Constant Air Flow Research Articles

Single-Stage Aerodynamic Separation of Fly Ash Produced after Pulverized Combustion of Coal from the Ekibastuz Basin

The single-stage separation of fly ash from field 1 of the electrostatic precipitator of Reftinskaya GRES (Regional Thermal Power Plant), which burns coal from the Ekibastuz Basin, was performed by aerodynamic classification with the use of a flow of air. It was found that, at a constant airflow rate of 50 m3/h, the morphologically uniform fractions of small spherical particles with a narrow distribution, for which dmax was 2, 3, and 4 μm and d90 was 4, 6, and 8 μm, can be separated by decreasing the speed of the classifier rotor from 22000 to 10000 rpm. At a minimum speed of 2000 rpm, the target product of separation was a narrow fraction containing large particles, which were characterized by dmax of 109 μm and d90 of 205 μm. It was established that SiO2 and Al2O3 were the basic chemical components of the fractions obtained, and the total concentration of these components was as high as 86–91 wt %. With increasing the size of fractions with dmax from 2 to 116 μm, a decrease in the concentration of SiO2 and an increase in the amounts of Al2O3 and Fe2O3 were observed. The dependence of phase composition on the particle size was established for the small fractions: as dmax was increased in a range of 2–25 μm, a monotonic decrease in the concentration of a quartz phase and an increase in the concentration of mullite were observed; the concentration of a Fe-containing spinel phase also increased.

Comparative study of vertical and horizontal indirect evaporative cooling heat recovery exchangers

This paper presents a comparative study of a counter-cross flow plate heat recovery exchanger, which operates as an indirect evaporative air cooler in cooling conditions. In the study, thermal performance of this exchanger with different placement modes (vertical and horizontal) was investigated by numerical simulation based on original mathematical model. To validate the numerical model, vertically and horizontally positioned prototypes with the same exchangers were made and tested on the test rig. According to the test results, the numerical model has a satisfactory accuracy. For these two types of prototypes, influence of supply and exhaust air inlet parameters (temperature and relative humidity) on the thermal performance of the two prototypes in both constant inlet airflow rate and variable inlet air flow rate was researched. The results show that, under conditions of constant airflow rate with variable supply air parameters, the outlet supply air temperature of the exchanger set vertically is 1.41–2.40 °C lower than that of exchanger set horizontally, meanwhile, 24–44% more cooling capacity is obtained by the vertical exchanger. It indicates that placement mode has important effects on thermal performance of the exchangers and the exchanger set vertically always shows a better performance. The main reason is considered to be the existence of larger dry areas in exhaust air channels of the horizontal exchanger that reduce the heat transfer between supply air and exhaust air. Therefore, characteristics of the heat transfer in horizontal exchangers was especially studied in this paper.

Performance Analysis of a Three-Stream Adaptive Cycle Engine during Throttling

One advantage of the adaptive cycle engine (ACE) is its ability of throttling with constant airflow by the combined control of variable geometries, resulting in an improvement of spillage drag. However, the improvement is achieved at risk of a complex technical solution and control. This article investigates the selection scheme of variable geometries and engine configuration. It focuses on the performance of a three-stream ACE during throttling, whose configuration and control schedule are simpler than other types of ACEs. Five variable geometries are selected from seven available options through comparison analysis. The uninstalled thrust decreases from 100% to 60.36% during the subsonic throttling and to 59.81% during the supersonic throttling. Benefitting from the decreased spillage drag, the installed performance of the three-stream ACE is improved to some degree during throttling. This improvement is less than the result of a three-bypass ACE, whose configuration and control schedule are more complex. Thus, the three-stream ACE is a compromise design considering the technical risk and variable cycle characteristic, which is a better platform to verify the component technology and control schedule for the further research on a more complex type of ACE.

Vascularization of the trachea in the bottlenose dolphin: comparison with bovine and evidence for evolutionary adaptations to diving.

The rigid structure of the mammalian trachea is functional to maintain constant patency and airflow during breathing, but no gas exchange takes place through its walls. The structure of the organ in dolphins shows increased rigidity of the tracheal cartilaginous rings and the presence of vascular lacunae in the submucosa. However, no actual comparison was ever made between the size and capacity of the vascular lacunae of the dolphin trachea and the potentially homologous structures of terrestrial mammals. In the present study, the extension of the lacunae has been compared between the bottlenose dolphin and the bovine, a closely related terrestrial Cetartiodactyla. Our results indicate that the extension of the blood spaces in the submucosa of dolphins is over 12 times larger than in the corresponding structure of the bovines. Furthermore, a microscopic analysis revealed the presence of valve-like structures in the walls of the cetacean lacunae. The huge difference in size suggests that the lacunae are not merely a product of individual physiological plasticity, but may constitute a true adaptive evolutionary character, functional to life in the aquatic environment. The presence of valve-like structures may be related to the regulation of blood flow, and curtail excessive compression under baric stress at depth.

