短线圈感应炉感应器—炉料互感系数M的计算方法

本文主要介绍在工频短线圈感应炉电参数计算中,应用查曲线法计算感应器－炉料互感系数Ｍ时如何重新做出一种适应短线圈应炉Ｍ系数计算的αＭ曲线。从而简便了电参数计算结果也符合实际要求。     

高速凸轮变系数多项式凸轮曲线的研究

提出一种七、九、十一次变系数多项式曲线设计方法,通过对凸轮曲线方程及特性参数进行计算,绘制其特性参数图谱,达到改变凸轮曲线的运动学和动力学特性,提高了凸轮曲线设计的灵活性和选择性的效果。     

小白菜热风干燥特性研究

研究了一定条件下风速与风温对经烫漂预处理的小白菜热风干燥过程的影响,拟合了干燥曲线方程,并计算了临界含水量、传热膜系数α与传质系数kH等热风干燥动力学参数。而各条件下的小白菜干燥曲线均符合Page方程。小白菜干燥过程中的传热膜系数α与传质系数kH受风机频率影响明显,且随风机频率增大而增大,但两者均基本不受干燥温度影响。     

电站锅炉效率的计算与过量空气系数调节曲线的制定

本文根据锅炉效率与过量空气系数、排烟温度、机组负荷、蒸发量等参数之间的关系,给出了一种简单、有效的锅炉效率经验计算算法,并据此制定了过量空气系数调节曲线,提出了不同机组负荷与环境温度下过量空气系数的调节方法。     

PCB回流焊温度曲线设定优化

回流焊接技术是现代电子产品组装工艺中最常用的技术,而回流焊温度曲线的设置是PCB组件回流焊接过程中最关键的技术。本文描述回流焊温度曲线设置和优化的一些方法和技术探讨。     

LED灯珠无铅回流焊接工艺曲线设定

讨论了3014LED灯珠基于95.5Sn3.8Ag0.7Cu无铅焊料的回流焊工艺。重点绘制了无铅回流焊接工艺曲线,分析了无铅回流焊工艺升温预热区、焊接区(回流区)和冷却区等各阶段所受温度的影响及其可能引起的不良后果,为LED灯珠无铅回流焊接工艺提供参考。     

筛板精馏塔点效率的研究

依据溶质渗透理论 ,得出了汽、液相传质单元数与传质系数、汽液接触时间、相界面积、物系性质及塔板结构的关联式 .采用汽相平推流液相完全混合模型计算点效率 ,计算值以 Col-burn推导的雾沫夹带对塔板效率的影响关系进行修正 .经小型筛板塔在全回流条件下的实验验证 ,点效率的预测值与实验结果吻合较好 ,在正常操作范围内 ,误差 <6 % .     

细纱机磁性加压机构的磁学分析

本文根据磁学基本原理,对细纱机磁性加压机构进行了系统的测试和分析.分析并测定了磁性加压机构的磁路和工作气隙基本参数,测定计算了它的漏磁系数和磁势损失系数,并求出它的负载线、永磁体的工作点和回复曲线。在这些测定和计算的基础上,提出了磁性加压机构永磁体的设计方法,为更好地使用磁性加压提供了系统的数据和必要的理论基础.     

酒精蒸馏甲醇塔设计回流比的确定

本文论述了酒精蒸馏甲醇塔设计确定回流比的意义及依据。最小回流比的计算及影响最小回流比大小的因素。对甲醇塔设计有一定的参考意义。     

盲孔法AB值的有限元法分析

采用ANSYS有限元软件,建立合适的钢管拉伸曲线,对X65材质不同应力下的盲孔法AB值进行了计算。采用形状改变比能系数S得到具体公式。该方法提高了大应力的测量精度。     

A Diffusion Model with a Concentration-Dependent Diffusion Coefficient for Describing Water Movement in Legumes During Soaking

A mathematical model based on Fick's diffusion equation with a concentration-dependent diffusion coefficient was proposed to describe the absorption of water by legumes. The equation was solved by using a numerical scheme. Parameter study was performed. The model is capable of predicting sigmoidal-shaped water uptake curves common to many legumes. Differences are discussed between the surface resistance boundary condition used in this study and the radiation boundary condition widely used for dehydration calculations. The validity of using the proposed model to described the water uptake of legumes was verified by the good fit between the experimental and theoretical curves.     

