Transient Computational Fluid Dynamics Model Research Articles

Integrated CFD-FEM approach for external gear pump vibroacoustic field prediction

In this work, a three-dimensional fluid-structural and vibro-acoustics coupled model of a gear pump is presented. Gear pumps represent the majority of the positive displacement machines used for flow generation in fluid power systems. Typically, the dynamics of gear pumps are dependent on the characteristics of the fluid dynamics inside the pump, which translates into vibrations to the housing. These vibrations then propagate to the surrounding medium and emit sound. The purpose of this study is to propose a three-dimensional fully integrated computational model to simulate the complete gear pump behaviour from the fluid dynamics to the structural vibrations, up to the vibroacoustic response. In this hybrid configuration, a transient CFD (Computational Fluid Dynamics) model is first developed to simulate the 3D flow field with a deforming and re-meshing approach to take into account the variation of the volume between the gears. Second, the internal pressure field calculated at each time step is then used as a loading into a structural FEM (Finite Element Method) model of the gear pump to compute the actual stresses and deformations of the housing. Third, the results of the structural response are used as excitation in a vibroacoustic sub-model to simulate the radiated noise using a high-order FEM technique. The comparison between the numerical and experimental flow curves validates the CFD model. The sound power calculations from the vibroacoustic model show good comparison with the sound intensity measurements around the pump casing, confirming the validity of the proposed coupled model. The described CFD-FEM approach proves to be a powerful gear pump design tool: it provides a reliable estimate of gear pump working parameters such as fluid power and vibroacoustic characteristics, starting from the CAD (Computer-Aided Design) geometry of the components. Furthermore, being one of the first multi-domain simulation models of a gear pump, this work can be useful to researchers as a starting point to correlate the noise emitted with the internal flow in full 3D conditions.

Analysis of cavitation and shear in bellows pump: transient CFD modelling and high-speed visualization

Pneumatic drive bellows pumps (PDBPs) are a crucial fluid control component in the semiconductor industry. However, when dealing with specific chemical mechanical polishing (CMP) slurries, agglomeration of particles can occur, leading to scratches, particle residues, pits, and other defects on the wafer surface. The leading cause of agglomeration has been proposed to be cavitation and excessive shear in PDBPs. A high-fidelity multiphase computational fluid dynamics (CFD) model, which fully resolves the response of check valves under hydrodynamic and other external loads, was established to evaluate cavitation behaviour and shear distribution in PDBPs. Moreover, a test rig was built to visualize cavitating flow patterns in PDBPs and verify the accuracy of the CFD model. Among different cavitation regions captured by high-speed visualization, the region near the inner leading edge of the end-ring of the inlet valve is dominant, with high intensity, long duration, and complex morphology evolution. Detailed initiation and development process of cavities in the dominant region are analysed numerically. The shear rate in different domains of PDBPs is estimated, and the inlet valve domain stands out from the other. The strongest shear rate is observed near the leading edge of the end-ring. Furthermore, an analysis of the relationship between cavitation and shear indicates that the high-intensity vortices generated owing to strong shear account for the inception of cavitation. This study contributes to understanding inner flow details in PDBPs and provides a guideline for further optimization of similar pumps.

Effect of baffle turbulators on the horizontal solar film evaporator of the humidification-dehumidification desalination system

The humidification-dehumidification (HDH) desalination system with a Horizontal Solar Film Evaporator (HSFE) is a sustainable and economical approach to providing freshwater in remote areas where conventional energy is limited or condensation irrigation in off-grid greenhouses. The present study investigates the baffle turbulators on heat and mass transfer of the HSFE of the HDH desalination system. To this aim, a comprehensive three-dimensional transient computational fluid dynamics model of the HSFE has been developed. The model is then used to evaluate the effect of various design parameters on the performance of the HSFE. The Design of Experiments methodology is adopted to determine simulated cases. The Response Surface Model is also applied for sensitivity analysis and parametric study, and the non-dominated sorting genetic algorithm II optimization algorithm is used to determine optimum design parameters. It is observed that baffle turbulators enhance the performance of the HSFE by generating vortices and consequently improving the flow mixing and the heat and mass transfer. According to the simulation results, the amount of evaporated water, the average humidity ratio, and the average outlet temperature of the optimum HSFE with baffle turbulators are 64%, 46.5%, and 2.4 °C, more than the conventional HSFE.

