Saturation Principles - CAIRE HELiOS Plus Technical & Service Manual

VII 1

Saturation Principles

Oxygen, in its normal state, is a colorless, tasteless, and odorless gas that is non-flammable, although it greatly accelerates combustion
in high concentrations. It constitutes about 21% of the Earth's atmosphere by volume. Oxygen in higher concentrations is medically
beneficial to patients suffering from certain respiratory diseases.
Oxygen, like most gases, will condense into a liquid with an increase in pressure or decrease in temperature. As a liquid, oxygen is
pale blue in color and is about 860 times as dense as its gaseous form. At atmospheric pressure (14.7 psia), oxygen condenses into its
liquid form at a temperature of about -297°F (-184°C). Liquid oxygen (LOX) is an efficient form of oxygen to meet a patient's port-
able, ambulatory oxygen needs. A volume of liquid oxygen, when vaporized, yields about 860 volumes of gaseous oxygen (Figure 1).
As you can see, a relatively small volume of liquid oxygen provides a much larger volume of gaseous oxygen for a patient to use.
In medical liquid oxygen systems, liquid oxygen, and the gaseous oxygen resulting from its vaporization or boiling, is stored under
pressure. The elevated pressure, typically 1.52 bar (22 psig), enables oxygen to flow to the patient at a selected, prescribed rate. To
sustain this oxygen flow to the patient, the liquid oxygen must be in a state that allows vaporization to readily occur. In other words,
the liquid oxygen must be in a state of saturation. Let's take a look at what liquid saturation is all about.
A saturated liquid is one that absorbs the maximum amount of heat possible at a given pressure without vaporizing into a gas. If ad-
ditional heat is added, the saturated liquid begins to vaporize (boil) while remaining at a constant temperature until all of the liquid
is vaporized. A common example of a saturated liquid is water at its boiling point of 212°F (100°C) at sea level. The constant addi-
tion of heat to the boiling water does not cause it to become hotter, but instead causes part of the liquid water to turn to water vapor
(Figure 14).
Figure 14: Saturated (Boiling) Water at Sea Level
The saturation (boiling) point of a liquid depends not only on temperature but also on pressure. If the pressure in a container of satu-
rated liquid increases, the temperature required for saturation to occur will also increase. This leaves the liquid unsaturated, that is,
capable of accepting more heat before it will boil (Figure 15).
Figure 15: Saturated (Boiling) Water at Higher Pressure
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HELiOS Portables Technical Service Manual • PN 20562190 Rev E