The Temperature Uniformity During Air Drying of a Colloidal Liquid Droplet

ABSTRACT

The mathematical analysis for drying of individual droplets containing dissolved or suspended solids has been given significant importance due to the increasing popularity of the spray drying operation in the production of various chemicals, ceramics, drugs, food, and dairy powders as well as nanoparticles. The physical and biological qualities of the final products primarily depend on the history experienced by the droplet within the dryer. It is, therefore, desirable to ‘estimate’ the droplet's behavior and various characteristics such as moisture content and temperature profiles accurately. In the literature, several models have been presented to estimate moisture and temperature profiles inside a particle considering various assumptions. One common assumption is the uniform temperature distribution within the droplets being dried. The present article has presented an estimation procedure to evaluate the temperature distribution within a porous skim milk droplet to determine whether the uniform temperature distribution assumption is reasonable. Here, the surface-center temperature differences were estimated by considering the one-dimensional, unsteady-state heat conduction equation for a spherical droplet. Shrinkage of droplets was taken into consideration during modeling. A new concept of the Biot number has also been applied in the current article to assist in the determination of the rate-limiting process.

Keywords:

• Droplet
• Drying
• Heat conduction
• Modeling
• Biot number
• Surface temperature

ACKNOWLEDGMENTS

The authors would like to thank Dr. S.X.Q. Lin for providing the experimental measurements on drying of the single skim milk droplets. The first author is the recipient of the University of Auckland Ph.D. scholarship and the third author is the recipient of the School of Engineering Ph.D. fee-waiver scholarship. We appreciate this funding.