Critical Heat Flux (CHF) Correlations for Subcooled Water Flow Boiling at High Pressure and High Heat Flux

The subcooled water flow boiling is beneficial for removing the high heat flux from the divertor in the fusion reactor,for which an accurate critical heat flux(CHF)correlation is necessary.Up to now,there are many CHF correlations mentioned for subcooled water flow boiling in the open literatures.However,the CHF correlations’accuracies for the prediction of subcooled water flow boiling are not satisfactory at high heat flux and high pressure for reactor divertor.The present paper compiled 1356 CHF experimental data points from 15 independent open literatures and evaluated 10 existing CHF correlations in subcooled water flow boiling.From the evaluation,the W-2 CHF correlation performs best for the experimental CHF data in all existing critical heat flux correlations.However,the predicted mean absolute error(MAE)of the W-2 correlation is not very ideal for all database and the MAE of the W-2 correlation is from 30%to 50%for some database.In order to enhance the CHF prediction accuracy in subcooled water flow boiling at high heat flux and high pressure,the present paper developed a new CHF correlation.Compared with other existing CHF correlations,the new CHF correlation greatly enhances the prediction accuracy over a broad range of pressures and heat fluxes which are desired in the cooling of high heat flux devices,such as those in the fusion reactor divertor.The validation results show that the new correlation has a MAE of 10.05%and a root mean squared error(RMSE)of 16.61%,predicting 68.1%of the entire database within±10%and 81.5%within±15%.The MAE of the new CHF correlation is 7.4%less than that of the best existing one(W-2 correlation),further confirming its superior prediction accuracy and reliability.Besides,the new CHF correlation works well not only for a uniform power profile but also for a non-uniform power profile in subcooled water flow boiling at high pressure and high heat flux.     

高热流密度微通道的周期性欠热沸腾

实验发现单微通道在高热流密度条件下会发生一种长周期/小幅度间歇性欠热沸腾现象.它发生在入口温度在室温到8℃的范围,出口温度及压差呈现非常有规律的小幅度脉动,且呈现反相.当热流密度略大于沸腾起始点时,脉动周期长达50～100 s.随着热流密度的增大,脉动周期变短.当热流密度接近临界值时,脉动周期在5～10 s.实验还发现在宽广的热流密度范围内.时均质量流速对于热流密度的变化不敏感,推断出在一个完整周期内,汽泡产生及逸出的时间相对较短.     

液氨高压喷雾特性实验研究

结合定容燃烧弹和高速摄影技术建立喷雾可视化实验平台,模拟柴油机缸内高温高压的喷射环境,研究环境温度、环境压力和喷射压力对液氨宏观喷雾特性的影响。结果表明,液氨喷雾对环境温度敏感性极高,提高环境温度和环境压力均可不同程度地提高氨蒸发比例,使其在喷雾体积空间内分布更均匀,进而形成高质量混合气。在高环境温度下提高喷射压力虽可改善蒸发效果,但对于蒸发速率的改善并不明显。     

高压共轨柴油机高海拔全负荷标定

高原标定是高压共轨柴油机开发过程中的重要环节.利用高海拔(低气压)标定试验系统进行了高压共轨柴油机不同海拔下的全负荷标定试验,研究了最佳喷油参数随海拔的变化,并进行了高压共轨柴油机不同海拔下的功率试验.研究结果表明,最佳循环喷油量随海拔的增加而减小,海拔每升高1 000,m,循环喷油量下降2%～4%;中高转速下最佳喷油提前角和轨压随海拔的增加而增大.海拔每升高1 000,m,最大转矩降低2.8%,标定功率下降2.9%.不同海拔下柴油机速度系数保持不变.不同海拔中高转速燃油经济性基本保持不变,低转速下燃油经济性恶化,海拔每升高1 000,m,低转速下燃油消耗率增加3.9%.     

不同水分下煤粉高压浓相输送的试验研究

试验依托一套输送压力可达4 MPa的干煤粉加压浓相气力输送实验装置,研究煤粉含水率(M=5.45%、8.94%、12.09%、14.20%、16.20%)、输送压差、流化风流量、补充风流量对流动特性的影响。结果表明:在流化风流量和补充风流量恒定,增大输送压差,固气比随压差的增大呈现先增大后减小的趋势;而保持压差和流化风流量不变,煤粉质量流量均随补充风流量的增加而降低;系统压差和补充风流量均不变,煤粉质量流量随流化风量的增大呈现出先增大后趋于不变;维持输送压差、流化风流量和补充风流量,垂直管和水平管压降变化幅度不大,而水平弯管的压降随含水率的增大而增大,垂直弯管的压降随含水率的增大呈现先增大后减小的情况。     

低温高水位工况下白山水电站混凝土重力拱坝变形及渗流分析

针对白山水电站大坝经历了低温高水位组合工况后出现的变形及渗漏增大问题,基于典型坝段的观测数据分析了大坝运行性态。结果表明,大坝在低温高水位工况下运行是其变形和渗漏量增大的主要原因,建议要加强监测力度,确保大坝安全运行。