水平管油气两相段塞流及其传热特性

海底油气管道的冷却传热过程是结蜡、水合物等海洋石油工业流动保障问题的关键控制因素。采用电容探针与热电偶、热电阻等流动及温度测量手段对不同冷却条件下空气-油段塞流的流动参数和传热参数进行实验测量,分析了空气-油段塞流流动参数对传热特性的影响,并与空气-水对流换热进行对比。结果表明,空气-油段塞流对流传热系数主要受液相折算速度的影响,且冷却液温度越低,管底热流体黏度越大,导致热边界层越厚,传热系数降低;受黏性力及边界层影响,对流传热系数远小于空气-水;沿管壁周向,从管顶到管底的对流传热系数不断增大。提出了适用于冷却条件下的油气段塞流传热关联式和传热模型。     

Holdup and heat transfer in horizontal slug gas-liquid flow

A correlation has been developed for the estimation of holdup in horizontal slug flow from the relationship of the bubble velocity and the liquid slug Reynolds number. Simple models for slug flow heat transfer based upon the momentum-heat transfer analogy for turbulent flow and the Graetz-Leveque equation for laminar flow are found to give reasonable agreement with the limited experimental data for horizontal gas—liquid slug flow.     

微小通道内低Reynolds数液-液两相流动与换热特性实验研究

实验研究了圆形微小通道内液-液两相流的流动和换热特性。选用去离子水为分散相,高黏度二甲基硅油为连续相。通过处理高速摄像所拍摄的可视化图像,总结了液-液两相流流型和液滴的长度/形状特征。并在此基础上考察了低Reynolds数下液-液弹状流对微小通道的换热作用。结果表明,平均Nusselt数随着Reynolds数的增加而增加,且油水比越大传热系数增加幅度越明显。Nu随着含水率的增加而降低。虽然含水率增加会使两相平均热容量提高,但在低Reynolds数下,这种提高被其长液滴内较弱的循环强度所抵消。选用三种不同形式接头在相同混合速度和含水率的情况下生成不同长度的液滴,发现短液滴更有利于换热。相同工况下,液滴长度的优化可以使整体传热系数提高近26%。     

Condensation heat transfer characteristics and flow regime in a horizontal rectangle channel of a multichannel cylinder dryer

The present study investigates the phenomenon of steam condensation in a rectangle horizontal channel with a mass flux range of 20–70?kg/m²/s and a vapor quality of 0.2–0.8. Mass flux and vapor quality were presented to primarily affect the heat transfer coefficient in shear-dominated flow regime, such as the mass flux is greater than 40?kg/m²/s. At the low mass flux, only slug flow, plug flow, and wave flow were observed. At the high mass flux, the wave flow and annular flow were observed even at the low-vapor quality, and the slug and plug flow were not found during the entire condensation process. Observed flow patterns agreed with Tandon’s flow pattern map. Four kinds of correlations are employed to predict the condensing heat transfer coefficient, and the result reveals that Cavallini’s correlation agrees with the experimental results relatively well. The measured pressure drop has a good agreement with the Lockhart–Martinelli correlation.     

壁面润湿性对微通道内二氧化碳-水两相流流动及传质性能的影响

在1 mm×1 mm矩形截面下微通道内,以二氧化碳-水为工作流体,研究壁面润湿性和气液表观流速对气-液两相流型和气液传质的影响,并研究了气、液表观流速对弹状流流体力学性质的影响。在亲水微通道中观测到了泡状流、泡状-弹状流、弹状流;在疏水微通道中观测到了非对称弹状流、拉长的非对称弹状流、分层流。实验表明亲水微通道中弹状流区域下气泡长度大体上随气相表观流速的增大而增大,随液相表观流速的增大而减小;液弹长度大体上随气相表观流速的增大而减小,随液相表观流速的增大先增大后减小;液侧体积传质系数k_La均随气、液相表观流速的增大而增大,随通道壁面润湿性的增强而增大。     

