Physical quantity synergy in laminar flow field of convective heat transfer and analysis of heat transfer enhancement

Based on the principle of field synergy for heat transfer enhancement, the concept of physical quantity synergy in the laminar flow field is proposed in the present study according to the physical mechanism of convective heat transfer between fluid and tube wall. The synergy regulation among physical quantities of fluid particle is revealed by establishing formulas reflecting the relation between synergy angles and heat transfer enhancement. The physical nature of enhancing heat transfer and reducing flow resistance, which is directly associated with synergy angles α,β,γ,φ,θ and ψ; is also explained. Besides, the principle of synergy among physical quantities is numerically verified by the calculation of heat transfer and flow in a thin cylinder-interpolated tube, which may guide the optimum design for better heat transfer unit and high-efficiency heat exchanger.     

场协同原理强化管外降膜吸收传热特性实验研究

对基于场协同原理设计的两种强化传热管型进行了LiBr降膜吸收水蒸气过程的传热实验研究,并与光滑铜管作比较,考查该传热管型在吸收过程中的强化作用.实验测量参数包括;溶液进出口温度、浓度,流量,冷却水进出口温度、流量等.实验结果表明,两种强化传热管型在低雷诺数时对LiBr降膜吸收传热的强化比分别为20%和50%,而且随着雷诺数的增大而增大.利用场协同理论和降液膜流动的波动特性分析了强化降膜吸收过程传热特性的物理机制,发现速度矢量与温度梯度的夹角及降液膜厚度形成的阻力对对流换热有一定影响.     

Optimization of flue gas turbulent heat transfer with condensation in a tube

Conservation equations for sensible and latent entransy are established for flue gas turbulent heat transfer with condensation in a tube, and the entransy dissipation expression is deduced. The field synergy equation is obtained on the basis of the extremum entransy dissipation principle for flue gas turbulent heat transfer with condensation. The optimal velocity field is numerically obtained by solving the field synergy equation. The results show that the optimal velocity field contains multiple longitudinal vortices near the tube surface. These improve the synergy not only between the velocity and temperature fields but also between the velocity and vapor concentration fields. Therefore, the turbulent heat and mass transfers are significantly enhanced.     

Application of a multi-field synergy principle in the performance evaluation of convective heat transfer enhancement in a tube

For laminar and turbulent convective heat transfer, the synergy among vectorial physical quantities of a fluid particle is analyzed to reveal the relation between the multi-field synergy mechanism and heat transfer enhancement. Additionally, the efficiency evaluation criterion (EEC) is proposed to evaluate the overall performance of heat transfer enhancement. Meanwhile, using synergy angles α,β,,γ and η, a unified evaluation system and corresponding evaluation indexes for heat transfer enhancement are suggested. A model of a heat-transfer-enhanced tube inserted with poles in a triangular configuration is built, and a corresponding numerical simulation is conducted to verify the proposed evaluation system and criterion. The calculation results show that there is correlation between synergy angles reflecting the direction of heat transfer enhancement and evaluation criterion reflecting the effect of heat transfer enhancement. In the Re number range of 300-1800, the performance evaluation criterion PEC lies in the range of 1.2-2.3, but the efficiency evaluation criterion EEC lies in the range of 0.33-0.45.     

高强化活塞内冷油腔振荡传热特性的场协同分析

为研究高强化活塞内冷油腔振荡强化传热机理,应用场协同理论对活塞内冷油腔中机油的振荡流动与传热过程进行分析.采用CFD软件Fluent模拟椭圆形油腔和水滴形油腔内机油的速度场、温度场的分布,得到2种结构油腔的平均场协同数和协同角余弦值在不同工况下的变化规律.结果表明,场协同理论能够很好地解释活塞内冷油腔的振荡强化传热性能...     

强化能量传输与转换过程-场协同与控制

给出了对流换热中速度场与温度场协同的一般公式并推广到湍流情况，阐明了强化对流热传输的物理机制。将场协同原理扩展到经典物理学与近代物理学中，并以实例说明场协同原理是强化能量传递与转换过程的一般原理。     

流体在螺旋管内对流换热和压降性能的数值模拟

分别对螺旋椭圆管和螺旋扁管建模并进行数值模拟和理论分析,对比研究两种螺旋管道的流动换热性能及沿程换热情况,结果表明:层流范围内,螺旋扁管的换热性能好于螺旋椭圆管,但流动阻力较大,根据综合性能评价因子得知螺旋扁管较好;湍流范围内,螺旋椭圆管性能好于螺旋扁管.沿程换热情况表明螺旋管长约为0.5 m时换热效果最佳,同时螺旋管几何尺寸对换热性能也有影响.     

