Increasing Air Velocity Research Articles

The coupled effect of temperature, humidity, and air movement on human thermal response in hot–humid and hot–arid climates in summer in China

Apart from temperature, relative humidity (RH) and air velocity (Va) also affect human thermal comfort, especially in hot–humid and hot–arid climate regions. To explore the coupling effects of temperature, humidity, and air movement on human thermal response in summer, two long–term field studies were conducted in Beihai (a typical hot–humid region in China) and Turpan (a typical hot–arid region in China), from which 610 and 1080 valid datasets were obtained respectively. Results show that the residents of hot–arid regions have higher tolerance to hot environment compared with residents of hot–humid regions. Within the same temperature range, the residents of hot–humid regions want cooler temperatures compared with the residents of hot–arid regions. The variation in RH does not have much influence on human thermal sensation, thermal comfort and thermal acceptability in hot–humid climates. However, in hot–arid climates, humidity shows an opposite effect on the thermal sensation of the human body in different thermal environments. In a slightly warm environment (30 °C–35 °C), humidity has no significant effect on thermal sensation. In an extremely hot environment (>35 °C), an increase in humidity may negatively affect thermal sensation. Meanwhile, in hot–humid regions, when the operative temperature was lower than 33.5 °C, the mean thermal sensation was significantly reduced by increasing air velocity. When the operative temperature exceeded 33.5 °C, increasing air velocity could significantly reduce mean thermal sensation only when the air velocity exceeded 1.0 m/s. However, a slight increment in air velocity can significantly improve thermal sensation in an extremely dry environment. Moreover, the willingness to increase air movement was higher among the residents of hot–humid regions than among the residents of hot–arid regions. These findings support climate adaptation theory and can serve as references for the design of low–energy buildings.

Pressure drop characteristics of reverse circulation pneumatic cuttings removal during coal seam drilling.

To solve the problems that the borehole depth is shallow and the drilling efficiency is low during the gas drainage drilling in soft coal seam with current cuttings removal method, a new technology of reverse circulation pneumatic cuttings removal is proposed. The working principle of reverse circulation pneumatic cuttings removal is analyzed, and the kinetic equation of cuttings in the inner hole of the drill pipe is established. Through experiments, the pressure drop in the drill pipe is measured to reveal the effects of air velocity, cuttings mass flow rate, and cuttings particle size on the pressure drop in inner hole of the drill pipe. When the cuttings mass flow rate is constant, the pressure drop increases with the increase in air velocity. When the air velocity is constant, the pressure drop increases with the increase in cuttings mass flow rate. At low air velocity, the pressure drop of cuttings is primary. As the air velocity increases, the pressure drop ratio of cuttings decreases. Under the same conditions, the order of pressure drop with different particle size cuttings is coarse cuttings > medium cuttings > fine cuttings. Empirical equation of pressure drop coefficient of cuttings is established, which is in good agreement with the actual data.

Design and simulation of mixer insulators to improve turbulence in intake manifold

This article presents an analysis of mixer insulators on the gasoline engine to find the most optimal design. A standard insulator has been redesigned by adding a scrambler of air flow placed in the intake manifold. Simulations are carried out on 10 variations, which include standard insulators, 5, 7, and 9 angled insulators which have slopes of 30°, 45° and 60°, and have a thickness of 5 mm. Each model was analysed using Computing Fluid Dynamic (CFD), with parameters of air velocity 10 m/sec and air pressure 101325 Pa. Simulation results show that mixer insulators with a thickness of 5 mm, 5 blades with a 45° slope angle produce the best turbulence intensity. Meanwhile, another design with a thickness of 5 mm, 9 blades with an angle of 60° slope angle produce the best effect to increase air velocity.

