Mass transfer at rotating finned cylinders

Rates of mass transfer at rotating finned cylinders were studied by an electrochemical technique involving the measurement of the limiting current for the cathodic reduction of potassiun ferricyanide in a large excess of sodium hydroxide. The variables studied were fin height and Reynolds number. The ratio of the fin height to the cylinder diameter (e/d) ranged from 0·0185 to 0·075 while the Reynolds number ranged from 1047 to 10 470. Under these conditions, the mass transfer data could be correlated by the equationJ=0·714(Re)^–0.39(e/d)^0.2 Nomenclature L _L limiting current (A) - K mass transfer coefficient (cm s^–1) - Z number of electrons involved in the reaction - C ferricyanide concentration (moles cm^–3) - F Faraday's constant - A projected cathode area (cm²) - u dynamic viscosity (g cm^–1 s^–1) - density (g cm^–3) - V peripheral velocity at the rotating cylinder (cm s^–1) - D diffusion coefficient of ferricyanide ion (cm²s^–1) - d cylinder diameter (cm) - e fin height (cm) - J (St)(Sc)^0.664 ColburnJ factor - (Sc) u/(D) Schmidt number - (Re) Vd/u Reynolds number - (St) K/V Stanton number     

Condensation of steam with and without the presence of non-condensable gases in a vertical tube

Condensation of steam and steam from non-condensable gases were investigated experimentally inside a vertical tube. The consistency and reliability of the measurements were checked by detailed energy balance. The experimental results show the effect of non-condensable gases on heat and mass transfer resistances in the gas phase of the condensation process. In the steam runs, the gas side heat transfer resistance was very small and the main resistance was due to condensate film. This resistance increased significantly for steam-air runs, particularly toward the top part of the tube. This occurred as a result of accumulation of the non-condensable gases near the surface as the condensation process proceeds, which act as an extra resistance to heat transfer.     

Condensation on vertical porous metal fins

The problem of condensation of vapors on a porous plate fin is formulated and the dimensionless heat transfer coefficients are found to be dependent on two system variables, viz., the fin and the porosity parameters. Numerical simulations indicated that the condensation heat transfer coefficients for a porous fin are larger than those for a non-porous one of similar cross-section. For design purposes, a dimensionless equation for predicting the mean condensation heat transfer coefficient is proposed. The significant increase in the condensation heat transfer coefficient suggests that the condenser section of a flat plate heat pipe can be made more efficient in operation with the use of porous plate fins instead of impermeable fins of similar cross-section.     

An observation of microbial cell accumulation in a finned tube

Biofouling in heat exchange equipment results in significant energy loss by increasing heat transfer resistance and fluid frictional resistance. This paper compares the deposition and distribution of attached microbial cells on a smooth tube and a tube with inner fins after 100 hours exposure. Preliminary results suggest a significantly different distribution of attached microbial cells on the finned tube.     

Performance tests on a vertical tube evaporator

A two-effect evaporator with a rated capacity of 10,000 l/d has been designed for measuring heat transfer coefficients, pressure drops, entrainment rates and scaling behavior in upflow and downflow VTE. The evaporator is in a closed loop system. The temperature operating range extends from 45 to 145°C. Foaming agent added to the sea-water is continuously recovered from the blow down in an extraction column. The performance of the two VTE effects is measured in dependance of temperature, brine flow, salt and foaming agent content.     

管束的空间排布对翅片管换热器热力性能影响的分析

对翅片管换热器热力性能(传热及流动阻力)的各影响因素进行了分析,其中作为换热器核心部分的换热管束,其空间排布(换热管排间距、管间距之间的数值关系)对换热器的热力性能有着至关重要的影响.综述了在场协同理论、等流速流动等相关理论的结合下的最新研究成果.并通过概述翅片管换热器研究中管束对传热及流动阻力影响的国内外研究现状,分析了在不同翅片及基管类型结构尺寸下,管束对换热器热力性能影响的规律,并在此基础上对管束排列形式的研究前景进行了展望.     

Plug conveying in a vertical tube

Plug conveying along a vertical tube has been investigated through simulation, using a discrete element simulation approach for the granulate particles and a pressure field approach for the gas. The result is compared with an experiment. The dynamics of a plug are described by porosity, velocity and force profiles. Their dependence on simulation parameters provides an overall picture of plug conveying.     

翅片管单管传热性能测试分析与评价

根据JB/TQ 537《空冷器翅片管单管传热性能测试方法》和GB/T 15386《空冷式换热器》的规定和要求,对不同参数规格的翅片管进行了单管空冷传热性能测试,得出了总传热系数K与有效通风截面积空气质量流速U的关系曲线和关联式,分析了影响传热性能的主要因素。     

加工参数对三维翅片铜管冷凝换热的影响

犁削-挤压加工成形工艺制造的新型三维外翅片管通过三维翅片、二维沟槽的微作用力增强传热。文中通过实验,研究了在不同加工参数下的三维整体外翅片铜管的传热性能,与光管相比,三维翅片管均能明显地起到强化传热作用。横管外的膜状冷凝时,与努塞尔积分方法求得的管外换热系数理论计算式相比,三维管管外换热系数的常数随给进量增大而减小。随切削深度增加到一定值后出现少许下降,管外换热系数的常数可以拟合为进给量多项式,从而得到了三维翅片管管外换热经验计算式与加工参数的关系。     

简析钎焊渗层螺旋翅片管省煤器

介绍了一种新型省煤器 ,即钎焊渗层螺旋翅片管省煤器。这种新型省煤器具有较高的传热效率 ,可有效地解决磨损问题 ,提高锅炉平均工作时间 ,是传统省煤器的理想换代产品。     

