共查询到20条相似文献，搜索用时 171 毫秒
1.
建立了单个液滴在高频感应热等离子体中内部传热传质的数学模型,考虑了希尔球形涡的影响,模拟了液滴在不同入射尺寸下的内部传热传质变化过程。结果表明,随着液滴入射尺寸的增大,液滴表面溶质质量分数到达饱和状态所需时间缩短,且其内部环流的对流作用占主导因素,使得溶质在液滴表面集中,易形成浓度集中的表面薄层。 相似文献
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关键部件湿化器性能的分析 总被引：7，自引：0，他引：7
建立了传热、传质微分方程以及能量、质量守衡方程,利用实验研究给出的传热与传质系数的经验关联式,沿湿化器高度积分,得到各参数及湿化器内传热传质推动力 焓差沿湿化器高度的变化,计算分析了湿化器的设计工况性能和变工况性能,为湿化器的设计和开发提供了理论依据 相似文献
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切片土豆干燥中传质过程模拟与分析 总被引：2，自引：0，他引：2
建立切片土豆内部传质模型，内部传热模型来研究土豆干燥过程的传质模拟，并进行了实验验证，验证结果表明：用整个物料平均水分来间接验证，模拟值和实测值十分接近，二者的最大相对偏差小于9．1％，模拟结果表明：土豆片表层水分在热风的作用下得到蒸发，水分下降很快，在表内水分差作用下内部水分向表层迁移，干燥过程中产生表低内高水分分布规律。 相似文献
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萃取过程包括液相到液相、固体到液相、气相到液相三种传质过程。但是在科学研究和生产实践中,萃取通常仅指液-液萃取过程,而将固-液传质过程称为"浸取",气液传质过程称为"吸收"。本文将讨论液-液萃取过程及设备。 相似文献
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多孔介质传热传质研究的意义与现状 总被引：9，自引：0，他引：9
本文简要论述在我国支持开展多孔介质传热传质基本研究的重要性和必要性,不仅对我国工农业发展有着广阔的实际应用背景,也是形成交叉和边缘学科的一个潜在生长点。 相似文献
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在金属表面络合网格状高分子膜实现滴状冷凝的MD模拟研究 总被引：4，自引：0，他引：4
提出了在铜表面络合上一种网格状高分子膜来实现水蒸汽滴状冷凝的新模型。预计这种单分子层的高分子膜可以被大片的配位键牢牢地粘附在金属表面上,并具有可自修复的特性,因而可望获得超长使用寿命和较高传热效率的滴状冷凝表面。根据相关的成膜或成滴的判据,用分子动力学模拟方法计算了水分子的内聚能和表面的吸附能。结果表明,在这种网格状高分子膜的表面上可以实现滴状冷凝。并且,通过观察粒子的平衡位型分布,可以看到网格状高分子中的大环结构可能起到核化中心位的作用。 相似文献
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焊接过程由于速度快，时间短，熔池成形迅速，所以对熔池形态的研完就显得非常复杂。本文主要是在分析TIG焊熔池中流体流动及传热过程本质的基础上，建立熔池的数学模型，特别对温度场模型进行了有限元化处理、并进行了初步的实验验证。 相似文献
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一、项目概况
温州市工业科学研究院成功研制了一种新型的过程强化设备：磁力驱动超重力旋转填料床。其工作原理是高速运转的填料转子会产生数百倍至千倍重力的离心力（即超重力）,由此液相在填料表面形成液膜,液膜快速向外环流动的同时厚度急剧减小,载体相界面积增加导致了由液相控制的传质、传热和反应过程得到极大的强化。 相似文献
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金属相变高温贮存太阳能的研究 总被引：3，自引：0，他引：3
本文讨论了太阳能金属相变高温贮能技术的有关问题。筛选出两种适宜于不同辐射强度下能高温贮能材料，并对其热物性参数进行了测量。研究了太阳能金属相变高温贮能过程的传热与传质。并介绍两种太阳能金属相变贮能技术装置。 相似文献
11.
We investigate single DNA stretching dynamics in a de-wetting flow over micropillars using Brownian dynamics simulation. The Brownian dynamics simulation is coupled with transient flow field computation through a numerical particle tracking algorithm. The droplet formation on the top of the micropillar during the de-wetting process creates a flow pattern that allows DNA to stretch across the micropillars. It is found that DNA nanowire forms if DNA molecules could extend across the stagnation point inside the connecting water filament before its breakup. It also shows that DNA locates closer to the top wall of the micropillar has higher chance to enter the flow pattern of droplet formation and thus has higher chance to be stretched across the micropillars. Our simulation tool has the potential to become a design tool for DNA manipulation in complex biomicrofluidic devices. 相似文献
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We conduct a numerical investigation and analytical analysis of the effect of slippage on the thermocapillary migration of a small liquid droplet on a horizontal solid surface. The finite element method is employed to solve the Navier-Stokes equations coupled with the energy equation. The effect of the slip behavior on the droplet migration is determined by using the Navier slip condition at the solid-liquid boundary. The results indicate that the dynamic contact angles and the contact angle hysteresis of the droplet are strictly correlated to the slip coefficient. The enhancement of the slip length leads to an increase in the droplet migration velocity due to the enhancement of the net momentum of thermocapillary convection vortices inside the droplet. A larger contact angle leads to an increase in the migration velocity which in turn enlarges the rate of the droplet migration velocity to the slip length. There is good agreement between the analytical and the numerical results when the dynamic contact angle utilizes in the analytical approach obtained from the results of the numerical computation, and the static contact angle is smaller than 50°. 相似文献
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Xiaowei Xu Lining Sun Liguo Chen Zhaozhong Zhou Junjian Xiao Yuliang Zhang 《Biomicrofluidics》2014,8(6)
Digital microfluidics based on electrowetting on dielectric is an emerging popular technology that manipulates single droplets at the microliter or even the nanoliter level. It has the unique advantages of rapid response, low reagent consumption, and high integration and is mainly applied in the field of biochemical analysis. However, currently, this technology still has a few problems, such as high control voltage, low droplet velocity, and continuity in flow, limiting its application. In this paper, through theoretical analysis and numerical simulation, it is deduced that a drive electrode with a crescent configuration can reduce the driving voltage. The experimental results not only validate this deduction but also indicate that crescent electrode can improve the droplet motion continuity and the success in split rate. 相似文献