On the energy performance of the geothermal dehumidifier of the humidification-dehumidification desalination system

The solar-driven humidification-dehumidification desalination system with a geothermal dehumidifier (SD-HDH-GD) has been given special attention, especially for subsurface irrigation. This contribution scrutinizes the performance of the geothermal dehumidifier of the SD-HDH-GD system. To this aim, a comprehensive three-dimensional transient computational fluid dynamics model of the geothermal dehumidifier and the surrounding soil is developed. An experimental setup is established to verify the developed numerical model. The effect of several operating parameters on the performance of the system is examined. The sensitivity of the water yield, recovery ratio, and gain output ratio to the studied parameters are analyzed. It is demonstrated that the system has different behaviors regarding these measures. Therefore, to gain a comprehensive understanding of the performance of the SD-HDH-GD system, all measures should be considered. According to the obtained results, the maximum amount of condensed water, gain output ratio, and recovery ratio obtained using the performed optimization are 180.05 kg/12 hours, 41.20%, and 0.31, respectively, for the open-air HDH cycle. Moreover, to reach the optimum system performance, the temperature of the inlet air stream to the geothermal dehumidifier should be in the range of 60 to 70 °C, and its relative humidity must be as much as possible.

Numerical Analysis of the Effect of Liquid Water during Switching Mode for Unitised Regenerative Proton Exchange Membrane Fuel Cell

As unitised regenerative proton exchange membrane fuel cell (URPEMFC) is progressing in terms of its performance, more emphasis should be placed on the understanding of the interaction between multiphase reactants and products and its effect during the switching mode. A 3D transient computational fluid dynamics model was utilised in this study to simulate the supply of liquid water into the flow field when the system switched from fuel cell mode to electrolyser mode. Different water velocities were investigated to identify their effect on the transport behaviour under parallel, serpentine, and symmetry flow fields. From the simulation results, 0.5 m·s-1 water velocity was the best-performing parameter in achieving optimal distribution. Among different flow field configurations, the serpentine design achieved the best flow distribution due to its single-channel model. Modification and refinement in the form of flow field geometric structure can be performed to further improve the water transportation behaviour in URPEMFC.

On the performance of solar humidification-dehumidification desalination system with subsurface condenser

The solar humidification-dehumidification desalination system with a subsurface condenser is a promising and sustainable approach to providing a sustainable water supply. In this study, a comprehensive three-dimensional transient computational fluid dynamics model of the system is developed. Due to the lack of an experimental study on the thermal performance of the subsurface condenser, an experimental setup of the subsurface condenser is built, and the obtained experimental results are used to validate the developed model of the subsurface condenser. The developed numerical model is used to evaluate the effect of several involving parameters on the system performance. The optimum system parameters are determined, and the annual simulation of the optimum system is performed. The results show that condenser inlet velocity is the most influential parameter on daily water yield and Gain Output Ratio (GOR). The GOR of the system with the maximum daily water yield is very low. However, despite having 60% less daily water yield, the proposed optimum system has a 1120 % higher GOR. Moreover, it is demonstrated that about 40% of vapor produced in the humidifier leaves the condenser without being condensed into freshwater. Therefore, it is recommended that the system be designed as a closed cycle.

