A novel pre-dilution,swirling jet diffuser to enhance effluent mixing: Hydrodynamics and dilution performance

Diffusers are widely-used to quickly dilute effluents in receiving water bodies. This study proposed a novel diffuser that pre-mixes effluent with ambient water before discharging and that uses the swirling jet to further enhance near-field dilution. The nozzle of the diffuser was examined in two ambient flow conditions: co-flow and counter-flow that are commonly-met in the environment such as oceans due to tidal effect. Physical experiments were first conducted in co-flow on its dilution performance and hydrodynamics, using heated water as the effluent. A 3-D CFD model was developed and calibrated the co-flow scenarios, and then used to investigate the diffuser in counter-flow. The results showed that the nozzle can effectively reduce the maximum temperature rise of the effluent by about 50 % before discharging. The swirling jet from the outlet has a larger shear area, half-width and entrainment rate, enabling the effluent to be rapidly diluted to a minimum of around 10 times at x/D = 6 in co-flow, whereas the dilution for conventional nozzles is about 1 because of the potential core. The flow amplification ratio (α) decreases gradually with increasing velocity ratio in co-flow but increases with increasing velocity ratio in counter-flow. The counter-flow reduces the water drawn into the device; however, the pre-dilution effect at the outlet remains stable. The near-field dilution in counter-flow was significantly enhanced than that in co-flow. Environmental regulations at outfalls and mixing zones can be more easily met using this novel diffuser.     

Generation,validation and application of dynamic load profiles in flow measurement using cavitating Herschel–Venturi nozzles

Today, utility meters for water are tested for measurement behavior at stable operating conditions at specified flow rates as part of the approval process. The measurement error that occurs during start and stop or when changing between flow rates may not be taken into account. In addition, there are new technologies whose measuring behavior under real-world conditions is only known to a limited extend. To take these facts into account, a new method has been developed and tested to determine the measurement behavior of water meters under dynamic load profiles as they occur in the real application. For this purpose, a test rig for flow rate measurement was extended by a cavitation nozzle apparatus and the generation of dynamic load profiles was validated. For the cavitation nozzles used, possible factors influencing the flow rate, such as temperature and purity of the water as well as the upstream pressure were investigated. Using different types of domestic water meters, the applicability of the dynamic test procedure was demonstrated and the measurement behavior of the meters was characterised.     

Experimental investigation of gas-liquid flow in a vertical venturi installed downstream of a horizontal blind tee flow conditioner and the flow regime transition

A venturi device is commonly used as an integral part of a multiphase flowmeter (MPFM) in real-time oil-gas production monitoring. Partial flow mixing is required by installing the venturi device vertically downstream of a blind tee pipework that conditions the incoming horizontal gas-liquid flow (for an accurate determination of individual phase fraction and flow rate). To study the flow-mixing effect of the blind tee, high-speed video flow visualization of gas-liquid flows has been performed at blind tee and venturi sections by using a purpose-built transparent test rig over a wide range of superficial liquid velocities (0.3–2.4 m/s) and gas volume fractions (10–95%). There is little ‘homogenization’ effect of the blind tee on the incoming intermittent horizontal flow regimes across the tested flow conditions, with the flow remaining intermittent but becoming more axis-symmetric and predictable in the venturi measurement section. A horizontal (blind tee) to vertical (venturi) flow-pattern transition map is proposed based on gas and liquid mass fluxes (weighted by the Baker parameters). Flow patterns can be identified from the mean and variance of a fast electrical capacitance holdup measured at the venturi throat.     

基于CFD技术优化50 L发酵罐内气体分布器

通过CFD模拟技术对50L通气搅拌发酵罐内不同气体分布器的传质混合效果进行气液双相流模拟。首先对发酵罐自带气体分布器进行流场模拟,针对模拟结果提出两种改进气体分布器。结果表明:双层环形气体分布器表现出一种较理想的混合传质效果,为此类发酵罐的优化和放大提供一种有效的技术手段。     

Two/three-dimensional reduced graphene oxide coating for porous flow distributor in polymer electrolyte membrane fuel cell

There are drawbacks to use stainless-steel plates as a flow distributor plate in fuel cell, due to some of their properties being inferior to graphite flow distributor plates in terms of electrical conductivity and corrosion resistance. To overcome these problems, many researches have been conducted to improve the properties of stainless-steel flow distributor plates through coating of carbon materials. Herein, two-dimensional Web-like graphene (WG) and self-assembled three-dimensional graphene (STG) are coated through superheat vaporization of micro-droplet method. WG is coated in porous Ni–Cr foam and STG is constructed on the flat flow distributor plate, and they exhibit the feasibility to be applied in flow distributors. Compared to uncoated Ni–Cr foam, the performance of the PEMFC system with the graphene coated foam is enhanced remarkably. Furthermore, the flow distributor plate with the STG exhibits potential to be used directly to flow distributor.     

