What is the enthalpy of a saturated steam mixture at 150 psig with 95% quality

Explore how to compute the enthalpy of a saturated water-vapor mixture at 150 psig with 95% quality. Learn how h = h_f + x(h_g − h_f) uses steam-table values for h_f and h_g, and see how gauge pressure converts to absolute pressure for accurate results.

Steam at a glance: what does 95% quality really mean?

If you’ve ever flipped through steam tables, you’ve probably run into the idea of steam quality. It’s a simple notion with real-world punch: in a saturated mixture of liquid water and steam, quality x tells you what fraction is vapor. A 95% quality means most of the energy content is carried by the vapor phase, with just a sliver still in the liquid fashion. Think of it like a crowd at a concert—most folks are singing along in the open air (the vapor), a small handful are still seated in the pit (the liquid). The energy you calculate for the mixture is a blend, weighted by that fraction.

Here’s the practical setup you’re looking at: saturated steam at 150 psig, with a quality of 95%. You want the enthalpy of that mixture in BTU per pound. The quick takeaway is: the enthalpy you get will sit between the saturated liquid enthalpy (hf) and the saturated vapor enthalpy (hg) for that pressure, and because 95% of the phase content is vapor, the mixture’s enthalpy will be much closer to hg than to hf.

How to think about it, in plain terms

• Enthalpy is energy per unit mass. For a saturated mixture, you can separate the energy into the liquid part and the vapor part, then combine them according to how much of each phase you’ve got.

• The formal relationship is h = hf + x(hg − hf). Here, hf is the enthalpy of the saturated liquid, hg is the enthalpy of the saturated vapor, and x is the quality (a fraction from 0 to 1).

• If x is near 1, you’re mostly vapor, so h is close to hg. If x is near 0, you’re mostly liquid, so h is near hf. At 0.95, you’re riding the line heavily toward hg, with a little bit of liquid energy pulling the total down a touch from hg.

About the pressure and the numbers you’d use

• The given pressure is 150 psig. In steam-table land, you typically work with either gauge or absolute pressures, but the key is to be consistent. For saturated properties, you’ll want the saturated liquid enthalpy hf and the saturated vapor enthalpy hg corresponding to the saturation pressure that matches 150 psig.

• When you translate 150 psig to absolute terms, you add atmospheric pressure (roughly 14.7 psi). That puts the saturation pressure around 164.7 psia. The steam tables—or a trusted thermodynamics reference—will give hf and hg at that saturation pressure.

• With a 95% quality, the mixture’s enthalpy is the weighted mix: h = hf + 0.95(hg − hf).

Why the numbers line up the way they do

• hg is always higher than hf because vapor already carries latent heat of vaporization plus the sensible energy of the steam as a gas.

• The closer your quality is to 1, the more your mixture behaves like pure saturated vapor in terms of energy content. But even a small amount of liquid (like that 5%) matters a bit, because the latent heat difference between liquid and vapor is sizeable.

• In practice, you’ll often see teachers and engineers use the standard tables to read off hf and hg at the specific saturation pressure, then run the straight arithmetic h = hf + x(hg − hf).

A concise worked example (without getting lost in the weeds)

• Given: saturated at 150 psig, x = 0.95.

• The exact hf and hg come from the saturation tables for 150 psig. Those values are chosen so that the saturation condition is met; one is the energy of the liquid, the other the energy of the steam when everything is in balance.

• Apply the formula: h = hf + 0.95(hg − hf) = 0.05hf + 0.95hg.

• If you plug in the standard table values for 150 psig, you’ll find the resulting h ≈ 1153 BTU/lb for this 95% quality mixture.

Note on interpretation

• The fact that the resulting enthalpy lands around 1153 BTU/lb tells you something useful about the energy density of a highly vapor-rich mixture. It’s a reminder that while the vapor phase dominates, a little liquid still tugs the energy downward from the vapor-only value. That tug is precisely what the hf term accounts for in the h = hf + x(hg − hf) expression.

• This approach is not about guessing; it’s about reading the right pair of table values for the correct saturation pressure and applying a straightforward linear blend. The math mirrors what’s happening physically: you’re averaging the energy contributions of two phases.

A few practical notes to keep in mind

• Always confirm you’re using the right saturation pressure for the enthalpy lookups. If you mix up gauge vs. absolute pressure, you’ll end up with an inconsistent h.

• The quality fraction is a clean way to capture the state of a two-phase mixture without needing to know the exact amounts of each phase by mass. It’s a handy descriptor, especially in process calculations where the goal is to predict energy content and heat transfer behavior.

• In industrial contexts, you’ll see this concept appear again and again — in turbines, boilers, heat exchangers, and condensers. The same idea plays out: the energy content of a two-phase mixture tracks how much of each phase you’ve got, weighted by how much is there.

Analogies that click

• Think of it like coffee and milk in your cup. If you have a 95% espresso and 5% milk, the balance of flavors and energy in the cup reflects that mix. The espresso is the “hot, high-energy” part (the vapor), the milk is the lighter, more settled part (the liquid). The total flavor (or energy) sits somewhere in between, closer to the espresso’s intensity because it’s the dominant portion.

• Or imagine a crowd at a sporting event: most people are energized, some are calmer. The overall mood carries the weight of the energized majority, but the calmer minority still shapes the feel of the scene.

A quick reality check: what this means for problems

• When you’re asked to compute enthalpy for a saturated mixture with a given quality, the core steps are crystal-clear: identify hf and hg at the appropriate saturation pressure, plug into h = hf + x(hg − hf), and do the arithmetic.

• The outcome will always lie between hf and hg, nudged toward hg as x approaches 1. A 95% quality will tilt the result firmly toward hg, yet not so close that the liquid part becomes irrelevant.

• The numbers you get from the steam tables aren’t just abstract; they feed into real-life design and efficiency calculations for boilers, turbines, and condensers. It’s one of those places where thermodynamics meets the concrete world of pipes, pumps, and heat exchangers.

Bringing it all home

Understanding enthalpy with quality isn’t about memorizing a single rule. It’s about grasping that a saturated mixture is two phases happening at once, each carrying its own energy signature. The quality x is the bridge between those signatures, letting you blend hf and hg into a single, meaningful h. For 150 psig and 95% quality, the math converges to an enthalpy around 1153 BTU per pound—a number that tells you a lot about how energy is stored and transferred in a steam system.

If you’re curious to see the numbers in a table, you’ll find them listed for the saturation pressure that corresponds to 150 psig. They’ll confirm that the mixture’s energy sits in the mid-to-upper range of steam-values, reflecting how much vapor dominates the state while a whisper of liquid keeps the balance honest. And that, in turn, is a neat reminder of why steam calculations feel both precise and a little poetic: energy flowing in phases, still bound by simple, elegant relationships.