Govt Exams
Isentropic efficiency = Actual work output / Isentropic work output = 0.85. It compares real process with ideal isentropic process.
For any cycle: ΔU_cycle = 0. First law: Q_net = W_net confirms energy conservation. 150 = 150 ✓
Throttling is an isenthalpic process (constant enthalpy). Temperature may change for real gases due to Joule-Thomson effect.
Using Mayer's relation: Cp - Cv = R. Therefore, Cp = 5R/2 + R = 7R/2
Heat transfer across finite temperature differences in the boiler creates maximum entropy generation and irreversibility among the four processes.
For isothermal process: ΔG = ΔH - TΔS = W_useful (non-PV work). This represents maximum useful work available.
Entropy is defined as dS = dQ_rev/T. Units: Joules/Kelvin = J/K. This is the fundamental SI unit for entropy.
In adiabatic process, Q = 0. From first law: dU = -W. During expansion, W > 0, so dU < 0, meaning internal energy and temperature decrease.
The first law states that dU = Q - W, where heat (Q) and work (W) are energy transfer mechanisms, not state properties. Internal energy (U) is a state property.
Maximum efficiency occurs in a Carnot engine: η = 1 - (T_cold/T_hot) = 1 - (300/500) = 1 - 0.6 = 0.4 or 40%