Air Velocity Distribution Research Articles

CFD and experimental study of heat dissipation from an anti-coning, pin vented, inboard mounted brake disc

Anti-coning brake discs are known for their superior NVH characteristics when compared to other disc designs, but also for poorer heat dissipation. Cooling characteristics of such a disc design are studied numerically and experimentally on a specially developed Thermal Spin Rig. The disc is installed inboard on a high-performance off-road vehicle, with portal axles and wheel drives, resulting in nearly fourfold higher disc rotational speeds in comparison to the wheel speeds. Being exposed to the free-flowing air and rotating much faster makes this application well worth the attention and deeper study in terms of disc cooling. Computational Fluid Dynamics (CFD) analyses show a detailed distribution of air velocities and pathlines, temperatures, pressures, and convective heat transfer coefficients. The results are all very coherent, conveying very useful information, both qualitatively and quantitatively. Their cumulative effect has been successfully validated by comparing the CFD predicted average convective heat transfer coefficients ( hconv) with the experimental results obtained on the Thermal Spin Rig, in a controlled environment. CFD results show to be very close to average hconv values calculated from measured cooling curves. The agreement is very good for the wide temperature and speed range. The overall relative differences are under 5%, and in most cases under 3%, except for the low disc rotation speeds, which show a maximum relative difference of 12.5% calculated at 200 rpm, for the disc heated to 300°C. Such outcomes give confidence in the CFD results for future work in both disc design and vehicle installations.

To the Theory of Grain Motion in an Uneven Air Flow in a Vertical Pneumatic Separation Channel with an Annular Cross Section

The possibilities of the action of uneven air flows on the grain material in the separating channels are still not used enough. The reason for this is the insufficient knowledge of the processes of interaction of the components of the grain material with an uneven air flow. The purpose of the research is to increase the efficiency of grain material separation according to aerodynamic properties by purposefully changing the diagram of air velocities in the channel sections using the actions of lateral and aerodynamic forces. The separation efficiency of grain material components was determined by trajectory analysis. The different geometry of the pneumatic separation channel was studied. The study of the distribution of air velocity and air pressure vectors in a vertical annular channel was carried out using the FlowVision software. It has been established that a change in the air velocity diagram can be implemented both by changing the geometric parameters of the channel and by additional distributed air supply through the perforation in the side walls of the pneumatic channel. Based on the analysis of the velocity field, an improved scheme of a pneumatic gravitational separator is proposed for separating grain material into three fractions according to aerodynamic characteristics.

CFD modeling of the building integrated with a novel design of a one-sided wind-catcher with water spray: Focus on thermal comfort

The rising energy demand for buildings has enhanced public awareness of sustainable energy sources and technologies. In particular, natural ventilation systems such as wind-catchers have attracted considerable new attention. A new wind-catcher design with single-stage direct-air evaporative cooling was proposed for indoor air conditioning. An Eulerian-Lagrangian approach employing the Realizable k-ε model was utilized to conduct the CFD simulations. Furthermore, the effects of inclining the bottom surface of the wind-catcher and installing a baffle across the flow path on the air temperature drop, water mass fraction, and air velocity distribution were studied. The inclined bottom surface led to more flow uniformity in the room compared to the conventional geometry. The baffled wind-catcher with β = 0, 30, 45, and 60° and unbaffled wind-catcher showed different flow patterns and thermal comforts. A methodology for evaluating the thermal comfort performance of evaporative cooling systems integrated into natural or passive cooling devices was also proposed based on the generated CFD results. The baffled wind-catcher with β = 60° combined with an evaporative cooling system significantly reduced the air temperature inside the building up to 17.4 °C and improved the occupants’ thermal comfort. The most suitable design for thermal comfort was also determined.

Field study of the effect of piston wind on the airflows at the controllable vents and exits of a subway station

Knowing the distribution of piston air flow at the controllable vents and exits can help to utilize the piston wind more effectively. Field test data were collected to analyse the air velocity distribution at the controllable vents and the ventilation volume of the station. The results showed that variations in the air velocity at the controllable vents within a cycle could be divided into four stages and that the air velocities in the third and fourth stages were high. The air velocity distributions at the controllable vents were uneven, showing a rapidly decreasing trend along the length of the platform. The air velocities at the controllable vents located at the front and the end of the platform were more than 3 m/s and less than 0.1 m/s, respectively. The ventilation volumes under Mode 1 (the controllable vents on one side of the platform are open) and Mode 2 (the controllable vents on both sides of the platform are open) were 89128 m3/h and 56488 m3/h, respectively. The ventilation volume under Mode 2 did not satisfy the ventilation volume requirement of the station. Therefore, opening the controllable vents on only one side of the platform is recommended.

