All-printed and highly stable organic resistive switching device based on graphene quantum dots and polyvinylpyrrolidone composite

We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope.     

Predicting friction reliably and accurately in journal bearings—A systematic validation of simulation results with experimental measurements

It is the aim of this work to predict friction in journal bearings reliably and accurately under realistic dynamic working conditions. To this purpose elastohydrodynamic (EHD) calculations using an extensive oil-model and including an approach to the conformal roughnesses of the bearing surfaces are carried out for transient loads typical for current utility vehicles (40 MPa) as well as for considerably higher specific loads (70 MPa) and for different lubricants (SAE10, SAE20, SAE30 and SAE40) to account for a large span of working conditions ranging from full film lubrication to mixed lubrication with metal-metal contact.The results obtained from this simulation model are compared to measurements performed on a journal bearing test rig. We find that the results of the presented approach agree very closely with the experimental values. The presented approach allows consequently to investigate the effectiveness of changes in bearing geometry, bearing materials, bearing surface roughness, lubricant viscosity and engine operating conditions to reduce friction in journal bearings.     

Effect of 3D lip deformations on elastohydrodynamic lip seals behaviour

The numerical simulation of comparative elastohydrodynamic lubrication between axisymmetrical and 3D elastic approaches on the radial lip seals is presented in order to determine the 3D effect of the elastic aspect of the seal lip. Indeed, the consideration of 3D model in other words the circumferential variation of the lip elastic deformation indicated a difference in the deformation distribution of the lip compared to the axisymmetrical approach. Consequently, the results show that the presence of the circumferential variation of the seal lip deformation has a significant effect on the pumping rate values.     

Lubrication properties of non-adsorbing polymer solutions in soft elastohydrodynamic (EHD) contacts

The in-use performance and processing of many consumer products in the food, home and personal care industries are dependent on their tribological properties. A major component of these products is often a high molecular weight polymer, which is typically used to thicken aqueous systems. Polymer solutions tend to be non-Newtonian, and in particular their viscosity varies with shear rate, such that it is difficult to predict their friction or hydrodynamic film-forming behaviour. The present work relates the tribology of aqueous polymer solutions to their rheological properties in thin films in ‘soft’ contacts at high shear rates. The friction properties of three types of polymers in aqueous solution, polyethylene oxide, PEO; xanthan gum, XG; and guar gum, GG, have been studied as a function of polymer concentration over a wide range of entrainment speeds in a point contact formed between silicone rubber and steel. This has enabled the boundary lubrication and isoviscous-elastic lubrication properties of the solutions to be investigated using both hydrophilic and hydrophobic silicone surfaces.It is found that the friction vs. entrainment speed dependence follows the shape of a classical Stribeck curve. In general, a lower friction is observed with increasing polymer concentration in the mixed-regime. Using scaling factors for the entrainment speed, we have shown that this decrease in friction is likely to be due to viscous effects and that the scaling factors represent effective high shear rate viscosities. In the case of PEO and XG, and GG at low concentrations, a good correlation is found between this effective viscosity and the apparent viscosity measured at the highest shear rates attainable with the available rheometer. However, for GG at concentrations above 0.2%, the effective viscosity decreases with increasing polymer content.The three polymers do not significantly reduce friction in the boundary regime and in general give essentially the same response as water when an effective viscosity is taken into account. However, a slight increase in friction in comparison to pure water has been observed for XG and GG on hydrophobic surfaces. It is suspected that this may be due to a blocking of fluid entrainment, or possibly exclusion of polymer from the contact, due to the large hydrodynamic volume and rigid nature of the two biopolymers. Finally, for PEO solutions with full-film elastohydrodynamic conditions were reached, the measured friction coefficient of the film correlated quite well with the value calculated from the effective viscosity.     

纯低温余热发电模型的研究

根据系统动力循环原理及工质循环发电的特点,组建了纯低温余热发电系统模型,并对EHD蒸发器,冷凝器等进行了设计,并在此基础上提出了应综合考虑"吨熟料余热发电量"和"混合热效率"来评价纯低温余热发电效率,该模型在纯低温余热发电工程中具有推广价值.     

