Distribution performance of gas–liquid mixture in the shell side of spiral-wound heat exchangers

The non-uniformity of gas–liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers(SWHEs).Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side.In order to investigate the influences of these parameters,an experimental test system was built using water and air as mediums and a novel distributor named"tubes distributor"was designed.The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed,where the mass flow rate ranged from 28.4 to 171.9 kg·h-1 and the content of gas changed from 0.2 to 0.8,respectively.The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow.It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4.Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.

Research on the falling film flow and heat transfer characteristics of FLNG spiral wound heat exchanger under sea conditions

As the key equipment of floating liquefied natural gas(FLNG)process,the performance of spiral wound heat exchanger(SWHE)influences operation costs and reliability of the whole system.The sea conditions destroy the falling film flow state of the refrigeration and then affect the heat transfer performance of FLNG SWHE.In order to design and optimize the SWHE,a cryogenic experimental device of FLNG process and a numerical model of falling film flow have been constructed to study the effects of sea conditions on the falling film flow and heat transfer characteristics of SWHE.The cryogenic experimental results show that the pitching conditions have larger effects on the heat transfer performance than yawing.Under the pitching angle of 7°,the natural gas temperature and gaseous refrigerant temperature increase by 3.22°C and 7.42°C,respectively.The flow rates of refrigerant and feed natural gas have a great impact on the heat transfer performance of SWHE under pitching and compound sloshing conditions.When the tilt angle increases to 9°,the tube structure with outer diameter D=8 mm and pipe spacing S=4 mm is recommended to reduce the drying area of the pipe wall surface.

Numerical and experimental study on the falling film flow characteristics with the effect of co-current gas flow in hydrogen liquefaction process

Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process(LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2spiral wound heat exchanger.The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.

Numerical investigation on gas flow heat transfer and pressure drop in the shell side of spiral-wound heat exchangers

As a critical facility,spiral-wound heat exchanger was(SWHE)has the been widely used in many industrial applications.boundary A computational fluid dynamics(CFD)model employed with smallest periodic element results and periodic conditions to examine around the the characteristics tube of the shell side of SWHE.Numerical simulation show that the heat transfer coefficients and initially mean increase absolute and subsequently decrease simulated 5%with heat radial angle because of the influence measured of backflow turbulent separation.nitrogen The deviation between is transfer coefficients and values for methane,drop,ethane,and are a mixture(methane/ethane)within when mean Reynolds number is over is 30000.For the pressure the simulated results values smaller than the measured values,and the absolute on deviation within 9%.Numerical simulation also tubes indicate that the pressure drop the and heat of transfer coefficients angle the shell side and of SWHE heat decrease as the winding the angle of the increases.Nusselt Considering effect winding on pressure drops transfer coefficients,modified correlations of_=0.308Re^(0.64)Pr^(0.36)(1+sin)^(1.38 )and friction factor f_=0.435Re^(-0.133)(sin)^(-0.36),are proposed.Comparing Nu number with the experimental data,the maximum deviations for heat transfer coefficients and pressure drops are less than 5%and11%respectively.

Feasibility of Intermediate Fluid Vaporizer with Spiral Wound Tubes

A novel intermediate fluid vaporization (IFV) technology for LNG re-gasification process with spiral-wound heat exchanging tubes is proposed. The new IFV project combines the advantage of running the shell and tube heat exchangers at high pressure with the advantage of compact space of heat exchangers. Thermal analysis on the two processes of forced convection and vaporization type heat transfer in the spiral wound tubes and vapor condensation /re-boiling type of heat transfer via intermediate fluid in shell side shows the feasibility of this promising technology.

圆管和扁形管的绕管式换热器壳侧流体降膜流动特性

为探究异型管绕管式换热器壳侧流体降膜流动和分布特性,建立了绕管式换热器三维物理模型,并基于流体体积(VOF)法多相流模型进行了数值模拟,对比分析了圆管和扁形管的管外流体降膜流动特性。结果表明:圆管和扁形管的管外轴向降膜流动分布均呈现“波谷-波峰-波谷”形状;扁形管的管外流体降膜流动速度明显大于圆管;圆管的管外液膜最薄处为圆周角120°处,扁形管的管外液膜最薄处在90°~120°之间;随着管间距的增加,圆管和扁形管的管外液膜平均厚度均呈下降趋势,扁形管周向液膜平均厚度比等周长圆管小10%~29%;随着缠绕角的增加,扁形管的管周向液膜平均厚度比等周长圆管小4%~28%。因此,推荐使用扁形管替代圆管作为绕管式换热器的缠绕管。

