凹槽微通道铜-水纳米流体传热与流动分析

对铜-水纳米流体在圆弧型凹槽微通道中的传热与流动特性进行了分析。比较了不同体积分数的铜-水纳米流体在深宽比分别为0.3和0.5的凹槽微通道中的温度和速度分布,分析了体积分数和凹槽深宽比对凹槽微通道中铜-水纳米流体的传热系数和流体输运动力因子的影响。凹槽强化了微通道对流传热,与平板型微通道相比,铜-水纳米流体在圆弧型凹槽微通通内呈现出不同的传热特性。纳米流体体积分数、流体输运动力因子和凹槽深宽比对凹槽强化微通道传热影响较大。分析结果与已有的实验结果符合较好。     

MoS_2/CNTs混合纳米流体微量润滑磨削加工表面质量试验评价

结合国内外对混合纳米流体微量润滑磨削的研究现状,研究二硫化钼和碳纳米管混合纳米流体微量润滑磨削镍基合金的工件表面质量。以工件表面粗糙度Ra值、表面轮廓曲线的自相关分析和工件表面微观形貌,作为表面质量表征参数。试验结果表明:纳米流体微量润滑由于纳米粒子高的强化换热能力从而避免了工件烧伤;混合纳米流体由于起到了"物理协同作用",较单一纳米流体得到了最低的表面粗糙度Ra值(0.311μm)和磨削温度峰值(52.8℃);随纳米流体质量分数的增加,表面粗糙度Ra值呈现上升趋势,这是由于质量分数的增加改变了微量润滑雾滴与工件的接触角,从而改变了浸润面积;而摩擦因数和磨削温度峰值在6%取得最低值后呈上升趋势,这是由于纳米粒子的团聚破坏了纳米流体性能。通过工件表面轮廓曲线的自相关分析进一步验证,纳米粒子在磨削区起到"润滑作用"和"微加工"作用,从而提高了加工精度。因此,综合磨削性能、表面粗糙度和自相关分析,选择混合纳米流体质量分数6%为纳米流体的优选质量分数。     

石墨烯/铜混合纳米流体对微量润滑车削304不锈钢的影响

为了揭示纳米粒子的协同作用机理,以少层石墨烯为载体,纳米铜作为负载金属粒子,在可生物降解润滑油基础上,分别采用分子水平混合和机械混合方法制备了石墨烯/铜混合纳米流体。在确定的石墨烯/铜比例及纳米粒子的质量分数条件下,进行了微量润滑切削AISI 304不锈钢的单因素试验研究。结果表明,配方合适的分子水平混合纳米流体协同润滑作用优于机械混合纳米流体,MQL加工时可降低切削温度,提高表面质量,减小刀具磨损。     

利用光压差分技术筛选细胞的影响参数

本文采用有限体积法建立了交叉型细胞分离模型,提出了一种基于光压差分的细胞筛选仿真方法,分析微流体中细胞筛选的影响因素。基于层流、流体流动粒子追踪、波动光学理论,利用有限元分析法建立了一种交叉型光学颗粒分离模型,研究了利用光压差分技术分离细胞的各种影响因素,其中包括微粒直径,激光功率、温度、光纤直径,分析了微粒在流体中因光辐射压力作用下的偏移距离。实验结果表明:在微流体中,激光功率、细胞直径、温度(20℃)和偏移距离大体上成正比关系,光纤直径和细胞直径在大小相当的情况下光辐射压力能够达到最大值,当激光通过光纤作用于直径分别为3,8和20μm的微粒时,光纤直径为7μm或8μm时光辐射压力最大,所以选用直径为8μm的单模光纤作为一个重要的实验光学器件。所得结论为深入研究细胞筛选影响因素的数值仿真精度提供了参考与借鉴。     

TiC-H_2O纳米流体流变及传热特性研究

通过"两步法"制备出分散稳定性能好的TiC-H_2O纳米流体,并研究了其流变特性及传热特性。结果表明,分散剂质量分数会影响纳米流体黏温特性,纳米流体随剪切速率的变化而表现出不同流体状态,纳米颗粒质量分数及粒径均会影响流体传热特性。     

