Mathe matical model and calculation for heat transfer during condensation on surfaces of corrugated plates

A mathematical model was established for condensation on surfaces of verticalcorrugated plates based on the mechanism of heat transfer enhancement to thin down the liquid filmdue to surface tension effect between corrugated plate surfaces and liquid films. The relative heattransfer coefficients of condensation on corrugation plates were calculated in contrast withequivalent vertical plane ones. The heat transfer enhancement effects for the main geometricparameters such as pitch, height, corrugation angle, tilt angle, and fillet radii of corrugationswere analyzed to guide the optimization of corrugation structure for application. A two-scalecorrugation is suggested, which can compromise both the enhanced heat transfer effect and adequatecross section area for flows, and it makes the heat transfer coefficient 1 to 2 times more than thatof an equivalent plane one.

A Cell Model to Describe and Optimize Heat and Mass Transfer in Contact Heat Exchangers

A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat and mass transfer at local moving force of the processes in each cell. The total process is presented as two parallel chains of cells (one for water flow and one for gas flow). The corresponding cells of the chains can exchange heat and mass, and water and gas can travel along their chains according to their transition ma-trices. The results of numerical experiments showed that the most part of heat transfer occurs due to moisture condensation from gas and the most intense heat transfer goes near the inlet of gas. Experimental validation of the model showed a good correlation between calculated and experimental data for an industrial contact heat exchanger if appropriate empirical equations were used to calculate heat and mass transfer coefficient. It was also shown that there exists the optimum height of heat exchanger that gave the maximum gain in heat energy utilization.

Condensing Heat Exchanger

The paper shows a method of designing a heat exchanger recovering heat from the condensation of water vapour contained in flue gases. A heat exchanger condenses water vapour and SO2 （sulphur dioxide） in the presence of inert gases （CO2, CO, N2, O2） contained in flue gases. A mathematical model and a sample design of a heat exchanger were presented. The heat exchange is capable of recovering from a dozen or so to several dozen percent of heat from flue gases escaping into the atmosphere. A second advantage of the heat exchanger is the possibility to reduce the emissions of SO2 considerably. Depending on the parameters, it can be even a sevenfold reduction in the emissions. The main mathematical tool used for designing the condensing heat exchanger is the Colburn-Hougen method. The authors omitted that part of the method which requires iterative calculations. The Mollier diagram was used instead.

Investigation of a falling film tube bank heat exchanger with baffle design for water recovery applications

Shell and tube heat exchangers(STHE)are essential thermal equipment and widely used in daily life.A novel thermosyphon system called falling-film thermosyphon(FFTS)is introduced and integrated into STHE system,resulting in a better thermal performance.In this study,a rectangular solid tube bank of FFTS bundles with a baffle design is studied.The numerical simulation for heat and mass transfer of the FFTS heat exchanger is developed to predict the condensation rate of the vapor in the flue gas,and a lab-scale prototype is also built up in COMSOL.The prediction is validated with the experimental data from references,and the model’s accuracy is verified within 10%-12%error.Also,the Non-dominated Sorting Genetic Algorithm,version 2(NSGA-II)is implemented to improve the thermal performance of rectangular tube banks in this paper.Several parameters,e.g.,baffle number,tube number,and tube space,are optimized.As a result,compact configurations with more baffles are preferred to enhance the performance associated with a high-pressure drop correspondingly.The optimized layout for the lab-scale prototype can increase by 18 to 32%condensation with a pressure loss of less than 200 Pa.

Theoretical Analysis of a Shell and Tubes Condenser with R134a Working Refrigerant and Water-Based Oxide of Aluminum Nanofluid (Al₂O₃)

The article analyzes a shell and tube type condenser’s thermal performance using concepts of efficiency and effectiveness. Freon 134a is used as a coolant flowing through the shell. Water or water-based aluminum oxide nanoparticles are at relatively low saturation pressure in the tube. The condenser consists of 36 tubes divided into three central regions for analysis: superheated steam, saturated steam, and subcooled liquid. The three regions contain four tubes with three steps each, that is, 12 tubes. Region I, superheated steam, includes three horizontal baffles. Profiles of temperature, efficiency, and effectiveness are presented graphically for the three regions, with fixed refrigerant flow equal to 0.20 kg/s and fluid flow rate in the tube ranging from 0.05 kg/s to 0.40 kg/s. The experimental result for vapor pressure equal to 1.2 MPa and water flow equal to 0.41 kg/s was used as one of the references for the model’s physical compatibility.