Experimental Study on Thermal Performance of FLNG Spiral Wound Heat Exchanger under Sloshing Conditions

The FLNG spiral wound heat exchanger(SWHE) is affected by the sea conditions, which leads to more complex flow process and decrease the heat transfer performance of the heat exchanger. In order to study the thermal performance of FLNG SWHE under heaving and swaying conditions, the experimental devices of FLNG SWHE and six-DOF(degree of freedom) sloshing platform were built. The effects of heaving and swaying motions on the pressure drop and heat transfer characteristics were analyzed at different sloshing amplitudes. The results showed that the heaving and swaying motions can cause the temperature rise and pressure fluctuation of SWHE, especially for swaying. The effect of sloshing on the heat transfer performance at the top of SWHE was greater than bottom. The pressure fluctuation percentage was within 7% and the amount of temperature change was less than 2℃, under the sloshing displacement among 120–255 mm.

不同螺旋缠绕异形管换热器壳程性能数值研究

缠绕管的形状对螺旋缠绕管换热器的传热能力有重要影响,本文建立了具有不同截面形状的螺旋缠绕管换热器模型,数值研究了八种不同截面形状的缠绕管对螺旋缠绕管换热器壳程流动与传热性能的影响。相比于传统圆管,三叶管和水滴管对壳程流体造成的扰动较大,增强了螺旋缠绕管换热器的综合换热性能,而三叶管则具有最大换热能力。进一步分析了不同冲刷方式对螺旋三叶管换热器和螺旋水滴管换热器壳程性能的影响,结果表明:在相同的进口工况下,螺旋三叶管换热器壳程努塞尔数相比于传统圆管提高了11.8%~15.5%,阻力系数增大了41.9%~49.6%;螺旋水滴管换热器壳程努塞尔数相比于传统圆管提高了2.8%~4.3%,阻力系数增大了3.2%~6.8%;在雷诺数为2 603~5 206的工况条件下,管截面与流动方向夹角为0°的三叶管换热器综合换热性能最好,而管截面与流动方向呈逆流形式的水滴管换热器综合换热性能优于顺流形式。

贫/富甲醇换热器壳程通道堵塞的原因及处理

某公司低温甲醇洗装置在生产运行期间,出现贫/富甲醇换热器壳程富硫甲醇循环量下降、管程贫硫甲醇温度升高、再吸收塔下塔积液、热再生塔液位偏低和尾气中携带甲醇等异常工况,伴随工况恶化,净化气中二氧化碳含量和硫化物含量经常超标。为此,制定并实施了一系列在线维护方案。装置开车后富硫甲醇循环量恢复正常,装置负荷由停车前的65.0%提升至76.5%。

缠绕管式换热器管板热-机械耦合场应力分析与安全评定

缠绕管式换热器作为高效节能装置广泛应用于诸多工业领域。由于该类换热器所处的温度和压力较大,考虑到其自身重力,管板处的受力非常复杂,安全问题较为突出,因此在设计缠绕管式换热器时有必要采用有限元软件对管板进行应力分析。结合工程案例,利用ANSYS软件,对换热器建立了有限元分析模型,得到管板热-机械耦合应力场,并进行安全评定。

绕管式换热器壳侧液体降膜流传热特性分析

为研究绕管式换热器壳侧传热特性,建立了以丙烷为模拟工质的三维液体降膜流传热模型,进行了不同流动工况下液体降膜流的传热数值模拟,分析了雷诺数、液相入口温度、换热管壁温、壳侧工作压力对绕管式换热器传热性能的影响。结果表明,流动工况对绕管式换热器的传热性能有显著影响;对于液体降膜流,传热膜系数随着雷诺数增大而增大,同时相同雷诺数时,随着换热管管层下降传热膜系数逐减减小;当液相入口温度升高时,传热膜系数增大,液相入口温度升高0.2 K时,平均传热膜系数升高约15%;当管壁温度与饱和温度间的温差较小时,升高管壁温度传热膜系数有明显增加,当管壁温度与饱和温度温差较大时,传热膜系数变化不显著。对于丙烷,工作压力增大时,液体降膜流的传热膜系数减小,当工作压力从0.2 MPa增大到0.3 MPa时,传热膜系数降低10%~15%,当工作压力从0.3 MPa增大到0.4 MPa时,传热膜系数降低约5%。所得结果可为绕管式换热器工艺设计提供参考。

