Flame Propagation Following the Autoignition of Axisymmetric Hydrogen, Acetylene, and Normal-Heptane Plumes in Turbulent Coflows of Hot Air

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Christos N. Markides ◽  
Epaminondas Mastorakos
Keyword(s):  
Flame Propagation ◽  
Air Temperature ◽  
High Speed ◽  
High Speed Camera ◽  
Stoichiometric Mixture ◽  
Air Velocity ◽  
Flame Propagation Velocity ◽  
Hot Air ◽  
Air Temperatures ◽  
Continuous Injection

Axisymmetric plumes of hydrogen, acetylene, or n-heptane were formed by the continuous injection of (pure or nitrogen-diluted) fuel into confined turbulent coflows of hot air. Autoignition and subsequent flame propagation was visualized with an intensified high-speed camera. The resulting phenomena that were observed include the statistically steady “random spots” regime and the “flashback” regime. It was found that with higher velocities and smaller injector diameters, the boundary between random spots and flashback shifted to higher air temperatures. In the random spots regime the autoignition regions moved closer to the injector with increasing air temperature and/or decreasing air velocity. After a localized explosive autoignition event, flames propagated into the unburnt mixture in all directions and eventually extinguished, giving rise to autoignition spots of mean radii of 2–5mm for hydrogen and 6–10mm for the hydrocarbons. The average flame propagation velocity in both the axial and radial directions varied between 0.5 and 1.2 times the laminar burning speed of the stoichiometric mixture, increasing as the autoigniting regions shifted upstream.

Flame Propagation Following the Autoignition of Axisymmetric Hydrogen, Acetylene and Normal-Heptane Plumes in Turbulent Co-Flows of Hot Air

2006 ◽  
Author(s):  
Christos N. Markides ◽  
Epaminondas Mastorakos
Keyword(s):  
Flame Propagation ◽  
Air Temperature ◽  
High Speed ◽  
Stoichiometric Mixture ◽  
Air Velocity ◽  
Flame Propagation Velocity ◽  
Hot Air ◽  
Air Temperatures ◽  
Intensified Camera ◽  
Continuous Injection

Axisymmetric plumes of hydrogen, acetylene or n-heptane were formed by the continuous injection of (pure or nitrogen-diluted) fuel into turbulent co-flows of hot air. Autoignition and subsequent flame propagation was visualized with a high-speed intensified camera. The resulting phenomena include the statistically steady ‘Random Spots’ and the ‘Flashback’ regimes. It was found that with higher velocities and smaller injector diameters, the boundary between Flashback and Random Spots shifted to higher air temperatures. In the Random Spots regime, the autoignition regions moved closer to the injector with increasing air temperature and/or decreasing air velocity. After a localized explosive autoignition event, flames propagated into the unburnt mixture in all directions and eventually extinguished, giving rise to autoignition ‘spots’ of mean radius 2–5mm for hydrogen and 6–10mm for the hydrocarbons. The average flame propagation velocity in both the axial and radial directions varied between 0.5 and 1.2 times the laminar burning speed of the stoichiometric mixture, increasing as the autoigniting regions shifted upstream.

Temperature Distribution of Hot Air Flow in Heating Zone for Drying Application

2014 ◽  
Vol 627 ◽  
pp. 153-157
Author(s):  
Nawadee Srisiriwat ◽  
Chananchai Wutthithanyawat
Keyword(s):  
Temperature Distribution ◽  
Air Temperature ◽  
Power Supply ◽  
Air Flow ◽  
Heating Zone ◽  
Velocity Control ◽  
Rectangular Duct ◽  
Air Velocity ◽  
Hot Air ◽  
Set Up

The temperature distribution of hot air flow in heating zone of a rectangular duct has been investigated for drying application. The experimental set-up consists of a heater and a fan to generate the hot air flow in the range of temperature from 40 to 100°C and the range of air velocity between 1.20 and 1.57 m/s. An increase of the heater power supply increases the hot air temperature in the heating zone while an increase of air velocity forced by fan decreases the initial temperature at the same power supply provided to generate the hot air flow. The temperature distribution shows that the hot air temperature after transferring through air duct decreases with an increase of the length of the rectangular duct. These results are very important for the air flow temperature and velocity control strategy to apply for heating zone design in the drying process.

