分布式小卫星SAR回波信号的相关性

本文通过建立单视复图像信号模型,提出并推导了分布式小卫星合成孔径雷达(SAR)回波信号之间新的相关系数模型.根据干涉复图像对的相位差与相关系数之间的关系,定义了方位向相位新概念,提出了分布式小卫星SAR干涉复图像对的相位差的均值包括干涉相位和方位向相位两部分,为了防止方位向相位引起较大的干涉相位估计误差,必须在数据处理中引入去方位向相位处理新方法,并给出了去方位向相位处理的具体实现方法.最后,进行了计算机仿真处理,仿真结果验证了本文分析的正确.     

Effect of axial conduction on the ice crystal growth in laminar falling filmsEffet de la conduction axiale sur la vitesse de formation de cristaux de glace à l'intérieur de films tombants laminaires

A finite volume numerical code has been developed to numerically approximate the rate of ice crystal growth in a laminar falling film flowing down a cooled vertical plate. The governing energy equation contains the phase energy as the source term. Enhancement of heat transfer as a result of suspended ice crystals is accounted for in the use of effective values of thermal conductivity, viscosity, thermal diffusivity, and specific heat as function of volumetric concentration of ice crystals in the falling film. Nusselt number, overall heat transfer coefficients between the fluid and cooled plate, and ice crystal growth rate were calculated for different film thicknesses with and without axial diffusion. Nusselt number and ice crystal growth rates were found to be dependent on film thickness. Axial diffusion effects were found to be negligible for larger film thickness (large flowrate).     

Numerical simulation of individual quick freezing of spherical foods

A one-dimensional three time level implicit finite difference computer program was developed to predict temperature profiles during the individual quick freezing of spherically shaped foods. Temperature varying thermal properties necessary for these predictions were calculated based upon properties of the unfrozen product. The centre temperatures of individual peas within a bed of peas being frozen under various conditions of fluidization were recorded. Comparison of experimental results and published data with predicted freezing curves showed good agreement.     

Modern freezing facilities

This paper gives a monograph of freezing and quick-freezing equipment. Following a brief summary of the theory of freezing time, the author reviews the principal industrial processes and equipment in use today, classifying them according to their technological characteristics.     

Measurement and prediction of freezing times of vacuum canned Pacific shrimp

Freshly cooked Pacific shrimp, vacuum packed in cans fitted with monitoring instruments, were frozen under industrial conditions. Surface heat transfer coefficients were determined experimentally using aluminium cyclinders. Freezing times were measured and also calculated using Plank's equation and the formulae of Cleland and Earle. The investigation indicated that the vacuum level had little effect on the freezing time and that freezing time essentially doubled when cans were enclosed in a commercial carton. For the prediction of freezing times, Cleland and Earle's method was found to be more accurate than Plank's for the tests performed, with predicted values within ± 10% of measured values.     

Experimentation and modeling of refrigerant flow through coiled capillary tubes

Air-conditioners use spirally coiled capillary tubes as an expansion device to enhance compactness of the unit. However, most empirical correlations for predicting refrigerant flow rate through capillary tubes were developed for straight capillary tubes without consideration of coiled effects. The objectives of this study are to investigate the flow characteristics of the coiled capillary tubes and to develop a generalized correlation for the mass flow rate through the coiled capillary tubes. The mass flow rate of R22 through the coiled capillary tubes and straight capillary tubes was measured for various operating conditions and tube geometries. The mass flow rates of the coiled capillary tubes decreased by 5–16% more than those of the straight capillary tubes at the same operating conditions. A generalized correlation for predicting refrigerant mass flow rate through coiled capillary tubes was developed by introducing the parameter of capillary equivalent length. The present correlation showed good predictions with the present database for R22, R407C and R410A in the straight and coiled capillary tubes, yielding average and standard deviations of 0.24% and 4.4%, respectively.     

《钢结构工程施工质量验收规范》(GB 50205-2001)中二级焊缝的无损检测抽检比例

对钢结构二级焊缝的无损检测抽检比例进行了分析,提出了正确理解和执行规范的方法。     

Freezing of a parallelepiped food product. Part 1. Experimental determination

A number of procedures are used to predict the freezing time of food. The objective of the project reported here was to test the adequacy and applicability of the various mathematical models and methods used to predict the freezing time of a small, parallelepiped food product. The approach was to compare experimental and predicted freezing times. In this paper the experimental methods and results are described; the freezing time and the thermophysical properties of both the frozen and non-frozen food were determined. Comparison between experimental and predicted freezing times will be given in a subsequent paper. The experimental conditions consisted of individually freezing the product in an air blast; the food product was french fries. The time required to lower the temperature of a french fry from 31 to −18°C in the −29°C air blast freezer used was approximately 1200 s. The mean moisture content of the fries was 73.7%. The average densities of the non-frozen and frozen fries were 1069 and 1012 kg m⁻³, respectively; the average thermal conductivities were 0.50 and 1.0 W m⁻¹ °C⁻¹; and the heat capaciti were 3420 and 1870 J kg⁻¹ °C⁻¹. The overall surface heat transfer coefficient of a parallelepiped object in the air blast freezer used for these experiments was 21.0 W m⁻² °C⁻¹. The low surface heat transfer coefficient resulted in a flat temperature profile within the fries.     

Theoretical and experimental freezing times of strawberries

Strawberries were frozen at different air velocities in an air blast freezer at −30°C. The freezing time was taken as the time required to lower the temperature at the geometric centre of the samples to −10°C. The freezing times measured in the experiments were compared with the values calculated using Plank's equation. The freezing times calculated by Plank's equation were fround to be higher than those found experimentally at any given air velocity. Freezing time decreased with increasing air velocity. This is attributed to the increase in heat transfer coefficient at increased air velocities.     

利用断面法计算机辅助测量料堆的体积

把工程中使用的断面法引入到计算机辅助测量技术中,提出了在计算机辅助测量料堆体积中一种新的体积计算算法,它包括整理原始数据点、建立三角剖分、建立截断面、对断面进行曲线拟合、计算断面体积(或计算相邻截面间料堆的体积)、计算料堆体积等步骤。在此算法的基础上,开发出一个应用系统,并通过实验验证了算法的正确性。