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Principles of dehumification lumber drying

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Basic heat pump (dehumidifier) theory is discussed
along witli the basic components and operation'of lowtemperature
and high-temperature lumber dehumid
ification drying systems. The heat transfer and thermo
dynamic characteristics in the basic components of a
typical heat pump, phase diagrams of different
refrigerants, and the advantages and limitations of
different compressors are discussed. The first genera
tion of low-temperature dehumidifiers suffered from
frequent compressor failures because they were unsuited
to be operated above 120°F kiln temperature. Specifical
ly, these compressor failures were usually caused by the
oil in the refrigerant (usually R-22 or R-12) oxidizing at
high temperature on the compressor valves and there
by causing the valves to leak. Second generation
dehumidifiers now overcome this problem by using open
or semi-hermetic compressors (when the electric motor is
not cooled by the refrigerant), refrigerant R-l 14 which is
more suited for high-temperature operation, or cen
trifugal compressors that do not require valves and have
less oil in the refrigerant. These modifications allow a
dehumidifier to be operated up to about 180°F so that
drying times can be equivalent to conventional drying
times below a wood moisturecontentofabout20 percent.
File Size:
2.7 MB
File Author:
Peter Y. S. Chen, Wayne A. Helmer
Submitted On:
05 Jul 2011
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