Air Velocity Research Articles

Effect of air distribution mode on jet flame and emission characteristics of high temperature gas-solid mixed fuel

The characteristics of the flame can not only intuitively reflect the flow, mixing and reaction processes of fuel and oxidant, but also provide detailed information on combustion efficiency and stability. The present study aims to delve into the jet flame characteristics and emission properties of high-temperature gas-solid mixed fuel. A comprehensive series of experiments were conducted on a custom-designed test platform. During the experiments, variations in both the position (h3 = 200, 600, 1000 mm) and velocity (v3 = 67, 138, 223 m/s) of the tertiary air were introduced. The study focused on analyzing the flame lift-off distance, the correlation coefficient of the flame root, the normalized root mean square temperature distribution within the flame body area, and the NOx emission characteristics across various air distribution scenarios. The experimental findings reveal that alterations in the position of tertiary air exert a greater influence on the flame lift-off distance than variations in its velocity. Furthermore, temporal fluctuations in the correlation coefficient of the flame root and the normalized root mean square temperature distribution within the flame body region serve as effective indicators of flame stability. Notably, an increase in both the tertiary air position and velocity leads to a notable reduction in NOx emissions. Additionally, through a quantitative analysis of flame stability, temperature distribution uniformity, and NOx emission characteristics, this study establishes a correlation between flame characteristics and pollutant emission profiles. This correlation offers a more comprehensive understanding of the combustion process involved in high-temperature gas-solid mixed fuel.

Experimental investigation of forced convection heat transfer of heat exchangers with different pin geometries in in-line and staggered design

In this study, the effects of forced convection heat transfer on the surfaces of pin plate heat exchangers with different geometries modified to the heat exchanger form were experimentally investigated. A total of 8 pin fin plate heat exchangers, four of which are staggered and the other four are in-line, were used in the experiments. The heat transfer surface areas of the pin plate heat exchangers are produced equally. The only difference is their geometry, which is produced in four different shapes: triangle, circle, ellipse and square. The experiments were carried out at air velocities of 1 to 6 m/s with 1 m/s increments and at 10 W and 50 W input powers with 10 W increments. The staggered configuration of the pin fin plates demonstrated high performance in heat transfer. The study found that heat exchangers with cornerless pin plates have lower heat transfer compared to those with cornered pin plates. The pressure drops increased as the velocity of the coolant air increased, and the highest-pressure drop was observed in staggered triangular and elliptical pin plate heat exchangers. This research is considered innovative as it involves an experimental comparison between staggered and in-line pin plate heat exchangers in four different geometries, all with equal surface area.

Improve Drying Performance of Noodles using Hot Air Combined with Infrared Stimulation

Noodles are a product that has a large amount of consumption in Thailand. Therefore, it is important to extend the shelf life and increase the value of the noodles by drying. However, drying noodles has a relatively high energy consumption. For this reason, it is necessary to develop an energy-efficient drying process. Therefore, this research aims to study the drying of noodles using hot air combined with infrared stimulation. The drying performance was compared between the case with and without infrared stimulation. The experimental conditions were as follows: drying temperatures were 45, 50, and 55°C and hot air velocity were 1.0, 1.5, and 2.0 m/s. Criteria used to evaluate drying performance include drying rate and specific energy consumption. The study found that increasing in drying temperature and hot air velocity resulted in an increase in the drying rate and power of the dryer. Meanwhile, the specific energy consumption has decreased. It was also found that the drying efficiency of noodles using hot air combined with infrared stimulation was higher than the drying efficiency without infrared stimulation.

Tunnel-type continuous multi-physical field drying equipment: Design, numerical simulation and application

In this study, a tunnel-type continuous multi-physical field drying equipment was developed to combine microwave, hot air, and infrared drying technologies. The microwave source arrangement and hot air equalizing plate were optimized based on numerical simulation to enhance the uniformity of the microwave field and hot air velocity distribution. Mode 4 and opening ratio 37.70% (r = 60 mm) were had the highest electric field distribution and hot air distribution. This equipment was further used to pre-dehydrate cowpeas and the effects of microwave, hot air, and infrared on food drying properties and quality of dried samples were investigated. The results showed that the moisture content was reduced by 20% and the ΔE value greater than 5 after pre-dehydration. Microwave treatment rapidly reduced the moisture content of cowpeas. The infrared treatment significantly improved the uniformity of temperature distribution and the texture profile of the dried sample. The hot air drying increased 10 °C for the overall temperature of the food material and balanced the internal water content of the food material. This study aims to provide future researchers with insights to develop novel microwave-based continuous drying equipment for its commercial applications.

