共查询到19条相似文献,搜索用时 281 毫秒
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对于种子干燥方面的研究,大多是针对其宏观传热传质即干燥动力学方面。本文采用热成象技术对单颗蚕豆种子的传热过程进行了研究,用实验求解导热方程反问题的方法计算出不同含水率下单颗种子的导热系数,对种子在非稳态下内部温度场进行了测试与分析.研究结果表明,在含水率小于 20%时,其导热系数随着含水率的增加而增大,当含水率大于 25%时则表现出较强的非均质性和非稳态性。对单颗蚕豆种子内部温度场测定而得到的种子热剖面温度分布表明,种子内部存在温度梯度其热扩散具有均匀性,同时反映出种皮传热热阻的存在。这些结果对于深入研究种子内部的传热传质机理,具有重要的实际意义。 相似文献
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蔬菜种子的干燥动力学及其活性 总被引:8,自引:1,他引:7
本文研究了初含水率、干燥周期、料层厚度相同时,不同供热方式(热风、热风与辐射、热风与辐射并加湿)的白菜种子在固定床的干燥动力学及其活性,与传统的只热风供热相比,当干球温度相同时辐射加热风干燥的种子终含水率比低13.8%、发芽率比高0.3%,而辐射加热风并加湿干燥其终含水率比低5.8%,发芽率比高0.8%。为确保种子活力,建立了褚-杨白菜种子临界温度Tcv方程,并已验证其正确性.该方程为蔬菜种子干燥提供了理论基础并有重要的工程意义。 相似文献
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双行程红外辐射振动流化种子干燥的传热传质研究 总被引:2,自引:0,他引:2
在深入研究单行程红外辐射振动流化种子干燥的基础上,本文开拓出双行程振动流化干燥,其特点是在干燥过程中种子与供热热风均经两次行程,干燥装置总高度不变,其干燥行程增加20%.通过非稳态干燥动力学实验研究表明,增加内行程种子总脱水率增加87%,总干燥周期为单行程的1/1.8,料温为其0.82(47℃/57℃)倍.由于增加内筒使恒速段延长并提高了梅这段的干燥速率,整个干燥过程适应种子的生理生化特性,因而可保持种子的活力。文中根据干燥速率方程分别实验研究了辐射、对流与导热在强化种子传热传质过程中的各自贡献.这些研究为我国的‘种子工程’尤其是品种繁多、特性各异干燥难度较高的蔬菜种子干燥提供了理论依据与技术基础。 相似文献
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蔬菜种子干燥中种皮的效应与优化传热传质机理 总被引:4,自引:1,他引:3
1前言含水率大的种子在贮存过程中极易发生劣变,使发芽力与发芽势降低山。种子干燥是一个复杂的传热传质过程,而且还涉及到生命力保存的问题。虽然种子的形态存有差异,但是种子的基本结构都是一致的。一般都由胚、胚乳和种皮三部分组成。种皮对种子具有保护与协调的功能,其透气性与透水性决定了种皮是种子与周围环境进行质量与能量交换的必经之路。为此本文综合种子的生物生理特性研究了蔬菜种子干燥中种皮的作用,并结合种皮的生物学功能探讨了优化传热传质的机理。2种皮对干燥的影响实验装置见文献[2],采用在线测量的方法可连续检… 相似文献
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基于多尺度模型预测木材含水率和温度的变化 总被引:1,自引:0,他引:1
了解木材干燥过程中的水分迁移和热量传递规律有助于提高木材的干燥质量,改善干燥工艺,节约能源。以樟子松(Pinus sylvestris)为材料,建立能够较准确模拟木材干燥过程中含水率和温度分布变化的多尺度单元表征模型,模型由宏观尺度上三个耦合方程一两个水分扩散方程和一个热量平衡方程,以及微观尺度上的单个细胞水分迁移的平衡方程组成。解析模型的过程为:分析初始条件和边界条件、有限元网格的生成、方程离散化、查找相应物性参数、MATLAB软件编程求解。最后通过实验分析验证了建立的多尺度模型的准确性,进行试件在80℃时各层含水率随时间变化的实验,实验结果与模拟值比较,曲线吻合性较好,多尺度模型可以反映木材干燥过程中含水率的分布。最后对建立的多尺度模型进行理论分析,预测了干燥过程中各层温度的变化和分布,进一步验证模型的准确性。从不同尺度建立的木材热质转移数学模型,能较为准确的反映木材含水率的变化和空间分布情况,为干燥过程水分和温度分布的研究提供了一定的理论基础和参考价值。 相似文献
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杏鲍菇作为一种营养价值高、市场需求量大的典型食用菌,热风干燥是其主要加工方法。本文以干燥条件和切片厚度为实验变量,探究热风干燥中杏鲍菇切片的干燥特性(干基含水率、干燥速率)随时间的变化规律。考虑切片的收缩变形和热物性(导热系数、比热容)随含水率的变化关系,建立了热风干燥条件下杏鲍菇切片的热质耦合数值模型。结果表明:杏鲍菇切片的干燥速率随干燥温度的升高而增大,随切片厚度的增加而减小;杏鲍菇切片在对流干燥过程的收缩变形存在明显的非线性,尤其是在降速干燥阶段。并且,数值模型的预测结果与实验测试数据吻合良好,为准确预测杏鲍菇切片的热风干燥特性提供了依据,对菌类干燥工艺优化有重要的指导意义。 相似文献
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布置在建筑物凹槽内的室外机,在环境风速作用下,其运行环境会发生变化。有时恶劣的热环境甚至会造成室外机无法正常工作。本文对不同环境风速下的高层建筑凹槽内空调室外机热环境开展研究,确定了侧面、正面风向下,室外机正常工作所能承受的临界风速。分析了不同风向条件下,凹槽内气流速度场、温度场,并给出温度沿高度方向的变化规律。研究发现,侧面风带走冷气流和楼层间热气流短路,都会造成上层进风温度升高;侧面吹风时,凹槽内上下游列室外机不同的热环境,是由凹槽内特殊旋涡流动导致的。对于正面吹风情形,临界风速应小于0.5 m/s。本研究探明了不同环境风速下高层建筑室外机热环境变化规律,可为考虑风速条件下室外机的选用安装提供参考。 相似文献
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The response to drying and storage at -20 degrees C or in liquid nitrogen was studied in seeds of the freshwater aquatic plant Najas flexilis. The seeds of this species show some desiccation sensitivity, although post-harvest storage in water at 16 degrees C resulted in improvements in desiccation tolerance. There was 63% germination of seeds dried to 9.5% moisture content (30% RH) following this maturation period. Optimum moisture contents for seeds stored at -20 degrees C for 3 months and in liquid nitrogen for 1 week were ~11% and ~15%, respectively. 相似文献
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《Journal of Macromolecular Science: Physics》2013,52(5):733-747
Native potato starch has been processed without the use of any additive. Moldings of initial high strength and ductility have been achieved. However, mechanical properties change with time. Thermogravimetric experiments at different temperatures show that aging takes place in three different steps. The first is characterized by a strong formation of double helices (as revealed by wide-angle X-ray scattering [WAXS]) in parallel with strong water loss. Hardness, strength, and elongation at break increase in this time range: Double helices act as reinforcing elements. When the yield elongation is surpassed, double helices are unraveled, providing a higher elongation at break. With further aging (drying), due to a shrinking process, a temporary reduction of double helices, causing a resoftening, seems to take place. In a third step, the starch moldings become quite brittle due to the lack of molecular mobility. At room conditions, it takes approximately 1 year (beginning of range 3) to lose the good mechanical properties. It is proposed that the mechanical behavior of starch moldings is controlled by a molecular network that consists of singlehelix molecules bound by double helices within an amorphous structure. 相似文献
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Pooja Devi Ashok Kumar Jain M. Someshwer Rao Bhishm Kumar 《Isotopes in environmental and health studies》2013,49(3):426-438
A continuous and reliable time series data of the stable isotopic composition of atmospheric moisture is an important requirement for the wider applicability of isotope mass balance methods in atmospheric and water balance studies. This requires routine sampling of atmospheric moisture by an appropriate technique and analysis of moisture for its isotopic composition. We have, therefore, used a much simpler method based on an isotope mass balance approach to derive the isotopic composition of atmospheric moisture using a class-A drying evaporation pan. We have carried out the study by collecting water samples from a class-A drying evaporation pan and also by collecting atmospheric moisture using the cryogenic trap method at the National Institute of Hydrology, Roorkee, India, during a pre-monsoon period. We compared the isotopic composition of atmospheric moisture obtained by using the class-A drying evaporation pan method with the cryogenic trap method. The results obtained from the evaporation pan water compare well with the cryogenic based method. Thus, the study establishes a cost-effective means of maintaining time series data of the isotopic composition of atmospheric moisture at meteorological observatories. The conclusions drawn in the present study are based on experiments conducted at Roorkee, India, and may be examined at other regions for its general applicability. 相似文献