凹凸板式换热器的研究现状

介绍了换热器性能评价方法和几种研究方式,比较了管壳换热器与板式换热器的优缺点,综述了凹凸板片强化传热机理、传热系数与压降之间的关系、板片结构设计优化以及加工工艺改进等方面的相关研究,从而提出了凹凸板式换热器有待解决的问题,并进行了总结和展望。     

换热器与相变材料的兼容性研究进展

相变材料是一类以潜热实现能量存储释放的储能材料,由于其在相变温度附近具有很大的储热密度,相变材料可以被用于建筑控温、太阳能热发电和高温传热蓄热等应用中。 换热器是相变储能设备的重要组成部分,可以将热量在供需两端进行传递和转移,保障需求一方的使用,随着相变材料研究的不断深入及其工程应用的广泛普及,换热器已在众多相变储能项目中发挥了重要的枢纽作用。 为了保证换热器的使用性能,需要对换热器在相变材料中的防腐蚀性进行全面的分析。 本文总结了大量国内外的文献,分析不同成分的相变材料对换热器材料的腐蚀性,为换热器材料的选择提供了参考。     

氧分压对固体氧化物电解池性能的影响

High-temperature (700–900 ℃) steam electrolysis based on solid oxide electrolysis cells (SOECs) is valuable as an efficient and clean path for large-scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steam methane reforming or coal gasification. The operation parameters, in particular the feeding gas composition and pressure, significantly affect the performance of the electrolysis cell. In this study, a computational fluid dynamics model of an SOEC is built to predict the electrochemical performance of the cell with different sweep gases on the oxygen electrode. Sweep gases with different oxygen partial pressures between 1.01 × 10³ and 1.0 × 10⁵ Pa are fed to the oxygen electrode of the cell, and the influence of the oxygen partial pressure on the chemical equilibrium and kinetic reactions of the SOECs is analyzed. It is shown that the rate of increase of the reversible potential is inversely proportional to the oxygen partial pressure. Regarding the overpotentials caused by the ohmic, activation, and concentration polarization, the results vary with the reversible potential. The Ohmic overpotential is constant under different operating conditions. The activation and concentration overpotentials at the hydrogen electrode are also steady over the entire oxygen partial pressure range. The oxygen partial pressure has the largest effect on the activation and concentration overpotentials on the oxygen electrode side, both of which decrease sharply with increasing oxygen partial pressure. Owing to the combined effects of the reversible potential and polarization overpotentials, the total electrolysis voltage is nonlinear. At low current density, the electrolysis cell shows better performance at low oxygen partial pressure, whereas the performance improves with increasing oxygen partial pressure at high current density. Thus, at low current density, the best sweep gas should be an oxygen-deficient gas such as nitrogen, CO₂, or steam. Steam is the most promising because it is easy to separate the steam from the by-product oxygen in the tail gas, provided that the oxygen electrode is humidity-tolerant. However, at high current density, it is best to use pure oxygen as the sweep gas to reduce the electric energy consumption in the steam electrolysis process. The effects of the oxygen partial pressure on the power density and coefficient of performance of the SOEC are also discussed. At low current density, the electrical power demand is constant, and the efficiency decreases with growing oxygen partial pressure, whereas at high current density, the electrical power demand drops, and the efficiency increases.     

Ni-Cu-P合金镀层在燃气冷凝换热器上的应用

研究硫酸铜镀液中浓度对Ni-Cu-P合金镀层的成分、组织结构及耐腐蚀性能的影响.EPMA、XRD和极化曲线镀层测试表明,以浓度为0.5g.L-1的硫酸铜作镀液镀层的耐蚀性能最优.在天然气冷凝液中考察了Ni-Cu-P、Ni-P合金镀层和铜基体的电化学耐腐蚀性能,Ni-Cu-P合金镀层的自腐蚀电位低,自腐蚀电流密度小,交流阻抗值最大.因此该镀层可作为铜质燃气冷凝换热器的耐蚀阻挡层和牺牲阳极保护镀层,防止铜管腐蚀穿孔,有效地延长铜质冷凝换热器的使用寿命.     

