Uniform Flow Distribution Research Articles

The Influence of Header Design on Two-Phase Flow Distribution in Plate-Fin Heat Exchangers

AbstractFluid flow maldistribution causes deterioration of heat transfer as well as pressure drop penalty in heat exchangers. A test bench was set up to investigate the effect of different header designs on air-water flow distribution in plate-fin heat exchangers (PFHX). Two-phase flow distribution was examined for air Reynolds numbers (ReG) of 28293542 and inlet qualities (x) of 46.3–64.0%. Two-phase flow distribution was seen to be more uneven in the heat exchanger in comparison with single-phase flow, the water distribution being more uneven than that of the air. For a fixed inlet quality, as the air flowrate was increased, the distribution of two-phase flow became increasingly nonuniform, showing a pattern similar to single-phase flow. Furthermore, the air distribution became more even, while the water flow became more unevenly distributed as the inlet quality increased. To mitigate the maldistribution, perforated plates were incorporated in the heat exchanger header. The improved headers significantly aided in distributing the two-phase flow more evenly. At ReG = 2829 and x = 46.3%, the heat exchanger effectiveness was expressed in terms of the unevenness in quality, Sx. The effectiveness decreased as the unevenness of the flow distribution was exacerbated, emphasizing the significance of uniform phase and flow distribution as a key element of heat exchanger design.

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

AbstractRiparian vegetation does not only affect the channel flow carrying capacity, but also plays significant roles in water management, stream restoration, and river rehabilitation. This study numerically investigates the flow characteristics through longitudinally discontinuous rigid vegetation occupying half width of the channel, with the help of three‐dimensional software FLUENT in which a Reynolds stress turbulence model was adopted. Three varying conditions of vegetation were considered comprising of vertically double‐layered vegetation (DLV), submerged vegetation (SV), and emergent vegetation (EV) while keeping the same vegetation density, as well as a varying discharge condition against DLV was also tested. The results indicated that the flow distribution becomes more complex through DLV and SV followed by multiple layers with an inflectional instability in the vertical velocity profile around submerged canopy top, as compared to the flow through EV where the uniform distribution of flow over the canopy column was observed. The velocity in the canopy zone decreased considerably because of the resistance due to vegetation, which influenced the channel carrying capacity, in comparison to that in the non‐vegetated zone. The flow velocities through the obstructed part of the channel, that is, canopy zone, in DLV arrangement reduced by a percentage difference of approximately 42 and 37% compared to that of SV and EV arrangements, respectively; whereas it was reduced by approximately 55% when the discharge was twice while keeping the same configuration of DLV. The inflectional instabilities and estimated mixing layer over the interfacial zone suggested a stronger lateral exchange of momentum for DLV configuration in comparison to that of SV and EV. Within the gaps between the patch zones, the flow velocity, turbulent kinetic energy, and turbulent intensity reduced significantly due to blockage effect and sheltering offered by the vegetation patches, signifying a positive flow response towards aquatic life and sediment deposition.

Numerical study of the non-uniform channel width arrangement effect on mini-channel heat sink performance

The mini/micro-channel heat sinks have already been a successful innovation for cooling of electronic devices, and many factors could affect their thermal performance. However, the flow distribution is one of the fatal factors influencing the performance of the mini/microchannel heat sinks. As we know, uniform flow strongly depends on the optimum structure design of the heat sinks. The particular focus of this work is the channel width arrangement effects on the flow uniformity and heat transfer inside mini-channel heat sinks (MCHSs). The mini-channel heat sinks with five non-uniform channel width arrangements were compared with a mini-channel heat sink with uniform channel width under four inlet flow rates and a fixed heat flux. Overall thermal resistance and pressure drop were used to evaluate the thermal performance of the heat sink. The simulation results show that the non-uniform channel width arrangement is significantly beneficial for achieving uniform flow distribution in the mini-channels and reduces the overall thermal resistance with up to 6.1%. It is found that the 5-type MCHS performs the best flow uniformity and the lowest thermal resistance with a moderate pressure drop. Besides, this study supplies a guideline to optimize the arrangement of channel width.