催化裂化管式待生剂分配器颗粒分配特性及内部流动特性的CPFD模拟

基于CPFD(Computational particle fluid dynamics)方法，对实验室前期研究的催化裂化管式分配器内的颗粒分配特性及内部流动特性进行了数值模拟，系统研究了输送风、松动风及分配器倾斜角度对颗粒分配不均匀指数的影响，并进一步考察了输送风和松动风对分配器各出口气体流量分布及内部气 固流动特性的影响。结果表明，增大输送风量、松动风量以及分配器的倾斜角度均可以降低颗粒分配不均匀指数，但改变松动风量的效果不如改变输送风量和倾斜角度显著。分配器倾斜角存在一个最优值时，颗粒分配均匀性最佳。输送风的增大会使得颗粒出料量最高的排料口的位置逐渐向分配器的末端移动，中间排料口所流出的气体流量占比增大，末端排料口排风量占比减小。引入松动风后，各出口的颗粒排料量更加接近，同时靠近末端排料口的气体流量占比明显增大。     

Performance curve available for non-steady flow through Venturi-like reverse flow diverter

A reverse flow diverter (RFD) consists of a driving nozzle, a diffuser, and a suction gap that separates the nozzle and diffuser. Thus, the RFD is a Venturi-like fluidic component with three ports. The jet flow emanating from the driving nozzle exit can entrain the ambient fluid and transport it to a high elevation. During this time, the flow through the RFD is non-steady, which makes it difficult to measure the flow depending on the pressure drop. In this study, a series of tests was carried out to evaluate this fluid flow with different contraction ratios, suction gap lengths, fluid properties, inlet flow rates, and inlet pressures. A performance curve was formulated that can be expressed as an exponential equation correlating the non-dimensional Euler number, pressure ratio, and suction factor. The performance curve is not affected by the driving nozzle exit diameter and suction length of the RFD. The performance curve makes it possible to measure the flow out of a RFD depending on the pressure drop.     

Evaluation of hydrodynamic behavior of the perforated gas distributor of industrial gas phase polymerization reactor using CFD-PBM coupled model

A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation.     

Detection of Multiple Blockages in Parallelized Microreactors

In a plant consisting of parallelized microreactors (MRs), the product quality is lowered because of a lack of flow uniformity among them when blockage occurs. It is not practical to install sensors in every MR from the viewpoint of cost when detecting the blocked MRs. In the previous study, the multiple blockage detection (MBD) method using a small number of sensors was proposed, but its performance became low when the number of sensors decreased. Here, the conventional algorithm for MBD is improved by considering the process behavior on blockage occurrence, and the effectiveness of the improved algorithm is demonstrated through a numerical case study. The effects of flow distributor types and sensor types on the MBD performance are numerically investigated.     

Low-pressure gas atomization of aluminum through a Venturi nozzle

A new concept of powder atomization based on the venturi phenomenon is presented in the current work. In the proposed method, the working gas speeds-up while flowing into the venturi nozzle. Under the low static pressure developing at the narrow part of the venturi, liquid metal is sucked and mixed perfectly with the gas. By controlling the operating parameters, metal powder of different sizes and shapes can be produced. Carbon dioxide and pure aluminum were mixed in the nozzle and the effect of different operating gas pressures on the produced particle size and shape were thoroughly investigated. Most of the particles were found to average to almost 150 μm, however, even sub-micron aluminum particles were produced at low mass fractions. With the increase of the gas pressure from 0.5 bar to 4 bar, finer aluminum particles are produced. One of the most attractive features of the proposed method is the low gas pressure required to cause melt atomization, which in certain cases may be up to 30 times lower compared to current industrial atomization methods.