共查询到14条相似文献,搜索用时 93 毫秒
1.
Experiments have been conducted on the pool boiling of binary mixtures in JK tubeswith porous surface and ribbed channels,attempting to enhace the boiling heat transfer coefficientsinvolved.The binary mixtures used in this study are R113 and R11.The results show that the boilingfi1m heat transfer coefficients for the R113 and R11 binary mixtures in JK2 and JK1 tubes are 2—8tirnes and 2—5 times greater than those in smooth tubes respectively.Based on this experimentaldata and simple theoretical analysis,a correlation has been proposed to predict the boiling heattransfer coefficients for R113/R11 mixtures in a horizontal JK tube with a relative error of less than16%. 相似文献
2.
A model of evaluation and prediction of enhancement of boiling heat transfer with additives has been proposed according to fuzzy fundamentals. Correlative appraisement of boiling heat transfer augmentation was done with the model based on 39 additives which were tested by the authors and other researchers. The results show that the evaluation of 35 additives is consistent with experiments, which means that the accuracy of the model is 89.7 percent. In addition, the prediction of the ability of boiling heat transfer enhancement with sodium oleate, polyethylene glycol and Tween-40 is also in good agreement with correspondent experiments. 相似文献
3.
The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes(CDs) and converging-diverging tubes equipped with twin counter-swirling twisted tapes(CDTs).The effects of Reynolds number(Re 10000-20000),pitch length(P 11.25,22.5 mm),rib height(e 0.5,0.8,1.1 mm),pitch ratio(δ1:8,5:4,8︰1),gap distance between twin twisted tapes(b 0.5,4.5,8.5 mm) and tape number(n 2,3,4,5,6) on Nusselt number(Nu),friction factor(f) and thermal enhancement factor(η) are investigated under uniform heat flux conditions,using water as working fluid.In order to illustrate the heat transfer and fluid flow mechanisms,flow structures in CDs and CDTs are presented.The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT,and both CD and CDT show better thermal performance than plain tube at the constant pumping power.It is also found that the increases in the Nusselt number and friction factor for CDT are,respectively,up to 6.3%-35.7% and 1.75-5.3 times of the corresponding bare CD.All CDTs have good thermal performance with η greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate. 相似文献
4.
Heat transfer, friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes (STT) and plain twisted tapes (PTT) are investigated experimentally using the water as working fluid. The tapes (STT and PTT) have three twist ratios ( , 4.4 and 6.0) and the Reynolds number ranges from 2000 to 12000. The experimental results reveal that heat transfer rate, friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance. Over the range considered, the Nusselt number, friction factor and thermal enhancement factor in a tube with STT are respectively, 1.03 to 1.14, 1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT. An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT. 相似文献
5.
This paper deals with the experimental investigation on Nusselt number, friction factor and thermal enhancement factor of a double pipe heat exchanger equipped with twisted tape consisting wire nails (WN-TT) and plain twisted tapes (P-TT) with three different twist ratios of y 2.0, 4.4 and 6.0. Test runs are conducted using the water as the working fluid with Reynolds number range between 2000 and 12000 for WN-TT and P-TT. It is found that Nusselt number, friction factor and thermal enhancement factor in the tube equipped with WN-TT appreciably higher than those in the tube fitted with P-TT and plain tube. Over the range considered Nusselt number, friction factor and thermal enhancement factor in a tube with WN-TT are respectively, 1.08 to 1.31, 1.1 to 1.75 and 1.05 to 1.13 times of those in tube with P-TT. The better performance of WN-TT is due to combined effects of the following factors: (1) common swirling flow generated by P-TT, (2) additional turbulence offered by the wire nails. Empirical correlations for Nusselt number, friction factor and thermal enhancement factor are also formulated from the experimental results of WN-TT and P-TT. 相似文献
6.
混合制冷工质的传热性能差,使得其应用受到一定限制,而采用适当的强化传热技术可以大大提高混合制冷工质传热性能。实验的热流密度范围内,在相同的热流密度条件下,非共沸混合制冷剂R134a/R142b在机械加工表面多孔管外沸腾传热膜系数是光滑管的1.78~3.33倍。 相似文献
7.
8.
测度了甲醇在9根第二代机械加工表面多孔管(JK-2管)、1根第一代机械加工表面多孔管(JK-1管)和1根光滑管上的单管饱和池沸腾传热系数,结果表明,JK-2管比JK-1管能更有效地强化甲醇的池沸腾传热。提出了一个简化的池核沸腾强化传热机理,并导出了相应的池核沸腾强化的传热关联式,该关联式与实验数据吻合良好。 相似文献
9.
分析和比较了作为CFCs替代物的混合工质R134a/R142b在光滑管和机械加工表面多孔管管束外的沸腾传热性能和管束效应,为氟里昂满液式蒸发器的设计提出了合理的建议,。 相似文献
10.
11.
12.
对水平横槽纹管内氨沸腾换热及其压降特性进行了实验研究,获得了不同热流密度、不同质量流速和不同局部蒸汽干度下沸腾换热和压降的实验数据。实验结果表明,在本实验的参数范围内,与光滑管相比,横槽纹管在压降增加不大的情况下可使管内沸腾换热系数提高30%~150%,横槽纹管的节距减小对传热强化的作用明显,而对槽深的影响不大。还给出了横槽纹管内氨局部沸腾换热和压降的无因次准则关系式。 相似文献
13.
以去离子水为工质,研究了钛合金螺旋扭曲管内的强化传热与流阻性能,并与钛合金圆管比较;根据实验数据拟合螺旋扭曲管内努塞尔特数和阻力系数的实验关联式,并与经典对流传热关联式比较. 结果表明,Dittus?Boelter方程、Sieder?Tate方程、Михеев方程和Gnielinski方程适用于模拟螺旋扭曲管内对流换热特性. 相似文献
14.
多孔表面强化沸腾传热的研究进展 总被引:2,自引:0,他引:2
本文综述了多孔表面用于强化沸腾传热的研究工作。即介绍了多孔表面的形成和结构表征方法、多孔表面的沸腾传热性能以及描述多孔表面沸腾传热机理的物理和数学模型,同时分析了影响多孔表面沸腾传热性能的因素,探讨了多孔表面强化沸腾传热研究的发展方向。 相似文献