Fluid Dynamics Simulation Method Research Articles

Structural parameter optimization for novel internal-loop iron–carbon micro-electrolysis reactors using computational fluid dynamics

Abstract It is generally recognized that internal-loop reactors are well-developed mass and heat-transfer multiphase flow reactors. However, the internal flow field in the internal-loop reactor is influenced by the structure parameter of the reactor, which has a great effect on the reaction efficiency. In this study, the computational fluid dynamics simulation method was used to determine the influence of reactor structure on flow field, and a volume-of-fluid model was employed to simulate the gas–liquid, two-phase flow of the internal-loop micro-electrolysis reactor. Hydrodynamic factors were optimized when the height-to-diameter ratio was 4:1, diameter ratio was 9:1, draft-tube axial height was 90 mm. Three-dimensional simulations for the water distributor were carried out, and the results suggested that the optimal conditions are as follows: the number of water distribution pipes was four, and an inhomogeneous water distribution was used. According to the results of the simulation, the suitable structure can be used to achieve good fluid mechanical properties, such as the good liquid circulation velocity and gas holdup, which provides a good theoretical foundation for the application of the reactor.

Establishment of a static nozzle atomization model for forest barrier treatment

Currently, the theory of using automatic target spray technology for forest barrier treatment in China has some shortcomings. Therefore, this study established an atomization model for two common brands of nozzles (Lechler and Feizhuo) used in this field. This model includes the two most important parameters: droplet size and spray axis velocity. A specific model for the two brands of nozzle was obtained. The obtained droplet size calculation model was validated with actual tools, which showed that at six different pressures, the average absolute error of the theoretical data for the droplet size obtained from the selected Lechler nozzles was 6.92 μm compared with the actual measured data, whereas the average relative error was 3.07%. The absolute and average relative errors for the Feizhuo nozzles were 11.41 μm and 4.43%, respectively. The model had a high degree of confidence. The test also verified that the droplet sizes at different distances from the same nozzle did not vary dramatically at a given pressure in the close-up range (30–50 cm). In addition, the droplet sizes at different angles did not significantly vary at given pressures and flow rates. However, droplet sizes that had the same angle increased as the flow increased. The classical theoretical model of spray axis velocity in connection to this study also improved, and the test results were verified by the computational fluid dynamic simulation method. Compared with the simulation data, the average absolute error of the improved theoretical data for the Lechler nozzle was 0.64 m/s for the selected nozzles, and the average relative error was 6.42%. The absolute and average relative errors for the Feizhuo nozzle were 0.67 m/s and 6.00%, respectively.

Investigation of operation performance of air carrying energy radiant air-conditioning system based on CFD and thermodynamic model

This study aims to investigate the operation performance of a new terminal form of radiant air-conditioning system called the air carrying energy radiant air-conditioning system (ACERS). Three summer operation conditions, namely steady condition (without opening door and window), open-door condition and open-window condition, are researched in a residential apartment using experimental, computational fluid dynamics (CFD) simulation and thermodynamic methods. The concept of dynamic synergistic operation of mechanical ventilation driven by the air-conditioning system and natural ventilation driven by the open door or window is proposed. A thermodynamic model formulated by the dynamic enthalpy equation, dynamic temperature equation and dynamic moisture equation is developed to analyze the heat and mass transfer process of the test room under the synergistic operation of mixing ventilation. Moreover, the CFD simulation results are used to analyze the synergistic operation and thermodynamic energy transfer of the test room under the mixing ventilation of ACERS and open door/window. It is indicated that ACERS is an important technology with a low temperature gradient of less than 0.1 °C between the head (1.5 m) and ankle level (0.1 m) and low velocity of approximately 0.1 m/s in the occupied zone under the steady condition. The thickness of the boundary zone under the orifice plate of ACERS under the steady, open-door and open-window conditions is 12, 6, and 8 cm, respectively, which can effectively prevent condensation. This study proves that ACERS is a promising technology for air conditioning in residential buildings in regions with hot and humid summers.

