Numerical investigation on freeze-drying of aqueous material frozen with pre-built pores

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.

真实气体效应对气波波动和能量传递过程的影响

气波制冷机通常根据理想气体模型进行设计与制造。随着天然气藏的操作参数逐渐向高压力、高压比工况下发展,真实气体效应已不容忽视。以新疆塔里木盆地牙哈气田真实天然气藏为介质,选取多参数BWR方程,建立了高压比条件下双开口气体波制冷机的二维计算模型,深入探讨了非连续边界条件下气波制冷机内真实气体效应对气波波动和能量传递过程的影响规律。数值计算结果表明,在不同工况下,理想甲烷和真实天然气的波系运动相似,但真实天然气的压缩波和膨胀波明显滞后于理想甲烷。真实天然气低温介质比理想甲烷更早完全排出,在低转速工况下两者之间的差异随着压比增加而逐渐增大,当压比为6时,低温端口的长度可以缩短56.5%。排出的真实天然气温度低于理想甲烷,因此真实天然气等熵膨胀制冷效率优于理想甲烷。本研究成果揭示了真实气体效应对气波运动和能量传递的影响,可为用于天然气地面工程的气波制冷机优化设计提供了支持。

气波振荡管波系运动与能量传递效率影响机制研究

建立了双开口气波制冷机振荡管三维大涡模拟模型,获得了气波振荡管内波系运动特征。针对高压入射喷嘴与气波振荡管在高速旋转交汇过程引发能量损失的问题,探讨了气波制冷机操作参数和结构参数对能量传递效率的影响机制。数值计算结果表明,在两者切入-覆盖-切出的交汇过程中,伴随着强烈的涡旋和湍流动能耗散。定义瞬时湍流动能损失比R定量评定能量损失程度。研究发现,涡旋中心处R值较大,且随绝压压比增大先增大后减小,当绝压压比为3.61时达到最大值9.0%。R值随转速提高而减小,当转速由1100 r/min提高至2000 r/min时,涡旋中心处R值由10.7%减小至6.0%。远轴壁面和近轴壁面涡旋中心处R值都随着管道宽度增加而减小,近轴壁面涡旋中心处的R值大于远轴壁面涡旋中心处,且两侧差值最大达3.2%。减小入射绝压压比、提高转速和增加气波振荡管宽度有助于减小R值,从而提高气波制冷机能量传递效率,对大流量气波制冷机设计具有指导意义。

Study on wave rotor refrigerators

As a novel generation of a rotational gas wave machine,the wave rotor refrigerator(WRR)is an unsteadyflow device used for refrigeration,in whose passages pressured streams directly contact and exchange energy due to the movement of pressure waves.In this paper,the working mechanism and refrigeration principle are inves-tigated based on the one-dimensional unsteadyflow theory.A basic limitation on main structural parameters and operating parameters is deduced and the wave diagram of WRR to guide designing is sketched.The main influential factors are studied through an experiment.In the DUT Gas Wave Refrigeration Studying and Development Center(GWRSDC)lab,the isentropic efficiency can now reach about 65%.The results show that the WRR is a feasible and promising technology in pressured gas refrigeration cases.

Functional delivery vehicle of organic nanoparticles in inorganic crystals

Encapsulation of bioactive substances for extended shelf life and controlled,targeted release is critical for their applications in food and drug delivery.Here,a new method has been developed to encapsulate bioactive molecules in the crystal composites,showing greatly enhanced stability and unique pHtriggered response.Chlorophyll,a model bioactive,is first loaded in shellac nanoparticles via coprecipitation with a high encapsulation efficiency,and then the chlorophyll-loaded nanoparticles are incorporated into calcite crystals grown from a gel media containing the nanoparticles.Under the protection of shellac nanoparticles and calcite crystals,chlorophyll shows excellent stability even under light.Encapsulated chlorophyll could only be released by first dissolving the calcite crystals under acidic condition and then dissolving the shellac nanoparticles under alkaline condition.The unique pHtriggered release mimics the pH change from acidic in the stomach to alkaline in the intestine and is thus well suited for controlled,targeted intestinal release.This work suggests that the crystal composites are an ideal delivery vehicle for the functional design of bioactive molecules.

Study on Wall Temperature Distribution of Oscillating Tube

The wall temperature distribution and heat transfer process of the oscillating tube have been investigated in thispaper using both numerical simulation and experimental method. The wall temperature of oscillating tube increasesrapidly in the inlet and then decreases slowly, moreover, the rally phenomenon of wall temperature nearthe closed end is observed. With the increase of jet flow frequency, the highest wall temperature increases and thelocation of that moves towards the inlet. The velocity of pressure wave in the oscillating tube almost remainsconstant even its intensity changes. The quantity of heat transfer between the gas and inner wall of the oscillatingtube determines the wall temperature of every location, and the pressure wave disturbance can cause the heattransfer quantity change. Each pressure wave has its own disturbance range. The wall temperature distribution canbe explained by the change of pressure wave intensity and its disturbance time. Besides, the step and rally of walltemperature are discussed, which shows that the conditions of heat transfer can be improved due to intersection orreflection of pressure waves.