分子结构对环氧树脂性能影响的分子模拟研究

采用分子动力学方法建立了二乙基甲苯二胺/双酚A缩水甘油醚环氧树脂体系(DETDA/DGEBA体系)和间苯二胺/双酚A缩水甘油醚环氧树脂体系(mPDA/DGEBA体系)的交联模型,在此基础上,分析了固化剂分子结构的差异对树脂性能的影响,研究发现mPDA/DGEBA体系的玻璃化转变温度、模量以及阻碍水分子的扩散性能均高于DETDA/DGEBA体系。为了进一步揭示交联环氧树脂分子结构与性能之间的关系,研究了上述两体系的自由体积和内聚能密度。结果表明,与DETDA/DGEBA体系相比,mPDA/DGEBA体系具有较小的自由体积和较高的内聚能密度。较小的自由体积和较高的内聚能密度是造成mPDA/DGEBA体系玻璃化转变温度、模量以及阻碍水分子的扩散性能均高于DETDA/DGEBA体系的原因。     

有机溶剂对ICP—AES分析性能影响的研究

研究了有机溶剂对电感耦合等离子体－原子发射光谱（ＩＣＰ－ＡＥＳ）分析性能的影响。ＭｏｎｔｅＣａｒｏｌ模拟结果和实验结果表明，只要选择合适的操作参数，有机溶剂直接引入ＩＣＰ不仅不会影响ＩＣＰ的稳定性，还会提高某些元素的灵敏度，从而提高了ＩＣＰ－ＡＥＳ的分析性能。     

喷嘴入射角对微型燃气轮机燃烧室性能影响的数值模拟

为了从结构方面改善Capstone C30微型燃气轮机燃烧室性能,选用预混燃料喷嘴入射角分别为25°、30°、35°、40°、45°来研究燃烧室的流场、温度场、NO_x生成分布。通过Fluent数值模拟软件,采用Standardk-ε双方程模型来封闭求解N-S方程,有限速率/涡耗散模型模拟燃烧化学反应,热力型和快速型NO_x模拟燃烧生成的NO_x,SIMPLE算法进行流场计算。结果表明:在入口条件不变的情况下,随着入射角不断变大,回流区尺寸不断增加,有利于稳定燃烧,流场分布更为合理,而出口温度不均匀系数和NO_x排放浓度震荡变化,综合分析,当入射角为45°时是最佳入射角,NO_x排放浓度和出口温度不均匀系数均有大幅改善。     

嵌入配位不饱和金属位对多孔芳香骨架材料储氢性能的影响

基于密度泛函理论(DFT)和巨正则蒙特卡洛(GCMC)模拟方法,系统地研究了引入配位不饱和金属位(CUS)对PAF-30n (n = 1–4)材料储氢性能影响的规律。结果表明,77 K下PAF-302MgO₂_PBE100的最大过量质量储氢量达到7.97% (w);77 K、10 MPa下100%醇镁功能化改性PAF-302和PAF-303的绝对储氢量分别达到9.9% (w) (65.9 g∙L^-1)和15.0% (w) (50.5 g∙L^-1),分别超过美国能源部(DOE)标准80% (64.8%)和173% (26.3%),均超过在相同条件下目前储氢性能最佳的NU-1101 (9.1% (w), 46.6 g∙L^-1)。即使在243 K、10 MPa下,其绝对质量和绝对体积储氢量也能分别达到5.13% (w)和34.19 g∙L^-1,占DOE质量与体积储氢标准的93.3%和85.5%,是目前为止常温储氢性能较为均衡的多孔材料之一。结合等量吸附热(Q_st)、径向分布函数(RDF)和质心几率密度分布(MCPD)方法进一步分析,发现有机链长度增加导致孔隙率增加和体积比表面积减小,是引起多孔材料绝对质量和绝对体积储氢量此消彼长的根本原因。另外,引入CUS能提高PAFs材料对H₂分子亲和力,显著增强其体积储氢量。     