Friction as a major uncertainty factor on torque measurement in wind turbine test benches

Most of the existing multi-MW nacelle test benches (NTB) measure the MN·m torque before load application system (LAS) to reduce the cross-talk effect of the multi-component forces and bending moments on torque measurement. This means that the friction torque of the LAS reduces the applied torque and consequently directly determines the input torque on the device under test (DUT). Therefore, the knowledge of the friction torque is necessary for the precise experimental investigations (e.g. efficiency measurement). At the beginning of this paper, a Computational Fluid Dynamics (CFD) simulation method for the determination of the friction torque of the LAS, which is suspended by hydrostatical plain bearings, is introduced. Subsequently, this method is validated with experimental results. Afterwards the friction torque of the LAS is quantified under different operation conditions (e.g. variation of rotational speed, multi-component load and temperature). Finally, the influence of the quantified friction torque on the uncertainty of the MN·m measurement is compiled.

Study of an integrated personalized ventilation and local fan-induced active chilled beam air conditioning system in hot and humid climate

A novel integrated personalized ventilation and local fan-induced active chilled beam (PV-ACB) air conditioning system is proposed and analyzed through energy and Computational Fluid Dynamics (CFD) simulation methods. Energy performance and indoor environmental conditions of this system are investigated via Integrated Environmental Solutions (IES) and ANSYS Fluent respectively. Energy simulation results illustrate that PV-ACB system, compared with the conventional variable air volume (VAV) system, could achieve 16% energy savings at 100% peak cooling load. A maximum 42% energy savings is obtained at 25% part cooling load, indicating the superior energy saving potential under part load conditions. Vertical thermal stratification is observed in CFD simulation results, 23–24 °C at the occupant level (0–2 m) and 26–27 °C in the upper zone (2–4 m). Horizontally, temperature around occupants is 22–23 °C, lower than the temperature of 26–27 °C in other areas, demonstrating the horizontal temperature difference caused by the conditioned outdoor air from personalized ventilation. Both energy and CFD simulation results illustrate that this novel PV-ACB air conditioning system is able to achieve considerable energy savings, superior occupant thermal comfort and enhanced indoor air quality (IAQ).

Study on correlation between wind turbine performance and ice accretion along a blade tip airfoil using CFD

In cold-region environments characterized by high wind speeds, low external air temperatures, and supercooled water droplets, wind turbines frequently experience ice formation along the leading edge of the blade tip, which has a higher angular velocity. This ice formation directly and negatively affects the wind turbine's power performance. As such, a clear understanding of the relationship between ice formation and wind turbine power performance is required. In this study, we used computational fluid dynamics (CFD) simulation methods based on the dispersed multiphase (DMP) droplet model to predict ice formation along a blade tip airfoil's leading edge. To validate the ice formation model, the CFD simulation results were compared with the previously published wind tunnel testing results. Following validation, the model was used to predict the ice formation along the leading edge of the National Advisory Committee for Aeronautics (NACA) 64-618 airfoil and estimate its aerodynamic performance under variable external environmental conditions. Steady power calculations for the National Renewable Energy Laboratory's (NREL) 5-MW wind turbine was performed using the BLADED software. The aerodynamic performance of the NACA 64-618 airfoil following ice formation and the power performance of the NREL 5-MW wind turbine were subsequently correlated. The results indicated that ice formation on the blade tip airfoil's leading edge caused wind turbine power performance to decrease by approximately 8–29%.

