循环床中气固两相局部传热传质规律的研究

本文对含湿颗粒在循环床中干燥过程的传热传质规律进行了实验研究。本文发展的一种利用双热电偶参考标定法，获得了气、固两相沿床高的局部温度。对气体表观流速，固体循环率，颗粒初始含湿量对传热传质的影响进行了分析和讨论。所获得的循环床中传热传质系数的实验关联式，可供干燥颗粒、造粒、粒面包裹等工业设计参考使用。     

中国垃圾的资源化利用

垃圾处理的要求是无害化、减量化和资源化.中国垃圾具有水分高、热值低、品质差的特点.文章分析了中国垃圾无害化、减量化和资源化的状况、优缺点,指出了资源化的目标和未来的发展方向,并讨论了相关国家政策的配套支持问题.     

Osmotic dehydration and convective drying of kiwifruit (Actinidia deliciosa) – The influence of ultrasound on process kinetics and product quality

The aim of this study was to assess the impact of ultrasound on two subsequent processes – initial osmotic dehydration and convective drying of kiwifruit (Actinidia deliciosa). The effect of ultrasound (at a frequency of 25 kHz) was assessed both in terms of process kinetics and product quality. During the study, three different osmotic agents were used – erythritol, sorbitol, and sucrose – in an aqueous solution at a concentration of 50% (w/w). The essential kinetic parameters were analyzed – water loss and increase of dry matter during osmotic dehydration, and evolution of moisture content and temperature of samples during convective drying (drying curves). Product quality was assessed on the basis of color, water activity, and content of relevant bioactive components – polyphenols and carotenoids. It was found that the application of ultrasound during osmotic dehydration resulted in higher water loss and solid gain. This surely results from the phenomena occurring during the propagation of the elastic waves in the liquid medium (mainly related to cavitation) and enhancement of the mass transfer. The use of ultrasound during convective drying also had a positive effect on the kinetics of this process. In most cases, during the ultrasonically assisted drying operations, a significant increase in drying rate was observed, leading to a reduction in drying time. This may be due to the intensification of both heat and mass transfer as a result of the mechanical and thermal effects of ultrasound. The assessment of product quality showed that the use of sugar alcohols was a good alternative to sucrose, and ultrasound-assisted convective drying increased the retention of valuable carotenoids and polyphenols. Moreover, in all dried kiwifruit slices, water activity was below 0.6, which can guarantee the microbiological stability of the tested samples.     

利用TD-NMR技术研究杨木高温干燥过程水分分布

木材中水分状态变化和迁移对木材的物理性质有重要影响.通过时域核磁共振技术(TD-NMR)可以从分子层面解读木材与水分的关系,可以为木材干燥、木制品加工提供理论依据和实践参考.该研究以北京杨为研究对象,通过对高温干燥过程中木材内部水分变化的自由感应衰减(FID)曲线和横向弛豫时间(T_2)进行测定与分析,探究木材干燥过程中水分状态变化及迁移过程.研究结果表明,FID和T_2信号量与木材含水率高度线性相关,由此可以计算木材在干燥过程中任意时刻的含水率.通过对干燥过程中水分T_2分布的分析表明:心材试件在干燥过程中,长弛豫时间自由水(c状态水分)的拟合面积出现了先减小后增大然后再减小的趋势,而边材试件中则不存在这种现象.在北京杨心材试件中含量最多的是弛豫时间为10 ms数量级的水分,而在边材试件中各状态水分含量差异较小,含量最多的是弛豫时间为100 ms数量级的水分.在高温干燥过程中,边材试件内各状态水分百分含量减少的速度快于心材,各试件中自由水的蒸发速度明显快于结合水.     

Pneumatic Drying of Solid Particle: Experimental and Model Comparison

Abstract

This article presents a mathematical model approach to studying the drying phenomena of solid particle in a pneumatic (flash) dryer. The analysis is focused on the pneumatic momentum, mass, and heat balance of the solid particle when it moves inside the reactor. A fixed bed fluidization model was used to calculate the forces balance on the single solid particle. By solving mass and heat balance occurred in the particle, the water/liquid removal efficiency can be calculated. To validate the model calculations, we conducted a set of experiments and compared the simulation with the experimental data. High-moisture, natural concrete sand, the additional material for portland cement, was used and dried along a vertical cylindrical tube with length of 2 m and diameter of 6.68 cm. The drying gas was supplied by a high-capacity air blower which was connected to the burner to produce 120 m³/h of drying gas with maximum temperature of 800°C.     

