Computational Fluid Dynamics Techniques Research Articles

Numerical analysis of key structural parameters of ejector for PEMFC system under low power conditions

In this study, a three-dimensional numerical model of an ejector is established, which is based on a 40 W power proton exchange membrane fuel cell (PEMFC) system. Computational Fluid Dynamics (CFD) technique is used to analyze the ejector in low power condition. The effects of two key structural parameters (distance from the mixing chamber to the nozzle and the mixing chamber diameter) on the ejector performance at different currents are investigated. It is found that ejector entrainment ratio changes slightly with the distance from mixing chamber to nozzle. The ejector entrainment ratio increases first and then decreases with the mixing chamber diameter. Moreover, with the increase of mixing chamber diameter, the turbulent kinetic energy and turbulent dissipation rate decrease obviously.

Decarbonization of a tissue paper plant: Advanced numerical simulations to assess the replacement of fossil fuels with a biomass-derived syngas

Numerical simulations based on Computational Fluid Dynamic techniques are performed to analyze the possibility of feeding a biomass-derived syngas into the combustion chamber upstream of the hoods for tissue-paper drying, to replace fossil fuels and thus decarbonize the plant. It was observed that, in the context of Favre-Averaged Navier–Stokes equations simulation, syngas requires detailed kinetics and finite-rate approaches, as the fast-chemistry ones, largely employed in the industrial practice for conventional fuels, lead to unreliable results. The actual chamber, originally designed to be fed with liquid petroleum gas, does not operate properly when fueled with syngas, with incomplete oxidation of carbon monoxide. Numerical simulations have proven how very few modifications of the chamber can be devised to permit feeding efficiently the syngas, obtaining low pollutant emissions and meeting the desired requirements in terms of flow and thermal uniformity for the drying process. The solution proposed in the present study, with the effective use of a biomass-derived syngas to feed the drying section of a tissue paper plant, will allow saving approximately 8500 ton/y of CO2 emissions in comparison with today’s fossil fuel carbon footprint.

The role of design parameters on the performance of diffuse ceiling ventilation systems – thermal comfort analyses for indoor environment

ABSTRACT Thermal comfort conditions profoundly affect the occupants’ health and productivity. A diffuse ceiling ventilation system is an air distribution system in which the air is supplied to the occupied zone with relatively a low velocity through the perforated panels installed in the ceiling. The current study evaluated the impact of diffuse ceiling design parameters, i.e. diffuse panel configurations and heat load distributions, on the thermal comfort condition of the occupants. In this regard, the computational fluid dynamics technique was used to evaluate thermal comfort conditions in a waiting room, meeting room and office. The central and dispersal configuration of active diffuse panels was considered. The PMV-PPD model was applied to evaluate the overall occupants’ comfort, while the draft rate was considered to assess local thermal comfort. The model validation was performed by comparing the collected laboratory measurement data. Overall, the results indicated that the central active diffuse panel configuration had a better thermal comfort than the dispersed one. The evaluation of dispersed configuration in realist scenarios, including office and waiting room, had the highest dissatisfaction, with a PPD value of 9%. Local thermal comfort assessment revealed that dispersed configuration had the highest draft rate of 14% in the office.

Milk chilling using nanoparticle enhanced phase change material capsuled inside a jacketed cylindrical module: A numerical and experimental study

In the present study, TiO2 nanoparticles at 0.20, 0.40 and 0.60% by weight fraction were used for developing nanoparticle enhanced phase change materials (NePCM) for rapid chilling of milk. NePCM capsuled inside the jackets of a cylindrical milk chilling module was taken as a test-rig for investigation. Transient energy storage and its discharge during passive milk chilling were numerically simulated using enthalpy-porosity and volume of fluid model of computational fluid dynamics (CFD) technique. The simulated results for the transient temperature fields and the solid-liquid fronts, validated with experiments, clearly visualized the rapidity of heat transfer using nanoparticles in different zones. Use of nanoparticles reduced the charging time, supercooling degree, phase-transition time and the energy discharging time during milk chilling by 25.49, 47.05, 30.18 and 42.90%, respectively. The fresh raw milk was passively chilled from 37 to below 10 °C within 1 h and the chilled milk was maintained below this safe limit using the NePCM inside the module. The test module along with charging set-up, thus studied, revealed the scope of developing a rechargeable, portable and passive chilling cum storage unit for maintaining cold-chain from the milk production points among the distantly located procurement and collection networks in the rural areas.

