Experimental verification of effect of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation

The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height （EDH） at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consis- tent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean.

Heat Transfer Characteristics and Pressure Drop in a Horizontal Circulating Fluidized Bed Evaporator

A vapor-liquid-solid horizontal circulating fluidized bed evaporation setup was constructed to study the thermal-exchange properties and pressure change.The influences of the operating variables,including the amount of added particles,heat flux,and circulating flow velocity,were systematically inspected using resistance temperature detectors and pressure sensors.The results showed that the heat transfer eff ect was improved with the increase in the amount of added particles,circulating flow velocity,and particle diameter,but decreased with increasing heat flux.The pressure drop fluctuated with the increase in operating parameters,except circulating flow velocity.The enhancing factor reached up to 71.5%.The enhancing fac-tor initially increased and then decreased with the increase in the amount of added particles and circulating flow velocity,fluctuated with increasing particle diameter,and decreased with increasing heat flux.Phase diagrams showing the variation ranges of the operation variables for the enhancing factor were constructed.

Thermal transfer experimental research of a horizontal tube evaporative condenser

The thermal resistances distribution in different wet-bulb temperatures, air velocities and spraying water densities were achieved by the experimental test. The fluctuation of the water film convection and the water-air interfacial thermal resistance were reviewed especially. In the distribution of thermal resistance, the rank of the thermal resistance proportion （from max to min） is air flow heat transfer resistance, heat transfer resistance between refrigerant and wall, water film convection resistance and wall heat transfer resistance. When the heat flux is constant, the total resistance lowers nearly along with the increasing of air flow and water spray density. But there are a best air flow value of 2.98 m/s and a best spray water density of 0.064 kg/（m ·s） respectively, if continue to increase them, condensation performance is not significantly improved any more. The test results are available to improve the evaporative condenser performance and the designing lever.

Effect of Flow Directions on Multiphase Flow Boiling Heat Transfer Enhanced by Suspending Particles in a Circulating Evaporation System

A circulating fluidized bed evaporator(including down-flow, horizontal, and up-flow beds) was constructed to study the effect of flow directions on multiphase flow boiling heat transfer. A range of experimental investigations were carried out by varying amount of added particles(0-2%), circulation flow rate(2.15-5.16 m^3/h) and heat flux(8-16 kW/m^2). The comparison of heat transfer performance in different vertical heights of the horizontal bed was also discussed. Results reveal that the glass bead particle can enhance heat transfer compared with vapor-liquid two-phase flow for all beds. At a low heat flux(q = 8 kW/m), the heat-transfer-enhancing factor of the horizontal bed is obviously greater than those of the up-flow and down-flow beds. With the increase in the amount of added particles, the heat-transfer-enhancing factors of the up-flow and down-flow beds increase, whereas that of the horizontal bed initially increases and then decreases. However, at a high heat flux(q=16 kW/m), the heat-transfer-enhancing factors of the three beds show an increasing tendency with the increase in the amount of added particles and become closer than those at a low heat flux. For all beds, the heat-transfer-enhancing factor generally increases with the circulation flow rate but decreases with the increase in heat flux.

Convective Boiling of Near-Azeotropic Refrigerant R410A in the Horizontal Micro-fin Tube

Using near-azeotropic refrigerant R410A as the working fluid, the experimental studies on the horizontal micro-fin tubes were conducted. Several factors affecting heat transfer coefficients were analyzed, and the characteristics of flow boiling of the refrigerant in the horizontal micro-fin tubes were discussed. The local heat transfer coefficients increase with mass flux, heat flux and quality. And the heat transfer enhancement factor of those testing tubes is about 1.6 to 2.2.

Numerical Study on Flow Heat Transfer Characteristics of Horizontal Tube Falling-Film Evaporator

As an efficient and energy-saving heat exchange technology, horizontal tube falling film evaporation has a great application prospect in refrigeration and air conditioning. The three-dimensional models of falling film flow evaporation outside horizontal single tube and inside evaporator were established, and the accuracy of flow and heat transfer simulation process was verified by comparison. For horizontal single tube, the results showed that total heat transfer coefficient was low and increased with larger spray density and evaporation temperature. The thickness of liquid film outside tube decreased gradually with the increase of tube diameter, and the total heat transfer coefficient of small tube diameter was significantly greater than that of the large tube diameter. The total heat transfer coefficient presented an increasing trend with larger liquid distribution height and density. In addition, the fluctuation of tube axial liquid film thickness distribution decreased with larger liquid distribution density. For evaporator, the results indicated that part of liquid refrigerant was carried into the vapor outlet. The temperature of tube wall and fluid presented a gradually rising trend in vertical downward direction, while tube wall temperature within the same horizontal and transverse row had little difference. The high-temperature zone on the outer wall of heat exchange tube moved towards the inlet and gradually decreased, and the outlet temperature of water in the tube also gradually decreased with the increase of refrigerant spray density. The local heat transfer coefficient of heat exchanger tube in the vertical direction presented a downward trend which was more obvious with the smaller spray density and it was obviously higher located in the middle of upper tube row and both sides of lower tube row for horizontal tube rows.

制冷用水平降膜式蒸发器研究进展

降膜式蒸发器目前在牛奶、制药、化工、海水淡化等行业取得了较为广泛的商业应用,它从上世纪90年代以后开始应用于制冷空调系统。目前针对制冷用水平降膜式蒸发器的研究目的主要是明确各个参数对蒸发器传热性能的影响以及他们之间的联系,由于降膜式蒸发器的独特结构和内部传热传质的复杂性,这些研究尚处于初步阶段。在介绍其工作原理的基础上,针对水平降膜式蒸发器,着重讨论了布液器的结构与高度、管束(包括管径、管排数、管道表面形状)、制冷剂(流型、流量)等参数对其性能的影响。由于经验关联式在实际应用中的巨大优势,还总结了前人提出的关联式及其适用的范围,文章将为制冷用降膜式蒸发器的进一步研究和应用提供参考。

R410A应用于内螺纹强化管的蒸发实验研究

R410A不会与臭氧发生反应,即不会破坏臭氧层,是国际公认的用来替代R22最合适的的冷媒之一。实验研究了环保替代制冷工质R410A、R22在水平内螺纹强化管管内蒸发的换热特性,探索了水流速度对换热特性、压降的影响。实验结果表明:制冷剂R410A、R22的换热系数和压降随质量流速的增大而增大,当质量流速小于300 kg/s.m2时,两者的换热系数hr和压降Δp曲线基本吻合,当质量流速大于300kg/s.m2时,R410A的换热系数hr和压降Δp小幅增加,而R22的换热系数hr和Δp增加幅度较大。因此在质量流速要求不太大的情况,R410A比R22有更好的换热效率和较小的压降,可以用来替代R22。

横管降膜蒸发闭式循环太阳能海水淡化装置的实验

基于盘形与竖式降膜太阳能海水淡化装置的优、缺点和横管降膜蒸发的理论分析 ,针对现有装置存在的问题 ,设计了横管降膜蒸发闭式循环太阳能海水淡化装置 ,并在不同的运行参数下进行了实验研究 ,分析了影响该装置性能的各种因素 .实验结果表明 ,在供能相同的情况下 ,该装置的产水率比单级盘式太阳能蒸馏器提高了 2～ 2 5倍左右 ;提高运行温度 ,有利于提高产水率及单位能耗产水率 ;热水流率取为 30 0～ 6 0 0kg/h ,海水流率取为 8～ 15kg/h ,有利于提高产水率 ,改善该装置的性能 .

水平管薄膜式蒸发装置传热研究

本文对影响水平管薄膜蒸发过程的部分因素进行了模拟 ,确定了一定范围内水平管薄膜式蒸发器的总传热系数与液体负荷、不凝气含量、管内蒸气流速、传热温差的相应关系 。

水平管降膜蒸发器管外液体流动研究及膜厚的模拟计算

针对应用于空调和制冷系统的水平管降膜式蒸发器,建立了FLUENT数值模拟计算的物理模型。以制冷剂R134a为研究对象,对不同流量、不同布液器开孔孔径、不同管束结构下管外制冷剂液体的流动情况进行了模拟计算;并实现了绕管周方向不同角度液膜厚度的读取。

水平管降膜蒸发器传热系数空间分布

为了得到水平管降膜蒸发器传热系数,建立了水平管降膜蒸发传热实验台。通过对实验结果的归纳,分析了水平管降膜蒸发器总传热系数随顶排管喷淋密度、蒸发温度的变化规律,并给出了总传热系数在水平管降膜蒸发器内部空间的分布。结果表明,总传热系数随喷淋密度、蒸发温度的增大而增大。在空间分布上,传热系数沿管长方向受凝结过程的影响前5m先增大,后3m逐渐减小;在垂直方向由上向下逐渐减小。另外传热系数随管排数的增加而降低,并且当喷淋密度较小时,总传热系数下降的趋势更明显。

水平管薄膜蒸发传热系数

采用智能化薄膜厚度测试仪实验研究了液体负荷、蒸发侧沸点、传热总温差和传热管管径等因素对水平光滑传热管外液膜厚度、波动状况以及因此而导致的蒸发侧传热膜系数的影响 ,得到了传热膜系数的关系式 ,突出了液膜波动的影响 .还讨论了多种操作参数对两侧传热膜系数和总传热系数的影响 ,为工业设计提供实验依据 .

