Minimizing investment cost for multi-period heat exchanger network retrofit by matching heat transfer areas with different strategies

Multi-period heat exchanger network(HEN) retrofit is usually performed by targeting and matching heat transfer areas. In this paper, based on the reverse order matching method we proposed previously, three strategies of matching heat transfer areas are proposed to minimize the investment cost for the retrofit of HEN in multiperiod, in which replacement of heat exchangers, addition of heat exchangers and addition of heat transfer areas are performed. We demonstrate the procedures through three scenarios, including maximum number of substituted heat exchangers after retrofit, minimum additional heat transfer areas in the retrofitted HEN, and minimum investment cost for retrofit. The strategies are extended to a single period HEN retrofit problem. The results of multi-period and single period HEN retro fit problems indicate the effectiveness of the strategies. Moreover, these results are better than those reported in literature. The strategies are simple and easy to implement,which are of great benefit to large-scale HEN retrofit in practice.

Measurement of temperature inside die and estimation of interfacial heat transfer coefficient in squeeze casting

As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.

The Research of Heat Transfer Area for 55/19 Steam Generator

A calculation method of heat transfer area for vertical natural circulated steam generator was introduced. According to the design requirements of steam generator 55/19 of CPR1000, its heat transfer area was calculated based on this method. The results show that the accuracy of partitional and overall calculation method is almost the same, but the result is different when using different calculation models. And the results are compared with the foreign companies for 55/19 steam generator.

Performance of Thermal Energy Storage Unit Using Solid Ammoniated Salt (CaCl₂-NH₃System)

The exothermic chemical reaction of CaCl2 (calcium chloride) with NH3 (ammonia) can be utilized as an energy storage system. Since this reaction is a typical gas-solid reaction, the reaction rate is controlled by the heat transfer rate. In order to improve the low heat transfer rate of the ammoniation and the deammoniation of CaCl2, the influence of a heat transfer media (Ti: titanium) on the heat transfer rate of the solid ammoniated salt (CaCl2&#46mNH3) was studied and tested experimentally. The performance tests were carried out under the conditions of various weight ratios of Ti. No decrease of the activation of chemical reaction and no corrosion of experimental apparatus were observed on the repeated runs (≥30 times each). The heat transfer rate of ammoniated salt was greatly improved by adding Ti under the constant pressure (0.5 MPa). The reaction time required for the ammoniation of CaCl2 mixed with Ti was approximately 16% - 54% shorter than that of CaCl2 alone, and the reaction time required for the deammoniation was also approximately 19% - 59% shorter than that of CaCl2 alone.

An Efficient Acceleration of Solving Heat and Mass Transfer Equations with the Second Kind Boundary Conditions in Capillary Porous Composite Cylinder Using Programmable Graphics Hardware

With the recent developments in computing technology, increased efforts have gone into simulation of various scientific methods and phenomenon in engineering fields. One such case is the simulation of heat and mass transfer in capillary porous media, which is becoming more and more important in analysing various scenarios in engineering applications. Analysing such heat and mass transfer phenomenon in a given environment requires us to simulate it. This entails simulation of coupled heat mass transfer equations. However, this process of numerical solution of heat and mass transfer equations is very much time consuming. Therefore, this paper aims at utilizing one of the acceleration techniques developed in the graphics community that exploits a graphics processing unit (GPU) which is applied to the numerical solutions of heat and mass transfer equations. The nVidia Compute Unified Device Architecture (CUDA) programming model caters a good method of applying parallel computing to program the graphical processing unit. This paper shows a good improvement in the performance while solving the heat and mass transfer equations for capillary porous composite cylinder with the second kind of boundary conditions numerically running on GPU. This heat and mass transfer simulation is implemented using CUDA platform on nVidia Quadro FX 4800 graphics card. Our experimental results depict the drastic performance improvement when GPU is used to perform heat and mass transfer simulation. GPU can significantly accelerate the performance with a maximum observed speedup of more than 7-fold times. Therefore, the GPU is a good approach to accelerate the heat and mass transfer simulation.

