空气-石蜡直接接触换热特性实验研究

在间壁式换热器中石蜡因为其热导率低影响了蓄热系统的换热速率,采用石蜡与空气直接接触换热可大幅提高蓄热系统的换热速率。把常温的空气通过气体分布器注入熔融状态的石蜡（100~150℃）中,具体考察了表观气速、静液位高度和传热温差等参数对石蜡-空气鼓泡换热中体积传热系数与气含率的影响。实验结果表明,随着表观气速的增大,体积传热系数与气含率随之增大,并且对于气含率,在较低的表观气速下的增长速率更快;在实验条件下,增加静液位高度都只会导致体积传热系数与气含率的降低,而改变气液温差对体积传热系数的影响不甚明显。根据实验结果获得了石蜡与空气直接接触换热的体积Nusselt数经验关联式。     

气固流化床外取热器内流动和换热特性分析

外取热器是维持催化裂化反应-再生系统热平衡和保持装置平稳运行的关键设备之一。外取热器的优化设计和合理调控,要求深入理解外取热器内的流动特性、换热特性及两者之间关系。在一套大型冷模热态实验装置上,分别考察了表观气速、颗粒质量流率对换热管附近的局部固含率和气泡频率、床层与换热管间传热系数的影响。结果表明:增加表观气速可以降低局部固含率、增加局部气泡频率、强化床层与换热管间换热;随着颗粒质量流率增加,局部固含率和局部气泡频率均增加;在较低表观气速下,增加颗粒质量流率不利于换热,而在较高表观气速下,传热系数随颗粒质量流率逐渐增加。不同流型下,气固流动特性对换热特性的影响不同。在鼓泡床流型下,过高的局部固含率不利于颗粒在换热表面的更新,增加换热管附近的局部气泡频率可以明显强化换热;而在湍流床流型下,换热管附近的局部固含率和气泡频率的增加,均使传热系数逐渐增大。建立了针对不同流型的换热经验关联式,预测值与实验值的平均相对偏差分别为6.9%和1.3%。     

三相流重力热管冷凝段传热性能研究

为拓展三相流强化传热和防、除垢技术的应用领域,优化重力热管的传热性能,设计并构建了1套三相流闭式重力热管系统。考察了固含率、加热功率、充液率等参数对于三相流重力热管冷凝段传热性能的影响。结果表明,三相流重力热管可以强化传热。冷凝段对流传热系数随着加热功率的增加而增大,随着充液率的增加而减小。充液率较低时,冷凝段对流传热系数随着固含率的增加而增大;而当充液率较高时,随着固含率的增加,对流传热系数则呈现出先增加,后降低,然后再增加的变化趋势。     

垂直下降沸腾管两相流传热恶化研究

<正>1引言 传热恶化有不同的类型,就工程换热设备设计和运行的实际需要来说,人们最关心的是以下几点：（1）传热恶化发生的位置（壁温飞升起始点）,一般用。cr来表示;（2）传热恶化发生后壁温飞升的最大值,一般用A儿。。来表示;（3）壁温飞升最大值的位置,一般用K。。。来表示;（4）传热恶化发生后的。mi。。本文着重分析讨论后3个问题。     

鼓泡塔列管传热系数的测量与估算

在φ500 mm×5000 mm的冷模实验装置中,使用自制传热探头,对无内构件的空塔和安装31根竖直换热列管的鼓泡塔内列管传热系数进行了测量.实验表明,列管传热系数随表观气速的增加而增大,传热系数沿径向呈抛物型分布,垂直列管内构件的加入使得传热系数的径向分布变得更为陡峭.基于表面更新理论,结合鼓泡塔内气含率和液速分布的测量及计算结果,提出了计算传热系数的数学模型.该模型既可以用于空塔的局部传热系数与平均传热系数计算,也可以用于安装列管束的局部传热系数与平均传热系数计算.模型计算值与实验数据符合良好,最大相对误差为5.62％.     

GAS HOLDUP AND HEAT TRANSFER FROM IMMERSED SURFACES IN TWO- AND THREE-PHASE SYSTEMS IN BUBBLE COLUMNS

Two experimental slurry bubble column facilities comprising of 10.8 and 30.5 cm diameter columns and appropriate for conducting hydrodynamic and heat transfer studies are described. The average and local gas holdup data are reported for the air-water system as a function of air velocity. The holdups for the three phases are also reported for the air-water-glass beads system over a range of air velocity values. The air holdup data are compared with the predictions of some of the commonly used correlations. The heat transfer coefficient for a 19 mm diameter cylindrical probe and the two- and three-phase dispersions are measured as a function of air velocity. Most of these hydrodynamic and heat transfer data correspond to the churn turbulent regime and the values obtained on the two columns differ appreciably from each other under similar operating conditions. This fact indicates that the scaleup of slurry bubble columns could be quite difficult on the basis of data obtained on the bench and pilot-plant scale units. The continuing data from these facilities on different systems will shed more light in the future on this important aspect which is crucial to the commercialization of indirect coal liquefaction technology.     

Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media

Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 ...     

三相流闭式重力热管的强化传热

将三相流强化传热技术应用于重力热管,构建了三相流闭式重力热管系统.以水为工质,固含率(体积分数)、固体颗粒的种类、大小及加热功率等作为参数,研究并分析了三相流重力热管的传热性能.结果表明:在一定的条件下,三相流闭式重力热管具有一定的强化传热效果.随着加热功率的增加,等效对流传热系数增大.加入φ5.5 mm的聚甲醛颗粒时...     

电场强化乙醚自然对流和池沸腾换热

外加电场强化传热是将电场及其理论引入传热学领域,利用电场力与流场和温度场的相互作用而达到强化传热的一种有效方法．     

The generalized Lévêque equation and its practical use for the prediction of heat and mass transfer rates from pressure drop

Based on the generalized Lévêque equation (GLE) a new type of analogy between pressure drop and heat transfer has been discovered, that may be used in the cross corrugated channels of chevron type plate heat exchangers, in packed beds, in tube bundles, in crossed rod matrices or in many other spacewise periodic arrangements.Experimental data on heat transfer in tube bundles in crossflow, both inline, and staggered arrangements, had been recently tested in greater detail. Using an empirical correlation for pressure drop in these arrangements from the literature that has been successfully tested against a large number of experimental pressure drop data, heat transfer data collected earlier could be very well represented from the pressure drop correlation and the GLE. The data for staggered bundles have been shown to be in better agreement with this new method, than with the existing empirical heat and mass transfer correlations. Somewhat larger deviations for inline tube bundles had been found at lower Reynolds numbers. Here a simple and physically reasonable correction function of Re is presented, which leads to a better agreement for the inline bundles, too.Additionally, it can be shown for a number of literature data on tube bundles and on crossed rod matrices that the agreement with the GLE prediction is even better if original pressure drop data from the same sources are available in place of a pressure drop correlation.The method results in reasonable heat or mass transfer predictions from frictional pressure drop, which may be widely used in chemical engineering applications.     

Gas Holdup and Solid‐Liquid Mass Transfer in Newtonian and non‐Newtonian Fluids in Bubble Columns

Gas holdup and surface‐liquid mass transfer rate in a bubble column have been experimentally investigated. De‐mineralized water, 0.5 and 1.0% aqueous solutions of carboxy methyl cellulose (CMC), and 60% aqueous propylene glycol have been used as the test liquids. Effects of column diameter, liquid height to column diameter ratio, superficial gas velocity and liquid phase viscosity on gas holdup and mass transfer rate are studied. Generalized correlations for the average gas holdup and wall to liquid heat and mass transfer coefficients are proposed. These are valid for both Newtonian and pseudoplastic non‐Newtonian fluids.     

振动流化床浸没水平管传热特性研究

为了深入研究振动流化床浸没水平管的传热特性,分别以沙子和玉米细颗粒作为实验物料,用水平探头测定了振动流化床中这2种床层颗粒与浸没水平管间的传热系数,分析了操作气速、振动频率、空气进口温度等因素对传热过程的影响。结果表明:在低气速下,振动是影响振动流化床中传热的主要因素,振动的引入可以明显改善流化作用,可以在低气速下得到较好的传热效果,同时达到节能的效果。通过分析实验结果,建立了振动流化床的传热关联式,模型计算值与实测值能较好吻合。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

纳米石墨冷冻机油对R600a流动沸腾换热的影响

搭建了纳米冷冻机油/制冷剂水平光管内流动沸腾换热测试实验台,研究了石墨/R600a纳米制冷剂在水平直光管内流动沸腾换热特性,分析了纳米石墨对含油制冷剂流动沸腾换热的影响。实验测试段为总长2.5 m、外径9.52 mm、内径8 mm、壁厚0.76 mm的紫铜管。在质量流速为150、200、250、300 kg·m^-2·s^-1下,分别测量纯R600a、含油R600a、不同质量分数(0.05%、0.1%、0.2%)纳米石墨冷冻机油和R600a混合物在水平光滑圆管内流动沸腾传热系数随干度的变化趋势。实验结果表明:纳米石墨的添加增强了含油制冷剂的流动沸腾换热。实验获得了基于石墨的含油纳米制冷剂流动沸腾换热关联式,关联式的预测值与94.5%的实验数据偏差在±15%以内。     

