| A vessel must have space for vapour as well as liquid. As the temperature rises, the liquid expands. The vapour-filled space becomes smaller. At a certain point, there will only be liquid in the vessel. Beyond this, even a slight increase in temperature causes great pressure to build up in the vessel as the liquid attempts to continue expanding despite the absence of the necessary space. The resultant forces are sufficient to rupture the vessel. To stop vessels being overfilled, regulations governing the storage of compressed gases specify the number of kilograms of refrigerant with which a vessel may be filled per litre of internal vessel volume. The maximum permissible capacity is calculated by multiplying this "charge factor" by the internal volume of the vessel. The charge factor for refrigerant used in motor vehicles is 1.15 kg/litre. |
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