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%.     

食品在低温箱和连续式冻结隧道中的冻结过程的比较分析

本文通过食品在低温箱中的冻结过程和在连续冻结隧道装置中的冻结过程的实验研究结果的进行对比分析，得出食品在低温中冻结时，冻品表面温度在冻结中心温度处于—1℃～—5℃的区域时会出现温度回升的现象，而连续式冻结隧道中不存在这个现象，并从理论上对其原因进行了分析。另外，冻结曲线的结果还表明，在相同冻品和品质要求的前提下，采用连续冻结隧道比较节能。     

鲜食玉米冻结过程传热分析及冻结时间的研究

采用数值方法，将鲜食玉米模拟为具有同轴的双层圆柱，建立数学模型，并用改进的焓法进行求解，对鲜食玉米的冻结过程进行传热分析和冻结时间的预测。研究结果表明，该模型可以用来预测具有同轴双层圆柱特征尺寸的食品的冻结时间，最大相对误差为5．6％。冻结过程中玉米轴部分相变界面的移动速度明显小于玉米粒部分。而且鲜食玉米冻结时间随着送风速度的不同有很大的变化。     

液氮冻结食品冻结时间的计算方法及实验验证

冻结时间是评价冻结食品质量的重要指标,正确计算冻结时间是食品冻结装置优化设计及运行的关键。本文通过建立液氮速冻实验平台,测试了食品的冻结时间,介绍了现有的理论模型,选择了几种典型的计算方法应用于食品冻结,并将各模型的理论结果与实验值进行比较,分析各偏差原因,获得计算食品冻结时间最准确的方法。以有限长圆柱状食品为例,通过研究发现在整个氮气温度场中国际制冷学会模型计算结果与实验值最相近,平均偏差为8.86%,分段计算法次之,平均偏差小于15%。     

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。     

食品冻结过程若干影响因素的实验研究

利用自行研制的多功能低温实验台,对猪肉、芋艿、香蕉和糯米小圆子等进行了冷冻实验研究,实验测得猪肉、芋艿、香蕉和糯米小圆子的初始冻结温度分别为:-1.62℃、-1.4℃、-1.24℃和-0.9℃;分析了这些食品的形状、堆积方式、传热方式、冷气流方向和食品纤维方向等因素对食品冻结时间的影响.并研究了采用不同包装材料包装食品后,在冷冻过程中对食品质量和冻结时间的影响.     

复杂形状食品冻结时间的几何因子预测法

本文阐述了用于计算复杂形状食品冻结晶解冻时间的几何因子法，给出了大平板冻结和解冻时间及多种复杂状食品形状因子的计算公式。经验证，利用形状因子法计算各种形状食品冻结和解冻时间的精度较高。     

冷冻食品与现代冻结装置

本文介绍目前国内外冷冻食品的发展动态,影响食品冻结时间主要因素的实验研究,以及现代食品冻结装置国内外的进展状况.     

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。     

有限长圆柱状食品冻结时间的计算方法及实验验证

食品冻结时间的准确计算关系到食品冻结装置的优化设计及运行.文中提出了一种新的食品冻结时间计算方法,将冻结时间划分为三个阶段:冷却阶段、冻结和再降温阶段,并对各个阶段建立了动态计算模型.通过对有限长圆柱状食品的实验研究,将普朗克计算式与通过该模型计算得到的结果和实验数据进行比较,结果证明建立的计算模型是可靠的.     

有限长圆柱状食品冻结时间的计算方法及实验验证

食品冻结时间的准确计算关系到食品冻结装置的优化设计及运行。本文提出了一种新的食品冻结时间计算方法，将冻结时间划分为三个阶段：冷却阶段、冻结和再降温阶段，并对各个阶段建立了动态计算模型。通过对有限长圆柱状食品的实验研究，将普朗克计算式与通过该模型计算得到的结果和实验数据进行比较，结果证明建立的计算模型是可靠的。     

Freezing time predictions for regular shaped foods: a simplified graphical method

A graphical method is proposed for the estimation of freezing times of foods been developed from the predictions of a numerical model which solves the heat balance for a food undergoing freezing. The method is valid for foods with different shapes (flat plate, cylinder and sphere) and covers a wide range of working conditions for industrial freezers. It also enables the prediction to be made for any given end temperature in the thermal centre of the food. Freezing times predicted by this method have been compared with published experimental data, giving an average error in the predicted values of only 4%.     

Freezing of foods under surface boiling boundary conditions

The surface boiling boundary condition is encountered in the freezing of foods when foods are immersed in boiling freezants such as R12. This phenomenon was incorporated in a mathematical model of the freezing process as a surface temperature dependent convective boundary condition. A finite difference numerical scheme was formulated to solve the model for one- and two-dimensional geometries. The pool boiling characteristic for R12 was obtained by inverse heat transfer analysis of the experimental quenching curves of a transient calorimeter. The model was used to simulate the experimental freezing processes with reasonable agreement.     

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.     

Freezing time and rate of cauliflower florets under different freezing conditions

In this study, the freezing time and rate of 1 cm³ cauliflower floret samples were determined under different freezing conditions in an air blast freezer. Four different air temperatures (−20, −25, −30 and −35°C) and six different air velocities (70, 131, 189, 244, 280 and 293 m min⁻¹) were applied in the freezer, and the freezing rate and time of cauliflower pieces were determined under each condition. The freezing time of cauliflower samples frozen with cold air at −20°C and 280 m min⁻¹ was similar to that of samples frozen with cold air at −35°C and 70 m min⁻¹. When the velocity of air was increased from 70 m min⁻¹ to 293 m min⁻¹, the freezing time was approximately halved.     

液氮冻结装置中液氮耗量与冷冻能力的分析

建立了焓法数学模型，利用数值诸方法计算了模拟对象黄瓜片冻结前后的能量变化量和冻结时间，分析了三种不同装置五种冻结条件下的液氮冷量利用量、液氮耗量、冷冻能力以及冻前预冷的影响作用，提出了更合理的装置使用方案和经济性措施。     

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,完全冻结时间越短;在冻结过程的初始时刻,接触角越小,液滴底部温度越低;当冻结时刻相同、液滴高度一致时,液滴表面的温度和液相分数均比液滴内部低;接触角相同时,溶液质量分数与液滴的开始冻结温度成反比,与完全冻结时间成正比。对比实验结果与模拟可知,不同质量分数的氯化钠液滴在接触角为60°和100°时,冻结时间的变化趋势一致,但实验值大于模拟值。