An Efficient Acceleration of Solving Heat and Mass Transfer Equations with the First Kind Boundary Conditions in Capillary Porous Radially Composite Cylinder Using Programmable Graphics Hardware

With the latest advances in computing technology, a huge amount of efforts have gone into simulation of a range of scientific phenomena in engineering fields. One such case is the simulation of heat and mass transfer in capillary porous media, which is becoming more and more necessary in analyzing a number of eventualities in science and engineering applications. However, this procedure of numerical solution of heat and mass transfer equations for capillary porous media is very time consuming. Therefore, this paper pursuit is at making use of one of the acceleration methods developed in the graphics community that exploits a graphical processing unit (GPU), which is applied to the numerical solutions of such heat and mass transfer equations. The nVidia Compute Unified Device Architecture (CUDA) programming model offers a correct approach of applying parallel computing to applications with graphical processing unit. This paper suggests a true improvement in the performance while solving the heat and mass transfer equations for capillary porous radially composite cylinder with the first type of boundary conditions. This heat and mass transfer simulation is carried out through the usage of CUDA platform on nVidia Quadro FX 4800 graphics card. Our experimental outcomes exhibit the drastic overall performance enhancement when GPU is used to illustrate heat and mass transfer simulation. GPU can considerably accelerate the performance with a maximum found speedup of more than 5-fold times. Therefore, the GPU is a good strategy to accelerate the heat and mass transfer simulation in porous media.

三套管式加肋相变蓄热单元的强化传热特性

相变蓄热技术在利用工业余热、太阳能等解决热能与用户之间的供需不平衡问题方面起着重要的作用,然而受相变材料自身物性的限制,蓄热熔化时仍存在蓄热速度低、熔化不均匀等问题。本文以三套管式相变蓄热单元为基本结构,利用FLUENT软件模拟研究了在考虑自然对流情况下添加纵向肋片的不同参数(肋片数量、长度、厚度、偏心距及肋片排布方式)对三套管式相变蓄热单元蓄热性能的影响。结果表明,三套管式蓄热单元内外双壁面共同加热,与普通套管式蓄热单元相比,换热面积增大,相变材料全部熔化需要的时间缩短;加装纵向直肋片的三套管蓄热单元的熔化速度进一步加快,相同数量肋片下,肋片的长度和厚度是影响蓄热单元蓄热量与平均蓄热速率的主要因素,肋片长度占相变材料区域径向长度的50%时,蓄热单元的熔化速度加快幅度明显且蓄热量与平均蓄热速率较高。通过优化设计,发现内管向下偏移距离e对相变材料的熔化过程作用显著,偏心距离较短时相变材料完全熔化所需时间最少,相比光滑管蓄热单元,相变材料的熔化速率提升了48.5%,偏移距离过长则会延长蓄热时间;通过加密蓄热单元底部外层肋片的排布,蓄热单元的熔化进程有不同程度的加快,总体蓄热速率较原肋片结构有所提高。

热作用下花岗岩能量演变的尺度分析

【目的】为了定量探究岩石受热作用损伤的过程。【方法】从能量角度出发,通过冷却法研究实验室尺度下不同尺寸类型花岗岩试件在空气中冷却时热物理参数演变规律,讨论花岗岩受非稳态传热全过程能量吸收、能量释放及能量耗散特性,揭示非稳态过程中能量演变规律与花岗岩试件尺寸特征的内在联系。【结果】结果表明:不同尺寸类型高温花岗岩试件空冷至室温的过程中,比热持续降低;非稳态传热能量演变过程中,同一种尺寸试件耗散能与耗散比的大小与初始高温状态呈正相关;花岗岩在非稳态传热条件一致的情况下,随试件体积的增大,用于损伤的这部分能量绝对值在增加但相对值在减小;随着试件比面的增大,用于损伤的这部分能量绝对值在减小但相对值在增大。研究结果能够丰富高温岩石力学理论研究的发展。