The relationship between occupant behaviour and indoor air quality in Malaysian hospital outpatient departments: A multistage cross-sectional study

IntroductionPoor indoor air quality (IAQ) in healthcare settings may adversely impact occupants’ well-being and promote transmission of infectious respiratory disease. However, evidence on its potentially modifiable determinants, including occupant behaviour, remains scarce. This study aims to determine the relationship between occupant behaviour and IAQ in Malaysian hospital outpatient departments (OPDs). MethodsA multistage cross-sectional study of six randomly selected Malaysian public hospital OPDs was conducted. In stage one, IAQ parameters, including temperature, relative humidity (RH), air velocity (AV), carbon dioxide (CO2), total bacterial count (TBC), and total fungal count (TFC) were measured. In stage two, an observation form based on the Korsavi and Montazami tool for measuring adaptive behaviour was used to examine occupant density, activities, and operation of building envelopes and appliances. Simple correlation, partial correlation, and linear regression analyses were performed to examine the relationship between occupant behaviour and IAQ parameters. ResultsThe IAQ of selected hospital OPDs complied with established standards, except for temperature and AV. Occupant density was positively correlated with temperature and CO2. Meanwhile, occupants' activities including slow walking and brisk walking were positively correlated with temperature, AV, CO2, TBC and TFC. Conversely, occupants' opening of windows and doors were positively correlated with temperature and AV but negatively correlated with CO2, TBC and TFC. Finally, turning on fans was positively correlated with AV but negatively correlated with TBC, whereas turning on air conditioner was positively correlated with CO2. Among occupants’ behaviour, opening of windows and doors contributed the most to variation in IAQ parameters. ConclusionsThe study findings suggest that IAQ in hospital OPDs are influenced by occupant density, activities, and operation of doors, windows, and appliances. Prospective hospital IAQ guidelines should incorporate policies and measures targeting these factors to ensure occupants’ best practices in maintaining healthy hospital indoor air environments.

Study on the deposition characteristics of fine particles at local components in air conditioning ventilation ducts

Air conditioning ventilation ducts are widely used in contemporary buildings. The change of airflow direction in the ducts local components can easily lead to the deposition of particles, which can easily form a secondary source of indoor air pollution and have an adverse effect on human health. Based on this, this paper utilizes the existing experimental data to validate the numerical simulation. The Reynolds stress turbulence model combined with the method of enhanced wall function was used to investigate the deposition characteristics of fine particles in different local components. For the first time, local deposition rates and deposition hotspots were proposed to analyze the simulation results. The results show that the local deposition rate of the particles with a particle size of 1μm do not differ much on each wall surface, and the particles are deposited more uniformly on each wall at the local components, with a difference of less than 10 %, and the maximum local deposition rate is on the outer wall of the local components. When the particle size is larger than 10μm, the local deposition rate on the outer wall of the local component increases significantly, with a maximum increase of 23.3 % (compared to 5μm particles), and the maximum local deposition rate increases slowly with increasing air velocity, with a maximum increase of less than 8 %. The effect of increasing particle size on the maximum local deposition rate is much greater than the increase in air velocity. With the increase of air velocity and particle size, the deposition hotspots of both the 90° bend and the T-type tee duct migrate to the middle of the wall, and the deposition hotspots of the 4-way duct migrate to the inside of the wall.

