Experimental Study of the Heat and Mass Transfer During Drying in a Fluidized Bed Dryer

Drying curves obtained in a pilot-scale fluidized bed dryer using biological source solids (sawdust, soya and fish meal) were used to estimate the parameters involved in heat and mass transfer phenomenas: heat transfer coefficient and moisture diffusivity coefficient. Parameters involved in mass transfer were estimated from drying models based on diffusional mechanisms and others that in addition consider internal and external resistance to the mass transfer. The estimate ef ective diffusivity coefficient was between 2x10-11 to lx10 (m2/s) for the considered products. Heat transfer coefficient was estimated from drying data points in the constant drying rate period when the external resistance to the mass transfer controls the process.     

Analysis of Fluidized Bed Drying Kinetics on the Basis of Interphase Mass Transfer Coefficient

A particular way to define fluidized bed drying kinetics on the basis of interphase mass transfer coefficient and the conception of general kinetic curve has been described. The presented method, which allows for minimization of laboratory tests, has been checked experimentally. The method for calculating of mass transfer interphase coefficient in the constant rate period of fluidized bed drying based on Kunii and Levenspiel bubbling bed model is shown.     

Analysis of Fluidized Bed Drying Kinetics on the Basis of Interphase Mass Transfer Coefficient

A particular way to define fluidized bed drying kinetics on the basis of interphase mass transfer coefficient and the conception of general kinetic curve has been described. The presented method, which allows for minimization of laboratory tests, has been checked experimentally. The method for calculating of mass transfer interphase coefficient in the constant rate period of fluidized bed drying based on Kunii and Levenspiel bubbling bed model is shown.     

超微粉体浆料惰性粒子流化床干燥过程传热传质特性

结合超微钛白粉和磁记录用钡铁氧体磁粉制备中粘性悬浮液混合浆料的脱水干燥过程,研究了在直径为145 mm的惰性粒子流化床中对悬浮液浆料进行脱水干燥的热量和质量传递的基本规律, 所得结果可为工程设计的操作参数选择提供依据, 对其他类似的超微粉体浆料的脱水干燥有参考价值.     

振动流化床中水平换热管与粗钛矿传热特性的研究

以粗粒级原钛矿为实验物料,测定了振动流化床与水平加热管间的传热系数,研究了粗钛矿在流化状态下的传热特性,并对影响传热过程的因素进行了分析,得出了适宜的操作条件。在操作气速0.1ms-1、振幅2mm及振动频率1100min-1的条件下,振动流化床水平换热管的传热系数达到最大值。实验结果为粗钛矿的高效节能干燥提供了重要实验依据。     

Heat and Mass Transfer Relationship in Combined Infrared and Convective Drying

Results from three experimental studies are reviewed in order to examine the relationship between the heat and mass transfer coefficients in the combined infrared and convective drying process. These results demonstrared that the heat     

Drying and Heat Transfer Characteristics for a Novel Fluidized Bed Dryer

Abstract

The use of a fluidized bed dryer with a lateral air flow and mechanical agitation to the drying of sludge from a wastewater treatment plant was investigated. Experimental curves of moisture content vs. drying time, as well as heat transfer coefficients and the size characteristics of the products, were determined at temperatures between 80°C and 110°C, a stirring rate of 55 rpm and air velocity of 0.9 m/s for 3 kg sludge batches with initial moisture contents of 0.55 and 0.65 (d.b.). Experimental drying kinetics were compared with values derived from three models based on Fick's second law, namely: the constant diffusivity model, the simplified variable diffusivity model, and the modified quasi-stationary model.     

Modelling Diffusion-Limited Drying Behaviour in a Batch Fluidized Bed Dryer

ABSTRACT

Fluidized bed dryers are often used to extract water from granular materials. When the drying process is mainly limited by the resistance against water transport inside the particle the drying behaviour is said to be diffusion-limited. In the literature there are several models that predict this drying process with very diverging results. In this study a model is set up to arrive at a better prediction for this drying process. The heat and mass transfer in the granular material and the drying air is described. The resulting equations are solved numerically. The model must be extended to incorporate the heat capacity of the dryer.     

滚筒干燥器内丝状物料的传热传质特性研究

干燥涉及众多生产领域,卷烟加工过程中存在干燥环节,滚筒烘丝机是用于干燥烟丝的主要设备。在滚筒烘丝机内,烟丝与周围环境进行热质交换,不同的运行控制条件,将直接影响烟丝的品质。由于干燥过程受众多因素的影响,至今烟草加工企业对烘丝机内部烟丝的传热传质特性缺乏深层次的认识,不利于烟丝品质的提高。针对上述背景,本文基于传热传质学、流体力学、多相流动等相关理论,通过计算机数值模拟方法,建立并求解滚筒内的传热传质数学模型,获得不同操作条件下烟丝温度、含水率变化的详细信息,并将所得结果与实际生产数据相验证。研究结果表明,烟丝与气流逆流流动条件下,干燥过程存在三个阶段：预热段、恒速段、降速段,烟丝含水率先升后降,烟丝温度经历先升高、后降低、再升高的过程;顺流流动条件下,干燥过程存在两个阶段：预热段与恒速段,烟丝含水率沿程单调下降,烟丝温度在预热段急剧上升,在恒速段平缓上升。     

Modelling Diffusion-Limited Drying Behaviour in a Batch Fluidized Bed Dryer

Fluidized bed dryers are often used to extract water from granular materials. When the drying process is mainly limited by the resistance against water transport inside the particle the drying behaviour is said to be diffusion-limited. In the literature there are several models that predict this drying process with very diverging results. In this study a model is set up to arrive at a better prediction for this drying process. The heat and mass transfer in the granular material and the drying air is described. The resulting equations are solved numerically. The model must be extended to incorporate the heat capacity of the dryer.     