Numerical modeling for the mechanism of shoulder and pin features affecting thermal and material flow behavior in friction stir welding

A three-dimensional transient computational fluid dynamics model is developed to analyze the influence of rotational/non-rotational shoulder and pin characteristics on the thermal and material flow behavior in friction stir welded (FSW) aluminum alloy joints. Four tool designs with rotational/non-rotational shoulder and the pin with/without triple facets are considered. The heat cycle of the rotational and non-rotational shoulder friction stir welded joint (RS-FSW and NRS-FSW) is simulated and experimentally verified, and the welding temperature fields are analyzed. The welding peak temperature of the RS-FSWed joint is the highest, and the non-rotational shoulder significantly reduces the welding peak temperature and the range of the heat-affected zone (HAZ). The rotational shoulder promotes material flow and enhances flow velocity, whereas the non-rotational shoulder reduces both. An increase in the triple facets on the pin facilitates the material flow during NRS-FSW. Viscosity is a physical quantity associated with the welding temperature and strain rate, which is affected by the tool characteristics. The deformation zone caused by the tool is related to the viscosity of the material, the closer the tool, the lower the viscosity of the material. The viscosity of the material gradually increases with an increase in the distance from the tool surface.

Investigation of 3D Transient Flow and Discharge Pressure Pulsation of Helical Roots Air Compressor for Hydrogen Fuel Cell Vehicle

The Roots air compressor has a great potential for air supply in a hydrogen fuel cell vehicle (HFCV) because of its high efficiency, reliable operation, and wide range of flow rates. However, pressure pulsation of the Roots compressor could causes early failure of components of a fuel cell system. In this paper, numerical and experimental investigation on the discharge pressure pulsation of a helical Roots compressor was presented. First, a three-dimensional transient computational fluid dynamics model was built to examine and evaluate the pressure fluctuation amplitude. Then, the influences of angle steps and rotating speed on the fluctuation amplitude of discharge pressure were explored based on the numerical model. Meanwhile, a test rig was carried out to investigate the performance of the air compressor. The maximal discrepancy between experiment and simulation was within 8%. Finally, the effect of the opening angle of the discharge port profile on pressure pulsation was studied. The results showed that the fluctuation amplitude decreased from 6.48% to 1.87% with the opening angle increasing from 77° to 90°. The distribution of velocity showed that the dominating vortexes gradually dissipated with the increase of opening angle, and consequently contributed to the attenuation of the pressure pulsation. It provides new guidance for the structural optimization design of Roots air compressor.

On the thermal performance enhancement of spiral-coil energy piles with a thermal recovery system

The pile foundation designed to ensure building stability when equipped with heat exchanger pipes to harvest geothermal energy is called an energy pile. Ground Source Heat Pump (GSHP) systems combined with energy piles have been used and developed as sustainable and efficient HVAC systems. Energy piles suffer from cold or heat accumulation in and around the pile, degrading their long-term performance. The current study seeks to alleviate this problem by proposing a thermal recovery system. The proposed system circulates ambient air in the pile foundation to extract the accumulated heat. A three-dimensional transient computational fluid dynamics model of the GSHP system coupled with the energy pile and the suggested recovery system is developed. This model is then used to investigate the effect of the various design parameters on the performance of the system and to determine the optimum system parameters. It is demonstrated that the maximum provided cooling load of the system with the proposed recovery system is 50% higher than the conventional system without the recovery. Moreover, the fifteen-year average COPannual of the system with double Ground-Air Heat Exchanger (GAHE) pipes and the system with one GAHE pipe is 30% and 16% more than the system without recovery.

Transient CFD Modelling of Air–Water Two-Phase Annular Flow Characteristics in a Small Horizontal Circular Pipe

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable ‘dry-out’ phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance.

Thermal performance analysis of an energy pile with triple helix ground heat exchanger

A Ground Source Heat Pump (GSHP) is a renewable energy-based HVAC system that extracts or supplies heat from/to the ground via a Ground Heat Exchanger (GHE). One of the most commonly used types of GHE in GSHP systems is the energy pile. In this realm, the GSHP system with a triple helix energy pile has become the focus of attention. To this aim, a comprehensive three-dimensional transient Computational Fluid Dynamics model of the energy pile with triple helix GHE and the surrounding soil is developed. The effect of several parameters, including helix pitch, helix diameter and pipe diameter, on the thermal performance of the system, is investigated. Simulated cases are chosen using the design of experiments methodology. To evaluate the thermal performance of GSHP, an objective parameter is defined as the ratio of the load provided to the load required by the building. The sensitivity of the objective parameter to the studied parameters and surface response curves are analyzed using the response surface model. Also, the optimization process was implemented to obtain the optimum system. It is demonstrated that, the tiple helix GHE enhance the objective parameter by 24% compared to conventional helix GHE. According to the obtained results, the helix pitch has the greatest impact on GSHP thermal performance. Furthermore, the pipe thermal interaction, in addition to the surface area between GHE pipes and the surrounding soil, plays an important role in thermal performance of GSHP.

