Factors affecting relative humidity during wood vacuum drying

Effects of pressure and temperature in the chamber during vacuum drying on the relative humidity and evaporation of wood surface were investigated by using the vacuum chamber. The setting temperature during vacuum drying included dry-bulb temperature ta, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the cooling water in the condenser. Results indicated that relative humidity during vacuum drying was affected by the dry-bulb temperature td, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the water in the condenser. Relative humidity of wood decreased with the increase in temperature at the given temperature of the water in the condenser. The relative humidity was affected slightly by pressure in the vacuum chamber pA, and it decreased from 70% to 65% with pA increased from 50 kPa to 101 kPa. Moreover, there was nearly no evaporation under the vacuum without external heating.

Drying Kinetics and Energy Consumption in Vacuum Drying Process with Microwave and Radiant Heating

The general objective of this work is to analyze energy input in a vacuum process with the incorporation of microwave heating. Thus, necessary criteria for designing an efficient freeze-drying operation are considered through the analysis of strategies based on the combination of different intensities of radiant and microwave heating.The other aim of this research topic is to study the kinetics of drying in relation to mass transfer parameters.Five freeze-drying strategies using both heating systems were used. Consequently, energy input could be related to diffusivity coefficients, temperature and pressure profiles during dehydration of the product and analyzed in comparison to a conventional freeze-drying process.

Vacuum press drying studies on two fast-growing Indian wood species

Two fast-growing Indian species, Melia composita Benth. and Eucalyptus tereticornis Sm., which have different sets of physical properties, were dried together in a vacuum press dryer(VPD) under two drying conditions,i.e., above boiling point(ABP) and below boiling point(BBP). The ABP and BBP conditions were maintained by keeping the temperature constant at 75 ℃ and maintaining two pressure levels: 300 mm of Hg(ABP) and 450 mm of Hg(BBP). In order to understand pressure conditions at the core during vacuum drying, a cylindrical brass pipe was inserted in both wood cores and attached with pressure gauges placed outside of the VPD. The results indicate that the Melia wood core attained equilibrium pressure immediately with the pressure of VPD, while Eucalyptus attained it very slowly, reaching equilibrium at later stages of drying when cracks and checks advanced to the core.The drying rate was higher for Melia than Eucalyptus under both drying conditions. The drying rate of Melia(ABP) was higher than Melia(BBP), however, the drying rate for Eucalyptus(ABP) was not significantly different from the BBP drying rate.

Effect of steam pretreatment on wood moisture content and characteristics of vacuum drying

The effects of high temperature steam pretreatment on the change in wood moisture content （MC） and characteristics of vacuum drying were investigated in this study. Poplar and manchurian walnut woods were pretreated with high temperature steam at 100~C and 140~C, prior to vacuum drying. A comparison of the characteristics of vacuum drying between steam pretreated wood and untreated wood was carried out. The results show that during steam pretreatment, the MC of wood decreased within a few hours. The reduction of MC varied with the temperature; the higher the temperature, the faster the MC dropped. During the vacuum drying stage, the rates of drying ofpretreated samples were higher than those of untreated samples when MC was below the fiber saturation point. Furthermore, the total drying time of samples treated at a steam temperature of 140~C was lower than that of untreated samples. Therefore, a vacuum procedure after steam pretreatment can effectively shorten the drying time when drying wood.

Application of Vacuum Drying to Silica Sol Ceramic Mold

Silica sol ceramic mold was made at room temperature with JN-30 silica sol, silica powder and NH4Cl. It is found that the harden time of silica sol ceramic mold is only 0.5 to 1.5 h under the amount of NH4Cl solution of 7% to 8% with 15% concentration, and less surface cracks occur by using vacuum drying. The proper vacuum drying process parameters： vacuum drying temperature is 80 to 100℃, drying time is 5 h and vacuum is 0.06 to 0.07MPa. The harden mechanics, vacuum drying mechanics and the reason of less surface cracks of silica sol ceramic mold by vacuum drying： were also analyzed in this paper.

