Question

Arrange the following based on enthalpy content at $100^{\circ}C$ per kg of water.
A. Saturated vapor
B. Superheated vapor
C. Vapor with 95% quality
D. Enthalpy of vaporization
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. B, A, C, D
• C. B, C, A, D
• D. A, B, D, C

Hint:

Quality ($x$) only applies to the "saturated dome." Anything superheated is $x > 1$ (metaphorically) and always has more energy because you've added sensible heat to a gas that's already finished boiling!

Answer 1

The Correct Option is B

Concept: Enthalpy ($H$) is a measure of the total heat content of a system. For water at a fixed temperature like $100^{\circ}C$ (the boiling point at 1 atm), enthalpy varies significantly based on the phase and quality of the steam.

Step 1: Rank the states by energy content.

• B (Superheated vapor): Contains the latent heat of vaporization plus additional sensible heat added above the saturation temperature. This has the highest enthalpy.
• A (Saturated vapor): Represents "dry" steam at 100% quality. It has absorbed the full latent heat of vaporization.
• C (Vapor with 95% quality): This is "wet" steam. It contains 5% liquid water by mass, so it has not absorbed the full latent heat ($H = H_L + 0.95 H_{LV}$).
• D (Enthalpy of vaporization): This is the value of the change in enthalpy ($H_{LV}$) required to convert liquid to vapor, which is less than the total enthalpy of the vapor itself (which includes the base liquid enthalpy $H_L$).

Step 2: Ordering.
From highest enthalpy to lowest: B (Superheated) $>$ A (Saturated) $>$ C (95% Quality) $>$ D (Latent heat).