定-转子反应器传热特性

采用蒸汽-水体系,在转子转速为400～1400 r·min^-1、水流量为0. 1～0. 5 m³·h^-1、蒸汽充足的实验条件下,研究了定-转子反应器(RSR)的传热特性,初步考察了操作参数对RSR液体分布的影响。实验结果表明：总传热系数随着转速的升高而增大,随着液量的增加而增大但增幅减小。小流量（0.1～0.3 m³·h^-1）与低转速（400 r·min^-1）时,温升不均,表明液体分布不均。最后采用因次分析法推导出定-转子反应器总传热系数关联式,且进行了统计检验,所得关联式与实验数据拟合较好。     

升膜蒸发管内流型可视化及传热性能

为了探究热流密度、真空度和流量对升膜蒸发器传热性能的影响,以及对升膜加热管内流体流型进行观测和分析,本文建立了升膜蒸发系统传热实验平台,对升膜蒸发器的传热特性和流体流型进行实验研究.实验所用升膜管管长2200mm,升膜管采用镀透明导电膜石英管,工作介质为水;升膜管蒸发侧采用电加热方式;研究了热流密度(6.71kW/m²≤ q≤ 26.79kW/m²)、流量(20L/h≤ M≤ 100L/h)和真空度(0≤ P≤ 15kPa)对升膜加热管流体流型和传热特性的影响.结果表明:通过电加热的方式可以实现石英管内溶液的升膜蒸发,并能观测到泡状流、块状流、弹状流、柱塞流、环状流和雾状流;热流密度低于6.71kW/m²时无法形成升膜蒸发,随着蒸发侧热流密度的增大,升膜管内环状流长度增大,管内传热系数增大;随着流量的增大,升膜管内液体湍流强度增大,管内传热系数增大;真空度对流体流型影响较大.     

高宽比对矩形通道内蒸汽冷凝传热特性及流型影响的研究

通过可视化流型观测及实验测量,研究了单边换热矩形小通道的高宽比对两相流型、平均冷凝传热系数及两相流动阻力的影响,采用高速摄像机拍摄了环状流、环波状流、波状流、弹状流、塞状流及泡状流6种典型流型。研究表明,高宽比为1：2及1：3的通道内出现流型种类较为全面,而在高宽比为1：5通道内基本无弹状流、塞状流及泡状流。1：5通道内环状流所占区域较1：2及1：3通道大,随入口蒸汽质量流速的增加,差值逐步减小。随着通道高宽比的减小,平均冷凝传热系数逐渐增大;不同高宽比通道中平均冷凝传热系数间的差值随入口蒸汽质量流速的增加而减小;蒸汽质量流速足够高时,高宽比对传热系数基本无影响。通道内两相流压降随通道高宽比的减小而增大;随着入口蒸汽质量流速的增加,不同比例通道内的两相流动压降差距逐渐增大。     

固液界面接触角对膜状冷凝传热强化的初步分析

引　言冷凝有两种形态 :膜状冷凝和滴状冷凝 .当液固表面自由能差Δσ≥ 33.3mJ·m- 2 [1] ,即液体完全不润湿固体表面时 ,蒸气在表面上将呈现滴状冷凝 ,其传热系数是膜状冷凝的几倍到几十倍 .这已是公认的事实 .但是 ,当表面自由能差在 0～ 33.3mJ·m- 2 范围内时 ,表面强化冷凝传热的效果将取决于表面自由能差值的大小 ,差值越大强化效果越明显 .为了更清楚地表示冷凝传热特性随冷凝液与表面自由能差的变化关系 ,把 0和 33.3mJ·m- 2 分别作为第 1临界值和第 2临界值 .当固液表面自由能差小于第 1临界值时 ,冷凝形态为传统的膜状冷凝 .…     

Heat transfer characteristics of coal-water mixtures

The heat transfer coefficient for the laminar flow of the coal-water mixture (CWM) in a round tube was measured in a preheater which included three inner pipes of radii 5 mm and an outer pipe of radius 40 mm and a length of 1.8 m. It was found that the heat transfer coefficient for the CWM could be estimated from a Newtonian correlation within the experimental error. Furthermore, theremal conductivities of CWMs from thirteen kinds of coals have been measured. A simple and accurate method to predict the thermal conductivity of coal is proposed in this study.     

