R141b气体水合物蓄冷过程现象与机理分析

描述了Ｒ１４１ｂ气体水合物的形成及其结构，分析了Ｒ１４１ｂ气体水合物蓄冷实验过程中的过冷度现象，指出丰度和竞争结构是过冷度出现的主要原因。     

Moderator Analysis of Wolsong Units 2/3/4 for the 35% Reactor Inlet Header Break with a Loss of Emergency Core Cooling Injection

Three-dimensional numerical calculations have been performed for a transient moderator circulation inside the CANDU (Canada Deuterium Uranium) calandria vessel of Wolsong Units 2/3/4. The porous media approach was applied for the core region containing 380 calandria tubes. An anisotropic hydraulic resistance model for the porous media has been developed based on the empirical pressure loss correlations. The selected event was the 35% RIH (Reactor Inlet Header) break with a loss of ECC (Emergency Core Cooling) injection, which has been known to give the largest heat load to the moderator among all the DBA's (Design Basis Accidents). The calculation has been successfully done until 1,200 s after the break, when most of the considerable heat transfer procedure has been completed. During this LOCA (Loss of Coolant Accident) transient, the local subcoolings in the vicinity of any PT/CT (Pressure Tube/Calandria Tube) contact does not drop below the experimentally derived subcooling threshold of 30°C. Because the minimum subcoolings reach only a few degrees to the threshold temperature during the initial 20-40 s, future work on the CANDU moderator circulation needs to be aimed at determining whether this small subcooling margin covers the uncertainty of the moderator analysis.     

Upper Plenum Dump during Reflood in PWR Loss-of-Coolant Accident

Upper plenum dump during reflood in a large break loss-of-coolant accident of PWR is studied with the emergency core coolant injection into the upper plenum in addition to the cold leg. Transient experiments were carried out by injecting water into the upper plenum and the simple analysis based on a one-dimensional model was done using the drift flux model in order to investigate the conditions under which water dump through the core occurs during reflood.

The most significant result is an upper plenum dump occurs when the pressure (hydrostatic head) in the upper plenum is greater than that in the lower plenum. Under those circumstances the flow regime isco-current down flow in which the upper plenum is rapidly emptied. On the other hand, when the upper plenum pressure (hydrostatic head) is less than the lower plenum pressure (hydrostatic head), the co-current down flow is not realized but a counter-current flow occurs. With subcooled water injection to the upper plenum, co-current down flow is realized even when the upper plenum hydrostatic head is less than the lower plenum hydrostatic head. The importance of this effect varies according to the magnitude of water subcooling.     

过冷度对蒸汽气泡破碎及微气泡喷射过程的影响

为研究过冷度对蒸汽气泡破碎及微气泡喷射过程的影响,利用高速摄像机记录不同过冷度下过冷池中蒸汽气泡凝结过程。实验结果表明:在低过冷度(ΔTsub=17K)下,蒸汽气泡界面波动发展缓慢,气泡不会破碎,而是逐渐分裂凝结;在高过冷度(40KΔTsub75K)下,蒸汽气泡表面上的波动剧烈发展,随后气泡会突然破碎,并形成大量微气泡;在ΔTsub=30K时,气泡突然破碎前会有小气泡分裂现象发生。40KΔTsub75K时气泡破碎形成的微气泡的直径和速度在量级上与气泡微细化沸腾区域的微气泡接近。随过冷度的升高,微气泡的直径减小,速度增加,且蒸汽气泡破碎前其表面上波动的波数迅速增加,波动的最大幅值先增加后减少。     

Investigation on Operational Unsteady Characteristics of CPL：The Effects of Evaporator and Reservoir

INTRODUCTIONTwo-phaseCapillaryPUmpedLoopasanewthermalcontrolsysteminspacetechniqueshasmanyadVantages.Ittransportsrelativelylargeamountofheatforalongdistance.TheevaporatorandreservoirofCPLactasimportantpartsinthedevice,thesteadyandunsteadyoperationalperformancesofCPLstronglydependonbothofthemli'2].T'heCPLunsteadycharacteristicsconsistofsac-upandoperationalunsteadycharacteristics.WhenthemeasuredtemperatureoftypicalCPLpointdeviatesfromitsnormalvalueanddisplayscontinualoscillationchara…     