Research on the thermal comfort of passenger compartment based on the PMV/PPD

With the increasing requirements of consumers for vehicle performance, the thermal comfort has become a key index of consumers. The thermal environment inside the passenger compartment directly determines the thermal comfort of vehicle. In this paper, the vehicle cabin and the heat fluxes are measured at different thermal environment. The thermal comfort of the passenger compartment is analyzed based on Computational Fluid Dynamics. The transient response of the thermal environment of passenger compartment is investigated, and the thermal comfort of the passenger compartment is evaluated based on the PMV/PPD (Predicted Mean Vote/Predicted Percentage Dissatisfied) evaluation index. By analyzing the air temperature and velocity distributions from the transient model, the effect of the field synergy angle is used to explain the different thermal distribution based on different heat dissipation conditions. The results showed that the smaller the field synergy angle, the stronger the heat transfer performance.

Influence of tunnel ventilation on the indoor thermal environment of a poultry building in winter

Tunnel ventilation systems are widely used to create thermal environments for poultry buildings in China. However, existing research mainly focuses on the indoor thermal environment in summer and rarely considers the winter season. A field test was conducted in a layer breeder building in Handan City, China to systematically investigate the characteristics and problems of the thermal environment in winter. Forty-two measuring points were set to analyze the indoor air velocity and temperature distributions, and the nonuniformity coefficient and temperature humidity velocity index (THVI) were adopted as the evaluation indices. Furthermore, the exhaust fan layout of tunnel ventilation was explored to improve the indoor thermal environment using a validated computational fluid dynamics (CFD) method. The results show that (1) the indoor air velocity distribution is quite nonuniform with a nonuniformity coefficient of 0.74, the maximum difference of which is as large as 0.62 m/s; (2) the nonuniformity coefficient of indoor air temperature distribution is 0.16, and the maximum temperature difference is as large as 12.9°C; (3) the indoor THVI is below the appropriate range of 18–25, making the thermal comfort zone only 61.4%; (4) separately installing exhaust fans at the front and end walls with the symmetrical locations and sizes can improve the distribution uniformities of indoor air velocity and temperature by 22.0% and 88.3%, respectively. The experimental results and parametric optimization of tunnel ventilation in this study will be beneficial for designing an appropriate thermal environment for poultry buildings during winter. • The non-uniformity coefficient of air velocity in experimental poultry house is 0.74. • The maximum difference of air temperature in experimental poultry house is 12.9 °C. • The thermal comfort zone in experimental poultry house is only 61.4% of entire space. • Separately installing exhaust fans on front and end walls improves the environment.

CFD Applied to the Analysis of the Operation of a Solar Still Pyramidal-type

This work shows the results obtained for the temperature distributions of the component elements of a pyramidal type solar still. The results of the air velocity and density distributions inside the still are also shown. The results indicate which are and where the maximum values of temperature, density, and airspeed are located. These results are useful because they help to establish how the geometry of the still influences its operating process. The study by the CFD technique turns out to be very useful because it allows the formulation of design criteria regarding the geometry of the still and how they could make improvements in the use of solar energy in solar stills.

Uniformity of Supply Air in the Plenum for Under-Floor Air Distribution Ventilation in a Circular Conference Room: A CFD Study

Underfloor air distribution (UFAD) systems are increasingly used for their advantages in improving energy savings, indoor air quality, and thermal comfort. In UFAD systems, an underfloor plenum delivers conditioned air to the air supply diffusers. The distribution of internal air velocity and static pressure in plenums determines the uniformity of the airflow to the occupied zones. As a result, the plenum has a detrimental effect on the characteristics of the supply air and, thus, the resulting indoor air quality and thermal comfort. Nevertheless, most existing studies on underfloor plenums focused on small-scale plenums with a single internal air duct. Large plenums and multiple air ducts in UFAD equipped in large premises are underexplored. In this study, a circular underfloor plenum with a large scale (radius of 15 m, height difference of 0.9−2.9 m) and 503 under-seat diffusers in a conference room was studied using computational fluid dynamics (CFD) simulation (ANSYS Fluent (16.0)). The distributions of airflow velocity and static pressure inside the plenum were analyzed and compared to one concentrated air supply mode and three uniform air supply modes. Based on the air velocity at the center of under-seat diffusers, the outgoing airflow uniformity from the diffusers under four cases was evaluated by the index of air velocity uniformity. The results showed that the multiple supply ducts with bottom air outlets yielded the best uniformity of supply air. The findings of this paper are expected to provide a technical basis for realizing the optimal design of the UFAD system in terms of uniformity of supply air.

