BOILING TWO-PHASE FLOW HEAT TRANSFER IN A HORIZONTAL BEND

Abstract

A paucity of heat transfer rate data for boiling two-phase flow through bends was noted after an extensive literature survey, The present work was undertaken to redress this shortcoming.

A boiling water loop, capable of being operated at pressures up to 1300 kpa, was used. The lest section was in the form of a U-tube with two straight horizontal sections connected by a 180^° return bend. Using this loop, pressure drop and heat transfer data were gathered over a wide range of mass and heat fluxes. steam qualities and system pressures.

The data obtained were used to investigate the variation in heal transfer coefficients around the radial positions of the bend. Correlations for heat transfer coefficients for four different radial positions (top. bollom, inside and outside of the bend) have been presented for the first time. A possible explanation for the observed variations in heat transfer coefficients has also been suggested.     

TWO-PHASE FLOW HEAT TRANSFER IN A HORIZONTAL STEAM WATER SYSTEM

There are various correlations available for predicting heat transfer coefficients during forced convective two-phase flow. The present work was undertaken to gather heat transfer rate data for the steam-water system and to evaluate (and if necessary, to modify) the available correlations in light of those data.

A boiling water loop, capable of being operated at pressures up to 1300 kPa, was used. The test section was in the form of a U-tube with two straight horizontal sections connected by a 180^° return bend. Using this loop, accurate pressure drop and heat transfer data were gathered over a wide range of mass and heat fluxes.

The data obtained were used to arrive at an improved correlation for the two-phase convective heat transfer coefficient h_pfor steam-water systems at relatively low pressures (800 kPa). The proposed correlation shows h_pis a much stronger function of Lockhart-Martinelli parameter than is indicated by most of the other correlations. Among the existing correlations evaluated, the correlation proposed by Davis and David [ 1964] and the one proposed by Dengler and Addoms (1956) fit our data best.     

TWO-PHASE FLOW HEAT TRANSFER IN A HORIZONTAL STEAM WATER SYSTEM

There are various correlations available for predicting heat transfer coefficients during forced convective two-phase flow. The present work was undertaken to gather heat transfer rate data for the steam-water system and to evaluate (and if necessary, to modify) the available correlations in light of those data.

A boiling water loop, capable of being operated at pressures up to 1300 kPa, was used. The test section was in the form of a U-tube with two straight horizontal sections connected by a 180^° return bend. Using this loop, accurate pressure drop and heat transfer data were gathered over a wide range of mass and heat fluxes.

The data obtained were used to arrive at an improved correlation for the two-phase convective heat transfer coefficient h_pfor steam-water systems at relatively low pressures (800 kPa). The proposed correlation shows h_pis a much stronger function of Lockhart-Martinelli parameter than is indicated by most of the other correlations. Among the existing correlations evaluated, the correlation proposed by Davis and David [ 1964] and the one proposed by Dengler and Addoms (1956) fit our data best.     

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。     

环隙内流动沸腾传热的计算

提出环隙内流动沸腾传热计算的数学模型和计算方法。将传热系数K与流动沸腾传热系数hb的计算结果与实测数据加以比较。对环隙与空管两种结构的流动沸腾传热性能也进行了分析对比。     

水平管束沸腾传热的实验研究

实验研究了水平单管管外沸腾以及二排、三排、六排管束的沸腾传热特性。结果表明,管束下排管热负荷大小影响上排管的沸腾传热系数。上排管的传热系数不仅取决于本身热负荷的大小,也和下排管或下几排管的热负荷大小有关。     

NON-EQUILIBRIUM TWO-PHASE FLOW IN A HORIZONTAL T-JUNCTION

The paper discusses the flow of saturated or nearly saturated water in a horizontal sharp edged T-J unction. Equations were developed to predict the vapour mass fraction and the splitting ratio in both the run and branch lines. Experimental measurements obtained showed that the mass of vapour formed in the branch line was much higher than that formed in the run line. The calculated vapour mass fractions in both the run and branch lines were higher than, but close to, the measured data. The measured branch line splitting ratio was higher than that calculated from the developed model. A good agreement was obtained between the experimental results and the model predictions.     