不同种类纳米流体微量润滑铣削钛合金实验评价

以航空航天常用钛合金Ti-6Al-4V作为工件材料,选取纯棉籽油微量润滑和6种不同种类的纳米流体微量润滑进行实验对比,用铣削力,表面粗糙度,工件表面微观形貌,对润滑性能进行实验评价。结果表明:采用纯棉籽油微量润滑时,铣削力最大,为448. 6 N。添加Al_2O_3、SiO_2纳米粒子在提高基础油的摩擦学性能上表现出了显著的效果,铣削力分别为291. 2 N和296. 5 N,比纯棉籽油微量润滑分别减小了35. 1%,33. 9%。采用纯棉籽油微量润滑时得到的工件表面粗糙度值最大,R_a为1. 772μm。添加Al_2O_3的纳米流体得到的工件表面粗糙度值最小,R_a为0. 594μm。六种纳米粒子得到的工件表面粗糙度值的大小关系为:Al_2O_3SiO_2MoS_2CNTs石墨SiC。Al_2O_3纳米流体微量润滑条件下得到的工件表面犁沟最小,工件表面质量最好。结合铣削力、表面粗糙度以及和工件表面微观形貌,Al_2O_3和SiO_2纳米粒子更适合作为基础油的添加剂。     

复合纳米粒子作为润滑油添加剂的摩擦学性能

研究了复合纳米粒子作为添加剂对润滑油摩擦学性能的影响.将改性纳米CaCO3和纳米Zn按一定质量分数进行复配后,加入到液体石蜡中,采用摩擦磨损试验机考察了其摩擦学性能;并采用正交试验方法分析了2种纳米粒子的最佳配比和最佳添加量.结果表明,复合纳米粒子综合了CaCO3和Zn 2种纳米粒子的性能,作为润滑油添加剂,比单一的纳米CaCO3和纳米Zn添加剂有更好的抗磨减摩性能;在本文试验条件下,纳米CaCO3和纳米Zn的质量比为1∶1,总质量分数为0.6%时,配制的润滑油具有更好的抗磨减摩性能.     

纳米添加剂Al2O3和MoS2在油包水滴射流冷却中的应用研究

淬硬钢高速切削加工易出现切削温度高和刀具磨损快等问题,因此有效冷却和润滑非常重要。提出油包水滴射流(OoW)与纳米粒子相结合的绿色冷却润滑方法,将Al₂O₃和MoS₂分别添加到水和大豆油中得到纳米流体,再混合雾化喷出纳米粒子油包水滴射流(N-OoW)。制备了0.25%和0.75%两种质量分数的纳米流体,形成N_0.25-OoW和N_0.75-OoW两种纳米粒子油包水滴射流方式,并与原OoW方式对比。开展摩擦磨损实验,对比分析摩擦系数及磨痕形貌,再开展两种车削速度下的车削实验,对比分析刀具寿命及刀具磨损。结果表明,N_0.75-OoW方式的摩擦系数、磨痕宽度、磨痕深度和刀具磨损均最小;在切削速度120m/min和200m/min时,相比于OoW,N_0.75-OoW方式的刀具寿命分别提高了29.6%和34.4%;纳米粒子油包水滴射中,单一纳米粒子优异的抗磨减摩性能以及纳米粒子之间的协同效应是降低摩擦磨损及提高刀具寿命的主要原因。     

硅油基磁性复合流体斜轴抛光特性研究

根据磁流体和磁流变体在流体性能方面各自特点,制备了硅油基磁性复合流体并对不锈钢材料进行了斜轴抛光试验,以研究硅油基磁性复合流体斜轴抛光特性。硅油基磁性复合流体由纳米级的Fe3O4,微米级的金刚石磨粒,微米级的铁粒子和α纤维素以及硅油等组成。测试了磁性复合流体的磁场流变特性,分析了磁性复合流体在磁场作用下形成磁链的质量和长度。在斜轴抛光设备上利用硅油基磁性复合流体进行抛光不锈钢表面试验,并测量了不锈钢表面微观形貌,获得R a0.020μm的表面粗糙度。     

TiO2—蒸馏水纳米流体在内螺纹铜管内表面传热试验研究

为研究TiO2—蒸馏水纳米流体在内螺纹管内的表面传热特性,自行设计并建立一套纳米流体表面传热试验系统和数据采集系统,试验系统核心部分分别采用铜光管和内螺纹铜管,将基液和TiO2—蒸馏水纳米流体分别应用于铜光管和内螺纹铜管内Re为3 000～8 000范围内进行表面传热试验研究,结果表明,在内螺纹铜管内,TiO2—蒸馏水纳米流体表面传热系数都是随着流速的增加而不断提高,随着纳米颗粒质量分数的不断增加,TiO2—蒸馏水纳米流体表面传热效果越来越差,而且弱于基液的表面传热效果,纳米颗粒质量分数不变的情况下,纳米流体表面传热效果随着流体平均温度的提高而加强。通过对纳米流体在不同圆管内试验结果进行对比,发现TiO2—蒸馏水纳米流体在内螺纹管内表面传热效果相对于光管内表面传热效果的强化程度低于基液的强化程度,TiO2—蒸馏水纳米流体不适用于内螺纹强化换热管。     