Graphite dust deposition on HTGR steam generator: Effects of particle-wall and particle-vortex interactions

Generated by abrasion of fuel spheres, graphite dust is an important issue for the operation and maintenance of high-temperature gas-cooled reactor (HTGR), because the transport of fission product is coupled closely with graphite dusts. AVR experiments on dust specific radioactivity indicated that graphite dust deposition on steam generator (SG) should be of special interest. Combined with computational fluid dynamics (CFD) simulation and discrete phase method, the deposition of graphite dust on the upper 5 layers of SG tubes is studied in this work. The results are then used to analyze the influence of various factors, including particle–wall interaction, vortex structure effect and deposition mechanisms. By incorporating the critical capture velocity into CFD simulation, the probability of particle rebound is quantitatively considered. The result shows that the deposition rate is highly overestimated if the simple assumption of hit-and-stick is adopted. The comparison between RANS and LES results indicate that the RANS simulation augments the deposition rate by more than one order. Due to the loss of vortex information in RANS, the number of particles in the near-wall regime is unphysically overestimated and thus leads to much larger deposition rate. Finally, the contributions of different deposition mechanisms are investigated by switching on/off certain terms in the simulation. It is shown that thermophoresis is more dominant for small particle up to 3–4 µm and Brownian diffusion is negligible for sub-micron particles.

Surrogate Fluid Experimental Study and CFD Simulation on the Hydraulic Characteristics of Vortex Diode

The vortex diode is a key candidate for the equipment of the passive safety system of the molten salt reactor. Experimental studies to determine the diodicity (ratio of reverse flow Euler number to the forward flow Euler number at the same Reynolds number) using high-temperature molten salt are strongly limited because of the huge technical effort and financial requirements for such studies; moreover, possible solutions that involve a scaling method that uses surrogate fluid to obtain the diodicity must be validated. To determine the diodicity and verify the scaling method, an experiment using one kind of heat transfer oil (Dowtherm-a) as the surrogate fluid was carried out. In addition, a computational fluid dynamics (CFD) simulation method was also adopted to study the flow characteristics in the vortex diode using three different fluids. The results show the following: it is feasible to study the diodicity of a vortex diode by a scaling experimental method using surrogate fluid, the CFD simulation method established in this paper can be applied to study the diodicity of the vortex diode, and the structure of the flow field and velocity distribution in the vortex chamber for reverse flow are independent of fluids and only related to the Reynolds number.

Improving wind environment design based on assessing spatial distribution of ventilation efficiency in regional space

This paper discusses the influence of design variations on spatial distribution of Ventilation Efficiency (VE) in idealized residential building groups. Series of design cases referring building length and spacing changing are investigated using Computational Fluid Dynamics (CFD) simulation method. Air change rate (ACH) and purging flow rate (PFR) are adopted as evaluation indices of ventilation efficiency. Simulation results indicate that these design changes have evident effects on distribution of spatial ventilation efficiency. Widening building spacing could improve ventilation efficiency of different spaces. However, the benefit is not linear improved as spacing distance increases. When the distance is higher than 15m, improving extent of spatial ventilation efficiency decreases evidently. Variations of building length also has effect on distribution of spatial ventilation efficiency. As building length increase, less wind could reach into space between south and north buildings, which lead to the decrease of wind ventilation for middle residential-unit. Preliminary study indicates that building length should be restricted within 5 residential-unit.

Modified airlift reactor with a cross-shaped internal and its hydrodynamic simulation by computational fluid dynamic method

ABSTRACTA modified airlift reactor (ALR) with a cross-shaped internal was developed to achieve beneficial flow conditions for an advantageous biological process. To study the effect of introduced internal on the reactor's hydrodynamics, computational fluid dynamics simulation method was applied to predict the flow characteristics verified with experimental data. The internal introduction into a conventional ALR resulted in increased liquid velocities in the riser and the downcomer for 12% and 16%, respectively, maintaining the superficial gas velocity of 3 cm/s. The internal allowed the total gas holdup slightly decreased for 4.8%, whereas the turbulent kinetic energy in the riser was significantly reduced for 13%. The cross-shaped internal modified the flow structure in the ALR's bottom zone due to, presumably, substitution of non-elastic collisions of liquid micro-lumps moving in counter-current directions with elastic collisions of micro-lumps with the wall of the internal, reducing the energy dissipation at the U-turn of the flow. The internal unified the direction of liquid velocity vectors in the bottom zone bringing an order to the liquid momenta in the flows close to the parallel ones and thus, saving energy in the ALR's operation.

