Simulation and Optimization of the Fluid Solidification Process in Brazed Plate Heat Exchangers

When a brazed plate heat exchanger is used as an evaporator,the working mass in the channel may undergo soli-dification,thereby hindering the refrigeration cycle.In this study the liquid solidification process and its optimi-zation in a brazed plate heat exchanger are investigated numerically for different inlet velocities;moreover,different levels of corrugation are considered.The results indicate that solidificationfirst occurs around the con-tacts,followed by the area behind the contacts.It is also shown that deadflow zones exist in the sharp areas and such areas are prone to liquid solidification.After optimization,the solidification area attains its smallest value when a corrugation spacingλ=4.2 mm is considered.

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.

REGRESSION OF HEAT AND MOISTURE EXCHANGE DIAGRAM OF SWISS LUWA AIR WASHER

The thesis has changed the heat and moisture exchange curves of Swiss Luwa air washer into double efficiency formulas which are widely used in our country with a computer, and also worked out the regression formula of heat transfer efficiency(X). This has created favourable condition for us to use computer in our calculation of Luwa air washer.

制冷装置柔性接触式密封机构性能提升的关键技术研究进展

柔性接触式密封机构在制冷装置中起到重要的隔热隔湿作用。针对装配状态下刚-柔多体接触对其性能提升带来的技术挑战,从柔性接触式密封机构技术特点和总体发展出发,综述了影响其性能提升的测量、建模等关键性问题的研究现状,并对未来的发展趋势进行了展望。结果表明:基于反向热平衡的热传递测量技术精度不足,引入滤波算法可降低热流信号噪声波动;现有示踪气体技术未考虑湿空气在刚柔接触界面中的流动扩散,应运用界面微观检测及接触动力学理论来明确流动型式,构建匹配的示踪源和检测回路;对柔性接触式密封机构热流固耦合建模研究尚处于空白,仅建立了传热数值模型与流动平均解析方程,可采用数值计算温度、变形场与解析计算渗流参数的迭代算法来建立耦合模型。未来,除开展测量与建模的基础研究外,还需突破“尺寸效应”技术瓶颈,实现密封组件间的良好配合,应用超低导热材料和电磁感应技术,以提升密封机构的隔热隔湿作用。

混合板换热器板片结构对流道内触点分布及流动换热性能的影响

混合板式换热器作为余热利用系统中高效节能设备,其换热性能对系统效率及稳定性有重要影响。该研究基于RNG k-?湍流模型,对M型和H型板式换热器流道内流动及传热过程展开数值模拟,研究板片结构对板间触点分布的影响,及雷诺数Re和板片组合对横向流道内流动及换热特性的影响规律。结果表明:M型板间触点呈“方格”,H型呈“菱形”,且H型流流体速度较大、温度场分布较均匀。随Re数增大,压降△P及平均努塞尔数■均增大;Re数较低时,H型的■明显提高,且△P增幅较小;而高Re数(Re=6000)时,与M型相比,H型■的增幅仅为△P的25%左右。随波纹间距s减小,触点数明显增多,△P和■均增大;s为12~16 mm较合适。研究结果为混合板式换热器的设计及优化提供理论依据。

低温风洞管翅式换热器上水室排空残留水层干燥速率试验研究

为解决低温风洞内管翅式换热器自重排水后上水室残留5 mm水层在风洞低温工况下的冻结问题,在管内、管外热风温度均为40~70℃、入口风速为2.78~10.56 m/s的条件下,对椭圆管和铝扁管两种管翅式换热器自重排水后上水室残留水层进行干燥试验研究,对比分析了管内热风与管外热风干燥方法对两种换热器干燥速率的影响。结果表明:铝扁管换热器干燥速率更快,管外热风干燥方法干燥速率更快,换热器干燥时间随着入口风速的增加而缩短,入口风速10.56 m/s相比2.78 m/s,干燥时间节约50.75%。通过试验数据拟合干燥速率经验关系式,其拟合结果与试验测量值平均误差小于6.1%,对低温风洞内管翅式换热器热风干燥速率有较好的预测能力。

