Effectiveness of radiation and Joule heating on hydromagnetic Carreau fluid through microfluidic channels with slip boundary conditions

Microsystem Technologies - In the present article, the fundamental flows (such as both the plates are moving in the opposite directions, lower plate is moving with constant velocity and other is at...     

Ferromagnetic nano model study for the peristaltic flow in a plumb duct with permeable walls

Microsystem Technologies - The purpose of the present enquiry is to analyse the mechanics of an incompressible fluid, with water as base fluid, through a radially symmetric plumb duct with...     

Steady flow around and through a permeable circular cylinder

The steady flow around and through a porous circular cylinder was studied numerically. The effects of the two important parameters, the Reynolds and Darcy numbers, on the flow were investigated in details. The recirculating wake existing downstream of the cylinder is found to either penetrate into or be completely detached from the cylinder. It is also found that, contrary to that of the solid cylinder, the recirculating wake develops downstream of or within the porous cylinder, but not from the surface of it. These new findings provide additional evidence to Leal’s conclusion (Leal LG. Vorticity transport and wake structure for bluff bodies at finite Reynolds number. Phys Fluids A 1989;1:124) that the appearance of recirculating wakes at finite Reynolds number is due to vorticity accumulation, but not a result of the same physical phenomena associated with separation in boundary layers in adverse pressure gradients. Also presented in the current study are the variation of the critical Reynolds number for the onset of a recirculating wake as a function of Darcy number and the variation of a newly defined parameter, the penetration depth, as a function of the Reynolds number and Darcy number.     

Compressible swirling flow through a significantly bent duct

The three-dimensional vortical flow of an inviscid compressible fluid through a bend in a slender duct is considered. The duct of simple cross-section gradually bends the flow through a substantial angle. The flow is motivated by industry and involves high speeds and short time intervals. The relative radius of curvature and the magnitude of the inertial forces are important factors here. Weakly and fully non-linear coupling between the streamwise and cross-sectional velocities is considered, and numerical results are derived for a duct of rectangular cross-section in each case, based on a fourth-order compact-differencing approach to solving the three-dimensional Euler equations. The governing equations are parabolic in the streamwise direction, enabling a forward-marching approach. The bend leads to significant growth in vorticity which mixes the streamwise velocity. The weakly non-linear study reveals a role for compressibility which is absent in the fully non-linear study when the cross-sectional area is constant. In both cases there is relatively little pressure loss, in contrast to viscous flows. Linear growth of the total streamwise vorticity in the bend is shown analytically to occur in keeping with the numerical solutions. Far downstream behaviours in finite bends and bends which continue indefinitely are investigated. The latter case leads to a more strongly non-linear flow structure far downstream due to continued evolution of the vorticity.     

Productivity through computer management of a fully automated transportation system

The Morgantown Personal Rapid Transit System is a fully automated, collection and distribution, origin to destination, non-stop transportation system. The system consists of a feet of 73 electrically powered, rubber tired, passenger carrying vehicles, operating on a dedicated guideway network at 15 second headways. The system provides a safe, comfortable non-polluting, reliable means of public transportation between the Central Business District of Morgantown, West Virginia, and the three separated campuses of West Virginia University.

This paper will address the unique application of computers in operating a public transit system which is considered the first of its kind anywhere in the world.     

Two-stage inventory models with a bi-modal transportation cost

This paper discusses inventory models over an infinite planning horizon with constant demand rate and two modes of transportation. These transportation options include truckloads and a less than truckload carrier. An optimal algorithm is derived for a one-warehouse one-retailer system. A power-of-two heuristic algorithm is also proposed for a one-warehouse multi-retailer system. Computational results are provided to show that, on the average, the heuristic algorithm is at least 94% effective.     

Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method

ZnO nanopowders were prepared through microwave heating method. ZnO thick film sensors were fabricated by using ZnO nanopowders as sensing materials. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The gas-sensing properties of the sensors based on ZnO nano-materials were investigated. It was found that the sensor based on ZnO nano-materials (low power, 10× 10 min) exhibited very high responses to benzene and toluene when operating at 440 and 370 °C, respectively; but the sensor based on ZnO (low power, 10× 10 min) showed very low responses to benzene and toluene when operating at 205–215 °C. The sensor based on ZnO (low power, 10× 10 min) showed high response and good selectivity to dilute formaldehyde when operating at 210 °C; especially, the response to 0.001 ppm HCHO attained 7.4 when operating at 210 °C.     