Optimizing airflow in spiral blast freezers

Spiral blast freezing is a common unit operation used in food processing facilities for rapidly freezing a variety of foodstuffs. The purpose of a blast freezer is to generate high velocity, low temperature air flow over food products being conveyed within refrigerated enclosures to accomplish the freezing process. However, air flow patterns observed within field operating blast freezers are often suboptimal, resulting in diminished system performance. This paper applies a Monte Carlo simulation technique to a food product freezing simulation in order to identify velocity profiles that optimize the freezing process. A one-dimensional food product model is used to evaluate the interplay between the time variation in the magnitude of the air velocity over food products conveyed through the freezing system and the resulting dwell time needed to achieve a target product core temperature at the blast freezer exit. Temporal heat transfer coefficients derived from field measurements made in a newly installed spiral blast freezer serve as a basis to calibrate the one-dimensional product model.The results of the Monte Carlo analysis show freezing system performance is improved when high and stable air velocities over the product are achieved early in the freezing process dwell time. Air flow patterns within a freezing system that result in high air velocity later in the freezing process dwell time are suboptimal. Field-measured data on a newly installed spiral blast freezer showed this suboptimal air flow pattern and the use of baffling within the spiral enables improved airflow leading to an estimated 10 % increase in production throughput.

A comprehensive objective and subjective assessment survey of indoor environmental quality in higher education classrooms in a hot arid climate

A few research studies about IEQ in university classrooms are reported from the hot arid climate despite the severity of this climate. In the reported study, the indoor conditions of university classrooms from a hot arid climate were evaluated considering the collective effect of the four main factors of IEQ, which are the thermal, visual, acoustic, and indoor air quality. The physical measurements were conducted for air temperature, globe temperature, relative humidity, air velocity, illuminance, sound pressure, and carbon dioxide levels. A questionnaire collected the students' sensation, satisfaction, and preferences of the classrooms' environments. The results reveal the sensitivity of the students' environmental experience to the thermal and acoustic conditions. In light of this, a novel IEQ model that considers the air temperature and sound pressure level has been proposed. The model is statistically reliable as it has an RMSE of 0.002. Griffith's method was used to calculate the comfort temperature at 23.0 ± 2.5 °C with a slope of 0.5/K. The findings of this study attempt to fill a gap in the knowledge regarding the IEQ conditions of university classrooms from the hot arid climate.

Modelling convectional oven drying characteristics and energy consumption of dehydrated yam (Dioscorea rotundata) chips

The influence of pre-treatments and different dehydrating temperatures on the drying dynamics, energy consumption, and quality attribute of yam chips was studied. Dehydration was executed employing a convectional oven dryer under four temperatures (50, 60, 70, and 80 °C) and 2.0 m/s air velocity. Yam chips were subjected to pre-treatment conditions of blanching (for 1, 2, 3, 4, and 5 min), citric acid (1 and 5 %), and ascorbic acid (1 and 5 %) solutions whereas, untreated yam chips samples served as the control. Dehydrated yam chips were further assessed for textural and colour properties. The drying rate was found to be faster at a higher temperature of 80 °C compared to lower temperatures of 50, 60, and 70 °C. The asymptotic model was established to be the suitable descriptive model for predicting moisture profile in the pre-treated yam chips based on highest R2 values (0.995–0.999), lowest χ2 values (4.422–18.498), and the root mean square error (RMSE) values (2.103–4.30). Pre-treatment and drying temperature had a significant (p <0.05) impact on the hardness and colour of dehydrated yam chips. Blanching at 4 min yielded yam chips with most preferred texture (hardness: 81.3 N) and lightness (L*) in colour values (71.07 %) after drying compared to other pre-treated samples. The effective moisture diffusivity values of the pre-treated samples were in the range of 5.17294 × 10−9m2/s to 1.10143 × 10−8m2/s for 5 % citric acid samples at 50 °C and all pre-treated samples at 80 °C respectively. The general findings of the study indicated a least energy usage of 43.68 kWh as a cost-effective method of drying. Also, 4 min blanching, 5 % citric acid, and 1 % ascorbic acid at 80 °C were found to be the optimum conditions for pre-treating yam chips based on lower energy level consumption rates and improved sensory properties thus attributing to the quality of the dried yam chips.

Numerical simulation of anti-icing cavity performance for an engine inlet lip

Abstract In this paper, the hot air of the engine lip is the research object, and the three-dimensional model is established. Through the calculation and quantitative analysis of the effect of ice protection at different gas diversion speeds and gas diversion temperatures, the influence of the above parameters on the effectiveness of ice protection is obtained. It shows that the air velocity is from 10 m/s to 40 m/s, and the lowest temperature of the ice surface rises from 266.4 K to 286.2 K. When the air temperature increases from 100°C to 130°C, the lowest temperature of the ice surface rises from 286.2 K to 307.1 K. Therefore, when the air introduction speed is not less than 15 m/s and the flow temperature is not lower than 380 K, the effective anti-ice of the short chamber lip can be realized.