Pinned Droplet Size on a Superhydrophobic Surface in Shear Flow

The recent development of a superhydrophobic surface enhances the droplet shedding under a shear flow. The present study gives insights into the effects of shear flow on a pinned droplet over a superhydrophobic surface. To experimentally simulate the change in the size of a sessile droplet on an aerodynamic surface, the volume of the pinned droplet is expanded by water supplied through a pore. Under a continuous airflow that provides a shear flow over the superhydrophobic surface, the size of a pinned water droplet shed from the surface is experimentally characterized. The air velocity ranges from 8 to 61 m/s, and the size of pinned droplets shed at a given air velocity is measured using an instantaneous snapshot captured with a high-speed camera. It is found that the size of the shedding pinned droplet decreases as air velocity increases. At higher air velocities, shedding pinned droplets are fully immersed in the boundary layer. The present findings give a correlation between critical air velocity and the size of pinned droplets shed from the pore over the superhydrophobic surface.

Drying characteristics of yam slices (Dioscorea rotundata) in a convective hot air dryer: application of ANFIS in the prediction of drying kinetics

This study applied Adaptive Neuro-Fuzzy Inference System (ANFIS) to predict the moisture ratio (MR) during the drying process of yam slices (Dioscorea rotundata) in a hot air convective dryer. Also the effective diffusivity, activation energy, and rehydration ratio were calculated. The experiments were carried out at three (3) drying air temperatures (50, 60, and 70 °C), air velocities (0.5, 1, and 1.5 m/s), and slice thickness (3, 6, and 9 mm), and the obtained experimental data were used to check the usefulness of ANFIS in the yam drying process. The result showed efficient applicability of ANFIS in predicting the MR at any time of the drying process with a correlation value (R2) of 0.98226 and root mean square error value (RMSE) of 0.01702 for the testing stage. The effective diffusivity increased with an increase in air velocity, air temperature, and thickness and the values (6.382E -09 to 1.641E -07 m2/s). The activation energy increased with an increase in air velocity, but fluctuate within the air temperatures and thickness used (10.59–54.93 KJ/mol). Rehydration ratio was highest at air velocity×air temperature×thickness (1.5 m/s×70 °C × 3 mm), and lowest at air velocity × air temperature×thickness (0.5 m/s×70 °C × 3 mm). The result showed that the drying kinetics of Dioscorea rotundata existed in the falling rate period. The drying time decreased with increased temperature, air velocity, and decreased slice thickness. These established results are applicable in process and equipment design, analysis and prediction of hot air convective drying of yam (Dioscorea rotundata) slices.

Experimental analysis of the humidification of air in bubble columns for thermal water treatment systems

The humidification-dehumidification process (HDH) for desalination is a promising technology to address water scarcity issues in rural regions. However, a low humidifier efficiency is a weakness of the process. Bubble column humidifiers (BCH) are promising for HDH, as they provide enhanced heat and mass transfer and have low maintenance requirements. Previous studies of HDH-systems with BCHs draw different conclusions regarding the impact of superficial air velocity and liquid height on the humidification. Furthermore, the impact of flow characteristics has never been investigated systematically at all. In this study, an optimized BCH test setup that allows for optical analysis of the humidifier is used and evaluated. Our test setup is validated, since the influence of water temperature on the humidification, which is exponential, is reproduced. Measurements with seawater show that the normalised system productivity is increased by about 56% with an increase in superficial air velocity from 0.5cm/s to 5cm/s. Furthermore, the system productivity is increased by around 29% with an increase in liquid height from 60mm to 378mm. While the impact of superficial air velocity can be traced back to temperature changes at the humidifier and dehumidifier outlets, the impact of liquid height is shown to be caused by a smaller heat loss surface in the humidifier with an increase in liquid height. For the impact of sieve plate orifice diameter, a clear influence on the humidification is not apparent, this parameter needs to be investigated further. Finally, our new test setup allows for analysing the humidification of air (1) in a systematic way, (2) in relevant measurement ranges and (3) in comparison with optical analyses of the flow characteristics.

