Uniform Flow Rate Research Articles

A Modelling Study of Segmentation of Naturally Ventilated Tall Office Buildings in a Hot and Humid Climate

The prevailing paradigm in indoor environment control of office buildings often excludes natural ventilation, due to the fact that its dynamic nature may not be compatible with the close control of mechanical conditioning systems. Due to the potential magnitudes of wind and buoyancy forces in tall buildings, the challenges are greater. This research is concerned with the prospect of purely naturally ventilated tall office buildings. The naturally available driving forces of wind and buoyancy are investigated separately or in combination. For the present study, it is proposed that “segmentation” might offer the least risky approach for envelope design of non-residential tall buildings. Two modelling approaches are adopted for investigating the segmentation effects. Firstly, the single-cell envelope flow model is evaluated under the steady state condition. Further dynamic effect with the multi-cell model is then examined using dynamic thermal simulation with an airflow network using ESP-r (ESRU, 2002). Segmented and non-segmented atrium buildings with ventilated double façades are adopted as the main building configurations in the second stage for coping with the potential magnitude of impinging wind at high levels. The overall objectives are to determine whether the magnitudes of airflow rates and the desired flow pattern through openings can be achieved over a range of specified conditions. Potential conditions where the design goals may not be ensured are identified. It is supposed that a seasonal control algorithm could be developed to provide the optimum desired flow pattern, sufficient flow rates for ventilated cooling and uniform air flow rates across floors. The control of segmentation can be achieved by the use of dampers between cavities for the naturally ventilated tall office building design in the climatic context of Taipei, Taiwan.

Numerical analysis of the gas flow rate uniformity in the molten carbonate fuel cell (MCFC) under various conditions

The gas distribution uniformity between anode channels in an indirect internal reforming type molten carbonate fuel cell (MCFC) is a crucial design parameter that influences both the electrical performance and durability. In this paper, a three-dimensional computational fluid dynamics (CFD) analysis was performed to investigate flow characteristics in the anode channels and manifold where shape, pressure drop and channel temperature conditions were varied. The combined mesh consists of a hexahedral mesh in the channels and a polyhedral mesh in the manifold. Results indicate that rotational flow develops at the left and right sides of the anode manifold that induces an uneven mass flow rate distribution in the anode channels. Gas flow rate uniformity is enhanced as the depth of the manifold decreases, as the pressure drop in the anode channels increases and as the temperature difference between the indirect internal reforming (IIR) channels and anode channels decreases.

Active surface tension driven micropump using droplet/meniscus pressure gradient

An active micropump with a simple layout and no moving parts is designed and fabricated which has on demand flow on/off capability. The micropump is based on droplet/meniscus pressure gradient generated by electrowetting on dielectric (EWOD). By altering the contact angle between liquid and solid using an electric field a pressure gradient was induced and a small droplet was pumped into the channel via a uniform flow rate. A surface tension based propellant method was introduced as a low power consumption actuation method in microfluidic devices. The liquid contact angle on the EWOD substrate was measured vs. electric potential and was used to obtain the capacitance of the substrate by fitting Young–Lippmann's equation. The capacitance of the EWOD substrate was also calculated to be 10±0.6μF/m2 by measuring the dielectric layer thickness which showed excellent agreement with the former method. EWOD setup parameters such as capacitance, saturation contact angle, hysteresis contact angle and onset voltage were discussed. A coupled theoretical–experimental model was developed to predict how much voltage is needed to start the micropump for different droplet sizes. The modeling results revealed that for droplets with a radius smaller than 0.4mm the droplet will start going into the channel even when no voltage is applied. For any larger droplet, a certain voltage is needed to start the pump. It was also shown that decreasing the size of the input droplet and increasing the voltage will result in an increase in the pump flow. A model for describing the shrinkage of the micropump input droplet was developed, based on direct observations, which was in agreement with the forced wetting described in literature. This model was compared to the other models used to describe passively pumped droplets and evaporating microdrops.

