共查询到19条相似文献,搜索用时 62 毫秒
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The effects of electrode polarities on EHD enhancement boiling heat transfer were investigated theoretically and experimentally based on the analysis of electric field distribution affected by superheat boundary layer and charge injection. The results showed that electric field distribution was changed by the charge induced by temperature gradients in the superheat boundary layer, but the change was independent of electrode polarities. However, when electric charge injection occurred, the electrode applied positive high voltage might generate different characteristics of charge injection from that generated by applied negative high voltage. If the electric field on the surface of heat transfer increased due to charge injection, the augmentation effects would increase. The experiments demonstrated that positive high voltage gave larger enhancement factors than negative high voltage. The experimental phenomena could be interpreted well on the basis of charge injection characteristics. 相似文献
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采用6种不同电极布置方式,进行了不同电势和热流密度下的R123池沸腾换热的试验研究。通过数值分析,计算了不同电极布置下换热面上的电场强度及分布。不同的电极布置,会导致换热面上电场强度和电场均匀性两方面的变化。结合试验和电场分布的计算结果,分析了电场均匀性、电场强度、热流密度与沸腾换热效果之间的关系。结果表明,在低热流密度下,电场分布对沸腾换热影响较大;而在高热流密度下,影响较小。电水动力学(EHD)强化换热效果是电场强度和电场均匀性综合作用的结果。 相似文献
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EHD强化换热能耗的热力学第二定律分析 总被引:1,自引:0,他引:1
引言 EHD(electrohydrodynamics)强化换热是一种主动强化传热方式,它必须消耗一定的电能,利用电场、流场和温度场的相互作用,才能达到强化传热的目的.从传热强化的效果来看,以往的研究,主要是用强化系数这一指标进行评判,实验结果表明[1],EHD强化换热效果显著,例如,对单相对流传热,传热系数最大可增加100倍[2].同时,很多实验结果也表明,相对于传热量,电功耗可以忽略不计[3~7].由于认为EHD电功耗很小,功耗问题的深入理论分析,尚未引起学者们的特别关注[1].作者依据热力学第二定律,提出了一个EHD强化换热能耗评价的方法,为EHD强化换热的经济性判别,提供了理论依据. 相似文献
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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
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为进一步探索电场强化沸腾换热的机理,利用高速摄像仪对沸腾汽泡在电场作用下的生长过程进行了可视化实验研究,实验观察到电场作用下汽泡生长的动态图像,并对电场作用下汽泡行为的改变对沸腾换热的影响进行了初步分析。研究结果表明:电场作用下汽泡沿场强方向伸长,随着场强的升高,汽泡的脱离长径比增大,脱离体积减小,脱离频率增大。汽泡变形是由于汽泡受到电应力的作用,电应力在赤道方向压缩汽泡,在极轴方向拉伸汽泡,使得汽泡沿场强方向变细变长。由于在电场作用下汽泡行为的变化使得沸腾传热系数和临界热流密度提高。 相似文献
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在对流动特性和换热机理进行分析的基础上,建立了垂直多孔表面管内高沸点工质强化流动沸腾换热的数学模型和数值计算方法.该模型认为环状流区域同时存在强制对流与核态沸腾两种换热方式.液膜厚度、速度与温度等参数通过求解液膜的质量守恒、动量守恒、能量守恒方程获得.核态沸腾换热则包括气泡脱离带走的热量及用于加热气化核心影响区流入液体的热量两部分.提出了流动沸腾情况下的多孔层气泡脱离直径及气化核心密度计算方法.对异丙苯在火焰喷涂型垂直多孔表面管内向上流动时的沸腾换热进行了数值预测,大部分工况的计算值与实验结果符合良好.在低干度区(x=0.1),核态沸腾在总换热中的比例约为50%.随着干度的增加,核态沸腾受到越来越大的抑制,当x为0.5时,这一比例降低到约15%. 相似文献
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The effect of a radial d.c. electric field on nucleate boiling heat transfer was investigated experimentally using a single-tube shell/tube heat exchanger. A dielectric liquid (Freon R. 114) was used in the shell and the tube was heated by circulating water through it.
It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis.
It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application 相似文献
It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis.
It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application 相似文献
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<正>1 引言 随着对传热过程这一客观规律认识的深化以及加工制造技术的进步,人们已能研制开发出各式各样的强化换热元件,并在工程实践中取代传统的光滑管从而取得省材节能的双重效果。T.C.Canavos曾预言:到目前为止,强化换热元件的工作还仅仅是个开始,但是它的好处是那样地明显,以至于普通光滑管之被淘汰只不过是一个时间的问题了。多年来的实践证明这种预言是正确的,在强化换热元件中,强化液体泡核沸腾的元件的研究进展尤为突出,自60年代末期以后,先后有4种管型实现商品化,其中一种就是T形翅片管(Gewa-T)。T形翅片管自1978年问世于原联邦德国的Wieland Worke公司以后,国内外已有多项研 相似文献
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引 言核状池式沸腾是一种成核现象 ,它包括气泡的产生、气泡的生长以及气泡的脱离 3个阶段 .在工程应用中 ,采用强化表面来获得较高的池式沸腾传热系数的例子已有许多 ,此种方法能在较小传热温差的情况下获得较大的传热通量 .例如在低品位热能的利用中就采用了这种方法 .另一个很有应用前景的领域是电子元件的冷却 .强化核状沸腾传热的方法有两种[1] ,一种是降低沸腾传热表面的润湿性 ,这可以通过在传热表面上涂覆低表面能材料如聚四氟乙烯来达到 ,但是这种方法又增加了传热的附加热阻 .另外 ,这种方法对于高润湿性的介质是不适用的 ,例如… 相似文献
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Based on the tests of more than ten different additives, several effective additives are found capable of improving the boiling heat transfer behavior of water pronouncedly. The mechanism of the enhancement of nucleate boiling with additives has been investigated, and the results indicate that one of the important reasons is that the nucleation sites have been increased. 相似文献
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<正>1引言 传热恶化有不同的类型,就工程换热设备设计和运行的实际需要来说,人们最关心的是以下几点:(1)传热恶化发生的位置(壁温飞升起始点),一般用。cr来表示;(2)传热恶化发生后壁温飞升的最大值,一般用A儿。。来表示;(3)壁温飞升最大值的位置,一般用K。。。来表示;(4)传热恶化发生后的。mi。。本文着重分析讨论后3个问题。 相似文献
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