Reducing the risk of viral contamination during the coronavirus pandemic by using a protective curtain in the operating room

BackgroundAirborne transmission diseases can transfer long and short distances via sneezing, coughing, and breathing. These airborne repertory particles can convert to aerosol particles and travel with airflow. During the Coronavirus disease 2019 (COVID-19) pandemic, many surgeries have been delayed, increasing the demand for establishing a clean environment for both patient and surgical team in the operating room.MethodsThis study aims to investigate the hypothesis of implementing a protective curtain to reduce the transmission of infectious contamination in the surgical microenvironment of an operating room. In this regard, the spread of an airborne transmission disease from the patient was evaluated, consequently, the exposure level of the surgical team. In the first part of this study, a mock surgical experiment was established in the operating room of an academic medical center in Norway. In the second part, the computational fluid dynamic technique was performed to investigate the spread of airborne infectious diseases. Furthermore, the field measurement was used to validate the numerical model and guarantee the accuracy of the applied numerical models.ResultsThe results showed that the airborne infectious agents reached the breathing zone of the surgeons. However, using a protective curtain to separate the microenvironment between the head and lower body of the patient resulted in a 75% reduction in the spread of the virus to the breathing zone of the surgeons. The experimental results showed a surface temperature of 40 ˚C, which was about a 20 ˚C increase in temperature, at the wound area using a high intensity of the LED surgical lamps. Consequently, this temperature increase can raise the patient's thermal injury risk.ConclusionThe novel method of using a protective curtain can increase the safety of the surgical team during the surgery with a COVID-19 patient in the operating room.

Computational and experimental study of a novel corrugated-type absorber plate solar collector with thermal energy storage moisture removal device

Removing moisture from fruits and veggies is an energy-intensive operation since extraction of moisture from the surface of raw products requires a substantial quantity of heat. As a response, designing novel, simplistic dryers with minimal energy consumption is essential. In this research, Corrugated-type Absorber Plate Solar Collector (CAPSC) integrated indirect moisture removers were designed, fabricated, and analyzed experimentally. In this aspect, the heat and airflow behaviour of CAPSC moisture removers with and without Thermal Energy Storage (TES) were explored utilizing the Computational Fluid Dynamics (CFD) technique. The feasibility of the developed CAPSC moisture removers was then experimentally investigated under various scenarios (i.e., 0.014 and 0.024 kg/s mass flow rates). The experimental and computational outcomes of this study demonstrated the efficient design of the manufactured CAPSC moisture removers. The maximum difference in CAPSC exit temperatures between computational and empirical observation was 4.27%. Interestingly, the CAPSC with TES moisture remover performed effectively than the CAPSC moisture remover without TES. As per the empirical observations at 0.024 kg/s mass-flow rate, the average Specific Moisture Extraction Rate (SMER) in CAPSC moisture removers with and without TES was 0.216–0.332 kg/kWh, and 0.224–0.427 kg/kWh, accordingly. Furthermore, the mean exergy efficiency of the dehydration unit of moisture removers was found to be between 43.30 and 46.64%. The overall outcomes of this research revealed the effectiveness of a moisture remover established for drying agricultural specimens.

Effect of blade curve shape on the hydraulic performance and pressure pulsation of a pump as turbine

As an economical and convenient device, a pump as turbine (PAT) is widely preferred in the energy recovery process and micro-hydropower plants. To study the operational stability of a PAT, a forward-curved impeller and a back-curved impeller were designed in this paper. A verified computational fluid dynamics technique is used to compare the two different impellers in terms of the external characteristics, energy loss, and pressure pulsation under the partial load flow rate (0.8Qr), design condition (1.0Qr), and overload flow rate (1.2Qr). The results show that the total entropy generation power of the forward-curved impeller is 41.6%, 49.2%, and 53.6%, respectively, which are lower than that of the back-curved impeller. At the best efficiency point, the head, shaft power, and efficiency of the forward-curved impeller are 9.8%, 18.4%, and 13.1%, respectively, which is obviously better than that of the back-curved impeller. Similarly, the main frequency of the pressure pulsation in volute is the blade-passing frequency, and that of the impeller is the shaft frequency. Compared with the back-curved PAT, the pressure pulsations of the forward-curved PAT are decreased by 92.24%, 73.18%, and 62.22% in volute, impeller, and draft tube, respectively. This paper reveals that the forward-curved impeller not only obviously improves hydraulic performance but also significantly improves pressure pulsations within a PAT.

Application of Double Piping Theory to Parallel-Arrayed Low-Pressure Membrane Module Header Pipe and Experimental Verification of Flow Distribution Evenness.

