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1.
实验研究了具有一定孔隙的非饱和多孔物料对液体物料冷冻干燥过程的影响。以甘露醇为主要溶质的待干料液采用“液氮制冰激凌法”制备非饱和物料进行冷冻干燥,并与常规饱和的冷冻物料相比较。结果表明,非饱和冷冻物料确实能够显著地强化液体物料的冷冻干燥过程。干燥产品SEM形貌分析显示,初始非饱和冷冻物料具有连续均匀的固体骨架和孔隙,固体基质更加纤细,孔隙空间更大,可以大大减小传质阻力。考察物料内部各点的温度变化发现,初始非饱和物料内部冰晶确实发生整体升华,但仍然存在主要升华区域;非饱和多孔物料的冷冻干燥过程主要是传热控制,而常规饱和物料冷冻干燥主要是传质控制。操作压力对过程的影响可以忽略。采用辐射/导热组合加热方式可改善初始非饱和多孔物料冷冻干燥过程的传热,进一步缩短干燥时间。  相似文献   

2.
为提高过程经济性,对初始非饱和液体物料冷冻干燥这一思想进行二维数值验证。建立含湿多孔介质冷冻干燥二维柱坐标数学模型,使用有限体积法对控制方程组进行数值求解。模拟结果显示,初始非饱和冷冻物料确实能够有效减少干燥时间,达到强化冷冻干燥过程的目的,干燥时间随着初始孔隙率的增大而减小。对模拟得到的不同时刻物料内部饱和度和温度的侧形进行分析。  相似文献   

3.
王朝晖  施明恒 《化工学报》1997,48(3):294-299
以非饱和含湿牛肉为例,进行了微波冷冻干燥实验研究。获得了干燥时间与物料初始饱和度近似成正比的结论。与升华面模型的计算结果比较表明,升华冷凝模型更符合实验规律,证实了非饱和含湿多孔介质微波冷冻干燥时升华冷凝区的存在。  相似文献   

4.
为了强化冷冻干燥过程,制备咖啡溶液的初始饱和与非饱和2种冷冻样品,分别使用石英与碳化硅底盘进行常规和微波冷冻干燥实验,同时采用电阻法测定溶液的共晶温度.结果表明,在温度为25℃、压力为22 Pa时采用石英底盘,初始非饱和物料冷冻干燥时间比饱和物料缩短了14.9%,适当提高操作温度可以强化冷冻干燥过程.在25℃、22 P...  相似文献   

5.
为了提高冷冻干燥过程的经济性,本文主要对初始非饱和物料的冷冻干燥过程进行数值模拟。建立了二维含湿多孔介质冷冻干燥数学模型,使用COMSOL Multiphysics 4.3a软件进行求解。液体物料的主要溶质为甘露醇。提出两种新的吸附-解吸平衡关系,并与实验数据进行了对比,分析了其适用条件。结果显示,初始非饱和冷冻物料能够有效减少干燥时间,模拟结果与实验数据吻合良好。通过分析物料内部温度、饱和度分布得知,升华界面随着干燥过程的进行逐渐向物料内部转移,干燥过程也发生在物料冰冻区域。适当提高环境温度有利于强化整个干燥过程。  相似文献   

6.
瓶装物料的冷冻干燥过程模拟与实验验证   总被引:4,自引:0,他引:4  
对于瓶装物料的冷冻干燥,在前面工作^「1」的基础上,以脱脂牛奶为物料对冻干过程进行实验研究和模拟计算,结果表明物料的温度分布近瓶壁处的温度较中心部分为高,因此说明瓶壁的热传导不可忽略:同时对模拟值与实验值进行比较,其结果吻合良好。  相似文献   

7.
具有预制孔隙多孔物料的冷冻干燥   总被引:2,自引:1,他引:2       下载免费PDF全文
李恒乐  王维  李强强  陈国华 《化工学报》2016,67(7):2857-2863
实验探究了具有初始预制孔隙多孔物料对冷冻干燥过程的强化作用。以注射用抗生素药剂--头孢曲松钠为主要溶质,采用“液氮制作冰激凌法”制备了具有不同初始孔隙率的冷冻物料,在相同的条件下进行冷冻干燥实验。结果表明,初始饱和度为0.3的冷冻物料(初始孔隙率为0.67)干燥时间比饱和物料(初始孔隙率为0)缩短了21.3%。干燥产品的SEM图显示,初始非饱和冷冻物料的固体骨架和孔隙结构连续而均匀,初始饱和度越低,骨架越纤细,可大大地降低传质阻力。对冷冻速率和退火处理的研究表明,冷冻速率对于两种物料干燥过程的影响甚微;退火处理能够提高冷冻干燥速率。适当提高操作温度可以明显缩短两种物料的干燥时间;操作压力对冷冻干燥过程几乎没有影响。  相似文献   

