Understanding Heat Transfer During the Secondary Drying Stage of Freeze Drying: Current Practice and Knowledge Gaps

Yoon, Kyu; Narsimhan, Vivek

doi:10.1016/j.xphs.2021.09.032

Cited by 8 publications

(6 citation statements)

References 45 publications

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“…The reason for this is that the cake shrinks and, as a result, partially loses contact with the vial. This may further reduce the heat transfer and/or favor that of the vial itself, as already suggested by Yoon and Narsimhan [ 19 ].…”

Section: Resultsmentioning

confidence: 81%

“…As depicted in Figure 4 , a large increase in heat flux was observed at a chamber pressure of 1.00 mbar. As expected, the increased chamber pressure resulted in a more intense heat transfer between the shelf and the vial because of the increased thermal conductivity of the gas trapped in the concave bottom of the vial, as the conductivity of water vapor is highly pressure dependent [ 19 ]. Such differences in heat flux values could also be attributed to the fact that there was no shielding from the surrounding dummy vials.…”

Section: Resultsmentioning

confidence: 87%

“…Due to the lack of shielding from the surrounding dummy vials, the sample temperature was higher than the set shelf temperature. It can be assumed that this effect is more pronounced in smaller freeze dryers such as the one used in this study [ 19 ]. This is partly due to differences in air chamber temperature and scattered radiation from the chamber walls that has escaped through gaps in the aluminum shielding foil.…”

Section: Resultsmentioning

confidence: 99%

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Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer

Sedmak,

Može,

Kambič

et al. 2023

Foods

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Vacuum freeze-drying as a process for achieving high product quality has attracted increasing attention in the last decade. Particularly in the pharmaceutical field and food processing industries, lyophilization can produce high-quality products compared to samples dried by conventional methods. Despite its benefits, lyophilization is a time-consuming and costly process that requires optimization of a number of process parameters, including shelf temperature, chamber pressure, freezing rate, and process time. This paper reports on the implementation of heat flux measurements that allow noninvasive real-time determination of the endpoint of the primary drying stage as an essential parameter for the effective optimization of the overall drying time. Quantitative analysis of the drying kinetics of five fruits (kiwifruit, avocado, Asian pear, persimmon, and passion fruit) was assessed by comparing the heat flux and temperature profiles of samples during the lyophilization process. For a 24 h lyophilization cycle, average heat fluxes in the primary drying phase ranged from 250 to 570 W/m2. A significant correlation was found between the temperature and heat flux distributions at the estimated endpoint of the sublimation process and the corresponding transition into the secondary drying stage. Furthermore, good agreement was also found for the freezing phase. The use of real-time heat flux measurements proved to be a cost-effective experimental method to better understand the process variables in order to reduce the lyophilization cycle time and overall energy consumption.

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Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer

Sedmak,

Može,

Kambič

et al. 2023

Foods

View full text Add to dashboard Cite

show abstract

“…1. For lyophilization, 1D modeling is nearly always used because its accuracy is comparable to that of multidimensional modeling while being much computationally cheaper and less complicated, whereas 0D modeling (lumped capacity) is not sufficiently accurate [39].…”

Section: Mechanistic Modelingmentioning

confidence: 99%

“…The main objective of secondary drying is to remove bound water; hence, the concentration of bound water c s is usually the variable of interest [4,6,14,20]. As can be observed from the model equations, the desorption kinetics are mainly influenced by the temperature T , so the concentration of bound water can be predicted accurately with only the energy balance and desorption kinetics equations [4,39,44]. As such, without loss of generality, mass transfer equations are omitted from the simulations and observer design.…”

Section: Mechanistic Modelingmentioning

confidence: 99%

Real-time Estimation of the Residual Moisture during Desorption with Temperature-based State Observers

Braatz,

Sris,

Barbastathis

2024

Preprint

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Monitoring the residual moisture during desorption is vital to ensuring the final product quality in many chemical processes. One particular application is the lyophilization of biotherapeutics, e.g., mRNA vaccines, in which the bound water is removed via desorption during secondary drying. Successful liquid removal provides long-term stability for the vaccines, allowing for storage at higher temperature. This article proposes a novel technique for real-time estimation of the residual moisture during desorption, with application to lyophilization. A state observer is employed, which combines temperature measurement and mechanistic understanding of heat transfer and desorption kinetics, without requiring any online concentration measurement. Results from both simulations and experimental data show that the observer can accurately estimate the concentration of bound water in real time for all possible concentration levels, operating conditions, and measurement noise. This framework represents the first state observer for monitoring and control of the residual moisture in desorption-related processes.

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Secondary Drying: Challenges and Considerations

Yoon

Narsimhan

2023

AAPS Advances in the Pharmaceutical Sciences Series

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Understanding Heat Transfer During the Secondary Drying Stage of Freeze Drying: Current Practice and Knowledge Gaps

Cited by 8 publications

References 45 publications

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer

Real-time Estimation of the Residual Moisture during Desorption with Temperature-based State Observers

Secondary Drying: Challenges and Considerations

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