In this study, the improvement effect of flow distribution evenness is evaluated quantitatively by applying the double piping theory to a parallel-arrayed low-pressure membrane module header pipe structure, and its feasibility is discussed. Orifice inner pipes to be inserted into a full-scale membrane module header pipe are designed via the computational fluid dynamics (CFD) technique, and the flow rates into 10 membrane modules are measured in real time using a portable ultrasonic flowmeter during operation to verify the effect. Results of CFD simulation and actual measurements show that the outflow rate from the branch pipe located at the end of the existing header pipe is three times higher than the flow rate from the branch pipe near the inlet. By inserting two inner pipes (with an open end and a closed end into the existing header pipe) and applying the double pipe theory, the flow distribution evenness is improved. The CFD simulation and experimental results show that the flow uniformity can be improved by more than 70% and 50%, respectively.

Dynamic characteristics of elastic ring squeeze film damper coupled high-speed ball bearings

This paper explores an elastic ring squeeze film damper (ERSFD) model incorporating high-speed ball bearings to study the journal dynamics at different rotor operating speeds and squirrel cage stiffness. Firstly, dynamic model of the ERSFD is established. The journal works under ball-outer raceway excitation rather than rotor unbalance force. Bearing high-speed characteristics including ball centrifugal force, contact angle change and heavy thrust-applied load are outlined in quasi-static model when deriving bearing force. Oil film pressure is governed by the Reynolds equation and solved iteratively using the central finite difference scheme. Flow performance through the orifice and its effect on the oil film pressure are analyzed using computational fluid dynamics (CFD) technique. Elastic ring deformation is addressed using a thin-walled ring model. Secondly, squirrel cage stiffness and rotor operating speeds were chosen as influence parameters to numerically examine the journal steady-state and transient dynamics, and finally the center orbit and vibration of the journal were experimentally measured. The results demonstrate that an increase in squirrel cage stiffness enables the journal to orbit at small size but leads to higher transmissibility. Small squirrel cage stiffness and rotor operating speed result in high amplitude and velocity oscillations and destabilize the journal; alternatively, higher squirrel cage stiffness is ineffective in transmissibility attenuation regardless of rotor operating speed. It was concluded that a small squirrel cage stiffness cooperating with high rotor operating speed contributes to stabilize journal and attenuate vibration effectively.

A 3D CFD model of novel flow channel designs based on the serpentine and the parallel design for performance enhancement of PEMFC

The flow field design is one of the crucial factors that directly affects on the proton exchange membrane (PEM) fuel cell performance. To increase mass transfer, water management, and cell performance, a novel design inspired by serpentine and parallel topologies is proposed. The principal criteria of this design are focused on pressure drop reduction and a more uniform distribution of the reactants via the flow fields. To achieve these objectives, 3D PEMFC models are analyzed using the computational fluid dynamic (CFD) technique for the novel (called V-Ribbed) and common flow fields. The results showed that the pressure and the velocity distributions are more uniform in the V-Ribbed design compared with the other cases. More oxygen penetration at the cathode electrode surface is seen when liquid water within V-Ribbed channels is reduced. This causes to improve the electro chemical reaction rate, current density, and cell efficiency. It is found that using V-Ribbed channels increased the average current flux density on the cathode side about 41.5% and 21.88% compared to serpentine and parallel channels, respectively. Furthermore, the results of the polarization curve showed an enhancement of 2.19% and 2.5% in V-Ribbed design compared to serpentine and parallel channels, respectively.

Effect of the Phase-Shift Angle on the vertical axis Savonius wind turbine performance as a renewable-energy harvesting instrument

Wind energy is the third-largest renewable energy source after hydro and solar energy, so it has great potential in increasing renewable energy as a percentage of national energy. However, wind energy installation is only at 0.25% of the existing potential; so, it still needs to be developed. One of the development efforts is to optimize the wind turbine rotor design. Savonius rotors are among the most popular rotors to convert wind energy into electrical energy. The Savonius turbine is a simple structure, easy to modify to upgrade Savonius performance, and can be operated at low velocity. Phase-shift angles of 0°, 30°, 60°, and 90° were utilized in this study on a two-stage Savonius wind turbine. This study was carried out using Solver CFX utilizing the Computational Fluid Dynamic technique on the ANSYS Student version software. An SST (shear stress transport) turbulence model with steady-state turbulence was used. The purpose of this study was to assess the influence of PSA on the performance of the Savonius two-stage turbine. Factorial design analysis was used in conjunction with the CFD approach. The results indicated that PSA influenced the Savonius turbine’s performance, with 30° being the optimal PSA. Simultaneously, the Cpmax may be obtained using 0.29. The factorial design study with two components revealed that the Phase-Shift Angle had a considerable effect on rotor performance, and the two factors (TSR and PSA) had an interaction.