Influence of Charging Oil Condition on Torque Converter Cavitation Characteristics

Cavitation inside a torque converter induces noise, vibration and even failure, and these effects have been disregarded in previous torque converter design processes. However, modern torque converter applications require attention to this issue because of its high-speed and high-capacity requirements. Therefore, this study investigated the cavitation effect on a torque converter using both numerical and experimental methods with an emphasis on the influence of the charging oil feed location and charge pressure. Computational fluid dynamics (CFD) models were established to simulate the transient cavitation behaviour in the torque converter using different charging oil pressures and inlet arrangements and testing against a base case to validate the results. The CFD results suggested that cavitating bubbles mainly takes place in the stator of the torque converter. The transient cavitation CFD model yielded good agreement with the experimental data, with an error of 7.6% in the capacity constant and 7.4% in the torque ratio. Both the experimental and numerical studies showed that cavitation induced severe capacity degradation, and that the charge pressure and charging oil configuration significantly affects both the overall hydrodynamic performance and the fluid behaviour inside the torque converter because of cavitation. Increasing the charge pressure and charging the oil from the turbine-stator clearance were found to suppress cavitation development and reduce performance degradation, especially in terms of the capacity constant. This study revealed the fluid field mechanism behind the influence of charging oil conditions on torque converter cavitation behaviour, providing practical guidelines for suppressing cavitation in torque converter.

Cell Inertia: Predicting Cell Distributions in Lung Vasculature to Optimize Re-endothelialization.

We created a transient computational fluid dynamics model featuring a particle deposition probability function that incorporates inertia to quantify the transport and deposition of cells in mouse lung vasculature for the re-endothelialization of the acellular organ. Our novel inertial algorithm demonstrated a 73% reduction in cell seeding efficiency error compared to two established particle deposition algorithms when validated with experiments based on common clinical practices. We enhanced the uniformity of cell distributions in the lung vasculature by increasing the injection flow rate from 3.81 ml/min to 9.40 ml/min. As a result, the cell seeding efficiency increased in both the numerical and experimental results by 42 and 66%, respectively.

CFD Modelling of the Thermal Performance of Fruit Packaging Boxes—Influence of Vent-Holes Design

The shelf life of perishable products depends mainly on the conservation of air temperature. Packaging boxes are usually used to accommodate food products during cold storage and transport and/or display. The design of the vent-holes of the packaging box must promote cold airflow and remove the field heat of the produce after harvest at a short time. This study describes the influence of the vent-holes design and its performance during cold storage. The cooling performance of the different packaging boxes is evaluated experimentally and numerically using Computational Fluid Dynamics (CFD). Three new packaging box configurations with the same size but different vent-holes design (size, shape and position) and a reference box are modelled. The transient three-dimensional CFD model predicts the airflow pattern and temperature distribution within the different packaging boxes. The best thermal performance packaging achieved a fruit model temperature 1.5 K to 5 K lower than the other configurations at the end of 8 h of cooling. These predictions allow the development of new packaging box designs that promote the shelf-life extension of perishable products.

