非均匀热流条件下螺旋管内流动与传热特性研究

发布时间：2018-03-23 20:49

本文选题：卧式螺旋管　切入点：流动沸腾　出处：《重庆大学》2015年硕士论文

【摘要】：螺旋管因其具有良好的传热性能、制造简单和结构紧凑等优点被广泛应用于动力、低温与制冷技术、化工、食品医药等工业行业中。同直管相比,螺旋管强化传热的机理是:由于弯曲通道内的流体受到了离心力的作用,在螺旋管内的流道横截面上产生了二次回流,管内的主流与二次回流的叠加使得流体在管内沿着管道轴向螺旋运动,从而增强了换热效果。前人已经对螺旋管内单相和两相流动与传热进行了大量的研究,然而这些研究主要针对的是螺旋管外壁为均匀热边界条件下的,对管外壁施加非均匀热边界条件的螺旋管内流动和传热性能的研究则鲜有报道。本文搭建了两相流动与传热实验台,以制冷剂R22为工质对卧式螺旋管在非均匀热边界条件下的两相流动与传热特性进行了实验研究;另一方面还对非均匀热边界条件下螺旋管内单相湍流流动与传热进行了数值模拟研究。实验方面,在热流密度q=3.88-19.4 k W/m2,质量流速G=182-303 kg/(m2s),质量干度x=0.07-0.53范围内,分别对三种热边界条件下的卧式螺旋管内流动沸腾换热特性进行了实验研究。三种热边界条件分别为:管外壁周向均匀热流条件,管外壁外侧均匀热流、内侧绝热条件和管外壁内侧均匀热流、外侧绝热条件。三种热边界条件下的螺旋管内局部流动沸腾传热系数均是随着热流密度和质量流速的增大而增大。在本文实验的干度范围内,局部沸腾传热系数随着质量干度的增大而增大。在三种热边界条件下对螺旋管外壁所施加的热量相同的基础上,将三种热边界条件下管内局部流动沸腾传热系数进行了对比,发现螺旋管外壁内侧均匀热流外侧绝热条件下管内沸腾传热系数最大,管外壁均匀热流条件下次之,管外壁外侧均匀热流内侧绝热条件下最小。数值模拟计算方面,建立了三种不同几何结构的螺旋管模型,以单相水为工质,通过改变进口雷诺数和热边界条件对螺旋管内单相湍流流动与传热特性进行了模拟计算,得到了不同热边界条件对管内流体温度分布、速度分布和管内二次流的影响,且三种不同热边界条件下管内单相湍流流动传热系数的大小规律为:内侧均匀热流外侧绝热最大,均匀热流条件下次之,外侧均匀热流内侧绝热时最小。总之,本文对非均匀热边界条件下螺旋管内单相和两相流动与传热进行了探索研究,为螺旋管在非均匀热边界下的应用提供了设计依据和基础数据。
[Abstract]:Spiral tubes are widely used in power, low temperature and refrigeration, chemical, food and pharmaceutical industries because of their good heat transfer performance, simple fabrication and compact structure. The mechanism of heat transfer enhancement in spiral tube is that the fluid in the curved channel is subjected to centrifugal force and secondary reflux occurs on the cross section of the channel in the spiral tube. The superposition of the main stream and secondary reflux in the tube makes the fluid move along the pipe axis, thus enhancing the heat transfer effect. Many researches have been done on the single-phase and two-phase flow and heat transfer in the helical tube. However, these studies mainly focus on the condition that the outer wall of the helical tube is uniform heat boundary. There are few reports on the flow and heat transfer performance in a helical tube with non-uniform heat boundary conditions applied to the outer wall of the tube. A two-phase flow and heat transfer experiment bench has been set up in this paper. The two-phase flow and heat transfer characteristics of a horizontal spiral tube under non-uniform heat boundary conditions were investigated experimentally with refrigerant R22 as working medium. On the other hand, numerical simulation of single-phase turbulent flow and heat transfer in helical tube under non-uniform heat boundary condition is carried out. Experimental results show that in the range of heat flux (Q) 3.88-19.4 k W / m ~ (2), mass velocity G _ (18) ~ (303) kg / m ~ (2) / s ~ (2) and mass dryness x ~ (0.07-0.53), The flow boiling heat transfer characteristics of horizontal helical tube under three kinds of heat boundary conditions are studied experimentally. The three heat boundary conditions are as follows: uniform heat flow around the outer wall of the tube, uniform heat flux outside the outer wall of the tube, The inner adiabatic condition and the uniform heat flux inside the outer wall of the pipe, The local boiling heat transfer coefficient of spiral tube increases with the increase of heat flux and mass flow rate under three kinds of heat boundary conditions. The local boiling heat transfer coefficient increases with the increase of mass dryness. On the basis of the same heat applied to the outer wall of the helical tube under three kinds of heat boundary conditions, the local boiling heat transfer coefficient in the tube under three kinds of heat boundary conditions is compared. It is found that the internal boiling heat transfer coefficient is the largest under the condition of uniform heat flux on the outer wall of the helical tube, followed by the uniform heat flux on the outer wall of the tube, and the minimum under the condition of the inner adiabatic heat flux on the outside of the outer wall of the tube. In the aspect of numerical simulation, Three kinds of helical tube models with different geometry are established. The flow and heat transfer characteristics of single-phase turbulent flow in helical tube are simulated by changing the inlet Reynolds number and heat boundary conditions with single-phase water as working medium. The effects of different heat boundary conditions on the temperature distribution, velocity distribution and secondary flow in the tube are obtained. The heat transfer coefficient of the single-phase turbulent flow in the tube under three different heat boundary conditions is as follows: the maximum adiabatic heat outside the inner uniform heat flux is obtained. Under uniform heat flow condition, the inner adiabatic time of outer uniform heat flux is the least. In a word, the single-phase and two-phase flow and heat transfer in helical tube under non-uniform heat boundary condition are studied. The design basis and basic data are provided for the application of helical tube under non-uniform thermal boundary.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK124

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