For calculation purposes, the oil pot is assumed to be a horizontal vessel with all dimensions entered into the calculator as internal to the vessel. If external measurements are used this will result in an over-estimate of the refrigerant inventory.
The Head Ratio is the ratio of the compressor’s diameter to its head diameter (twice the individual head dimension). Ellipsoidal heads with a ratio of 2:1 are the most common.
The Vessel Length includes the shell length and both heads. The length of a 2:1 ellipsoidal head is ½ the diameter.
An easy way to determine the amount of oil in the pot is to observe the frost level, since frost does not form where oil is present inside the vessel. Thus the calculator asks for the height of unfrosted oil pot from the bottom up to the top. The tool then assumes the remainder of the vessel contains liquid ammonia to determine the inventory. The small vapor space above the liquid ammonia is assumed as all liquid to be conservative in the calculation.
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