水平管外R404A降膜蒸发传热的实验研究

搭建了降膜蒸发实验台,研究了水平单管外的降膜蒸发传热特性。测试管为外径19mm、有效实验长度为2500mm的光滑管和强化管。实验采用R404A作为管外降膜蒸发工质,与管内热水进行换热。布液采用喷嘴喷淋的方式,通过21个喷口当量直径为2mm的喷嘴完成。分别在变饱和温度(0、5、10、15℃)、变热流密度(从8到30kW/m2)和变喷淋量(从0.07到0.11kg/(m·s)时进行实验,研究了降膜蒸发换热性能相应的变化情况,得到R404A的管外降膜蒸发换热的一些规律,这对降膜蒸发器的设计及应用具有一定的参考作用。     

制冷换热器双侧强化换热管的实验方法对比

大型制冷系统中的换热管通常采用管内、管外表面双侧强化结构,因不便在壁面布置温度传感元件,双侧强化管需要特别的实验方法来测定其性能,包括Wilson图解法(WPM)、修正Gnielinski公式法(MGF)、Wilson-Gnielinski公式法(W-GF)。不同的方法有各自的应用场合和使用局限性。本文针对双侧强化管提出一种便于应用的新方法,称为待定指数法(UEM),通过线性拟合和优化得到关联式中的待定参数,可有效分离管内、管外对流换热表面传热系数。在双侧强化管上进行了R134a管外蒸发、水管内流动的两组实验,以此对包含新方法的4种实验方法进行应用对比。结果表明：4种实验方法得到的强化管管内、管外对流换热表面传热系数的强化倍率分别在2.88～3.23、3.15～3.54之间,不同方法得到的管内、管外对流换热表面传热系数差异分别在15%、11%以内。4种实验方法可根据不同的应用条件选择使用,UEM限制条件少、应用方便,是一种更加高效、准确的实验方法。     

肋类型对水平单管管外沸腾换热性能影响

本文选用近共沸制冷剂R4I0A,对相同尺寸的一根光管和两根双侧强化管进行了管外沸腾换热实验研究。对于光管管外沸腾换热,将实验结果分别结合Coper公式和Gaenflo公式得到的管内表面传热系数与经验公式计算值进行了对比,结果显示两者误差保持在15%以下,验证了实验结果的准确性。运用Wilsn图解法分别求得两根换热管管内换热强化倍率分别为1.85~2.05和2.02~2.25,通过不同方式改变热流量,综合对比1#换热管和2#换热管总传热系数与管两侧表面传热系数,结果 均显示由于强化管肋类型的不同, I#换热管管外表面结构更有利于汽化核心形成气泡,比2#换热管总传热系数高约10%,管外 表面传热系数高约20%~25%,更加符合强化水平单管管外池沸腾换热的要求。     

一种冷凝强化换热管传热性能的试验研究

以目前广泛使用的R22为工质,对一种冷凝强化换热管管外冷凝换热性能进行了实验研究.管内以乙二醇为冷却介质.在恒定热流密度、变乙二醇流速与乙二醇流速不变条件下,改变乙二醇进口温度得到一系列实验数据,再通过威尔逊(Wilson)图解法同时得到管内外换热关联式.给出了不同管内流速时管外冷凝换热性能对比图.该冷凝强化换热管管外冷凝换热性能与普通光管相比,传热强化倍率为4.48.由于管内表面有细微的凹凸形状,使管内对流换热系数达到光滑管的1.33倍.     

R404A在水平强化管外的冷凝实验及数据处理方法

针对一种双侧强化换热管,实验测试和分析了制冷工质R404A在管外凝结与水在管内对流的传热规律,采用"Wilson图解法"和"Gnielinski法"两种不同的方法对实验数据进行了处理。经理论分析和实验研究表明,Wilson图解法对于双侧强化换热管管内、管外表面传热系数实验容易产生较大误差,"Gnielinski法"是更合适的方法。实验得出了管内对流传热和管外凝结传热的计算关联式及传热的强化倍率。对于制冷剂R404A,在强化管外凝结的表面传热系数随着壁面过冷度的增加而增大,呈现出与纯工质光滑管外冷凝时不同的变化趋势。     