基于圆台波浪形换热管的潜热储热单元性能分析

为提高潜热储热单元(latent heat storage unit,LHSU)的储热性能,提出了三种优化换热管结构的新型LHSU,分别为圆台形换热管潜热储热单元、波浪形换热管潜热储热单元和圆台波浪形换热管潜热储热单元(frustum wavy heat transfer tube latent heat storage unit,FW-LHSU)。基于数值模拟方法,比较了传统圆柱形换热管潜热储热单元(cylindrical heat transfer tube latent heat storage unit,C-LHSU)和三种新型LHSU的储热性能。此外,针对FW-LHSU研究了换热管壁面倾斜角度对储热性能的影响。结果发现,所提出的三种新型换热管结构均能增强储热性能,其中FW-LHSU储热效果最好,与C-LHSU相比,FW-LHSU的熔化时间缩短了32.64%,储热速率密度提高了48.1%。当增加FW-LHSU的换热管壁面倾斜角度时,其储热性能可进一步提高。当换热管倾斜角度从2°增加到8°时,FW-LHSU的储热时间可缩短37.00%、储热速率密度可提高48.44%。

基于热传递减法集对势的区域水资源承载力评价

为有效评估区域水资源承载力系统演变特征并诊断脆弱性影响因素,引入物理学热传递思想,在集对分析传统减法集对势基础上进一步深化确定性项和不确定项之间的势差概念,构建了基于热传递减法集对势的区域水资源承载力评价方法,并应用于安徽省江淮丘陵区。结果表明:2011—2018年安徽省江淮丘陵区除合肥市外,其余地市水资源承载力水平整体有所改善,合肥市水资源承载力等级较低;人均水资源量、产水模数、生态用水率等因素是影响安徽省江淮丘陵区水资源承载力变化的重要脆弱性因素。整体而言,本文计算分析结果与传统减法集对势及半偏减法集对势计算结果基本一致,这表明构建的基于热传递减法集对势的水资源承载力评价方法计算结果合理有效,且丰富和发展了集对势的内涵,可为开展区域水资源承载力评价及脆弱性因素识别提供新的研究途径。

基于中低温相变材料的管壳式储热单元传热性能数值分析

针对管壳式相变储热单元换热效率低的问题,设计一种带有径向矩形翅片的复合盐管壳式相变储热单元,进行数值模拟并与实验研究对比验证,然后选择适当的性能指标分析模拟结果。采用ANSYS FLUENT进行三维瞬态仿真,改变换热流体入口温度及储热单元翅片间距进行储热过程的数值计算,对相变材料温度变化、传热过程及熔化情况进行对比分析。结果表明:提高换热流体温度和缩小翅片间距是有效强化换热的手段。在本工作中,换热流体与相变材料复合盐CH_(3)COONa·3H_(2)O-KCl相变温差每增加5℃,相变材料熔化速率分别提升54.98%、 34.67%、 23.92%、 18.13%、 14.45%,潜热储热速率分别提升61.56%、 45.79%、 35.15%、27.04%、22.31%,速率提升效果均逐渐减弱。翅片间距每缩短10 mm,相变材料熔化速率分别提升32.37%、41.26%、38.66%,储热量随之减少6.40%、11.95%、6.55%,储能密度降低0.53%、10.97%、1.57%,实际应用中需综合换热能力、成本等方面问题选择合适的翅片间距。本工作可为实际工程中储热单元的设计优化提供理论支持。

夏热冬冷地区动态传热保温设计室外典型气象参数确定方法

GB50176-2016《民用建筑热工设计规范》中围护结构外墙保温设计采用稳态方法,但夏热冬冷地区由于特有的建筑运行模式,使外墙传热方向发生逆转,故稳态方法难以满足冬季室内热环境水平提升的实际需求。提出一种基于动态传热的冬季外墙保温设计室外计算温度确定方法,探究室外干球温度和太阳辐射逐时波动的最不利组合,将保温设计的目标由“日”提升到“时”。基于典型城市2007-2017年逐时气象数据,以外墙内表面温度的累计不保证天数作为热工设计指标,将累计不保证天数恰好不为0(指各朝向外墙内表面温度低于室内基本热舒适条件下所能允许温差的天数)时作为典型日挑选的依据,并将典型日出现频率最高的日期作为室外计算温度选取的依据,获得冬季保温设计典型日,并获得了典型日计算时长的影响。可为夏热冬冷地区围护结构外墙保温设计室外计算参数的挑选提供理论支撑。

