversible, leading to an increase in entropy. These situations require accounting for heat exchange with the surroundings or within the system itself, affecting energy calculations and system behavior. Understanding nonadiabatic processes is critical for comprehending real-world systems, as true adiabatic conditions are rarely perfectly achievable.

Nonadiabatic meaning with examples

• The engine's combustion cycle is inherently nonadiabatic. During fuel combustion, significant heat is released, and much of this thermal energy transfers to the cylinder walls and exhaust gases, meaning there is significant heat exchange during the process and thus it is nonadiabatic. This contrasts with an ideal engine cycle assuming no heat loss for ease of calculation, a simplification.
• When a cup of hot coffee cools, the heat transfer to the surrounding air makes this process nonadiabatic. The coffee's temperature decreases as thermal energy flows from the hot coffee to the colder environment. Consequently, the coffee's internal energy decreases as it gets closer to the temperature of the surroundings. A closed system is assumed.
• The Earth's atmosphere constantly experiences nonadiabatic processes due to solar radiation, cloud formation, and interactions with land and oceans. These processes involve the absorption and emission of radiation, conduction and convection, all of which create significant heat transfer. This intricate energy balance determines global climate patterns.
• The rapid compression of a gas inside a diesel engine is often approximated as adiabatic, but some heat exchange with the cylinder walls occurs, making the process slightly nonadiabatic. This heat loss affects the overall efficiency of the engine by lowering the combustion temperature and impacting the pressure curve.