蒸发式冷凝器顺流式和逆流式换热性能实验

对蒸发式冷凝器顺流式和逆流式两种不同方式的换热性能进行实验研究。搭建了蒸发式冷凝器换热性能实验台,分别在顺流式和逆流式条件下,对冷凝器喷淋密度和迎面风速对换热性能的影响进行理论和实验研究。结果表明:随着迎面风速的提高,喷淋密度增大,在顺流和逆流条件下,总换热系数均呈现上升的趋势,最后达到一个最大值,逆流式条件下的换热性能高于顺流式;在迎面风速为3.28 m/s,喷淋密度为0.057 kg/(m·s)条件下,顺流式的总传热系数最大为616 W/(m2·K),逆流式总传热系数可达到628 W/(m2·K)。在相同条件下,逆流式的传质系数及能效比EER均优于顺流式。     

R134a表面增强型蒸发强化传热管的实验研究

介绍了国外空调冷冻设备中采用的一种新型商用表面增强型蒸发强化传热管,并对其进行了实验研究.发现对使用R134a环保制冷工质,在低热流密度的条件下,表面增强型蒸发强化传热管具有十分优异的强化效果.在实验的换热工况下,保持进口水温不变而改变管内水流速,这种强化管的总换热性能是普通低翅蒸发强化管的 2.2到2.6倍,管外换热系数是普通低翅蒸发强化管的1.3～1.9倍.     

R410A和R22在小管径水平管内冷凝换热特性研究

本文搭建了冷凝换热实验台,对R410A和R22管内冷凝换热系数性能进行对比研究,实验工况为质量流速200~800kg/(m^2·s)、饱和温度40℃、干度0~1、5 mm外径水平光滑铜管,分析了质量流速和干度对管内冷凝换热的影响,并将应用于传统管道的关联式与实验所得数据进行对比。结果表明:冷凝换热表面传热系数与质量流速和干度呈正相关,高干度区域时的冷凝换热表面传热系数增幅显著;M. M. Shah[4]关联式来预测实验数据的效果并不理想,与实际值相比偏差最大可达60%,但是预测低质量流速和低干度区的数据较为理想;当质量流速较小(G=200 kg/(m^2·s))时,R410A的冷凝换热表面传热系数要低于R22;随着质量流速的增大(G=400 kg/(m^2·s)),二者冷凝换热表面传热系数的差距减小;当达到中高质量流速(G=600kg/(m^2·s))时,R410A的冷凝换热表面传热系数与R22的相似;当质量流速继续增大(G=800 kg/(m^2·s))时,R410A的冷凝换热表面传热系数随着干度的增大开始高于R22的。     

内翅板蒸发式冷凝器降膜流动与传热特性

为了增强蒸发式冷凝器板外气液两相流动与传热,基于数值模拟方法对比分析了几种新型的板片结构,研究了板片构型、喷淋水喷淋密度、空气入口速度等因素对气液两相流流体流动及传热性能的影响。结果表明:半圆波纹板有较长的水膜稳定时间和较大的换热面积,换热性能较好;不同板片结构的蒸发式冷凝器具有不同的最佳喷淋水喷淋密度,最佳喷淋密度区间范围为0.48~0.93 kg/(m·s);空气入口速度一定时,半圆波纹板的壁面温度随喷淋密度增大而增大,气液界面温度随喷淋密度增大而减小;当空气入口速度小于2.5 m/s时,空气入口速度的适当增大能够有效减薄半圆波纹板板外水膜厚度,强化换热。     

R417A在水平双侧强化管外沸腾换热研究

对3根双侧强化管在饱和温度为8℃工况下进行了水平管外R417A沸腾换热特性研究。采用Wilson热阻分离法得到管外沸腾表面传热系数,并对实验结果进行了热阻分析。实验结果表明:管内轧制出0.32~0.34 mm的螺旋槽道,可以使管内对流传热系数提高到光管Gnielinski公式计算值的2.524~2.658倍。相同管型的强化换热表面,其沸腾传热系数随壁面温差变化的趋势相似,肋密度42fpi的E30管沸腾传热系数比50fpi的E32管大4.5%,表明沸腾传热系数的大小及变化趋势与肋密度(孔隙直径)及管型密切相关。双侧强化管外R417A沸腾换热,管外热阻约占总热阻的70%,管外仍需进一步强化,才能明显提高总体传热性能。R417A在强化管外沸腾传热系数仅为近似条件下其主要组分R134a的三分之一,表明混合工质沸腾换热与纯工质有较大差异。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.