Synthesis of Large-scale Multistream Heat Exchanger Networks Based on Stream Pseudo Temperature

Effective temperature level of stream, namely stream pseudo temperature, is determined by its actual temperature and heat transfer temperature difference contribution value. Heat transfer temperature difference con-tribution value of a stream depends on its heat transfer film coefficient, cost per unit heat transfer area, actual tem-perature, and so on. In the determination of the suitable heat transfer temperature difference contribution values of the stream, the total annual cost of multistream heat exchanger network (MSHEN) is regarded as an objective func-tion, and genetic/simulated annealing algorithm (GA/SA) is adopted for optimizing the heat transfer temperature difference contribution values of the stream. The stream pseudo temperatures are subsequently obtained. On the ba-sis of stream pseudo temperature, optimized MSHEN can be attained by the temperature-enthalpy (T-H) diagram method. This approach is characterized with fewer decision variables and higher feasibility of solutions. The calcu-lation efficiency of GA/SA can be remarkably enhanced by this approach and more probability is shown in search-ing the global optimum solution. Hence this approach is presented for solving industrial-sized MSHEN which is difficult to deal by traditional algorithm. Moreover, in the optimization of stream heat transfer temperature differ-ence contribution values, the effects of the stream temperature, the heat transfer film coefficient, and the construc-tion material of heat exchangers are considered, therefore this approach can be used to optimize and design heat exchanger network (HEN) with unequal heat transfer film coefficients and different of construction materials. The performance of the proposed approach has been demonstrated with three examples and the obtained solutions are compared with those available in literatures. The results show that the large-scale MSHEN synthesis problems can be solved to obtain good solutions with the modest computational effort.

Performance Evaluation Methods for Multi-stream Plate-Fin Heat Exchanger

Mathematical model of cross type multi-stream plate-fin heat exchanger is established.Meanwhile,mean square error of accumulative heat load is normalized by dimensionless,and the equations of temperature-difference uniformity factor are improved.Evaluation factors above and performance of heat exchanger are compared and analyzed by taking aircraft three-stream condenser as an example.The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages.So it can be influenced by passage arrangement,flow inlet parameters as well as flow patterns.Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns.Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns.It remains basically unchanged under a certain range of flow inlet parameters.

Theoretical analysis of a method for segmented heat exchanger design

In the process of the design of heat exchangers,it is difficult to establish the factors governing the optimal points of the design objective functions due to the contradictions and uncertainties of the design objectives.The variation of fluid properties is one of the main factors causing this type of uncertainty.Conventional design methods have not completely solved these problems.In the present work,based on the logarithmic mean temperature difference,a new heat exchanger design method(called the segmented design method) is proposed which takes into account the variation of fluid properties with respect to the temperature.In this method,the whole heat exchanger is first divided into several segments.Then by applying the principle of the conservation of energy and taking into account the initial conditions as well as the connecting conditions of the adjacent segments,the inlet and outlet temperatures of each segment are determined.Finally,the application of the logarithmic mean temperature difference method on each segment defines the heat transfer area.

Novel Radiation-Adjustable Heating Terminal Based on Flat Heat Pipe Combined with Air Source Heat Pump

The electrification of building heating is an effective way to meet the global carbon target. As a clean and sustainable electrified heating technology, air-source heat pumps (ASHPs) are widely used in areas lacking central heating. However, as a major component of space heating, heating terminals might not fit well with ASHP in order to achieve both intermittency and comfort. Therefore, this study proposes a novel radiation-adjustable heating terminal combined with an ASHP to achieve electrification, intermittency, and better thermal comfort. Radiant terminals currently suffer from three major problems: limited maximum heating capacity, inability to freely adapt, and difficulty with combining them with ASHPs. These problems were solved by improving the structural design of the novel terminal (Improvement A–E). Results showed that the maximum heating capacity increased by 23.6% and radiation heat transfer ratio from 10.1% to 30.9% was provided for users with the novel terminal. Further, new flat heat pipe (FHP) design improved stability (compressor oil return), intermittency (refrigerant thermal inertia), and safety (refrigerant leakage risk) by reducing the length of exposed refrigerant pipes. Furthermore, a new phased operation strategy was proposed for the novel terminal, and the adjustability of the terminal was improved. The results can be used as reference information for decarbonizing buildings by electrifying heating terminals.

Innovative Production of PCMs （Phase Change Materials） Preparation by Vacuum Impregnation： Thermal Insulation Efficiency

Energy is essential for every human activity for more comfortable life, but it also consumes more natural resources. Fossil fuel is the major energy source for energy consumption, and it also emits a lot of air pollution during usage to atmosphere and not reproductively. Electrical energy is the secondary energy sources from fossil fuel which is used to operate air conditioning system. In order to control human comfort temperature, it is usually required when the temperature differences swing between indoor and outdoor temperatures. PCMs （phase change materials） are the high latent heat materials which can be used in building materials for energy conservation purpose. PCMs can store thermal energy and prevent heat to pass through temperature control areas. Paraffin has been used as PCMs which is absorbed into the pore of fly ash as paraffin/fly-ash composite and mixed into the buildings materials. Paraffin is an organic material with high melting point （-59 ~C） and nonflammable material, therefore, it can be used as the building materials for the function of PCMs for energy saving purposes. Composite PCMs can be prepared by vacuum impregnation process. Paraffin in liquid form will be impregnated into the pore of fly ash by vacuum capillary force to form paraffin/fly ash composite PCMs. Vacuum impregnation pressures, vacuum times, impregnation times of liquid paraffin in fly ash pores and temperatures for melting the solid paraffin into the liquid form are all affect on the thermal properties of paraffin/fly ash composite PCMs. Composite PCMs will be selected by the optimum thermal properties with optimum of the production conditions for replace the cement powder in the mortar plate compositions. Cement mortar plate with and without composite PCMs will be tested for the thermal insulation properties by comparison as the real day and night time for 8 h period from spot light turn on and off. Temperature detection on the surface and inside the model building under mortar plate with and without composite PCMs is detected every 1 min. Temperature differences between surface of mortar plate over the model building and inside temperature of model building under mortar plates increase with more composite PCMs contents in mortar plates. Thermal insulation efficiency in the building can be enhanced by the composite PCMs utilization as the composition of the building materials.

土壤源热泵地埋管侧水系统优化运行研究

本文基于江苏无锡某典型厂房土壤源热泵空调项目的实测数据,以地源侧系统总能耗最低为目标,构建设备模型对地源水泵运行工况进行优化,并与两种传统控制策略的运行效果进行对比,据此提出进一步的优化建议。结果表明:基于负荷的优化控制策略,其节能效果要明显优于定频控制策略,冬夏季典型测试日平均节能率分别为28.33%和13.27%,相比于5℃温差变频策略节能了3.61%和2.21%。适当增大地埋管的埋管深度或管径,可以进一步提升该优化控制策略的节能效果。传统的定温差控制策略在负荷率大于60%时,可在5℃基础上将温差增加1~5℃以提升节能效果。

润滑油加氢装置缠绕管式换热器设计与应用

换热器是影响润滑油加氢装置安全运行的关键设备,为提高换热器长周期运行效率,对螺纹锁紧环式传统换热器与缠绕管式换热器进行了比对研究,发现缠绕管式换热器运行稳定、管程与壳程之间产生内漏的可能性极小,是一种换热效率较高的换热设备。在某公司600 kt/a润滑油加氢异构脱蜡装置改造中,通过换热参数计算,用1台缠绕管式换热器代替了3台螺纹锁紧环式换热器,运行结果表明:热端温差下降了20℃、节省燃料气0.08t/h,总压降减小了200kPa,压缩机耗电功率减小了18kw/h。改造后3年运行期间没有出现质量缺陷,可以在同类装置中推广使用。