scholarly journals Optimisation of energy consumption of a solar-electric dryer during hot air drying of tomato slices

2019 ◽  
Vol 50 (3) ◽  
pp. 150-158 ◽  
Author(s):  
Nnaemeka R. Nwakuba
Keyword(s):  
Energy Consumption ◽  
Air Temperature ◽  
High Energy ◽  
Slice Thickness ◽  
Air Velocity ◽  
Hot Air Drying ◽  
Air Drying ◽  
Hot Air ◽  
Drying Conditions ◽  
Desirability Index

High-energy demand of convective crop dryers has prompted study on optimisation of dryer energy consumption for optimal and cost effective drying operation. This paper presents response surface optimisation of energy consumption of a solar-electric dryer during hot air drying of tomato slices. Drying experiments were conducted with 1 kg batch of tomato samples using a 33 central composite design of Design Expert 7.0 Statistical Package. Three levels of air velocity (1.0, 1.5 and 2.0 ms–1), slice thickness (10, 15 and 20 mm) and air temperature (50, 60 and 70°C) were used to investigate their effects on energy consumption. A quadratic model was obtained with a high coefficient of determination (R2) of 0.9825. The model was validated using the statistical analysis of the experimental parameters and normal probability plot of the energy consumption residuals. Results obtained indicate that the process parameters had significant quadratic effects (P<0.05) on the energy consumption. The energy consumption varied between 5.42 kWh and 99.78 kWh; whereas the specific energy consumption varied between 5.53 kWhkg–1 and 150.61 kWhkg–1. The desirability index method was applied in predicting the ideal energy consumption and drying conditions for tomato slices in a solar-electric dryer. At optimum drying conditions of 1.94 ms–1 air velocity, 10.36 mm slice thickness and 68.4°C drying air temperature, the corresponding energy consumption was 5.6 8kWh for maximum desirability index of 0.989. Thermal utilisation efficiency (TUE) of the sliced tomato samples ranged between 15 ≤TUE ≤58%. The maximum TUE value was obtained at 70°C air temperature, 1.0 ms–1 air velocity and 10 mm slice thickness treatment combination, whereas the minimum TUE was obtained at 50°C air temperature, 2.0 ms–1 air velocity and 20 mm slice thickness. Recommendation and prospect for further improvement of the dryer system were stated.

Impact of Environmental Conditions on Frost Crystal Structure

2020 ◽  
Vol 28 (02) ◽  
pp. 2050014
Author(s):  
Tongxin Zhang ◽  
Dennis L. O’Neal ◽  
Stephen T. McClain
Keyword(s):  
Crystal Structure ◽  
Air Temperature ◽  
Wall Temperature ◽  
Environmental Conditions ◽  
Strong Influence ◽  
Aluminum Surface ◽  
Air Velocity ◽  
Air Temperatures ◽  
Crystal Type ◽  
Frost Growth

Frost crystal type and distribution were characterized in the initial periods of frost growth on an aluminum surface. Experiments were carried out for a range of wall temperatures from [Formula: see text]C to [Formula: see text]C, air temperatures from [Formula: see text]C to [Formula: see text]C, relative humidities from 15% to 85%, and air velocities from 0.5 to 5.0[Formula: see text]m/s. The results showed that frost crystal type was strongly dependent on the wall temperature and humidity. Changing the air temperature shifted the region of some frost crystal types. Decreasing the air temperature from 22 down to either [Formula: see text]C or [Formula: see text]C led to the decrease of feather crystals but increased the region of scroll crystals. Air velocity had smaller impacts on frost crystal type but had a strong influence on the distance between the crystals, particularly at lower air velocities. The results were compared to prior researchers. The results should provide a better understanding of frost morphology during the early stages of frost growth on metal surfaces.

