冻结速度与冻结时间估算方法研究

针对淮南地区张集煤矿井筒冻结施工的关键技术进行深入研究,对现场实测数据进行分析,探讨冻结速度和冻结时间的不同估算方法。通过对比分析,提出冻结速度和冻结时间的有效估算方法,为设计人员提供参考。     

冻结速度对黄土物理性质影响的试验研究

冻结速度堆黄土物性参数具有总要影响。使土样在封闭系统开展天然状态不同冻结速度的冻融循环试验。试验表明：土在冻结过程中,环境水分向冻结锋面迁移,致使土体的含水量增大;随着冻结速度的增大,即冻结时间的缩短,环境水分迁移的量减小。对于冻结速度较慢的情况,水分冻胀作用对黄土的体积影响不明显;对于冻结速度较快的情况,冻结速度越大,体积变化越小,液塑限越大。试验表明昼夜温差的变化对黄土土性的影响大于数月温度缓慢变化的影响。     

冻结速度对黄土物理性质影响的试验研究

冻结速度堆黄土物性参数具有总要影响。使土样在封闭系统开展天然状态不同冻结速度的冻融循环试验。试验表明：土在冻结过程中，环境水分向冻结锋面迁移，致使土体的含水量增大：随着冻结速度的增大，即冻结时间的缩短，环境水分迁移的量减小。对于冻结速度较慢的情况，水分冻胀作用对黄土的体积影响不明显：对于冻结速度较快的情况，冻结速度越大，体积变化越小，液塑限越大。试验表明昼夜温差的变化对黄土土性的影响大于数月温度缓慢变化的影响。     

冻结过程中流场分布改变对冻结特性的影响

为考察鼓风冻结过程中流场分布对食品冻结的影响,针对两排圆柱形食品模型(马铃薯泥)建立了鼓风冻结的三维数值模型,进行了三维非稳态模拟,实验验证表明该模型与实际情况吻合较好,冻结时间相对误差为3.2%。以冻结曲线、冻结速率、温度变异系数、冻结时间不均匀度和能耗为指标,研究马铃薯泥冻结过程中的位置改变对其冻结特性的影响,即在冻结了80 min,100 min,120 min时将两排马铃薯泥对调。结果表明,在预冷段进行位置改变的影响效果小于相变段;在相变段的3个时刻中,t=100 min时改变马铃薯泥位置效果最好,能够缩短冻结时间6.7%,降低能耗9.7%以及减小冻结的不均匀性。冻结过程中食品的位置改变(实际中也可以改变风向)能够有效缩短冻结时间,减小冻结不均匀度,在保证冻品质量的前提下,达到节能目的。     

连续冻结隧道的冻结时间分析及其对能耗的影响

冻结时间影响速冻食品的质量和能耗 ,本文通过对冻结时间的编程计算 ,并针对不同的隧道冷却介质温度、隧道吹风速度和不同的食品厚度情况下的冻结时间进行分析比较 ,得出根据冻结时间来选择设备的运行工况 ,既可以节能 ,又可以使装置得到最合理使用的结论     

接触角和质量分数对液滴冻结过程的影响

本文通过Fluent软件的凝固/熔化模型,模拟了接触角及质量分数对纯水和氯化钠溶液在冷表面冻结过程的影响,选择铜片为亲水表面,纳米膜表面为疏水表面,对液滴在不同表面特性条件下的冻结过程进行实验研究.结果表明:液滴在冷表面的冻结特性与接触角、质量分数有关.当溶液质量分数一定时,接触角越小,液滴冻结速度越快,完全冻结时间越...     

带喷嘴的连续冻结隧道装置的设计及其冻结效果分析

本文以一个冻结能力为800 kg/h的网带速冻装置为原型,对现有连续冻结隧道装置增设喷射结构,经过静压箱均混的气流再经喷嘴射流后,吹风速度加快,食品冻结时间缩短.理论计算表明:本设计的冻结时间减少到原来的65.3%,单位时间内冻结量提高了53%.     

