UsingMassonpineasspecimens,whendryingmediumsareoverheatedsteamandhot-airrespectively,preheatingcharacteristicsofwoodundervacuum-floatingpressuredryingarediscussedbymeasurementofinternaltemperaturefieldandvariationofmoisturecontentduringperiodofpreheating.Therelationshipbetweendryingmediumconditionsanddryingrateofwoodrevealsthat,firstly,comparedwithprocessofair-drying,timeneededtobepreheatedundervacuum-floatingdecreaseddramatically,meanwhile,themagnitudeofcondensationonthesurfaceisrelativelylarger.Secondly,dryingrateofwoodundervacuum-floatingpressureincreasescoupledwithtemperatureofmedium,reductionofabsolutepressure,andraiseoffluctuationrateofpressure.Thesequenceoffactorscontributiontodryingrateislistedasfollowing:temperatureofmedium(t)>fluctuationrateofpressure(f)>absolutepressure(p).