Comparison between airborne ultrasound and contact ultrasound to intensify air drying of blackberry: Heat and mass transfer simulation,energy consumption and quality evaluation

This study aimed at investigating the performances of air drying of blackberries assisted by airborne ultrasound and contact ultrasound. The drying experiments were conducted in a self-designed dryer coupled with a 20-kHz ultrasound probe. A numerical model for unsteady heat and mass transfer considering temperature dependent diffusivity, shrinkage pattern and input ultrasonic energies were applied to explore the drying mechanism, while the energy consumption and quality were analyzed experimentally. Generally, both airborne ultrasound and contact ultrasound accelerated the drying process, reduced the energy consumption and enhanced the retentions of blackberry anthocyanins and organic acids in comparison to air drying alone. At the same input ultrasound intensity level, blackberries received more ultrasound energies under contact sonication (0.299 W) than airborne sonication (0.245 W), thus avoiding the attenuation of ultrasonic energies by air. The modeling results revealed that contact ultrasound was more capable than airborne ultrasound to intensify the inner moisture diffusion and heat conduction, as well as surface exchange of heat and moisture with air. During air drying, contact ultrasound treatment eliminated the gradients of temperature and moisture inside blackberry easier than airborne ultrasound, leading to more homogenous distributions. Moreover, the total energy consumption under air drying with contact ultrasound assistance was 27.0% lower than that with airborne ultrasound assistance. Besides, blackberries dehydrated by contact ultrasound contained more anthocyanins and organic acids than those dried by airborne ultrasound, implying a higher quality. Overall, direct contact sonication can well benefit blackberry drying in both energy and quality aspects.     

可降解有机物湿解实验研究

选用杂草作为城市生活垃圾中可降解有机物的典型组分,研究了湿解参数对湿解后固体、气体和液体比例的影响,以及固体成分中有机质、黄腐酸、胡敏酸和大量营养元素的影响。结果表明,湿解应采用适当的高温和短的反应时间,如在 480 K 下湿解 0.25 h,固体成分保留最多,有机质含量最丰富,腐殖化程度最高,但大量营养元素的含量也最低。     

基于植物根系仿生的土壤热湿迁移数值模拟

以实验数据为依据,把土壤中的水分含量和水分梯度分布作为影响植物根系生长的环境因子,结合非饱和多孔介质中传热传质的数学模型,对冬小麦的根系生长进行仿生模拟,分析根系吸水对非饱和土壤湿分与热量传递的影响。在相同环境条件下,对裸土和有作物覆盖的土壤床中的热、湿迁移也进行了模拟比较。     

利用热像与生理实验法研究种子的优化传热传质

本文运用工程热物理和种子生理学科交叉的研究方法，在辐射振动流化干燥装置中，对白菜种子的动、静态干燥进行了热象测试分析，并且同步进行了种子的生理实验研究．结果表明种子的临界干燥温度是干燥时间和含水率的函数，当含水率较低及干燥周期较短时，种子的临界干燥温度可以提高，为种子的优化传热传质提供了理论依据．     

Moisture Migration in Wood Under Heating Measured by Thermal Neutron Radiography

The article addresses the transport of moisture due to high-temperature gradients resulting from heating by means of thermal neutron radiography. Moisture migration due to heating is quantified along the orthotropic directions of two wood species, spruce and beech, with high spatial and moisture content resolution. As the heat wave is propagating into the wood, the moisture content in the heated zone rapidly decreases, and moisture is transported due to the high-temperature gradient ahead of the heated zone, resulting in a zone with higher moisture content. Both the drying and the moisture accumulation areas evolve non-uniformly, depending on wood microstructure and orientation.     

