【摘要】 对大气压下纳米流体在竖直细小圆管内自然对流沸腾特性和临界热通量(CHF)进行了试验研究。工质使用了水和水-氧化铜的纳米流体。试验中加热管长L=200～500mm,管径d=2.1～5.4mm和纳米流体浓度ω=0.1～1.0%(wt)。试验主要研究了不同浓度的纳米流体对CHF的影响。试验结果表明:相对于纯水而言,随着纳米浓度的增加,纳米流体的沸腾特性有所劣化,这主要是因为纳米颗粒在传热面上形成吸附层降低了传热表面的粗糙度,减少了表面活性核化密度,增加了传热面热阻,因此降低了传热能力。随着纳米浓度的增加,纳米流体的临界热通量也随之增加。纳米流体的临界热通量不仅与管长与管径比有关,而且还与纳米浓度有关;氧化铜颗粒质量浓度为1%(wt)的纳米流体的CHF比纯水的增加了30%以上。更多还原

【Abstract】 An experimental study was performed to investigate the natural convective boiling characteristics and critical heat flux(CHF) of water and water-based CuO nanoparticle-suspensions(nanofluids) in vertical tubes.The experiments were carried out under the conditions of the heated tube length L = 200～500 mm,tube diameter d = 2.1～5.4 mm and the nanoparticle mass concentration ω = 0.1～1 %(wt).The effect of the nanoparticle mass concentration on the boiling heat transfer and CHF was investigated.The experiment results show that,since the decrease of the numbers of the active nucleate cavities and the solid-liquid contact angle on the heating surface caused by a very thin layer of adsorbed nanoparticles,the boiling heat transfer of nanofluids is somewhat poorer than that of the base fluid.It was also found that,comparing with the base fluid,the CHF of nanofluid increases significantly.An empirical correlation was proposed for predicting the CHF of nanofluid during natural convective boiling in vertical tubes.更多还原