Transient behavior of subcooled forced-convective boiling with twisted tape inserts

An internal twisted tape, when used to initiate subcooled swirling flow boiling, is a very effective method of cooling components which are subject to a high heat flux in a fusion reactor. In this study, the swirled channel was constructed using a copper cylinder (8 mm inside diam., 190 mm outside diam., and 100 mm heating length), which was equipped with a twisted aluminum tape (approx. 0.5 mm thick and 7.5 mm wide). The values of the tape-twist ratio y (the length required to complete a single 180-degree twist of the tape divided by the inside tube diameter) were approximately 1.8, 2.5, 3.2, 4.2, and infinity. Critical heat flux dependence on flow velocity and tape-twist was determined. Heating and cooling processes of large thermal capacity and inertia were used to obtain the wall heat flux via quasi-steady conditions, and several results for these limited cases are presented in the transition region near atmospheric pressure. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res 25(3): 178–191, 1996     

Study of injected water subcooling effect on falling water limitation in countercurrent two-phase flow in vertical channels

This study analytically investigated the subcooling effect of injected water on the falling water limitation in countercurrent two phase flow (CCFL) in vertical channels, by applying a new model of momentum balances for both liquid and gas phases over the entire length of the channel. The subcooling effect of injected water on CCFL, which is one of the dominant parameters, had been clarified neither analytically nor experimentally because the CCFL phenomena is very complicated thermodynamically. As a result of the present study, it has been clarified that the analytical model proposed here could give good predictions of the existing data on the subcooling effect of experiments simulating the performance of emergency core-cooling water injection during a loss-of-coolant accident in pressurized light-water reactors. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res. 25(1): 25–38, 1996     

节流前过冷度和压力对液氮节流特性的影响

节流在普冷领域应用广泛。其在基于林德循环、克劳德循环等低温液化循环、焦汤氦制冷系统、低温推进剂热力排气系统中也都有涉及。为了深入揭示低温流体相比室温气体的节流特殊性,设计并搭建了一套低温流体气液两相节流可视化试验系统。针对渐缩渐扩管型的节流元件,分析了节流前过冷度和压力对液氮节流特性的影响。研究表明：节流前压力一定,节流后温降及气相质量分数随节流前过冷度增加而增加;节流前过冷度一定,节流后温降及气相质量分数随节流前压力增大而增大;增大节流前压力,减小节流前过冷度,会减少节流后流体的单位质量制冷量。     

中等过冷度下含不凝性气体蒸汽冷凝传热特性

通过对竖直圆管外表面含不凝性气体蒸汽在中等壁面过冷度条件下的冷凝传热实验研究,分析了混合气体压力0.4～0.6 MPa、空气含量0.07～0.52以及壁面过冷度13～25℃时,蒸汽的冷凝换热特性,给出了冷凝传热过程中的经验关联式,并对氦气的存在及其对换热过程的影响进行了初步分析。结果表明：在混合气体压力及不凝性气体含量不变的条件下,壁面过冷度的降低利于冷凝传热系数的增长;所得到的经验关联式在低过冷度条件下能较好地对换热过程进行预测,且其与实验值的误差在±15%以内;实验条件下未发生氦气分层现象,相同不凝性气体质量分数条件下,氦气的存在会使冷凝传热系数降低约20%。     

机房空调室内外机间配管长度对机房空调性能影响的研究

以名义制冷量为71.4kW的制冷机组为对象,研究室内外机管长在水平和垂直方向变化时,系统制冷量、压缩机耗功的变化情况,从而为需要配置长配管的系统管长的确定提供参考.计算结果表明,压缩机耗功随着配管长度的增加而增加,系统制冷量变化与管道的水平或垂直方向有关.