Heat transfer characteristics of air cross-flow for in-line arrangement of spirally corrugated tube and smooth tube bundles

An experimental study on heat transfer and resistance coefficients of linearly arranged smooth and spirally corrugated tube bundles in cross-flow was performed. The heat transfer and resistance coefficients are presented in this paper with transverse and longitudinal tube-pitch and tube geometries taken into account. The experiment's results can provide technical guidelines for application to horizontal air preheater with arranged in-line spirally corrugated tube bundles, especially to the air preheater for CFBCBs (Circulating Fluidized Bed Combustion Boilers).     

螺旋槽式翅片管沸腾强化传热特性的研究

为研究一种新型强化传热管的传热效果,对光管、普通翅片管和螺旋槽式翅片管在不同流量条件下的传热特性进行了比较研究。实验中管程工质为水蒸气,壳程通入饱和液态水作为冷源。结果表明,螺旋槽式翅片管的换热量明显高于光管和普通翅片管,并且随着流体流量的增加,传热效率的提高也更加明显。当蒸汽温度140℃时,螺旋槽式翅片管沸腾传热系数约为光管的1.4倍,换热量为1.5倍;蒸汽温度为160℃时,螺旋槽式翅片管沸腾传热系数约为光管的1.5倍,换热量为1.8倍。     

Evaluation of the heat transfer performance of helical coils of non-circular tubes

This study addresses heat transfer performance of various configurations of coiled non-circular tubes, e.g., in-plane spiral ducts, helical spiral ducts, and conical spiral ducts. The laminar flow of a Newtonian fluid in helical coils made of square cross section tubes is simulated using the computational fluid dynamic approach. The effects of tube Reynolds number, fluid Prandtl number, coil diameter, etc., are quantified and discussed. Both constant wall temperature and constant heat flux conditions are simulated. The effect of in-plane coil versus a cylindrical design of constant coil, as well as a conical coil design is discussed. Results are compared with those for a straight square tube of the same length as that used to form the coils. Advantages and limitations of using coiled tubes are discussed in light of the numerical results.     

真空条件下表面多孔管的池沸腾传热性能

设计了2种分别由6根管子组成的不同管束排列在沸腾室中.实验以去离子水为介质,研究了常压及低于大气压下压力对光滑管束和烧结表面多孔管束核池沸腾传热性能的影响.实验结果表明,在真空条件下这2种管束的沸腾传热系数与在常压条件下一样随着压力值的升高而增大.在相同的操作参数条件下,与光滑管相比较,当压力值在10～100kPa之间变化时,烧结表面多孔管的传热系数提高了0.2～4倍.此外,实验数据还表明在真空条件下烧结表面多孔管及光滑管均存在管束效应.     

Experimental Study on Heat Transfer and Pressure Drop of Micro-Sized Tube Heat Exchanger简

A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of the MTHE tubes was proposed and compared with previous experimental data in the Reynolds number range of 500—1 800. The average deviation of the correlation in calculating the Nusselt number was about 6.59%. The entrance effect in the thermal entrance region was discussed. In the same range of Reynolds number, the pressure drop and friction coefficient were found to be considerably higher than those predicted by the conventional correlations. The product of friction factor and Reynolds number was also a constant, but much higher than the conventional.     

基于Fluent螺旋槽管沸腾换热的数值模拟

基于FLUENT软件对制冷剂R134a在水平螺旋槽管管外沸腾换热进行了三维数值模拟,得到了其饱和泡状沸腾过程中体积含汽率的分布规律和换热系数,并和光管进行了比较。结果表明螺旋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了质量流量、热流密度的变化对螺旋管管外沸腾换热系数的影响。     

