Verified answer

The symbol ø usually refers to a diameter . I interpret 150ø as having a diameter of 150mm. I do not know any relationship to temperature. This could refer to some vacuum chamber having a 150 mm diameter opening .

If you ask a question of this type it is a good idea to provide more details of the reference - preferably the sentence or paragraph in which it appeared. I am afraid that "recently seen this ø in chemistry"is not enough information for anybody to come to a conclusion that may help you.