The Phi-factor is equivalent to the sample or sample mixture compared to that of the vessel or sample container that is the ratio of mass and specific heat capacity. The closer the Phi-factor is to 1, the lower the influence of the container.
Reference Definition by Aiche.org/ccps: A Phi-factor is a correction factor which is based on the ratio of the total heat capacity of a vessel (mvesCp,ves) and the total heat capacity of the vessel contents (mCp). The phi-factor (=1+(mvesCp,ves/mCp)) approaches the value of one for large vessels, for extremely light vessels, or at genuine adiabatic conditions.
Related Definitions in the Project: The Property and Unit