THEORETICAL CONSIDERATION ON THE INFLUENCE OF THE Z-VALUE OF A SINGLE-COMPONENT TIME-TEMPERATURE INTEGRATOR ON THERMAL-PROCESS IMPACT EVALUATION

The allowed difference in z-value between a single component time/temperature integrator (SCTTI) and target attribute to measure the impact of a thermal process with a given accuracy was examined theoretically. For isothermal heating profiles, the issue and the degree of over- or underestimation of the actual process-value can be predicted as a function of z-value difference and reference temperature. The closer the processing temperature approaches reference temperature, the larger the allowed difference in z-value. As target attributes are characterized by a higher z-value, the allowed z-value difference between SCTTI and target attribute increases. For non-isothermal heating profiles, over- or underestimation depends in addition on the temperature history of the product. In order to obtain a safe estimate of the impact value, whatever the shape of the time/temperature profile, a new approach is suggested based on a SCTTI with a z-value below the target z-value in combination with the use of a reference temperature above or equal to the maximum processing temperature.