海水淡化中降膜蒸发过程的实验研究

由于横管降膜蒸发具有传热系数高、热耗低、可利用低品位能源等优点,横管降膜蒸发技术成为低温多效海水淡化技术中应用最广泛的方法。搭建了单管横管降膜试验台,观测了横管降膜蒸发的流动过程,研究了横管降膜蒸发过程中的流动特性和传热特性,归纳了管间距、喷淋密度对横管降膜蒸发过程中流动特性和传热特性的影响。实验结果表明:喷淋密度的增加,有助于传热系数的提高,横管顶部传热系数要高于底部。

蒸发波导高度水平非均匀性对路径损耗的影响

探讨了对流层波导模型参数的水平非均匀性.利用抛物方程法,通过仿真分析了蒸发波导高度和逆变层基底高度的水平非均匀性对对流层波导条件下电波路径损耗分布的影响.仿真结果表明:某些条件下蒸发波导高度的水平非均匀性不能忽略,并由此提出新的对流层波导模型.此外,还应用新的模型对路径损耗进行了反演.仿真结果显示,新反演模型可以有效改善反演计算的效果.

机械蒸汽再压缩蒸发技术高盐度废水处理系统的性能分析

提出了采用机械蒸汽再压缩蒸发结合水平管降膜蒸发的技术方案,依据平衡方程和传热机理建立了完整的系统数学模型,并围绕进料预热温度、蒸发传热温差、蒸发温度以及进出料浓度等因素对系统性能的相关影响进行了计算与分析。结果表明,选择合适的进料温差(1～4℃)和传热温差(3～7℃),并保持系统进出料浓度的稳定性是保证整个系统具有良好经济性和节能性的关键。

水平管外降膜蒸发传热实验研究

以水为工质,对直径为19 mm的铝黄铜管外降膜蒸发传热过程进行实验研究。实验通过测量管表面和饱和蒸气温度,计算得到平均和局部传热系数。由实验数据分析喷淋密度、蒸发温度、热流密度、管间距等参数对管外平均传热系数的影响,并与直径25.4 mm铝黄铜管降膜蒸发传热系数进行比较,讨论局部传热系数随周向角度的变化。结果表明,在实验范围内,管外平均传热系数随温度的升高而增大,随喷淋密度的增大先增大,后略微下降。小管径管的降膜蒸发传热系数大于大管径管的传热系数。

水平管降膜蒸发传热系数影响因素的实验研究

搭建水平管降膜蒸发实验台,分别进行实验流体为海水和纯水的实验,将其结果在不同热流密度、雷诺数(Re)、蒸发温度等条件下进行比较。研究结果表明,在小温差和较低雷诺数下,热流密度对水平管降膜蒸发传热系数基本无影响;两种流体的传热系数均随雷诺数的增大而出现先增后减的趋势;随蒸发温度的升高,海水的传热系数逐渐降低,淡水则逐渐升高;两种流体具有不同的水平管降膜蒸发临界雷诺数。

卧式喷淋降膜蒸发站在麦草浆黑液蒸发中的应用

针对草浆黑液的物理性能及蒸发浓缩的困难 ,研制了卧式喷淋降膜蒸发器。生产实践表明 ,该蒸发器可应用于草浆的黑液浓缩。以安徽某纸厂亚铵法麦草浆黑液五体四效蒸发站 (单台传热面积 2 50m2 )为例 ,进行了应用结果的分析 ,测试出各效的传热系数为 1 2 357～ 1 4 779kJ/(m2 ·h·K) ,蒸发强度平均为 2 0 88kg/(m2 ·h) (黑液浓度由 7%蒸浓到 53 % ) ,并且具有良好的防垢和除垢性能。

蒸发温度对水平正反齿压花齿型肋管池沸腾换热的影响

随着节能减排的大力推广,管外沸腾强化传热技术得到了广泛的研究和发展。设计建立了水平双侧强化管管外沸腾试验系统,以R134a为循环工质试验研究了不同热通量工况下,蒸发温度对正反齿压花齿型三维肋管池沸腾换热特性影响,并结合试验结果分析探讨了其理论描述方法。结果表明:蒸发传热系数随蒸发温度变化趋势线的斜率随热通量呈现非线性变化;在同一蒸发温度下,管表面传热系数均随热通量单调递增,但增长率随热通量增加而逐步降低;回归分析获得不同热通量下蒸发温度对正反齿压花齿型蒸发管表面传热系数影响的统一表达式;等热通量工况强化传热因子在热通量超过10 k W·m^(-2)后升至2以上,在热通量接近20 k W·m^(-2)时达到极大值2.588,但在热通量接近5 k W·m^(-2)时接近1;蒸发温度及其与热通量合同对正反齿压花齿型蒸发管表面传热系数的作用机理与理论描述方法有待进一步深入研究。