Improved indoor environment through optimised ventilator and furniture positioning: A case of slum rehabilitation housing, Mumbai, India

This study optimized the ventilator and furniture location of a tenement unit in a low-income urban habitat to obtain maximum experiential indoor environmental quality (e-IEQ) over the breathing zone. Hypothetical interior layouts using a combination of the two design parameters of ventilator location and bed position were generated for optimizing the design layout. This layout could promote maximum indoor airflow and minimum indoor air temperature and contaminant concentration. In this study, an improved indoor environment is hypothesized to be attainable through improved natural ventilation and thermal performance in the occupied zones. A sequential methodology involving “parametric design modeling–computational simulation–multiobjective optimization–multicriteria decision making”-based framework was selected. Results exhibited that the currently designed tenement unit had a poor indoor environment, whereas the hypothesized iterated layout “optimized design layout, scenario 3 (ODL 3)” derived from the optimization and decision-making algorithm performed effectively in providing e-IEQ. An increase in experiential indoor air velocity by 0.2 m/s and a decrease in temperature by 2 °C were observed over the monitoring point in the ODL 3 considering the existing scenario. Therefore, this study can find a way toward the development of sustainable habitat design guidelines under upcoming slum redevelopment policies across the nation.

Heat transfer characteristics of activated coke in the moving bed for sulphur resource recovery

A counter-flow moving bed and tube heat exchanger was designed and built for the heat transfer process of activated coke desorption, the heat transfer law between particles and tube wall surface in the moving bed was studied. The results show that with the increase of hot air inlet temperature and moving velocity of activated coke particles, the heat transfer coefficient inside the tube largely increases and then remains a small change. As the air velocity increases, the heat transfer coefficient inside the tube also shows increasing trend. In addition, with the increase of air temperature and particles moving velocity, total heat transfer coefficient of the moving bed and heat transfer coefficient outside tube increase first and then decrease. Finally, based on experimental data, the correlation coefficient of heat transfer coefficient outside the tube is obtained.

Numerical simulation of water spray transport along a plate of a heat exchanger

Water spraying is widely being used in many industrial applications because of the benefits it has shown over cooling. This paper presents a numerical investigation to simulate evaporating water spray along a plate of an exchanger. Indeed, we were interested in a horizontal channel whose lower wall is the plate of the exchanger maintained at a heating flow. This plate is exposed to a turbulent airflow in which water droplets were injected. The equations governing the continuous phases (air) and the dispersed phase (water) were developed. These equations were solved using Comsol Multiphysics. A comparison of the simulation results and those of the experiment reveals an acceptable concordance. Therefore, the numerical results present the thermal behavior by studying transversal and longitudinal evolution of temperature. Moreover, the maximum evaporated water flow (mmaxew) and the plate temperature are investigated for several physical parameters of the continuous phase, such as velocity, relative humidity and inlet temperature. The results show that these parameters have significant impact on the cooling of the plate. In addition, mmaxew witnesses a remarkable decrease by increasing relative humidity. However, increasing air velocity and inlet air temperature could improve mmaxew.

Exploring the Polymer Drawing of the Air Centrifugal Spinning.

The air-flow field of the air centrifugal spinning is simulated and measured. The simulated air velocities coincide well with the measured ones, confirming the correctness of the air-flow field model. The polymer drawing in the air-flow field of the air centrifugal spinning is modeled and simulated. Effects of the rotation speed and initial air velocity on the diameter and radius vector of the threadline are investigated. The air velocity is found to decrease with the increase of the distance away from the nozzle exit. Simulation results show that both larger rotation speed and higher initial air velocity can reduce the threadline diameter. The radius vector of the threadline increases rapidly with the increase of the initial air velocity, which is helpful to reduce the threadline diameter.

Effect of superficial air and water velocities on the erosion of horizontal elbow in slug flow

During the development of oil and gas fields, it is common for elbow suffering from sand wear. In this study, the erosion performance of 316 L stainless steel at the elbow was analyzed using the slug flow erosion experiment loop. The experiment was conducted under slug flow with different superficial air and water velocities using a detachable elbow. After weighing the mass loss and analyzing the sample surface, the erosion rates in different parts of the elbow were quantified and the erosion regularity was analyzed. The results indicate that the increase in superficial air velocity has a greater impact on the erosion rate than that in the superficial water velocity. The maximum erosion damage occurs at the outer wall in the 67.5° position. With the increase in superficial air and water velocity, the number of scratches on the maximum erosion position reduces.

