共查询到20条相似文献,搜索用时 140 毫秒
1.
2.
3.
4.
5.
6.
7.
液氮喷淋流态化速冻系统及冷冻性能研究 总被引:5,自引:0,他引:5
液氮喷淋流态化速冻新系统是以液氮为冷源,结合液氮喷淋预冻和流态化速冻两种冻结方法于一体的食品速冻装置。本文建立了基于新系统的食品冷冻过程的焓法数学模型,计算了黄瓜片在不同冻结条件下的降温过程和冷冻时间,同时对冻品质量进行了分析。 相似文献
8.
9.
激光诱导间质肿瘤热疗的数值模拟和实验研究 总被引:1,自引:0,他引:1
本文在考虑生物组织物性动态变化的情况下建立了激光诱导间质肿瘤热疗(LITT)的物理数学模型,采用MonteCarlo方法数值模拟了LITT中激光能量在生物组织内的传输过程,基于Pennes生物传热方程和Arrhenius方程数值求解了组织内的温度分布和热损伤体积的变化,分析了热物性及血液灌注率的动态变化对LITT过程的影响,并与相应的离体实验结果进行了对比。数值模拟结果表明,组织的热物性及血液灌注率的动态变化对于热损伤体积的变化具有重要的影响。因此在激光诱导间质肿瘤热疗的数值模拟中应该考虑热物性及血液灌注率的动态变化以期为临床治疗方案的制定提供更为准确的依据。 相似文献
10.
研究了不同冷冻速率下蚕豆热物性的变化规律。利用Hot Disk得到蚕豆在-30~30℃下的热导率变化曲线;通过DSC和低温冷冻实验台,冷冻速率在5~80℃/min条件下将蚕豆切片进行冷冻实验,得到了不同冷冻条件下冻结点、结晶点及比热容的变化规律。测试结果表明:蚕豆热导率随着温度的降低先减小再增大;冻结点随着降温速率的增大而增大;蚕豆的结晶点在降温速率小于20℃/min时出现浮动,但总体上,结晶点随着降温速率的增大而降低。在不同降温速率下,比热容随温度的变化规律基本相同,但在冷冻相变过程中发生剧烈变化。通过对冷冻过程中蚕豆热物性的实验研究,为冷冻干燥种子的传热传质分析提供了实验数据的支撑。 相似文献
11.
Fast radial NMR microimaging protocols are presented for studying time dependent profiles of unfrozen water and ice during the freezing of extruded pasta (spaghetti). The radial imaging profiles of unfrozen water are analysed with an approximate analytic solution based on a generalized Plank model of freezing as well as by a more exact numerical simulation. The potential of the imaging technique for studying freezing kinetics in other food materials is discussed. 相似文献
12.
13.
14.
Esad Tombarević & Igor Vu&scaron anović 《advances in applied mathematics and mechanics.》2011,3(3):354-369
Phase change in ice-water systems in the geometry of horizontal
cylindrical annulus with constant inner wall temperature and adiabatic
outer wall is modeled with an enthalpy-based mixture model. Solidification
and melting phenomena under different temperature conditions are
analyzed through a sequence of numerical calculations. In the case of freezing
of water, the importance of convection and conduction as well as the influence
of cold pipe temperature on time for the complete solidification is examined.
As for the case of melting of ice, the influence of the inner pipe wall
temperature on the shape of the ice-water interface, the flow and temperature
fields in the liquid, the heat transfer coefficients and the rate of melting
are analyzed. The results of numerical calculations point to good qualitative
agreement with the available experimental and other numerical results. 相似文献
15.
We overview several recent experimental and numerical observations, which are at odds with the vortex glass theory of the freezing of disordered vortex matter. To reinvestigate the issue, we performed numerical simulations of the overdamped London-Langevin model, and use finite size scaling to analyze the data. Upon approaching the transition the initial vortex-glass-type criticality is arrested at some crossover temperature. Below this temperature the time scales continue growing very quickly, consistent with the Vogel-Fulcher form, while the spatial correlation length ξ stops exhibiting any observable divergence. We call this mode of freezing the vortex molasses scenario. 相似文献
16.
