MICROWAVE FREEZE DRYING CHARACTERISTICS OF BEEF

ABSTRACT

Microwave freeze drying characteristics of unsaturated raw beef were studied experimentally for various levels of electric field strength, vacuum pressure, sample thickness and initial saturation. The results show that drying time is proportional to initial saturation and inversely proportional to the electric field strength and sample thickness. The effect of vacuum pressure on drying time is negligible. Some advantages of microwave freeze-drying over conventional freeze drying with radiant heating are pointed out     

FREEZE DRYING CHARACTERISTICS OF MEDICINAL HERBS

The demand on traditional herb medicine shows a tremendous increase. Conventionally, medicinal herbs are dried at high temperatures, causing quality deterioration. The freeze-drying characteristics of medicinal herbs were studied, and the quality of the freeze-dried products assessed. The herbs studied were medicinal ginger and Javanese pepper.

It was found that drying time, was more influenced by chamber pressure and freezing rate than by the surface temperature of the product. Higher chamber pressures and faster freezing rates tended to shorten the initial (primary) drying time but lengthen the secondary drying time. Quality of the freeze-dried product was assessed as slightly lower than the quality of the raw material, but higher than when oven dried at 35-40°C, and met the MMI standard.     

非饱和含湿多孔介质微波冷冻干燥过程传热传质分析

基于升华冷凝模型,对非饱和含湿多孔介质微波冷冻干燥过程作了数值计算．结果表明,干燥过程中不饱和含冰区内的冰饱和度有较大变化．通过与不考虑升华冷凝区相比较,表明升华冷凝区的存在不可忽略．     

初始饱和度对微波冷冻干燥过程传热传质的影响

以非饱和含湿牛肉为例,进行了微波冷冻干燥实验研究。获得了干燥时间与物料初始饱和度近似成正比的结论。与升华面模型的计算结果比较表明,升华冷凝模型更符合实验规律,证实了非饱和含湿多孔介质微波冷冻干燥时升华冷凝区的存在。     

MOISTURE DIFFUSIVITY BEHAVIOR DURING FREEZE DRYING UNDER MICROWAVE HEATING POWER APPLICATION

The necessary criteria for the design of a freeze-drying operation, where radiant and microwave heating are combined, are analyzed in this work. Microwave heating presents indubitable advantages for enhancing drying kinetics. Modifications of different value characteristics must be also considered. Different freeze-drying strategies using MW heating are analyzed taking into account kinetics and diffusivity behavior compared to a constant diffusivity model. A microwave on-off cycled strategy with simultaneous up-down modification of pressure was found an acceptable power regulation system when magnetrons, whose field strength exceeds the breakdown voltage of gas, are used. In this case, chamber pressure becomes a convenient control parameter to avoid plasma discharge and subsequent melting of product. Different evolutions of specific power inputs per gram were proposed depending on the size and disposition of the product.     

MOISTURE DIFFUSIVITY BEHAVIOR DURING FREEZE DRYING UNDER MICROWAVE HEATING POWER APPLICATION

The necessary criteria for the design of a freeze-drying operation, where radiant and microwave heating are combined, are analyzed in this work. Microwave heating presents indubitable advantages for enhancing drying kinetics. Modifications of different value characteristics must be also considered. Different freeze-drying strategies using MW heating are analyzed taking into account kinetics and diffusivity behavior compared to a constant diffusivity model. A microwave on-off cycled strategy with simultaneous up-down modification of pressure was found an acceptable power regulation system when magnetrons, whose field strength exceeds the breakdown voltage of gas, are used. In this case, chamber pressure becomes a convenient control parameter to avoid plasma discharge and subsequent melting of product. Different evolutions of specific power inputs per gram were proposed depending on the size and disposition of the product.     

SHRINKAGE CHARACTERISTICS OF STRAWBERRIES OSMOTICALLY DEHYDRATED IN COMBINATION WITH MICROWAVE DRYING

The subject of this paper is to study the shrinkage of strawberries as a function of the moisture ratio during microwave-convective drying. Strawberries were pre-treated and osmotically dehydrated and dried at power levels 0.1 and 0.2W/g, based on initial mass. The main results showed that the shrinkage has a linear relation with moisture ratio; the equivalent diameter of the strawberry has a reciprocal logarithmic function with moisture ratio; the change in volume was bigger for the fruits osmotically dehydrated than for the not osmotically dehydrated ones, power level exerts influence on shrinkage and equivalent diameter for pre-treated and osmotically dehydrated samples.     