Heat transfer in a reciprocating plate column

A pilot‐scale (5.08 cm internal diameter) reciprocating plate column has been modified by the insertion of a brass test section for heat transfer measurements. Heat is supplied to liquid (water or a glucose solution) in the column from an electrical heating tape wound round the brass section, the walls of which contain thermocouples. Reciprocation of the plates in the column results in up to a seven‐fold improvement In heat transfer coefficient, to single phase liquids. Conditions are turbulent with oscillatory Reynolds numbers up to 20000. The effect of plate reciprocation is much less pronounced when the liquids are agitated by a stream of gas bubbles. The single‐phase heat transfer coefficients have been correlated for 5 different types of plates using approaches already available in the literature for turbulent systems in steady flow. The best‐fit oscillatory flow correlation differs slightly from the existing correlations for steady flow.     

An experimental study of air-water Taylor flow and mass transfer inside square microchannels

Flow and mass transfer properties under air-water Taylor flow have been investigated in two square microchannels with hydraulic diameters of 400 and 200 μm. Experimental data on Taylor bubble velocity, pressure drop and liquid side volumetric mass transfer coefficient (k_La) have been presented. It was shown that the measured Taylor bubble velocity in square microchannels could be well interpreted based upon an approximate measurement of the liquid film profile therein. Then, the obtained two-phase frictional pressure drop values in both microchannels were found to be significantly higher than the predictions of the correlation proposed by Kreutzer et al. [2005b. Inertial and interfacial effects on pressure drop of Taylor flow in capillaries. A.I.Ch.E. Journal 51, 2428-2440] when the liquid slug was very short, which can be explained by the inadequacy of their correlation to describe the excess pressure drop caused by the strong inner circulation in such short liquid slugs. An appropriate modification has been made to this correlation in order to improve its applicability in microchannels. Finally, the experimental (k_La) values in the microchannel with hydraulic diameter of 400 μm were found to be in poor agreement with those predicted by the existing correlations proposed for capillaries with diameters of several millimeters. The observed deviation was mainly due to the fact that mass transfer experiments in this microchannel actually corresponded to the case of short film contact time and rather poor mixing between the liquid film and the liquid slug, which was not in accordance with mass transfer assumptions associated with these correlations. A new empirical correlation has been proposed to describe mass transfer data in this microchannel.     

垂直风冷翅片管中氨水鼓泡吸收特性

详细描述了垂直风冷翅片管吸收器中氨水鼓泡吸收的传热和传质过程。管外侧套用翅片,管内侧中氨水吸收溶液和氨气都从吸收器的底部流入、顶部流出。根据质量守恒方程和能量守恒方程建立了热质传递的微分数学模型。该模型分析了吸收器中两相流(即波动流、弹状流、泡状流)的变化,同时考虑了不同的两相流中气液相之间的热质传递以及两相流与管外空气之间的热量传递。通过解模型的微分方程,得到了一些重要参数(温度、摩尔分数)的局部值以及这些参数在吸收高度方向上的变化趋势。     

Transient heating and cooling of cocurrent three-phase fluidized beds

The thermal transient behaviour of three-phase fluidized beds have been investigated for a liquid viscosity ranging from 35 to 75 mPa · s. For the operating conditions used in this study, a 6 mm glass particle bed was found to have a thermal response similar to that of a fixed bed. The transient responses, which were not significantly affected by gas sparging, were, however, faster for heating than for cooling. This result has been analyzed from a model assuming liquid plug flow through stationary particles using combined free and forced convection correlations for heat transfer around the particles. Different correlations are then proposed to predict the contribution of natural convection to the liquid-to-particle heat transfer in heating and cooling modes. The effect of gas sparging was found to strongly affect The 2.0 mm particle bed responses but only moderately the 3.9 mm bed responses. These responses were analyzed using axial dispersion models for the liquid and solid phases. For the 3.9 mm particle bed, the axial dispersion coefficient of the solids, E_ZS, was found to be of the same order of magnitude as that of the liquid coefficient, E_ZL. However, the value of E_zs for the 2 mm particle bed was found to be five times that of E_ZL.     

