Simultaneous synthesis of sub and above-ambient heat exchanger networks including expansion process based on an enhanced superstructure model

Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work.A stream that expands through expanders can produce work and cold load,while expansion through valves barely affects heat integration.In addition,expansion through expanders at higher temperature produces more work,but consumes more hot utility.Therefore,there is a need to weigh work production and heat consumption.To this end,an enhanced stage-wise superstructure is proposed that involves synchronous optimization of expander/valve placement and heat integration for each pressure-change sub-stream in stages.A mixed-integer nonlinear programming(MINLP)model is established for synthesizing sub and aboveambient heat exchanger networks with multi-stream expansion,which explicitly considers the optimized selection of end-heaters and end-coolers to adjust temperature requirement.Our proposed method can commendably achieve the optimal selection of expanders and valves in a bid for minimizing exergy consumption and total annual cost.Four example studies are conducted with two distinct objective function(minimization of exergy consumption and total annual cost,respectively)to illustrate the feasibility and efficacy of the proposed method.

Corrosion risk analysis of tube-and-shell heat exchangers and design of outlet temperature control system

This study deals with the high-risk shell-and-tube heat exchangers in the effluent system of hydrogenation reaction of the petrochemical industry.The process of hydroprocessing reactor effluent system is simulated in Aspen Plus to study the distribution of corrosive medium in the three phases of oil,gas and water.The least-squares method is utilized to calculate the ammonium salt crystallization temperature.Then,the heat exchanger with risk of ammonium salt crystal corrosion is identified.Dynamic mathematical modeling of the heat exchanger is established to determine the transfer function.A temperature control system with proportional integral derivative(PID)control of the heat exchanger outlet is designed,and fuzzy logic is used to implement self-tuning of PID parameters.After MATLAB simulation,the results show the control system can achieve rapid control of the heat exchanger outlet temperature.

Heat transfer analysis and experimental verification of cast heat exchanger

From the viewpoints of environmental conservation and energy efficiency,seawater-source heat pump system(SWHP) to provide district cooling and heating is applied in coastal areas.Based on the system,a heat transfer model was established for cast heat exchanger(CHE) adopted by SWHP systems.The CHE consists of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of SWHP system.An experimental study was carried out to test the validity of the model.A program was developed in VB language and the effects of inlet temperature,flow rate of the secondary refrigerant and length of CHE on the results were investigated.The results of the numerical simulation are in consistence with the experiments in both winter and summer conditions.As a result,application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment.

Devise of a W serpentine shape tube heat exchanger in a hard chromium electroplating process

In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath.Normally, a conventional U shape heat exchanger is installed in the bath, but it provides low heat removal.Thus, this study designs a novel W serpentine shape heat exchanger with identical heat transfer area to the conventional one for increasing heat removal performance.The performance of the heat exchange is tested with various flow velocities in a cross-section in range of 1.6 to 2.4 m·s^(-1).Mathematical models of this process have been formulated in order to simulate and evaluate the heat exchanger performance.The results show that the developed models give a good prediction of the plating solution and cooling water temperature, and the novel heat exchanger provides better results at any flow velocity.In addition, the W serpentine shape heat exchanger has been implemented in a real hard chromium electroplating plant.Actual data collected have shown that the new design gives higher heat removal performance compared with the U shape heat exchanger with identical heat transfer area; it removes more heat out of the process than the conventional one of about 23%.

Mathematical Simulation of Dynamic Heat Transfer in a Human-Clothing-Environment System

A mathematical model has been developed to describe the dynamic heat transfer in the clothing microclimate under transient wear conditions. This model is solved numerically by the implicit finite difference method. If the physical activity and ambient conditions are specified, the model can predict the thermoregulatory response of the body. Experimental measurements with garments made of fibers with different levels of hygroscopicity are compared with predictions by the model. There is good agreement between prediction and experiment for the temperature of the clothing microclimate.

Modelling plant canopy effects on water-heat exchange in the freezingthawing processes of active layer on the Qinghai-Tibet Plateau

The effect of vegetation on the water-heat exchange in the freezing-thawing processes of active layer is one of the key issues in the study of land surface processes and in predicting the response of alpine ecosystems to climate change in permafrost regions. In this study, we used the simultaneous heat and water model to investigate the effects of plant canopy on surface and subsurface hydrothermal dynamics in the Fenghuoshan area of the QinghaiTibet Plateau by changing the leaf area index(LAI) and keeping other variables constant. Results showed that the sensible heat, latent heat and net radiation are increased with an increase in the LAI. However, the ground heat flux decreased with an increasing LAI. The annual total evapotranspiration and vegetation transpiration ranged from-16% to 9% and-100% to 15%, respectively, in response to extremes of doubled and zero LAI, respectively. There was a negative feedback between vegetation and the volumetric unfrozen water content at 0.2 m through changing evapotranspiration. The simulation results of soil temperature and moisture suggest that better vegetation conditions are conducive to maintaining the thermal stability of the underlying permafrost, and the advanced initial thawing time and increasing thawing rate of soil ice with the increase in the LAI may have a great influence on the timing and magnitude of supra-permafrost groundwater. This study quantifies the impact of vegetation change on surface and subsurface hydrothermal processes and provides a basic understanding for evaluating the impact of vegetation degradation on the water-heat exchange in permafrost regions under climate change.