Improvement of a scraper heat exchanger for pre-heating plant-based raw materials before concentration

When heating liquid and paste-type products, enterprises in the food industry commonly use scraper heat exchangers, which, given their high heat treatment intensity, make it possible to retain the original properties of the treated raw materials. Most heat exchangers demonstrate an unstable stabilizing effect: the vapor pressure ‒ the temperature that leads to damage to raw materials, under conditions of significant energy- and metal capacity. It is possible to eliminate these drawbacks by using a temperature-stable flexible film resistive electric heater of the radiating type as a heater in an improved scraper heat exchanger. We have proposed applying a hinged blade with a cutting edge (with a reflective heating surface) as a stirring element of the heat exchanger to obtain the uniform distribution of a product layer thickness at the working surface and to additionally heat by the blade's reflective surface. The heat exchanger can be supplemented with a cooling shell with ring channels to pass the refrigerant, which is placed on the outer surface of the non-thermally insulated flexible electric heater. Such a solution provides the possibility of cooling to −15 °C and it simultaneously serves the additional air thermal insulation in the absence of the carrier in it. We have determined the uniformity of heat flow distribution over the heating surface of the model design of the improved unit (60.3...60.5 °C) and at the reflective surface of the hinged blade with a cutting edge (60.0...60.3 °C). The total thickness of a liquid layer has been established depending on the shaft rotation frequency of the proposed hinged blade with a cutting edge: at 50 min –1 – 1–2.65 mm, at 350 min –1 –1.5 mm, compared with a standard hinge blade (a layer thickness is from 5.0 mm to 1.5 mm), in terms of product consumption W=50 l/h. The improved scraper heat exchanger is characterized by a 1.48-time decrease in the specific energy consumption (170.4 kJ/kg), used to heat a product volume unit, compared to the heater with a steam shell – 252.6 kJ/kg. The research result is the confirmed efficiency of using the improved scraper heat exchanger, as well as its proposed structural scheme

CFD investigation of the effect of manifold and microchannel ratio on the hydrodynamic performance of microchannel heat sink

Flow distribution of working fluid greatly affects the performance of microchannel heat sinks (MCHSs). Uniform flow distribution prevents the development of hot spots and dead zones. Major parameters that govern the flow distribution in MCHSs are manifold and microchannel geometry. Many studies involved complicated manifold designs or novel approaches which may not be easily incorporated. Also, many researchers have examined various microchannel geometrical parameters. However, simultaneous alterations of more than one parameter is scarce. The present study focuses on the effect of simple manifold layouts, namely rectangular manifold (Rect_MCHS), circular manifold (Circ_MCHS), and triangular manifold (Tria_MCHS), and microchannel geometry, defined by microchannel ratio, a ratio of microchannel width to microchannel spacing, on the hydrodynamic performance of MCHSs using three-dimensional computational fluid dynamic (CFD). The hydrodynamic performance of MCHSs was evaluated in terms of pressure drop, velocity distribution, and coefficient of flow nonuniformity. Results showed that higher inlet flow rates and smaller microchannel ratios produced better flow distribution performance in which the latter has a higher positive impact on the hydrodynamic performance of MCHSs. Smaller microchannel ratio designs have larger microchannel spacing which served as a barrier to create flow dispersion effect. This effect was further amplified at higher inlet flow rates. Generally, Rect_MCHSs produced the best hydrodynamic performance. Furthermore, variation in temperature showed negligible impact on the hydrodynamic performance of MCHSs, compared to inlet flow rate and microchannel ratio. This suggests that studies which concern with flow distribution performance could be conducted without the energy aspect to reduce computational time.

Mitigation of Flow Maldistribution in Minichannel and Minigap Heat Exchangers by Introducing Threshold in Manifolds

