Vapour phase motion in cryogenic systems containing superheated and subcooled liquids

The development of vent pipelines, and venting storage tanks for cryogenic liquids requires the knowledge of the law of motion as well as regularities of vapour content variation in the liquid and heat dissipation by the vapour phase. This is a theoretical study of the effect of superheating (subcooling) of the liquid, relative acceleration and reduced pressure upon the size and velocity of noninteracting vapour bubbles, moving in the liquid, and upon their resistance and heat transfer coefficients.     

一氧化碳变换系统存在问题及改造措施

介绍中原大化分公司500kt／a甲醇项目变换系统流程及变换技术特点,分析系统运行中存在的问题及危害,提出了改造措施。实施后从根本上消除了隐患,保证了变换系统的安全稳定运行。     

连铸机中间包温度的控制

分析了连铸中间包钢水温度对钢材产量和质量的影响,根据不同的计算方法和控制方案,结合石钢自身特点制定了稳定中间包温度及其过热度的措施,提高了钢材的产量和质量。     

循环流化床锅炉高温过热器爆管事故的原因分析

为预防循环流化床锅炉高温过热器爆管事故的发生,除保证设计、制造、安装质量外,运行管理水平异常重要.分析引起爆管的原因,以达到避免爆管、提高效益的目的.     

熔体过热对Sb-Bi合金凝固组织的影响

以Sb-4.6%Bi合金为研究对象,在限定其它因素保持不变的情况下,考察了熔体过热温度对凝固过程的影响。,实验结果发现,随着熔体过热温度的提高,合金形过冷度增大,凝固组织显著细化,研究表明,熔体过冷倾向是熔体结构状态的一个必然反映,熔体结构状态随温度发生变化是导致合金结晶过冷度发生明显的变化的原因,随着过热温度的提高,Sb-4.6%Bi合金晶粒显著细化,其原因是经过热处理的合金熔体在较大的过冷度下凝固。     

一段转化炉盘管运行损坏情况分析与对策

介绍一段转化炉混合原料气盘管及高压过热蒸汽盘管在运行中暴露出的问题及损坏情况,提出设备修复及工艺改进方法,保护盘管安全运行。     

上汽670 MW超临界汽轮机闷缸经验

对华电潍坊发电有限公司670MW超临界汽轮机闷缸经验进行介绍,对闷缸过程中的有关注意事项进行总结,为同类型机组抢修时快速停盘车提供实践依据.     

Investigation of the effect of superheating on the performance of a refrigeration system using low temperature different refrigerant blends in porous media

A comparative experimental investigation on the effect of superheating of R‐22, R‐404A, R‐407C, and R‐422A as low‐temperature refrigerant blends on the performance of a vapor compression refrigeration system is conducted. Empty and porous evaporators with porosities of (40%, 43%, and 45%) are used during the tests, to predict good alternatives to the refrigerant R‐22, which has high ozone depletion potential and high global warming potential. Condensation, evaporation temperatures, degree of subcool are kept constants at 40°C, ?26°C, and 6°C (±0.5°C), respectively. The effect of superheating on the compressor discharge temperature, evaporating pressure drop, evaporating capacity, volumetric refrigeration capacity and coefficient of performance (COP) of these refrigerants has been analyzed. Refrigerants, R‐422A and R‐404A showed greater performances than that of R‐22. The percentages of increase in evaporation capacities of R‐407c, R‐22, R‐404A, and R‐422A are approximately 144%, 168%, 146.3%, and 161.5%, respectively, when changing the degrees of superheat from 6°C to 16°C and changing the porosity from empty evaporator to 40%. The percentages of increase in COP are approximately 319%, 320%, 312%, and 350%, respectively. The percentages of increase in evaporation capacities of R‐422A and R‐404A when compared with R‐22 under the same conditions are 18.6% and 8.8%, respectively, while the percentages of increase in COP when compared with R‐22 are 17% and 12%, respectively.     

Influence of melt superheating on microstructures of Mg-3.5 Si- 1 A1 alloys

The influence of melt superheating treatment on the microstructures of Mg-3.5Si-1A1 alloys unmodified and modified with 0.2% Sr-Sb (mass fraction) was investigated. The results show that when the melt superheating temperature increases from 750 to 900 ℃, the average size of primary Mg2Si in the unmodified alloys decreases progressively from about 27 to about 19 μm, while that in Sr-Sb-modified alloys,is refined considerably from about 14 to about 7 μm when the temperature increases from 750 to 850℃, and then slightly increases to about 9 μm with temperature further increasing to 900 ℃, which might be attributed to the burning loss of Sr and Sb in melts. However, the superheating temperature only has a slight effect on the morphologies of both primary and eutectic Mg2Si phases in unmodified and Sr-Sb-modified alloys.     

Thermodynamic analysis of subcooling and superheating effects of alternative refrigerants for vapour compression refrigeration cycles

This paper presents a computer‐based first law and exergy analysis applied to vapour compression refrigeration systems for determining subcooling and superheating effects of environmentally safe new refrigerants. Three refrigerants are considered: R134a, R407c and R410a. It is found that subcooling and superheating temperatures directly influence the system performance as both condenser and evaporator temperatures are affected. The thermodynamic properties of the refrigerants are formulated using artificial neural network (ANN) methodology. Six ANNs were trained to predict various properties of the three refrigerants. The training and validation of the ANNs were performed with good accuracy. The correlation coefficient obtained when unknown data were used to the networks were found to be equal or very near to 1 which is very satisfactory. Additionally, the present methodology proved to be much better than the linear multiple regression analysis. From the analysis of the results it is found that condenser and evaporator temperatures have strong effects on coefficient of performance (COP) and system irreversibility. Also both subcooling and superheating affect the system performance. This effect is similar for R134a and R407c, and different for R410a. Copyright © 2005 John Wiley & Sons, Ltd.