Drying characteristics and quality attributes of apple slices dried by a non-thermal ultrasonic contact drying method

Drying is one of the most prevalent methods to reduce water activity and preserve foods. However, it is also the most energy-intensive food processing unit operation. Although a number of drying methods have been proposed and tested for the purpose of achieving a time- and energy-efficient drying process, almost all current drying methods still rely on thermal energy to remove moisture from the product. In this study, a novel use of power ultrasound was explored for drying of apple slices without the application of heat. The non-thermal ultrasound contact drying (US-CD) was performed in the presence of an air stream (26–40 °C) flowing over product surface to remove mist or vapor produced by the ultrasound treatment. The effects of the non-thermal US-CD, hot-air drying (HAD), and freeze drying (FD) on the changes in rehydration ratio, pH, titratable acidity, water activity, color, glass transition temperature, texture, antioxidant capacity, total phenols, and microstructures of the samples were evaluated. The moisture content of the apple slices reached below 5% (w.b.) after 75–80 min of US-CD, which was about 45% less than that of the HAD method. The antioxidant capacity and total phenol contents of the US-CD samples were significantly higher than that of the AD samples. The non-thermal ultrasonic contact drying is a promising method which has the potential to significantly reduce drying time and improve product quality.     

Effects of low-frequency ultrasonic pre-treatment in water/oil medium simulated system on the improved processing efficiency and quality of microwave-assisted vacuum fried potato chips

The effects of low-frequency ultrasonic pre-treatment in water/oil medium simulated system on the improved processing efficiency and quality of microwave-assisted vacuum fried potato chips were investigated. The water medium system (distilled water and 5% NaCl osmotic solution) and oil medium system (90 °C) were designed with different power levels of ultrasound to simulate the ultrasonic conditions. Results showed that the changes of moisture content, water loss, solid gain and dielectric properties of potato slices were facilitated by the ultrasonic treatment. LF-NMR analysis showed the binding force between the moisture and structure in the material was significantly (p < 0.05) weakened. The changes become greater with the increase of ultrasonic power levels. Microscopic channels and disruptions were induced on the microstructure by the ultrasonic treatment. The effective moisture diffusivity of vacuum fried (VF) potato chips was increased by about 56.2%-67.0% and 53.9% with the combination of microwave energy and the ultrasonic pre-treatment in water and oil medium simulated system, respectively. The oil uptake, hardness, shrinkage, total color change and water activity of vacuum fried samples were significantly (p < 0.05) decreased by the assist of microwave energy combined ultrasonic pre-treatment.     

Jet Impingement Cooling of a Hot Moving Steel Plate: An Experimental Study

In the current study, a hot moving steel plate of 6 mm thickness with an initial temperature of 900°C has been considered for jet impingement cooling. The experiment has been designed with the help of Design of Expert software to optimize the process parameters based on the highest cooling rate. The various subsurface transient temperature histories have been measured during the cooling process. The surface heat flux and surface temperature were calculated with the help of a commercial inverse heat transfer solver called INTEMP. The experimental result has been presented in terms of cooling rate and critical heat flux.     

The effect of frozen soil layer thickness on thermal emission at the wavelengths 3.6–11 cm

The results of experimental investigation of temporal dynamics of radiobrightness temperature at the wavelengths 3.6, 5, and 11 cm in the course of frost penetration and thawing are presented for the soils with different humus content. Using the method of simulating emission from a horizontally stratified medium, it is shown that radiobrightness temperature variation is related to changes in the frozen soil layer thickness. It is noted that that dielectric permittivity of the frozen layer at the temperatures around 0 °C is controlled by non-frozen bound water, whose content depends on the soil type. It is also underlined that in certain cases proper interpretation of the experimental data requires inclusion of the soil moisture motion towards the cold front into consideration. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 5–10, September, 2006.     