Experimental and Numerical Investigation of the Heat and Mass Transfer for Cut Tobacco During Two-Stage Convective Drying

In this article, a two-stage convective drying strategy was presented for dehydration of flue-cured tobacco. In order to develop the multistage drying method of tobacco, two-stage drying as well as traditional single-stage drying of cut tobacco was experimentally evaluated and accurately simulated by proposed heat and mass transfer models. The experiments were performed in a dual fixed bed dryer. Different air temperature combinations of 120°C/90°C, 110°C/80°C, and 100°C/70°C were employed during two-stage drying. The drying rate and temperature variations of cut tobacco were investigated. The results showed that the average drying rates during two-stage drying were nearly 50% higher than those obtained from lower-temperature single-stage drying. On the other hand, the two-stage drying method, which used high air temperature for the early period and low temperature for the late period, could reduce the exposure of tobacco to high temperature due to the low final temperature of the dried sample. The temperature and moisture evolution of cut tobacco at different air temperature combinations were consistent with simulation results by developed heat and mass transfer models. This indicated that the models had a good prediction precision for two-stage drying of cut tobacco. The model predictions can be useful for the design of a feasible two-stage drying process for flue-cured tobacco.     

振动流化床与浸没水平管间局部传热系数的测试方法

本文提出了振动流化床中测试水平加热管局部传热系数的新方法。该法考虑了管体温度场的非均匀性对测量结果的影响。根据管体的材质和结构。扣除了由于分布引起热损失。从而采用较简单的测试手段就能够获得较准确的局部传热系数数据。将本所所得测试结果与其他研究者的测试结果作了比较。并上局部热系数求得的平均传热系数和实测的平均传热作了比较。结果表明,本文提出的测试方法可靠。     

Contact-Sorption Drying of Penicillium bilaii in a Fluidized Bed Dryer

A fluidized bed dryer and drying system have been designed, constructed and operated to produce a powdered formulation of the fungus Penicillium bilaii. The dryer includes an air-shear atomizer and rotatable air vibrator to produce particles which are evenly coated with P. bilaii. The drying system included a humidifier, oven, vacuum pump and instrumentation to ensure precise control of operating conditions. Instant skim milk powder was found to be the best particle source for fixing the spores due to its solubility in water, its highly porous nature and because its moisture isotherms were similar to those of the spores. The dryer was operated at 35°C to maximize the drying rate while still preventing thermal death of the spores. The fluidizing air was best provided at an RH of 30%, thereby producing skim milk/spore particles with just the right amount of moisture to ensure long term storage viability. Storage under refrigeration conditions showed little long term decline in spore viability after 3 months of tests. Room temperature storage demonstrated a small decline rate in spore viability with little significant change if held at room temperature for a few days. © 1997 SCI.     

高初始含湿多孔介质喷雾干燥过程的热质耦合传递

多孔介质是大量干燥过程的主体,由于实际多孔介质干燥过程的复杂性,建立通用的干燥过程传热传质模型十分困难。通过分析喷雾干燥过程中高初始含湿多孔介质与干燥介质之间的传热传质机理以及各因素对传热传质的影响,根据马歇尔方程探讨了干燥介质与料雾之间的水蒸汽分压差在干燥过程中的变化情况,反映了多孔湿介质在喷雾干燥操作中的传热传质过程的几种特性,为确定实际生产中喷雾干燥器的操作条件指明了新的出路。     

International Heat and Mass Transfer Forum

ABSTRACT

Results from three experimental studies are reviewed in order to examine the relationship between the heat and mass transfer coefficients in the combined infrared and convective drying process. These results demonstrared that the heat     

Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media

Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 ...     

离心流化床中的干燥特性的实验研究

报道了多种不同形状的萝卜、韭菜等蔬菜及粮食种子在离心流化 中干燥特性的实验结果,得出了恒速干燥阶段的传热准数关联式,并找出了影响整个干燥过程干燥速率的因素,同时讨论了不同操作条件对干燥速率的影响。     

回热式热泵干燥高湿稻谷的试验研究

应用带有嵌入回热器的热泵装置,对华南地区高湿稻谷进行干燥试验,测定其干燥速率、能耗和品质。并与同期作业的燃油低温循环稻谷干燥机进行对照。试验结果表明：回热式热泵干燥机的干燥速率较燃油低温循环干燥机提高20％,干燥周期缩短约12％,而干燥能耗及费用可节省30％以上,干燥品质两者无差异。