In the present paper, a detailed numerical investigation has been carried out to analyze the flow maldistribution in 50 parallel rectangular cross-section (1 mm depth and 1 mm width) minichannels and minigap section (1 mm depth and 99 mm width) with rectangular/trapezoidal manifolds in Z-type flow configuration. The author carried out numerical investigation with various mass flow rates, namely 0.05 kg/s, 0.1 kg/s and 0.2 kg/s which results in Reynolds number of 1532, 3064, 6128 respectively. A novel approach for the mitigation of non-uniform flow has been proposed introducing threshold at the entrance of the minigeometry section. The conventional case without threshold (as reference) and 1 mm, 3 mm and 7 mm threshold were introduced. The threshold has been employed by making a manifolds’ depth bigger than section’s depth. The maldistribution coefficient can be reduced twice in minigap section or three times in the minichannel section already with the 1 mm threshold as compared to the arrangement without threshold. It is found that rectangular manifold gives lower maldistribution coefficient than trapezoidal manifold which corresponds with actual state of the art. The distribution is more uniform in minichannel section than in minigap section for the same inlet parameters. To obtain uniform distribution of fluid flow should be stabilized already at the inlet manifold, at the entrance to the minichannel or minigap section. That was done by introducing the threshold in the manifolds, which is novelty of this study.

Influence of Hydrophobic Fin Configuration in Thermal System in Relation to Electronic Device Cooling Applications

In this study, heat and flow analysis of the cooling system incorporating fins with hydrophilic and hydrophobic wetting surfaces has been considered in relation to electronic cooling applications. Temperature and velocity fields in the solution domain are simulated for various fin numbers and sizes. A temperature parameter is introduced to assess the thermal performance of the system. Fin count is introduced to formulate the number of fins in the solution domain. The Nusselt number and pressure drop between the inlet and exit ports due to different fin configurations of the cooling system for various fin counts are presented. It is found that the temperature parameter attains high values for large sizes and small fin counts, which is more pronounced for low Reynolds numbers. Increasing number of fins results in almost uniform flow distribution among the fin, which is more pronounced for the hydrophobic fin configuration. The Nusselt number attains larger values for the hydrophilic fin configuration than that corresponding to the hydrophobic fin, and it attains a peak value for certain arrangement of fin count, which differs with the Reynolds number. The pressure drop between the inlet and exit ports reduces for hydrophobic fin; hence the slip velocity introduced for hydrophobic fin improves the pressure drop by 6% to 16% depending on the fin counts in the cooling system.

Experimental investigation on hydrogen production by methanol steam reforming in a novel multichannel micro packed bed reformer

A novel multichannel micro packed bed reactor with bifurcation inlet manifold and rectangular outlet manifold was developed to improve the methanol steam reforming performance in this study. The commercial CuO/ZnO/Al2O3 catalyst particles were directly packed in the reactor. The flow distribution uniformity in the reactor was optimized numerically. Experiments were conducted to study the influences of steam to carbon molar ratio (S/C), weight hourly space velocity (WHSV), reactor operating temperature (T) and catalyst particle size on the methanol conversion rate, H2 production rate, CO concentration in the reformate, and CO2 selectivity. The results show that increase of the S/C and T, as well as decrease of the WHSV and catalyst particle size, both enhance the methanol conversion. The CO concentration decreases as the S/C and WHSV increase as well as the T and catalyst particle size decrease. Moreover, T plays a more important role on the methanol steam reforming performance than WHSV and S/C. The impacts on CO concentration become insignificant when the S/C is higher than 1.3, WHSV is larger than 1.34 h−1 and T is lower than 275 °C. A long term stability test of this reactor was also performed for 36 h and achieved high methanol conversion rate above 94.04% and low CO concentration less than 1.05% under specific operating conditions.

Analysis Exploring the Uniformity of Flow Distribution in Multi-Channels for the Application of Printed Circuit Heat Exchangers

The maldistribution of fluid flow through multi-channels is a critical issue encountered in many areas, such as multi-channel heat exchangers, electronic device cooling, refrigeration and cryogenic devices, air separation and the petrochemical industry. In this paper, the uniformity of flow distribution in a printed circuit heat exchanger (PCHE) is investigated. The flow distribution and resistance characteristics of a PCHE plate are studied with numerical models under different flow distribution cases. The results show that the sudden change in the angle of the fluid at the inlet of the channel can be greatly reduced by using a spreader plate with an equal inner and outer radius. The flow separation of the fluid at the inlet of the channel can also be weakened and the imbalance of flow distribution in the channel can be reduced. Therefore, the flow uniformity can be improved and the pressure loss between the inlet and outlet of PCHEs can be reduced. The flow maldistribution in each PCHE channel can be reduced to ± 0.2%, and the average flow maldistribution in all PCHE channels can be reduced to less than 5% when the number of manifolds reaches nine. The numerical simulation of fluid flow distribution can provide guidance for the subsequent research and the design and development of multi-channel heat exchangers. In summary, the symmetry of the fluid flow in multi-channels for PCHE was analyzed in this work. This work presents the frequently encountered problem of maldistribution of fluid flow in engineering, and the performance promotion leads to symmetrical aspects in both the structure and the physical process.