Mathematical Models for Vacuum Drying Characteristics of Pomegranate Aril

The aim of this study was to investigate and determine the best mathematical models in describing vacuum drying characteristic of pomegranate arils in the range of 55-75 ℃. The vacuum batch dryer used in the evaluation was successful in drying a thin layer of pomegranate arils from the initial moisture content of 464.02% （d.b.） to 6.18% （d.b.） within 6.5 to 13.5 hr of continuous drying at the above mentioned temperature range. The drying rates increased with an increase in temperature and drying time. Five of the well known semi-theoretical and empirical models were fitted to the vacuum drying of pomegranate arils. The semi-empirical Midilli model has shown an excellent fit to predict drying behavior of the pomegranate arils because this model gave the highest coefficient of determination （RE）, the least chi-square （X2）, and the lowest root mean square error （RMSE）. The total drying occurs during falling period, signifying the influence of moisture diffusion during the drying. The effective diffusivity varied from 1.25× 10^10 to 2.91 × 10^10 m^2/s over the temperature range. Temperature dependence of the diffusivity was well documented by Arrhenius models. The activation energy of moisture diffusion during drying was found to be 40.46 kJ/mol.

Factors affecting relative humidity during wood vacuum drying

Effects of pressure and temperature in the chamber during vacuum drying on the relative humidity and evaporation of wood surface were investigated by using the vacuum chamber.The setting temperature during vacuum drying included dry-bulb temperature td, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the cooling water in the condenser.Results indicated that relative humidity during vacuum drying was affected by the dry-bulb temperature td, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the water in the condenser.Relative humidity of wood decreased with the increase in temperature at the given temperature of the water in the condenser.The relative humidity was affected slightly by pressure in the vacuum chamber pA, and it decreased from 70% to 65% with pA increased from 50 kPa to 101 kPa.Moreover, there was nearly no evaporation under the vacuum without external heating.

Artificial neural network techniques to predict the moisture ratio content during hot air drying and vacuum drying of Radix isatidis extract

Background:To predict the moisture ratio of Radix isatidis extract during drying.Methods:Artificial neural networks were designed using the MATLAB neural network toolbox to produce a moisture ratio prediction model of Radix isatidis extract during hot air drying and vacuum drying,where regression values and mean squared error were used as evaluation indexes to optimize the number of hidden layer nodes and determine the topological structure of artificial neural networks model.In addition,the drying curves for the different drying parameters were analyzed.Results:The optimal topological structure of the moisture ratio prediction model for hot air drying and vacuum drying of Radix isatidis extract were“4-9-1”and“5-9-1”respectively,and the regression values between the predicted value and the experimental value is close to 1.This indicates that it has a high prediction accuracy.The moisture ratio gradually decreases with an increase in the drying time,reducing the loading,initial moisture content,increasing the temperature,and pressure can shorten the drying time and improve the drying efficiency.Conclusion:Artificial neural networks technology has the advantages of rapid and accurate prediction,and can provide a theoretical basis and technical support for online prediction during the drying process of the extract.

A valid evaluation method for UPLC fingerprint analysis and moisture ratio prediction model:application to microwave vacuum drying of Radix isatidis extract

Background:Drying is a necessary component of traditional Chinese medicine extracts.The heating principle of microwave vacuum drying is different from that of the conventional heat method.However,at present,there is paucity of information on the drying process of traditional Chinese medicine extract by microwave vacuum drying,and the results of such process are unclear.Methods:To study the dynamic changes in the chemical characteristics of microwave vacuum drying under different drying conditions,ultrahigh-performance liquid chromatography fingerprint profiles were established using Radix isatidis extract as a model drug and analyzed using similarity analysis,partial least squares-discriminant analysis,and semi-quantitative analysis.In addition,a backpropagation artificial neural network model was developed to predict the moisture ratio of the drying process.Results:Qualitative results showed that the similarity between different drying conditions was greater than 0.95,and 2 amino acid components(peaks 5 and 6)affected by process fluctuations were screened out.The quantitative results showed that the mass concentration of component 1 fluctuated after drying,while that of component 2 increased.The optimal backpropagation artificial neural network model structure used to predict the moisture ratio was 5-4-1,with regression and mean squared error values of 0.996 and 0.0003,respectively,after training,which were well fitted and had a strong approximation ability.Conclusion:Upon comparison of fingerprints and the evaluation of statistical methods,common components of Radix isatidis extract had little variation under different drying conditions,and the selected components provided a reference for the establishment of process evaluation indexes.The establishment of backpropagation artificial neural network provides a theoretical basis for the application of microwave vacuum drying technology and online monitoring of moisture ratio.