蒸发式冷凝器中蒸发冷条件下单管换热实验研究

以蒸发式冷凝器为模型,搭建了在蒸发冷条件下单管的换热试验台,并以水蒸气为实验工质对试验台的热力性能进行实验,为蒸发式冷凝器确定统一标称提供实验依据。结果表明:本试验台换热管两侧为冷壁面,其对冷凝效果影响显著,按蒸发式冷凝器理论计算结果,实验测得冷凝量提升30%到40%;考虑换热单管两侧冷壁面对喷淋水的影响,通过理论计算得到的结果与实际测试结果较为一致;经过测试,喷淋密度0.078 kg/(m·s),迎面风速为3 m/s时,冷凝效果最优。     

表面活性剂与血红蛋白的作用对转移电子数的影响

将不同浓度(0.15-10.0 mmol·L-1)的双十二烷基二甲基溴化铵(DDAB)和血红蛋白(Hb)依次修饰到热解石墨电极(PG)上, 制备了稳定的Hb-DDAB/PG电极. 利用循环伏安和紫外光谱研究了Hb-DDAB/PG电极的性质. 由Laviron模型得到的转移电子数表明该电化学反应由双电子过程逐步过渡到单电子过程, 进而证明DDAB膜厚的增加导致血红蛋白亚基间作用的减弱和亚铁血红素的释放.     

迁移管形状对希托夫法测定离子迁移数结果的影响

在希托夫法测定Cu~(2+)离子迁移数的物理化学实验教学中,目前常用直形和U形两种类型的迁移管,其中使用U形迁移管从阴极区溶液浓度变化算出的迁移数误差较大。以CuSO_4为电解质,Cu电极为电解电极,采用分光光度法分别测定了通电后直形、U形和n形三种迁移管中CuSO_4溶液浓度随高度的分布情况。研究发现,迁移管的形状对中部区溶液的浓度有较大影响。对于U形和n形迁移管,由于阴极位于迁移管底部,主要受重力作用引起的对流因素的影响,通电后中部区浓度会发生明显改变,并影响到阴极区溶液浓度,导致误差较大;使用直形迁移管受该因素的影响很小,能得到更为准确的结果。     

Heat Transfer Enhancement on the Adsorber of Adsorption Heat Pump

Three methods for improving the heat transfer of the adsorber have been developed in this paper. First, an electrically conductive polyaniline was applied for enhancing the thermal conductivity of adsorbent bed. A thermally conductive composite of polyaniline and adsorbent was prepared by chemical oxidative in situ polymerization of aniline onto the surface of adsorbent particles. A thin thermal conducting net on the surface of the adsorbent particles was grown. The experimental results indicated that the thermal conductivity of this composite could be increased to approximately 4 times that of the raw adsorbent. Second, the adsorbent bed was shaped by a compressing process. This process can reduce the thermal resistance among the adsorbent particles and the contact thermal resistance between the adsorbent bed and the heat exchanger. The thermal conductivity of the shaped adsorbent bed itself from the tests can be increased 30% when the density of the solid adsorbent bed is 1.5 times that of its original density. Furthermore, the adsorption capacity of the above treated adsorbent did not decrease obviously. Third, a proper design of adsorber has been introduced and analyzed. Further tests of this design will be conducted soon.     