对硫酸装置二氧化硫转化系统设计的初探

当进转化器气体中φ(SO_(2))<5.5%时,不建议采用二转二吸工艺。模拟了进转化器气体中不同的二氧化硫浓度下需采用“3+2”转化工艺的临界氧含量。对转化换热流程的选取进行了分析,指出当进转化器气体中φ(SO_(2))≤6.5%时,建议采用ⅣⅠ-ⅢⅡ换热流程,并指出了该流程的缺点。建议对含一氧化碳的二氧化硫气体进行转化计算时,考虑65%左右的一氧化碳在一段床层发生转化。提出了转化器催化剂床层进气温度选择的原则及方法,针对转化设备、管道的设计选材和转化系统散热量的选取等问题进行了探讨。

一维换热器中温差场均匀性原则的证明

The uniformity principle of temperature difference field is a phenomenological principle,which has not been theoretically proved.For one-dimensional two-and three-stream heat exchangers,the extremum principle of entransy dissipation was used to optimize the heat transfer process by variational calculus.It was indicated that the temperature difference field between the hot and cold fluids should be completely uniform if the entransy dissipation reached a minimum for a given heat duty,or if the heat duty reached a maximum for a given entransy dissipation.So,the uniformity principle of temperature difference field of heat exchangers was primarily proved.

地源热泵地埋管换热器传热研究(4):系统耦合运行特性

采取数值计算与解析计算相结合的方法,在构建地埋管换热器与地上机组耦合模型的基础上,研究了夏季变热流边界条件下单U形地埋管换热器与地上机组耦合运行的非稳态特性。分析了连续运行工况和间歇运行工况下地源热泵机组COP、单位管长换热量、埋管进出口流体温度及钻孔壁面平均温度随运行时间的变化规律。

稳定运行的土壤源热泵系统管群内外土壤温度场对比分析

基于上海某工程实例,对长时间(≥10h)稳定运行的土壤源热泵中央空调系统单U型地埋管换热器外壁土壤温度场、管群内土壤温度场、管群外土壤温度场变化进行全年测试,并对三种测试数据做了对比分析。测试结果表明:管群外浅层土壤(深度≤25m)温度一年四季变化波动比较大,且地下浅层土壤温度出现最高月份相比于地上环境出现最高温度的月份存在一定的延迟性;管群内的土壤温度会随着系统的长时间稳定运行呈现升高趋势,使地埋管换热器表面与周围土壤之间换热温差减小,导致换热效率下降。通过数据对比分析发现,对于冷负荷明显大于热负荷的建筑采用土壤源热泵系统,若长时间连续稳定运行对地埋管与土壤之间换热造成的影响夏季明显高于冬季。研究结果表明,适当增加钻孔间距、对地源热泵系统采取间歇性运行的模式对加强地埋管换热器与土壤之间的换热至关重要。

基于经济评价的换热器最优传热温差

换热器选型是化工过程设计工作的重要部分。换热器的传热温差△T设计取值,左右着一次投资与能量回收效率之间的优化权衡。其结果强烈取决于因资源有限性和制造科技进步所决定的、不断增加的能源与设备的比价。本文在运用经济学理论对换热过程的热火用损失计价和换热器投资估算方法进行深入的分析、探讨和回归的基础上,发展了换热器最优传热温差的数学模型,开发了可实用于工程设计的换热器△T计算机辅助优化计算软件。此项研究的应用实例表明,采用优化的换热器的传热温差△Topt的设计,能够取得显著的节能和经济效益。

多股流换热器设计的量纲1温差场均匀性优化因子

The concept of dimensionless temperature-difference uniformity optimization factor was proposed.The application of this factor to path arrangement was studied.The study showed that dimensionless temperature-difference uniformity optimization factor was an effective evaluation criterion of path arrangement of multi-stream heat exchangers and the design of multi-stream heat exchangers could be guided by this factor.

