不同强化管传热特性的数值模拟与实验研究

对横纹槽管、缩放管和螺旋槽管在夹套间进行了传热特性实验,研究了传热效率指标随雷诺数的变化规律.运用FLUENT软件,采用二维轴对称方法和k-ε模型对夹套间流体流动传热进行了数值模拟,并将模拟结果与实验结果进行对比.从场协同的角度研究了速度场与温度场夹角对传热膜系数的影响.     

管内Cu-水微米颗粒流湍流强化传热研究

传统光管在高雷诺数下的传热效果不理想,因此提出在水介质中添加微米Cu颗粒作为工作介质来强化管内换热的方法。建立了Cu-水微米流的多相流传热物理模型,采用基于颗粒动力学的欧拉-欧拉双流体模型,对粒径分别为10μm、50μm、100μm和500μm,流速分别为1 m/s、1.5 m/s、2 m/s和2.5 m/s,颗粒体积分数分别为5%、10%、15%和20%进行了传热Nu和阻力损失f数值计算,结果表明:Cu-水微米流的努塞尔数Nu随雷诺数Re和颗粒体积分数的增大而增大,而随粒径的增大而总体趋势减小;摩擦因子f随颗粒体积分数的增大而增大,而随雷诺数Re增大而增小;传热综合性能评价因子η随颗粒体积分数的增大而增大,随着粒径的增大而总体趋势减小。粒径10μm的传热综合性能在研究的粒径范围内最佳,η达到1.1~2.3。     

基于CFD的盲三通流动与换热影响因素分析

该文研究盲三通的流动与传热特性,利用Solidworks建立盲三通三维物理模型,运用CFD软件对盲三通流动与换热进行数值计算,探讨雷诺数、夹角、盲端长度以及支管直径对盲三通流动与换热的影响,并结合正交试验分析各影响因素的显著性强弱。努塞尔数Nu、压降Δp随着雷诺数Re、夹角θ的增大而增大,随着盲端长度L₃、支管直径d的增大而减小;阻力系数f随着雷诺数Re、盲端长度L₃、支管直径d的增大而减小,随着夹角θ的增大而增大。支管近右壁处流体流速增大,入口主管段区域温度梯度分布不明显;利用多元非线性拟合给出盲三通流动与换热准则关联式;各因素对阻力系数f的显著性强弱为：支管管径D>夹角B>雷诺数A>盲端长度C;对努塞尔数Nu和压降Δp的显著性强弱为：雷诺数A>支管管径D>夹角B>盲端长度C。盲三通压降的最优组合为A₁B₅C₅D₅,阻力系数最优组合为A₃B₁C₃D     

交叉缩放椭圆管冷压成形的数值模拟

对新型强化换热管——交叉缩放椭圆管的冷压成形过程进行了有限元数值模拟。计算了成形后交叉缩放椭圆管的残余应力分布并比较了三个典型截面上的残余应力状况。分析了模具过渡段倾斜角对成形的影响。结果表明残余应力最大值出现在换热管过渡段的内壁面;模具过渡段倾斜角较小时将使换热管表面的残余应力显著增大。分析结果有利于加工过程中控制参数的合理选择。综合考虑交叉缩放椭圆管的换热性能和加工后的残余应力状况,给出了模具过渡段倾斜角的参考值。     

横纹管强化传热机理的数值分析

通过对横纹管内流体速度及压力损失进行数值模拟,分析横纹管内流体的速度、压力分布情况和管内速度模量分布、径向速度分布及湍流强度分布,探讨横纹管强化传热的机理.横纹管由于其特有的结构,产生了径向的扰动和轴向旋涡,使传热能力大大增强.     

基于横纹管氨水溶液垂直管外降膜吸收性能的变化规律

针对三根不同尺寸规格的横纹管,通过实验研究提高其吸收效率,选择吸收性能最优的管型。实验结果表明,随着压差和管内冷却水流速的增大,溶液吸收氨气的量增加,管外溶液传质系数增大。当管外氨水溶液喷淋密度从小变大时,光滑管和横纹管的传质系数均先增加后减小,过程中出现了最大值。该系列实验的结果表明横纹管比相同工况的光滑管有更高的强化传热和传质能力,当溶液喷淋密度为479.6kg/(m?h)时,横纹管比光滑管的传质系数增大了97.8%。三组实验中均发现一个共同的规律,横纹管的传质系数随凹槽尺寸变化而改变,2号横纹管表现出更强的吸收氨气能力。该管凹槽宽度与横纹管外径的比值为0.0814。通过对凹槽内溶液流动模型分析,比较了溶液通过凹槽时掺混和涡流的流动形态,得出了不同尺寸规格横纹管吸收性能差异的一个原因。     