Experimental and numerical study of the flow dynamics and thermal behavior inside a car cabin: Innovative air diffusers and human body plumes interactions

In confined spaces, such as vehicle cabins, airflow and temperature distribution are the most critical factors affecting thermal comfort and pollutant dispersion. To develop innovative and energy-efficient HVAC systems, a deep understanding of the interaction of the jet flow from the air diffusers on the development process of the human thermal plume became essential to improve the knowledge of airflow patterns for optimizing ventilation system design, thermal comfort, and, indirectly, the energy efficiency. The human thermal plume is one of the most challenging phenomena to capture with optical measurement methods and validate with complex numerical models, given its unsteady nature governed by the buoyancy forces. This study aims to validate the interaction of jet flows from classical and innovative air diffusers on the thermal plume by comparing measured data and numerical simulation results. This validation was made with a specific approach by comparing PIV fields from measurements and CFD results with boundary conditions of air velocity distribution from LDV data. The PIV measurements for flow distributions at the air vents and the thermal plume of an advanced thermal manikin in the driver’s seat were performed in a 1:1 scale mock-up of a Renault Megane car cabin in a climatic chamber. The results obtained with both methods showed good agreement regarding air velocity ranges and distributions. Despite the confined cabin space restricting the development of the thermal plume, a difference in maximum velocities of 0.08 m/s was observed when the distance between the top of the head and the ceiling was doubled. With innovative air diffusers, air velocity distribution showed a more uniform flow than classical diffusers.

Orthogonal optimization for effective classification of different tea leaves by a novel pressure stabilized inclined chamber classifier

AbstractIn the field of tea separation and processing, modern high‐tech can realize the nondestructive separation of tea and improve the quality of tea. In this study, a novel pressure‐stabilizing inclined chamber classifier was proposed, which was used to adjust the particle size distribution of tea at the entrance of the classifier. A suitable cavity can control the change of wind speed so that tea leaves are not easy to bend and deform, and the success rate of grading is improved. Second, three parameters that affect the success rate of tea classification are put forward: suction wind speed V, suction distance H, and suction distance L. When the parameters are V = 6 m/s, H = 40 mm, and L = 20 mm, the best response value is obtained, thus the most suitable entrance shape is obtained. Finally, the internal flow field of the classifier is analyzed, and different sizes of tea leaves are classified according to the change of air pressure flowing through the closed structure cavity. With the distribution of air velocity, tea leaves fall into collectors with different widths. Therefore, the flow field simulation test shows that the classifier can classify high‐quality tea according to the airflow. The model lays a foundation for further study of the fluid–solid coupling process and interaction between particles.Practical ApplicationsIn this study, a novel pressure‐stabilized inclined chamber classifier was designed, and three parameters that affect the success rate of tea classification were put forward. The process conditions were optimized by orthogonal tests, and the number of experiments was reduced. This method can be used to evaluate the influence of various technological parameters on tea classification. In order to improve the classification success rate, it is necessary to statistically discuss the results of the orthogonal test and flow field analysis.

An aisle displacement ventilation system for twin-aisle commercial airliner cabin

The environmental control system in most commercial airliner cabins supplies air from shoulder and ceiling level and exhausts air at floor level on both sides of walls. The ventilation system mixes air in the cabins to create a uniform air temperature distribution that is great for thermal comfort. However, the mixing ventilation also enhances airborne contaminant transfer. Displacement ventilation has been proposed for use in cabins, but they may create high air temperature stratification and draft. This investigation developed an aisle displacement ventilation (ADV) system that can reduce air temperature stratification and be easily installed in cabins. By installing the system in a five-row, twin-aisle cabin mockup, our study found that ADV can create a low air velocity distribution in the cabin and can maintain an acceptable air temperature stratification without draft. The system created an uprising flow that can effectively remove airborne contaminant generated from respiratory activities. The experimental data were used to validate a computational-fluid-dynamics (CFD) program. The validated CFD program was used to compare the ADV with the under-seat displacement ventilation (USDV) and the underfloor air distribution (UFAD) along the aisles. The ADV had better thermal comfort than the other two systems, but the cabin air quality of the three ventilation systems was similar.