Effects of Different Drying Processes on the Effective Components of Stichopus japonicus Viscera

Drying is a basic link in seafood processing, and the effects of forced air drying and vacuum drying on the effective components of Stichopus japonicus viscera were compared with the moisture, total saponin and polysaccharide contents as the detection indexes. The contents of effective components obtained using forced air drying were slightly lower than those obtained using vacuum drying, but the forced air drying method used short drying time and low economic energy consumption. Excellent drying effects and low cost of forced air drying made it can be adapted to the requirements of large-scale production applications.

Effect of different drying methods on the taste and volatile compounds,sensory characteristics of Takifugu obscurus

Pufferfish is prone to deterioration due to abundant nutrients and high moisture content.Drying technology can extend the shelf life and enhance the flavor quality of aquatic products.The study investigated the effect of hot air drying(HAD),microwave vacuum drying(MVD)and hot air assisted radio frequency drying(HARFD)on the taste and volatile profiles of Takifugu obscurus.Different drying methods had significant influence on the color,rehydration,5’-nucleotides,free amino acids and volatile components(P<0.05).The results showed that HAD and HARFD could promote the flavor of T.obscurus by producing higher equivalent umami concentration(EUC)values,which were about two times of MVD group,and more pronounced pleasant odor according to sensory analysis.HAD is more appropriate for industrial application than HARFD and MVD considering the economic benefits.This study could provide a reference for the industrial application of drying T.obscurus.

Design of ZigBee-WiFi Gateway for Vacuum Oven

In the process of power battery production, it is necessary to put battery into vacuum oven for drying, the temperature, the vacuum degree and other factors directly influence the quality of the power battery. In order to remotely control the temperature and vacuum degree of vacuum oven in the process of power battery manufacturing, the wireless communication system based on the ZigBee-WiFi gateway for the power battery production is presented. The system uses wireless module CC2530 as the core chip, to complete the machine networking in workshop, and use of WiFi wireless module ESP8266 to complete data interconnection ZigBee and WiFi network, implement the data information exchange and sharing between the vacuum oven and the Internet. This wireless communication system has the characteristics with easy networking, low power consumption and low cost. So, this communication system can meet the requirement of data transmission and sharing in power battery manufacturing and other production activities.

乏燃料干法贮存工艺中真空干燥速率的优化研究

随着核电产业迅速发展,乏燃料管理问题已经成为制约核电发展的关键问题之一。乏燃料贮存方法包括湿法贮存和干法贮存,我国目前引进了NUHOMS系统来进行干法贮存工作。乏燃料干法贮存是现将乏燃料装进密封贮存容器中,经过一系列排水、真空干燥、氦气回填、焊接等操作将乏燃料密封在贮存容器中,最后通过转运容器将其推入到水平贮存模块中的一种工艺。介绍了NUHOMS乏燃料干法贮存工艺中的真空干燥过程,着重分析了真空干燥过程中存在的问题,如吹扫效果差、管线布置不合理、硼结晶堵塞管线等,并提出了相应的优化建议和措施。

除臭风口布置对污水处理厂内硫化氢气体分布影响的模拟研究

污水处理厂在对污泥采用低温真空脱水干化一体机技术进行处理时,会产生对人体有害的硫化氢气体,因此需要合理设计除臭风口,将硫化氢气体从室内高效排出。以泰和污水处理厂污泥脱水干化系统为研究对象,利用仿真软件建立数值模型,对2种除臭风口布置方案,即分别将除臭风口置于密封罩内和置于密封罩外的污水处理厂内部硫化氢气体浓度分布进行了模拟,对比分析了室内不同方向上硫化氢气体的积聚情况。模拟结果表明,将除臭风口置于密封罩内时,去除硫化氢气体的效率为将除臭风口置于密封罩外的5.46倍,可快速降低室内的硫化氢气体浓度,另外建议将硫化氢传感器设置在密封罩附近。