A Study on Flow Characteristics and Flow Uniformity for the Efficient Design of a Flow Frame in a Redox Flow Battery

As global environmental problems are worsening, the efficiency of storage systems for renewable energy are gaining importance. The redox flow battery (RFB), a promising energy storage system (ESS), is a device that generates or stores electricity through reduction–oxidation reactions between active materials constituting electrolytes. Herein, we proposed a flow frame design that reduces flow resistance in the flow path and causes uniform flow distribution in the electrode to develop an efficient redox flow battery. Through computational fluid dynamics (CFD) and experimental verification, we investigated the flow characteristics and flow uniformity inside the conventional redox flow battery cell. An analysis of the flow characteristics of the conventional flow frame revealed a non-uniform distribution of the flow discharged to the electrodes, owing to the complex (branched) flow path geometry of the inlet channel. To address this problem, we proposed a new flow frame design that removed and integrated bifurcations in the flow path. This new design significantly improved flow uniformity parameters, such as the symmetry coefficient ( C s y m ), variability range coefficient ( R i ), and maximum flow rate deviation ( D m ). Ultimately, we decreased the pressure drop by 15.3% by reducing the number of flow path bifurcations and chevron repositioning.

Modeling of flow uniformity by installing inlet distributor within the inflow part of a pressurized module using computational fluid dynamics

Uniform flow distribution is a significant parameter for designing pressurized membrane modules because non-uniform flow distribution can cause serious local flux and fouling problems within a module. Thus, this study investigated the fluid behavior with regards to the evenness of water distribution using newly designed inlet distributors in the inflow part of a pressurized membrane module. From the results of velocity and pressure at the cross-sectional and outlet planes, we confirmed that a conventional membrane module with no distributor (non-distributor) had fluid that was concentrated at the central part. Case 1, which had a cross-shaped distributor, reduced the central concentration tendency, and Case 2, which had a round-shaped distributor, displayed a relatively uniform flow based on the velocity, pressure, flux, and standard deviation data. Here, the non-uniformity coefficient (<i>N</i>) and energy utilization (<i>η</i>) for Cases 1 and 2 showed a lower non-uniformity coefficient (0.030 and 0.017, respectively) than for the Non-distributor (0.039). The energy utilization of Cases 1 and 2 were higher (1.35e-0.5 and 1.46e-05) than the Non-distributor (1.64e-05). Overall, we confirmed that the inlet distributors led to increased evenness of flow distribution within an inflow part.

Comparison of structured activated carbon and traditional adsorbents for purification of H2

RPSA technology can offer a more compact, cost-effective and energy-efficient solution for H2 recovery when compared to conventional PSA. The adsorption rate of adsorbents has become a key factor affecting the development of RPSA. Activated carbon, widely used as adsorbent for CO2 in H2 purification is in urgent need for further development to suitable for RPSA system. In this study, a structured activated carbon adsorbent was prepared using the dip-coating method, with nickel foam as a framework. The adsorption characteristics of the material for CO2 adsorption at different adsorption pressures, volume flow rates, and lamellar spacing parameters were investigated, and the kinetic behaviour was studied by the breakthrough curve. The results showed that the activated carbon was bonded to the nickel foam skeleton via an organic-inorganic binder with excellent mechanical strength. Structured adsorbents bed has uniform gas flow distribution, the pressure drop is about 1/3–1/7 of particles packed bed, and the breakthrough curve was sharper than particles. It indicated that the mass-transfer resistance in the structured adsorbents is low and has high effective diffusivity for CO2. The adsorption rate constant was calculated using the Yoon-Nelson model, and the correlation between the model calculation data and experimental data was greater than 0.98. Structured activated carbon adsorbent manufactured by dip-coating method, has a higher mass transfer coefficient and a shorter mass transfer zone length. It is a potential alternative adsorbent for RPSA.