타워형 태양열 발전용 공기흡수기의 열전달 성능해석

In this study, a heat-transfer performance analysis is carried out for a multi-channel volumetric air receiver for a solar power tower. On the basis of a series of reviews regarding the relevant literature, a calculation process is proposed for the prediction of the wall- and air- temperature distributions of a single channel at given geometric and input conditions. Furthermore, a unique mathematical model of the receiver effectiveness is presented through analysis of the temperature profile. The receiver is made of silicon carbide. A total of 225 square straight channels per module are molded to induce the air flow, and each channel has the dimensions of . The heat-transfer rate, temperature distribution and effectiveness are presented according to the variation of the channel and module number under uniform irradiation and mass flow rate. The available air outlet temperature applied to the solar power tower should be over . This numerical model was actually used in the design of a 200 kW-level commercial solar air receiver, and the required number of modules satisfying the thermal performance could be obtained for the specified geometric and input conditions.

An efficient channel clustering and flow rate allocation algorithm for non-uniform microfluidic cooling of 3D integrated circuits

Heat removal problem has been a bane of three dimensional integrated circuits (3DICs). Comparing with other passive cooling techniques, microfluidic cooling appears to be an ideal cooling solution due to its high thermal conductivity and scalability. Without regarding to the fact of non-uniform power distribution of integrated circuits, existing microfluidic cooling with uniform cooling effort incurs large thermal gradient and wastes pump power. This can be avoided by the customized non-uniform cooling scheme proposed in this paper. The microfluidic channels are divided into clusters of relatively homogeneous power distribution and an appropriate flow rate setting is applied to each cluster based on the total flow rate and the maximum allowable temperature of the 3DIC. This paper proposes an efficient clustering algorithm to guide the division of microchannels into clusters and the allocation of cooling resources to each cluster in order to achieve an effective microfluidic cooling with minimal total flow rate. A compact steady state thermal simulator has been developed and verified. Supported by this fast and accurate thermal model, the proposed cooling method and clustering algorithm have been applied to a 3D multi-core testbench for simulation. Compared to the uniform flow rate cooling, the maximum temperature and thermal gradient were reduced under the same total flow rate settings. On the other hand, for a specific peak temperature constraint, up to 21.8% saving in total flow rate with moderate thermal gradients is achieved by the proposed clustered microfluidic cooling.

A Novel Multifilter PM10–PM2.5Sampler (MFPPS)

A novel multifilter PM10–PM2.5 sampler (MFPPS) that enables the collection of four PM10 and four PM2.5 samples simultaneously has been developed and tested. The MFPPS uses a PM10 impactor as the inlet and operates at 33.4 L/min. After the inlet, the aerosol flow is divided half by a Y-type fitting. Half of the flow is directed into four PM10 filter cassettes, while the other half is directed into four PM2.5 filter cassettes after the aerosols are further classified by a PM2.5 impactor. An active flow control system consisting of two mass flow controllers (MFCs), one for PM10 and the other for PM2.5, is used to fix the total flow rate of 16.7 L/min for four PM10 or four PM2.5 channels based on the ambient pressure and temperature. To ensure flow rate uniformity through each of the four PM10 or four PM2.5 filter cassettes, an orifice is assembled behind each of the filter cassettes to increase the pressure drop, such that the flow rates of eight sampling lines are nearly equal using just two MFCs. The MFPPS...

Out-scaling electrohydrodynamic atomization systems for the production of well-defined droplets

Industrial use of single-nozzle electrohydrodynamic atomization for producing aerosol particles of uniform size is limited by the small throughput of the method. To increase it, out-scaling by means of multiple nozzles is inevitable. We designed and tested a multi-nozzle system with a circular symmetry that provides a uniform flow rate and the same electric field intensity to all nozzles. Stability of particle production from multi-nozzle electrospray systems strongly depends on the precision of the liquid feeding system that typically requires high-cost pumps. A constant-head feeding system is a cost-effective alternative that can deliver the same performance. In order to describe the relation between flow rate and particle size in the constant-head operating mode, we developed a semi-empirical model that predicts the flow rate through the system. This model can be used with the conventional scaling law for predicting the diameter of the produced droplets.

Monitoring and measurement of radon activity in a new design of radon calibration chamber

Abstract A new radon calibration chamber has been designed, constructed and tested to set various desired environmental parameters. The chamber is cubic with two trapezoid sides with a total volume size of 0.498 m 3 . The three parameters, temperature, humidity and flow are controlled in the range of 20–45 °C (±2 °C), 10–70% (±2.5%) and 0.2–10 m 3 /min (±0.1 m 3 /min) respectively. The chamber is equipped with a controllable speed centrifugal fan to achieve a desirably uniform radon flow rate. Many parts of this system are controlled and monitored with a PLC (Programmable Logic Control) and HMI (Human Monitoring Interface) software (Citect Scada). Finally a radon detector (Alpha-Guard) registers the activity parameter.

Geometrical optimisation of a biochip microchannel fluidic separator

This article reports on the geometric optimisation of a T-shaped biochip microchannel fluidic separator aiming to maximise the separation efficiency of plasma from blood through the improvement of the unbalanced separation performance among different channel bifurcations. For this purpose, an algebraic analysis is firstly implemented to identify the key parameters affecting fluid separation. A numerical optimisation is then carried out to search the key parameters for improved separation performance of the biochip. Three parameters, the interval length between bifurcations, the main channel length from the outlet to the bifurcation region and the side channel geometry, are identified as the key characteristic sizes and defined as optimisation variables. A balanced flow rate ratio between the main and side channels, which is an indication of separation effectiveness, is defined as the objective. It is found that the degradation of the separation performance is caused by the unbalanced channel resistance ratio between the main and side channel routes from bifurcations to outlets. The effects of the three key parameters can be summarised as follows: (a) shortening the interval length between bifurcations moderately reduces the differences in the flow rate ratios; (b) extending the length of the main channel from the main outlet is effective for achieving a uniformity of flow rate ratio but ineffective in changing the velocity difference of the side channels and (c) decreasing the lengths of side channels from upstream to downstream is effective for both obtaining a uniform flow rate ratio and reducing the differences in the flow velocities between the side branch channels. An optimisation process combining the three parameters is suggested as this integration approach leads to fast convergent process and also offers flexible design options for satisfying different requirements.

Geometric design of slider-crank mechanisms for desirable slider positions and velocities

In problems requiring uniform cutting speeds uniform flow rates etc. slider-crank mechanisms provide economical solutions. Thus, the problem of designing slider-crank mechanisms for desirable slider positions and velocities is handled within a geometric framework in this paper. Here, the rotation of the crank has been related to the translation of the slider through a linear function. A unified methodology comprising the so-called Subdomain, Galerkin methods together with the classical collocation method is implemented to find the values of the parameters involved. The effectiveness of the methodology has been demonstrated on numerical examples. Since more than one solution results from the solution process, it is always possible to form multi-loop mechanisms. Moreover, designs with low velocity errors in the forward stroke exhibit similar feature in the backward stroke too.

Performance prediction of an improved air-cooled steam condenser with deflector under strong wind

For an air-cooled steam condenser (ACSC), environmental wind can cause a large flow rate reduction in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a heat transfer reduction. This leads to an increase of turbine back pressure, and occasional turbine trips occur under extremely gusty conditions. A new method is proposed in this paper to remove the strong wind effect by adding deflecting plates under the air-cooled platform, which contributes to forming a uniform air mass flow rate in the axial fans by leading enough cooling air to the fans in the upwind region. Numerical simulation is made of the thermal-flow characteristics and heat transfer performance of the improved ACSC with deflectors. A heat exchanger model is used for simulating the flow and heat transfer in the ACSC, in which the heat exchanger is simplified to a porous medium and all flow losses are taken into account by a viscous and an inertial loss coefficient. A fan model is used for reaching the flow condition at the heat exchanger inlet with the actual performance curves of the fan. It is found that the improved ACSC with deflector shows a significant enhancement in both the cooling air mass flow rate and the heat rejection rate compared with the conventional ACSC. The higher the wind speed is, the larger the heat transfer enhancement of the improved ACSC is. The effect of the plate inclination is also investigated, and the inclination angle of 45° is found to be the optimum value for the arrangement of the deflector.

Design and Control Techniques for the Numbering-up of Capillary Microreactors with Uniform Multiphase Flow Distribution

The results of experimental studies on the parallelization of both single-phase and biphasic liquid−liquid slug flow in capillary microreactors are presented. Various flow distributor designs were investigated with respect to the uniformity of liquid−liquid flow in eight parallel capillaries and the two most promising concepts were identified. A novel multichannel phase splitting unit was installed at the downstream end of the capillaries to ensure well-defined phase separation. Further investigations on more complex reaction systems, in which the hydrodynamics depend on conversion and/or selectivity (e.g., polymerization), suggest that an active flow control for individual capillaries will be necessary in such cases. The uniformity of flow rate and flow structure could be achieved using a noninvasive capacitative measurement to characterize the flow in conjunction with specially developed microvalves and actuators for the regulation of flow rates and the manipulation of slug flow structure in each capillary.