Ammonia Dispersion in the Closed Space of an Ammonia Engine Room with Forced Ventilation in an Industrial Plant

Air pollution is a global problem that is responsible for more than four million premature deaths each year. Air exchange in ammonia engine rooms is a priority for normal operating conditions, as well as in the event of an emergency release. A numerical approach with the use of computational fluid dynamics techniques can provide detailed data, such as spatial gas dispersion. Therefore, the objective of this study was to prepare a mathematical tool for the assessment of ammonia distribution in an engine room equipped with forced ventilation as a prediction tool for dangerous industrial setup working configurations. This study analyzed the uncontrolled release of ammonia during the production process in an engine room using Ansys Fluent software. It was observed that emergency ammonia leakage of 0.1 kg/s in the assumed air flow poses a great threat to the mechanics. In many simulated scenarios, ammonia spread to the entire building. Moreover, the mass fraction of ammonia was the highest in the gas stream right after its release. After being released, ammonia often accumulated in the ceiling zone, and in inactive exhaust chimneys, air inlets, and doors. It was observed that the effectiveness of the ventilation analyzed depended on the number of active air vents and exhausts, as well as their spatial distribution throughout the building.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Computational Fluid Dynamics of Wind Flow and Air Pollution Modelling: A Review on 3D Building Model Standards

Computational Fluid Dynamics (CFD) simulations are used to monitor air pollution events supported by real-world conditions digitally. Besides, wind flow that has a close relationship with air pollutants dispersion also can be visualized by using CFD simulation. The presence of a building, especially in terms of the building’s geometry, impacts the air pollution dispersion and wind flow that occur around a building or in a specific research area. As there is an involvement of building models in the simulation, some of the standards for the building modelling: Computer-Aided Design (CAD), City Geographic Markup Language (CityGML), and Building Information Modelling (BIM), are being utilized in this type of study. Many types of research have been conducted to study the pollutants and wind flow using the CFD technique of these three standards. Hence, this review paper is used to presents several pieces of research on this related topic. Through this review paper, some of the drawbacks of the study were identified, such as the detailing of the building’s geometry and the compatibility of each standard to be implemented in the CFD simulation.

An optimized numerical tornado simulator and its application to transient wind-induced response of a long-span bridge

The long-span bridges in the tornado-prone area would be potentially struck by extreme transient winds. In this study, the tornado-like wind field is simulated by the numerical Ward-type tornado simulator based on computational fluid dynamics (CFD) techniques. To minimize the discrepancy between the simulated and field-measured tornado winds, the optimization strategy is developed to achieve optimal parameters of the numerical Ward-type tornado simulator, namely the inflow angle (θ) and translation speed (VT). To facilitate the optimization process, a multi-fidelity surrogate model is utilized to effectively integrate both low-fidelity and high-fidelity data for accurate and efficient simulations. Specifically, the cokriging model is constructed by the CFD data associated with both low-cost Reynolds-averaged Navier-Stokes (RANS) equations and high-cost large-eddy simulation (LES) techniques. The “best” parameters (i.e., θ and VT) based on the multi-fidelity surrogate model are input to the numerical Ward-type tornado simulator (using LES technique), and the obtained wind field matches excellently with the field measurements. Finally, the transient wind field generated using the validated numerical Ward-type tornado simulator is employed as the dynamic inputs to the finite element (FE) model of a long-span bridge, and the results highlight the important contribution of the transient bridge aerodynamics.

Key Challenges for High Temperature Thermal Energy Storage in Concrete—First Steps towards a Novel Storage Design

Thermal energy storage (TES) allows the existing mismatch between supply and demand in energy systems to be overcome. Considering temperatures above 150 °C, there are major potential benefits for applications, such as process heat and electricity production, where TES coupled with concentrating solar power (CSP) plants can increase the penetration of renewable energies. To this end, this paper performs a critical analysis of the literature on the current and most promising concrete energy storage technologies, identifying five challenges that must be overcome for the successful exploitation of this technology. With these five challenges in mind, this paper proposes an approach that uses a new modular design of concrete-based TES. A preliminary study of the feasibility of the proposed system was performed using computational fluid dynamics (CFD) techniques, showing promising results.