卧式套管潜热蓄热单元偏心与肋片结构优化模拟

利用偏心布置增强相变蓄热单元内部自然对流是提高相变蓄热系统性能的新思路,为了更深入地研究偏心布置对相变蓄热系统性能的影响,基于焓-孔隙率法建立了卧式套管相变蓄热单元的三维数学模型,并利用Fluent软件对环形空间相变材料熔化过程进行数值模拟,通过对熔化过程流场、液相率及温度云图的分析,将熔化过程划分为三个阶段:导热主导的初始阶段,随后是自然对流和导热的混合作用的阶段,以及导热再次占主导地位的最终阶段,并将相变材料环形空间划分为两个区域,据此提出新的评价参数“偏心面积比”。结果表明:硬脂酸作为相变材料时较佳的偏心面积比位于16∶1附近,熔化时间相对于同心布置缩短了45.8%,但同时会使蓄热单元㶲效率略有降低,并且预测对于其他材料,预期的最佳偏心面积比与使用材料的自然对流强度和导热能力之间的比值有直接相关。利用偏心结构与肋片结合的方法进一步强化传热,比较了螺旋肋、十字肋和X形肋三种肋片,发现X形肋具有较佳性能,与相应偏心无肋结构相比熔化时间缩短了36.7%,比螺旋肋和十字肋结构分别缩短了20.3%和7.1%。

烧结冷却烟气低温余热ORC系统建模与热经济性能

本文以烧结冷却烟气低温余热为有机朗肯循环(organic Rankine cycle,ORC)系统热源,建立超临界ORC系统热力和经济模型,并选取R134a为ORC工质,研究变温热源下膨胀机的进口温度和压力,以及工质冷凝温度对系统热经济性能的影响。研究结果表明:系统净输出功随膨胀机进口温度的增加而增加,随膨胀机进口压力和工质冷凝温度的增加而减小,但系统单位温度的传热量随之均减小。当系统热力参数一定时,热源进口温度越大,系统净输出功和单位温度的传热量越大。在实际操作过程中,存在适宜的热源进口温度和系统热力参数使得ORC系统获得较大的净输出功和较小的单位温度传热量。

气侧均流装置对冷却三角单元流动传热特性影响的实验研究

对于间接空冷系统冷端基本传热元件−冷却三角单元,通过在其加装及相邻未加装气侧均流装置冷却三角单元内的两侧冷却柱沿散热管束横向布置风速、风温、壁温测点,进一步在左右两侧出水柱布置壁温测点,对比分析两侧冷却柱沿散热管束横向迎风风速、风温、壁温及出水壁温的变化规律,研究气侧均流装置对冷却三角单元流动传热特性及出水壁温分布的影响机制。研究结果表明:加装气侧均流装置后冷却三角单元两侧冷却柱沿散热管束横向迎风风温、壁温分布更加均匀,两侧出水柱壁温均值更低,且降低了两侧出水柱壁温差,气侧均流装置优化了两侧冷却柱的换热均匀性。

关中地区中深层地埋管换热器长期运行性能研究

我国关中地区地热资源丰富,中深层地热能供暖技术具有广阔的应用前景,而地质参数是影响中深层地埋管供暖系统性能的决定性因素。针对陕西关中地区中深层地埋管供暖性能展开研究,通过梳理关中地区咸阳市兴平市、咸阳市渭城区、西安市高陵区、西安市鄠邑区、西安市长安区5个典型区域的地质参数,结合典型地埋管结构参数,对长期运行下的换热器性能及热作用半径变化规律进行模拟计算。结果表明,不同地区换热器运行之初的性能变化较为显著,但均在经过5 a左右运行后趋于稳定。地埋管深度从2000 m增至2500 m时,出口水温有着明显的提升,同一时刻下出口水温的涨幅可达8%,各采暖季末的出口水温随深度增加的变化更为显著。由于长期运行,年平均取热功率呈现下降趋势,20 a内的总降幅为11%~12%;随着换热器埋深的增加,取热功率涨幅可达41.41%~53.23%。热作用半径受埋深的影响不显著,不同埋深管道运行20 a后的井底最大热作用半径均在50 m左右;土壤温度受与换热器距离及运行时长的影响更大,距离20 m以内的土壤温度呈现明显的波动下降趋势,而距离在60 m以外的土壤温度在20 a的运行期内降幅很小。此外,由于具有大厚度新近系张家坡组(N2z)和新近系蓝田-灞河组(N2l+b)的地质条件,西安市鄠邑区、高陵区以及咸阳市兴平市等地区地埋管的出口水温、取热功率较高,更适宜开展中深层地热能供暖利用。研究成果有望为关中地区中深层地热能高效利用提供参考。