Investigation on fixed pitch Darrieus vertical axis wind turbine

Small-scale Darrieus wind turbines have a wide scope in areas that are isolated from the power grid for such small-scale household applications. Applications of wind turbines on house roofs are one potential way to generate electricity from wind energy harvesting in low-wind urban locations. This work studies the aerodynamic behavior of a vertical axis wind turbine based on a MATLAB programming mathematical model. The NACA0021 airfoil profile blade was used in this present research investigation. The turbine was fabricated with dimensions such as chord length, c = 95 mm, blade height, h = 600 mm, and turbine diameter, D = 600 mm. The experimental results of the turbine for air velocity from 1 to 12 ms−1 were used in this paper and compared with analytical results. It has been observed that the fixed-pitch turbine does not start by itself at a low air velocity of 1 to 5 m/s due to a minimum and negative torque.

Analysis of drying characteristics and quality attributes in peach slices dried via electrohydrodynamic, hot air and electrohydrodynamic-hot air methods

This study aimed to investigate drying times mathematical models and assess the color, rehydration capacity, and microstructure of dried peach using electrohydrodynamic (EHD), hot air, and electrohydrodynamic-hot air (EHD-hot air) drying methods. Peach samples were subjected to drying with two different air temperatures (50 and 55 °C) and electric field (EF, 6.67 and 10 kV cm−1) under constant air velocity (1.5 m s−1). The longest drying durations were obtained in the EHD method (720 and 600 min), followed by hot air (290 and 260 min) and EHD-hot air method (120, 140, 170, and 200 min), respectively. The drying curves were best described by the Midilli et al. and Logarithmic models. The L* values of the samples subjected to hot air drying were found to be lower than those obtained through other methods. No significant effect of the electric field on rehydration capacity was observed. The study revealed that increased temperature and electric field led to surface cracks on the peach. The study highlights the compatibility of the EHD method with the hot air method, suggesting its potential application within the drying industry. From these findings, it was seen that the EHD-hot air combination method could be an alternative to the hot air method in the food industry by reducing the drying time of peaches and considering that the color parameters are generally better than the hot air method.

MFIX–DEM simulation of gas-solid flow dynamics in a dual fluidized bed system

Abstract To overcome the operational difficulties associated with bubbling and circulating fluidized bed gasifiers, a new gasification technology termed dual fluidized bed gasification (DFBG) has evolved. To strengthen the understanding of the gasification and combustion processes in the DFBG system, a thorough analysis of bed hydrodynamics is of paramount importance. Furthermore, the complexity of the hydrodynamics escalates while incorporating diverse fuels like biomass and coal, along with bed materials fluidized in a single reactor due to its nonlinearity and transience. As a result, the study of hydrodynamics in such a system is indispensable. The present study focuses on the discrete element model (DEM) simulation of the bed hydrodynamic behaviour within the gasifier of a DFBG system. The simulation was conducted using Multiphase Flow with Interphase eXchanges (MFiX) software. The influence of superficial velocity on the number of particles in a gasifier was analyzed using the 2-D discrete element model (DEM). In this numerical investigation, transient variation of pressure drop, axial and radial solid volume fraction, and particle velocity was evaluated, and the data were analyzed using the ParaView software. The simulation results of the gasifier indicated an increase in the bed pressure drop with the rise in inlet air velocity. The effective height of solid volume fraction also increased with the surge in superficial velocity. The solid velocity profile and streamlines were also investigated to understand its variation pertaining to the location within the fluidized bed.

The Impact of Ventilation System Type on the Microclimate of Boar's Pen and Their Clinical Triad Parameters