THIN-LAYER DRYING CHARACTERISTICS AND MODELING OF CELERY LEAVES UNDERGOING MICROWAVE TREATMENT

The effect of microwave drying on moisture content, moisture ratio, drying rate, drying time, and effective moisture diffusivity of celery leaves (Apium graveolens) was investigated. By increasing the microwave output power from 180 to 900 W the drying time decreased from 34 to 8 min; by increasing the sample amount from 25 to 100 g, the drying time increased from 25 to 49 min. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among the models proposed, the semi-empirical Midilli et al. model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on the Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

多孔纤维状物质的冷冻干燥模型

通过对草菇进行冷冻干燥实验,研究了过程中样品的中心温度及水分率随时间的变化关系．对冻干过程中物料干燥层和冰冻层进行质量和热量衡算,建立了升华─吸附─解吸数学模型．实验值与模型计算值吻合良好．     

MICROWAVE DRYING OF MULTICOMPONENT SOLS

Extensive studies on microwave drying of multicomponent materials have been carried out in order to determine dielectric properties of metalsiloxane sols, define the healing and drying characteristics of metalsiloxane sols and gels, develop the mathematical model of thermal processing, and design the continuous microwave dryer that could be used in an industrial scale     

MICROWAVE DRYING OF MULTICOMPONENT SOLS

ABSTRACT

Extensive studies on microwave drying of multicomponent materials have been carried out in order to determine dielectric properties of metalsiloxane sols, define the healing and drying characteristics of metalsiloxane sols and gels, develop the mathematical model of thermal processing, and design the continuous microwave dryer that could be used in an industrial scale     

FREEZE DRYING WORLD UPDATE IN DRYING TECHNOLOGY

Spectral Sciences, Inc. is developing a multipoint humidity monitor for drying application in the pulp and paper industry. The humidity is measured by monitoring near-infrared optical absorption in the process stream atmosphere. An array of sensor heads distributed throughout the plant is linked by fiber optic cables to a single source/readout device which can be located in a control room hundreds of meters away. The sensor heads and cables are modular. allowing for raid installation and reconfiguration of a distributed sensor system in process control applications. The method used for quantifying the optical absorption provides substantial stability, accuracy, and signal processing advantages over standard wavelength scanning or band pass techniques. The laser diode's output wavelength is actively locked to the center of a water absorption line, thereby providing a constant monitor of water vapor concentration which is insensitive to all other species in the process stream. Wavelength modulation and second harmonic detection techniques are used to quantify the water vapor concentration. A simultaneous temperature measurement then permits an output of the absolute humidity or humidity ratio for process monitoring or control     

EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING

ABSTRACT

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.     

EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.     

冷冻干燥法制备羟基磷灰石多孔支架

采用冷冻干燥法制备出多孔羟基磷灰石(hydroxyapatite,HA)支架,观察了支架的微观形貌,研究了HA浆料固含量和孔隙率、冷冻速率和孔径尺寸的关系.结果表明:通过调整工艺参数可以使制备出的多孔支架的孔隙率和平均孔径尺寸分别在45%~85%、100~800μm之间变化,孔的连通性较好.支架孔隙率随着浆料固含量的降低而升高,孔隙率最高可达到85%.孔径尺寸随着冷冻速率的升高而减小,减小的速度不断降低.当冷冻速率在1.3~3℃/min之间变化时,孔径尺寸约为800~300μm;当冷冻速率分别为9℃/min和11℃/min时,得到支架的孔径尺寸却相差不大,在90～110μm之间.     

SHRINKAGE OF STRAWBERRIES DURING MICROWAVE DRYING

ABSTRACT

Strawberries were pretreated with ethyl oleate and sodium hydroxide solution to make the skin transparent to moisture diffusion. The treated berries were dried with convective air at 45°C and microwaves at two power levels of 0.1 and 0.2 W/g. During the drying process change in shrinkage ratio with respect to moisture ratio was studied. Also, the change in equivalent diameter of strawberries in correlation with moisture ratio was investigated. During drying the variation in surface and centre temperatures with moisture content and time was studied. It was observed that there is a direct relation between the shrinkage and moisture ratio. The equivalent diameter of the berry has a logarithmic function with respect to the moisture ratio.     

MICROWAVE VACUUM DRYING OF BANANA SLICES

Vacuum drying of banana slices was studied in a domestic microwave oven. The results show that banana temperature rises uniformly and rapidly to the saturation water vapor temperature corresponding to the vacuum used then rises slowly until most of the free moisture is lost. The thermal and drying efficiencies were found to drop from almost 100% at the beginning of the drying (high moisture content) to as low as 40% and 30% respectively at the end of drying. Both efficiencies were found to increase with the use of vacuum, especially at low moisture content.