横掠管束降膜流动和传热特性

为了明确绕管式换热器壳侧降膜流动特性对传热性能的影响,建立三维壳侧计算域,采用VOF模型,在干度工况范围为0.1~0.9,热流密度为1 275~8 000 W/m^(2),质量流率为120 kg/(m^(2)·s)时,分析了乙烷在绕管式换热器壳侧降膜流动过程。结果表明:对于乙烷工质,流型依次为层状流、半环状流、液滴流。干度为0.3,热流密度为4 000 W/m^(2)时为层状流向半环状流转化点;干度为0.6和0.7,热流密度4 000 W/m^(2)时为半环状流向液滴流转化点;在层状流向半环状流及半环状流向液滴流转化点传热系数均下降。干度为0.1~0.2,传热系数与干度成正相关;干度为0.3~0.7,传热系数与干度成负相关;干度为0.8~0.9,传热系数随干度变化不明显;流型为层状流和半环状流时,热流密度与传热系数成正相关。流型为液滴流时,热流密度与传热系数成负相关。

缠绕管式换热器全模型研究

缠绕管式换热器由于结构紧凑、换热效率高,在化工领域有广泛的应用,但其复杂性也为研究带来困难。利用mixture模型和相变模型构建了全三维尺度下的数值方法,实现了缠绕管式换热器壳程和管程流动、传热过程的计算。搭建了米级换热器实验及测试平台,建立了相应的全三维、同尺寸数值模型;采用Lee相间传质模型,实现了蒸发-冷凝模拟,获得换热器器件尺度传热系数和相变总量。计算的传热系数与实验测量值的相对误差为4.98%。基于所构建的全模型,数值研究了操作条件对传热特性和相变的影响,分析了换热段长度和缠绕管层数对传热性能的影响,为缠绕管式换热器的设计开发提供了数据和平台支持。

螺旋管内超临界二氧化碳换热性能的模拟和试验研究

对超临界二氧化碳(S-CO_(2))在螺旋管内的对流换热性能进行模拟和试验研究。探讨了热流密度q、质量流量G、节距P、管内径d、螺旋半径R等流动、结构特性对流动传热的影响,并对各结构特性灵敏度做了量化分析;搭建了闭式循环的S-CO_(2)测试平台,对螺旋管内S-CO_(2)对流换热性能进行了试验研究,并基于试验工况数据验证了数值模拟的准确性;对数据进行处理,拟合出了S-CO_(2)的传热关联式。该研究为S-CO_(2)螺旋管式换热器的热力设计方法奠定了基础,并在核电及光热发电领域具有一定的工程应用价值。

螺旋缠绕管式换热器传热性能优化与计算程序开发

螺旋缠绕管式换热器作为新型换热设备,与传统换热器相比,更为紧凑的管排列方式,增大了设备单位体积内的传热面积,且流体流动过程更易多流股化,从而提升传热综合效率;对设备的传热特性进行研究并与计算机技术相结合实现性能优化与计算方法改善,对于实际设备设计生产与使用具有重要意义;通过计算流体力学(CFD)方式,对螺旋缠绕管式换热器进行简化计算模型结构工作并开展数值模拟,研究不同管排列方式,相邻管层间距,壳程流速,换热管使用材料在设备换热性能方面的影响情况,得到设备优化结构,实现设备性能提升;选定管内径,管缠绕圈数,壳程流速以及管缠绕半径4个因素及其相对应水平参数开展正交试验,并分析单因素对于绕管式换热器综合传热性能PEC的影响情况及各因素的主次程度;运用Visual Basic语言进行计算程序开发,通过对流体物性参数、管内径、管缠绕圈数及管程数等进行输入并自动计算,实现压降,传热系数,综合性能指数等结果的可视化,提高后期设计工艺计算精度。