Heat transfer of gas flow through a packed bed

This paper reports an experimental study of both the transient and steady-state heat transfer behaviour of a gas flowing through a packed bed under the constant wall temperature conditions. Effective thermal conductivities and convective heat transfer coefficient are derived based on the steady-state measurements and the two-dimensional axial dispersion plug flow (2DADPF) model. The results reveal a large temperature drop at the wall region and the temperature drop depends on the axial distance from the inlet. The 2DADPF model predicts the axial temperature distribution fairly well, but the prediction is poor for the radial temperature distribution. Length-dependent behaviour of the effective heat transfer parameters and non-uniform flow behaviour are proposed to be responsible. A comparison with previously published correlations and data in the literature shows that the relationships proposed by Bunnell et al. and Demirel et al. agree well with the measured effective radial thermal conductivity, whereas the wall-fluid heat transfer coefficient is better represented by the Li-Finlayson correlation.     

超临界压力下纳米流体竖直管内流动换热

对超临界压力下Fe₃O₄-煤油纳米流体竖直管内的换热特性进行了实验研究,分析了不同压力、质量流量、热通量和纳米颗粒浓度对超临界压力下纳米流体换热特性的影响。超临界压力下,纳米流体在竖直管内沿管长呈现不同的换热规律。流体质量流量的提高或者工作压力的提高均会使纳米流体在竖直管内流动换热效果变好。而热通量的增大或纳米颗粒的添加对超临界压力下纳米流体的换热具有恶化效果。最后给出了纳米流体在超临界压力下的传热关联式,其计算值和实验值吻合良好。     

叉排微柱群内顶部缝隙对传热效率的影响

以去离子水为工质,实验研究了直径为500 μm、高度为500 μm以叉排排列的微柱群内顶部缝隙对传热效率的影响规律。采用电加热棒进行加热,测量微柱群板Reynolds数在8～400之间在不同顶部缝隙时的进出口温度与流量,获得微柱群内流动阻力系数及Nusselt数,进而掌握微柱群内传热效率与Re关系。研究结果表明,在较低Re时,顶部缝隙对微柱群内流动阻力和Nu影响较小;随着Re增加,其对流动阻力与Nu的影响越来越显著。微柱群传热效率一开始随着Re增加而快速增加,随着Re进一步增加,其传热效率开始缓慢增加甚至出现下降。根据实验结果,尽管微柱群顶部缝隙存在降低了其内Nu,但提高了微柱群的传热效率。     

Survey of heat transfer mechanisms in a slurry bubble column

Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil‐free compressed air, tap water and 35 μm glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time‐averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model.     

Convective heat transfer in a rotary kiln

An experimental study of convective heat transfer from hot air to the solid charge and walls in a non-fired rotary kiln is reported. Ottawa sand was heated by passing it counter-current to a flow of preheated air in a 2.5 m × 0.19 m I.D. rotary kiln. Axial temperature profiles of gas, wall and solids were measured. Local and average convective heat transfer coefficients from gas to solids and from gas to wall were determined assuming plug flow of gas and solids. Solid feed rates to 1750 kg/m² h and air rates to 3300 kg/m² h were investigated at rotational speeds to 6 r/min, holdup ratios to 17% and gas temperatures from 350–590 K. The gas/solids convective coefficient was found to depend on the gas through-put and to a lesser extent on solids holdup and rotational speed. Over the range tested, the angle of kiln inclination, solids throughput and particle size showed no significant effect on heat transfer. Gas/wall coefficients were about a factor of ten below gas/solid coefficients. Heat transfer results are compared to the limited data available in the literature, and to commonly used equations. Correlations of the experimental data on gas/solids, and gas/wall coefficients are presented; data from the literature on the wall/solids heat transfer coefficient are summarized.     

Bubble column with internals: Effects on hydrodynamics and local heat transfer

Local heat transfer and column hydrodynamics are investigated in a bubble column in presence of internals of different configurations. The liquid phase used is tap water and the gas phase is oil-free compressed air. The gas velocity is varied over a wide range of 0.03–0.35 m/s. The heat transfer variations are measured with a fast response probe capable of capturing bubble dynamics as well as detect local flow direction and deduce local liquid velocity. Measurements obtained in presence of internals are compared with those without internals to elucidate the effects of different internals design. Comparisons are based on average values and temporal variations obtained with the fast response probe. The average gas holdup, local liquid velocity and bubble fractions holdups obtained with and without internals are also compared to further point out the differences. The observed differences are discussed based on the insights provided by these comparisons. The results obtained show influence of internals design on column hydrodynamics which need to be considered for their proper design and modeling.     

Nanofluid impingement jet heat transfer

Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters.