JNTU B.Tech II THERMAL SCIENCE Previous Question Paper (March - 2022 - R13)

The continuum hypothesis treats matter as a continuous distribution of mass rather than as a collection of discrete molecules. In this model, properties such as density, pressure, and temperature are defined as point functions that vary smoothly throughout the medium. This assumption is valid when the characteristic length scale of the system is significantly larger than the mean free path of the molecules, allowing for the use of macroscopic thermodynamic analysis.

The continuum assumption becomes invalid in rarefied gas dynamics, such as in high-altitude aerodynamics or vacuum systems. When the mean free path of the molecules is comparable to or larger than the characteristic dimensions of the flow (quantified by a high Knudsen number, Kn > 0.01), the discrete nature of the molecules dominates, and statistical mechanics must be used instead of continuum mechanics.

Thermodynamic systems are classified based on the exchange of mass and energy with their surroundings:

• Closed System (Control Mass): A system where only energy (heat and work) can cross the boundary, but no mass enters or leaves. The total mass remains constant. Example: A gas trapped in a cylinder with a piston.
• Open System (Control Volume): A system where both mass and energy can cross the boundary. These systems often involve steady or unsteady flow processes. Example: A turbine, pump, or nozzle where fluid flows through the device.
• Isolated System: A system that exchanges neither mass nor energy with its surroundings. The total energy and mass of the system remain constant. Example: A perfectly insulated, rigid, and sealed container.