Models for fiber stress utilization in air jet yarns

Abstract

The coefficient of fiber stress utilization of air jet viscose staple spun yarns was predicted from the experimental specific stress-strain curves of both fiber and yarns. The coefficient of fiber stress utilization was calculated from Gegauff’s model, single integral model (SIM) and double integral model (DIM). Results showed that the single integral model overestimated the coefficient of fiber stress utilization considering actual stress-strain relationship which was not considered by Gegauff’s model. When fiber orientation effect in the air jet yarn was considered in double integral equation, the predicted coefficient of fiber stress utilization was in good agreement with the experimental coefficient of fiber stress utilization before the process of break. Furthermore, the yarn specific stress was also evaluated from the predicted coefficient of fiber stress utilization from double integral model and experimental fiber specific stress-strain curve for all three air jet viscose yarns. The predicted yarn specific stress-strain curves were in good agreement with experimental yarn specific stress-strain curves for all air jet yarns.     

Short communication: A new mathematical model for thin layer drying of fruits

The aim of this study was to fit a new mathematical model on the thin layer drying curves of fruits. Thin layer drying studies at different temperatures (60, 80 and 100 °C) were carried out on two varieties each of kiwifruit and apricot. The new model was compared statistically with three other drying models (Henderson and Pabis, Page and logarithmic) published in the literature. The proposed equation gave the highest coefficient of determination for both varieties of kiwifruit and apricot and closely followed by the Page equation. Statistical evaluation of the experimental and predicted moisture ratio showed that the proposed equation consistently gave the lowest reduced Chi‐square, root mean square error and mean relative percentage error. The results indicate that the proposed equation has the best curve fitting ability for both fruits. However, there is no theoretical basis offered for the good curve fitting ability of the equation.     

COMPARISON OF MULTISTAGE EXTRACTION INSTALLATIONS WITH SEPARATION OF THE SOLID PHASE BETWEEN THE STAGES IN HOPS (HUMULUS LUPULUS L.) EXTRACTION

The multistage extraction installations using cross-flow and back-flow schemes are successful in hops extraction. Both types of extraction process have been investigated, comparing the installations in order to specify the most appropriate scheme and determine the number of stages required. A three stage extraction with separation of a part of the solid phase between the stages was carried out. The parameters of each extraction stage of a cross-flow and a back-flow installation were calculated. It was established that in the cross-flow scheme the third stage was unnecessary since a minimal part of the bitter substances was extracted in it and the extract yield was too low. Moreover in the cross-flow installations a very high extraction efficiency was achieved, (94, 67%) but with a large consumption of extracting solvent (3,24.10^?2m³/kg) whilst in the back-flow scheme the extraction efficiency was much lower (71,4%) but with a reduced solvent consumption (1,2.10^?2m³/kg). The comparison of both installations demonstrates that the back-flow scheme is not very successful and that it is advisable to use a cross-flow installation with one or at most two extraction stages. The results obtained enable the proposal of a more rational scheme of hops extraction, where a one or two stages cross-flow process with separation of a part of the solid phase results in a final granulated product, a mixture of the extract and partly extracted raw material.     

CHARACTERISTIC DRYING CURVE and MATHEMATICAL MODELING of THIN-LAYER SOLAR DRYING of PRICKLY PEAR CLADODE (OPUNTIA FICUS INDICA)

Thin‐layer solar drying experiments were conducted for the prickly pear cladode grown in Marrakech, Morocco. the experimental drying curves obtained show only a falling rate period. the results verified, with good reproducibility, that the drying air temperature is the main factor in controlling the drying rate. the expression of the drying rate equation was determined empirically from the characteristic drying curve. Eight different drying models were compared according to their correlation coefficient (r²) to estimate solar drying curves. the Page model could satisfactorily describe the solar drying curves of cladode with an r² of 0.9995. the coefficient of this model could be explained by the effect of drying air temperature with an r² of 1.0000.     