scholarly journals Pinned Droplet Size on a Superhydrophobic Surface in Shear Flow

Aerospace ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 34
Author(s):  
Mitsugu Hasegawa ◽  
Katsuaki Morita ◽  
Hirotaka Sakaue ◽  
Shigeo Kimura
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Droplet Size ◽  
Water Droplet ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
High Speed Camera ◽  
Sessile Droplet ◽  
Air Velocity

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.

scholarly journals Kinetic parameters identification of conductive enhanced hot air drying process of food waste

2020 ◽  
pp. 223-223
Author(s):  
Mihailo Milanovic ◽  
Mirko Komatina ◽  
Ivan Zlatanovic ◽  
Nebojsa Manic ◽  
Dragi Antonijevic
Keyword(s):  
Food Industry ◽  
Convective Drying ◽  
Diffusivity Coefficient ◽  
Drying Method ◽  
Drying Process ◽  
Air Velocity ◽  
Drying Time ◽  
Hot Air ◽  
Air Temperatures ◽  
Drying Curves

The efficient utilization of waste from food industry is possible after thermal treatment of the material. This treatment should be economically feasible and compromise the energy efficient drying process. The main goal of this investigation is to determine drying characteristics of nectarine pomace as a waste from food industry. The measurements were performed in an experimental dryer by combined conductive-convective drying method with disk-shaped samples of 5, 7 and 10mm thickness and 100 mm in diameter at the air temperatures of 30, 40, 50, 60 and 70oC, hot plate temperatures of 50, 60 an 70oC and air velocity of 1.5 m/s. The drying curves were compared to a few semi-theoretical mathematical models. The Logarithmic model showed the best correspondence. On the basis of experiments, it is determined that the drying process takes place in a falling rate period and it is accepted that the main mechanism of moisture removal is diffusion. The effective coefficient of diffusion was determined using experimental results by calculating the slope of the drying curves. Drying time and equilibrium moisture are determined for each experiment. Analysis of drying curves showed that the conductive-enhanced drying method reduces drying times and increases the diffusivity coefficient. The character of drying rate curves for conductive-enhanced drying was analyzed and compared with pure convective drying of nectarine pomace.

Hot Air Drying Characteristics of Sukkari Date (Phoenix dactylifera L.) and Effects of Drying Condition on Fruit Color and Texture

2015 ◽  
Vol 11 (3) ◽  
pp. 421-434 ◽  
Author(s):  
Alhussein M. Al-Awaadh ◽  
Bakri H. Hassan ◽  
Khaled M. A. Ahmed
Keyword(s):  
Phoenix Dactylifera ◽  
Fruit Color ◽  
Air Velocity ◽  
Hot Air Drying ◽  
Drying Time ◽  
Air Drying ◽  
Drying Temperature ◽  
Hot Air ◽  
Air Temperatures ◽  
Before And After

Abstract Convective hot air drying was used to dry date fruits at different air temperatures and velocities. The kinetics of drying was evaluated by 10 common models. The fruit color and texture were examined before and after drying. Drying time increased as both drying temperature and air velocity decreased. Best fits to the experimental data were provided by the Midilli and Kucuk model, followed by the logarithmic, two-term exponential, and Henderson–Pabis models. Drying affected the fruit color and texture. To minimize such changes, the range of drying temperature and air velocity should be 60–70°C and 2 m/s, respectively.

