Ball’s Formula Method Revisited

This manuscript describes a review and analysis of the correction factor for come-up time (CUT), introduced by Dr. C. Olin Ball in his famous Formula Method for thermal process calculations. This correction factor has commonly been considered applicable only to the Ball Formula method. In the alternative General Method, the effect of CUT is automatically included in the calculated lethality value as long as numerical integration is carried out over the entire cold spot temperature-time profile from the point when steam is turned on. The hypothesis of this communication is that Ball’s formula method, just like the General Method, also includes the effect of CUT in its calculations, regardless of where the zero time line is placed within the come-up time. Several computer simulation studies were carried out with the zero time shifted to different locations within the come-up time, resulting in the calculated heating lethality determined by Ball’s method being almost the same as that generated by the General Method. This work confirmed that it is not necessary to shift the zero time in Ball’s formula method because the calculations will always reflect the effect of CUT regardless of where the zero time is chosen.