An Affordable and Simple Novel Approach to Obtain the Heat Transfer Coefficient (Kv) for Primary Drying Models Without Product Temperature Sensors

Abstract

In this paper a novel method to obtain the heat transfer coefficient Kv value by the gravimetric method without using product temperature sensors is described. The sublimation front temperature is measured manometrically (indirectly by measuring the pressure). The key finding is a method to obtain the Kv value by using a primary drying model with a tailored algorithm. The authors have named it the gravi-manometric method. Kv values at different pressures are presented for two different containers: a freeze-drying stainless-steel cup, and for nested vials. The traditional gravimetric method has been compared against the new gravi-manometric method. Product temperature measurement can be challenging in applications with complex accessibility, as in large batch freeze dryers or when using protective membranes which enclose the product. This novel method is presented as an affordable and simple procedure by which the Kv value is obtained. The gravi-manometric method has the advantage that all the Kv values for a whole batch of vials can be obtained, as it is not limited to a discrete number of product temperature sensors.

Keywords: freeze drying cup; heat transfer coefficient; lyophilization; manometric temperature measurement; primary drying model.