Boundary condition, an old but not well solved problem, linked from nanometer to macroscale

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A key issue of the flow and heat transfer in channels is to determine the boundary condition, which is affected by various parameters, such as the solid-fluid potential interactions, solid wall roughness, surface wettability etc. We summarize the progress that has been made in recent years. In the first part of this paper, we reviewed the three-atom-model, leading to an important criterion number governing the boundary conditions. The molecular dynamics (MD) simulations verified the effectiveness of the criterion number. The second part of this paper reports the multiscale simulation of the flow field in channels, adjoining the molecular dynamics (MD) simulation and the continuum fluid mechanics. Three types of boundary conditions (slip, non-slip and locking) were identified over the multiscale channel sizes. The slip lengths are found to be mainly dependent on the interfacial parameters with the fixed apparent shear rate. The channel size has little effects on the slip lengths if the size is above a critical value within a couple of tens of molecular diameters. The slip, non-slip and locking interfacial parameters yield positive, zero and negative slip lengths, respectively. The three types of boundary conditions existing in “microscale” still occur in “macroscale”. However, the weak dependence of the slip lengths on the channel size yields decreased slip velocities with increases in channel sizes for all three types of interfacial parameters.This study is supported by the National Natural Science Foundation of China (No. U1034004 and 50825603), and the Basic Research Program (973 program) with the contract number of 2011CB710703

Evaluation of electroosmotic pumping effect in microporous media flow

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In this paper, the electroosmotic flow (EO) in desiccant powders of micro porous is investigated regarding to the flow rate caused by the electroosmosis and the gravity. In particular, the coupling effect of electroosmosis and dehumidification in the flow is studied. It is noticeable that the actual electroosmosis pumping force maintains at a certain rate (10μL/min for the designed system). It is interpreted that the actual voltage from bench power is kept constant which exerts same effect of electric field on the desiccant particles. And during this stage the resistance inside the channel deceases with the rate of water entering into the electroosmosis pumping section which is affected by the capacity of dehumidification of the desiccant particles. Moreover, the mass flow rate by the effect of electroosmosis pumping can be achieved at 0.746 gm-2m-1 under 5V DC supply. These experimental results in this study provide useful instructions of electroosmosis performance for designing the micro porous channel in such as filtering the compounds of drug delivery, particle purification and liquid separation applications etc

Numerical simulation of viscous fingering phenomenon in immiscible displacement of two fluids in porous media using Lattice Boltzmann method

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In the present study, viscous fingering phenomenon, which occurs when a less viscous fluid (e.g. supercritical carbon dioxide) is injected into simplified porous media to displace a more viscous fluid (e.g. crude oil), is investigated by a mesoscopic approach-the lattice Boltzmann method (LBM). Due to its convenience in dealing with complex fluids of different viscosities, the pseudo-potential model is employed to study the effects of the capillary number, Bond number and viscosity ratio between the displaced fluids and displacing fluid; as such effects reflect the competition of viscous force and surface tension and gravity forces during viscous fingering. The numerical procedure is validated against a series of droplet tests, in which surface tension can be determined. By changing the injecting velocity of the displacing fluid and gravitational acceleration, the displacement processes under conditions of different capillary number and Bond number are investigated. The finger pattern is presented in this paper. The effects of capillary number, Bond number and viscosity ratio are discussed in detail. The ability and suitability of the lattice Boltzmann method for simulating multi-component fluids displacement in porous media are proved in our work.This work is supported by China Scholarship Council (CSC)

Casimir Dispersion Forces and Orientational Pairwise Additivity

A path integral formulation is used to study the fluctuation-induced interactions between manifolds of arbitrary shape at large separations. It is shown that the form of the interactions crucially depends on the choice of the boundary condition. In particular, whether or not the Casimir interaction is pairwise additive is shown to depend on whether the ``metallic'' boundary condition corresponds to a ``grounded'' or an ``isolated'' manifold.Comment: 6 pages, RevTe

Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV

We report on a search for a high mass, narrow width particle that decays directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence of lepton flavor violating decays is found. Limits are set on the production and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex

Comparison of Temperature-Dependent Hadronic Current Correlation Functions Calculated in Lattice Simulations of QCD and with a Chiral Lagrangian Model

The Euclidean-time hadronic current correlation functions, $G_P(\tau, T)$ and $G_V(\tau, T)$, of pseudoscalar and vector currents have recently been calculated in lattice simulations of QCD and have been used to obtain the corresponding spectral functions. We have used the Nambu-Jona-Lasinio (NJL) model to calculate such spectral functions, as well as the Euclidean-time correlators, and have made a comparison to the lattice results for the correlators. We find evidence for the type of temperature dependence of the NJL coupling parameters that we have used in previous studies of the mesonic confinement-deconfinement transition. We also see that the spectral functions obtained when using the maximum-entropy-method (MEM) and the lattice data differ from the spectral functions that we calculate in our chiral model. However, our results for the Euclidean-time correlators are in general agreement with the lattice results, with better agreement when our temperature-dependent coupling parameters are used than when temperature-independent parameters are used for the NJL model. We also discuss some additional evidence for the utility of temperature-dependent coupling parameters for the NJL model. For example, if the constituent quark mass at T=0 is $352 {MeV}$ in the chiral limit, the transition temperature is $T_c=208 {MeV}$ for the NJL model with a standard momentum cutoff parameter. (If a Gaussian momentum cutoff is used, we find $T_c=225 {MeV}$ in the chiral limit, with $m=368 {MeV}$ at T=0.) The introduction of a weak temperature dependence for the coupling constant will move the value of $T_c$ into the range 150-170 MeV, which is more in accord with what is found in lattice simulations of QCD with dynamical quarks

Ubiquitous e-learning System for dynamic mini-courseware assembling and delivering to mobile terminals

From 2000, mobile Learning (m-Learning) and ubiquitous Learning (u-Learning) has been the hottest research topic in e-learning, and now, integrating ubiquitous learning into mainstream of education and train has been the direction in the area, which demand new generational e-learning system. The paper introduces our research efforts in this direction. Based on the key concepts, such as ubiquitous learning object, mini-courseware, a new generational ubiquitous e-learning system is designed, which can be used for new requirements in m-Learning and u-Learning environments. In the system, learning resource related to a course is encapsulated into different ubiquitous learning objects, and mini-courseware can be assembled dynamically with learning resource extracted from these ubiquitous learning objects, accordingly, a mini-courseware player is designed for the situation. Based on these work, a resource based ubiquitous e-Learning system is designed considering pedagogical requirements under m-Learning and u-Learning environment