Surface permeability tests: experiments and modelling for estimating effective permeability

This paper presents a technique for determining the near surface permeability of geomaterials and involves the application of a uniform flow rate to an open central region of a sealed annular patch on an otherwise unsealed flat surface. Darcy’s flow is established during attainment of a steady pressure at a constant flow rate. This paper describes the experimental configuration and its theoretical analysis via mathematical and computational techniques. The methods are applied to investigate the surface permeability characteristics of a cuboidal block of Indiana limestone measuring 508 mm. An inverse analysis procedure is used to estimate the permeability characteristics at the interior of the Indiana limestone block. The resulting spatial distribution of permeability is used to estimate theeffective permeabilityof the tested block.

Gas−Liquid Two-Phase Flow in Minichannels with Liquid Side Introduction

In the present work, computational fluid dynamics (CFD) modeling with a volume of fluid (VOF) method was used to understand gas-liquid two-phase flow in PEM fuel cell flow channels under typical fuel cell flow conditions. Simulations with different liquid water introduction manners to flow channels were discussed to resemble liquid water transport in flow channels in active fuel cells. Those introduction methods included side liquid introduction through a number of ports, continuous liquid introduction along the channel with uniform and nonuniform flow rates, and liquid water introduction from the inlet together with the gas phase. The simulated results showed that the side introduction of water increases the water accumulation near the end of the channel and the gas slugs are significantly elongated, compared to the cases with water introduction from the inlet. When water was introduced nonuniformly along the channel with more near the outlet of the channel, there appears to be less probability of slug formation in the channel. With low liquid to gas volumetric flow ratios as encountered in fuel cells, the flow pattern changed between slug flow and stratified flow, depending on different liquid introduction manners. When water was introduced into the channel from ports on the bottom wall, it emerged and accumulated near the port region before slugs formed, detached, and purged out of the channel, causing high pressure drop and pressure drop fluctuations. When the wettability, or contact angle, of the channel walls varied, liquid water tended to attach to the wall surface with low contact angles, namely, more hydrophilic surface. In addition, the change in surface contact angle can also lead to the change in flow patterns. The slug frequency decreased with an increase in the port size. With increasing of the port number, more liquid tended to accumulate in the channel.

Kinematic Analysis of a Swash-Plate Controlled Variable Displacement Axial-Piston Pump With a Conical Barrel Assembly

Variable displacement, swash-plate controlled, axial-piston pumps are widely used in applications that require high pressure and variable flow rates. The pump consists of a rotating barrel assembly that houses several pistons in a circular array. A swash-plate is used to control the displacement of the pistons to adjust the output flow of hydraulic fluid. As the barrel rotates, the pistons slide along the angled swash-plate and draw oil from the supply and then discharge oil into the high pressure circuit. This results in an almost constant output flow rate. This paper analyzes the kinematics of a pump based on its geometry dependent characteristics. The analysis assumes an idealized case in which there is no oil leakage and the fluid is considered to be incompressible. It is revealed through the analysis that the piston displacement and the pump output flow are slightly increased by using a conical barrel. Instantaneous and mean flow rate equations are used to describe the output flow characteristics and flow ripple effect. The output flow rate ripple profile is found to be a function of both swash-plate angle and the conical barrel angle. A term defined as the flow rate uniformity coefficient is used to better quantify the flow ripple phenomenon. A frequency analysis is performed on the output flow rate and an additional order is found to be present when using a conical barrel pump versus one with a cylindrical barrel when the pumps have an odd number of pistons. Conical barrel piston pumps are found to have a slight increase in piston displacement, velocity, and acceleration relative to the rotating barrel frame of reference over a pump with a cylindrical barrel. This translates into an increase in the output flow rate for a conical piston pump under the same operating conditions. The conical barrel is also found to have a reduction in the rotational inertia allowing for faster angular acceleration. The presence of an extra order from a frequency analysis for a conical pump with an odd number of pistons has the potential to cause unwanted noise or vibration to the structure or components attached to the pump.

용융탄산염 연료전지 Anode 유로 채널에서의 가스 유동 분포에 관한 수치해석적 연구

A three-dimensional computational fluid dynamics (CFD) analysis is performed to investigate flow characteristics in the anode channels and manifold of the internal reforming type molten carbonate fuel cell (MCFC). Considering the computational difficulties associated with the size and geometric complexity of the MCFC system, the polyhedral meshes that can reduce mesh connectivity problems at the intersection of the channel and the manifold are adopted and chemical reactions inside the MCFC system are not included. Through this study, the gas flow rate uniformity of the anode channels is mainly analyzed to provide basic insights into improved design parameters for anode flow channel design. Results indicate that the uniformity in flow-rate is in the range of ±1% between the anode channels. Also, the mal-distributed inlet flow-rate conditions and the change in the size of the manifold depth have no significant effect on the flow-rate uniformity of the anode channels.

Highly sensitive and quickly responding ultrasonically sprayed nanostructured SnO 2 thin films for hydrogen gas sensing

Nanostructured SnO 2 thin films were prepared by ultrasonic spray pyrolysis technique. Aqueous solution (0.05 M) of SnCl 4 ·5H 2O in double distilled water was chosen as the starting solution for the preparation of the films. The stock solution was delivered to nozzle with constant and uniform flow rate of 70 ml/h by Syringe pump SK5001. Sono-tek spray nozzle, driven by ultrasonic frequency of 120 kHz, converts the solution into fine spray. The aerosol produced by nozzle was sprayed on glass substrate heated at 150 °C. The sensing performance of the films was tested for various gases such as LPG, hydrogen, ethanol, carbon dioxide and ammonia. The sensor (30 min) showed high gas response ( S = 3040 at 350 °C) on exposure of 1000 ppm of hydrogen and high selectivity against other gases. Its response time was short (2 s) and recovery was also fast (12 s). To understand reasons behind this uncommon gas-sensing performance of the films, their structural, microstructural, and optical properties were studied using X-ray diffraction, electron microscopy (SEM and TEM), and UV–vis spectroscopy, respectively. The results are interpreted.

CFD based investigations into optimization of coal pulveriser performance: Effect of classifier vane settings

Abstract In coal-fired power plant, pulveriser is the first major component, whose performance dictates the total power plant efficiency. Uniform flow rate and desired size fraction at outlet pipes along with higher classifier efficiency are three important measures which decide the pulverizer performance. Optimization of pulverizer at its best operating conditions has been considered as a potential area that needs to be addressed for improving unit performance, emissions, operations, and maintenance. The best operating conditions are optimum air velocity and classifier vane settings. In this investigation, numerical simulations of a typical pf coal based pulveriser have been carried out for different classifier vane settings to evaluate uniform flow rate and desired size fraction at outlet pipes along with high optimum classifier efficiency. The optimum opening for the vanes has been determined based on the above measures, which not only reduces unburnt CO, SO x and NO x emissions at boiler end but also minimise energy consumption of mill (in terms of reductions in regrinding cost). Computational Fluid Dynamics (CFD) simulations of the coal classifier physical model indicate good agreement with the plant data, in terms of internal flow patterns, particle collection efficiency and desired cut size. From the simulation studies, optimum opening for the vanes is found to be 65% for selected utility which leads to closest uniformity with 60% classifying efficiency wherein 70% particles pass through 75 μm sieve.

S0504-3-1 スリット噴流と自励振動噴流群の共存効果について(噴流,後流および剥離流れの流動解析と応用(その3))

Particle Image Velocimetry (PIV) flow visualization measurements are performed in the efflux jet-stream field to determine the functions of slit flows coexisting with the flip-flop flow which generates multiple jet-flow groups of uniform flow rate accompanied by self-sustained oscillations. Various arrangements are tested with different ways of attaching the slit flows with the flip-flop flow unit. It is disclosed that flow shear induced by the slit-flow streams stretches the longitudinal vortices which are generated in the flip-flop flow in the flow direction. As a result, the efflux flow stream elongates in the flow direction and simultaneously suppresses flow velocity reduction. The functions are useful in the creation and elongation of air curtains.

Calculation of Fluid Flow Distribution Inside a Compact Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop.