Periodical shedding of cloud cavitation from a single hydrofoil in high-speed cryogenic channel flow

In order to explain criteria for periodical shedding of the cloud cavitation, flow patterns of cavitation around a plano-convex hydrofoil were observed using a cryogenic cavitation tunnel of a blowdown type. Two hydrofoils of similarity of 20 and 60 mm in chord length with two test sections of 20 and 60 mm in width were prepared. Working fluids were water at ambient temperature, hot water and liquid nitrogen. The parameter range was varied between 0.3 and 1.4 for cavitation number, 9 and 17 m/sec for inlet flow velocity, and −8° and 8° for the flow incidence angle, respectively. At incidence angle 8°, that is, the convex surface being suction surface, periodical shedding of the whole cloud cavitation was observed on the convex surface under the specific condition with cavitation number and inlet flow velocity, respectively, 0.5, 9 m/sec for liquid nitrogen at 192°C and 1.4, 11 m/sec for water at 88°C, whereas under the supercavitation condition, it was not observable. Periodical shedding of cloud cavitation occurs only in the case that there are both the adverse pressure gradient and the slow flow region on the hydrofoil.     

Ultra-rapid freezing by spraying/plunging: pre-cooling in the cold gaseous layer

A thermophysical model is established to analyse the influence of pre-cooling of a biological specimen in the cold gas layer associated with spray-freezing techniques. The basic principles governing the process of pre-cooling are provided. It is concluded that pre-cooling is one of the major limiting steps in attaining an overall ultra-rapid cooling rate. Pre-cooling has a substantial influence on the nature of the final frozen specimens. In order completely to avoid crystallization before entry into the liquid cryogen and maximize the overall cooling rate of the specimen, precautions should be taken to control the height of the gaseous layer and the size of the specimen. The probability of the specimen being frozen in the cold gaseous layer is reduced by increasing the entry speed. The effectiveness, however, becomes less marked at speeds greater than 10 m/s. In order to minimize the risk of misinterpreting the measured cooling rate, it is necessary to specify the pre-cooling conditions. The pre-cooling effect is much more evident in liquid helium than in cryogens such as propane, ethane, Freon 12, 13 and 22.     

低温储罐预冷过程预测

为了能输送和存储单相低温液体,保证输送管道和低温储罐的安全,预冷过程不可或缺。对预冷时间、预冷介质消耗量进行预测有利于指导实际操作。从热力学基本理论出发,采用稳态与变热导率的热力学分析方法,建立储罐预冷时间与预冷介质消耗量数学模型,推导了储罐温度随时间的变化关系,探讨进口流量与预冷时间、预冷介质消耗量之间的相互影响。将不同的计算方法相结合,指导选取最佳预冷流量。     

MATERIALS FOR RETENTION OF LIQUID CRYOGENS CONTAINED IN SPACE QUALIFIED COOLER

1.IntroductionAlight,smallcryogenc00lerf0rcry0genicopticalsystemhasbeendevelopedinourgroup-Thiscoolerhasadewarwithitscross-sectionbeingat0roidalshapeforthepurposeofcompactness.The0pticalsystemwouldbel0catedinthecavityofthedewar.Whenthetor0idaltankisfilledwithliquidnitrogen(LN2),andtheopticalsystemisc00leddowntobelow100K,theLN2suppliesarestopped.Afterwards,itisrequiredtomaintainthetemperature0fthetankwallsurroundingthe0pticalsystemc0nstallts0thatthetemperatureoftheopticalsystemwithinthemisal…     

激光溶脂手术脉冲式制冷剂喷雾冷却数值研究

无创激光溶脂发展潜力巨大,但水对近红外激光的吸收可能导致真皮热损伤。目前尚无有效的正常组织冷保护措施,制约了激光溶脂的发展。提出采用多脉冲喷雾冷却的方式对人体皮肤进行冷保护,建立皮肤组织多层均匀模型,结合Pennes生物传热方程数值模拟制冷剂R134a连续和脉冲式喷雾对皮肤深层组织的冷却效果。发现相同累计喷雾时间下多脉冲喷雾的冷却深度大于连续式喷雾,从冷却温度和冷却深度上更适合于激光溶脂的皮肤冷却。在单次喷雾时间10 ms、间隔时间2500 ms、喷雾次数10次、占空比0.004的条件下,冷却深度达到5000 μm,1 mm深度的皮肤组织喷雾中心温度最低能达到11℃,可以有效满足激光溶脂对皮肤冷却深度的要求。     

压缩式热泵精馏中的工质选择

热泵精馏是一项高效节能技术。本文分析了压缩式热泵精馏中不同类型工质应用的特点,比较了它们的实际适用条件,这埘推广热泵精馏的工业应用有一定的指导意义。     

溴化锂吸收式制冷机冷剂水溢出故障分析及排除

叙述了溴化锂吸收式制冷机冷剂水溢出故障的分析及其排除方法。     

Protection of superconducting coils by induction coupling

A model that predicts temperature rise in perfectly coupled circuits is presented. The use of frozen cryogen in a secondary protection circuit coupled to a superconducting coil is discussed in this paper. Formulas for the required amount of the frozen cryogen and conducting metal in the protection circuit are derived as a function of the desired final temperature in the protected coil.     

激光手术喷雾冷却中单个液滴蒸发特性

制冷剂喷雾冷却(CSC)是激光治疗鲜红斑痣(PWS)手术的重要辅助手段。为了深入了解制冷剂喷雾特性以提高冷却效率、优化喷嘴设计,利用质量传递数法推导传质方程,通过选取合适的阻力系数经验关联式建立了动量方程,考虑液滴蒸发以及与环境气体的对流换热建立了液滴能量方程,初步建立了单个制冷剂液滴平衡蒸发阶段蒸发冷却理论模型。利用建立的模型模拟悬挂水滴冷冻过程的过冷阶段,并在变物性条件下预测了制冷剂液滴温度随飞行距离的变化,结果与实验对比证明了模型的有效性。有关液滴初始参数对液滴蒸发冷却特性影响的研究结果表明,本模型可以为制冷剂喷雾冷却实际应用于激光治疗鲜红斑痣手术提供有效的分析方法。     

冷剂制冷-油吸收复合凝液回收工艺的应用

为了进一步提高天然气凝液装置的产品收率,本文针对凝析气田中气源压力高,无压差可利用的工况条件,应用冷油吸收原理,通过工艺流程模拟分析与研究,确定了冷剂制冷一油吸收复合凝液回收工艺原理流程。通过流程模拟,分析了影响丙烷回收率的主要因素。本文实例研究表明：相同制冷温度下,冷剂制冷一油吸收复合工艺的丙烷回收率比原冷剂制冷工艺可提高23％～27％。适当提高吸收塔的压力,对增大丙烷回收率有利,但吸收塔压力的确定要综合考虑原料气压力和外输气压力的大小。吸收剂循环流量对丙烷回收率、两塔热负荷的影响是十分显著的,吸收剂循环流量越大,丙烷收率越高,但吸收剂流量增大到一定值后,丙烷回收率增加量变缓,同时脱乙烷塔、塔冷凝器以及重沸器热负荷显著增加,吸收剂循环流量比控制在0．7～0．75之间比较合理。