MHD flow in a rectangular duct with a perturbed boundary

The unsteady magnetohydrodynamic (MHD) flow of a viscous, incompressible and electrically conducting fluid in a rectangular duct with a perturbed boundary, is investigated. A small boundary perturbation $\epsilon$ is applied on the upper wall of the duct which is encountered in the visualization of the blood flow in constricted arteries. The MHD equations which are coupled in the velocity and the induced magnetic field are solved with no-slip velocity conditions and by taking the side walls as insulated and the Hartmann walls as perfectly conducting. Both the domain boundary element method (DBEM) and the dual reciprocity boundary element method (DRBEM) are used in spatial discretization with a backward finite difference scheme for the time integration. These MHD equations are decoupled first into two transient convection–diffusion equations, and then into two modified Helmholtz equations by using suitable transformations. Then, the DBEM or DRBEM is used to transform these equations into equivalent integral equations by employing the fundamental solution of either steady-state convection–diffusion or modified Helmholtz equations. The DBEM and DRBEM results are presented and compared by equi-velocity and current lines at steady-state for several values of Hartmann number and the boundary perturbation parameter.     

Direct computation of the noise induced by a turbulent flow through a diaphragm in a duct at low Mach number

A direct computation of the noise radiated by a turbulent flow in a duct obstructed by a diaphragm is performed by compressible large-eddy simulation. For the low Mach number configuration considered, a two-step hybrid method could be less expensive, but would fail at characterizing sound-flow interactions. The application of direct calculation is thus challenging but gives both the acoustic and aerodynamic fields in the same computation in order to shed light on the noise generation mechanisms. Acoustic energy is produced and dissipated in the asymmetric jet-type flow issuing from the diaphragm. A low-frequency radiation is correlated with the breakdown of the coherent jet-column structures as the plane jet reattaches the upper wall. The Kelvin-Helmholtz vortices in the shear layers of the jet constitute the primary instabilities but do not radiate sound. On the contrary, this vorticity shedding seems to dissipate waves propagating upstream by enforcing the unsteady Kutta condition.     

New control problems associated with a proposed future space transportation infrastructure

Operation management is an essential technology for the “OTV (Orbital Transfer Vehicle) Network” which has been proposed as a promising space transportation infrastructure for the next century. In addition to the nominal mode scheduling, the management system must quickly re-make the schedule in the case of failures of some system elements, inputs of urgent missions or mission alterations. This paper analyses this management as a new control problem, and proposes a distributed artificial intelligence-type system architecture to deal with it. The effectiveness of the system has been verified by simulation studies assuming practical problem settings.     

Flow of a newtonian fluid in a blood vessel with permeable wall—A theoretical model

A perturbation solution of the flow of a homogeneous Newtonian fluid through a tube of finite length with a permeable wall is analysed through a theoretical model in view of its applications in hemodynamics. The flow is characterized by three important parameters: G, the characteristic Reynolds number associated with the pressure outside the tube, β the ratio of radius to length of the tube, and ε a filtration coefficient. ε is assumed to be small so that the validity of the perturbation method is ensured. Perturbation solutions obtained up to O(ε²) are discussed.     

Logical models of the transportation network of a plant with progressive operations

A technique for describing a complex structural diagram of plants with progressive operations in the form of a system of logical functions whose variables can be both aggregates of the transportation network of the plants and larger blocks, i.e., channels is proposed. A method for searching and eliminating potentially false paths of the system is devised as well as a method for taking into account specified constraints on the mutual operation of parallel channels.     

Solving bicriteria solid transportation problem with fuzzy numbers by a genetic algorithm

The proposed Genetic Algorithms (GAs) are incorporated with problem-specific knowledge and the decision maker's degree of optimism, and the criteria space approach for bicriteria linear program conductive to find out the nondominated extreme points in the criteria space.     

Cooling load prediction in a district heating and cooling system through simplified robust filter and multilayered neural network

Cooling load is a heat value of cold water used for air conditioning in a district heating and cooling system. Cooling load prediction in a district heating and cooling system is one of the key techniques for smooth and economical operation. In this article, cooling load prediction in such a district heating and cooling system is considered. Unfortunately, since actual cooling load data usually involve measurement noises, outliers, and missing data for several reasons, a prediction method considering the effect of the outliers and missing data is desirable. In this article, a new prediction method using a simplified robust filter to improve a numerical stability problem of a robust filter and a three-layered neural network, is proposed. Applications of the proposed method and some other methods to actual cooling load data in a district heating and cooling system involving outliers and missing data show the usefulness of the proposed method.     