A Numerical Study of Response Surface Based Shape Optimization Using Neural Networks

Industrial pipes that are used for fluid transport generally have to undergo many changes of shape to accommodate interfacing equipment related to plant operation, which results in flow maldistribution zones and higher pressure drops, and in turn leads to higher power consumption. In an attempt to redress this problem, ANSYS, a commercial Computational Fluid Dynamics (CFD) software, is used to perform numerical simulations based on a deterministic computational model of the internal fluid flow using the Reynolds Averaged Navier Stokes equations (RANS), a multi objective optimization study employing Response surface methodology and artificial neural networks. This numerical analysis has been performed on a galvanized steel duct for water recirculation. The focus of the paper is the study of the effect of a chosen set of several geometrical dimensions on the pressure drop and flow distribution inside the duct. Subsequently, a new set of designs with different geometrical parameters has been obtained to minimize the pressure drop and achieve a more uniform flow distribution by using artificial neural networks to generate a response surface and further employing Screening (Shifted-Hammersley sampling) as the optimization method that was used to select the best designs from amongst those that have been generated from the response surface.

Study of the parameters and operating modes of the installation for aerosol treatment of seed grain

One of the modern elements of agrotechnologies is the presowing treatment of seeds with bio-stimulating preparations, providing a complex effect on seeds, which, along with improving the sowing and productive qualities of seeds, can increase the resistance of plants to adverse environmental factors, diseases and pests. Recently, world agricultural production is increasingly focused on environmentally friendly technologies, where preparations based on components of natural origin become important. Preparations based on humic acids are among them. The effectiveness of their use in the process of presowing treatment of seeds to a certain extent depends on the technology and technical means used. This article discusses the design of the developed seed dresser and explores the basic physical processes that affect the quality of seed treatment. The effectiveness of seed treatment with growth stimulants has been studied depending on the intensity of heat exchange processes taking place in the processing chamber of the developed device, where heat transfer from the vapor of humates to the downward flow of grain occurs. Herewith, the dependence of heat transfer on the residence time of the grain in the treatment chamber, heat carrier temperature (aerosol of humates) and uniform distribution of coolant flow in the treatment chamber was determined.

고온 상태의 열처리 챔버의 냉각을 위한 급/배기관 형상에 대한 연구

This paper is a numerical study of the structure of the supply/exhaust pipe for safe cooling inside the heat treatment chamber at high temperature. The chamber of this study maintains the internal temperature at over 400°C. The cooling and exhaust pipe structure is essential for the cooling process to be efficient, safe and fast. Against this background, this paper compares the results according to the shape of the supply/exhaust pipe through the flow analysis and experiments inside the chamber, and compares Deriving the exhaust structure. Through the study of this paper, it was confirmed that the vertical air exhaust system exhibits the most uniform flow and temperature distribution, and the structure will be applied to chamber development and production. The temperature distribution was improved from about 130°C to 80°C. The reliability of the test results is within 6.14%.

The Effect of Using the Flow Separator Blade to Increase the Uniformity of Flow in the Intake Manifold

ABSTRACTIn this paper, an idea to make the flow uniform inside the manifolds of four and six cylinder engines without changing their main geometries is presented. In general the uniform distribution of air flow among the engine cylinders is very important. Non-uniform flow in the intake manifold outlets causes inadequate feeding of the cylinders, inappropriate combustion and reduces engine volumetric efficiency. So this matter is vital for improving engine performance. A flow guide blade is added into the manifold and uniformity of the air flow is studied in different regime using transient numerical simulations. The amount of air exited from each outlet and the effect of this blade on flow uniformity is investigated. The results showed that the blade has made the flow more uniform in the manifold outlets and it was also found that in the four-cylinder and six-cylinder engines the flow uniformity is increased by 67% and 75%, respectively. In other words, as the number of engine cylinders increase, the effect of using this blade increases.