螺旋隔板单管换热器性能实验研究

以水一水换热为实验对象,研究了螺旋隔板单管换热器的传热与流阻性能。实验结果表明,在相同的Re值下,螺旋隔板花瓣管单管换热器的壳程传热准数Nu是螺旋隔板光滑管单管换热器的2—4倍,压降只是它的1．4—1．8倍,证明花瓣管具有十分优越的强化传热性能,其与螺旋隔板搭配构成的换热器具有良好的传热与压降性能。在实验范围内,花瓣管翅片高度的增加、翅间距的减少都有利于传热强化性能的提高。     

Rib height selection for roughness-enhanced tube

1 Introduction A well known method to increase heat transfer from a surface is to roughen the surface by use of regular geometric roughness elements, such as transversely-ridged tube, spirally-ridged tube or converging-diverging tube, etc., on the surface…     

螺旋折流片强化管壳式换热器内管束传热数值模拟

介绍了一种用于强化管壳式换热器壳侧传热和支撑管束的螺旋折流片新型结构,该结构是对换热器管子相间地套上螺旋折流片以产生旋涡流动.研究模型是在正方形布置的4个管子中的2个对角管子套上螺旋折流片后形成的通道,利用FLUENT软件对该上述四管通道模型的流场和温度分布情况进行了数值模拟;分析了四管通道模型中螺旋折流片对强化传热和流动阻力随雷诺数的变化关系的影响.算例结果显示该新型结构可比相同尺寸的光管通道中的情形传热系数提高约40%～55%,同时也将伴随较高的流动阻力.可以相信螺旋折流片式换热器将会在许多工业领域有良好的应用前景.     

波形折流杆换热器的开发和工业化实验研究

The conventional heat exchanger with segmental baffles is prone to bring forth fluid-induced vibration of heat transfer tubes and increase the pressure drop of shell-side greatly at higher fluid flow velocity. In order to avoid the above defects, the ROD-baffle heat exchanger has been developed. However, its collocation of heat transfer tubes is conventionally in square, which leads to fewer heat transfer area per unit volume. Based on the ROD-baffle heat exchanger, a new type curve-ROD baffle has been developed, and an industrial investigation of the curve-ROD baffle heat exchanger with normal triangular collocation has been carried into execution. In this paper, two equations using the Reynolds number were acquired to predict the heat transfer coefficients of the shell-side and tubeside. The experimental results show that the shell-side heat transfer and pressure drop characteristics of the curve-ROD baffle heat exchanger are superior to those of the segmental baffle one.     

多孔陶瓷管式露点间接蒸发冷却器的设计计算

为了提高管式间接蒸发冷却器壁面的亲水性,提出了一种采用多孔陶瓷材料的新方法.该方法将多孔陶瓷材料与蒸发冷却技术有机结合,从一次空气风量和二次空气风量、一次空气状态参数和二次空气状态参数、冷却器结构、固体多孔陶瓷管的传热以及冷却器阻力等方面对多孔陶瓷管式露点间接蒸发冷却器进行了设计计算.计算结果表明该设计合理可行.最后,依据设计制作出多孔陶瓷管式露点间接蒸发冷却器.     

螺旋隔板花瓣管单管换热器的数值模拟

采用FLUENT6．0软件对整个螺旋隔板花瓣管单管换热器的一段的流场、温度场进行数值模拟，结果显示壳程内的主体流动趋势仍是螺旋状，但在翅片附近速度场的大小和方向变化较大，证明翅片的存在激发了流体的边界层分离和湍动，从而强化了传热。     

Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow

Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M _s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, thek-∈ two-equation model and the Fluctuation-Spectrum-Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gasphase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data. Project supported by National Natural Science Foundation for Distinguished Young Scholars (No. 50025618)     

交叉三角形波纹通道的传热与流动特性的研究

为获得层流条件下交叉三角形波纹通道的传热和流动特性的实验数据,利用热线风速仪和热电偶对流过该设通道的风速和温度进行了测量,在充分考虑入口端流体力学和热力学效应情况下,对周期性通道的实验数据进行处理,并获得平均摩擦因数fD和平均努塞尔数NuD.将实验数据与Fluent数值模拟结果作了对比,误差结果小于±15%.     

