【作者】 徐岩；

【导师】 蔡英春；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2012， 硕士

【摘要】 高频-对流双热源木材干燥,若采用适宜的干燥工艺,可在保证干燥质量前提下大幅度提升干燥速度,促进木材高效、合理利用,同时干燥周期的缩短也为国内相关干燥企业带来巨大经济效益。本研究以50mmm厚俄罗斯落叶松板材为对象进行了高频-对流双热源干燥,研究了干燥过程中木材温度在线检测方法,研究确定了双热源干燥工艺基准、适宜隔条厚度和高频发振时机及时间。研究主要结果如下：1)高频-对流干燥过程中木材温度在线检测方法的研究：选用非导磁性T型热电偶、Pt100传感器以及多路温度巡回检测仪表,实验确定了其测温精度修正公式,探讨了使用锡箔纸对其屏蔽、用高频电容滤掉高频反射波、可靠接地等有效处理措施,实验研究了传感器的使用注意事项,获得了干燥过程中木材温度分布的较精准在线检测法。2)高频-对流联合加热干燥工艺基准的研究：计算了干燥1m350mm厚落叶松板材所需高频发振功率,为2.4kW；对试材施双热源不同匹配、不同介质温湿度条件的加热干燥,检测分析能耗、干燥品质、干燥速度等参数,进而确定了在确保干燥质量条件下快速高效干燥的较佳热源匹配(在含水率30%-20%之间同时投入高频热源)、较适宜工艺基准(如表3-3)。3)适宜隔条厚度的确定：将50mm厚锯材用不同厚度隔条堆垛,以确定的适宜基准干燥,检测高频加热能耗、对流加热能耗、总能耗、温度分布、干燥品质、干燥速度,分析上述参数确定了合理隔条厚度,为15mm-20mm。4)高频发振时机和时间的确定：在对试材进行外部对流加热的同时,在不同含水率阶段实施不同强度的高频加热,探讨了材温分布变化规律：15mmm厚隔条的材堆高频发振5min后心表层温度差达到9℃,静置15min后降到7℃,35min后降至4℃,约60mmin后稳定为1℃。20mm厚隔条的材堆高频5min后达到9℃,静置10min后降到7℃,约30min后降至4℃,总时间50min后稳定为1℃。进一步分析确定了满足干燥基准要求的高频发振时机和时间：以纤维饱和点之上为例,材堆保持心表层温度差3℃,15mm隔条材堆需高频ON2min,OFF20min；20mm隔条材堆需高频ON2.5mmin,OFF15min。更多还原

【Abstract】 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.更多还原