8.
结合水对冷冻干燥过程影响的研究   总被引:1,自引:0,他引:1  
本文通过分析三种结合水去除机理下的数学模拟结果,并辅以一定的实验验证进行了结合水对冷冻干燥过程影响的研究。以脱脂牛奶的瓶装冻干为对象,对残余水含量、物料温度、干燥时间、湿含量分布等参数,进行了比较和分析。结果表明,结合水对冷冻干燥过程有重大影响;结合水在升华阶段的解吸过程不能忽略,这一冻干机理对冻干时间与物料干燥层的湿含量分布的预测,以及对冷冻干燥过程的现象描述与规律阐述都极为重要。  相似文献   

9.
径向热质传递对瓶装物料冷冻干燥的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
基于经验证了的二维冻干模型对瓶装物料的冷冻干燥过程进行了数值计算 ,利用计算结果对径向热质传递的影响进行了分析 .结果表明 :瓶侧面的径向传热影响显著 ,但忽略水蒸气在径向上的传递作用不会给模拟计算结果带来明显误差 .  相似文献   

10.
非饱和含湿多孔介质微波冷冻干燥过程传热传质分析   总被引:3,自引:2,他引:3  
王朝晖  施明恒 《化工学报》1996,47(2):131-136
基于升华冷凝模型,对非饱和含湿多孔介质微波冷冻干燥过程作了数值计算.结果表明,干燥过程中不饱和含冰区内的冰饱和度有较大变化.通过与不考虑升华冷凝区相比较,表明升华冷凝区的存在不可忽略.  相似文献   

11.
Porous frozen material approach to freeze-drying of instant coffee   总被引:2,自引:0,他引:2  
Abstract

Porous frozen material with a certain initial porosity was prepared to explore its influence on freeze-drying experimentally. Soluble coffee was selected as the solute in aqueous solution and liquid nitrogen ice-cream making method was used to prepare the frozen materials. Results showed that freeze-drying can be significantly enhanced using the initially porous frozen material compared with the traditionally solid one. By keeping the same sample mass and moisture content with sole radiation heating, drying time of the porous frozen sample was about one third shorter than that of the solid one under the same tested operating conditions. SEM images of dried products revealed that the porous material had a loose and tenuous structure that was favorable to the transportation of sublimated vapor and the desorption of bound moisture. Appropriately increasing the chamber surface temperature benefited the freeze-drying process and changing the chamber pressure had little effect on the process. Combined radiation and conduction heating can further promote the freeze-drying process and save as much as 36.4% of the drying time. The porous frozen material was found to have a wider range of operating temperature and result in relatively lower residual moisture content.  相似文献   

12.
To save drying time and increase productivity, a novel idea was proposed for freeze‐drying of liquid materials by creating an initially unsaturated frozen structure. An experimental investigation was carried out aiming at verifying the idea using a multifunctional freeze‐drying apparatus. Mannitol was selected as the primary solute in aqueous solution. Liquid nitrogen ice‐cream making method was used to prepare the frozen materials with different initial porosities. Results show that freeze‐drying can be significantly enhanced with the initially unsaturated frozen material, and substantial drying time can be saved compared with conventional freeze‐drying of the initially saturated one. Drying time was found to decrease with the decrease in the initial saturation. The drying time for the initially unsaturated frozen sample (S0 = 0.28 or 0.69 of initial porosity) can be at best 32% shorter than that required for the saturated one (S0 = 1.00 or zero porosity). This unique technique is easy to implement and improves the freeze‐drying performance of liquid materials. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2048–2057, 2015  相似文献   

13.
14.
具有预制孔隙的维生素C水溶液微波冷冻干燥   总被引:1,自引:0,他引:1       下载免费PDF全文
张朔  王维  李强强  唐宇佳  董铁有 《化工学报》2019,70(6):2129-2138
设计和组装了一套实验室规模的多功能微波冷冻干燥装置,探究了具有初始孔隙的非饱和物料微波冷冻干燥过程。以维生素C为溶质,采用“软冰”冷冻技术制备了初始饱和与非饱和的冷冻样品。结果表明,软冰冷冻制备的样品能够避免崩塌。在35℃和20 Pa条件下,初始非饱和物料的干燥时间比饱和物料缩短了30.4%。SEM表征显示,非饱和物料具有疏松的球状孔隙结构、连通性好,有利于水蒸气的迁移。采用吸波材料碳化硅辅助的微波加热能够进一步强化冷冻干燥过程。在相同条件下,非饱和物料的微波冷冻干燥(5 W功率)时间比常规冷冻干燥(0 W功率)缩短了28.1%,比饱和物料的常规冷冻干燥缩短了50.0%。吸波材料辅助的初始非饱和物料微波冷冻干燥实现了传热传质的同时强化。  相似文献   

