A comparative study of single stage and non-stationary convection
drying of apples utilizing non-invasive measurement devices
showed the advantages of on-line monitoring of important
state variables as product temperature, colour and shrinkage. Itwas
possible to determine the influence of both the strategy and process
conditions on drying kinetics, temperature and quality development
throughout the process.
Results presented allow deduction for optimised process conditions.
Segmentation of the drying process into phases with
different drying conditions and control strategies shows potential.
Additionally, an active integration of information derived from
pictures taken continuously throughout the process into the control
system is conceivable.
Based on the results obtained adaptive control systems for
existing and newly designed drying devices can be developed.
Increasing process temperature during the first phase of drying will
reduce processing time and, therefore, increase throughput and
reduction of specific energy demand while the integration of optical
systems might allow for more targeted control of specific
product characteristics. Integration of active product temperature
control can prevent overheating of the product and therefore
increased degradation.
Initial tests on other products, such as onions and leek, showed
that the control strategies can be applied to these products with
similar results regarding drying time and product quality. Implementation
of sensors and control systems in existing tray dryers
was successful. However, further research is necessary to determine
correct settings, especially concerning the influence of differences
in drying rate of particles depending on their relative
position to the air inlet.
A comparative study of single stage and non-stationary convectiondrying of apples utilizing non-invasive measurement devicesshowed the advantages of on-line monitoring of importantstate variables as product temperature, colour and shrinkage. Itwaspossible to determine the influence of both the strategy and processconditions on drying kinetics, temperature and quality developmentthroughout the process.Results presented allow deduction for optimised process conditions.Segmentation of the drying process into phases withdifferent drying conditions and control strategies shows potential.Additionally, an active integration of information derived frompictures taken continuously throughout the process into the controlsystem is conceivable.Based on the results obtained adaptive control systems forexisting and newly designed drying devices can be developed.Increasing process temperature during the first phase of drying willreduce processing time and, therefore, increase throughput andreduction of specific energy demand while the integration of opticalsystems might allow for more targeted control of specificproduct characteristics. Integration of active product temperaturecontrol can prevent overheating of the product and thereforeincreased degradation.Initial tests on other products, such as onions and leek, showedthat the control strategies can be applied to these products withsimilar results regarding drying time and product quality. Implementationof sensors and control systems in existing tray dryerswas successful. However, further research is necessary to determinecorrect settings, especially concerning the influence of differencesin drying rate of particles depending on their relativeposition to the air inlet.
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