Analysis of refrigerant flow and deformation for a flexible short-tube using a finite element model

A finite element model was used to simulate single-phase flow of R-22 through flexible short-tubes. The numerical model included the fluid-structure interaction between the refrigerant and the deformation of the short-tube as upstream pressure was varied. The finite element model was developed using a commercially available finite element package. Short-tubes with moduli of elasticity ranging from 5513 to 9889 kPa were studied. Four upstream and downstream pressures were applied and the upstream subcooling was held at a constant value of 16.7 °C. Mass flow rates from the numerical model were compared to available published experimental results. The study showed that upon deformation the short-tube resembled the shape of a converging-diverging nozzle. Both tube inlet and outlet had a chamfered-like shape after deformation which reduced the pressure drop at the tube inlet. The smaller the modulus of the tube, the larger the chamfered-like angle at the inlet and the higher the pressure drop along the tube due to the higher tube contraction. The results illustrated that as the upstream pressure was increased by 45%, there was almost a 60% decrease in the flow area. The more flexible (5513 kPa) short-tube restricted the mass flow rate more than the most rigid (9889 kPa) short-tube used in this study. The mass flow rates estimated with the finite element model were as much as 14% higher than those from experimental results reported in the literature.     

Numerical and experimental studies of refrigerant circuitry of evaporator coils

This study attempts to analyze the performances of evaporator coils with complex refrigerant circuitry using a distributed simulation model, which has three elements: branch, tube and control volume. The governing equations for a control volume are presented in the paper together with the computer simulation procedure for branches, tubes and control volumes of a coil. The model predictions on four test coils are validated with experimental data collected under different airflow conditions using R134a as a refrigerant. Using this model, the heat transfer and fluid flow characteristics of the coils are studied. The study shows that while the thermal resistance of refrigerant side is comparable to that of airside, the coil comprehensive performance can be improved by changing the refrigerant mass velocity along the flow path. Compared with a common coil, using a complex refrigerant circuitry arrangement where the refrigerant circuits are properly branched or joined may reduce the heat transfer area by around 5% in coil design. A guideline is proposed for the refrigerant circuitry arrangements to improve the coil performance.     

The influence of a low viscosity oil on the pool boiling heat transfer of the refrigerant R507Influence d'une huile à faible viscosité sur le transfert de chaleur lors de l'ébullition libre du frigorigène R507

This paper describes the influence of a low viscosity polyolester based lubricating oil on the pool boiling heat transfer of the refrigerant R507. The pool boiling heat transfer coefficients for this refrigerant–oil mixture are measured on a smooth tube and on an enhanced tube. The investigation is made for oil mass fractions up to 10% and for saturation temperatures between −28.6°C and +20.1°C. For the smooth tube the heat transfer increases for increasing oil mass fractions up to 3% at lower saturation temperatures. At higher saturation temperatures the heat transfer decreases for increasing oil mass fractions for both tubes. For oil mass fractions greater than 1% at the higher saturation temperatures a range of decreasing heat transfer coefficient is found for increasing heat flux. The effect is caused by the different miscibility of the oil and the components of the refrigerant mixture.     

Condensation and evaporation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficient and pressure drop were measured for condensation and evaporation of R410A and HCFC22 inside internally grooved tubes. The experiments were performed for a conventional spiral groove tube of 8.01 mm o.d. and 7.30 mm mean i.d., and a herring-born groove tube of 8.00 mm o.d. and 7.24 mm mean i.d. To measure the local heat transfer coefficients and pressure drop, the test section was subdivided into four small sections having 2 m working length. The ranges of refrigerant mass flow density was from 200 to 340 kg/(m² s) for both condensation and evaporation of R410A and HCFC22, and the vapour pressure was 2.41 MPa for condensation and 1.09 MPa for the evaporation of R410A. The obtained heat transfer data for R410A and HCFC22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of spiral one for condensation and are slightly larger than those of spiral one for the evaporation. The measured local pressure drop in both condensation and evaporation is well correlated with the empirical equation proposed by the authors.     