WHR （Waste Heat Technology） Method in Tri-generation Model

This paper is focused on description of cool production in using WHR （Waste Heat Technology） Technology-a new method of centralized production of heat by using the waste heat from generated exhaust gas, which has been in 2009 developed and operated by companies HELORO s.r.o, and COMTHERM s.r.o.

空调器冷凝器结构参数对其制冷剂积存量及系统性能的影响

在保持R290空调器系统性能的前提下,为降低冷凝器中制冷剂积存量,建立冷凝器性能综合评价模型,对冷凝器不同支路数流程的结构参数进行优化研究。结果表明:管径减小使得制冷剂积存量下降、COP下降;管间距和翅片厚度增大以及翅片间距减小均使得制冷剂积存量下降、COP升高;对冷凝器的制冷剂积存量和系统COP进行多目标优化,得到最优设计结构参数为四支路流程,管径5.74 mm,管间距19.67mm,翅片间距1.43mm,翅片厚度0.092mm。本研究可为R290房间空调器减少制冷剂充注量提供参考。

喷雾耦合降温强化旋风分离器脱除细颗粒物的研究

通过在冷凝换热器前耦合喷雾的方式,将雾化团聚和水汽相变团聚结合以提高旋风分离器对细颗粒物的脱除效果,用于湿式除尘器后近饱和高湿烟气的深度处理。通过开展实验室试验和某金属冶炼厂烟气旁路试验,考察了该技术对颗粒物的脱除特性。实验室研究结果表明,典型工况下喷雾耦合降温能够显著增强旋风分离器对颗粒物的脱除,比单独喷雾或降温具有更好的增强效果。提高喷雾量和换热器温降,细颗粒物脱除效率先升高后趋于稳定,在温降6℃、喷雾量0.046 L/m^(3)时达到最优脱除效果。烟气温度越高,湿度越接近饱和,细颗粒物脱除效率越高。工业烟气旁路试验表明,该系统适用于湿式除尘后的近饱和高湿烟气,且对波动工况的适应性强,当入口颗粒物浓度不超过2000 mg/m^(3)时,出口颗粒物浓度可保持在20 mg/m^(3)以内,平均脱除效率超过99.2%。

烟气凝变过程中SO_(3)酸雾凝结长大与脱除特性模拟研究

烟气冷凝技术能够回收湿烟气中的废水和余热,同时降低SO_(3)酸雾排放量。该文通过建立烟气冷凝、颗粒运动及颗粒凝结长大模型,对烟气凝变过程中SO_(3)酸雾的凝结长大和脱除特性进行研究,分析关键影响因素,并讨论了酸雾长大和脱除机理。结果表明:SO_(3)酸雾经过凝结长大后在换热器出口粒径呈双峰分布,最高数量浓度在微米范围;亚微米粒径的酸雾捕集机理以热泳和扩散泳为主,提高入口烟气温度和相对湿度,降低壁面温度和入口烟气流速都有利于酸雾粒径的增长和脱除。微米粒径的酸雾捕集机理以惯性碰撞和拦截为主,提高烟气流速有助于微米粒径酸雾的脱除。

水平微肋管内R513A冷凝换热特性研究

采用实验方法研究了R513A在光管和不同齿密度微肋管内的冷凝换热性能,并通过对比冷凝换热系数实验值与关联式的预测值,探究了现有关联式对R513A的适用性,实验在冷凝温度33、35、38℃,质量流速50~150 kg/(m^(2)·s)的工况范围内进行。实验结果表明:冷凝换热系数随质量流速的增大而增大,在低质量流速区域,微肋管的冷凝换热系数增长幅度更大;随着齿密度的增加,管内换热面积增大,但管内表面张力作用增强,相应的流动阻力增强,强化传热作用被削弱;与R134a相比,微肋管对R513A的强化传热效果更优;对于光管,Bashar关联式的预测效果最佳,Cavallini关联式与Dobson关联式在低质量流速区域的预测误差偏大;对于微肋管,Yu关联式的预测效果最理想,Cavallini关联式与Kedzierski关联式均低估了管内冷凝换热特性。以Kedzierski关联式为基础,拟合了新的修正关联式,修正关联式的预测值与实验值的一致性较好,其平均绝对误差与标准差分别为7.8%、8.5%。

