ON THE ANALYSIS OF NONCATALYTIC GAS-SOLID KINETICS DATA HAVING WEAK TEMPERATURE DEPENDENCE

Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the rate is controlled by surface kinetics. However, there are a number of examples in the literature where apparent activation energies less than 10 kcal/mol have been reported as being representative of intrinsic kinetics. This conclusion is often based on electrobalance data in which large gas Row rates were used to eliminate mass transfer resistance and the fact that fractional conversion-time results are consistent with the surface kinetics control version of a gas-solid reaction model.

The oxidation of FeS was studied in an electrobalance reactor as a function of O₂ mol fraction, temperature, and gas flow rate. The global rate was first-order in O₂ and weakly dependent on temperature and flow rate. Data analysis used the approximate solution to the grain model. The single-resistance surface kinetics variation of the model provided good match with the conversion-time data, but the apparent activation energy was only about 7 kcal/mol. A two-resistance mass transfer-product layer diffusion variation provided equally good match with the data, and the dependence of reaction coefficients on reaction variables was in general agreement with theory.     

两种高岭土的酸浸反应宏观动力学的比较

考察了两种不同品质和结晶形态的高岭土经煅烧活化后的酸浸反应特性 .结果表明 ,活化后的仙游高硅铝比高岭土的表观浸取率低于硅铝比接近标准值 2∶ 1的朔州煤系高岭岩 .示性分析给出前者所含高岭石的真实含量 ,依此计算推得与后者相同的最大真实浸取率 .粒度分析和对这两种活化高岭土的酸浸反应宏观动力学特性 ,两者均符合粒径不变的缩芯反应模型 ;在较低温度时 ,均为表面反应控制 ;较高温度时 ,均为灰层扩散控制 ;同时又得到数值相当的酸浸反应的活化能 .表明高岭土中只有属于高岭石结构的组分经煅烧活化为偏高岭石后才能进行酸浸反应的实质     

制备工艺对PTC复合材料阻温特性的影响

研究了密炼工艺对聚乙烯／炭黑复合材料室温电阻率及ＰＴＣ强度的影响,针对一定配方找到了最佳密炼工艺条件。电子束辐照交联能有效消除ＮＴＣ现象和提高材料的电性能循环稳定性,有助于制备低电阻率、高ＰＴＣ强度并具有较好电性能循环稳定及热敏开关特性和电路保护元件。     

CO高温变换反应动力学研究

本文通过对纯铁氧化物及工业催化剂 B107进行程序升温还原(TPR)、程序升温氧化(TPO)以及高温变换反应动力学实验,认为铁基氧化物催化剂上进行变换反应是以 Redox 机理进行。Redox 过程中的控制步骤可能随温度和浓度变化而发生转移,并提出了适合控制步骤转移的动力学方程,对动力学实验数据回归得出了模拟参数。     

THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE KINETICS OF VACUUM DRYING OF KETOPROFEN

ABSTRACT

This paper explores the influence of temperature and pressure on drying kinetics of 2-(3-benzoylphenil propionic acid) ketoprofen, in a vacuum dryer on laboratory scale, Experimentally determined relations between moisture content and drying rate vs time, were approximated with an exponential model. Model parameters were correlated with drying conditions (temperature, pressure) and defined by functions of their potentions.

From an energy balance of the process, a mathematical model for simulating dependence of sample temperature vs drying time, and moisture content of material, has been developed.

Simulation of the drying kinetics and sample temperature, by use of those functional dependencies shows good agreement with experimental results.     

THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE KINETICS OF VACUUM DRYING OF KETOPROFEN

This paper explores the influence of temperature and pressure on drying kinetics of 2-(3-benzoylphenil propionic acid) ketoprofen, in a vacuum dryer on laboratory scale, Experimentally determined relations between moisture content and drying rate vs time, were approximated with an exponential model. Model parameters were correlated with drying conditions (temperature, pressure) and defined by functions of their potentions.

From an energy balance of the process, a mathematical model for simulating dependence of sample temperature vs drying time, and moisture content of material, has been developed.

Simulation of the drying kinetics and sample temperature, by use of those functional dependencies shows good agreement with experimental results.     

温度对煤和炭吸附甲烷的影响

用容量法测定了不同温度下甲烷在无烟煤及其炭化亲上的吸附特性。结果表明甲烷在无烟及其炭化样上吸附平衡时间分别由５０℃时的５ｈ和３ｈ增加到－２１℃时的２５ｈ和１６ｈ，吸附热分别为１５ＫＪ／ｍｏｌ和１２ＫＪ／ｍｏｌ。     

sialon块体的变温氧化动力学

揭示了sialon块体材料的变温氧化机理,建立了变温氧化的定量氧化模型,并用此模型拟合β-sialon-Al2O3材料,O'-sialon-ZrO2-SiC材料和β-sialon-15R材料的变温氧化行为,所得结果与前人的实验结果符合得较好.结果表明:该模型能较好地定量描述sialon在变温氧化过程中氧化分数和温度及升温速率的关系,对预测sialon的氧化行为有一定的理论指导作用.     

STABILITY ANALYSIS FOR THE PREDICTION OF THE MINIMUM TEMPERATURE OF FILM BOILING

The stability of film boiling on a vertical, constant temperature wall is analyzed by a steady-state small perturbation method. It was found that large amplifications of the perturbations in the downstream direction are predicted when the vapor Reynolds number falls below a critical value, indicating a great tendency to collapse the vapor film. Using a relatively simple model for the film thickness, the minimum wall temperature required to sustain the vapor film is calculated. The results show a tendency which is in agreement with experimental observation. It is suggested, however, that using a more accurate model for the film thickness can lead to a good prediction of the minimum wall temperature and explain the large effect of liquid subcooling, system pressure, surface tension and other fluid properties.     

ON THE STUDY OF TIME-VARYING TEMPERATURE DRYING—EFFECT ON DRYING KINETICS AND PRODUCT QUALITY

The ability of heat pump dryer to produce controlled transient drying conditions, in terms of temperature, humidity and air velocity, has given it an edge over other drying systems. Exploiting this characteristic, we studied and compared the effect of different temperature-time profiles on the quality of agricultural products in a tunnel heat pump dryer capable of providing up to 14.6 kW of cooling capacity. The product quality refers to the color change of the products. Samples of banana and guava were dried in batches in a two-stage heat pump dryer. The effects of the starting temperature of a selected profile and the cycle time on both drying kinetics and product quality were studied. It was observed that by employing a step change in drying air temperature with the appropriate starting temperature and cycle time, it was possible to reduce significantly the drying time to reach the desired moisture content with improved product color.     

铬铁矿液相氧化的热力学分析

液相氧化法生产铬酸盐技术是对传统火法焙烧技术的突破．在600～900K温度范围内对液相氧化法处理铬铁矿的熔盐体系各反应趋势及物相组成的热力学进行了分析研究，对液相氧化法处理铬铁矿各体系的反应自由能变化（△G°R）与温度（T）关系的计算结果表明，铬铁矿中的（Mg,Fe）（CrO2）2在较低温度下与NaOH、O2具有较强的反应趋势，比传统的火法焙烧方法反应温度降低了873K，节约大量能源;铬铁矿中的杂质相在反应温度下进行一系列副反应，生成硅酸盐、铝硅酸盐等新相．     

纳米二氧化钛粉体粒径表征研究

采用水解沉淀法制备了纳米二氧化钛粉体，对其XRD衍射谱用Voigt函数拟合精修，得到精确的(101)和(200)面晶粒度，将结果与SEM和TEM测定的粒径进行比较，结果表明：3种方法所测值差异较大，3种粒径相比，XRD测定的粒径值小但变化较大，其平均值与TEM测定值比较接近；SEM测定的粒径大但相对比较稳定，平均增加约53％；TEM测定的粒径比较稳定。产生上述结果的主要原因：一方面是分析测试手段如XRD的精修参数和计算模式选择不同所致，另一方面与粉体样品的制备过程，以及纳米颗粒的结构特征有关。     

低阶煤低温氧化过程热力学规律的研究

采用pulse calorimeter仪器,分别研究了低温下低阶煤在湿的氮气气氛下凝结热与蒸发热间的热力学规律,以及在湿的氧气气氛下反应热与蒸发热间的热力学规律;还研究了低阶煤在干燥氧气下经三次低温氧化反应的热力学规律.结果表明,在湿的氮气下,凝结热和蒸发热均随温度的增加而减少,在温度299.15 K～323.15 K范围内,凝结热明显大于蒸发热值,随着温度增加二者差值变小;在湿氧气气氛下,随温度增加,反应热先减少后增加,其蒸发热与湿氮气条件相比,二者的热值及热力学规律基本相同;低阶煤经三次低温氧化反应过程,其中二、三次氧化反应的反应热与第一次相比显著降低.     

集总动力学的模糊分析初步

本文利用广义H(?)kel方法,在对石脑油中17个典型组分的分子轨道计算基础上,利用模糊分析方法,从理论上提出了1个寻找最佳集总方案的普遍原则.利用该原则,本文在对上述17个典型组分分析的基础上,分析了石脑油催化重整过程,得到了处于不同λ截集水平的集总方案.这些方案与文献中已提出的石脑油催化重整集总模型比较的结果表明,各λ截集水平的集总方案与文献中报道的集总模型基本一致.由本文提出的普遍原则可知:Smith的四集总模型的λ截集水平为λ=0.93;Mobil公司的十三集总模型的λ截集水平为λ=0.97;Kmark的二十二集总模型的λ截集水平为λ=0.98.     

EFFECTS OF VARIOUS TREATMENTS ON THE DRYING KINETICS OF Muscatel GRAPES

ABSTRACT

The drying kinetics of Muscatel grapes at 60°C and a relative air humidity of 22% were determined after various pretreatments had been applied to the grapes. The pretreatment parameters varied were the chemical agent (potassium carbonate solution with or without olive oil, or sodium hydroxide solution); the duration of pretreatment; and the temperature and concentration of the solution. A 3 minute pretreatment with an aqueous solution of K₂CO₃ and olive oil at 60°C reduced drying time from about 80 h to 20 h. Optimal drying load corresponded to a single layer of almost close-packed grapes on each tray. The experimental drying kinetics were satisfactorily reproduced by a model in which both grape size and the effective coefficient of diffusion are functions of moisture content.