On the modeling of electro-hydrodynamic flow in a wire-plate electrostatic precipitator

Modeling of the flow velocity fields for the electrohydrodynamic (EHD) flow in a wire-to-plate type electrostatic precipitator (ESP) was achieved. Solutions of the steady, two-dimensional Navier-Stokes equations have been computed. The equations were solved in the conservative finite-difference form on a fine uniform rectilinear grid of sufficient resolution to accurately capture the momentum boundary layers. The numerical procedure for differential equations was used by SIMPLEST [Michel, 2002], a derivative of Patankar’s SIMPLE algorithm, to bring rapid convergence. The Phoenics (Version 3.5.1) CFD code, coupled with Poisson’s and ion transport equations and electric body force in the momentum equation, developed in this study, was used for the numerical simulation. From calculations for the flow employing different flow models, the Chen-Kimk-ε turbulent model appeared to be the most appropriate choice to obtain a quantitative image of the resulting mean flow field and downstream wake flow of the rear wire, although this was obtained from a qualitative analysis due to the lack of experimental verification. The flow velocity field pattern showed a strong EHD secondary flow, which was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re_CW=12.4). Secondary flow vortices were also caused by the EHD with increases in the discharge current     

Electrohydrodynamic (EHD) enhancement of boiling heat transfer of R 113+WT4% ethanol

Nucleate boiling heat transfer for refrigerants, R113, and R113+ wt4% ethanol mixture, an azeotropic mixture under electric field was investigated experimentally in a single-tube shell/ tube heat exchanger. A special electrode configuration which provides a more uniform electric field that produces more higher voltage limit against the dielectric breakdown was used in this study. Experimental study has revealed that the electrical charge relaxation time is an important parameter for the boiling heat transfer enhancement under electric field. Up to 1210% enhancement of boiling heat transfer was obtained for R113+wt4% ethanol mixture which has the electrical charge relaxation time of 0.0053 sec whereas only 280% enhancement obtained for R113 which has relaxation time of 0.97 sec. With artificially machined boiling surface, more enhancement in the heat transfer coefficient in the azeotropic mixture was obtained.     

Electrohydrodynamic pulsatile flow in a channel bounded by porous layer of smart material

Electrohydrodynamic dispersion due to pulsatile flow in a channel bounded by porous layer of smart material is studied considering both steady and unsteady cases using both BJ and BJR-slip conditions. We found that in the case of steady flow, the dispersion coefficient, decreases with an increase in electric number W_e but increases with an increase in porous parameter σ_p in the case of BJ-slip condition. However this nature is different in the case of BJR-slip condition in the sense that the dispersion coefficient, increases for certain values of W_e and then decreases with an increase in W_e. In the case of unsteady flow, the dispersion coefficient, , decreases with an increase in W_e and σ_p for both BJ and BJR conditions. In particular, we found that the value of for steady flow in the case of BJ-slip condition is less than that of unsteady flow. The opposite is true for BJR condition. The findings are useful in the design of robust and efficient artificial organs in the human body.     

Hydraulic Squeeze Bearing

Prior researchers find that: Where one of two horizontal parallel plates immersed in a fluid is forced to oscillate up and down, a load may be carried, providing the fluid is compressible. Application of Reynolds equation to such a squeeze film bearing supports the condition of compressibility.

However, analysis of the squeeze film bearing, including inertia terms in the Navier-Stokes equations, removes the restriction on compressibility.

Theoretical design of a hydraulic squeeze bearing driven sinusoidally shows that load capacity is improved over a similar gas squeeze bearing under usual design conditions, provided cavitation is prevented. Two cases are considered of a fixed and a free bearing. Torque, work input, and the effects of centrifugal force are analysed.     

On the Dynamics of Lubricated Cylindrical Roller Bearings,Part II: Linear and Nonlinear Vibration Analysis

This article is the second part of two companion papers. In the first article, curve-fitted relations of stiffness and damping coefficients of a single roller-to-race contact of lubricated roller bearings were developed. In the present work, these relations are applied to a rotor–bearing system. Two cases are studied to investigate the influence of lubricated cylindrical roller bearings on the vibration characteristics of the rotor system. In the first case, lubricated contacts are simulated as a linear spring–damper model. The overall stiffness and damping matrices are calculated by using the dynamic coefficients of individual load sharing rollers. These matrices are used in the finite element analysis of flexible rotor. In the second case, the nonlinear structural vibration of a lubricated cylindrical roller bearing is studied. Equations of motion of bearing elements are derived using the Lagrange equation. A nonlinear load–deflection contact model developed through the derived curve-fitted relations of dynamic coefficients is used in the equations of motion. Equations of motion are solved by a fourth-order Runge-Kutta integration method. The response of bearing elements under free vibration and due to rotating unbalance is studied for damped and undamped cases. Furthermore, results obtained using elastohydrodynamic finite and infinite contact theories are compared.