水平椭圆多孔管外降膜沸腾传热的研究

将椭圆截面多孔表面管用于强化水平管外喷淋式降膜沸腾传热过程,研究了强化传热机理,分析了各种因素对该传热过程的影响,并将实验数据拟合成数学关联式。实验结果表明,椭圆截面多孔表面管能够显著地提高水平管外喷淋式降膜沸腾传热性能。     

添加剂对流动沸腾传热的影响

研究了添加剂对垂直管内流动沸腾传热的影响,选用W/O型聚丙烯酰胺(简称PAM)和十八烷胺(简称ODA)为添加剂,研究添加剂水溶液的性质、添加剂浓度、流速、热通量、聚合物分子量等因素对流动沸腾传热的影响.采用X光射线光电子能谱仪测试了添加剂分子在管壁上的吸附情况,并对壁面特性进行了分析.研究结果表明,W/O型聚丙烯酰胺和十八烷胺都具有强化流动沸腾传热的性能,而且有最佳浓度范围。PAM还具有减阻性能,因而可提高流速来强化流动沸腾传热。     

FLOW BOILING HEAT TRANSFER WITH FLUIDIZED SOLID PARTICLES

In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling heat transfer in such a three-phase flow boiling were carried out.Based on the analysis of heat transfer characters of this three-phase flow boiling,a mathematical mod-el for the heat transfer coefficient of flow boiling was developed.The experiments show that,in thepresence of particles the boiling heat transfer is enhanced and is about 2 times that of the vaporliquid two phase one with better flow stability.The fluidized particles rub the heat transfer wall toprevent and to clean the fouling.     

非共沸混合工质R32/R134a在水平微翅管内流动沸腾特性

对非共沸混合工质R32/R134a在5种水平微翅管内的流动沸腾特性进行了实验研究,获得了传热系数随质量流量、热通量及干度的变化关系,并对各种工况下的换热机理进行了分析和讨论.同时,对R22和R32/R134a在微翅管与光管内水平流动沸腾传热系数进行了比较.     

FLOW BOILING HEAT TRANSFER IN A NEW VAPOR-LIQUID-SOLID THREE-PHASE CIRCULATING FLUIDIZED BED EVAPORATOR

In order to enhance heat transfer and solve the fouling problems in boiling processes, a boiling system was designed by adding solid particles to the boiling liquid. In this paper, both theoretical analyses and experimental studies on the flow boiling heat transfer in a vapor-liquid-solid three-phase circulating fluidized bed evaporator were carried out. Based on the analysis of the heat transfer characters of this three-phase flow boiling, a mathematical model for predicting the flow boiling heat transfer coefficients of the vapor-liquid-solid three-phase circulating fluidized bed evaporator was developed. The experiments show that, in the presence of solid particles the flow boiling heat transfer is enhanced and is about 2 times that of the vapor-liquid two-phase one. The predicted results of the flow boiling heat transfer coefficients agreed well with the experimental data.     

混合物流动沸腾传热研究

引言由于热泵技术发展的需要,多组分混合物流动沸腾传热的计算方法已成为当前传热研究的前沿课题．经研究发现当前的流动沸腾传热模型并非都能适用于多组分的计算．比如,加和模型由于抑制因子S与混合工质的种类及组成有关,而当前又尚未研究出一个通用算式,故使该模型在用于多组分混合物流动沸腾传热时遇到困难．造成困难的主要原因是混合物流动沸腾传热过程中传质阻力的影响不容忽视,然而混合物传质系数的计算又非常困难,目前尚无可用于实际系统的理论方法,实验数据也很少,还停留在经验阶段．近些年虽然对流动沸腾传质阻力的校正提…     

汽液固三相流动沸腾传热计算与实验研究

对汽液固三相循环流化床中流动沸腾传热进行了理论分析和实验研究 ,在此基础上结合渐进模型及表面更新机理建立了汽液固三相流动沸腾传热模型 ,模型计算值和实验数据吻合较好 ,最大偏差在 18%以内     