椭圆型套管-管翅式蒸发式冷凝器传热传质性能及实验研究

介绍了一种椭圆型套管-管翅式蒸发式冷凝器,通过搭建的蒸发式冷凝器性能测试实验系统,研究该蒸发式冷凝器在不同循环水配比、不同地区环境以及“风冷”“水冷”“蒸发冷凝”和“全工况”4种不同运行模式下的传热传质性能与运行特性的变化规律。结果表明:在相同条件下“全工况”模式的热流密度高于“风冷”和“蒸发冷凝”两种模式,而“水冷”模式由于其传热面积远小于其它模式,所以其热流密度最高;“全工况”模式在保持配风量及循环水总量一定的条件下,热流密度随循环水配比的增大而先增大后减小,喷淋水与冷却水的流量最佳配比为2∶5;“全工况”模式在严寒干燥地区、寒冷地区以及夏热冬暖地区的总热流密度分别为5879.64、3964.28及2933.05 W/m^(2),因此不同地区环境运行的传热性能相差较大,该冷凝器“全工况”模式在空气干燥的地区,喷淋冷却水温度范围为13~18℃运行时传热性能较优。在相同的条件下,“蒸发冷凝”模式的水膜传质系数高于“全工况”模式,且两者均随喷淋密度的增大先增大后减小。

多联式空调冷凝水能量回收系统设计及CFD模拟研究

通过智能控制与能量回收提高暖通空调系统的使用效率,降低制冷、制热能源消耗,是实现建筑节能的有效方式。目前空调冷凝水的就近或集中排放,造成了水量和冷量的浪费。通过设计冷凝水导液仓连接器和套管式换热器,实现冷凝水冷量和冷凝器侧液态制冷剂热量的交换,起到回收冷凝水冷量,增加制冷剂过冷度,提高制冷循环效率的目的。使用CFD模拟软件,分析制冷剂入口温度、冷凝水入口温度、制冷剂入口质量流量和冷凝水入口质量流量对制冷剂出口平均温度、过冷度、壁面热流、性能系数和压缩机功耗的影响,提出能量回收装置的热量交换规律和最佳换热工况,对工程应用具有较强的理论指导意义。

罗茨真空机组系统稳定性的提升

为解决螺杆真空系统运行效率低、真空稳定性差的问题,增强对螺杆真空控制系统的温度、电流、压力的监控,降低了事故处理的滞后性;增加板式换热器及列管冷凝器,冷却了热态气体,降低了真空泵负荷,提升了真空泵运行效率;对三级真空泵进行变频升级,有效调整了产能需求,保证了设备运行的最佳效率。通过以上工艺、设备、电气方面的调整,螺杆真空泵持续、高效的稳定运行得以实现。

中央空调冷凝热回收技术在大型商业建筑中的应用

为建筑维持室内环境舒适度时,由于传统的空调系统冷却塔排热高并产生大量余热,这些热量通常被直接排放到大气当中,不仅造成了能源的浪费,还加剧了城市热岛效应。为了解决这一问题,对中央空调冷凝热回收技术在大型商业建筑中的应用展开研究,通过热交换器将高温冷凝热与回收水进行热量交换,根据冷凝负荷和加热负荷对板式换热器、热泵机组和冷却塔间进行负荷控制,最后通过调节水泵转速的方式调整热水循环量,从而达到保温、制冷和节能的目的。实验结果表明,在测试工况下,冷却塔的排热总量都在标准范围内,能够满足机组冷凝热的排放要求。

内含鼓胀式热交换器的反应缩合釜的振动特性研究

运用solidworks simulation软件模拟计算了内含鼓胀式热交换器的反应缩合釜鼓胀板对的第一阶固有频率、最大应力分布位置,对比加固前和加固后的两种方案,确定加固效果。为此类设备如何高效抵抗振动提供了一种新的思路。

