Thermodynamics Flashcards

In a steady-flow system, the energy equation per unit mass is: h1 + V1²/2 + gz1 + q = h2 + V2²/2 + gz2 + w. For an adiabatic nozzle with negligible elevation change and no work, which simplification applies?

Answer: h1 + V1²/2 = h2 + V2²/2

With q = 0, w = 0, and Δz ≈ 0, the energy equation reduces to h1 + V1²/2 = h2 + V2²/2.

Which of the following is a valid statement of the second law of thermodynamics?

Answer: No heat engine can have 100% thermal efficiency

The Kelvin-Planck statement of the second law prohibits any cyclic device from converting heat entirely to work.

For a van der Waals gas, the equation of state is (P + a/v²)(v - b) = RT. The term a/v² accounts for:

Answer: Intermolecular attractive forces

The term a/v² corrects for intermolecular attractive forces that reduce the effective pressure.

In a Rankine cycle, what component increases the pressure of the working fluid?

Answer: Pump

The pump increases the pressure of the liquid condensate from condenser pressure to boiler pressure.

For an ideal gas, the internal energy is a function of temperature only. This means that (∂u/∂v)_T equals:

Answer: 0

For an ideal gas, internal energy depends only on temperature, so (∂u/∂v)_T = 0.

The polytropic process PV^n = constant becomes isothermal when n equals:

Answer: 1

When n = 1, PV = constant, which for an ideal gas gives T = constant (isothermal process).

A heat pump has a COP of 4 and delivers 8 kW of heat to a building. How much power does it consume?

Answer: 2 kW

COP_HP = Q_H / W_net → W_net = Q_H / COP = 8 / 4 = 2 kW.