Effect of microwave, infrared, and convection hot-air on drying kinetics and quality properties of okra pods

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Hany S. EL-Mesery ◽  
Mona A. Elabd
Keyword(s):  
Energy Consumption ◽  
Air Temperature ◽  
Specific Energy ◽  
Specific Energy Consumption ◽  
Drying Methods ◽  
Air Velocity ◽  
Rehydration Ratio ◽  
Drying Time ◽  
Shrinkage Ratio ◽  
Hot Air

Abstract Okra pods were dried using the following drying regimes; microwave (MWD), infrared (IRD) and convective hot-air drying (CHD). The objective of this investigate was to report the influences of drying methods on okra quality under different drying conditions. Data analysis showed that rehydration ratio and colour change increased with increase in drying air temperature and air velocity while specific energy consumption and shrinkage ratio decreased with increase in drying air temperature under (CHD). The rehydration ratio and colour of dried okra increased with increase in both infrared intensity but it also increased with a decrease in air velocity under (IRD). In the MWD method, drying time, specific energy consumption and shrinkage ratio decreased with increases in microwave power while the rehydration ratio and colour increased. Optimum drying period, specific energy consumption, colour, shrinkage and rehydration ratio were obtained for microwave drying. The model of Midilli et al. is the greatest for describing the drying curves of okra under all the drying processing conditions.

Modeling of Basil Leaves Drying by GA–ANN

2013 ◽  
Vol 9 (4) ◽  
pp. 393-401 ◽  
Author(s):  
Amin Taheri-Garavand ◽  
Shahin Rafiee ◽  
Alireza Keyhani ◽  
Payam Javadikia
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Relative Humidity ◽  
Moisture Content ◽  
Air Temperature ◽  
High Accuracy ◽  
Air Velocity ◽  
Feed Forward Neural Network ◽  
Air Temperatures ◽  
Hidden Layer

AbstractIn this research, the experiment is done by a dryer. It could provide any desired drying air temperature between 20 and 120°C and air relative humidity between 5 and 95% and air velocity between 0.1 and 5.0 m/s with high accuracy, and the drying experiment was conducted at five air temperatures of 40, 50, 60, 70 and 80°C and at three relative humidity 20, 40 and 60% and air velocity of 1.5, 2 and 2.5 m/s to dry Basil leaves. Then with developed Program in MATLAB software and by Genetic Algorithm could find the best Feed-Forward Neural Network (FFNN) structure to model the moisture content of dried Basil in each condition; anyway the result of best network by GA had only one hidden layer with 11 neurons. This network could predict moisture content of dried basil leaves with correlation coefficient of 0.99.

scholarly journals Temperate Air Breathing Increases Cycling Performance in Hot and Humid Climate Environment

Life ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 911
Author(s):  
Clovis Chabert ◽  
Aurélie Collado ◽  
Olivier Hue
Keyword(s):  
Air Temperature ◽  
Cycling Performance ◽  
Humid Climate ◽  
Constant Intensity ◽  
Male Athletes ◽  
Perceived Effort ◽  
Sports Events ◽  
Hot Air ◽  
Air Temperatures ◽  
Hot And Humid Climate

Practicing physical activity in a hot and humid climate (HHC) is becoming increasingly common due to anthropogenic climate change and the growing number of international sports events held in warm countries. The aim of this study was to understand the physiological and psychological effects of breathing two air temperatures during cycling exercise in HHC. Ten male athletes performed two sessions of exercise in HHC (T°: 32.0 ± 0.5 °C, relative humidity: 78.6 ± 0.7%) during which they breathed hot air (HA, 33.2 ± 0.06 °C) or temperate air (TA, 22.6 ± 0.1 °C). Each session was composed of 30 min of pre-fatigue cycling at constant intensity, followed by a 10 min self-regulated performance. During pre-fatigue, TA induced a better feeling score and a lower rating of perceived effort (respectively, +0.9 ± 0.2, p < 0.05; 1.13 ± 0.21; p < 0.05) with no changes in physiological parameters. During performance, oxygen consumption and mechanical workload were increased by TA (respectively, +0.23 ± 0.1 L min−1, p < 0.05 and +19.2 ± 6.1 W, p < 0.01), whereas no significant differences were observed for psychological parameters. Reducing the breathed air temperature decreased the discomfort induced by HHC during exercise and increased the performance capacity during self-regulated exercise. Thus, breathed air temperature perception is linked to the hardship of training sessions and directly contributes to the performance decrease in HHC.

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