载有螺旋扰流装置的直触式换热器结构设计

本文探讨直触式技术在高温烟气-低温液体间换热的应用研究。所开发直触式换热器主要由立式布局的上、下锅体组成,采用喷淋为主要换热方式,重点针对气-液间直触换热过程设计螺旋扰流装置。主要结构特点:通过螺旋式扰流盘所形成的过流通道,优化烟气流动路径,增大烟气行程的同时也能起到导流换热作用;通过给水供给机构,利用产出蒸汽预热水管,提高烟气利用效率。通过理论计算完成直触式换热器结构关键尺寸和性能指标的设计,设计出载有螺旋扰流装置的换热器,此装置结构紧凑、换热效率更高、避免了雾化和液滴漂移等不足,且具有提前预热、增大烟气行程等优势,可以更好地适用于小型工业生产和满足居民日常生活所需。

Heterogeneity of Surface Heat Exchange of Slopes and Potential Drivers of the Initiation of Thaw Slump,Qinghai‑Tibet Plateau

In the mountainous permafrost area,most thaw slumps are distributed in north or northeast-facing shady slope areas.It is commonly known that there is a heterogeneity in permafrost between diferent slope aspects,but there has been a lack of detailed measured data to quantitatively evaluate their relationships,and in-depth understandings on how the slope aspects are linked to the distribution of thaw slumps.This study examined the heterogenous thermal regime,soil moisture content,and surface radiation at two slope sites with opposing aspects in a warming permafrost region on the Qinghai-Tibet Plateau(QTP).The results indicate that similar air temperatures(T_(a))were monitored on the two slopes,but there were signifcant diferences in ground temperature and moisture content in the active layer from 2016 to 2021.The sunny slope exhibited a higher mean annual ground surface temperature(T_(s)),and over the fve years the mean annual temperature at the top of permafrost was 1.3–1.4℃warmer on the sunny slope than the shady slope.On the contrary,the near-surface soil moisture content was about 10–13%lower on the sunny slope(~22–27%)than the shady slope(~35–38%)during the thawing season(June–September).Radiation data indicate that signifcantly higher shortwave downward radiation(DR)appeared at the sunny slope site.However,due to the greater surface albedo,the net radiation(Rn)was lower on the sunny slope.Slope aspect also afects the ground ice content due to its infuence on ground temperature,freeze-thaw cycles,and soil moisture.Shady slopes have a shallower burial of ice-rich permafrost compared to sunny slopes.The results highlight greatly diferent near-surface ground thermal conditions at the two slope sites with diferent aspects in a mountainous permafrost region.This helps identify the slope-related causes of increasing thaw slumps and provides a basis for predicting their future development.

某海上平台原油入罐温度高原因分析及处理措施

某海上生产平台处理油田生产出来的原油并储存至合格油罐,通过外输油轮靠泊外输方式外输原油。随着油田大泵提液及油井含水的上升,生产处理平台生产流程出现瓶颈,其中进入原油储罐的原油温度大大提升,长期高于设计的入罐操作温度,加大了平台原油储罐的运行风险。为降低原油入罐温度,平台对入罐温度高的原因进行分析并针对性的提出了一些处理措施,取得了良好的效果。

烟气循环干法熄焦与热量回收再利用技术研究

当前利用炽热焦炭冷却处理的过程需要消耗大量的水资源,且存在热能浪费的问题。为此,针对新的烟气循环干法熄焦与热量回收再利用技术展开研究。在干熄炉内令炽热红焦与循环烟气相互接触,在接触过程中令炽热红焦温度下降,当温度降至一定值后由干熄炉底部排出;在此过程中,烟气受炽热红焦温度影响,温度提升并流入干熄焦锅炉内,加热其中的水形成高压或中压蒸汽;烟气温度下降至200℃左右时,利用循环风机再次进入干熄炉内,再次与炽热红焦进行接触换热,实现烟气循环;而高温烟气所形成的蒸汽进入热量回收再利用系统内。实验结果显示,循环烟气流量一致的条件下,烟气内水汽含量越高,焦炭出口温度越低;烟气初始温度越低,焦炭出口温度越低;利用该技术回收的热量进行供热、供汽具有较好的经济效益。

全焊宽通道板式换热器在精馏装置热量耦合中的应用

宽通道板式换热器的板束间距可调,适用于燃料乙醇、制糖、造纸、氧化铝等含有大量固体、晶体、纤维、浆状物质及高粘度介质的流体换热工艺场合。传统的可拆卸宽通道板式热交换器因为密封垫片受温度、压力及介质等方面约束,应用场合很受局限。已开发的全焊接宽通道板式换热器虽在个别领域得到广泛应用,但因其管侧为焊接定位柱或压成多触点形式,不适用于双介质均为高固含量、晶体、纤维等工况推广应用。广西中粮生物能源有限公司采用的开放式定距柱焊接板对,不但具承压高的特点,而且易清洗,只需将盲板打开,即可对双侧流道进行清洗,具有广泛的推广应用前景。