具有防融霜装置的蒸发器结霜特性及性能仿真研究

以具有防融霜装置的蒸发器为研究对象,建立基于理想最小防融霜补热量和结霜量无量纲关联式的空气源热泵动态模型,并依据实验数据验证其精确性,通过数值模拟分析不同环境参数对具有防融霜装置的蒸发器性能的影响。结果表明:后置式与跨越式系统蒸发器换热系数要高于前置式与传统电辅热系统,霜层厚度更小,分布更均匀;当相对湿度一定时,蒸发器换热系数随温度升高而增大;当空气温度不变时,换热系数随相对湿度的下降而减小,霜层更均匀;温度对蒸发器换热系数的影响比相对湿度更大。

大功率质子交换膜燃料电池建模及仿真

针对70 kW大功率燃料电池系统进行建模,基于Simulink平台搭建质子交换膜燃料电池电堆系统模型。基于该模型在稳态下研究温度、膜含水量、压力对电池输出性能的影响,分析水气跨膜运输情况。仿真结果表明电流密度在0.4~1.0 A/cm范围内时,电堆输出电压保持稳定。然后在新欧洲驾驶循环(NEDC)动态工况下,分析电池系统输出性能和水气跨膜传输情况,结果表明所建模型可用于大功率车用PEMFC研究。

板翅式换热器传递函数动态模型及参数确定方法

飞机综合环控/热管理系统迫切需要建立快捷高效的换热器动态仿真模型,以满足先进控制系统设计需求。基于此,针对板翅式换热器动态模型,提出一种包含2个延迟环节和4个一阶惯性环节的传递函数矩阵形式,并从换热器机理模型出发,利用拉普拉斯变换推导模型中4个时间常数的计算公式,提出基于换热器效率的传热热阻计算关系式的辨识方法,解决了主要模型参数设置难题。以板翅式换热器为研究对象,在Simulink仿真平台搭建其传递函数动态模型,并与AMESim仿真平台搭建的机理模型进行对比分析,结果显示:2种模型所得空气和冷却水出口温度分别随入口温度和质量流量阶跃变化的动态响应曲线吻合很好,其中,4种工况空气和冷却水出口温度最大稳态偏差分别为0.034℃和0.029℃,当冷却水入口质量流量阶跃变化时,空气出口温度动态响应相对偏差最大,为9.27%,当空气入口质量流量阶跃变化时,冷却水出口温度动态响应相对偏差最大,为7.03%。

煤矿井下钻机用数字比例阀静动态特性研究

针对数字比例阀在煤矿井下钻机电液系统应用中特性开发不足的问题,从数字比例阀的原理出发,构建其数学模型,阐述先导级和主阀之间的耦合关系,发现先导流量是决定主阀静动态特性的关键指标。研究建立了数字比例阀的AMESim模型,仿真结果表明,控制数字比例阀的PWM信号频率为20 Hz时,占空比对流量的线性调控范围为0.2~0.8,主阀输出流量波动幅值为3.16 L/min,数字比例阀静动态特性表现良好。调整好PWM信号频率后将数字比例阀运用于钻机给进回路中,经过测试试验,数字比例阀控给进回路的钻机位移误差较传统阀控回路由2.8%提升至1.9%。

基于多场耦合的无线电侦扰一体主机散热特性分析

针对无线电侦扰一体主机因高度集成引起的高热流密度导致散热难的问题,通过分析整机的散热路径,构建传热网络图;应用传热学和流体力学理论,建立主机热−流−固耦合散热数学模型;基于ANSYS Icepak仿真平台,构建主机的三维全尺寸数值模型研究其散热特性。结果表明:当风扇风量约为56 m^(3)/h时,无线电侦扰一体主机的散热性能较好且噪声较小;当电源箱的热源同侧分布,侦扰箱和导航诱骗箱的热源异侧分布,且热源靠近进风口或出风口时,主机的散热性能好且效率高;当支架孔隙和设备间距分别为15 mm和10 mm时,主机的散热性能较好且结构强度高,同时主机质量和体积均较小;当散热器翅片的高度、厚度和间距分别为7.5 mm、1 mm和5 mm时,强化散热效果较好且主机质量小。

计及区域建筑群生长特性的动态冷热负荷预测

考虑区域建筑群的动态生长特性,结合负荷计算理论、灰色Verhulst模型及等维新息灰色理论,采用MATLAB构建完整的区域动态冷热负荷预测方法,以常州高铁新城2017—2022年的建筑面积为历史数据,对区域未来10年的冷热负荷进行预测.结果表明,采用基于等维新息灰色理论的Verhulst灰色模型建立的3种业态面积预测方程拟合精度均达到一级.高铁新城未来10年冷热负荷先快速增长后缓慢增长直至饱和,达到饱和的时间约为2030年,冷、热负荷饱和规模分别为436、228 MW,与采用面积指标法的计算结果(冷负荷为472 MW、热负荷为285 MW)相比,分别降低了约7.52%、19.86%.