Research on a large power thermal bubble micro-ejector with induction heating

The present study investigates a large power thermal bubble micro-ejector with induction heating device. The traditional thermal-bubble ejectors adopted resistors as the heating resources, it can only work with lower power and convey liquid with lower flow rate. Induction heating devices are adopted to replace the resistor for heating liquid in this paper. With this heating method, there is no physical contact between the heating core and the external power supply circuit. The liquid in the chamber of micro-ejector is heated by the induction heating device and changes from liquid phase to gas phase, generating vapor bubbles in the micro chamber of the micro ejector. The bubble expands rapidly and ejects droplets through the nozzle. The prototype of the micro-ejector is fabricated and experiments are carried out. Continuous droplets are ejected out from the nozzle as the applied AC current is 0.6–0.65 A with the power frequency of 100 kHz. The total volume of the continuous droplets is ranging from 18.84 to 49.87 nL, and the corresponding flow rate is about 0.52–1.36 μL/min. Furthermore, this new micro-ejector can be adopted in conveying of micro-scale liquid, the injection of trace drugs and the 3D printing.     

Microfluidic phase change valve with a two-level cooling/heating system

A phase change (PC) microvalve with an integrated two-level cooling/heating system is developed for microfluidic applications in this article. This PC microvalve utilizes the liquid–solid PC of a small portion of the working medium in a microchannel to switch on/off the flow in the microchannel. The size of the working medium for the PC microvalve is 5-mm long, 50-μm high, and 80-μm wide (50 μm × 80 μm is the cross-sectional area of the channel) in this study. The switch is actuated by using a two-level cooling/heating system integrated on the chip. The first-level cooling/heating unit keeps the working medium in the valve area in the temperature range of supercooling state. Based on the supercooling state, the second-level cooling/heating unit either heats up or cools down the medium in the valve area to trigger its PC between liquid and solid for valving purposes. The proposed microfluidic PC microvalve is characterized experimentally in microfluidic chips. The thermal impact of one PC microvalve in one particular microchannel on its adjacent channels is discussed by establishing a preliminary analytical model and a numerical model. In addition to no leakage and no moving element, this PC microvalve with a two-level cooling/heating system can achieve a very short cooling time (i.e., 2.72 s).     

Natural convection boundary layer of a non-Newtonian fluid about a permeable vertical cone embedded in a porous medium saturated with a nanofluid

An analysis was performed to study the effect of uniform transpiration velocity on free convection boundary-layer flow of a non-Newtonian fluid over a permeable vertical cone embedded in a porous medium saturated with a nanofluid. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing partial differential equations are transformed into a set of non-similar equations and solved numerically by an efficient implicit, iterative, finite-difference method. Comparisons with previously published work are performed and excellent agreement is obtained. A parametric study of the physical parameters is conducted and a representative set of numerical results for the velocity, temperature, and volume fraction profiles as well as the local Nusselt and Sherwood numbers is illustrated graphically to show interesting features of the solutions.     

Solder bonding with a buffer layer for MOEMS packaging using induction heating

In this paper, the selective induction heating technology is applied to glass–glass and glass–silicon solder bonding for MOEMS (optical MEMS) packaging. The Ni bumping with a buffer layer is successful to release the thermal stress for avoiding delamination. The Au wetting layer must be thick enough to prevent from being solved entirely into Sn, and it will improve bonding strength. The bonding specimens are soaked into 25°C water and placed into 85°C/85% RH oven, respectively. No moisture penetrates into the cavity after 1 day in both test conditions. In the test condition of 125°C leakage-test liquid (Galden HS260), no bubble is observed. The lowest bonding strength is 3 MPa.     

Solder bonding with a buffer layer for MOEMS packaging using induction heating

In this paper, the selective induction heating technology is applied to glass–glass and glass–silicon solder bonding for MOEMS (optical MEMS) packaging. The Ni bumping with a buffer layer is successful to release the thermal stress for avoiding delamination. The Au wetting layer must be thick enough to prevent from being solved entirely into Sn, and it will improve bonding strength. The bonding specimens are soaked into 25°C water and placed into 85°C/85% RH oven, respectively. No moisture penetrates into the cavity after 1 day in both test conditions. In the test condition of 125°C leakage-test liquid (Galden HS260), no bubble is observed. The lowest bonding strength is 3 MPa.

     

Contracting cleaning services in a European public underground transportation company with the aid of a DSS

This paper deals with the selection of a supplier for cleaning services in a European public underground transportation company as established in the European Community directives, where several conflicting criteria, such as improving service levels and reducing total service costs, must be taken into account simultaneously. The problem is analyzed in depth using the decision analysis methodology, and a decision support system, the Generic Multi-Attribute Analysis system, is used to allay the operational difficulties involved. This system can deal with incomplete information about decision-maker preferences, accounts for uncertainty about offer performance, and uses so-called decision-making with partial information to identify the best offer, taking advantage of imprecise inputs.