Air flow inside a vertical pipe induced by a free-falling water jet

The air flow induced by a water jet freely falling inside a vertical pipe with its top and bottom both open to the atmosphere was investigated experimentally and numerically. In the experiments, the radial air velocity distribution and the air pressure variation along the vertical pipe were measured. The air drag of the falling water jet was related to the jet surface disturbance and analyzed by introducing the equivalent friction factor. A predictive model was developed for the air flow inside a 3-m-high pipe based on the momentum equation and its results compared well with the experimental measurements. Numerical simulations were also conducted by approximating the free-falling water jet as a continuous moving solid with diameter and velocity varying in the direction of motion. The effects of pipe size on the air velocity profile and the induced air flow rate were examined. The simulation results showed that the streamwise air velocity profiles inside pipes of different sizes approached the same after a certain traveling distance. The maximum induced air flow rate was found at the pipe diameter of about 20 times of initial water jet diameter.

Performance evaluation of fin-and-tube heat exchangers in an outdoor unit considering air flow mal-distribution

The heat transfer capacity of air conditioning outside units is inextricably related to fins and airflow distribution, and research on the combination of the two is lacking. To analyze the fins and fin-and-tube heat exchanger, three-dimensional numerical models of the fins and flow field of the outdoor unit are created in this paper. On the one hand, the heat transfer and fluid flow characteristics of the fins are quantitatively evaluated and analyzed. On the other hand, the resistance coefficients of the porous media are numerically fitted to study the uniformity of the air velocity distribution on the surface of the heat exchanger. Two indexes, the total integrated heat capacity and JF-factor, are applied to evaluate the performance of the fins and fin-and-tube heat exchanger on the overall and specific levels, respectively. The results indicate that slit fins perform better than wave fins at heat transfer, whereas plain fins perform the worst. However, improved heat transfer performance results in increased pressure drop, which has a two-sided effect. It causes both a decrease in air volume flow rate and an increase in air distribution uniformity. Comparing the comprehensive performance of different fins, JF-factors of slit fins and wave fins are on average 20.95% and 14.36% higher than plain fins. In terms of overall performance, slit fins and wave fins have higher integrated heat exchange capacities than plain fins by 18.0% and 9.33%, respectively.

Erratum in “Experimental measurements and modelling of vapor-liquid equilibria for four mixtures of 2,3,3,3-tetrafluoropropene (R1234yf) with 1,1,1,2-tetrafluoroethane (R134a) or 1,1-difluoroethane (R152a) or trans-1-chloro-3,3,3-Trifluoropropene (R1233zd(E)) or 2-Chloro-3,3,3-trifluoropropene (R1233xf)” [Int. J. Refrigeration, 140 (2022) 172–185, https://doi.org/10.1016/j.ijrefrig.2022.05.006

The heat transfer capacity of air conditioning outside units is inextricably related to fins and airflow distribution, and research on the combination of the two is lacking. To analyze the fins and fin-and-tube heat exchanger, three-dimensional numerical models of the fins and flow field of the outdoor unit are created in this paper. On the one hand, the heat transfer and fluid flow characteristics of the fins are quantitatively evaluated and analyzed. On the other hand, the resistance coefficients of the porous media are numerically fitted to study the uniformity of the air velocity distribution on the surface of the heat exchanger. Two indexes, the total integrated heat capacity and JF-factor, are applied to evaluate the performance of the fins and fin-and-tube heat exchanger on the overall and specific levels, respectively. The results indicate that slit fins perform better than wave fins at heat transfer, whereas plain fins perform the worst. However, improved heat transfer performance results in increased pressure drop, which has a two-sided effect. It causes both a decrease in air volume flow rate and an increase in air distribution uniformity. Comparing the comprehensive performance of different fins, JF-factors of slit fins and wave fins are on average 20.95% and 14.36% higher than plain fins. In terms of overall performance, slit fins and wave fins have higher integrated heat exchange capacities than plain fins by 18.0% and 9.33%, respectively.

Experimental investigation of self-regulating capability of open-cathode PEMFC under different fan working conditions

Self-regulation capability of the open-cathode PEMFC generally means that the stack itself can adjust its state to response to different operating conditions to achieve better performance when the external control strategy remains unchanged. In this paper, self-regulating capability of the stack are analyzed when its cooling fan works under blow or suction mode at different voltages. The result of output voltage shows that the stack achieves better self-regulation when the fan operates at 8.5 V in both blow mode and suction mode. Analysis of impedance spectra reveals that the stack can realize self-regulating function by adjusting activation resistance and ohmic resistance, and the cathode activation resistance is dominant. Furthermore, the result of a cycle load test indicates that the stack can better reflect the self-regulating capability in fan suction mode than in blow mode, and the stack can achieve better water and heat regulation in suction mode. Finally, according to the air velocity distribution and temperature change, it is found that self-regulating capability in suction mode play a better role due to more uniform heat remove. A suitable fan operating voltage and mode are critical for the self-regulating capability of the open-cathode PEMFC stack to maintain a water-heat balance.