Field synergy principle of heat and mass transfer

Simultaneous heat and mass transfer widely exists in nature and engineering, and it is of vital importance to enhance heat and mass transfer efficiency. In this paper, field synergy equation of heat and mass transfer is derived from its energy equation. Results show that the total transferred heat （including the conducted heat and the heat transferred by mass diffusion through the heat transfer interface） is determined by the values of fluid velocity and enthalpy gradient as well as the value of synergy angle α of velocity vector and enthalpy gradient field. Decreasing the value of α enhances the heat and mass transfer. This means the higher the synergy of velocity vector and enthalpy gradient field, the higher the total transferred heat. By the synergy principle of heat and mass transfer, some methods may be developed to improve the heat and mass transfer efficiency.     

离心力场作用下对流换热场协同理论的实验验证

对离心流化床(CFB)干燥器中气体与被干燥颗粒物料之间的强制对流换热进行了实验研究．实验结果表明，在一定转速范围内，当气流速度方向和热流方向(即温度梯度方向)一致时，离心力场作用下气体流过颗粒层的对流换热准则关联式与由场协同理论中推导的结果具有同样形式，从而验证了场协同原理的正确性．     

Optimization of flue gas convective heat transfer with condensation in a rectangular channel

Conservation equations of sensible entarnsy and latent entransy are established for flue gas convective heat transfer with condensation in a rectangular channel and the entransy dissipation expression is deduced. The field synergy equation is obtained on the basis of the extremum entransy dissipation principle for flue gas convective heat transfer with condensation. The optimal velocity field is numerically obtained by solving the field synergy equation. The results show that the optimal velocity field has multiple longitudinal vortices, which improve the synergy not only between the veloctiy and temperature fields but also between the velocity and vapor concentration fields. Therefore, the convective heat and mass transfers are significantly enhanced. Flow with multiple longitudinal vortices close to the optimal velocity field can be generated by discrete double-inclined ribs set in the rectangular channel. The numerical results show that the total heat transfer rate in the discrete double-inclined rib channel increases by 29.02% and the condensing heat transfer rate increases by 27.46% for Re = 600 compared with the plain channel.     

不同热流下平行平板微槽内流体滑移流动与层流换热

对两侧不同定热流热边界条件下,流动与热充分发展的平行平板微槽在滑移流区内的层流换热进行了理论分析,研究了微槽内温度场的分布和换热特性,并讨论了Kn、热流比、动量协调系数、热协调系数等的影响.     

新型强化传热螺杆结构传热性能数值研究及场协同分析

利用CFD软件fluent对普通螺杆结构和新型强化传热螺杆结构在塑化计量段中的三维非等温流场进行数值模拟,研究两种结构流道内熔体的速度场、轴向和径向温度场、对流传热系数及场协同角的不同。结果表明：在塑化过程中,新型强化传热结构存在着径向的对流传质过程,加强了径向的对流传热,因此有较好的径向温度分布;新型结构较普通螺杆结构有较高的对流换热系数和较好的场协同性,从而加强了螺杆的对流传热。     

场协同原理在强化换热与脉管制冷机性能改进中的应用(上)

简要地介绍了场协同原理的基本思想，综述了文献中应用数值分析方法讨论场协同原理在强化单相对流换热分析中的应用情况，说明场协同原理可以将现有文献中关于强化单相对流换热的3种说法统一起来，因而是强化单相对流换热的统一理论。     

采暖炉水套内部流动和传热的数值模拟

采暖炉是广泛使用的一种民用取暖兼炊事设备。研究采暖炉中的流动及传热规律 ,从而设计出高性能、安全的采暖炉有着重要的实用价值。该文对双孔采暖炉水套内的流动换热进行了数值模拟。采用三维变密度雷诺平均 Navier-Stokes方程和 SIMPL E算法 ,湍流模式为修正的 Spalart-Allmaras模式 ;通过修正水的热传导系数考虑沸腾汽化的影响 ;根据工程实际问题的特点 ,通过计算边界条件考虑与计算域边界耦合的热传导、对流换热及辐射传热过程。所得数值结果与实验符合很好     

