Abstract
The freeze-drying process removes water from a product through freezing, sublimation and desorption procedures. However, the extreme conditions of the freeze-drying environment, such as the limited space, vacuum and freezing temperatures of as much as −50 °C, may block the ability to use certain diagnostic sensors. In this paper, an ultrasonic transducer (UT) is integrated onto the bottom of a specially designed frozen bottle for the purpose of observing the freeze-drying process of water at varying amounts. The temperatures and visual observations made with a camera are then compared with the corresponding ultrasonic signatures. Among all of the diagnostic tools and technologies available, only ultrasonic and visual records are able to analyze the entire progression of the freeze-drying process of water. Compared with typical experiment settings, the indication of drying point for water by the amplitude variations of ultrasonic L3 echo could reduce the process period and energy consumption. This study demonstrates how an innovative frozen bottle, an integrated ultrasonic sensor and diagnostic methods used to measure and optimize the freeze-drying process of water can save energy.
Highlights
Dehydration extends food’s usage period longer than that of fresh food by preserving it in a stable and safe condition [1,2]
In the primary drying stage, the air in the vacuum chamber is exhausted and the chamber pressure is reduced below the vapor pressure of ice
The measured ultrasonic signatures are compared with the temperature and visual records
Summary
Dehydration extends food’s usage period longer than that of fresh food by preserving it in a stable and safe condition [1,2]. Artificial methods are more advantageous than the natural methods [7] because they can remove large amounts of moisture efficiently by being able to control the different parameters involved such as the temperature, drying air flux and time of drying and so forth. The water contained in food is cooled down and becomes ice during the freezing stage. This stage governs the sublimation and desorption rates and the quality of the lyophilized product [12]. In the primary drying stage, the air in the vacuum chamber is exhausted and the chamber pressure is reduced below the vapor pressure of ice. the shelf temperature increases gradually to sublimate the ice. The residual water inside the food will be desorbed thoroughly in the secondary drying stage [13]
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