热电联产机组与热网的耦合特性分析与仿真

为研究热电联产机组与供热管网之间存在的耦合特性,建立了330 MW抽汽式热电联产机组的精确模型,以及5路并联的多级供热管网和热用户的模型。采用控制输入扰动仿真,分析了机组模型结构特点和动态特性;通过传统炉跟机协调控制与供热测PID控制,分析了热电联产机组和供热管网之间的瞬态特性。仿真结果表明,供热管网中存在较强的热惯性,调节热负荷能够快速改变发电负荷的动态响应,说明利用热网的热惯性可以提高热电联产机组的调频调峰能力。

BHDB-M701F4-Q1余热锅炉动态建模与仿真

文章给出BHDB-M701F4-Q1型号的三压再热自然循环余热锅炉的动态数学模型,使用MATLAB仿真软件,以该余热锅炉为对象进行模块化建模,对给水流量扰动和烟气流量扰动下的动态响应模型进行仿真。仿真结果表明,建立的数学模型能够正确反映对象的动态特性,有较好的动态响应特性,可为联合循环机组中余热锅炉结构和控制系统的设计提供理论依据。

Simulation on Dynamic Characteristic of Negative Resistance Arc in Pulsed TIG Welding

A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the mathematical model is run in MATLAB environment, and the discussion is focused on the way the peak current ranging from 29 A to 50 A and the time constant of arc in the span of 0.003—0.006 s influence the simulating results and the dynamic characteristic. The simulating data are close to that of welding experiments and correspond to the theoretical conclusion.

塔式太阳能光热发电系统蒸发器动态特性研究

以Solar Two塔式熔盐光热电站中蒸汽发生器为研究对象,基于质量守恒和能量守恒搭建了蒸发器动态数学模型。以动态数学模型为基础,通过水侧和熔盐侧扰动实验对蒸发器的动态特性进行分析,得到了蒸发器的出口参数响应曲线和时间常数。结果表明:发生扰动后蒸汽发生器需要205 s达到新的平衡,而由于蒸汽侧热容量较大的影响,参数对扰动响应较慢,蒸汽的品质会影响机组的安全性及经济性;与熔盐相比,水和蒸汽具有更高的比容和储液量,水侧参数响应较慢,而熔盐侧响应速度较快。

Simulation of Gas-Liquid Mixture Movement through a Pipeline on the Seabed, Taking into Account the Heat Exchange Process

In the paper, a dynamical model of gas-liquid mixture motion through a pipeline with regard to change of rheological properties that occur as a result of heat-exchange process, is constructed, and the solutions of the obtained connected differential equations are given. Analytic expression allowing to determine pressure change along the length of a pipeline, is obtained.

墙体抗震试验台泵控缸恒力加载控制方法研究

墙体抗震耐久性加载试验台需施加恒定纵向载荷,根据试验台技术要求,设计力恒定泵控差动缸,建立泵控缸控制系统数学及仿真模型,提出一种基于差值补偿的分段PID控制方法。结果表明:该控制方法可实现差动缸随墙体偏摆保持输出力恒定,响应时间可达0.035 s,输出力误差可控制在35 N以内,满足建筑墙体抗震试验加载标准。

基于需求侧用户响应分析的电-气-热综合能源系统低碳经济调度

在低碳经济的背景下,为充分发挥供需双侧的互动潜力,提出一种考虑综合需求响应(IDR)和碳交易的电-气-热综合能源系统(EGH-IES)双层低碳经济调度模型。首先,提出考虑多能负荷自身特性、耦合特性和反弹效应的IDR模型和用户权衡经济效益、响应方式和用能偏好的综合效益模型。基于此,建立上层模型为引入奖惩阶梯型碳交易机制的EGHIES低碳经济调度,下层模型为IDR策略的双层优化调度模型。然后,通过Karush-Kuhn-Tucker(KKT)条件、对偶定理和线性化方法将双层模型转换为混合整数线性规划问题进行求解。最后,算例分析表明,综合考虑碳交易和多元负荷特性能促进供需双侧的联合优化,充分发挥EGH-IES的经济低碳性。

动热源摆式单轴MEMS热加速度计敏感机理的研究

该文揭示了一种动热源摆式单轴微机电系统(MEMS)热加速度计的敏感机理。在给出敏感结构原理的基础上,通过建立二维物理研究模型、划分网格、加载加速度等方法对敏感结构内的温度场进行了计算。结果表明,开机1.8 s后在敏感结构内形成了一个稳定的以动热源为中心的温度场;输入加速度a时,动热源沿着加速度方向偏移,温度场随之偏移,敏感轴方向上对称设置的两个热线温差ΔT X随着输入加速度a的加大而呈线性增长,温度灵敏度为7.1×10^(-2)mK/g。根据输入-输出(a-V X OUT)特性曲线给出数学模型,得到该加速度计灵敏度为0.5 V/g,非线性度为2.8%,从而揭示了敏感机理。