水基氧化石墨烯纳米流体表面张力实验研究

以去离子水为基液,以氧化石墨烯纳米粒子为添加剂,制备成水基氧化石墨烯纳米流体,研究纳米流体在不同浓度、温度以及不同纳米粒子粒径下的表面张力,表面张力采用吊环法进行测量。实验结果表明,纳米流体的表面张力随着浓度增大而增大,但相对于去离子水,最大浓度(0.1wt%)的纳米流体表面张力仅增加了2.9%;纳米流体的表面张力随着温度的升高而降低,但降低的幅度小于去离子水随温度的降低幅度;纳米流体的表面张力随着纳米粒子粒径的减小而降低。本文的研究结果可为吸收式制冷循环吸收液的研究提供参考。     

低过冷度冰蓄冷溶液的实验研究及节能效益分析

加入成核添加剂能有效地降低冰蓄冷溶液的过冷度,使制冷主机的蒸发温度提高。分别对大过冷度和低过冷度、低过冷度和无过冷度结冰过程进行了实验比较,结果表明：使用低过冷度冰蓄冷溶液时,可采用较高的制冷主机蒸发温度,结冰时间较短,在工程实际应用中能起到较好的节能效果。     

凝汽器冷却水温度和流量对凝结水过冷度影响的研究

凝结水过冷度对汽轮机运行的经济性和安全性均产生很大影响,但目前还很少有文献进行冷却水温度和流量对凝结水过冷度影响机理的研究.以某300MW汽轮机所配凝汽器为例,通过定量分析冷却水温度和冷却水流量对凝汽器汽阻和凝汽器凝结水膜的影响,研究了冷却水温度和流量对凝结水过冷度的影响机理,为运行中减小和控制凝结水过冷度奠定了理论基础.     

敲击振动触发过冷三水醋酸钠（SAT）凝固释能实验研究

利用实心钢球敲击不锈钢圆角矩形蓄热单元表面,根据测定诱导时间和触发敲击次数实验研究不同敲击动量及位置对单元内过冷SAT溶液触发凝固性能的影响。结果表明,敲击振动是触发该过冷水合盐相变材料凝固释能的有效方法,结晶最大温升速率为3℃/s,且最高表面温度达到53℃,比理论相变温度低5℃;凝固从开始触发位置为中心以8～10 mm/s的速度向四周扩散。敲击动量越大,诱导时间越短,最短仅为10 s;敲击位置靠近密封盖或蓄热单元边角诱导时间更短。实验结果为SAT过冷蓄存太阳热能用于采暖或热水供应释能控制提供方法和指导。     

添加纳米颗粒的石蜡非等温凝固过程研究

采用差示扫描量热仪对石蜡以及石蜡纳米氧化铜混合物进行非等温凝固过程热分析,探究纳米氧化铜颗粒的添加份额以及降温速率对石蜡相对结晶度、凝固时间、成核率等的影响。结果表明,在凝固过程初期,添加纳米氧化铜颗粒提高了石蜡的成核率,在晶核成长阶段则阻碍了石蜡的凝固。相比之下,降温速率对凝固过程的加速作用更为明显。     

氧化石墨烯的改良制备及吸附性能研究

在改良hummers法制备氧化石墨烯的基础上,对制备过程各步骤进行精准化控制,总结了氧化石墨烯在制备过程中出现的问题,分析成因并进行改进,得到了一种鳞片石墨制备氧化石墨烯的简便、低成本且环保的方法。利用制得的氧化石墨烯对亚甲基蓝模拟染料废水进行吸附实验研究,结果表明,氧化石墨烯投加量为0.1 g,转速为300 r/min,时间为90 min,亚甲基蓝的去除率达到98.7%。     

石墨烯/环氧树脂复合涂层在散热器传热过程的实验研究

提出一种用于空气源热泵-散热器系统的涂层材料,即石墨烯复合涂料。受空气源热泵热水机组出水温度的限制,需提高散热器的散热能力。主要通过实验分析,分别制备石墨烯质量分数为0%、2.5%、5%的样品,比较喷涂前后散热器散热能力的大小。结果表明:石墨烯质量分数为5%的复合涂层的散热器散热效果最好,供水温度为50℃时,散热量约为纯环氧树脂的13倍;随着供水温度的升高,样品的散热量增加,但增加的幅度逐渐减小。     

细圆管内氧化铜颗粒悬浮液流动与对流换热的实验研究

实验研究了氧化铜纳米悬浮液在内径为0.68mm不锈钢细圆管内迫流动和对流换热。氧化铜纳米颗粒悬浮液的质量分数W为0.02-0.06,分别去离子水和水－纳米颗粒悬浮液的流动,传热特性进行了实验测定。实验结果表明：所研究尺度下,层流向湍流过渡早于常规大尺度流动,悬浮液的压降要大于去离子水的;纳米颗粒的质量分数越大,压力降也越大,悬浮液的对流换热系统随颗粒质量分数的增大而增大。     

功能化氧化石墨烯作为锂硫电池正极硫载体的性能研究北大核心CSCD

随着便携式电子设备、新能源电动汽车和储能电网的快速发展,人类对经济高效的电化学储能(EES)系统的需求越来越大。锂硫电池由于成本低、取材广、效率高、质量轻、硫元素零污染等优势,已成为当前EES系统中应用范围最广的储能器件之一。然而,因正极硫的利用率低、锂枝晶生长、体积膨胀和长链多硫化物的穿梭效应等问题,严重制约了其商业化进程。因此,寻找新的硫宿主材料迫在眉睫。本工作通过开发煤基氧化石墨烯复合材料试图解决上述问题,设计了一种含氧官能团的煤基氧化石墨烯,对多硫化物的空间限域或物理捕捉。并通过煤基石墨烯(G)和被氧化后的煤基氧化石墨烯(GO),组装成完整的扣式锂硫电池;实现了在高倍率3 C条件下进行500次长循环,比容量从初始622.5 mAh/g维持到448.2 mAh/g,比容量保持率为72%,比容量的衰减率为0.056%,经过多次验证,得出含有丰富功能基团的煤基氧化石墨烯能够为中间产物多硫化锂提供更丰富的极性位点,在一定程度上显示出更高的亲硫性,再经过一系列的电化学表征来证明该材料在锂硫电池中的优势,为锂硫电池的进一步发展提供借鉴和方法。     

实验炉内钢坯传热过程及其氧化烧损的数值模拟研究

以实验加热炉为研究对象,建立三维非稳态钢坯加热过程的氧化烧损模型,并根据等效热阻法和等效质量法,将钢坯加热时氧化层的动态增长过程,转化为氧化层的当量导热系数和当量密度的动态变化过程.基于数值模拟方法,研究了实验炉内钢坯加热过程中表面氧化烧损量以及氧气浓度、所处位置的氧化层对钢坯加热过程的影响及其氧化烧损量随时间变化规律.结果表明:在钢坯加热的过程中,氧化层增大了钢坯与烟气之间的换热热阻,加热到最终温度时,换热热阻是原来的2倍,钢坯升温速率明显减小;在炉内的加热时间越长,钢坯氧化烧损逐渐增加,到一定程度之后趋于平缓;当加热到相同温度,氧气浓度从0.41％升至0.995％时,氧化烧损量从9.5 kg/m2增加到16.8 kg/m2.     

Supercooling behaviour and non-isothermal crystallization processes of aqueous suspensions of carbon nanotubes

采用添加碳纳米管形成悬浮液的方法可以有效地提高基液的导热系数,碳纳米管的存在还将对悬浮液的固液相变行为产生可观的影响.利用差示扫描量热仪对低浓度碳纳米管水悬浮液的过冷度进行了非等温结晶实验测试,对比分析了不同浓度(质量分数最高为1%)的悬浮液在不同降温速率情况下过冷度的变化规律.实验结果表明,由于碳纳米管的存在,悬浮液的过冷度较之纯水有所降低.随着浓度的提高,悬浮液的过冷度呈逐步下降的趋势.在最高浓度1%时,悬浮液的过冷度较之纯水下降了约7 ℃.此外,悬浮液的过冷度随着降温速率的增大略有升高,其中浓度为0.01%的悬浮液在降温速率为10 ℃/min时较2 ℃/min时增大了约4 ℃.采用碳纳米管悬浮液作为蓄冷工质对整个非等温结晶过程并未体现出加速的效果,但能在较慢的降温速率下有效地降低水的过冷度.     

氧化石墨烯对脉动热管传热性能的影响

实验选用外径为4mm、内径为2mm的铜质脉动热管研究了氧化石墨烯对以去离子水和体积分数为50%的乙醇溶液为工质的脉动热管传热性能的影响。实验分别采用加有少量氧化石墨烯的去离子水溶液(简称氧化石墨烯水溶液)和体积分数为50%的乙醇溶液(简称氧化石墨烯乙醇溶液),氧化石墨烯质量分数均为0.03%。实验发现：氧化石墨烯对以去离子水为工质的脉动热管传热性能具有强化作用,对以体积分数为50%的乙醇溶液为工质的脉动热管传热性能的影响较差,但都和脉动热管的加热功率密切相关。对于以去离子水为工质的脉动热管,在加热功率低于20W时,氧化石墨烯对脉动热管的强化作用较弱;当加热功率在30～60W之间时,氧化石墨烯对脉动热管的强化作用较强,在3.71～11.33%之间,且强化作用随加热功率的增大呈逐渐增强趋势;但随着功率继续增大,氧化石墨烯的强化作用逐渐减弱,当加热功率达到80W后,热管传热性能减弱,原因可能是氧化石墨烯颗粒出现了沉降现象。     

Growth control of cobalt oxide nanoparticles on reduced graphene oxide for enhancement of electrochemical capacitance

The high capacitance and cyclic stability of graphene nanosheets decorated with Co₃O₄ nanoparticles as a material for supercapacitor electrodes are reported here. Hydrothermal method is adopted to deposit cobalt oxides on the reduced graphene oxide (RGO) sheets in a mixture of water and dimethylformamide (DMF) as the solvent with different volume ratios. The water volume ratio presents a crucial factor in the nucleation and growth process. In addition, it affects dispersion, particle size and the amount of nucleated cobalt oxide particle on the graphene sheets. By decreasing the water volume, the nucleation and growth occur mainly on graphene rather than in solution. According to the obtained results from transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis, a model for growth of nanoparticles on graphene sheets is proposed. Based on the obtained results, the presented model can also be used for the synthesis of other graphene-metal (oxide) composites. Electrochemical measurements indicate that water volume ratio in the mixture solvent influences on capacitance of the RGO/Co₃O₄ composite electrodes. The highest obtained specific capacitance is 440.4 F g⁻¹ with 50% volume ratio of water at current density of 5 A g⁻¹.     

Effect of surface functional groups on hydrogen adsorption properties of Pd dispersed reduced graphene oxide

Pd/reduced graphene oxide (Pd-RGO) composites were successfully prepared from graphite and PdCl₂ precursors using wet impregnation and reverse micro emulsion methods. From hydrogen adsorption studies it is confirmed that spillover of hydrogen from Pd to graphene layers occurs at room temperature. However, at low temperatures there is negligible spillover effect and this is explained based on lower kinetic energy available with hydrogen atoms to overcome the activation barrier involved in diffusion. Detailed ¹³C MAS NMR and Raman spectroscopic studies confirmed that small amounts of structural units (functional groups) like carboxylate and polyacetylenic linkages are retained in Pd-RGO samples prepared by wet impregnation and reverse micro-emulsion methods, respectively. Such structural moieties facilitate the atomic scale mixing of Pd with the graphene layers thereby improving the spillover efficiency.     

Reduction of carbon dioxide to methanol on the surface of adenine functionalized reduced graphene oxide at a low potential

In this study, the surface of reduced graphene oxide (rGO) was modified with adenine via diazonium reaction. Then, to prepare Pt@Adenine-rGO, Pt was deposited on the surface of adenine-rGO, using cyclic voltammetry in the range of ?0.30 to +1.30 V at a scan rate of 100 mV s^?1 in a solution containing Pt salt. Afterward, it was characterized by various techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. Electrochemical studies showed the efficient electrocatalytic behavior of Pt@Adenine-rGO for the reduction of CO₂ to methanol at ?0.30 V. The products formed on the surface of Pt@Adenine-rGO were monitored using different techniques including Raman spectroscopy, gas chromatography, gas chromatography-mass spectrometry, and ¹³C NMR spectroscopy. Our findings indicated that methanol with a reasonably high Faradaic efficiency up to 85% and a current density of 0.5 mA cm^?2 as the main product of CO₂ reduction on the surface of Pt@Adenine-rGO.     

Influence of the reduction of graphene oxide (rGO) on the structure and photoactivity of CdS-rGO hybrid systems

Solvothermal and chemical reduction of graphene oxide with N₂H₄ or HI affect the surface composition, rupture and delamination degree of reduced graphene oxide (rGO). Higher reduction and stacking of rGO was achieved by chemical reduction with HI, while solvothermal reduction and, especially, the chemical reduction with N₂H₄ lead to higher delamination of rGO. The incorporation of the different rGO to CdS implies changes in the characteristics and photoactivity of the CdS-rGO hybrids. A promoter effect was observed in all CdS-rGO hybrids respect to the photoactivity of bare CdS, observing the better photoactivity on the hybrid in which the graphene oxide was reduced with HI (CdS-rGO/HI). The variations in the photoactivity of CdS-rGO hybrids are analyzed in terms of changes in the structure, surface and light absorption ability of CdS and also analyzing the contact of CdS with rGO. The greater concentration of small CdS nanostructures with strong quantum confinement is in the origin of the enhancement in photoactivity observed in the CdS-rGO/HI hybrid.     

Facile synthesis of reduced graphene oxide supported PtAg nanoflowers and their enhanced electrocatalytic activity

In this work, a simple and facile method is developed in the synthesis of well-dispersed PtAg nanoflowers on reduced graphene oxide nanosheets (PtAg/RGOs) under solvothermal conditions, using ethylene glycol as a reducing agent and hexadecyl trimethyl ammonium bromide (CTAB) as capping and stabilizing agents. The as-prepared nanocomposites show a superior electrocatalytic activity, good tolerance, and better stability toward the oxidation of formic acid and ethylene glycol in alkaline media, compared with the commercial Pt/C (10 wt%) catalyst. For the oxidation of formic acid, the PtAg nanoflowers own thirty times higher of the catalytic currents than those of the commercial Pt/C catalyst. Meanwhile, for the oxidation of ethylene glycol, the ratio of forward current (j_F) to reverse current (j_R) is high up to 8.4, which is almost four times higher than that of the commercial Pt/C catalyst. This strategy provides a promising platform for direct formic acid and ethylene glycol fuel cells.     

Rapid room-temperature synthesis of Pd nanodendrites on reduced graphene oxide for catalytic oxidation of ethylene glycol and glycerol

In this paper, a simple, fast, and green method is developed for preparation of uniform Pd nanodendrites anchored on reduced graphene oxide (Pd/RGO) at room temperature, with the assistance of octylphenoxypolye thoxyethanol (NP-40) as a soft template, while no seed, organic solvent, or special apparatus involved. The as-prepared nanocomposites show the improved CO tolerance, enhanced catalytic activity, and better stability for ethylene glycol (EG) and glycerol (Gly) electrooxidation in alkaline media, compared with commercial Pd black and Pd/C catalysts. The synthetic strategy can be extended to fabricate other electrocatalysts in direct alcohol fuel cells.