15.
吸波材料辅助的液体物料微波冷冻干燥多物理场耦合模型   总被引:1,自引:0,他引:1  
杨菁  王维  张朔  宋春芳  唐宇佳 《化工学报》2019,70(9):3307-3319
为了研究吸波材料辅助微波加热对传统冷冻干燥过程的强化作用,建立了多孔介质温度、浓度和电磁场耦合的多相传递模型;以烧结的碳化硅(SiC)为吸波材料、以甘露醇水溶液为待干料液进行了微波冷冻干燥实验,并测定了甘露醇固体的介电特性。模拟和实验结果均表明,吸波材料对初始非饱和多孔物料微波冷冻干燥具有显著的强化作用。初始非饱和样品微波冷冻干燥时间比传统冷冻干燥缩短了18%,比常规饱和样品传统冷冻干燥缩短了30%。模拟结果与实验数据吻合良好。这表明提出的新型干燥方法确实能够实现过程传热传质的同时强化。通过考察样品内部温度、饱和度和电场强度的实时分布,分析了微波冷冻干燥过程的传热传质和电磁波传播与耗散机理。在微波冷冻干燥过程中,初始非饱和样品累计吸收的辐射能和微波能的总和与传统冷冻干燥相当。这说明,该干燥方法只是提高了能量效率,从而大幅缩短了冷冻干燥时间。  相似文献   

16.
具有预制孔隙多孔介质冷冻干燥的多相传递模型   总被引:2,自引:0,他引:2       下载免费PDF全文
基于局部质量非平衡假设,建立了多相多孔介质热、质耦合传递数学模型,理论验证具有预制孔隙的初始非饱和多孔物料对冷冻干燥过程的强化作用。模型考虑了多孔介质的吸湿效应,构建了3种吸附-解吸平衡关系。模型使用基于有限元法的COMSOL Multiphysics软件平台数值求解,并与实验数据进行了比较。结果表明,初始非饱和冷冻物料能够有效地强化冷冻干燥过程。采用不同函数形式的吸附-解吸平衡关系模拟的干燥曲线均与实验数据非常吻合。通过分析物料内部的饱和度、温度和质量源分布,探讨了初始非饱和物料冷冻干燥过程的传热传质机理。初始非饱和物料的干燥速率控制因素主要是传热。模拟考察环境辐射温度对冷冻干燥过程影响的结果表明,所建模型具有良好的预测能力。  相似文献   

17.
Freeze-drying of the initially porous frozen material with pre-built pores from liquid material was found experimentally to save drying time by over 30% with an initial saturation being 0.28 compared with the conventional operation with the initial saturation being 1, using mannitol as the solid material. In order to understand the mass and heat transfer phenomena of this novel process, a two-dimensional mathematical model of coupled mass and heat transfer was derived with reference to the cylindrical coordinate system. Three adsorption–desorption equilibrium relationships between the vapour pressure and saturation value namely, power-law, Redhead's style and Kelvin's style equation, were tested. Kelvin's style in exponential form of adsorption equilibrium relation gave an excellent agreement between the model prediction and experimental measurement when the equation parameter, γ, of 5000 was applied. Analyses of temperature and ice saturation profiles show that additional heat needs to be supplied to increase the sample temperature in order to promote the desorption process. Simulation also shows that there is a threshold initial porosity after which the drying time decreased with the increase in the initial porosity. Enhanced freeze-drying is expected to be achieved by simultaneously enhancing mass and heat transfer of the process.  相似文献   

18.
冷冻干燥过程强化中冷冻阶段优化的研究进展   总被引:1,自引:0,他引:1       下载免费PDF全文
张朔  王维  李一喆  唐宇佳  刘楠 《化工进展》2020,39(8):2937-2946
冷冻干燥产品质量高,但时间长、能耗高。本文综述了冷冻干燥过程强化中冷冻阶段的优化方法,控制冷冻速率、调节冰晶成核和退火处理可以获得大而均匀的冰晶从而提高升华干燥阶段速率,但物料内部比表面积的减小会降低解吸干燥阶段速率,这类常规的冷冻阶段优化方法对弱吸湿性的物料有一定的强化效果。有机溶剂具有较高的蒸气压,作为共溶剂时可以增加传质推动力,但较低的有机溶剂残留量要求阻碍了其进一步应用。“初始非饱和多孔介质冷冻干燥”的技术思想是将液体物料首先制备成具有一定初始孔隙的冷冻物料,然后再进行冷冻干燥。物料具有的初始孔隙为水蒸气的迁移提供了便捷的通道,而且纤薄的固体基质也有利于结合水的解吸,可以同时强化升华干燥阶段和解吸干燥阶段。该技术思想是过程低消耗和产品高质量的完美结合,为解决冷冻干燥过程速率低的问题提供了新的方案。  相似文献   

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