水平单管外纳米流体降膜传热的数值研究
摘要：降膜蒸发是一种先进的传热技术，但其传热性能依赖于工质的导热系数。现有工质的导热系数偏低，不利于液膜侧传热的进一步强化。基于液体中加入纳米颗粒能大幅提高其导热系数及传热性能这一研究结果，提出了一种采用纳米流体技术的降膜传热增强方法。通过数值模拟研究了水平单管外纳米流体的降膜传热特性。结果表明：纳米颗粒浓度对液膜厚度影响不大；随着周向角度的增大，表面传热系数可分为停滞区、搅动区、热发展区和脱离区4个不同的区域；在给定的周向角度范围内，局部表面传热系数随着纳米颗粒浓度的增大而增大；纳米颗粒浓度升高导致降膜流动的表面传热系数增大。
关键词：水平单管降膜蒸发纳米流体数值模拟强化传热传热系数
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Numerical study on falling-film heat transfer of nanofluid outside a single horizontal tube
Abstract: Falling-film evaporation is an advanced heat transfer technology, but its heat transfer performance depends on the thermal conductivity of the working fluid. The thermal conductivity of the existing working fluid is low, which is not conducive to the further enhancement of heat transfer on the liquid film side. Based on the research results that adding nanoparticles to liquid can greatly improve its thermal conductivity and heat transfer performance, a method for enhancing falling-film heat transfer using nanofluid technology is proposed. Falling-film heat transfer properties of a horizontal single-tube outer nanofluid are investigated by numerical simulation. The results show that the concentration of nanoparticles has little effect on the thickness of the liquid film. With the increase of the circumferential angle, the surface heat transfer coefficient can be divided into four different regions including the stagnation region, the agitation region, the heat development region and the detachment region. Within a certain circumferential angle range, the local surface heat transfer coefficient increases with the increase of the nanoparticle concentration and the increase of the nanoparticle concentration leads to an increase in the surface heat transfer coefficient of the falling-film flow.
Keywords: single horizontal tube; falling-film evaporation; nanofluid; numerical simulation; enhanced heat transfer; heat transfer coefficient;
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