纵向涡强化片式散热器换热性能的数值分析

为提高油浸式变压器用片式散热器的综合换热性能,在散热器空气侧安装新型六边形翼涡流发生器,通过数值模拟研究涡流发生器的纵向间距、攻角以及形状对片式散热器换热性能的影响,并运用场协同原理从速度场和温度场相协同的角度阐述纵向涡强化换热的机理。结果表明：同等面积下六边形翼的阻力因子较矩形翼有所增大,但其努塞尔数的提高更加显著;当六边形翼C涡流发生器布置间距为60 mm、攻角45°时,速度矢量与热流矢量间的夹角最小,速度场和温度梯度场协同性最好,散热器综合换热性能最佳,比普通片式散热器的综合换热性能提高26.52%。     

Experimental study on convective heat transfer in tube-side of water jacket-tube heat exchanger by electrohydrodynamics effect

The electrohydrodynamics (EHD) enhancement of convection heat transfer of water in a jacket tube heat exchanger was studied through an experimental method in this paper. In the experiment,a DC high voltage electrode was set in the central tube-side of the heat exchanger,and the high voltage electrode in the tube-side was adjustable in the range of 0-40 kV. Five differ-ent combinations of heat transfer enhancement experiments were conducted under the different voltage and rate of flow. The results indicate that the maximal enhancement coefficient θ is 1.224 when the flow rate of tube-side inlet is 0.1 m3/h. It is proved that,for the work medium of water,the convective heat transfer can be enhanced by applying high electric field. The performance of EHD-enhanced is sensitive to the variation of flow rate,and in the same flow rate,there exist an optimized voltage in the EHD-enhanced process ra-ther than the monotonic positive-correlation relationship.     

凝汽器壳侧换热特性影响因素研究

影响电站凝汽器换热的因素有多种,研究这些影响因素有利于提高凝汽器换热性能。建立凝汽器壳侧流体流动与换热带有多孔介质概念的准三维数值模型,使用数值模型模拟实验凝汽器内部换热特性。在实验中,考虑冷却水入口质量流量、入口温度、蒸汽负荷、漏空气量对换热特性的影响;同样研究了湍流黏度、网格数对计算结果的影响。凝汽器入口参数直接影响凝汽器换热特性,漏空气量增大传热热阻,增大传热端差,降低传热系数;湍流黏度取值不同对数值结果有一定的影响;网格数对凝汽器实时仿真影响很大。     

垂下液膜式水平管蒸发器的换热特性

采用层流和紊流两种模型对一水平管外垂下液膜的强制对流蒸发换热性能进行了数值计算．对管顶部的冲击滞止区和管侧部的自由绕流区分别采用不同的坐标变换方法进行微分方程组简化．根据滞止区计算结果确定自由绕流区的初始边界条件,排除了以前类似计算中人为假定计算边界条件的缺陷．紊流计算采用壁面函数法．数值计算结果确认了液膜蒸发量对换热系数的影响可以忽略,液膜内温度分布不能近似为线性分布．计算结果和作者的实验数据及其他研究的实验数据进行了比较,实验值处于层流解和紊流解之间,更靠近紊流解．对水和Ｒ１１两种工质,紊流解和实验值吻合得很好     

汽车排烟余热回收强化换热管的数值模拟与分析

对汽车排烟余热回收装置的双斜向流线型内肋换热管进行了数值模拟研究,主要分析了内肋的结构特性参数对换热性能的影响。结果表明,流线型内肋在肋长、肋倾角、肋高度和肋间距上存在最优值,分别为38mm,45°,2.5mm和60mm。当Re=1.2×104～5×104时,与同条件下普通圆管相比,努塞尔数Nu可增加54.5%～90.7%,摩擦阻力系数f增加157.6%～204.2%;同时,双斜向流线型内肋管内场协同角从90°减小到80°,换热效果显著提升。运用场协同理论分析,发现管内场协同角在每一个内肋附近都出现骤减现象,并体现其为换热效果增强的主要原因。     

引入惰气强化对流传热过程研究

引入惰气增强传热具有清洁、增加的压力降小和不干扰流体流动等优点．在传热实验装置的竖直向上矩形管道入口处引入氮气,通过对一般对流传热与引入氮气情况下的传热实验进行对比,考察了引入氮气对传热的增强作用。结果表明：混合对流传热时。传热的增强更加显著,引入惰气对对流传热的增强程度要明显好于对过冷沸腾传热的增强．通过对惰气增强传热的机理进行分析,提出惰气对传热的增强作用,是气泡引起液速增加而产生的湍动增强和气泡滑移而产生的边界层湍动增强这两种机理叠加作用的结果。