In instances where suction gases, or materials entrained in the suction gases, might freeze inside an ejector, an external heating jacket is often employed. High vacuum steam jet ejectors, such as V and W stages which operate below 4.5 torr (the partial pressure of water ice at 32o F), will have a partial external steam heating jacket running from the end of the suction head to the beginning of the bore section of the throat. Low pressure steam at 10-15 psig is often used to keep the ejector wall temperatures at > 40o F, thus preventing ice build up inside the throat. (Ice build up restricts the flow through the throat. This can lead to erratic or poor high vacuum ejector performance.) External steam tracing coils may also be used.
In the plastics industry it is common to use a full hot oil jacket on an ejector, covering the suction connection, the suction head and the entire throat all the way to the discharge connection. Entrained polymers often freeze at several hundreds of degrees, so the ejector walls have to be kept at temperatures exceeding this freezing point to prevent build-up.
Sulfur pit ejectors, entrain sweep air and sulfur laden vapors at slightly below atmospheric pressure. To keep elemental sulfur from freezing inside the ejector, a full steam jacket with 50 psig (or more) steam, is frequently used to keep the ejector walls at about 300o F.
Conversely, in situations where ejectors have to handle short duration, high temperature gas loads (e.g. rocket engine testing), steel ejectors have been equipped with external water cooling jackets. This obviates the need for expensive high temperature alloys in the construction of the jets.