Comparing lattice Boltzmann simulations of periodic fluid flow in repeated micropore structures with longitudinal symmetry and asymmetry

Pumping of a particulate suspension back and forth through a membrane of periodic axisymmetric pores results in no net flow of the fluid; however, the particles are transported along the pores from one side of the membrane to the other. The movement of the particles is dependent on the geometry of the pore walls. Current simulations for this problem utilise standard computational fluid dynamics techniques (e.g. finite element method, boundary element method). However, there are difficulties associated with applying these techniques to this problem, such as the requirement of many spatial periods. The lattice Boltzmann method overcomes these disadvantages by utilising periodic boundary conditions, which are straightforward to implement. Flow simulations in longitudinally symmetric and asymmetric pores with various Reynolds numbers are compared. The importance of pore shape and viscous effects is showcased through streamline plots.

Effect of Fans’ Placement on the Indoor Thermal Environment of Typical Tunnel-Ventilated Multi-Floor Pig Buildings Using Numerical Simulation

An increasing number of large pig farms are being built in multi-floor pig buildings (MFPBs) in China. Currently, the ventilation system of MFPB varies greatly and lacks common standards. This work aims to compare the ventilation performance of three popular MFPB types with different placement of fans using the Computational Fluid Dynamics (CFD) technique. After being validated with field-measured data, the CFD models were extended to simulate the air velocity, air temperature, humidity, and effective temperature of the three MFPBs. The simulation results showed that the ventilation rate of the building with outflowing openings in the endwall and fans installed on the top of the shaft was approximately 25% less than the two buildings with fans installed on each floor. The ventilation rate of each floor increased from the first to the top floor for both buildings with a shaft, while no significant difference was observed in the building without a shaft. Increasing the shaft’s width could mitigate the variation in the ventilation rate of each floor. The effective temperature distribution at the animal level was consistent with the air velocity distribution. Therefore, in terms of the indoor environmental condition, the fans were recommended to be installed separately on each floor.

Performance of a New Aeronautic Oil-Guiding Splash Lubrication System

Among ever-increasing demands for low power consumption, low weight, and compact reducer systems, an oil-guiding splash lubrication method integrating the oil-guiding cylinder and pipes is suggested to be more suitable for light helicopters, instead of conventional splash or oil jet lubrication. Aiming at improving the lubrication and cooling performance of this special lubrication method, this paper introduces an oil-guiding channel to increase oil quantity reaching the driving gear, bearings, and spline. Firstly, the lubrication and cooling effect of the oil-guiding channel in the main gearbox is investigated at various speeds and oil depths by leveraging with a computational fluid dynamics (CFD) technique. Then, a specialized test bench is set up and utilized for experiments to verify the CFD study. These results show that the numerical results are very satisfactory with the data of experimentation, and the maximum value of relative errors is no more than 15%. What is more, the oil flow rate passing through the monitoring plane with the oil-guiding channel is much greater than that without the channel by about three orders of magnitude. It also suggests that the oil-guiding channel could dramatically increase the lubricating oil in the meshing gear pair, and significantly improve the lubrication and cooling effect.

Retroauricular/Transcranial Color-Coded Doppler Ultrasound Approach in Junction With Ipsilateral Neck Compression on Real-Time Hydroacoustic Variation of Venous Pulsatile Tinnitus.

Alterations in dural venous sinus hemodynamics have recently been suggested as the major contributing factors in venous pulsatile tinnitus (PT). Nevertheless, little is known about the association between real-time alterations in hemodynamics and the subjective perception of venous PT. This study aimed to investigate the hydroacoustic correlations among diverticular vortices, mainstream sinus flow, and PT using various Doppler ultrasound techniques. Nineteen venous PT patients with protrusive diverticulum were recruited. The mainstream sinus and diverticular hemodynamics before and after ipsilateral internal jugular vein (IJV) compression were investigated using an innovative retroauricular color-coded Doppler (RCCD) method to examine the correlation between the disappearance of PT and hemodynamic alterations. To reveal the hydroacoustic characteristics of disparate segments of venous return, a computational fluid dynamics (CFD) technique combined with the transcranial color-coded Doppler method was performed. When the ipsilateral IJV was compressed, PT disappeared, as the mean velocity of mainstream sinus flow and diverticular vortex decreased by 51.2 and 50.6%, respectively. The vortex inside the diverticulum persisted in 18 of 19 subjects. The CFD simulation showed that the flow amplitude generated inside the transverse–sigmoid sinus was segmental, and the largest flow amplitude difference was 20.5 dB. The difference in flow amplitude between the mainstream sinus flow and the diverticular flow was less than 1 dB. In conclusion, the sensation of PT is closely associated with the flow of kinetic energy rather than the formation of a vortex, whereby the amplitude of PT is correlated to the magnitude of the flow velocity and pressure gradient. Additionally, the range of velocity reduction revealed by the RCCD method may serve as a presurgical individual baseline curative marker that may potentially optimize the surgical outcomes.