毛细管绝热节流过程焓变化特性的理论分析与实验验证

计算分析了焓相等和滞止焓相等情况下毛细管中R22节流特性参数及其变化规律．并将两种情况下所选取的毛细管与真实制冷系统毛细管比较。理论计算和实验结果都表明滞止焓相等才是毛细管绝热节流的基本特性,而绝热节流焓相等的理论不够准确。     

Numerical study of heat transfer characteristics of downward supercritical kerosene flow inside circular tubes

The heat transfer characteristics of China RP-3 aviation kerosene flowing in a vertical downward tube with an inner diameter of 4 mm under supercritical pressures are numerically studied. A ten-species surrogate model is used to calculate the thermophysical properties of kerosene and the re-normalization group (RNG) k-ε turbulent model with the enhanced wall treatment is adopted to consider the turbulent effect. The effects of mass flow rate, wall heat flux, inlet temperature, and pressure on heat transfer are investigated. The numerical results show that three types of heat transfer deterioration exist for the aviation kerosene flow. The first type of deterioration occurred at the tube inlet region and is caused by the development of the thermal boundary layer, while the other two types are observed when the inner wall temperature or the bulk fuel temperature approaches the pseudo-critical temperature. The heat transfer coefficient increases with the increasing mass flow rate and the decreasing wall heat flux, while the inlet bulk fluid temperature only influences the starting point of the heat transfer coefficient curve plotted against the bulk fluid temperature. The increase of inlet pressure can effectively eliminate the deterioration due to the small variations of properties near the pseudo-critical point at relatively high pressure. The numerical heat transfer coefficients fit well with the empirical correlations, especially at higher pressures (about 5 MPa).     

波纹板表面凝结传热的数学模型与计算

基于波纹板表面与液膜之间的表面张力作用能减薄液膜厚度而强化传热的机理，建立了竖直波纹板表面的凝结过程的数学模型．计算了波纹板对应于当量平板的凝结传热增强系数．分析了波纹的主要几何参数如波纹节距、波纹板高度、波纹角、波纹倾斜角、波纹圆角半径等对强化传热的影响效应以指导波纹结构的优化．提出了一种能兼顾强化传热效果和适当的流动截面积的双尺度波纹，其凝结传热系数可比当量平板增强1～2倍．     

Computational fluid dynamic simulation of an inter-phasing pulse tube cooler

An inter-phasing pulse tube cooler （IPPTC） consists of two pulse tube units, which are connected to each other at hot ends of the pulse tubes through a needle valve. This paper presents the computational fluid dynamic （CFD） results of an IPPTC using a 2D axis-symmetrical model. General results such as the phase difference between pressure and velocity at cold end and hot end, the temperature profiles along the wall, the available lowest temperature as well as its oscillations and the coefficient of performance （COP） for IPPTC are presented. The formation of DC flow and its effects on the performance of the cooler are investigated and analyzed in detail. Turbulence, which is partially responsible for the poor overall performance of a single orifice pulse tube cooler （OPTC）, is found to be much reduced in IPPTC and its performance is improved significantly compared with the single OPTC.     

杆支撑换热器壳侧单元流道的三维模拟

1 Introduction The traditional segmental baffle heat exchangers(SHE) can be si mply manufactured and run reliably,but they are mainly suitable for the situation of lowerflow velocity. When fluid velocity becomes higher inthe shell side ,the pressure dropi…     

电站锅炉鳍片管传热特性的数值分析

鳍片管传热性能分析对各种换热元件的设计有着重要意义,目前工业应用中大多基于设计经验。本文利用通用有限元分析软件ANSYS10.0的APDL语言编写仿真程序,对雷诺数在6400左右的电站锅炉环形鳍片管单管换热过程进行数值分析,得到平均换热系数。并详细分析了不同的鳍片管结构尺寸和不同工况对传热特性的影响规律。为电站锅炉环形鳍片管的结构设计与优化提供参考。