The purpose of the study was the impact of different types of ventilation systems in boar`s pen on the microclimate and their physiological parameters. The control group of boars was kept in a house with a transverse ventilation system, and the animals of the experimental group were kept in a geothermal air supply. It was found that, regardless of the season, transverse ventilation provides a significantly higher air velocity and relative humidity: in Winter - 0.15 m s–1 and 5.4%; in Spring - 0.35 m s–1 and 5.3%; in Summer - 0.41 m s–1 and 0.7%; in Autumn - 0.28 m s–1 and 8.1%. Maintaining a stable temperature by the normative values in the boar housing was due to geothermal ventilation, regardless of the season, especially the "basement effect" was observed in the summer months, where the air temperature was cooled to 4.5°C (P &amp;lt; 0.001), compared to the transverse ventilation system. Compared with the boars in the experimental group, under the influence of the temperature increase in Summer, the boars in the control group increased significantly the respiratory rate to 50.9 ppm (P &amp;lt; 0.001) and heartbeat rate of 45.7 ppm (P &amp;lt; 0.001). An increase in rectal temperature in boars at elevated ambient temperature under both air ventilation systems was not found. The obtained results make it possible to introduce the use of cost-effective geothermal air supply technology in pig farms to harmonize the physiological parameters of boars to meet their biological needs, even in closed housing to improve their welfare.

Heat transfer simulation for re-design of tray dryer to reduce the energy consumption in the cocoa bean drying process

Abstract The tray dryer for the cocoa bean drying process is a solution to overcome conventional drying methods that rely on solar heat. The tray dryer is expected to facilitate the cocoa farmers to dry cocoa beans because it is faster and does not depend on weather conditions. However, even though the current condition of the tray dryer can reduce the energy consumption of drying cocoa beans (from Gunung Kidul, Yogyakarta, Indonesia) compared to the solar heat method, it remains unknown whether the cocoa beans drying quality is good enough. Therefore, this research analyzed the heat transfer phenomena of the cocoa drying process using the computational simulation method to re-design the current tray dryer design so that the new design can fit the drying characteristic of the cocoa bean and reduce energy consumption. As a result, for the air velocity of 25.91 m/s and the ½ opening of the gas valve in 10 minutes, which is already at steady-state conditions, the temperature distribution in the existing tray dryer is not suitable with the characteristics of the cocoa beans drying process. The temperature can be increased by reducing the airflow velocity or increasing the heating value by opening the valve. However, with a new design, the temperature can be increased by up to 37.00% at a velocity of 25.91 m/s with a ½ gas valve opening. Furthermore, the new design can achieve the same conditions as the existing design by only using an opening for a 1/8 gas valve. Thus, using the new design, the tray dryer can achieve the drying characteristics of cocoa beans and reduce energy consumption.

Experimental and numerical studies of the processes of spraying coal-water slurries with pneumatic nozzle

The article presents the results of spraying tests of highly viscous coal-water slurries with a pneumatic nozzle and numerical studies of the structure of the gas-drop jet. An increase in the viscosity of coal-water slurries was ensured by introducing a third component into its composition – industrial waste (pyrogenetic liquid). The moderate effect of the slurry viscosity on the average droplet size of coal-water slurries in the jet is due to the high efficiency of the aerodynamic characteristics of the pneumatic nozzle. Introduction of pyrogenetic liquid in the amount of 20 % by weight into the composition of coal-water slurry significantly increases its viscosity. The value of the surface tension of such a slurry is more than doubled. The increase in the average droplet size was no more than 25 % when pyrogenetic liquid content in the composition of coal-water slurry was over 10 % by weight. The average droplet size of coal-water slurries varied in the range from 180 to 210 microns in the study area of gas droplet jet. The results of experimental and numerical studies have shown good convergence. High air velocities at short distances from the nozzle ensure high crushing efficiency of the jet of coal-water slurry. The breakdown of the boundary layer of the liquid from the periphery of the droplets of coal-water slurries and its subsequent destruction was observed at short distances from the nozzle. The values of the Weber number were 100<We<350. At considerable distances from the nozzle (more than 0.5 m), droplets of coal-water slurries were subjected to vibrational crushing (We<50).

Study on the influence of spray characteristics and air flow direction on heat transfer of spray evaporative condenser

Spray cooling is effectively utilized in evaporative condensers to achieve efficient heat and mass transfer transmission, while also effectively preventing performance degradation caused by packing blockage. The heat transfer efficiency is strongly affected by the relative flow direction between the spray and air flow. This work employs computational fluid dynamics to evaluate and examine the heat transfer effects of parallel and countercurrent air and spray flow in evaporative condensers. The findings indicate that increasing spray density and wall temperature enhances heat transfer efficiency. Smaller droplets with lower initial velocity exhibit superior heat transfer capabilities in parallel flow, while smaller droplets also perform well in countercurrent flow as long as the initial velocity is not too high. Additionally, a slight increase in air velocity improves heat transfer efficiency in both parallel and countercurrent flow conditions. It is important to note that the countercurrent condition has a larger heat transfer effect than the parallel flow.