空气源热泵性能的实验研究

通过设计并建立空气源热泵系统实验台和系统测量设备，在不同运行工况进行了实验研究，分析了冷凝器入口水温与冷凝温度对系统换热量、制热量、压缩机状态及系统COP的影响。结果表明，蒸发器进风温度为9．3℃、冷凝器入口水温为26～45℃时，系统COP最高可达3．4。

流速及传热温差对换热器传热系数的影响

针对换热器热交换不充分的问题,研究给定结构壳管式换热器热空气流速以及传热温差对其传热系数的影响,把不同的传热温差,不同的气体流速下的实验数据进行分组,采用控制变量法,分别对以上两个因素的单独进行分析,做出k-ΔT,k-v的拟合曲线,得到经验函数。取整个换热器为研究对象,采用数值模拟的方法,运用多孔介质,k-ε模型,采用二阶迎风模式,压力速度耦合运用SIMPLE算法,给出整个换热器的温度场以及传热系数的分布规律,最终给出以上两个因素对传热系数的影响趋势。

多管程换热器网络的最小温差分析与夹点设计

在实际生产过程中,多管程换热器广泛应用,其中既存在逆流换热也存在并流换热。针对多管程换热器网络中并流换热与逆流换热时换热温差对夹点特性尤其是换热网络综合的影响,定量分析最小温差的选择与夹点特性及其总费用的关系。兼顾管程数目的选择以及换热网络总费用两方面因素,以年度化总费用最低为目标,优化求解多管程换热器网络的最小温差。然后,将求得的最小温差作为夹点温差,遵循夹点设计原则综合换热网络。同时,计算得出多管程换热器网络的FT修正因子,并对结果进行分析。最后,结合示例对比分析求解结果,证明方法的有效性。

基于有限元分析方法对换热器结构的改进设计

采用三维有限元分析方法对BEM型管壳式换热器进行强度分析 ,发现原设计不符合要求。根据正常操作工况下温度载荷高 ,液压试验工况下压力载荷高的特点 ,先提出采用减少管板厚度的方案 ,随后 ,在此基础上提出法兰与壳体连接处加筋板的设计方案。该方案通过三种工况的强度校核 ,从而可对该换热器进行合理的改进。

空调系统排风热回收换热器的试验研究

对用于回收空调系统余热的通风换热器进行了试验研究。在冬季工况下对其进行了性能测试。试验结果表明,该换热器具有换热效率高、阻力小的特点;在风速为2.6m/s的工况下,其换热效率达到64.5%。

空调冷水大温差技术工程应用分析

结合某宾馆空调系统节能改造,定性分析了大温差系统对冷水泵输送能耗、冷水机组以及末端设备换热性能的影响,发现采用冷水大温差后,尽管可以减少冷水输送量、降低水泵能耗,减少水系统初投资,但对于同一台机组,由于水流量减少,蒸发器水侧换热系数减小,机组的COP也减小。认为可以采用增加表冷器排数、增大传热面积、改变表冷器管程数等办法来保证大温差机组的运行性能,以使冷水大温差技术在宾馆项目改造中节能效果最大化。

小压差大温降工艺在榆林气田的应用

直接节流膨胀制冷工艺是轻烃回收用低温分离方法中最常见的一种,要求天然气必须有较大的可利用压能和压差。为了在低压气田、气井上应用直接节流膨胀制冷工艺,首先采用动态模拟方法分析了小压差产生大温降的原理,采用节流阀小压差节流制冷、大面积换热预冷,换热与节流所形成的温差差距相互推动,最终能形成稳定的低温,从而获得大的温度降。小压差大温降工艺在长庆榆林气田上古生界气藏得到了应用并获得良好效果,为低压气田采用直接膨胀制冷工艺实施轻烃回收提供了现场试验依据。