叉排微通道换热器的换热性能

[目的]探究叉排微通道换热器在船用燃气轮机间冷过程中的实验换热性能及其影响因素.[方法]针对增材制造加工的叉排微通道换热器,在低流动工况条件下进行对流换热实验,从结构和流动因素研究叉排微通道换热器的换热性能.[结果]通道宽度减小0.50 mm使叉排换热器换热性能增强106.9%~61.9%;通道数增加1.6倍导致同流量下换热性能平均降低21.9%~50.8%,而同流速下换热性能平均降低11.6%;进口流量增加6.3倍,换热器换热性能提升44.0%;但换热性能受热侧空气进口温度的影响较小,相邻工况条件计算值变化最大仅为5.4%.[结论]工艺条件允许下减小通道尺寸可提升叉排微通道换热器性能,而增加通道数量则会带来负面影响;冷侧水进口流量增大能提升叉排微通道换热器换热量,从而增强换热性能;热侧空气进口温度的影响则较为复杂.

空气源分体式热管-热泵供暖系统在煤矿井口防冻中的特性研究

为提高空气源热泵的性能,同时更好地满足煤矿井口防冻特殊工艺要求,将空气源热泵与热管技术相耦合,使用小压比热泵机组搭建了空气源分体式热管-热泵供暖系统实验平台。该耦合系统中蒸发器和冷凝器两端均采用相变传热的方式,并对其进行不同运行工况下的性能特性研究,结果表明:该耦合供暖系统即使在0℃左右的室外条件下,耦合机组的系统制热性能仍可达到4.5以上,远远优于传统空气源热泵机组。

寒冷地区外窗热工性能对建筑采暖空调负荷的影响

【目的】通过研究外窗热工性能对建筑采暖空调负荷的影响,得出各项外窗热工性能参数对建筑节能效果的影响程度,有助于提升建筑的节能效果。【方法】利用DeST-h,建立寒冷地区(郑州)75%节能标准居住建筑基本模型,以太阳得热系数、窗墙比、外窗传热系数为变量进行单因素影响计算,以窗墙比和太阳得热系数、建筑层数和太阳得热系数为变量进行多因素分析,研究太阳得热系数、窗墙比、外窗传热系数对建筑采暖空调负荷的影响。【结果】结果表明,窗墙比、传热系数对建筑采暖空调负荷影响趋势明显,均呈正相关;太阳得热系数对建筑采暖空调负荷影响趋势与建筑窗墙比、建筑层数有关。【结论】建筑外窗节能应优先考虑窗墙比、传热系数,同时在确定当地太阳得热系数时应兼顾窗墙比和建筑层数,以满足更高的节能标准。

溴化锂吸收式冷水机组吸收器传热管腐蚀特性研究

本文采用挂样试验的方式,通过模拟溴化锂吸收式冷水机组吸收器与发生器中溴化锂溶液浓度45%与61%条件下,氧含量分别为0.5%、1%、5%、10%、20%、30%时对B30传热管的腐蚀情况,研究了B30传热管的有氧腐蚀特性,分析了溴化锂溶液浓度与氧含量的腐蚀影响因素与机理,结果表明当溴化锂溶液浓度为45%时,只要氧含量高于5%,B30传热管就会出现麻点状腐蚀,氧含量高于20%,B30传热管明显点蚀,深度达到0.5mm;当溴化锂溶液浓度为61%时,只有当氧含量达到30%,B30传热管才会出现明显的腐蚀麻坑。