Two-phase heat transfer to a refrigerant in a 1 mm diameter tubeTransfert de chaleur vers un frigorigène circulant dans un tube d'un diamètre d'un mm

A study of two-phase flow and heat transfer in a small tube of 1 mm internal diameter has been conducted experimentally as part of a wider study of boiling in small channels. R141b has been used as the working fluid. The boiling heat transfer in the small tube has been measured over a mass flux range of 300–2000 kg/m² s and heat flux range of 10–1150 kW/m². In this paper the boiling map for a mass velocity of 510 kg/m² s and heat flux of 18–72 kW/m² is discussed and the problems of determining heat transfer coefficients in small channels are highlighted.     

虚拟现实技术在电力培训中的应用

虚拟现实技术的出现,使现代教育培训发生了很大变化。究其原因主要是虚拟培训有着传统培训方式无法比拟的优势。虚拟教育培训是指利用虚拟现实技术来模拟现实生活中的环境,学员在培训的过程中始终感觉自己在现场进行真实培训。虚拟现实技术利用先进的交互设备在视觉、听觉、触觉上对虚拟环境中的事物进行感知,有利于实际操作技能的提高。该文论述了虚拟现实技术在教育培训应用中的必要性和优越性。以电力培训系统的构建为例,阐述了如何利用3DSM Max和OpenGL构建虚拟培训系统,实现了虚拟现实与教育培训的有机结合。     

French Rationalism: A Broken Tradition

From the golden era of 1960s Rationalism to the present Inquietude Lucide, Joseph Abram describes the Rationalist tendencies in French architecture. Once dominated by the spectres of Le Corbusier and Auguste Perret, the rational was deeply embedded in French tectonic culture. Despite the current reassertion of the rational, the future, as Abram explains, appears less certain. Copyright © 2007 John Wiley & Sons, Ltd.     

Heat transfer and pressure drop during condensation of refrigerants inside horizontal enhanced tubesTransfert de chaleur et chute de pression lors de la condensation de frigorigènes à l'intérieur de tubes horizontaux à surface augmentée

This paper presents a critical review of correlations to compute heat transfer coefficients and pressure drop, for refrigerants condensing inside commercially available tubes with enhanced surfaces of various types, and a theoretical analysis of the condensation phenomenon. Predictions from some of the above equations are compared with experimental data. In addition, information is presented about the influence of small amounts of compressor oil on the condensation of refrigerants in enhanced tubes.     

Pressure effect on the release of supercooled water with dissolved air

It is proposed that vapor has been elucidated to having relation to the release of supercooled water.In this study, considering that the vapor has a relation to dissolved air, a supercooling experiment is performed to test tubes of pure water with three patterns of initial dissolved oxygen (DO_i = 4.1, 7.5, and 12.6 mg L⁻¹), i.e. dissolved air. The initial DO in each test tube is kept to the value as constant as possible during supercooling. And the pressure effect on supercooling release of pure water is observed by measuring supercooling degree and by visualizing bubbles enclosed to the ice after full crystallization of the pure water.From this study, it appeared that the factors such as cooling rate, initial DO and pressure of pure water are related to the release of supercooling (supercooling degree and supercooling time). Moreover, the initial DO was confirmed to the confined bubble in fully frozen ice of pure water.     

机械化黄酒生产中酵母的生长及控制

机制黄酒始于20世纪50年代,主要采用纯种发酵工艺,酵母菌的生长对酒质影响较大。以85#酵母、生麦曲和苏-16#纯种培养熟麦曲混合曲(9∶1)为糖化发酵剂,采用大罐发酵工艺,探讨糖度变化与酵母生长条件的关系。试验结果表明,机制黄酒最高糖化温度仅31℃左右;酵母接种量以2.5%～3.0%为宜,接种酵母应为稳定期,即培养40h左右的速酿酵母,可有效缩短酵母生长迟缓期;在酵母对数生长期,应保持有充足的糖分提供给酵母营养,一般为50～150g/L;稳定期酵母浓度可达4亿/ml左右,糖度下降速度可达7.5g/L·h,酒精度上升1.75%/h左右;当醪液酒精度达到10%(v/v),糖度4～5g/L,酵母浓度3亿/ml左右时,即进入衰退期;衰退期的酵母不再增殖,当酒精度达18%(v/v)时,出现酵母凝聚现象,发酵液变清,酵母出芽率几乎为零,揭示整个发酵结束。(一平)