Continuous microwave drying of germinated brown rice: Effects of drying conditions on fissure and color, and modeling of moisture content and stress inside kernel

Suitable fissures in kernels and the golden yellow color are the desired visual quality to evaluate germinated brown rice (GBR) subjected to drying processing. To improve the visual quality of GBR dried in a continuous microwave dryer, the effects of microwave intensity (1–5 W/g), air velocity (0–2 m/s), drying duration for per drying pass (2–10 min), and material layer thickness (4–12 mm) on the formation of visual quality of GBR in terms of fissure and color were investigated by using bench experiments and numerical modeling. The results showed that temperature and moisture content of the final dried GBR had high uniformity in the continuous microwave dryer, and most of the dried GBR kernels were in a “mild” (1–2 fissures in kernels) and “moderate” (3–4 fissures in kernels) fissure degree at the microwave intensity of 2–3 W/g. The increasing air velocity may weaken the effects of interior stress caused by moisture content gradients on fissures in GBR kernel. The chroma b*, representing the golden yellow color index of GBR, significantly (P < 0.05) increased with the microwave intensity and the drying duration for per drying pass of 4–6 min. The material layer thickness lower than 10 mm was suitable for the formation of golden yellow color appearance of GBR. The simulation results confirmed that microwave intensity had a positive effect on the formation of fissures for GBR in a continuous microwave dryer due to the rising stress along the short-axis direction of GBR kernel. The distribution of moisture content inside GBR kernel was relatively uniform under the microwave intensity lower than 3 W/g, and the higher moisture content gradients aggravated the evolution of fissures in kernels. Considering the desired visual quality of the final GBR, the appropriate microwave drying conditions of GBR were developed as microwave intensity of 2 W/g, air velocity of 1.0–1.5 m/s, drying duration of 6 min for per drying pass and 8 mm material layer thickness, which induced the generation of suitable fissures and the formation of golden yellow color for GBR under the continuous microwave dryer. This study may provide a preference for the industrial application of microwave drying of cereal materials such as GBR.

Optimum spacing between grooved tubes: An experimental study

An experimental study on optimum spacing between grooved tubes is reported in this paper. Two grooved tubes having pitch of 10 mm and 15 mm and a plain tube were considered for the heat transfer analysis. The spacing between two tubes with same pitch was varied from 10 mm to 35 mm with a step size of 5 mm. Velocity of air flowing over the tube surfaces was changed from 0.4 m/s to 1 m/s using a blower fan. Based on Nusselt number (Nu) the optimum spacing between the tubes was decided. The optimum spacing between grooved tubes of pitch 10 mm and 15 mm was compared with that of plain tubes. From the experimental analysis it was noticed that with increase in air velocity (increase in Reynolds number) the tube surface temperature reduced irrespective of any tube considered. Nu increased with increase in air velocity for all the tubes. The important conclusion drawn from the present study was that, there exists a limiting spacing (optimum) between the tubes above which no change in Nu was observed. Spacing of 30 mm was found to be the optimum spacing between the tubes irrespective of its surface geometry modifications.

Transient Investigation of Stack-driven Air Flow Through Multiple Upper-vents in the Presence of Constant Indirect Flow Velocity in Rectangular Ventilated Building

The paper investigates the time independent effect of Stack- driven airflow in cross- ventilated building with multiple opening in the presence of constant indirect flow velocity. The dimensionless model of momentum and energy equations are analyzed, using second order linear differential equation to develop the explicit expression for velocity, temperature profiles together with volumetric and mass- transfer by means of separation of variable method. Some numerical examples are presented graphically in order to illustrate the effects of physical parameters involved in the study. From the course of investigation, it was observed air temperature and velocity increase with the increase in both parameters (θ0), (Pr) and (Gr). Respectively. In addition, comparison with previously published work by A. L. Muhammad et. al (2016) was performed. In which, the study concluded that, the results for present work is more effective and efficient than the previous work in term of ventilation process. Finally, from the course of investigation, it was observed air temperature and velocity increase with the increase in both parameters (θ0), (Pr) and (Gr) respectively.