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.

Pollutants Concentration during the Construction and Operation Stages of a Long Tunnel: A Case Study of Lowari Tunnel, (Dir–Chitral), Khyber Pakhtunkhwa, Pakistan

Long tunnels with significant overburden, changeable geological conditions, a steep gradient, water infiltration, and heavy traffic flow are susceptible to environmental concerns during both construction and operation. The availability of fresh air and visibility is the most important necessity in excavation for tunnel workers inside the tunnel during the construction phase, as well as those crossing the tunnel during operation. Lowari Tunnel’s tunnel air pollutants were researched. Carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), hydrogen sulfide (H2S), sulfur dioxide (SO2), nitrogen oxide (NO), ammonia (NH3), nitrogen dioxide (NO2), PM1, PM2.5, PM10, air velocity, dust morphological and particle size distribution analysis are among the parameters under consideration. The findings provide evidence for the development of tunnel air quality.

Modeling and Simulation of the Aerodynamic Noise of High-Speed Train’s Pantograph

This article aims to investigate the aerodynamic noise of the pantograph of the high-speed trains in different operating conditions. CFD technique was used to assess the acoustic noise of the pantograph components. Three-dimensional computational simulations were performed using FLUENT software. Comprehensive analyses of the acoustic pressure and the air velocity distributions were accomplished for the detailed full-scale pantograph components. Good agreement was found between the obtained results and the reported results in the literature. Vortex shedding was the main source of noise at the pantograph panhead and knee. A modified model for the pantograph was introduced to reduce the aerodynamic noise of the pantograph’s panhead. A different design profile for the collector was presented as a possible solution for the reduction of both the aerodynamic noise and the reduction of the fluctuating forces at the panhead-catenary interaction, which affects the quality of the power transmitted to the high-speed train. The cylindrical cross-section of the panhead bars was replaced with different cross-sections. It was noticed that at a speed of 250 km/hr, the use of an elliptic cross-section has resulted in an almost 23.1% reduction in the acoustic sound pressure for the pantograph.

Experimental and numerical investigation of thermal performances of R290 and R1234yf refrigerants in a cold room

In today’s world, most of the currently used refrigerants in refrigeration systems have an important influence on global warming. This study presents the experimental and numerical consumption of thermal and energy performances comparison of new generation low GWP R290 and R1234yf refrigerants for a cold room. Evaporator temperatures of −9 °C, −6 °C, −3 °C, and condenser temperatures of 25 °C, 30 °C, 35 °C were utilized as the operational parameters. Results revealed that the highest COP values in the system for R290 and R1234yf were 3.99 and 3.41, respectively. An average 11.1% increase in the cooling capacity was determined with R290 compared to the R1234yf refrigerant. In the second part of the study, evaporator surface temperature and air velocity distributions in the cold room for R290 and R1234yf refrigerants occurring until the cold room temperature reached from the ambient temperature to 0 °C were numerically shown using Ansys Fluent 18.1. Numerical analysis using experimental data indicated that the evaporator surface had a lower temperature with R290 refrigerant than R1234yf. Results of the study highlighted the usability of R290 refrigerant instead of R1234yf in refrigeration systems in terms of thermodynamic performance.

The design of fuel dryer in palm oil processing industries by utilizing the heat product of boiler based on computational fluid dynamic

Incomplete combustion process from boiler in palm oil processing industry usually discharged into the air in the form of black smoke due to the high water contain in the fuel of the boiler which will pollute the air. With this problem the research was conducted of designing a simulation of fuel dryer to dry out the boiler fuel before it used by utilizing the exhaust heat of the combustion system in the boiler. The simulation design of the fuel dryer is based on computational fluid dynamic (CFD) with parameters control are air velocity and heat temperature of fuel dryer. The results obtained the distribution of air velocity in the dryer has a value range of 0-40 m/s with the highest velocity occurring when hot exhaust air enters the dryer while the temperature distribution inside the dryer has a value range of 90-270 °C with the highest temperature appearing around hot air inlet exhaust and the lowest temperature appears in the hot air outlet section of the dryer.