Application of directional freezing for seawater desalination: Parametric analysis using experimental and computational methods

Directional freezing is valuable due to their capability to provide excellent relocation of impurities away from ice crystals and thus produce higher desalination efficiency. In this work, desalination of surrogate seawater using directional freezing in radial and vertical directions of a cylindrical crystallizer was assessed experimentally and numerically. Experiments on the effect of different brine concentration and freezing direction on the salinity at various spatial locations was conducted. Moreover, a transient computational fluid dynamics model of multispecies flow which allows for solidification and melting was developed in order to simulate the experimental set-up. Subsequently, a modified model was developed to investigate the role of stirring on the solutes distribution during the directional ice growth. The developed model showed good agreement with the experimental results. The model also showed a successful directional freezing by obtaining the anticipated salinity gradient due to salt diffusion away from the ice growth layer. Performance metrics such as effective partition coefficient, removal efficiency and energy consumption of the desalination process were evaluated. Results showed that better partition and removal efficiency were achieved under lower salinity brine, top freezing instead of bottom or radial freezing, and with stirred flow versus stagnant configurations. Freeze desalination (FD) consumed less energy as compared to multi-stage flash distillation (MSH), humidification-dehumidification (HDH). The FD consumed 11.34 kWh/m3 as compared to MSH and HDH which require 24.6kWh/m3 and 123kWh/m3, respectively. Although the energy consumed in FD (11.34 kWh/m3) was more that of reverse osmosis (RO) (8.2 kWh/m3), it was relatively close.

Numerical Investigation on Churning Loss Torque and Oil Distribution of Reducer Based on Lattice Boltzmann Method

Churning loss and lubrication performance are key issues that need to be considered for the efficiency of electric vehicle reducers. In this article, a 3D transient computational fluid dynamics model based on the lattice Boltzmann method is proposed to determine the oil distribution and churning loss of an electric vehicle reducer. The effectiveness of this method in the calculation of the churning loss is verified by comparing the calculation results with previously published experimental data. The advantages of mesh-free methods over mesh-based methods in two-phase flow simulations are also demonstrated. The oil distribution in an electric vehicle reducer is visualized using numerical computations. The churning loss torque is obtained under different operating conditions determined by changes in the input rotating speed, oil level, and oil temperature. The results of the present study demonstrate that the input rotating speed and oil level have important influences on the oil distribution and churning loss torque, whereas the oil temperature has little effect.

Investigation of interaction between thermodynamic processes and pressure pulsation based on transient CFD model of a reciprocating compressor

This paper presents a transient computational fluid dynamics (CFD) model of a reciprocating compressor to study the interaction of the thermodynamic process and pressure pulsation. To realize the interaction between the thermodynamics and the pressure pulsation, the most difficult procedure lies in dealing with the valve motion and flow through the valve channel both precisely and effectively. Therefore, a discretization method for the flow channel of the ring valve to generate structured grids is proposed. Then, the subsequent model is embedded in the flow channel of the compressor model. User-defined functions are employed to calculate the independent velocity of each valve plate based on the real-time pressure differences across the valve plates. After verified, the influences of the discharge pipeline configuration, pressure ratio, and rotational speed were examined. The results of the numerical model agreed well with the experiment. The maximal deviation between predictions and experiments at the pressure ratio of 3 was 6.14% of indicated power. The maximum deviation increased to 7.42% at the rotational speed of 480 rpm. The results for the discharge pipeline configuration verified that the buffer tank directly following the nozzle of the compressor contributed greatly to attenuating the pressure pulsation. A fast Fourier transform analysis of pressure pulsation showed that at all speeds, the amplitudes were almost the same below the eighth harmonic, and then gradually increased for the higher harmonics.

A winged solar biomass reactor for producing 5-hydroxymethylfurfural (5-HMF)