Computational Fluid Dynamics Model of Air Velocity through a Poultry Transport Trailer in a Holding Shed

HighlightsComputational fluid dynamics modeling was an effective tool to simulate conditions on transport trailers in holding broilers for slaughter, to understand the performance of existing and alternative system configurations;Model simulation and measurements indicated that less than 32% of airflow generated by the cooling fans in the existing fan configuration in this study actually penetrated through the bird-occupied spaces;Simulations suggest that higher air velocity in the bird occupied zone within the modules can be achieved by alternative fan configurations at the holding shed, such as employing one fan per module, or with the addition of a transition enclosures from each fan outlet to the face of the receiving module. Abstract. The configuration of cooling systems in commercial holding sheds, where live broilers wait in cage modules for slaughter, varies between processing plants, with cooling system efficacies largely unknown. A computational fluid dynamics (CFD) model was developed to simulate airflow through cage modules in a poultry trailer in a typical holding shed configuration. Three alternative design configurations were simulated in order to better understand the air velocity profiles and to explore potential improvements for better cooling performance. Experimental data were collected within modules in a poultry trailer, parked in an existing commercial holding shed during warm summer conditions. Results from the CFD model had reasonable agreement with measured field data. Simulated air velocities were mostly within one standard deviation of measured values. Simulation of airflow through modules in the base configuration showed that less than 32% of airflow from the fans actually penetrated through the bird-occupied space. Module tiers experienced different airflow penetration due to the ad hoc positioning/alignment of the fans relative to the modules. In the base industry configuration, fans were in fixed positions and the number of fans and their centerline discharge axes did not align with the modules on the trailer. Regions not aligned with the faces of the fans, such as the uppermost and bottommost tiers, and horizontal locations offset from the fans, received the least airflow through the modules. Sections of modules experienced lower air velocity with increasing distance from the fans. Simulation of Design Alternative 2 (which added additional fans so that a fan was centered on each row) predicted an improved fan airflow of 3.08 and 3.05 kg s-1 through the cages in two adjacent rows, compared to 1.52 and 2.15 kg s-1 predicted for the original configuration. The increased air velocity using the alternative design illustrates the potential improvement and need to further optimize the design of these holding sheds. This research showed that a CFD model is an effective tool to simulate airflow conditions on poultry trailers in holding sheds to explore various holding shed cooling configurations and strategies. Keywords: Air velocity, CFD, Poultry Transportation, Poultry welfare.

Numerical simulations of the combustion characteristics for a 660MW tangentially fired boiler with different closing-to-wall air velocities

To solve the problem of high temperature corrosion of water-cooled wall of power station boiler, this paper proposes a new type technology of closing-to-wall air. Taking a 660MW tangentially fired boiler as the research object, numerical simulations were conducted to study the influences of closing-to-wall air velocity on the combustion characteristics in the boiler. The results show that O2 concentration in the flowing region is significantly increased, CO concentration is significantly reduced, and the oxidizing atmosphere in the near-wall region is enhanced. As the closing-to-wall air velocity increases, the rigidity of the airflow is gradually stronger, and the penetration depth of the airflow increases, so that the coverage area of the airflow is increased. The influence of the closing-to-wall air velocity on the combustion effect of the boiler is negligible.

Drying mechanism of Indian dark red onion slices at high velocity

Drying of onion is a moisture removal process to increase shelf life. Convection drying experiments are conducted at a drying temperature of 50 ℃, 60 ℃, 70 ℃, and at four high airflow velocity (2, 3.6, 5.7, and 7.7 m/s) for Indian dark red onion. The objective is to analyze the drying mechanism of Indian dark red onion slices at high velocity. The work diverges from the literature in analyzing the drying mechanism of Indian dark red onion slices at air velocity above 2 m/s. Moisture content removal curves for upper velocities (i.e., for 5.7 and 7.7 m/s), shows seamless logarithmic in nature. Dehydration process from Indian dark red onion accelerates as velocity increases. Air velocity 2, 3.6, and 5.7 m/s exhibit a better moisture removal rate at 60 ℃ than 50 and 70 ℃. It is observed that the weight basis moisture content per unit mass flow rate of air decreases as velocity increases. The effective moisture diffusivity averagely increases with an increase in air temperature and air velocity. The values for the arithmetic mean of effective moisture diffusivity lies between 1.096646×10-11 to 1.295467×10-11 and activation energy observed in the range of 10.8709 to 12.7719 kJ mol-1.