Pool boiling heat transfer to zinc oxide-ethylene glycol nano-suspension near the critical heat flux

Experimental study is conducted on the thermal performance of the ZnO nanoparticles dispersed in water-ethylene glycol (water/EG) as the base fluid under the pool boiling condition. Experimental facility provides condition to apply heat fluxes up to the critical heat flux point. Influence of different operating parameters such as heat flux and mass concentration on the boiling heat transfer coefficient and thermal fouling resistance is investigated. Results showed that with an increase in heat flux and mass concentration, the heat transfer coefficient increases; however, at concentration of 0.5 % by weight for ZnO/water/EG nano-fluid. Deposition of particles on the heating surface was a significant disadvantage of the nano-fluid. However, with an increase in mass concentration of nanoparticles, the critical heat flux point is enhanced, which is due to the enhancement in deposition layer of the nanoparticles, resulting in capillary wick and keeping more liquid inside the deposition layer.

     

Pressure effects on Coriolis mass flowmeters

The current status of available work regarding the pressure effect on Coriolis mass flowmeters is reviewed, which shows significant improvement in the latest generation of Coriolis flowmeters. A theoretical method using the linear damping model is proposed to understand the pressure effect. This new method applied to Coriolis flow sensors provides intuitive insight into the flow-generated signal by studying undamped natural frequencies and mode shapes. Most importantly this method can be used to model virtually any shape and configuration of flow sensors as found in the practical design. It is found that when the pressure changes it alters the superimposed contribution and the mass flow measurement can deviate from the reference condition. Experimental results from both low and high pressure flow tests are reported, which are in general agreement with the theoretical prediction. Further specific work is finally suggested which may advance our understanding and improve the Coriolis mass flow measurement technology.     

Flow and pressure drop characteristics of R22 in adiabatic capillary tubes

The objective of this study is to present flow and pressure drop characteristics of R22 in adiabatic capillary tubes of inner diameters of 1.2 to 2.0 mm, and tube lengths of 500 to 2000 mm. Distributions of temperature and pressure along capillary tubes and the refrigerant flow rates through the tubes were measured for several condensing temperatures and various degrees of subcooling at the capillary tube inlet. Condensing temperatures of R22 were selected as 40, 45, and 50°C at the capillary tube inlet, and the degree of subcooling was adjusted to 1 to 18°C. Experimental results including mass flow rates and pressure drops of R22 in capillary tubes were provided. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tube was presented considering major parameters which affect the flow and pressure drop characteristics.     

纳米流体微量润滑磨削硬质合金温度场模型与实验验证

温度过高是目前磨削加工硬质合金的技术瓶颈。相比传统的干磨削工况,纳米流体微量润滑(NMQL)的冷却润滑方式是解决磨削热损伤的有效措施。为了验证纳米流体微量润滑工况下磨削硬质合金的可行性,建立了硬质合金的传热模型,并在此基础上对硬质合金的磨削温度场进行了数值仿真研究。对硬质合金(YG8)进行了不同工况下的表面磨削试验。结果表明,以干磨削工况下的磨削温度(227.2℃),微量润滑(MQL)工况和纳米流体微量润滑工况下磨削区温度分别降低了20.42%和39.48%。数值仿真温度与实验测量温度的误差为6.3%。从宏观参数(比磨削力、磨削温度)和微观参数(砂轮表面形貌)出发,研究了不同工况对砂轮磨损的影响。实验结果,进一步证明纳米流体微量润滑适用于硬质合金的磨削加工。     

Experimental and numerical investigation on the performance of small-sized cavitating venturis

Cavitating venturis (CVs) are simple devices which can be used in different industrial applications to passively control the flow rate of fluids. In this research the operation of small-sized CVs is characterized and their capabilities in regulating the mass flow rate were experimentally and numerically investigated. The effect of upstream and downstream pressures, as well as geometrical parameters such as the throat diameter, throat length, and diffuser angle on the mass flow rate and critical pressure ratio were studied. For experimental data acquisition, three CVs with throat diameters of 0.7, 1 and 1.5 mm were manufactured and tested. The fabricated CVs were tested at different upstream and downstream pressures in order to measure their output mass flow rate and to obtain their characteristic curves. The flow inside the CVs was also simulated by computational fluid dynamics. The numerical results showed agreement with the experimental data by a maximum deviation of 5–10% and confirmed that the numerical approach can be used to predict the critical pressure ratio and mass flow rate at cavitaing condition. It is found that despite the small size of venturis, they are capable of controlling the mass flow rate and exhibit the normal characteristics. By decreasing the throat diameter, their cavitating mode became more limited. Results also show that increasing the diffuser angle and throat length leads to a decrease in critical pressure ratio.     