Biomass-derived alcohols such as 5-Hydroxymethylfurfural represent a promising intermediary energy and species carriers for hydrogen and value‐added chemical production. Solar-driven reforming of biomass to 5-HMF at the desired reaction condition (e.g., at ~150 °C and ~5 bars) offers a sustainable route, but the lack of a rooftop-based solar biomass reactor represents a substantial impediment. In this work, a unique, low-profile “winged” solar concentrator with an evacuated tube reactor was designed for the renewable production of 5-HMF. The viability of this design was examined in detail, using sucrose as the feedstock for 5-HMF production in the presence of sulfuric acid. The optical study indicated that the winged structure significantly increased the effective concentration ratio (by ~42%) and that the design has a broader acceptance angle (from 60° to 90°) compared to CPC alone. During outdoor experiments, the wings boosted the thermal efficiency from 18% to ~25% when operating at 150 °C, and achieved a maximum 5-HMF yield of ~21 mol % (under a solar irradiance of ~800 W/m2). In parallel, a transient computational fluid dynamics model was developed to further elucidate the heat and mass transfer phenomena inside the reactor and to investigate a broader range of operating conditions and reactor design parameters. The numerical and experimental results were in agreement that a specific energy consumption for 5-HMF production of ~23 kWh/kg was achievable and that a full-scale system (~3 L reactor volume, 2.1 m2 gross area) can produce ~0.45 kg of 5-HMF per day, with an average daily solar input of 5 kWh/m2.

Heat transfer modeling within the microclimate between 3D human body and clothing: effects of ventilation openings and fire intensity

PurposeThe purpose of this study is to determine the effect of ventilation openings and fire intensity on heat transfer and fluid flow within the microclimate between 3D human body and clothing.Design/methodology/approachOn account of interaction effects of fire and ventilation openings on heat transfer process, a 3D transient computational fluid dynamics model considering the real shape of human body and clothing was developed. The model was validated by comparing heat flux history and distribution with experimental results. Heat transfer modes and fluid flow were investigated under three levels of fire intensity for the microclimate with ventilation openings and closures.FindingsTemperature distribution on skin surface with open microclimate was heavily depended on the heat transfer through ventilation openings. Higher temperature for the clothing with confined microclimate was affected by the position and direction of flames injection. The presence of openings contributed to the greater velocity at forearms, shanks and around neck, which enhanced the convective heat transfer within microclimate. Thermal radiation was the dominant heat transfer mode within the microclimate for garment with closures. On the contrary, convective heat transfer within microclimate for clothing with openings cannot be neglected.Practical implicationsThe findings provided fundamental supports for the ease and pattern design of the improved thermal protective systems, so as to realize the optimal thermal insulation of the microclimate on the garment level in the future.Originality/valueThe outcomes broaden the insights of results obtained from the mesoscale models. Different high skin temperature distribution and heat transfer modes caused by thermal environment and clothing structure provide basis for advanced thermal protective clothing design.

Numerical analysis of the heat transfer of radiant tubes and the slab heating characteristics in an industrial heat treatment furnace with pulse combustion

For a heat treatment furnace, the precise study of the flow characteristics, combustion and heat transfer in the furnace is essential to know the temperature distribution in a slab during the heating process. In this context several different three-dimensional CFD (Computational Fluid Dynamics) models have been developed to simulate the combustion and heat transfer process in the furnace. These models were developed based on direct fired reheating furnaces with continuous fuel input. In this paper, a novel three-dimensional transient CFD model used to investigate the slab heating characteristics in the heat treatment furnace with pulse combustion was developed. The transient calculation in the furnace was performed based on the steady-state simulation of the furnace temperature, and the movement of slabs on the rollers in the furnace was simulated using dynamic mesh. By comparison, the results from the EDC with two different reaction mechanisms showed good consistency. However, the EDC with the two-step reaction mechanism required one fifth the calculation time of the EDC with the GRI-Mech3.0, and was thus the preferred model. In contrast to direct fired reheating furnaces, the outer radiant tube walls were treated as the coupled boundary conditions in the model to realize indirect heat transfer between the process gas in the furnace and the combustion gas in the radiant tubes. Furthermore, a pulse combustion method was proposed to control the working states of the burners based on UDF (User-Defined Function), in order to realize the pulse combustion process in the heat treatment furnace. By the validation of “Black Box”, the temperature variation of the slab and the gas temperature in the furnace predicted by the model agreed well with the experimental results. The simulation revealed that the temperature distribution of the radiant tubes and furnace gas was uniform and the maximum temperature difference on the outer radiant tube walls was less than 84 K. During the slab transient heating process, the slab temperature distribution became more uniform in the soaking zone and the maximum temperature difference along the thickness of the slab was below 13 K at discharge.