TBAB包络化合物浆潜热输送的固液两相流流动与传热模拟

GIEC OpenIR > 中国科学院广州能源研究所

	TBAB包络化合物浆潜热输送的固液两相流流动与传热模拟
其他题名	Solid-liquid Two-phase Flow Simulation of TBAB Clathrate Hydrate Slurry using for Latent Heat Transportation
	宋文吉
导师	冯自平
	2009-05-27
学位授予单位	中国科学院广州能源研究所
学位授予地点	广州能源研究所
学位名称	博士
关键词	Tbab Chs 潜热输送固-液两相流模拟流动对流传热
摘要	TBAB包络化合物浆（CHS）被证明是一种具有广阔应用前景的潜热输送材料，在中央空调及区域供冷系统中替代冷水作为载冷介质，进行冷量的输送。因为CHS可以在5-12℃发生固液相变，载冷密度远大于冷水，由此可以减小输送管道的尺寸，降低输送泵的能耗，从而达到节能的目的。首先，建立了管内流动的3-D模型，实现对CHS固--液两相流特征的全面描述。模型包含重力对颗粒分层流动的影响，使用相间滑移速度描述相间作用力；给出了层流时固相黏度的计算公式，使控制方程组得以封闭。湍流流动基于RNG k-ε模型理论，针对靠近壁面的层流底层区和远离壁面的旺盛湍流区分别建立k-ε控制方程。在流动计算结果的基础上，将对流传热模型简化为2-D模型，模拟定热流密度条件下的水平管内对流换热情况。通过固--液相间的能量及质量传递进行相间耦合，模型计算范围涵盖层流及湍流流动。分别从层流及湍流能量方程出发，利用源强化概念及场协同理论，从理论上解释了CHS这类潜热型功能流体强化换热的物理机理。随后，搭建了CHS流动与传热实验台，测得CHS在水平管内的流动阻力及定热流密度下的平均对流换热系数，对所建模型的计算结果进行验证。结果显示，在固相含量χ<30%范围内，3-D流动模型可以较好地模拟流动阻力问题，相对误差在±12%以内；2-D传热模型可以较好地模拟对流换热问题，相对误差在±10%以内。证明本文所建立的固--液两相流流动与换热模型可以实现对CHS真实情况的模拟，且达到了精度要求。实验测定了A型和B型CHS的粒径分布。深入剖析了CHS管内流动情况。截面速度分布规律显示，随着固相含量的增大，层流流动表现出由剪切流发展为“塞状流”的趋势，由此判断CHS固--液两相混合流体整体上呈现出非牛顿流体特征。发现了定流速下的“再层流化现象”。截面颗粒浓度分布表明，在较低流速的层流流动区，边界层内出现比较明显的分层流动，随着流速的增大，分层流动逐渐消失，表现为非均匀流甚至均匀流。通过对平均流速、固相含量及管径的正交分析结果得知，流速是影响流动阻力的最主要因素，固相含量次之，管径最小。在实验得到的CHS实际粒径分布范围内，颗粒直径大小对流动阻力的影响可以忽略。详细分析了CHS在定热流密度条件下的管内对流换热特性。CHS的换热能力大约是纯溶液的1.5~3.5倍。通过截面温度分布，显示层流换热主要通过颗粒及液体的导热作用传递热量，由于潜热的释放增大了径向的温度梯度；湍流换热改善了速度场与温度梯度的协同程度，使得主要的换热热阻存在于热边界层内，同时，由于潜热的释放延缓了壁面温度升高的速度。计算得到了CHS换热过程中沿管长方向出现的未融化区、正在融化区和完全融化区的边界线。CHS对流换热能力的影响因素中，平均流速起决定性作用，固相含量和潜热通过改变混合流体的等效比热容而影响换热性能。实际粒径分布范围内对层流换热的影响可以忽略，较大颗粒对湍流换热起强化作用。热流密度大小对换热性能几乎没有影响。最后，展示了所建立的固--液两相流动与换热模型在CHS潜热输送过程的应用。对A型和B型CHS，计算求得了不同固相下的临界沉降速度，为CHS的安全输送提供了依据。从优化输送泵功角度，得到了B型CHS最佳的固相含量范围（χ=26%附近），输送该固相含量范围的CHS，可以得到最佳的节能效果。
其他摘要	The Tetra-n-Butyl-Ammonium Bromide (TBAB) Clathrate Hydrate Slurry (CHS) is one of promising media for latent heat transportation.It can be used as substitute secondary coolant in centralized air-conditioning systems and district cooling systems. Because CHS releases its latent heat during phase change at atmosphere pressure in the temperature range of 5~12℃, it can carry more cold energy per unit. Based on that, CHS latent heat transportation could cut energy consumption of pumps because of downsizing pipeline diameters, and then realize the aim of energy saving. There are six main parts in this paper. Firstly, the related references about the latent heat transportation applications of TBAB CHS were summarized and analyzed comprehensively. And it shows that the fundamental researches about momentum transfer and heat transfer mechanism are still not exhaustive. One theoretical model for CHS flow and heat transfer, from the aspect of solid-liquid two-phase flow, will be significant supplement. Secondly, based on above, one 3-D theoretical model for CHS flow in horizontal pipe was established, which could give better expression to the solid-liquid two-phase flow characteristics. In the model, the effect gravity forced on solid particles was included, and slip velocity between particles and liquid was used to describe interphase forces. Solid viscosity expression made control equations complete. Turbulent flow was based on RNG k-ε model, and two different expressions were used for laminar sublayer and vigorous turbulent region separately. One simplified 2-D theoretical model for CHS convective heat transfer with constant heat flux in horizontal pipe was established. Mass transfer and heat transfer between solid and liquid phase were coupled with source items in continuity equations and energy equation. Source enhancement and field coordination theory, deduced from energy equation, could give better explanation to heat transfer enhancement phenomenon for TBAB CHS. Then, in order to verify our numerical calculation, one experiment stand was set up, and pressure drop and mean convective heat transfer characteristics of CHS in pipe flow were investigated experimentally. Comparison between experimental and numerical results in the range of χ<30%, show that 3-D model for CHS flow behaviors and 2-D model for CHS convective heat transfer characteristics present good agreement within a maximum error equal to ±12%. After that, the flow behaviors of CHS were analyzed in detailed from the aspect of solid-liquid two-phase flow. The velocity profile shows a flow pattern transform tendency from shear flow to plug flow with the increasing of solid fraction in laminar flow region, which can owe to its non-Newtonian as single phase fluid. The solid concentration distribution profiles indicate that obvious stratified flow appears in sublayer at laminar flow region, and it disappears when flow velocity increases. Based on the results of orthogonal analysis, mean flow velocity is the most important factor for flow resistant of CHS, solid fraction is the second and pipe diameter is the last. In the range of CHS particle size distribution, particle diameters show little effects on pressure drop of CHS pipe flow, and it can be neglected. Meanwhile, the convective heat transfer characteristics of CHS pipe flow were discussed comprehensively. Contrast to TBAB aqueous solution (χ=0), CHS could enhance heat transfer up to 1.5~3.5 times. The section temperature profiles express thermal transfer process from tube wall to fluids. In laminar region, conductivity is the main way for thermal transfer, and the releasing of latent heat of CHS particles increases temperature difference along radial direction. In turbulent region, turbulent kinetic enhances heat transfer in core flow region and its thermal resistant concentrates in sublays, and the releasing of latent heat decreases wall temperature. Along axis direction, there exist three regions—non-melting region, melting region and melted region, and boundaries among them were obtained. Among parametric variations effecting CHS convective heat transfer, the mean flow velocity is the most crucial factor, solid fraction and latent heat value are second class, and heat flux shows little effect on heat transfer coefficient. In the range of CHS particle size distribution, particle diameters show a bit better effect in turbulent region than that in laminar region. Lastly, two main applications in latent heat transportation were introduced by use of the established solid-liquid two-phase model. Critical deposition velocities, which stand for transformation from moving bed flow to heterogeneous flow, were obtained for type A and type B CHS separately. These could ensure the safe transportation for CHS. Another application is optimizing pump power consumption by adjusting solid fraction in CHS and flow velocity. For type B CHS, contrast to cold water, there exists an optimum solid fraction range (around χ=26%), in which the power consumption for transportation could be minimum.
页数	113
语种	中文
文献类型	学位论文
条目标识符	http://ir.giec.ac.cn/handle/344007/5830
专题	中国科学院广州能源研究所
推荐引用方式 GB/T 7714	宋文吉. TBAB包络化合物浆潜热输送的固液两相流流动与传热模拟[D]. 广州能源研究所. 中国科学院广州能源研究所,2009.

条目包含的文件		下载所有文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
200618014924008宋文吉_p（1753KB）			开放获取	--	浏览下载