Experimental Study on Latent Heat Storage Characteristics of W/O Emulsion by Ultrasonic Wave Impression

The flowable latent heat storage material like Oil/Water type emulsion, microencapsulated latent heat material-water mixture or ice slurry, etc., is enabled to transport the latent heat in a pipe. Supercooling phenomenon of the dispersed latent heat storage material in continuous phase is obstructed by a latent heat storage. The latent heat storage rates of dispersed waterdrops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The waterdrops in emulsion have the diameter within 3 - 25 μm, the averaged diameter of waterdrops is 7.3 μm and the standard deviation is 2.9 μm. Supercooling release of waterdrops in emulsion is examined by short time impressing of the ultrasonic. The direct contact heat exchange method is chosen as the phase change rate evaluation of waterdrops in W/O emulsion. The supercooled temperature is set as parameters of this study. The previous obtained experimental result, as the condition without impressing ultrasonic wave, showed that the 35 K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It is clarified that it is possible to reduce 20 K of supercooling degree by impressing the ultrasonic.

热害矿井采区大焓差降温系统实验研究

基于热质交换原理与实验理论,设计了大焓差降温除湿实验系统,实验研究不同喷淋压力、气水比、喷水温度下对喷和顺喷的大焓差降温装置降温效果及其热工性能,结果表明大焓差降温装置的适应性强,可满足不同热害程度的采区降温需求。计算了热交换系数和热交换效率,结果表明,对喷方式的热交换效率和热交换系数分别为0.952和0.988,而顺喷方式的热交换效率和热交换系数分别为0.936和0.978。综上,喷嘴对喷方式降温除湿效果稍优于顺喷方式。并由实验数据拟合得到大焓差降温装置的对喷和顺喷的热交换效率系数及热接触系数的经验公式,可更精准的指导热害矿井采区降温工程与大焓差降温装置的设计。

液压胀接残余接触压力计算及相关参数影响分析

胀接压力适宜控制范围的确定,关键在于准确计算胀接后换热管与管板间的残余接触压力。现有残余接触压力理论计算方法忽视换热管反向屈服问题,导致残余接触压力计算值与实际不符。文中基于材料理想弹塑性和平面应变假设,给出了Mises屈服准则下胀接残余接触压力理论计算方法详细推导过程,讨论分析了换热管弹性模量、屈服强度、壁厚等变化对残余接触压力的影响,该方法可适用于先焊后胀胀接工艺下胀接残余接触压力预测。

超声功率对铁棍山药超声强化热泵干燥水分迁移的影响

为探讨铁棍山药超声强化热泵干燥的水分迁移规律,对山药进行直触超声强化热泵干燥试验,研究超声功率对干燥特性及水分变化的影响。结果表明:在热泵干燥过程中施加超声有利于加快脱水进程。随着超声功率从0 W提高至60 W,干燥时间从630 min缩短至390 min,平均干燥速率由0.0053 g/(g·min)提高到0.0086 g/(g·min),有效水分扩散系数由0.887×10^(-10)m^(2)/s,增大至1.393×10^(-10)m^(2)/s。扫描电镜结果表明:施加超声使物料组织结构变疏松,产生微孔道。随着超声功率的提高,微孔道数量变多,孔隙率变大。低场核磁共振分析表明:铁棍山药中存在自由水、不易流动水和结合水3种状态水,且在干燥过程中其内部水分能够相互转化。自由水的含量不断降低,直至被完全去除;不易流动水的含量在干燥过程中先增高后降低,在干燥结束时仍存在部分不易流动水;结合水的含量在超声强化热泵干燥过程中几乎不变。铁棍山药的核磁共振成像显示,在干燥过程中,物料水分从外到内逐渐流失。提高超声功率能有效加快物料内部水分迁移,促进水分的去除。本研究结果可为果蔬超声强化热泵干燥技术的研发与应用提供参考。

基于可得然-氯化锂复合吸附剂的除湿换热器热湿性能研究

除湿换热器将换热器与固体干燥剂结合,可显著提高空调系统的除湿效率。干燥剂的吸附特性对除湿换热器的除湿性能有重要影响。研制了可得然-氯化锂复合吸附剂,用ASAP麦克吸附仪及STA同步热分析仪,从等温吸附及动态吸附特性等角度分析了其吸附特性,实现了材料的组分优化,并将优化后的复合吸附剂应用于除湿换热器,验证了该新型除湿换热器高效的深度除湿性能。实验结果表明,可得然复合吸附剂具有深度除湿的能力,即使在30℃、30%RH干燥工况下,其除湿量高达2.65 g/g,吸附速率系数k为2.1×10^(-4) s^(-1);所制备复合除湿换热器的MRC可以达到3.78 g/kg。本研究实现了除湿性好、循环性能稳定的低成本高性能新型除湿换热器的开发,为深度除湿系统的技术研发提供参考。

钛双极板表面碳掺杂氮化钛耐腐蚀涂层制备

为改善钛双极板在质子交换膜(PEM)水电解槽环境中的耐腐蚀性能和导电性能,采用电泳沉积-热处理两步法在钛基底表面制备碳掺杂氮化钛(C-TiN)复合保护涂层,并在0.5 mol/L的H_(2)SO_(4)和5 mg/L的F-溶液中模拟PEM水电解槽阳极环境测试其电化学腐蚀性。结果表明,电泳沉积及热处理改善了氮化钛纳米颗粒的连通性,增强了涂层与衬底的粘附力,实现了电子在电活性材料中快速传递。400℃下制备的碳掺杂氮化钛涂层(C-TiN-400℃),其导电性与耐蚀性均得到明显提升;相比于未处理的样品,镀有C-TiN-400℃涂层的样品在146.3 N/cm^(2)压力下的接触电阻可达到2.25 mΩ·cm^(2)。

锅炉烟气低品位余热回收技术综述

为了强化锅炉低品位余热回收,优化低品位余热回收技术方案,在介绍热湿耦合迁移和热交换2种烟气余热综合回收技术的基础上,进行了比较分析,归纳总结了各自的优缺点,分析了技术发展的趋势。指出将排烟焓值降低到接近周围环境空气焓值,就是烟气余热回收的极限。认为针对低品位余热回收,深入研究吸湿溶液吸收法和直接接触换热法,以及将两种方法结合会更有前景与意义。

Analysis of the effects of the heat of sorption on the process of heat transfer in moisture exchange across a membrane

A theoretical study has been conducted to investigate the effects of mass transfer on heat transfer in moisture exchange across a membrane and a mathematical model describing the heat transfer process with consideration of the heat of sorption was established. A dimensionless variable, Ψ =JLλ /δ (T 10−T 20), which controls the effect of the heat of sorption on the heat transfer in membrane process, was obtained through theoretical analysis, and the effects of Ψ on the heat transfer process were analyzed. Results showed that in the case that the temperature gradient and mass transfer are in the same direction, the effective heat flux changes the direction at Ψ=1. For Ψ【1, the heat transfers from high to low temperature sides through the membrane, and the total thermal resistance increases with increasing the moisture flux across membrane or reducing the temperature difference between the bulk flows on the two sides of membrane. For Ψ】1, the overall effect of the heat and mass transfer is that the effective heat flux points from low to high temperature sides and the total thermal resistance decreases with increasing the mass flux or reducing the temperature difference. In the case that the temperature gradient and mass transfer are in the opposite directions, the existence of the heat of sorption acts to enhance the heat transfer from high to low temperature sides, causing a reduced total thermal resistance, and the greater the mass flux or the smaller the temperature difference, the smaller the total thermal resistance.

管壳式换热器扩管平口工序优化

以管壳式换热器为研究对象,基于实际生产加工参数,建立了换热管与管板扩管平口工序的仿真模型,利用Abaqus软件对其进行仿真分析,研究了扩管工序后的残余接触压力分布情况,并在此基础上进一步分析了平口工序中切削深度对残余接触压力的影响。结果表明,扩管工序后,换热管与管板接触部分中间区域的残余接触压力小于两端的残余接触压力。在平口工序中,随着切削深度逐渐增大,接头处残余接触压力受切削力影响而分布不均的程度越加显著,当切削深度大于1.28 mm时,平口工序会使接头处出现间隙,从而破坏前道工序形成的密封效果,为了不增加额外的胀管工序,需在加工过程中合理选择切削参数,控制平口工序切削力。