通气式搅拌槽的传热特性

研究了通式搅拌槽槽壁给热系数（ｈｗ）随通气速率和搅拌转速变化的规律和机理，在搅拌过程中存在一个临界转速，它决定了通气是增大还是减小ｈｗ。通过引入综合反映操作条件对ｈｗ影响的无因次数Ｈｚ，获得了一个偏差较小并且简单实用的ｈｗ半经验关联式。     

Solid effects on hydrodynamics and heat transfer in an external loop airlift reactor

The effect of a solid presence on global hydrodynamic parameters and heat transfer in an external loop airlift reactor has been experimentally investigated. Results obtained in both two- and three-phase flow are presented in this study. Two different external loop airlift reactor sizes have been used and local hydrodynamic characteristics including local gas hold-up and bubble velocity have been obtained in two-phase flow. Optical and ultrasound probes have been used to obtain this information, respectively. It was found that an increase of solid hold-up leads to a decrease of liquid velocity and heat transfer coefficient. Measured in a two- and three-phase reactor using a horizontal-heating probe, a correlation of the average gas hold-up and heat transfer coefficient is proposed. Correlation parameters are identified in homogeneous and heterogeneous flow regimes, which have been derived from the gas slip velocity concept. The experimental liquid velocity and gas hold-up in the riser have been represented in a satisfactory way by a hydrodynamic model, either in the absence or in the presence of solid particles.     

硅基微通道中周期性沸腾的光学可视化

以丙酮为工质,在三角形截面的硅基微通道内进行了微尺度沸腾传热实验研究。在对汽液两相流流型进行光学可视化测量的同时,对压力、温度等信号进行了同步动态测量。发现了周期在毫秒级的微时间尺度的周期性沸腾传热。1个完整的周期可以分成3个子过程：进液阶段,汽泡核化、增长、聚合及爆炸阶段,瞬变液膜蒸发阶段。总结出1个完整周期内所存在的4种汽液两相流流型。鉴别出了沸腾起始点。分析了沸腾传热系数随干度的变化关系,结果表明在本实验工况下：当干度小于0.4时,起主导作用的传热机制为核态沸腾;而当干度大于0.4时,起主导作用的传热机制为强制对流沸腾。     

微通道内离子液体/乙醇混合溶液吸收CO2的传质特性

采用高速摄像仪对微通道内离子液体/乙醇混合溶液吸收CO₂的传质行为进行了实验研究。考察了弹状流型下气液两相流量比和离子液体浓度对液侧体积传质系数k_La和液侧传质系数k_L的影响。当离子液体浓度不变时,k_La、k_L均随气液流量比的升高而增大并逐渐趋于恒定。当液相流量不变时,对于不同浓度的离子液体溶液,液侧体积传质系数k_La和液侧传质系数k_L随气液流量比的变化曲线出现了交叉点。在交叉点之前,k_La和k_L均随着离子液体浓度的增大而减小;在交叉点之后,k_La和k_L均随着离子液体浓度的增大而增大。提出了用于预测液侧体积传质系数k_La的新的量纲1经验关联式,预测效果良好。     

考虑界面蒸发时的降液膜流动传热

The interfacial evaporative heat transfer was included in the semi-empirical study of the heat transfer for the falling liquid film flow. The investigations showed that, the inclusion of the interfacial evaporative heat transfer in the turbulent model would lower the predicted convective heat transfer coefficient. Predictions of the new model resulted in a prominent deviation from that predictions of the normal model in the case of large mass flow rate and low wall heat flux. This deviation will be decreased with increasing wall heat flux, such that it will be asymptotic zero at very high wall heat flux. Predictions of the new model agreed well with the current experimental measurements. This study has verified that the Reynolds number is not the sole crucial parameter for heat transferof falling liquid film flow, and wall heat flux will be another important independent parameter. This result is consistent with our previous studies.     

平行流热管管内两相流动可视化实验研究

平行流热管换热器综合热管轴向高效换热和平行流换热器管外高效换热的优点,是一种新型的热管换热器。为了研究平行流热管工作机理及管内流动过程,搭建了平行流热管可视化实验台并对不同结构参数、不同加热功率和不同充注工质下的启动特性和传热传质规律进行了实验研究。实验结果表明：平行流热管工作机理复杂,并联管路内气柱和液柱在重力和不平衡压力的共同作用下进行互激振荡流动,并且管内出现泡状流、弹状流、环状流等多种流型,同时较高的加热功率和较大的管径会加剧工质在并联各管路之间的往复振荡,增加工质在蒸发段和冷凝段的扰动,提高热管的换热性能。