Thermodynamics Flashcards

Entropy generation during an irreversible process is always:

Answer: Positive

The Second Law requires that entropy generation S_gen > 0 for any irreversible process; it is zero only for reversible processes.

In a regenerative Rankine cycle, the regenerator (feedwater heater) is used to:

Answer: Preheat feedwater using extracted steam, improving efficiency

Extracted steam from the turbine preheats feedwater before the boiler, reducing the heat input needed and increasing overall cycle efficiency.

The Clapeyron equation relates the slope of the saturation curve (dP/dT) to:

Answer: Latent heat, temperature, and specific volume change between phases

The Clapeyron equation dP/dT = h_fg / (T·v_fg) relates the saturation pressure slope to enthalpy of phase change, temperature, and volume change.

Which dimensionless number represents the ratio of inertial forces to viscous forces in fluid flow, and is often relevant to heat transfer analysis?

Answer: Reynolds number

The Reynolds number Re = ρVL/μ represents the ratio of inertial to viscous forces and determines whether flow is laminar or turbulent.

For a reversible adiabatic compression of an ideal gas from V1 to V2, the work done ON the gas is:

Answer: W = nCv(T2 - T1)

For a reversible adiabatic process, Q = 0, so by the first law, W_in = ΔU = nCv(T2 - T1).

The Second Law of Thermodynamics, in the context of engines, states that it is impossible to construct a device that:

Answer: Operates in a cycle and produces work while exchanging heat with only one reservoir

The Kelvin-Planck statement says no heat engine can operate in a cycle while exchanging heat with a single thermal reservoir and producing net work.

Van der Waals equation of state corrects the ideal gas law by accounting for:

Answer: Molecular volume and intermolecular attractive forces

Van der Waals equation (P + a/v²)(v - b) = RT corrects for intermolecular attractions (term a/v²) and finite molecular volume (term b).