Влияние погодных условий на завязываемость семян рапса озимого в условиях центральной зоны Краснодарского края

The purpose of the research was to study the influence of temperature and air moisture, wind velocity, cloud coverage, and precipitation amount on seed set of winter rapeseed in the central zone of the Krasnodar region. The objects of the research were winter rapeseed cultivars Elvis, Loris, Sarmat, Selegor, and Olivin. The conditions of 2022 during flowering period were favourable. The air temperature varied from 14.3 to 18.3 °C, precipitation amounted 12.4 mm, and they did not prevent pollination. The wind velocity in average by ten-day periods was 5.1 m/sec, cloud coverage (32.2%) and air moisture (61.1%) were op-timal both for self-pollination and for pollen transfer by wind and insects. The seed set in average was 81.3%. The weather conditions of 2023 were less fa-vorable. Lowered air temperatures – from 12.2 to 16.1 °C, frequent precipitations – 40 mm, air velocity from 2.8 to 4.7 m/sec, increased cloud coverage – to 85%, and air moisture to 77.3% negatively influenced self-pollination and prevented pollen transfer by wind and insects, and thereby decreased the realization of a potential productivity by 23.9%. The cultivars Sarmat and Selegor demonstrated the highest seed set both in favorable and unfavorable conditions. The cultivar Elvis was less sensitive to weather changes during flowering. The variation of a trait of seed set in favorable conditions was insignificant (CV = 2.4–7.1%). Changing of a trait of seed set in a pod to highly variable (CV = 11.7–28.3%) in 2023 certifies the genotype selection with high seed set ability is able only in unfavorable for pollination weather con-ditions.

Optimization of Processing Parameters for Continuous Microwave Drying of Crab Apple Slices via Response Surface Methodology.

To improve product quality and obtain suitable processing parameters for crab apple slices (CASs) produced by continuous microwave drying (CMD), the effects of processing parameters, including slice thickness, microwave power, air velocity, and conveyor belt speed, on the evaluation indexes in terms of temperature, moisture content, color (L*, a*, b*), hardness, brittleness, and total phenolic content of CASs were investigated via the response surface method. The results indicated that microwave power has the greatest effect on the evaluation indexes applied to the CASs under CMD, followed by air velocity, slice thickness, and conveyor belt speed. To produce the desired product quality, the appropriate parameters for CMD of CASs were optimized as 1.25 mm slice thickness, 14,630 W microwave power, 0.50 m·s-1 air velocity, and 0.33 m·min-1 conveyor belt speed. Following that, the moisture content under CMD was found to be 13.53%, the desired color, hardness 0.79 g, brittleness 12.97 (number of peaks), and the total phenolic content 5.48 mg·g-1. This research provides a theoretical framework for optimizing the processing parameters of CASs using the response surface method.

Assessment of thermal performance of energy-active window systems in hot climates

Window systems, particularly in hot climates, are the source of considerable heat transfer that affects the buildings’ indoor environment and energy consumption. Proper design and optimization of its thermal performance significantly contribute to the overall envelope energy performance. Using a multi-layer glazing system, Energy Active Window (EAW) adapts window insulation technology to reuse low-grade air from the HVAC system, keeping the temperature at the internal surface of the window close to the indoor air temperature, minimizing heat exchange between indoor and outdoor. This study aims to reduce energy consumption by optimizing EAW to increase its thermal resistance by channeling the return air (RA) from the HVAC system into the curtain frame, thereby lowering the temperature of the air gap and air film layer. The study examined the window system’s exhaust/return air behavior using the Computational Fluid Dynamics (CFD) tool (Fluent) to simulate the heat exchange between outdoor and indoor building environments. The CFD simulation was validated using experimental measurements. Results show a surface temperature decrease of 4 to 7 °C based on the inner and outer pane airflow conditions when the outdoor temperature is 45 °C with an 8 % margin of error. Various EAW components were tested, including air velocity, air–gap width, volume, and outdoor temperatures, examining both triple and double-glazing layers.