新型纵向流一体式翅片管换热性能数值模拟

为达到提高壳侧传热系数的同时又具有较低的压力损失的目的,提出了新型纵向流一体式翅片管。针对翅片与管壁夹角的变化影响传热效率的问题,根据有无翅片、翅片夹角的不同、翅片种类的不同,利用计算流体力学(CFD)软件建立了7种周期性单元流道,并对壳侧流场和传热场进行了三维数值模拟,分析了不同流速的介质在流道中的扰动、压降及温度变化。模拟结果表明,在所有的翅片管中翅片夹角为105°翅片管的换热系数最高,翅片夹角为105°翅片管换热系数约为光管的1.4—1.6倍,压降仅为横向掠过的圆形翅片管的0.018—0.15倍。翅片夹角为105°时,翅片管综合性能较优,对烟气换热器应用提出了数值保障。     

T形翅片管卧式重沸器和蒸汽发生器性能研究及应用

介绍T形翅片管卧式重沸器和蒸汽发生器的研究开发过程和工程应用效果,包括T形翅片管的结构特征、机加工技术研究、小试及工业试验、计算数模及使用范围、计算软件、设备系列图的开发,并介绍了T形翅片管重沸器和蒸汽发生器在沸腾传热过程中的应用和取得的节能、节资效果,以及在装置扩能改造、解除瓶颈中发挥的作用。     

Friction factors for a tube rotating about its own axis

Experiments have been carried out to determine pressure drops and flow patterns for fluids flowing through a tube rotating about its own axis. A newly developed pressure tap enabled the determination of pressure drops between two points in a rotating tube. The effect of rotation is to increase the friction factor in the laminar flow region and to decrease it in the turbulent flow region. Rotation also tends to suppress turbulence and to extend the laminar flow region to higher Reynolds numbers.     

Circulation rates of boiling liquids in a vertical tube

An experimental study of heat transfer to boiling liquids under natural convective flow has been carried out in a single tube vertical thermosiphon reboiler to investigate the effect of heat flux and submergence on circulation rates. The test liquids used were distilled water, various concentrations of propan-2-ol in water and their azeotrope. The test section was an electrically heated stainless steel tube of 25.56 mm i.d., 28.85 mm o.d. and 1900 mm long with twenty-one spot welded copper constantan thermocouples to measure the variations in wall temperature along its axis. The uniform heat fluxes in the range of 3.5–42.4 kW/m² were employed while inlet liquid sub-cooling varied from 0.2 to 30.7 °C. The liquid submergence levels were maintained in the range 30–100%. The typical experimental data has been graphically presented and discussed. An empirical correlation has been developed from the experimental data of the present study through regression analysis.     

螺旋隔板三维翅片管传热实验研究与数值模拟

文章对冷却水在换热器管程流动并与壳程的热油逆流换热条件下,对螺旋隔板三维翅片管换热器的传热与压降性能进行了实验研究,并与光滑管进行了对比。在相同壳程Reynolds数下,三维翅片管的壳程Nusselt数是光滑管的2.2—2.9倍,而压降是光滑管的2.3倍左右。采用计算流体力学软件F luent 6.0对螺旋隔板三维翅片管和光滑管换热器进行了数值模拟。结果表明,螺旋流条件下光滑管表面速度矢量均匀、稳定,而三维翅片表面的速度矢量因翅片激发流体而产生湍动和不规则的二次流,从而强化了流体的对流传热。对于螺旋隔板三维翅片管换热器,壳程Nusselt数和压降的数值模拟结果与实验计算值吻合良好,最大偏差分别为6.3%和9.8%。     

Local heat transfer and heat flux distributions in finned tube heat exchangers

A detailed analysis of the effect of local heat transfer distributions, which were determined experimentally, on temperature distributions in the fins and in the fluid between two adjacent fins of finned tube heat exchangers is presented. The heat transfer distributions, obtained by a mass transfer technique, prove to be very inhomogeneous over the fin surface, leading to variable results for fin efficiency calculated by the conventional method. In addition, the effect of temperature variation in the fluid, which is usually neglected in fin analysis, is shown in many cases to exert a very strong influence on fin efficiency and total heat flux. For the optimization of fin designs, a combined analysis of local heat transfer, conduction resistance in the fin and temperature variation in the passage is indispensable.     

Deposition of suspensions in the entrance of a vertical tube

The deposition of aerosols with gravity acting in the direction of flow in a vertical circular tube was investigated numerically for developing, fully developed and uniform laminar flows. It was found that the deposition depends on the velocity ratio of terminal velocity to the average fluid velocity and decreases with increasing velocity ratio. The curves for the fractional penetration in a vertical tube at any velocity ratio were found to fall between that for uniform flow and that for fully developed flow due to diffusive effect alone when a proper dimensionless distance was used. Results for suspension flow in a vertical parallel-plate channel were also presented.     

锅炉螺旋翅片管式省煤器泄漏故障预防与处理

为满足锅炉烟气排放环保达标要求,省煤器结构型式由光管式改为螺旋翅片管式,改造后的省煤器具有传热效果好、不易积灰的优点,但也有安装检修难度大、易磨损泄漏的缺点.本文从采购、安装、检修、使用等环节对省煤器泄漏故障进行了初步探讨,并从采购质量监控、规范安装焊接、改进检修工艺和实施防磨改造、优化脱硝工艺等方面提出了改进措施,为...