Influence of the Electromagnetic Forces on Momentum and Heat Transfer in a 3-Phase ac Plasma Reactor

A new 3-phase ac plasma reactor has been developed within the framework of research on hydrocarbon cracking for the production of carbon black and hydrogen. ^(1,2) One of the main characteristics of the system is related to the 3-phase, 50 Hz ac current plasma generator which induces a very particular arc motion affecting the heat and mass transfer inside the reactor. In a first step, the general flow inside the reactor in the absence of hydrocarbon injection has been studied. A simplified approach to characterize the heat and mass transfer inside the reactor is presented in this paper. The arc zone analysis is carried out simultaneously by a theoretical analysis of the electromagnetic forces and by an ultrahigh-speed cine-camera analysis. The flow in the reactor is modeled with a CFD commercial code. Results are compared with experimental temperature measurements.     

润湿性表面强化冷凝传热的研究进展

固体表面的润湿特性对冷凝传热具有重要的影响。本文分析了冷凝传热的机理,介绍了现阶段对不同冷凝方式的判定方法,总结了不同润湿性表面的制备方法,概述了蒸汽在亲水表面、疏水表面和组合表面上的冷凝传热性能,总结了该领域目前存在的问题。本文为利用表面润湿性强化传热提供了较为系统的综述,为强化冷凝传热提供思路。     

电沉积表面修饰对染料敏化太阳电池微观性能影响机理研究

为了改善染料敏化太阳电池内电子的传输复合过程, 研究者尝试不同方法制备或改性TiO₂薄膜. 对TiO₂薄膜进行后处理, 在其表面引入一层小颗粒层, 是一种有效的方法并被广泛研究. 通过对TiO₂薄膜不同时间的电沉积表面修饰, 细致研究了表面修饰后染料敏化太阳电池微观性能的变化机制. 采用阳极氧化法在TiCl₃水溶液中对TiO₂薄膜进行电沉积后处理, 将溶液pH值调至2.2, 装置的反应速率由恒电位仪控制. 不同沉积时间电池带边移动以及电子传输复合的动力学过程, 借助强度调制光电流谱(IMPS)/强度调制光电压谱(IMVS)和电化学阻抗谱(EIS)等探测技术表征. 研究表明, 电沉积在TiO₂薄膜表面引入了大量浅能级陷阱态, 以致电势较高时电容随沉积时间延长增加明显. 不同时间的电沉积表面修饰在TiO₂薄膜表面形成了新的小颗粒层并改善了TiO₂颗粒间接触, 在改善电子注入及收集过程的同时, 也有效抑制了内部电子复合. IMPS/IMVS结果表明, 电沉积对动力学过程改善的效果受光强影响明显, 弱光下作用更为突出. 此外, 电池开路电压主要受带边移动及内部复合变化影响, 随沉积时间延长, 表面电荷的增多使TiO₂薄膜带边逐渐正移, 有效改善了光电流却限制了开路电压的提升. 在适合的电沉积时间下, 电沉积表面修饰可以同时改善光电流和光电压.     

Influence of Forced Internal Air Circulation on Airflow Distribution and Heat Transfer in a Gas Double-dynamic Solid-state Fermentation Bioreactor

Internal air circulation affects the temperature field distribution in a gas double-dynamic solid-state fermentation bioreactor (GDSFB). To enhance heat transfer through strengthening internal air circulation in a GDSFB, we put an air distribution plate (ADP) into the bioreactor and studied the effects of forced internal air circulation on airflow, heat transfer, and cellulase activity of Trichoderma viride L3. Results showed that ADP could help form a steady and uniform airflow distribution, and with gas-guide tubes, air reversal was formed inside the bioreactor, thus resulting in a smaller temperature difference between medium and air by enhancing convective heat transfer inside the bioreactor. Using an ADP of 5.35 % aperture ratio caused a 1 °C decrease in the average temperature difference during the solid-state fermentation process of T. viride L3. Meanwhile, the cellulase activity of T. viride L3 increased by 13.5 %. The best heat-transfer effect was attained when using an ADP of 5.35 % aperture ratio and setting the fan power to 125 V (4.81 W) in the gas double-dynamic solid-state fermentation (GDSF) process. An option of suitable aperture ratio and fan power may be conducive to ADPs’ industrial amplification.