利用三维分子动力学模拟方法,研究了纳米尺度水滴撞击冷壁面的结冰过程.数值模拟中,统计系统采用微正则系综,势能函数选用TIP4P/ice模型,温度校正使用速度定标法,牛顿运动方程的求解采用文莱特算法,水滴内部结冰过程则通过统计垂直方向水分子温度分布来判定.研究发现,当冷壁面温度降低时,水滴完全结冰的时间减小,但水滴降至壁面温度的时间却增大;同时随着壁面亲水性降低,水滴内部热传递速度减慢(尤其是冷壁面与水滴底端分子层间),水滴内部温度趋于均匀,但水滴完全结冰时间延长. 相似文献
17.
The onset of spin-glass freezing in dilute Ising systems with long-range interactions is investigated with the use of numerical simulations. We show that taking pair correlations explicitly into account results in the renormalization of the interaction matrix and suppression of the density of localized states compared with conventional mean field theory. Application of the theory to the RKKY interaction in the dilute limit raises the question of the appropriate boundary eigenvalue of the effective interaction matrix that separates localized and extended states. We identify the onset of spin-glass freezing with the temperature T
g at which this boundary eigenvalue is equal to one. Numerical simulations reproduces the linear concentration dependence of T
g in the very dilute limit, in agreement with scaling relations, and show a significant improvement over the conventional mean-field theory in the value obtained for the freezing temperature. 相似文献
18.
Water that remains unfrozen at temperatures below the equilibrium bulk freezing temperature, in the presence of ice, is sometimes called unfreezable or bound. This paper analyses the phenomenon in terms of quantitative measurements of the hydration interaction among membranes or macromolecules at freezing temperatures. These results are related to analogous measurements in which osmotic stress or mechanical compression is used to equilibrate water of hydration with a bulk phase. The analysis provides formulas to estimate, at a given sub-freezing temperature, the amount of unfrozen water due to equilibrium hydration effects. Even at tens of degrees below freezing, this hydration effect alone can explain an unfrozen water volume that considerably exceeds that of a single 'hydration shell' surrounding the hydrophilic surfaces. The formulas provided give a lower bound to the amount of unfrozen water for two reasons. First, the well-known freezing point depression due to small solutes is, to zeroth order, independent of the membrane or macromolecular hydration effect. Further, the unfrozen solution found between membranes or macromolecules at freezing temperatures has high viscosity and small dimensions. This means that dehydration of such systems, especially at freezing temperatures, takes so long that equilibrium is rarely achieved over normal experimental time scales. So, in many cases, the amount of unfrozen water exceeds that expected at equilibrium, which in turn usually exceeds that calculated for a single hydration shell. 相似文献
19.
The time-resolved fluorescence spectrum I(, t) of the porphyrin derivative Fe(TPP)Cl in solution is measured. Experiments show that when the temperature is at least 5 K above the freezing point of the solvent, the sample fluorescence does not change with temperature. But when the temperature approaches the freezing point of the solvent, the fluorescence relaxation of the high concentration sample solution is faster than that of the above normal one. Furthermore, fluorescence spectra for various times after excitation have different shapes. Analysis shows that in this case the fluorescence is composed of two components with different relaxations and spectra. The two components are attributed to monomer and aggregates respectively. 相似文献
20.
Ping Chen Wenjuan Liu Yanmin Zhao Tianlong Huang Xiaofei Li 《Journal of Macromolecular Science: Physics》2020,59(7):427-439
AbstractThe technique of thermally induced phase separation (TIPS) is favorable for the fabrication of a porous scaffold due to a number of advantages. In this work the poly(L-lactide-co-glycolide-co-ε-caprolactone) (PLLGC) terpolymer was synthesized by melt copolymerization and porous scaffolds thereof from its solution in 1,4-dioxane were fabricated by using the TIPS method. The effects of fabrication parameters, including polymer concentration and freezing temperature, on the morphology, pore size and mechanical properties were studied. The results showed that the average pore size of the PLLGC porous scaffold increased with a decrease in PLLGC concentration and the pore size resulting from freezing at 4?°C (about 20–100?μm) was significantly larger than for other samples (20–50?μm) frozen at lower temperatures. The porosity of the scaffolds decreased with increasing PLLGC concentration or decreasing freezing temperature. On the other hand, the compressive strength of the scaffolds increased with the increase of PLLGC concentration or the decrease of freezing temperature, as would be expected. The present results can be applied in design to control the processing parameters of TIPS for a scaffold with desired pore morphology. 相似文献