Experimental study on refrigerant maldistribution in a fin-and-tube evaporator for a direct expansion air-conditioning system

In this paper, the design concept of the face split evaporator with a retrofitted suction header and choked flow in the capillary tubes was adopted to improve a direct expansion air-conditioning system with a designed air flow rate of 20,000 m3/h. The novel design of the direct expansion air-conditioning system was experimentally tested and validated. Face split evaporator reduced the refrigerant pressure drop in the suction header and the choked flow design limited the maximum flow rate across each branch circuit, which both contributed to the uniform refrigerant flow distribution of the improved system. Consequently, the cooling capacity and COP of the improved system was 10.5% and 13.4% higher than the original system. With the refrigerant mass flow rate of the improved system varying from 1.33 kg/s to 2.05 kg/s, the measured cooling capacity ranged 240–350 kW and the ratio of the system COP to the ideal COP of the reversed Carnot cycle with the same evaporating and condensing temperatures maintained at 0.72–0.74. The experimental results demonstrated that the improved system performed a relatively uniform refrigerant flow distribution among the branch circuit of the evaporator regardless of the refrigerant mass flow rate. This study is beneficial to the optimization design of the multi-circuit evaporator for a direct expansion air-conditioning system with a large air flow rate in engineering applications.

Optimization Based on Product and Desirability Functions for Flow Distribution in Multi-Channel Cooling Systems of Power Inverters in Electric Vehicles

The onboard charger (OBC)/low-voltage DC-DC converter (LDC) integrated power inverter for electric vehicles comprises multiple electrical elements that can heat up, which can cause performance degradation and system instability issues in electric vehicles. To address this, a cooling system is included in the OBC/LDC integrated power inverter, which primarily uses water as a coolant. In this water cooling method, controlling the flow rate of water is critical for uniform cooling of the component. Thus, we propose an optimization method that helps determine the design variables to ensure uniform flow rate in each channel of the water-cooled system. The control variables for fluid-flux flow distribution optimization are selected by performing flow analysis for the initial design shape and analyzing their effects on fluid-flux flow distribution. For optimization analysis, the central composite design technique was applied; in addition, multi-response surface optimization using the same flow rate for each channel was performed. The optimization results were compared and verified using desirability functions based on the flow ratio of the cooling water channel, product function, and error function. Among single-response objective functions, the product function showed excellent performance. However, optimization using a multi-response objective function showed significantly higher prediction accuracy than the single-response function: using the optimized design obtained with the multi-response objective function improved the fluid-flux flow distribution uniformity by approximately 90% or more than the initial design.

Flow sharing and turbulence phenomena in proton exchange membrane fuel cell stack headers

The distribution of the gas flow in a PEMFC stack is of paramount importance to the stack's performance and lifetime. Uneven flow distribution influences the flow rate through each cell, which in turn causes uneven distribution of the current flow of the entire cell stack and ultimately reduces the performance of the fuel cell stack. In this work, different simulation methods are compared, and large eddy simulations are selected to investigate the flow characteristics in a model stack and study the effects of operating conditions on flow sharing. The simulation results indicate different flow patterns in the inlet header and outlet header; the former features a turbulent entrance region that progressively transits to a laminar region, whereas the latter exhibits a complex flow with jets mixing downstream. Moreover, the flow patterns and distributions for different inlet/outlet configurations, i.e., U-type and Z-type, are investigated. The distribution of the flow through the unit cells for both configurations is different. The Z-type arrangement offers a more uniform flow distribution and has a smaller number of fluctuations than the U-type. The effects of different inlet flow velocity and jet inflow pattern are also studied. The findings from this work can provide guidelines to improve header design.

Optimization of electrolyte flow and vanadium ions conversion by utilizing variable porosity electrodes in vanadium redox flow batteries

The proper flow and uniform distribution of vanadium electrolyte inside the electrode are crucial factors to improve battery performance. In this study, the novel gradient and double-layered porous electrode (GPE and DLPE) with optimized properties were investigated. More vanadium ions conversion occurs due to more uniform distribution of electrolyte flow with promptly supplementing of reactants and timely removing of products. Thus, the larger cell capacity and output power as well as higher energy efficiency are obtained in the electrodes with a linear or stepwise increasing in porosity at the same inlet flow rate. In the other case with the same pressure difference between the inlet and outlet, the larger cell capacity and efficiencies occur in the electrodes with a constant maximum porosity or a linear decreasing porosity due to the larger average inlet flow velocity. The better battery performance can be obtained by optimizing porosity arrangement in the electrodes.