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In this study, droplet formations in microfluidic double T-junctions (MFDTD) are investigated based on a two-dimensional numerical model with volume of fluid method. Parametric ranges for generating alternating droplet formation (ADF) are identified. A physical background responsible for the ADF is suggested by analyzing the dynamical stability of flow system. Since the phase discrepancy between dispersed flows is mainly caused by non-symmetrical breaking of merging droplet, merging regime becomes the alternating regime at appropriate conditions. In addition, the effects of channel geometries on droplet formation are studied in terms of relative channel width. The predicted results show that the ADF region is shifted toward lower capillary numbers when channel width ratio is less than unity. The alternating droplet size increases with the increase of channel width ratio. When this ratio reaches unity, alternating droplets can be formed at very high water fraction (wf = 0.8). The droplet formation in MFDTD depends significantly on the viscosity ratio, and the droplet size in ADF decreases with the increase of the viscosity ratio. The understanding of underlying physics of the ADF phenomenon is useful for many applications, including nanoparticle synthesis with different concentrations, hydrogel bead generation, and cell transplantation in biomedical therapy. 相似文献
15.
Spherical and non-spherical wax microparticles are generated by employing a facile two-step droplet microfluidic process which consists of the formation of molten wax microdroplets in a flow-focusing microchannel and their subsequent off-chip crystallization and deformation via microdroplet impingement on an immiscible liquid interface. Key parameters on the formation of molten wax microdroplets in a microfluidic channel are the viscosity of the molten wax and the interfacial tension between the dispersed and continuous fluids. A cursory phase diagram of wax morphology transition is depicted depending on the Capillary number and the Stefan number during the impact process. A combination of numerical simulation and analytical modeling is carried out to understand the physics underlying the deformation and crystallization process of the molten wax. The deformation of wax microdroplets is dominated by the viscous and thermal effects rather than the gravitational and buoyancy effects. Non-isothermal crystallization kinetics of the wax illustrates the time dependent thermal effects on the droplet deformation and crystallization. The work presented here will benefit those interested in the design and production criteria of soft non-spherical particles (i.e., alginate gels, wax, and polymer particles) with the aid of time and temperature mediated solidification and off-chip crosslinking. 相似文献
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Here, we report a unique microfluidic technique that utilizes a membrane filter and plug-in tubes to remove oil and pack water-in-oil droplets for controlled incubation of droplet-based assays. This technique could be modularly incorporated into most droplet-generation devices without a need to alter the original designs. Our results show that removing excess oil to form tightly packed droplets allows for extended and controllable incubation for droplets traveling in microchannels. The efficiency of this technique was evaluated and confirmed using a time-dependent enzyme assay with a fluorometric readout. The system is also readily generalizable to control inter-droplet distance, crucial for studying droplet communication and pattern formation. 相似文献
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We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results. 相似文献
18.
This paper proposes a simple scenario to describe the coalescence of sessile droplets. This scenario predicts a power-law growth of the bridge between the droplets. The exponent of this power law depends on the driving mechanism for the spreading of each droplet. To validate this simple idea, the coalescence is simulated numerically and a basic experiment is performed. The fluid dynamics problem is formulated in the lubrication approximation framework and the governing equations are solved in the commercial finite element software COMSOL. Although a direct comparison of the numerical results with experiment is difficult because of the sensitivity of the coalescence to the initial and operating conditions, the key features of the event are qualitatively captured by the simulation and the characteristic time scale of the dynamics recovered. The experiment consists of inducing coalescence by pumping a droplet through a substrate which grows and ultimately coalesces with another droplet resting on the substrate. The coalescence was recorded using high-speed imaging and also confirmed the power-law growth of the neck. 相似文献
19.
锅炉排烟温度过高会造成热损失,增设低压省煤器对于降低电厂排烟温度,提高电厂热经济性,保护空气预热器的安全运行具有重要意义。H型鳍片管是一种广泛应用于低压省煤器的换热元件。本文以一种H型鳍片管为例,通过数值模拟对其传热过程进行了分析,获得了H型鳍片管翅片侧表面传热系数和流动阻力随烟气流速和鳍片节距的变化规律。 相似文献
20.
One challenge of generating a liquid aerosol is finding an efficient way to break up bulk amounts of the compound into micron-sized droplets. Traditional methods of aerosol generation focus on the principle of creating the liquid droplets by blowing air at high speed over or through a liquid. In this study, a novel micropump droplet generator (MDG) is proposed based on a microfluidics device to produce monodisperse droplets on demand (DoD). The micropump design was employed to both pump the fluid into the air and to encourage droplet breakup and aerosol formation. Computational simulation modeling of the new MDG was developed and validated with comparisons to experimental data for current generators. The device was found to produce an aerosol similar to a vibrating orifice DoD device. Most importantly, the input power required by the newly proposed device (MDG) was several orders of magnitude below existing DoD generators for a similar droplet output. Based on the simulation results obtained in comparison with current DoD generators, the MDG device performed effectively at higher frequencies, smaller nozzle diameters, and regardless of the liquid viscosity of the solution. 相似文献