真空冷冻干燥机真空系统特性的研究

本文阐述了真空冷冻干燥机真空系统的性能参数 ,介绍了能满足冻干要求的几种真空系统 。

用制冷机低温泵获得清洁无油高真空

制冷机低温泵以其抽速大和无污染的特点,在各行各业得到了广泛的应用。文章介绍了制冷机低温泵的工作原理、结构和特点,以及在国外空间环境模拟设备上的使用情况。着重介绍了自主设计生产的制冷机低温泵在国内最大的空间环境模拟设备中调试和测量的情况,为获得清洁无油高真空取得了良好的效果。

冻干设备真空系统设计及其节能运行控制方式的应用研究

介绍了SZDG200冻干设备真空系统设计,系统中真空机组选用罗茨泵+罗茨泵+水环泵(带大气喷射泵)三级真空泵组;在干燥仓设一电动调节充气阀,通过控制干燥仓内充气量来控制干燥仓内的压力;采用预抽真空机组和维持真空机组组合的方式实现真空机组节能控制运行。实际工程应用表明,该真空系统能较好的满足冻干生产需要。在进行冻干小葱实验时,真空机组采用节能控制运行方式比普通运行方式可节能27%,节能效果明显。

基于干燥均匀性的真空脉动干燥加热控制技术

为解决真空脉动干燥中加热板差异和气流扰动引起的物料干燥不均匀问题,设计了基于过零触发控制的加热板辐射强度控制硬件电路,将PID控制理论和离群点检测方法相结合,提出了加热板温度离群点优化积分分离PID控制策略,以含水率均匀一致的面片作为试验原料,以干燥均匀度为考核指标,对控制系统的控制效果进行试验验证。试验结果表明:该控制系统可以有效缩小不同加热板间的辐射强度差异,平均温度控制精度±0. 8℃,初始阶段调节时间120 s,在受到气流扰动干扰后能够迅速恢复;在干燥均匀性方面,离群点优化PID控制优于独立PID控制和整体PID控制,可以减小气流扰动对干燥整体均匀性的影响,面片干燥均匀度由90%左右提高到95%以上。

ZDG-160 食品真空冷冻干燥设备

介绍了ZDG－160食品真空冷冻干燥设备及其自动控制系统。该设备可用于生产果蔬、肉类、海产品等食品，营养保健品、中草药等的冻干产品。该设备系统设计合理紧凑、操作简单、运行可靠、自动化程度高、工艺先进、节能显著。

适宜添加剂预处理提高罗非鱼片冻融-热泵干燥品质

为了获得添加剂预处理对罗非鱼片冻融-热泵干燥品质的综合影响,并为真空冷冻干燥提供常压低温干燥的替代比较,以罗非鱼片为试验材料,选取海藻糖、山梨醇和麦芽糊精3种添加剂,进行了不同质量分数的添加剂浸渍预处理对罗非鱼片冻融结合热泵干燥过程影响的系列试验,获得了干燥曲线,品质指标变化规律和试验条件下的最佳工艺条件,并与热风干燥,热泵干燥和真空冷冻干燥所得样品性能进行了对比试验。结果表明:合适的预处理添加剂及其质量分数能对冻融结合热泵干燥方式产生有利的促进作用,能取得提高干燥速度和改善干燥品质的双重效果,且以质量分数为15%的海藻糖溶液浸渍处理获得的效果较佳,在较佳工艺下获得的罗非鱼片的干燥品质综合评分比热风干燥和常规热泵干燥分别提高了40.18%和33.57%,相比于不经添加剂预处理的对照组有25.41%的提高,与真空冷冻干燥比仅低了4.39%,但其常压干燥条件比真空冷冻干燥的真空条件有较大程度的改善,研究结果能为水产品的常压低温干燥提供参考。