Blockage characterization of particles for gas–solid two phase flow in the broken zone around drainage borehole

Borehole sealing is the significant measure for improving coalbed methane (CBM) drainage effect. Based on the technology of using particles to seal the air-leakage fractures around drainage borehole, the deposition and blockage characteristics of particles in the coal (rock) broken zone were experimentally investigated under the gas–solid two phase flow conditions, and the porosity formed by the filled glass beads with different particle sizes (3 mm, 4 mm, 5 mm and 6 mm) in the porous medium zone was used to simulate the broken fractures around boreholes in this paper. The results showed that the particle mass flow rate increased with the inlet air velocity for blockage boundary, and the change trend could be divided into three stages: slow growth stage, rapid growth stage and medium growth stage with the increase of inlet air velocity. Furthermore, the relationship between inlet air velocity and particle loading ratio for blockage boundary in the porous medium displayed a scoop-shaped curve: with increasing inlet air velocity, the particle loading ratio decreased at first and then increased rapidly, subsequently increased slowly, which is different from the existing research. In addition, the effects of conveying pressure and particle size of porous medium on the blockage boundary were also studied. The research work is beneficial to engineering applications of the sealing technology.

Multi-Physical Coupling Field Study of 500 kV GIL: Simulation, Characteristics, and Analysis

With the construction of a large number of hydropower stations, transmission lines crossing a river and urban utility tunnels, gas insulated transmission line (GIL) has been applied widely due to its large transmission capacity, low environmental impact and high reliability. Accurate modelling of physical quantities and their characteristics of GIL provides a theoretical basis for its design and operation, which is of great significance to ensure the safety and reliability of GIL operation. The mathematical model and their relationship of GIL multi-physical fields are analyzed at first, upon which simulation model of GIL is built. Secondly, multi-physical coupling field model of electric, magnetic, thermal, fluid and stress field for GIL is studied, while simulation results are basically in consistent with experimental data to verify effectiveness of the model. Thirdly, distribution of multi-physical fields and their relationship are simulated and analyzed, while proximity effect, edge effect and compression factor of GIL multi-physical field are discussed. The results show that the radial temperature inside GIL is higher at the top, lower at the bottom, leading to uneven distribution of thermal expansion displacement, while the axial temperature distribution is basically uniform, which falls firstly and then rises near basin insulator thus results in edge effect. Proximity effect leads to asymmetric distribution and a slight increase of temperature inside GIL as well as a dramatic increase of air velocity around GIL. In addition, when ambient temperature is lower than -5 °C, the compression factor is much lower than 1 and the effect of compression factor should be considered in simulation.

Heat transfer performance analysis of a large-scale separate heat pipe with a built-in tube

Large-scale separate heat pipes (SHP) are preferable to establish passive cooling systems for spent fuel pool (SFP). But the SHP performs not well in long heat transport applications. In this paper, a built-in tube separate heat pipe (BTSHP), which is a modification of SHP by inserting a straight smooth tube in the heat pipe evaporator is proposed to improve the heat pipe performance. Based on the SHP numerical model, which is validated by experimental results, the BTSHP heat transfer model is established. And the heat transfer performances of both SHP and BTSHP under different filling ratios, heat transport distances, and thermal loads are studied. It is found that BTSHP generally shows 8–28% extra heat transfer capacity than SHP. And the maximum thermal resistance is 5.2 °C/kW, which is 1.6 °C/kW lower than that of SHP. Compared with SHP, the BTSHP evidently decreases the overall circulation resistance and considerably improves the heat transfer capacity, especially in long heat transport distance, moderate and high filling ratio applications. Besides, when the cooling air velocity increases, the BTSHP can further release its potential by reducing fraction of liquid that flows into the built-in tube and get a better performance than SHP.