横纹管氨水降膜吸收温度场与浓度场计算与测量

根据降膜吸收传质双膜模型,分析了氨气热量、质量和动量传递过程中相关物理量的变化规律和传递机理。建立了氨气降膜吸收过程能量、质量守恒方程组,使方程组离散化,然后利用Gauss-Seidel迭代法求解。得到了光滑管和横纹管降膜吸收氨水溶液氨质量分数沿降膜管高度的变化曲线。并绘出了横纹管降膜吸收过程氨水溶液和冷却水模拟计算温度随降膜管无量纲高度的变化曲线。横纹管相比光滑管在相同工况下有较强的降膜吸收性能,吸收能力在冬夏季节分别提高了118.5%和167.7%。实验结果表明,2号横纹管氨水溶液与冷却水沿降膜管高度的模拟计算温度与测量温度在溶液降膜吸收过程中吻合良好。     

流体横掠叉排平行板束对流换热的数值模拟研究

用商用软件Fluent模拟在不同的Re(雷诺数)下,流体横掠不同的结构参数叉排平行板束的流场、温度场的分布,同时分析影响换热的无量纲数。本文的模拟中只选取一个代表性的单元区域,用该区域代表当流动与换热达到充分发展阶段时整体的流场和温度场的分布,同时分析了在不同的Re下Nu和f的变化情况。结果表明:在层流范围内,一定结构参数下,流场随Re的增大,流体的湍流度加大,换热增强;在相同Re下,不同结构参数下,长宽比较小时,流体湍流度大,换热强;在层流范围内,Nu随Re呈指数变化,f在层流范围内也随Re也呈指数变化;J/f与Re是线性变化,并提出相关结论。     

微肋渐扩细通道流动与传热特性分析

为进一步提高渐扩细通道热沉的综合性能,设计了3种微肋渐扩细通道,分别为:矩形肋、圆形肋和三角形肋渐扩细通道。采用CFD软件对不同结构微肋渐扩细通道的流动和传热特性进行数值研究,并将结果与光滑的渐扩细通道和直细通道进行对比。结果表明:微肋能有效地提高渐扩细通道的传热性能,但同时也增大其流动压降。在所研究的微肋渐扩细通道及工况范围内,矩形肋渐扩细通道的传热系数最高,其传热系数分别比直细通道和渐扩细通道平均高104.01%和119.1%。圆形肋渐扩细通道的压降最小,其压降分别比直细通道和渐扩细通道平均高190.65%和287.43%。此外,圆形肋渐扩细通道的综合性能最好,在所研究的工况范围其综合传热强化因子的范围为1.16—1.47,比渐扩细通道平均高28.59%。     

水平管外沸腾强化换热的数值模拟与场协同分析

应用FLUENT软件对制冷剂R134a在光管和横纹槽管水平管外沸腾传热进行三维数值模拟,得到其饱和泡状沸腾过程中体积含气率的分布规律,并比较它们的换热系数。结果表明横纹槽管外侧能够很好地强化沸腾传热。此外,还通过改变边界条件分析质量流量、热流密度的变化对横纹槽管管外沸腾换热系数的影响。最后应用场协同理论,从局部换热角度分析其强化机制。研究表明,横纹槽管水平管外沸腾换热得到强化的原因是其凹槽前后的速度场与温度梯度场之间夹角较小,协同程度更好。     

斯特林型脉管制冷机中惯性管的优化设计

介绍了斯特林型脉管制冷机中惯性管调相的原理和惯性管的传输线理论模型,给出了惯性管尺寸的优化计算方法.采用该方法对现有的脉管制冷机中惯性管的调相能力进行了模拟计算,研究了PV功、压比和气库容积等参数对最佳惯性管尺寸的影响,并与实验结果进行了对比,计算结果与实验结果符合较好.     

