Equal Flow Distribution Research Articles

Gas-liquid hydrodynamics of a fractal flow mixer

Gas-liquid hydrodynamics of a micro-structured device (fractal flow mixer) was experimentally investigated. Experiments were conducted for a range of liquid-to-gas superficial velocity ratios (VSL/VSG). High-speed imaging was used to identify the flow regimes inside the microchannels of the device at different VSL/VSG. At different VSL/VSG, two or more flow regimes were observed simultaneously in different micro-channels. Consequently, a new flow regime map was developed. An optical probe was used to measure the bubble mean size and velocity. The effect of the VSL/VSG towards the bubble mean size, mean velocity, and frequency were analyzed. The bubble mean size decreases with the increase of the VSL/VSG, which can be attributed to the uniform shearing of gas slugs across all channels. To check the consistency of the fractal flow mixer in producing gas bubbles over a single experiment run, the global relative standard deviation (RSD) was used. The fractal flow mixer was able to generate equal flow distribution across the 16 outlets and maintain a Taylor flow over a range of VSL/VSG. . However, depending on the VSL/VSG, the GB and GS vary to a certain extent, governed by the capillary effect and the back-pressure.

Maldistribution on a Vertical Manifold With Guide Vanes

Abstract Wall-Modeled Large Eddy Simulation (WMLES) has been used to study a subsonic vertical manifolds (VMs) in terms of maldistribution, i.e., how much the flow splitting deviates from an equal flow distribution between the outlets. The analyzed configuration is characterized by a wide-angle plane diffuser and by four outlets and it has been studied at high Reynolds number (Re*=10000, with Re*=u*Dh/ν, where u* is the friction velocity at the inlet, Dh=4A/P is the hydraulic diameter with A the cross-sectional area at the inlet and P the perimeter, ν is the kinematic viscosity). In the basic configuration, a jet flow develops in the diffuser with two stable flow separation regions at the inclined walls, which prevent an equal flow distribution at the outlets, and determine a maldistribution around ε=37%, where ε is a parameter that quantifies the flow rate deviation from an equal distribution. To increase the equal flow distribution between the outlets, guide vanes have been used. A conceptual model to reduce the maldistribution has been developed using the momentum and the mechanical energy conservation laws. The model uses as main parameter the relative distance between the guide vanes, and it allows to minimize ε. Taking advantage of this method, the maldistribution has been reduced from ε=11.20%, for the case of equally distributed guide vanes, to ε=0.32% in the optimized configuration. The methodology is of general use also for hydraulic systems.

Comparison of Conventional and Conformal Cooling Channels in the Production of a Commercial Injection-Moulded Component

Cooling channels are critical in injection mould tooling as cooling performance influences component quality, cycle time, and overall process efficiency. Additively Manufactured moulds allow the incorporation of cooling channels conforming to the shape of the cavity and core to improve heat removal. These conformal channels can reduce the cycle time, reduce mould temperature, and enhance the temperature uniformity on the mould's surface, leading to improved quality of the moulded components and reduced wastage in the production. The design of such channels is more challenging than conventional channels; thus, Computer-Aided Engineering (CAE) has a significant role within the design process. In this paper, a novel design for conformal cooling channels for the production of a commercial component from an industrial partner is investigated. This component had issues of high cycle time and a high defect rate due to residual stresses, resulting in component shrinkage. First, the existing conventional drilled cooling channels in the mould were simulated in Autodesk Moldflow Insight to evaluate temperature distribution and cycle time. Based on the temperature distribution, conformal cooling channels were designed in Solidworks, addressing the problem areas. Next, a simulation of fluid flow in the conformal channels was conducted in ANSYS-Fluent to ensure equal flow distribution in the entire circuit, iteratively arriving at an optimal configuration. Finally, the results of the new conformal channels, including mould temperature and cycle time, were compared with conventional cooling channels in simulation. The results showed a significant reduction in cycle time and improvement in the temperature distribution, thereby minimising residual stresses and shrinkage.