牛血清清蛋白在聚乙二醇—无机盐体系中的分配特性

采用3种聚乙二醇-无机盐双水相体系,即聚乙二醇-硫酸盐、聚乙二醇-柠檬酸盐、聚乙二醇-磷酸盐双水相体系,研究成相浓度、起始牛血清清蛋白总浓度、外加有机溶剂及外加盐对牛血清清蛋白分配特性的影响.对聚乙二醇-硫酸盐体系,改变起始牛血清清蛋白的总浓度,得到平衡时上、下相牛血清清蛋白浓度随起始牛血清清蛋白总浓度变化的曲线方程,上相宜用“饱和型”方程表示,下相适合用线性方程表示,分配系数K的表达式与实验数据拟合较好.     

Modeling and predicting non-isothermal microbial growth using general purpose software

Published experimental isothermal growth curves of Clostridium perfringens cells in ground ham were fitted with a modified three-parameter version of the logistic equation as a primary model and the temperature dependence of the three parameters by ad hoc empirical secondary models. These were used to predict the organism's non-isothermal growth curves under three different cooling regimes. The assumption has been that the organism's instantaneous (or momentary) non-isothermal growth rate is the isothermal rate at the given temperature at a time that corresponds to its instantaneous population size. This could be translated into a differential rate model equation, whose coefficients are constructed from terms that reflect the changing growth parameters with temperature and hence with time. The continuous rate equation, however, can be solved incrementally by a numerical procedure that can be implemented in similar purpose software like Microsoft Excel(R). In all three cases, there was good agreement between the growth curves predicted by the model and those found experimentally. This demonstrated that the procedure can be used to generate growth curves under complicated thermal histories that may include regular and irregular temperature oscillations.     

高维变系数线性系统特解的探求

给出了高维变系数线性齐次系统和高阶变系数线性齐次微分方程具有指数型解的充要条件,提供了探求变系数线性系统指数型解的一个新的实用的有效方法,推广了经典的常系数线性系统的解法.     

Drying Kinetics and Time-Temperature Distribution of Pregelatinized Bread

ABSTRACT: The experimental method of measuring the effective moisture diffusivity of bread, the representative hygroscopic porous material, was investigated. Drying curves and temperature profiles were obtained from cylindrical bread samples (0.3 and 0.6 porosity, and 0.011 and 0.018 m dia) under convective hot air conditions (50 to 90 °C oven temperatures and 1 to 3 m/s air velocity). The normalized drying curves were linear, suggesting that Fick's diffusion equation was applicable in determining the diffusion coefficient, and the effective moisture diffusivities were in the range of reported values. Experimental determination of the temperature dependent diffusion coefficient requires isothermal conditions to exist in the material, but temperature gradients existed throughout drying of the bread samples. Thus, the linearity of normalized drying curves is not a guarantee that the moisture diffusivity is properly determined. The need to develop an apparatus to achieve isothermal conditions during experimental measurement of the effective moisture diffusivity is shown.     

Mathematical modelling of the drying curves of kiwi fruits: influence of the ripening stage

The drying behaviour of kiwi fruits at different stage of ripeness has been evaluated. A diffusional model solved by a finite difference method has been proposed to simulate the drying kinetics at different temperatures. Drying curves of ripe kiwis exhibited only one diffusional period, whereas two different diffusional periods could be observed on the drying curves of green and half‐ripe kiwis. Furthermore, the drying curves of green and half‐ripe kiwis were coincident. The effective diffusional coefficient, which was identified at different temperatures (from 40 to 80 °C) from experimental data, varied with temperature according to the Arrhenius equation. An adequate simulation of the drying curves using the proposed model was achieved. Thus, the percentage of explained variance for the drying curves of green and half‐ripe kiwis (considering two diffusional periods) was 99.7 and 99.3% for the ripe kiwis (only one diffusional period). Regarding to the characteristics of the dried kiwis, it was observed that the colour of the samples was mainly affected by the drying temperature, whereas functional properties such as hydration and fat retention capacities were mostly influenced by the stage of ripeness of the fruit. Copyright © 2004 Society of Chemical Industry