冰浆的管道输送热流动特性

发布时间：2018-05-16 13:30

本文选题：区域供冷 + 管道输送　；参考：《大连理工大学》2013年博士论文

【摘要】：在区域供冷系统中,以冰浆代替传统载冷介质是实现系统经济性投运的理想途径之一。冰浆的管道输送是冰浆在区域供冷系统中应用时重要的组成环节,伴随着浆体的管道输送,冰浆呈现出区别于纯流体的非均质性流动及潜热释放等特有的物理现象。这些物理现象的存在,极大地增进了对冰浆热流动规律的认知及刻画难度。因此,作为冰浆工程推广的基础性研究,获知冰浆输送中非均质流动的场特征、量化冰粒子非均匀分布对流变及流阻规律的改变、探索冰浆热流动的基本传热规律及其对流动特性产生的影响将具有重要的理论意义及实用价值。针对上述目标,本文采用两相流理论与计算流体力学相结合的方法,研究了不同形状管道内冰浆的流动特性及传热特性。对于冰浆流动特性,首先,将冰粒子间的相互作用类比于稠密气体分子间的相互作用,应用两相流欧拉-欧拉模型及颗粒动力学的相关理论研究了水平、垂直及90。弯管道内冰浆非均质性等温流动的场特征。其次,基于冰浆非均质性等温流动的场特征,分段考虑了因冰粒子非均匀分布对冰浆流变特性的改变,基于分段流变模型和混合模型求解出冰浆非均质性流动阻力分布规律。而后,结合两相流欧拉-欧拉三维微分模型,引入颗粒浓度扩散方程和非均质流动曲面方程,建立出适用于工程设计阶段的冰浆非均质性等温流动阻力“准二维”模型,并验证了数学模型的有效性。最后,根据对冰浆非均质性等温流动的场特征、流变特性及流动阻力规律所取得的理论认知,在专业实验室内搭建冰浆非均质性等温流动实验测试平台,基于实验研究方法进一步探讨了冰浆流动特性的基本规律。同时,对比了“准二维”模型、欧拉-欧拉模型、混合模型及拟单相流模型对冰浆流动阻力的预测性能。对于冰浆传热特性,采用热焓多孔介质模型与两相流欧拉-欧拉模型相结合的方式,研究了水平管道内冰浆热流动过程中冰粒子的相变传热特性及其对流动规律产生的影响。研究结果表明,对于冰浆流动特性,基于颗粒动力学理论的两相流欧拉-欧拉模型能够有效刻画出不同形状管道内冰浆非均质性等温流动的场特征。整体而言,随着流速的减小、冰粒子浓度的升高以及颗粒直径的增大,冰浆非均质性流动过程增强。在水平和竖直管道内,当局部区域内冰粒子浓度及流速高于某一限值时,冰粒子浓度分布出现反转。在90。弯管道内,冰浆流经弯管段时逐渐呈现出“二次流”现象,这一作用加剧了冰粒子与载流体间的混合。针对所选取的非均质性流动工况及冰浆构成,应充分考虑随运行工况变化时冰浆由牛顿向非牛顿流变特性的转变。当流速较高时,Thomas粘度方程能够较为准确地刻画出冰浆粘度。随着流速降低,可借助非牛顿宾汉流变模型加以描述。基于分段流变模型及混合模型,能够量化出管道顶部冰粒子聚集对剪切应力产生的影响,获得因冰粒子非均匀分布所产生的流阻规律。为了进一步提高冰浆非均质性流动阻力的求解效率,基于欧拉-欧拉三维微分模型,建立了冰浆非均质性流动阻力“准二维”模型。该模型充分考虑了非均质性流动的场特征,同时还能够分项量化出各流体相所占的阻力份额。对于冰浆传热特性,其对流换热过程将随着冰粒子浓度及流速的增大而增强。沿着管道流动方向冰粒子的相变使得冰浆的非均质性流动过程减弱,冰浆的流动阻力降低。
[Abstract]:In the regional cooling system, ice slurry is one of the ideal ways to replace the traditional carrier cooling medium. The pipeline transportation of ice slurry is an important component of the application of ice slurry in the application of the regional cooling system. With the pipeline transportation of the slurry, the ice slurry presents the inhomogeneous flow and latent heat release, which is distinguished from the pure fluid. The existence of these physical phenomena greatly enhances the recognition and characterization of the thermal flow law of the ice slurry. Therefore, as a basic study of the application of ice slurry engineering, the field characteristics of the inhomogeneous flow in the ice slurry transport are known, the changes in the flow and flow resistance of the ice particles are quantified, and the heat flow of the ice slurry is explored. The basic heat transfer law and its influence on the flow characteristics will have important theoretical and practical value.
In view of the above objectives, the flow characteristics and heat transfer characteristics of the ice slurry in different shape pipes are studied by combining the two phase flow theory with the computational fluid mechanics. The correlation theory of particle dynamics is used to study the field characteristics of isotherm flow of ice slurry in horizontal, vertical and 90. bend pipes. Secondly, based on the field characteristics of isotherm flow of inhomogeneous ice, the changes in the rheological properties of the ice slurry are divided into sections, which are based on a piecewise rheological model and a mixed model to solve the ice slurry. Then, combined with the Euler Euler three-dimensional differential model of two phase flow, the particle concentration diffusion equation and the inhomogeneous flow surface equation are introduced. The quasi two-dimensional model of the isothermal flow resistance of the ice slurry is established for the engineering design stage, and the validity of the mathematical model is verified. Finally, according to the theory, The theoretical cognition of the field characteristics, rheological properties and flow resistance laws of the inhomogeneous isothermal flow of the ice slurry, the experimental platform for the experimental testing of the isotherm flow of the ice slurry is built in a professional laboratory. Based on the experimental research method, the basic rules of the flow characteristics of the ice slurry are further discussed. The Euler model, the mixed model and the quasi single phase flow model are used to predict the flow resistance of the ice slurry. The heat transfer characteristics of the ice slurry and the Euler Euler model of the two phase flow are combined to study the heat transfer characteristics of the ice particles in the heat flow process in the horizontal pipeline and the shadow of the flow. Ringing.
The results show that the Euler Euler model of two phase flow based on particle dynamics theory can effectively describe the field characteristics of isotherm flow of ice slurry in different shape pipes. As a whole, with the decrease of flow velocity, the increase of ice particle concentration and particle diameter, the inhomogeneous flow of ice slurry. In a horizontal and vertical pipeline, the concentration distribution of ice particles is reversed when the concentration and flow velocity of ice particles in the local area is higher than that of a certain limit. In the 90. bend pipe, the "two flow" phenomenon is gradually presented when the ice slurry flows through the elbow section. This effect aggravates the mixing between the ice particles and the carrier fluid. The qualitative flow conditions and the composition of the ice slurry should fully consider the change of the slurry from Newton to non Newton when the operating conditions change. When the flow velocity is high, the viscosity equation of the Thomas can be more accurately depicted. As the flow velocity decreases, the non Newton Bingham flow model can be described. The mixed model can quantify the effect of the ice particle aggregation on the shear stress and obtain the flow resistance law due to the non uniform distribution of ice particles. In order to further improve the efficiency of solving the inhomogeneous flow resistance of the ice slurry, based on the Euler Euler three-dimensional differential model, the inhomogeneous flow resistance of the ice slurry is established "quasi two". The model fully considers the field characteristics of the inhomogeneous flow and can also be used to quantify the resistance share of each fluid phase. For the heat transfer characteristics of the ice slurry, the convection heat transfer process will increase with the increase of the ice particle concentration and flow velocity. The heterogeneity of the ice slurry along the phase transition of the flow side of the pipe to the ice particles The flow resistance is weakened and the flow resistance of the slurry is reduced.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU831

【参考文献】