A Comparative Study and Flow Analysis of Multiple Branch Pipe Flow Header used in Tube Heat Exchangers

Objectives: The aim of this paper is to increase the performance of heat exchangers. A flow header having number of small multiple branch pipes are commonly used in boilers and heat exchangers. In the beginning, the headers were designed to give equal flow distribution. But experimentally, it is not equal. In this paper, the uneven distribution of flow in the heat exchangers which affects the performance is rectified. Analysis Method: In this project, the flow distribution among the branch pipes of flow header is analyzed for two different geometrical flow nature (square and circular). The flow distribution are analysed with the use of CFD software. After analyzing the square and circular header tubes, the result values are compared with Osakabae’s laboratory experimental results. Result Extraction: Based on the result values, it is found that header shape will determine and by choosing the better shapes the performance of the Heat Exchanger can be increased and the fuel consumption can be reduced and can increase the total performance of the Boiler. Applications: The uniform flow distributions in the flow header definitely increase the performance of Heat exchangers.Keywords: Branch Pipes, Flow Header and Heat Exchanger, Headers, Non-Uniform

Numerical simulations to evaluate basic geometrical shapes as headers for equal liquid flow distribution

ABSTRACTThe study presents computational fluid dynamics (CFD) simulations for evaluation of basic geometrical shapes as headers for equal liquid flow distribution. The headers that have been evaluated are conical header, cylindrical header, pyramidal header, rectangular header and spherical header. The computational approach used in the study has been validated by comparing predictions of numerical simulations with experimental results for a cylindrical header. The effects of volume of header, flow rate, diameter of outlets and pressure imbalance at outlets on flow distribution have been studied. At low flow rates, there is no significant difference in the performance of the headers of different geometrical shapes. At higher flow rates, spherical header is found to be better. The possibility of ensuring equal flow distribution by having outlets of varying cross‐sectional area is discussed. The results reported in the study provide useful insights relevant for header design problems. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Research on Equal Flow Distribution of Pulverized Coal-Air Mixture in Parallel Pipeline

It is very important to maintain the flow rate of pulverized coal-air mixture in different pipelines equal to each other in power generation units. As the usual practice, the resistance regulation is done to get an equal air flow velocity with the absence of pulverized coal. The paper indicates that such regulation can not ensure the equal flow rate of the mixture with pulverized coal. The purpose of this paper was to develop a method to achieve the same velocities of the mixture with certain concentration. The resistance characteristics of the pipeline and the adjustable plate corresponding to the pulverized coal-air mixture were taken into account to study the flow difference between pipelines. According to the initial flow difference, the method to regulate the flow rate without pulverized coal is got and thus the equal flow state of the mixture is ensured.

Influence of Fluid Flow Distribution in Micro-Channel Arrays to Phase Transition Processes

Microstructured heat exchangers are well suited for such phase transition processes as evaporation of liquids due to their heat transfer capabilities, being two to three orders of magnitude higher than those of conventional heat transfer devices. Controlling liquid evaporation inside micro-channels to provide full evaporation in a stable way is not trivial. In most cases, such instabilities as slug flow, bubbly flow, or vapor clogging occur, based on cross-talk possibilities between the individual micro-channels of a channel array, normally caused by open void inlet structures. Therefore, fluid inlet distribution is inhomogeneous, which results, in the best case, in a parabolic shape of a stable evaporation frontline. The parabolic shape occurs due to the residence time distribution of the fluid, generated by shorter path length in the array center and longer ones in the outer areas of the micro-channel array. Computational fluid dynamics simulation approves this result. Such a frontline can be kept stable when the process parameters are well controlled. Small deviations of the inlet parameters may lead to strong disturbances of the evaporation process, destabilizing it. When changing the inlet fluid distribution system to provide the most equal flow distribution possible, the span of the parabolic shape of the evaporation frontline can be reduced drastically. Finally, a stable evaporation frontline perpendicular to flow direction can be obtained. This status is no longer very sensitive to process deviations. This article presents an optimized micro-channel device for the optical investigation of phase transition phenomena. The device allows the exchange of integrated micro-channel arrays to investigate different designs for their suitability. It is separated into three independent sections, which can be heated or cooled individually. Therefore, very strict and rapid temperature jumps can be obtained within relatively short distances. The micro-channel array foils used for the experiments have been manufactured by mechanical micro-machining. Thus, the cross-sections of the micro-channels are always rectangular. Hydraulic diameter and length of the micro-channels, as well as the shape of the inlet and outlet voids, can be varied. Using a simple triangular or rectangular open inlet void, a stable evaporation line was generated, showing a parabolic shape. Depending on the mass flow and the size and shape of the inlet void, the span of the parabolic arc was influenceable.