水平微肋管内流动蒸发换热特性的实验研究

为了研究微肋管结构尺寸及工况等对管内流动蒸发性能的影响,对4种微肋管和1根9.52 mm光管进行了实验,4根微肋管中管外径为9.52 mm和7 mm的各2根,所用工质为R22.实验中质量流速变化范围为90～400kg&#8226;m^-2&#8226;s^-1,所选工况为：蒸发温度7℃,入口干度15%～20%,出口过热度5～6℃.获得了蒸发换热性能随质量流速的变化,讨论了微肋结构尺寸和管径等对蒸发换热性能的影响.两根9.52mm微肋管的传热系数比光管分别分别提高了130%和180%,而其内表面积只比光管分别增加了40%和70%.     

垂直管内降膜沸腾传热的研究

本文提出了降膜沸腾传热的物理模型和数学模型,全面考虑了对流流动与核式沸腾对膜传热系数的影响,以及液体流动对液膜内核式沸腾的抑制作用。该模型计算值与实验值吻合较好。     

TRANSITION BOILING HEAT TRANSFER IN A VERTICAL ROUND TUBE

Transition boiling heat transfer coefficients have been obtained for water at pressures of 25 to 75 psia (1.72 to 5.17 bars) and mass velocities from 14,000 to 140,000 Ibs/hr ft² (19-190 kg/m² · sec). The water flowed inside a 0.40 in (1.02?cm) ID tube and was heated by hot mercury flowing in an annulus around the tube. Thermocouple pairs placed on the outside of the central tube and outer pipe at several axial elevations allowed the rate of heat transfer to be determined. The data agreed reasonably with the correlation previously proposed.¹⁷ However, the observed heat transfer coefficients show less of a decrease with increasing temperature than was seen in previous tests¹² in which the water flowed in an annulus.     

加入惰性固体粒子的二元物系的流动沸腾传热特性

引　言流动沸腾传热广泛存在于石油、化工、轻工、动力及能源等各个领域 ,但三相流动沸腾传热的研究极少 .李修伦等[1]在流动沸腾系统中加入惰性固体粒子 ,进行了汽 -液 -固三相流沸腾传热的初步研究 .李修伦、闻建平[2 ,3]进一步将三相流和沸腾换热相结合 ,较好地解决了沸腾传热强化和防垢、除垢问题 .李修伦、张利斌等[4 ]又采用循环流化床技术 ,结合粒子在沸腾系统中的强化特性 ,开发了汽 -液 -固三相循环流化床蒸发器 ,它具有良好的强化传热和防、除垢性能 .上述研究均属于单组分三相流动沸腾传热 ,而关于二元物系三相流动沸腾传热的研…     

ELECTROHYDRODYNAMIC ENHANCEMENT OF NUCLEATE BOILING HEAT TRANSFER IN HEAT EXCHANGERS

The effect of a radial d.c. electric field on nucleate boiling heat transfer was investigated experimentally using a single-tube shell/tube heat exchanger. A dielectric liquid (Freon R. 114) was used in the shell and the tube was heated by circulating water through it.

It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis.

It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application     

水平管泡状流相分布特性

<正>气液两相泡状流的主要特征是连续液相中携带散布其中的细小气泡,气泡的存在不仅对气液两相流的传热、传质及阻力特性有很大的影响,而且对两相流动的稳定性也有很大的影响.前人有关泡状流的研究大多偏重于两相流的平均参数,对于两相流局部统计参数如局部空隙率等参数的变化规律是近年来两相流研究的新趋势.对于垂直管内的流动已经积累了相当数量的数据,而同样有广泛应用的水平管内相分布规律还知之甚少.气泡对气液两相流的传热、传质及流动结构影响机理的研究必须以了解相分布及气泡的局部统计参数为前提,同时对相分布特性的深人研究也为气液两相流的数学模型化提供实验依据.本文以空气、水为工质,研究水平管内气液两相流的相分布特性,给出了典型泡状流的时域信号图,研究了相分布随气液两相流量的规律变化,并与前人的有关结果进行了比较.