差压式涡街质量流量计取压位置的研究

在涡街流量计中，流体通过涡街发生体后会产生压力损失及由旋涡引起的压力波动，根据这一特点，本文提出利用差压检测技术，通过单路差压传感器同时感受由涡街发生体引起的流体双重变化特性，测量流体质量流量的新方法。本文重点对差压检测取压位置进行研究，利用空气和水两种流体介质进行了一系列实验，得到不同取压位置的差压信号与流量关系，确定了能正确测量质量流量的差压取压位置。结果表明，该测量方法结构简单，是测量质量流量的有效方法。     

Application of small size cavitating venturi as flow controller and flow meter

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. The flow rate is a function of the upstream pressure, the throat area, the density and saturation pressure of the liquid. An experimental setup with capability of supplying water flow rate and constant upstream pressure was designed and manufactured. Three cavitating venturis with throat diameter of 5, 2.5, and 1 mm were designed and built to investigate the effect of venturi size on its mass flow rate. Three different sets of experiments were conducted to investigate the performance of the venturis. In the experiments, the mass flow rates were examined under different downstream and upstream pressure conditions and time varying downstream pressure. The results show for the ratio of downstream pressure to upstream pressure less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever the pressure ratio exceeds 0.8, the venturi acts like an orifice. This pressure ratio has been predicted analytically to highlight the affecting parameters, mainly the geometry of the venturi and viscous losses. It is found that the venturi size has no effect on its expecting function to keep mass flow rate constant. Also, it is shown that by applying a discharge coefficient and using only upstream pressure, the cavitating venturi can be used as a flowmeter with a high degree of accuracy in a wide range of mass flow rate.     

纳米铜在润滑油中烷基苯三唑分散剂的制备和性能研究

为提高铜纳米颗粒在润滑油中的分散性能,以苯并三氮唑和卤代烃为原料,合成烷基苯并三氮唑分散剂,并通过红外光谱和核磁共振确定化合物的结构;通过沉降试验、流变性能的测试考察了分散剂的烷基链长、分散剂的用量对分散性能的影响,并通过热分析和TEM对分散剂的分散性能做进一步考察。结果表明：分散剂的链长为十八时,分散剂质量分数为0.1%-0.2%时分散剂的分散性能最好;并且分散剂的质量分数小于0.2%时对润滑油流变性能的影响很小;分散剂与纳米铜的结合不仅有物理吸附还有化学吸附。在四球摩擦磨损试验机上进行的摩擦学性能试验结果表明,采用所合成的分散剂分散的铜纳米微粒添加剂能够显著提高基础油的极压性能,同时具有良好的减摩性能。     

3D打印燃气轮机天然气喷嘴的流场仿真分析

开展3D打印天然气喷嘴流场仿真研究,为小型化燃气轮机控制技术的提升奠定基础。利用Solidworks、ANSYS ICEM CFD软件进行3D打印天然气喷嘴模型建模和网格划分,基于FLUENT仿真完成不同压力工况下稳态天然气喷射流场的数值模拟计算。在天然气喷嘴外流场中形成的几何回流区会随着供气压强的增大而消失,中心回流区会随着工况压力的增大而逐渐向下游区域移动;天然气喷嘴的体积流量会先随着供气压强的增大而增大,供气压强大于0.15 MPa时体积流量逐渐饱和趋于平缓;质量流量随着压力工况的增大而呈线性增大;在距离喷嘴出口70mm处的不同压强工况下的不均匀度小于0.37。从仿真上研究天然气的分布以及气流的流动特性为3D打印喷嘴安全稳定运行及合理组织流场提供参考依据,为3D打印技术在燃气轮机制造中的应用提供了理论基础。     

润滑油对R32在水平光管内流动沸腾换热特性及压降的影响

对R32在φ5mm和φ7mm的水平光管内的流动沸腾时,润滑油对换热与压降特性的影响进行了试验研究,试验的质量流量范围为100~500 kg/(m~2·s),润滑油的含量在0~5%之间。结果表明,沸腾换热系数随着质量流量的增大而增大。在低干度区,换热系数随干度的增大而增大,当干度达到0.7~0.8时,换热系数达到最大。随着润滑油含量的增大,局部换热系数在减小。压降随着管径的减小和质量流量的增大而增大。润滑油含量的增大,导致压降的增大。在5mm管内,润滑油含量对换热系数和压降影响比较明显。