Thermodynamics Flashcards

The Joule-Thomson coefficient μ_JT is defined as (∂T/∂P)_h. For an ideal gas, μ_JT equals:

Answer: 0

For an ideal gas, enthalpy depends only on temperature, so throttling (constant h) causes no temperature change; thus μ_JT = 0.

Which statement about entropy is CORRECT?

Answer: Entropy change for a reversible adiabatic process is zero

A reversible adiabatic (isentropic) process has ΔS = 0 because δQ = 0 and there is no irreversibility.

For a steady-flow device, neglecting kinetic and potential energy changes, the energy balance simplifies to:

Answer: Q̇ − Ẇ = ṁ(h2 − h1)

The steady-flow energy equation reduces to Q̇ − Ẇ = ṁ(h2 − h1) when kinetic and potential energy terms are negligible.

The reduced pressure and reduced temperature used in the generalized compressibility chart are defined as:

Answer: PR = P/Pc and TR = T/Tc

Reduced properties are dimensionless ratios: PR = P/Pc and TR = T/Tc, where Pc and Tc are critical point values.

A heat pump has a COP of 4.5 and consumes 2 kW of power. How much heat does it deliver to the heated space?

Answer: 9.0 kW

COP_HP = Q̇_H / Ẇ → Q̇_H = COP × Ẇ = 4.5 × 2 kW = 9.0 kW.

In a Rankine cycle, increasing the boiler pressure (while keeping condenser pressure constant) generally:

Answer: Increases efficiency but increases moisture content at turbine exit

Higher boiler pressure increases cycle efficiency (higher average heat addition temperature) but also increases the moisture fraction in the low-pressure turbine stages.

The specific heat ratio γ = cp/cv for a monatomic ideal gas is:

Answer: 1.67

A monatomic ideal gas has cv = (3/2)R and cp = (5/2)R, giving γ = cp/cv = 5/3 ≈ 1.67.