Research On The Schedule Of The Hybrid Drying In Wood With Radio-Frequency And Convective Heating

Guaranteeing drying quality, the speed of the process of Hybrid Drying with Radio-Frequency and Convective Heating can be highly improved by using proper drying technology, which brings effective promotion on reasonable wood use and high economic benefit to the domestic enterprises. Russian larch which is50mm in thickness was taken as the subject of study, and then different drying quality and efficiency caused by different environmental parameters were discussed.According to the primary research on the heat and mass transfer principle in the hybrid drying process of larch, the variation of MC and temperature finally influenced the efficiency of radio-frequency heating by making an effect on the dielectric property of the wood. What’s more, the oscillation power needed for drying1m350mm thick larch sawn timber was2.4kw, and the drying schedule for Hybrid drying process was set based on the one of conventional drying by the method of comparative analysis.Firstly, Pt100platinum thermal resistance and T-type thermal resistance were calibrated, then the temperature detective leader wire was isolated from heat by wrapping Teflon, shielded from radio-frequency electromagnetic waves by covering grounding aluminized paper, and the end of the leader wire was connected with temperature calibration instruments after filtered by a HFK. Finally the temperature distribution in wood could be precisely detected.The rationality of the thickness of the wood stickers using in different wood piles were estimated from the drying speed, energy consumption and other factors by keeping all the drying conditions steady other than the thickness of the wood stickers. From which the results showed that drying rates of different woodpiles were positively corrected with wood sticker thickness when MC was beyond fiber saturation point, and then converged around MC, during which the rate disparity appeared with the decrease of MC, but in the end of the drying process they were negatively corrected with wood sticker thickness.The efficiency of heat and moisture exchange on wood surface was promoted by the augment of wood sticker thickness, the evaporation of surface moisture was relatively faster than that of the core moisture, which led to the increase of the disparity of the MC from different layers and then caused internal stress, meanwhile the growth of periodic energy consumption increased and was synchronized with time. In summary,15mm and20mm thickness wood stickers were suitable for the experiment.After choosing the thickness of the wood stickers, the radio frequency vibration time was decided by researching on the principles of the temperature increase in the high-frequency field and convective circumstances, which showed that as the processing time went by, the temperature gap between the core and surface part of wood grew, the effect that wood stickers made to the change of temperature in the same MC period decreased and the less MC was, the faster the temperature changed.The best time to add radio-frequency vibration was identified by analyzing the change of the time and energy consumption of the whole drying process, during which the drying speed was faster, the MC diversity was smaller and the drying defect was less compared with conventional drying, what’s more, energy consumption decreased with the bigger decrease of MC in the later period of the drying process, in summary, adding the high-frequency vibration when MC was20%-30%was the best approach for the experiment.