Research on suction capacity and dust suppression performance of a reverse circulation air hammer in tunnel drilling

The presence of respirable dust in underground space causes serious health hazards for workers while in tunnel drilling, which could result in pneumoconiosis and silicosis. In order to control the dust dispersion and improve the environment quality of underground space while in tunnel drilling, an innovative drilling system with a reverse circulation (RC) air hammer is proposed. In addition, the structure of the RC air hammer with double-row suction nozzles is specially designed, which contributes to the improvement of suction capacity of the air hammer. Totally four structural parameters of the RC air hammer are optimized, and the effects of four structural parameters on suction capacity of the air hammer also have been investigated by means of Computational Fluid Dynamics (CFD) simulation method, which is crucial for the dust suppression performance of the RC air hammer drilling system. Simulation results have shown that the inclination angle (θs) has the greatest influence on suction capacity among the four structural parameters, which is descendingly followed by the defection angle (θd), the vertical space (L) and the horizontal space (S). Meanwhile, the optimal parameters configuration of the air hammer with double-row suction nozzles has been obtained. Additionally, the laboratory and field tests on the RC drilling system with optimal parameter configuration have been subsequently conducted, and no dust or rock cuttings were suspended in the underground space, which dramatically improves the internal working conditions of tunneling drilling. In conclusion, the suction capacity of the air hammer with optimized structural configuration is outstanding, and the dust suppression performance of the RC air hammer drilling system is excellent, which is applicable to eliminate the dust dispersion in underground tunnel drilling.

Effects of nozzle structure on the gas mixture uniformity of marine gas engine

Natural gas is a preferred fuel choice owing to its easy availability, clean combustion, and low emission levels, especially in the field of marine engines. Recently, manifold multi-point gas injection technology was adopted by engine manufactures to improve the response of the marine gas engine to load changes and the consistency of gas fuel supplied to each cylinder. The characteristics of manifold gas injection have a significant influence on the combustion and emissions of marine gas engines. It is therefore vital to investigate the effect of gas nozzle structures on the gas mixture formation and combustion process. In this study, based on the validation through experimental method, a computational fluid dynamics simulation method was adopted to analyze the influence of the nozzle structure on the uniformity of the intake gas mixture in a natural gas engine, and the combustion process was analyzed to show the further effects of nozzle structure on combustion characteristics. The results show that, at high engine load, the structure of the cross multi-hole gas nozzle can help achieve a more homogeneous gas mixture, which is beneficial to the in-cylinder combustion; it yet yields higher NO emission. The single-hole gas nozzle structure yields an inhomogeneous mixture during the intake stroke and has negative effects on combustion. However, at lower engine load, employing a cross multi-hole gas nozzle results in the deposition of gas fuel residue in the intake port during the intake process, thereby inhibiting complete combustion. The structure of the single-hole gas nozzle can provide higher kinetic energy, which has positive effects on fuel intake efficiency and combustion intensity, although there is still an increased NO emission associated with it, owing to a higher cylinder temperature.

Failure analysis and erosion prediction of tee junction in fracturing operation

Erosion wear in piping is an unavoidable degradation process in the oil and gas industry that causes pipe wall thinning and leads to economic losses and potentially produce personal injuries. The mechanism of pipe erosion remains poorly understood. This study focused on predicting the erosion of a tee junction (T) under various flow types during fracturing operation. The failure analysis of tee junction was determined from its macroscopic features and scanning electron microscope (SEM) images and allowed definition of the failure mode and failure mechanism were defined, which appeared to be significantly different from what has been considered to be traditional. The failure analysis and fluid mechanics theory were used to build a computational fluid dynamics (CFD) simulation method to predict the erosion of the tee junction. The model of two-phase flow in a tee junction indicated that the solid-phase flow is determined by combined effects of the main tube flow, the flow inertia, and the turbulent flow. The distribution of the erosion in the tee was significantly different for various flow types and the simulation results were consistent with the results of the failure analysis. This model of predicted local distribution of erosion wear can assist the monitoring of pipe walls to prevent accidents and reduce maintenance labor.