半环对撞流干燥的实验研究

进行了半环对撞流干燥的流动与干燥特性实验．得出了反映系统流动规律的颗粒停留时间随载带率的变化、颗粒速度沿径向与周向的分布及气团相对速度沿运动方向的变化等;研究了空气温度、载带率及物料初始合湿量等因素对干燥过程的影响,并得出了相应的实验关联式．根据实验与计算结果,提出了提高半环对撞流干燥速率的有效途径．     

Some dielectric properties of monoclinic lysozyme crystals

The frequency dependences of the dielectric loss tangent and the magnitude of the impedance for monoclinic lysozyme single crystals and the solution used for preparing the crystals were investigated. The measurements were performed in the frequency range 1–10⁷ Hz under exposure of the crystals at a temperature of 25°C, cooling to ?20°C, and subsequent heating. The analysis of the experimental dielectric properties of the crystals demonstrated that drying of the crystals at room temperature in air initially led to the removal of “free” water with the content approximately equal to 65% of the total content. Further drying resulted in the removal of “bound” water. The solvent contained in the crystals (～26 wt %) was frozen at a constant temperature of approximately ?6.5°C. The permittivity of the dehydrated crystal at high frequencies was considerably higher than that of ice.     

The Effect of Post Hot Compaction on Crystallinity and Thermal Behavior of Ultra-High Molecular Weight Polyethylene Fiber Laminates

Thermal compacting of previously prepared ultra-high molecular weight polyethylene (UHMWPE) fiber laminates can raise its melting temperature and crystallinity. In this article, thermal shrinkage and the effect of post hot compaction on a commercial UHMWPE fiber laminate at various temperatures was investigated. The temperature range of post hot compaction was between 115 and 145°C, while other processing parameters like pressure, time, and cooling rate were kept constant during compaction. The shrinkage of the fiber laminates increased slowly up to 138°C; as soon as the temperature passed 140°C, the shrinkage increased rapidly and reached its maximum value very quickly. The crystallinity of the fiber laminates increased with rising temperature up to 135°C, then decreased at 145°C.     

Experimental Investigations on Latent Heat Storage Unit using Paraffin Wax as Phase Change Material

Thermal performance of a latent heat storage unit is evaluated experimentally. The latent heat thermal energy storage system analyzed in this work is a shell-and-tube type of heat exchanger using paraffin wax (melting point between 58°C and 60°C) as the phase change material. The temperature distribution in the phase change material is measured with time. The influence of mass flow rate and inlet temperature of the heat transfer fluid on heat fraction is examined for both the melting and solidification processes. The mass flow rate of heat transfer fluid (water) is varied in the range of 0.0167 kg/s to 0.0833 kg/s (1 kg/min to 5 kg/min), and the fluid inlet temperature is varied between 75°C and 85°C. The experimental results indicate that the total melting time of the phase change material increases as the mass flow rate and inlet temperature of heat transfer fluid decrease. The fluid inlet temperature influences the heat fraction considerably as compared to the mass flow rate of heat transfer fluid during the melting process of the phase change material.     

Hydrothermal hot pressing for recycling of waste glass

Abstract

Recycling of waste glasses has been conducted by a hydrothermal hot-pressing method to produce high density compacts. Our research was focussed on the intluence of various reaction variables (temperature, time, water content and loading pressure) during compaction of several types of waste glasses. The compaction of all glasses starts around 120°C and proceeds rapidly with increasing temperature. Under hydrothermal hot pressing conditions, the compaction of the waste glass is most strongly controlled by temperature and water content, and affected to a lesser degree by reaction time and loading pressure. A maximum tensile strength of 65 MPa was obtained for ‘blue’ glass at 200°C, 10wt% water content, after applying 60 MPa loading pressure for 2 hours.     

Y_(0.5)Gd_(0.5)Ba_2Cu_3O_(7-δ)体系中通氧时间对超导转变温度的影响

研究了高温氧化物超导体Y0.5Gd0.5Ba2Cu3O7-δ体系中通氧时间对超导转变温度及超导转变温区的影响。Y0.5Gd0.5Ba2Cu3O7-δ样品是按相等摩尔数的Gd与Y元素配比,采用传统的固相反应法烧结而成的多晶块材。实验结果显示:Y0.5Gd0.5Ba2Cu3O7-δ烧结样品与YBa2Cu3O7-δ烧结样品均具有很好的单相性,在一定的通氧条件下其超导临界转变温度TC与超导初始转变温度TCO值相对YBa2Cu3O7-δ烧结样品有提高。文中对此结果进行了讨论。