凝汽器在线清洗和加药除贝装置在海水冷却机组中的应用

凝汽器是火电机组重要的换热设备,凝汽器真空是衡量煤电机组性能的关键指标,凝汽器管内清洁度是影响凝汽器真空的重要因素。海水冷却凝汽器易因海生物贝类的滋生蔓延而影响换热效果。基于此,介绍了一种新型的加药除贝装置,能够在线清洗时快速除去管内贝类,提高凝汽器管内清洁度,降低汽轮机热耗,维持机组理想真空,降低煤耗,达到了节能减排、环保经济的综合目的。

直接空冷火电机组乏汽余热利用技术

火电厂汽轮机排汽(乏汽)需要冷凝成液态水用于系统循环,湿冷、干冷机组都需要消耗大量能量来冷凝乏汽。北方缺水地区采用直接空冷火电机组,大量乏汽通过空冷岛散热。从热力学第二定律来看,乏汽已无做功能力,但是汽化潜热与做功能力无关,在能够提供真空环境确保乏汽流动性和需要加热远低于乏汽温度的工质的情况下,乏汽中的汽化潜热仍具有很高的回收价值。尤其对于直接空冷火电机组,其汽轮机排汽压力和温度均高于湿冷机组,可以采用汽水换热器直接回收乏汽热量加热厂区生水,降低电厂辅助蒸汽的消耗量,提高电厂收益。

火电厂烟气潜热和凝结水回收的试验研究

介绍了使用氟塑料换热器回收大型火电厂烟气潜热和凝结水的试验研究.火电厂湿法脱硫系统出口温度为50~55℃的饱和或过饱和烟气,其烟气水蒸气浓度为12％~18％.烟气中的水蒸气携带大量潜热,降低了锅炉效率.拟在脱硫系统出口烟道中加装冷凝换热回水装置（换热器）,以实现高水分烟气的深度凝结,回收大量水分,同时回收气化潜热.为此,在某褐煤电厂搭建中试试验系统,抽取实际烟气进行试验.结果显示：当烟气温度降低9~10℃,将结果折算到全烟气量（2500000 m3/h,标准状态,下同）,可以回收凝结水92．25 t/h,回收热量226．97 GJ/h；该系统可实现褐煤机组湿法脱硫零耗水,这对干旱地区的水资源保护有重要意义.

伴随有水蒸气凝结的烟气对流换热的实验研究

本文通过实验研究了冷凝式燃气热水器中烟气伴随有水蒸气凝结的受迫对流换热过程。着重介绍实验系统、测试方法和对塔板式换热器和肋片板式换热器的实验研究结果。实验表明，有水蒸气凝结时的烟气对流换热系数远大于无凝结时的换热系数，可提高数倍。在冷凝式换热器中，塔板式换热器的换热系数大于肋片板式换热器。

LNG接收站BOG处理工艺优化——以青岛LNG接收站为例

蒸发气(Boil Off Gas,缩写为BOG)的处理是LNG接收站必须考虑的关键问题之一,关系着LNG接收站的能耗及安全、平稳运行。为此,介绍了LNG接收站BOG处理的4种工艺:①BOG直接压缩工艺;②BOG再冷凝液化工艺;③BOG间接热交换再液化工艺;④蓄冷式BOG再液化工艺。运用HYSYS软件建立了采用不同BOG处理工艺的LNG接收站模型,对比了目前主要采用的BOG直接压缩工艺和再冷凝液化工艺在工艺流程及能耗方面的差异,并分析了外输量、外输压力及再冷凝器压力对BOG处理工艺节能效果的影响,在此基础上提出了BOG再冷凝液化工艺的改进措施——BOG进入再冷凝器前进行预冷,可比原工艺节约18.2%的能耗。同时还针对青岛LNG接收站提出了BOG再冷凝液化及直接压缩工艺混合使用的优化运行方案,可使进入再冷凝器的LNG流量保持恒定,没被冷凝的BOG经过高压压缩机提压到外输压力,与完成气化的LNG混合后外输,可避免BOG进入火炬系统而造成的能源浪费,同时减小再冷凝器入口流量的波动,使装置运行更稳定、更经济。