April 13, 2023

Dissolved gas analysis: Gas measurements technologies – Part 1

As the temperature is increased, there is a corresponding increase in the vigour of translational and rotation motions of all molecules.

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As the temperature is increased, there is a corresponding increase in the vigour of translational and rotation motions of all molecules, as well as the vibrations of atoms and groups of atoms within molecules. Experience shows that many compounds normally exist as liquids and solids; and that even low-density gases, such as hydrogen and helium, can be liquified at a sufficiently low temperature and high pressure. A clear conclusion to be drawn from this fact is that attractive intermolecular forces vary considerably and that the boiling point of a compound is a measure of the strength of these forces. Thus, to break the intermolecular attractions that hold the molecules of a compound in the condensed liquid state, it is necessary to increase their kinetic energy by raising the sample temperature to the characteristic boiling point of the compound. In that manner, it is evident in Fig. 1 that even if the temperature remains constant, the substance, water, in this case, may become gas not only by increasing temperature. For large power transformers, it is relevant when the temperature increases even within the normal limits, then some liquids in the power transformer become gaseous and may affect the transformer operation, as activate alarms.

The phase diagrams for hydrocarbons are quite different than for water, yet they are still depending on both pressure and kinetic energy or what we call temperature. A liquid may transform into vapour at much lower temperatures than the boiling point. If one leaves a half-filled open glass with water for several days, the water will vanish, and it will surely become vapour at room temperature.

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