天然气液化主低温换热器流动换热特性教学实验设计

基于油气储运工程专业课程实验少有涉及天然气液化工艺中主低温换热设备,自主设计了天然气液化主低温换热器流动换热特性测试装置,装置具有较好的通用性,可实现不同类型的低温换热器流型观测和性能测试。同时基于可拆卸的测试段设计,能够实现绕管式换热器、印刷电路板式换热器等不同换热器结构参数、换热管型等对换热特性影响的研究。介绍了该装置的工艺流程和测试实验件的设计,分析了实验系统用于课程实验的可行性。结合本科生液化天然气利用技术以及传热学等相关课程的教学内容,设计了用于低温换热的绕管式换热器和印刷电路板式换热器的相关教学实验,得出了典型测试条件下流型观测结果及换热和压降特性曲线。

缠绕管式换热器结构参数多目标优化数值模拟研究

为分析缠绕管式换热器关键几何结构对其流动和传热性能的影响,采用多目标遗传优化算法对壳侧的流动和传热特性进行了数值模拟研究,并对通过中心复合设计得出的实验点进行了计算。研究结果表明:缠绕管式换热器的壳侧压降随着层间距、缠绕角、同层管间距的增大而减小;壳侧换热系数随着层间距的增大而减小,随着管外径的增大而增大,随着螺旋角的增大先增大后减小。通过敏感度分析可知:螺旋角和层间距对缠绕管式换热器的流动和传热性能影响最大,在计算工况下,层间距对压降和换热系数都呈负相关;螺旋角与压降呈负相关,与换热系数呈正相关。同时,应用多目标遗传算法在连续响应面的基础上对原结构进行优化,得到3组优化结果,换热系数平均增加了2.93%,压降平均降低了40.27%,综合传热性能均好于原结构。该研究成果可为缠绕管式换热器的优化设计提供理论基础。

我国大型换热器的技术进展

大型管壳式换热器、缠绕管式换热器、板壳式换热器在我国许多工业领域的应用日益增大。介绍与大乙烯、大炼油、大型煤化工等成套装置相适应的大型管壳式换热器、缠绕管式换热器、板壳式换热器的技术难点。大型管壳式换热器传热流动特性与结构设计的协同性研究、超长换热管材料的技术要求、大型管板的设计与制造技术等方面在十一五期间都取得了显著的进展。大型多股流缠绕管式换热器、低焊接残余应力镍基合金对接焊接接头的高压缠绕管式换热器、组合结构的低温甲醇洗装置原料气冷却器等大型缠绕管式换热器产品的研制相继取得成功。兼顾流体分布与传热性能的换热板片、整板分次步进模压成型工艺、氩弧焊/电阻焊焊接工艺、新型进料喷雾分布器等关键技术为超大型板壳式换热器的国产化提供了保证。本文还列举了大型换热器具有代表性的典型产品。我国已能生产换热面积超过10 000 m2的管壳式换热器、换热面积超过7 000 m2的缠绕管式换热器,换热面积超过10 000 m2的板壳式换热器,并在煤化工和石油化工装置上得到成功应用。从混合介质的实际相变机理研究、高效传热元件的采用和可靠性研究等方面指出了大型换热器在国产化进程中存在的不足之处和发展方向。

绕管式换热器的结构形式分析及应用前景

介绍绕管式换热器的基本结构和性能特点,综述国内外绕管式换热器中绕管的结构发展状况,重点阐述了绕管的表面形态和缠绕方式,结合国内外学者的试验和模拟研究结果,说明不同绕管换热器的技术特性,并展望绕管式换热器的应用前景。

LNG缠绕管式换热器试验研究中的热物性计算方法

在基本负荷型的LNG工厂中,多股流缠绕管式换热器是应用最广泛的主低温换热器,多组分介质在管程和壳程的传热与流动特性是主低温换热器试验研究的关键,而混合介质的热物性(密度、动力黏度、导热系数、比热容)对试验研究的影响较大。为此,在考虑了压力对气态混合物热物性计算影响的情况下,对气态和液态混合介质的4种基本热物性的计算方法进行了提炼、集成,并将计算结果与HYSYS的计算结果进行了比较,结果表明:相关的热物性计算方法是可行的,计算误差均控制在工程允许范围内。该计算方法为国内开发大型冷塔提供了技术支撑,有助于早日实现LNG缠绕管式换热器冷塔的国产化。