CURRENT STATUS AND PROSPECTS FOR HYBRID
HEAT PUMP DRYING TECHNOLOGIES
S. K. Chou1 and K. J. Chua
Department of Mechanical Engineering,
National University of Singapore, Singapore
1E-mail: mpehead@nus.edu.sg
Keywords: energy efficiency, product quality and control strategy
ABSTRACT
Heat pumps have been known to be energy efficient when used in conjunction
with drying operations. The principal advantages of heat pump dryers emerge
from the ability of heat pumps to recover energy from the exhaust as well
as their ability to control the drying gas temperature and humidity. Many
researchers have acknowledged the importance of producing a range of
precise drying conditions to dry a wide range of products and improve their
quality.
At the same time, several researchers have mentioned the need to optimise
component and system design to increase energy efficiency in heat pump
systems.
The present lecture will provide an overview of recent development in heat
pump drying (HPD), their operational features, research results and some
ideas on future trends.
Applications of HPD in the food and timber industries will be discussed.
Other specific topics covered include: energy efficiency, multi-stage heat
pump cycle, novel on-line control methods to enhance product quality and
the potential application of hybrid HPD technologies e.g. radio frequency
or infrared assisted HPD, pressure-regulator HPD etc to solve various
industrial drying problems.
The role of new hybrid HPD technologies in applying to various drying
industries will be discussed in the light of recent product quality and
energy conservation requirements. It is found that generally hybrid HPD
technologies provide the advantages of higher heat transfer rates, shorter
drying time to achieve desired moisture content, improved product quality
and better energy efficiency. Finally, a new concept involving the design
of a HPD system which uses a single low capacity HP to supply drying air to
several different chambers according to a pre-programmed schedule is
presented.
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