Evaporation in Solar Thermal Collectors During Operation—Reasons and Effects of Partial Stagnation

Evaporation in solar thermal collectors normally takes place when the collector pump is not running—the so-called full stagnation. But it is possible that part of the heat transfer fluid evaporates inside a solar thermal collector field although the pump is operating and the collector field outlet temperature is significantly below the evaporation temperature. This operating status is called partial stagnation since only parts of the collector are affected by evaporation. Partial stagnation happens at a pronounced nonuniform temperature distribution in combination with a low mass flow rate and/or a high temperature level. A main reason for an irregular temperature distribution is a nonuniform flow distribution inside the solar thermal system. The paper presents an experimental investigation that analyzes the reasons and effects of partial stagnation occurrences. For this, outdoor measurements were made with a direct-flow vacuum tube collector. Criteria that promote partial stagnation have been identified, such as a coaxial tube design, a low system pressure, and a high gas content of the fluid. Performance measurements show no efficiency reduction during partial stagnation in the system investigated at a horizontal or positive collector slope. A high degree of partial stagnation, however, might pass into a complete evaporation of the collector volume although the collector pump is still running. This could lead to a complete blockage of the flow and a high thermal load of the system components. In all cases, partial stagnation leads to an unstable operation and a high load of the collector fluid and should, therefore, be avoided by design measures. A minimized risk for evaporation during operation is achieved by a more equal flow distribution inside the collector and the whole collector field, air bubbles, and solid particles should be completely removed. In addition, the gas content dissolved in the fluid may be reduced and the system pressure level may be increased in order to raise the boiling temperature.

A multishear microfluidic device for quantitative analysis of calcium dynamics in osteoblasts

Microfluidics is a convenient platform to study the influences of fluid shear stress on calcium dynamics. Fluidic shear stress has been proven to affect bone cell functions and remodelling. We have developed a microfluidic system which can generate four shear flows in one device as a means to study cytosolic calcium concentration ([Ca 2+] c) dynamics of osteoblasts. Four shear forces were achieved by having four cell culture chambers with different widths while resistance correction channels compensated for the overall resistance to allow equal flow distribution towards the chambers. Computational simulation of the local shear stress distribution highlighted the preferred section in the cell chamber to measure the calcium dynamics. Osteoblasts showed an [Ca 2+] c increment proportional to the intensity of the shear stress from 0.03 to 0.30 Pa. A delay in response was observed with an activation threshold between 0.03 and 0.06 Pa. With computational modelling, our microfluidic device can offer controllable multishear stresses and perform quantitative comparisons of shear stress-induced intensity change of calcium in osteoblasts.

Two-Phase Flow Distribution and Phase Separation Through Bot Horizontal and Vertical Branches

The present study investigated two-phase flow distribution and phase separation of R 22 refrigerant through various types of branch tubes. The key experimental parameters were the orientation of inlet and branch tubes (horizontal and vertical), diameter ratio of branch tube to inlet tube (1 and 0.61), mass flux (200-500 kg/m2s), and inlet quality (0.1-0.4). The predicted local pressure profile in the tube with junction was compared and generally agreed with the measured data. The local pressure profile within the pressure recovery region after the junction has to be carefully investigated for modeling the pressure drop through the branch. The equal flow distribution case can be found by adjusting the orientation of the inlet and branch tubes and the diameter ratio of the branch tube to the inlet tube. The T-junction with horizontal inlet and branch tubes showed the nearly equal phase distribution ratio. The quality at the branch tube varied from 0 to 1 us the orientation of the branch tube changed, while it varied within ±50% as the orientation of the inlet tube changed.

Flow regulation by automatically controlled overflow weirs

In larger sewage plants, motor-regulated overflow weirs are sometimes used to achieve a uniform flow distribution into the secondary settling tanks, backed up by simultaneous control of the immersion depth of the upstream aerating units. It is demonstrated that, if these overflow weirs are arranged in series on one side of the feed channel, they are unable, with a fixed setting, to ensure equal flow distribution when there is a variable inflow. If flowmeters are mounted in the discharge pipes, with feedback controls to the motor-regulated weirs, it is then possible to achieve equal flow distribution.

Multilevel Infusion Catheter for Use with Thrombolytic Agents

A new multilevel infusion catheter for administration of thrombolytic agents is described that provides near equal flow distribution through each of four infusion ports. Advantages of the catheter include fluoroscopically visible infusion length markers, small size (4.7 F), and secure positioning of the catheter within the occluded segment of graft or vessel. This catheter was used for infusion of urokinase in the treatment of 20 peripheral vascular occlusions. Complete or near complete thrombolysis was achieved in all cases.

Dividing-Flow Manifolds with Square-Edged Laterals

A method of analysis for dividing-flow junction losses based on correlation of numerous data sets is presented. Illustrative examples are given to describe the use of the analytical procedure to evaluate dividing manifold problems. The entry loss coefficients for laterals discharging from a dividing-flow manifold are found to bear lineal relationships to the squares of the ratios of manifold-to-lateral velocities. The entry loss coefficients for short laterals are larger than those for long laterals. Since the entry loss characteristic dictates dividing-flow distributions, the preferred design technique will compel equal flow distribution by maintaining the same manifold-to-lateral velocity ratio at every junction point.