全岩冻结井筒快速掘砌施工技术

针对马鞭山措施井井筒全岩冻结的实际情况，对掘砌施工中的关键工艺爆破技术、出碴、衬砌进行了论述，在井筒掘砌过程中加强与冻结施工的积极配合，极大地提高了循环掘砌速度，缩短了建井时间。提高了社会经济效益，对今后类似井筒的掘砌施工具有一定的指导意义。     

不同冻结速率对毛豆冻藏过程中品质的影响

以毛豆为试材,研究了-35℃鼓风冻结(风速8 m/s)、-35℃静止冻结和-18℃静止冻结三种冻结方式对毛豆冻结温度变化曲线及冷冻毛豆在-18℃冻藏过程中解冻后汁液流失率、硬度、细胞膜透性、丙二醛、叶绿素、维生素C等品质指标的变化,为选择适宜的毛豆速冻方式提供参考。结果表明:-35℃鼓风冻结冷冻速度最快,毛豆通过最大冰晶生成带的时间最短,仅为40 s,而-35℃和-18℃静止冻结所用时间分别为6 min和1 h左右。三种不同冻结方法对冷冻毛豆贮藏过程中解冻后的质构和汁液流失率,及冻藏过程中的细胞膜透性、丙二醛、叶绿素和维生素C含量等指标有显著影响。毛豆冻结过程中冻结温度越低、风速越高,毛豆冻藏过程中的质构、细胞膜完整性和营养成分等劣变速度越慢。-35℃鼓风冻结的毛豆在冻藏过程中品质显著好于-18℃静止冻结,是较好的毛豆冻结方法。     

食品冻结时间的数值计算

本文对常见的平板状食品冻结时间进行了计算机模拟,建立描述食品冻结过程传热特性的偏微分方程（温度模型、焓模型）,采用有限差分法进行数值求解,并与实测值,简易公式计算值对比,结果表明,数值法计算食品冻结时间具有较高的精度,与实测值吻合得较好。     

不同参数下的单、双层圆柱壳体速度场研究

研究圆柱壳体表面速度场的重构：疗法对潜艇水下辐射噪声的预报具有重要的意义。采用了分区段重构轻外壳速度场的思想，在此基础上建立无限流体中的有限长单、双层加肋圆柱壳模型，分析了壳体表面速度场随不同结构参数的变化规律，并对单、双层圆柱壳体，以及双层圆柱壳体内、外壳的振动响应性能作了一定的比较。得到了单区段壳体长度的选取、模型刚度特性以及不同频段内壳体间耦合作用等对壳体速度场的影响，为研究潜艇轻外壳速度场重构方法提供了理论依据。     

Freezing time of an infinite cylinder and sphere using the method of lines

An energy balance model has been developed to simulate freezing processes for infinite cylinders and spheres. The mathematical model (1) was numerically solved using the method of lines. In this method, spatial derivatives are discretized by the finite difference method and the resulting system of ordinary differential equations in time is integrated using an appropriate solver. Freezing times obtained with the proposed model were compared to experimental data and results calculated by different published methods. The freezing times predicted by the proposed model agreed well with the published experimental results and predictions by other published methods. Model (1) gives a percentage error in the range −4.61 ≤ E (%) ≤ 6.81, which includes the experimental data for the 123 spheres analyzed and 30 infinite cylinders, within range −2.96 ≤ E (%) ≤ 3.34.     

阻尼层对水下圆柱壳辐射声场的去耦特性影响

基于模态叠加法,采用Navier方程描述阻尼层,建立敷设粘弹性阻尼层的水下圆柱壳振动声辐射模型。与数值计算结果比对,验证了计算模型的可靠性。分析圆柱壳的径向均方振速和辐射声功率,研究了粘弹性阻尼层对水下圆柱壳辐射声场的去耦特性影响。结果表明,粘弹性阻尼层的径向均方振速频响曲线可以分作三个频段,当频率较高时,粘弹性阻尼层能降低辐射声功率;与壳体厚度相比,阻尼层厚度对阻尼层去耦特性的影响更大。     

充液圆柱壳的波传播和功率流特性研究

以一无限长弹性充液圆柱壳为研究对象，分别用Ｆｌｕｇｇｅ壳体理论与Ｈｅｌｍｈｏｌｔｚ方程分析管壁结构波运动和管内声场，通过管壁内表面的运动协调条件，建立此耦合系统的运动微分方程。分析了耦合波的传播特点。重点讨论在自由传播波作用时，由壳体中各内力传播的功率流，从能量角度分析了各种波的传播特点。     

壳间连接介质对双层壳声辐射性能的影响

研究了不同壳间连接介质的加筋双层壳的振动声辐射特性.基于Flügge壳体理论和Helmholtz波动方程,求解了双壳体声-流体-结构耦合方程,计算了有限长双层壳体在径向点激励下的声功率和振动速度级.结果表明,水层的耦合作用随频率的增高而降低,托板的耦合作用随频率的增高而增加,托板在内、外壳的振动传递中起着较大的作用.为了减小托板对振动及声辐射的影响,提出了阻尼托板结构,即在托板上添加阻尼材料,对含阻尼托板的圆柱壳声学特性进行了数值研究.结果表明,在中高频段,阻尼有效抑制了振动能量的传递,壳体的辐射声压明显降低,这对水下结构的减振降噪设计具有重要的参考意义.     

Singularities on the flow between two rotating surfaces

Summary Two coaxial surfaces of revolution rotate about the common axis of symmetry with almost the same angular velocity. At large Reynolds numbers, three singular surfaces are found. One over each surface of revolution and a cylindrical shear layer touching the outer surface. Outside the cylinder the velocity is determined by the velocity distribution over the two boundary layers, while inside the cylinder the fluid is at rest.With 5 Figures     

Vibration control of a simply supported cylindrical shell using a laminated piezoelectric actuator

Summary This paper develops a novel laminated piezoelectric actuator (LPA) to control the vibration of a cylindrical shell structure, which is fabricated through bonding multiple piezoelectric layers of the same property together. The electromechanically coupled equations of the system are derived based on the classic shell theory. A parametric study is then conducted to evaluate the effects of geometric and physical properties of the actuator on actuating forces. The results show that as the number of layers increases, the actuating forces per voltage produced by LPA in the axial, circumferential and radial directions of the shell all increase noticeably. The active vibration control of a simply supported cylindrical shell using LPA of different layer numbers is simulated as well under a velocity feedback scheme. It is indicated that with the same control voltage the LPA can obtain a better control performance than the conventional single layer piezoelectric actuator as expected and the targeted radial modal vibration of the shell is attenuated significantly.     

The Lyophilization of Dispersed Systems: Influence of Freezing Process,Freezing time,Freezing Temperature and RBCs Concentration on RBCs Hemolysis

ABSTRACT

In this work, we studied the influence of different parameters controlling cooling stage on biological dispersed system injury. The human red blood cell (RBCs) was chosen as work model. The study examined the influence of two freezing processes on RBCs hemolysis, one process producing big crystals, the other producing small crystals. Using both processes, we examined the effect of freezing temperature, freezing time, and RBCs concentration on injuries to RBCs. Freezing damage was assessed by the hematocrite measure before freezing and after thawing. The process producing a small number of big ice crystals (Pa) seems—in relation to the one producing a large number of small ice crystals (Pb)—to be less traumatic for the RBC, although the two are not statistically different. Freezing temperature and freezing time influence the preservation of RBCs. At 0 and ?20°C there were high preservation and total hemolysis, respectively. At ?5°C and ?10°C, the RBC hemolysis depends on freezing temperature and freezing time. The RBCs hemolysis rates increases when freezing time increases and when freezing temperature decreases. The rates of RBCs preserved decreases with RBCs concentration some with either the freezing process used (Pa or Pb). More, an accentuation of the difference between the two used freezing processes on RBCs hemolysis was retrieved. The analysis of the conductivity evolution within the RBCs suspension frozen showed that the destruction of the RBCs is had essentially to the solution effects. When the crystallization eutectic takes place, the RBCs are already completely destroyed.