Thermal Comfort-CFD maps for Architectural Interior Design

Within the context of nearly Zero-Energy Buildings, it is debated that the energy-centred notion of design, proposed by regulatory frames, needs to be combined with a further focus toward users’ comfort and delight. Accordingly, the underlying theory of the research is that designers should take responsibility for understanding the heat flows through the building parts and its spaces. A design, which is sensible to the micro-thermal conditions coexisting in space, allows the inhabitants to control the building to their needs and desires: for instance, maximising the benefits of heat gain from the sun moving a series of internal partitions so as to avoid the danger of over-heating.It is thus necessary that existing simulation software tools are tested to the purpose of modelling and visualising the indoor thermal environment complexity. The research discusses how thermal comfort maps, which are prepared with the use of Computational Fluid Dynamic simulation method, could integrate energy simulation outputs to uphold qualitative architectural design decisions. Mean radiant temperature maps were thus used to design the retrofit of a small educational building in Copenhagen. The thermal opportunities of movable interior partitions (operated by the users) could be estimated, providing a new layer of information to the designer. The applicability of the thermal maps within an architectural design process is discussed adopting standard energy simulation comfort outputs as a reference. The capabilities and the limitations of the method are appraised.

The effect of actuator parameters on the performance of a liquid-jet hammer associated with its jet behavior

Bi-stable fluidic amplifier containing no moving parts was used for switching fluid flow passing through it into an actuator in a liquid-jet hammer. So far, there has been no design basis for developing a liquid-jet hammer with high performance. To provide a guidance, this paper elaborates on the computational fluid dynamics simulation method for investigating the effect of actuator parameters on the performance of a liquid-jet hammer associated with its jet behavior. Given that couple mechanism exists between the flow field in the bi-stable fluidic amplifier and the actuator, dynamic mesh technique and a user-defined function written in C programming language were used to update the mesh in the simulations. Two evaluation criteria—pressure recovery and flux utilization ratio—for a liquid-jet hammer were used in this study. Experimental tests were conducted to verify the simulation results, by which the accuracy and reliability of this computational fluid dynamics simulation method was proved. Besides, comprehensive analysis of the flow behavior in the fluidic amplifier of a liquid-jet hammer was performed by the use of computational fluid dynamics visualization method.

Investigation of heat load calculation for air carrying energy radiant air-conditioning system

Radiant heating and cooling has been widely acknowledged as an important energy-saving technique for building air-conditioning. This paper put forward the concept of Air Carrying Energy Radiant-air-conditioning System (ACERS) to solve some of the limitations of existing radiant air-conditioning systems. Since the orifice plate of ACERS would enable radiant and convective heat transfer with indoor surfaces, using the traditional load calculation method could result in inaccuracy. Therefore, a correction coefficient method for load calculation for ACERS was developed. Based on experiments conducted in summer and winter, in a room installed with ACERS, the cooling and heating loads of the test room were calculated by traditional and newly developed Computational Fluid Dynamics (CFD) simulation method. Then the cooling and heating load calculation results of two methods were compared as the approximate correction coefficient of ACERS, which was validated as about 0.75 in summer cooling and 0.8 in winter heating. Furthermore, the components of air-conditioning load calculation are unrelated with room type, so this simplified load calculation method can be extended to other rooms with ACERS. The load calculation is the foundation of ACERS design and application, and should also contribute to energy conservation in usage of Heating, Ventilating, Air-conditioning (HVAC).