汽车空调管片式换热器用内螺纹管替代光面管的可行性分析

为了研究与套管式换热器连接的不同管型单根铜管的换热性能,测试密封水的温度变化过程。试验结果表明,内螺纹管的换热性能优于光面管的,前者的换热效率约为后者的2～3倍。因此推断汽车空调管片式热交换器采用内螺纹铝管替代光面铝管是具有可行性的。     

钢制管材在空调水系统中的选型及应用

阐述了空调水系统中几种常用钢管管材的应用范围和不同连接方式;分析了开式空调水系统和闭式空调水系统之间的区别,并结合不同的空调水处理方式给出了不同的空调水系统中推荐应用的钢管管材及其连接方式和几点应用原则。     

热声振荡可视化演示装置的研制及初步实验

介绍制作的2套可视化型的热声振荡演示装置。利用这2套装置不仅能更好地理解热声现象,而且据此能定性的分析热声振荡的特性和机理。     

脉管制冷机中脉管内的气柱位移分析

脉管在脉管制冷机中所起的作用,主要体现在热力学和动力学两方面。由热力学平衡计算可决定脉管制冷机的尺寸,但同时也要进行动力学上的匹配。着重利用Dr.deBoer的热力学分析方法对脉管内的气柱位移进行了定量计算 ,给出了计算结果 ,并进行了讨论     

Analysis on the stirling-type pulse tube refrigerator in consideration of dynamics of linear compressor

This paper describes the performance analysis of Stirling-type pulse tube refrigerator (PTR) in conjunction with the dynamics of the accompanied linear compressor. The dynamic behavior of the piston in the linear compressor is directly influenced by the load condition of the PTR. In this paper, the dynamic equation of the piston is simultaneously solved with the thermo-hydraulic governing equations of the PTR using linear analysis model and the performance of the PTR is predicted with the accompanied thermal losses. The developed analysis code is verified with the experimental results. The effect of the inertance tube length which plays an important role in the PTR is also specifically investigated from the experimental and simulation results. It clearly shows the effect of the flow impedance of the inertance tube on the dynamic response of the piston as well as the cooling performance of the PTR.     

Comparison of two different ways of using inertance tube in a pulse tube cooler

It is well known that the pressure wave should lead the volume flow rate at the ambient end of the pulse tube for a high-efficiency operation of a pulse tube cooler. Inertance tube can provide such a phase relationship without DC flow problem. However, inertance tube is always connected with a reservoir in previous literatures. Through theoretical calculation here, inertance tube without a reservoir can also provide a rather large phase-leading effect. Thus phasor diagram is used to analyze the relationship between phase-leading requirement and the pulse tube geometry. Roughly speaking, a larger void volume of pulse tube would require a larger phase-leading effect. Comparison experiments are also done on a thermoacoustically-driven pulse tube cooler. With i.d.2 mm tube as inertance tube, the tube without reservoir yields close results in terms of lowest temperature to that of the tube with reservoir and both give much better performance than that of an orifice with reservoir. Finally, the advantages of using inertance tube without reservoir are given.     

关于内螺纹管及光管冷凝器换热效果的实验分析

采用实验方法,对比分析采用7mm的内螺纹管和光管冷凝器对冷冻系统整机性能的影响。测试结果表明,采用内螺纹管的冷凝器,冷凝温度降低1K,压损增大30%,功率减小1.5%,换热量增大2.5%,能效比增加3.3%。     

Innovative phase shifter for pulse tube operating below 10 K

Stirling type pulse tubes are classically based on the use of an inertance phase shifter to optimize their cooling power. The limitations of the phase shifting capabilities of these inertances have been pointed out in various studies. These limitations are particularly critical for low temperature operation, typically below about 50 K. An innovative phase shifter using an inertance tube filled with liquid, or fluid with high density or low viscosity, and separated by a sealed metallic diaphragm has been conceived and tested. This device has been characterized and validated on a dedicated test bench. Operation on a 50–80 K pulse tube cooler and on a low temperature (below 8 K) pulse tube cooler have been demonstrated and have validated the device in operation. These developments open the door for efficient and compact low temperature Stirling type pulse tube coolers. The possibility of long life operation has been experimentally verified and a design for space applications is proposed.     

Experimental investigation of vortex tube refrigerator with a divergent hot tube

Energy separation performance of vortex tube can be improved by using a divergent hot tube. Experiments are carried out to investigate the influence of the geometrical parameters on vortex tube refrigeration capacity by using nitrogen as the working fluid. In this work, the parameters are focused on the divergence angle of hot tube, length of divergent hot tube and number of nozzle intakes. Experimental results present that there is an optimum angle for obtaining the highest refrigeration performance, and 4° is the optimal candidate under our experimental conditions. Divergent tube length which exceeds a critical length has slight effect on the refrigeration capacity. The critical length to diameter ratio is L/D = 12 in our experiment. Increasing number of nozzle intakes increases the sensitivity of temperature reduction and can obtain the highest possible temperature reduction. Moreover, similarity relations for the prediction of the cold exit stream are presented and confirmed by the experimental data.