Friction characteristics of sliding guideway material considering original surface functional parameters under hydrodynamic lubrication

The most common failure modes for guideway are wear and contact fatigue, which are significantly influenced by the friction properties of the contact surfaces. In this paper, three-dimensional surface parameters of surface roughness are investigated to evaluate guideway surface. First, an effective three-dimensional surface model is achieved using wavelet transform method and a reverse engineering software (Geomagic Studio). Secondly, effects of the functional surface parameters on friction force, mean pressure, and friction coefficient are studied using the computational fluid dynamics simulation method, and a regression model to predict friction force is achieved. Thirdly, the optimal surface parameters combinations are analyzed looking at friction property index, and the simulation results are compared. Finally, a verification test is conducted to detect the validity of the simulation research. The results show a good agreement between the experimental results and simulations. This study provides theoretical guidance for the manufacture of guideway.

Performance Study of a Fluidic Hammer Controlled by an Output-Fed Bistable Fluidic Oscillator

Using a no-moving-component output-fed bistable fluidic oscillator to control fluid flows into a parallel path has been recognized for a considerable time, but as yet it is not so widely adopted as its obvious benefits would deserve. This may be attributed to the encountered problems associated with its jet behavior, complicated by its loading characteristics. In order to investigate a typical case for the application of the output-fed fluidic oscillator, this paper elaborates on the computational fluid dynamics (CFD) simulation method for studying the performance of a fluidic hammer controlled by an output-fed bistable fluidic oscillator. Given that couple mechanism exists between the flow field in the fluidic oscillator and the impact body, dynamic mesh technique and a user-defined function written in C programming language were used to update the mesh in the simulations. In terms of the evaluation of performance, the focus is on the single-impact energy and output power of the fluidic hammer in this study, to investigate the effect of different parameters of the impact body on them. Experimental tests based on the noncontact measuring method were conducted to verify the simulation results, by which the accuracy and reliability of this CFD simulation method was proved.

Adsorption Kinetics Emulation With Lattice Gas Cellular Automata

ABSTRACTLattice gas cellular automata (LGCA), as a fluid dynamic simulation method, are conceptually simple and can be applied to deal with thermal interface effects to a wide array of boundary conditions. Based on LGCA, the lattice Boltzmann method has been successfully used to model a number of typical continuous fluid dynamic problems. In this research, however, we extend the general Frisch, Hasslacher, and Pomeau method from LGCA to the microscopic scale to emulate the surface adsorption process. Specifically, hexagonal grids topology and geometry are applied in two dimensions with 6-bit digits to represent different states of each grid node. The rule space is then determined as 66. A two-dimensional porous network is constructed for simulating a practical adsorbent material structure. The lattice gas collision and movement are implemented within periodic space boundary conditions. Local rules of lattice gas interaction with network surface are defined and examined. The adsorption probabilities on each adsorptive site, corresponding to adsorption potential with relationship to temperature, are taken into account. As a result, an intuitive visualization of physical surface adsorption kinetics is achieved.

Modeling of Liquefied Natural Gas Release and Dispersion: Incorporating a Direct Computational Fluid Dynamics Simulation Method for LNG Spill and Pool Formation

Computational fluid dynamics (CFD) modeling is a useful tool for studying the spillage, dispersion, and related safety issues of liquefied natural gas (LNG). This paper presents a CFD code that directly models the complete spill and pool formation process (direct CFD simulation method), taking into consideration heat and mass transfer governing equations and the Monin−Obukhov similarity theory for atmospheric stability. The model was validated against experimental data from the Burro test series under atmospheric conditions which allowed the LNG dispersion to be predominately gravity-driven. The direct CFD simulation method clearly provides better predictions than the conventional approach, which simply estimates the pool size from natural gas inlet conditions and uses a fixed vaporization rate. The direct CFD simulation method was further applied to investigate the effect of an impoundment on LNG spill and dispersion mitigation. It was clearly shown that an impoundment can confine the LNG spill and contr...