Venturi tube calibration for airflow and volume measurement

Ventilation measurement by Venturi meters (Vm) has not been validated for human ventilation application in basic and applied physiology. This project aimed to demonstrate the feasibility of the Vm as an inexpensive, robust method for inspiratory ventilation measurements used in Indirect Calorimetry. A differential pressure transducer sensitive from 0 to 1000 Pa combined with Vm made from retail PVC tubing (50 mm Inside Diameter (ID) at inlet, 17.5 mm ID throat section) allowed for airflow measurement of 1–8 L s−1. A Turbine (Ti) was used as the criterion method. Variable airflow of atmospheric, temperature, pressure saturated (ATPS) conditions, were produced through manual 3 LATPS manoeuvres of a calibration syringe and constant airflow was induced using a commercial air compressor. The Vm produced valid volumetric airflow (V̇) estimates across non-steady state pulsatile flow conditions ( ± 0.22 L s−1 95% confidence limits with zero bias for Bland-Altman). The Vm also made valid V̇ measurements for steady-state continuous flow ( ± 0.065 L s−1 95% confidence limits with zero bias for Bland-Altman). Column statistics revealed Vm mean estimates of 3 L calibrated syringe manoeuvres at different flow rates (0.1–8 L s−1) to be 2.972 ± 0.020 vs. 3.066 ± 0.022 L for Ti, respectively, with less than half the percentage error (0.9 vs. 2.2%, respectively). The results indicate that air flow measured by a Vm has similar accuracy to a criterion device for simulated human inspiratory airflow conditions. Further instrumentation and validation studies will lead to potential use of the Vm for measurements in human ventilation, such as airflow (L·s−1), tidal volume (VT) and minute ventilation (L·min−1).

Drying kinetics of tobacco strips at different air temperatures and relative humidities

The effects of air temperature and relative humidity (RH) on the drying kinetics of two kinds of flue-cured tobacco strips (C3F and B3F) were studied using a thermogravimetric device in this work. The drying experiments were carried out with drying air temperatures of 60, 70, 80, and 90 °C and RH values of 0, 10, 20, 30, and 40% at a constant airflow. Taking the effect of RH into consideration, a modified Arrhenius-type equation of diffusivity was proposed. In addition, comparing five thin-layer drying models and five equilibrium moisture content models to describe the drying kinetics and the desorption isotherms of tobacco strips, high coefficients of determination (R2) and low reduced Chi-square (χ2) and residual sum of squares (RSS) values indicated that the Logarithmic model and the Modified Oswin model appeared to be the most suitable for predicting the moisture ratio and the moisture desorption relationship of tobacco strips. The effective moisture diffusion coefficient under different temperatures and RHs ranged from 1.68 × 10−11 to 6.81 × 10−11 m2 s−1 for C3F and from 1.62 × 10−11 to 6.68 × 10−11 m2 s−1 for B3F. A modified Arrhenius-type equation with an RH term was found to be effective for describing the drying behavior of two flue-cured tobacco strips, and the activation energy (Ea) values were 34.6 and 35.2 kJ mol−1 for C3F and B3F, respectively.

Characterization of Radial Curved Fin Heat Sink under Natural and Forced Convection

Heat exchangers are important structures widely used in power plants, food industries, refrigeration, and air conditioners and now widely used in computing systems. Finned type of heat sink is widely used in computing systems. The main aim of the design of the heat sink is to maintain the optimum temperature level. To achieve this goal so many geometrical configurations are implemented. This paper presents a characterization of radially curved fin heat sink under natural and forced convection. Forced convection is studied for the optimization of temperature for better efficiency. The different alternatives in geometry are considered in characterization are heat intensity, the height of the fin and speed of the fan. By recognizing these alternatives the heat sink is characterized by the heat flux usually generated in high-end PCs. The temperature drop characteristics across height and radial direction are presented for the constant heat input and air flow in the heat sink. The effect of dimensionless elevation height (0 ≤ Z* ≤ 1) and Elenbaas Number (0.4 ≤ El ≤ 2.8) of the heat sink were investigated for study of the Nusselt number. Based on experimental characterization, process plan has been developed for the selection of the similar heat sinks for desired output (heat dissipation and temperature distribution).

Survival in Vivo Canine Phonation Model Without Stimulation.

We describe a survival nonstimulated in vivo canine phonation model using distending laryngoscope, cramp frame, and constant humidified glottal airflow to elicit phonation. Five beagle dogs were involved in this study. One cuffed endotracheal tube was placed below the glottis through the tracheotomy and delivered humidified airflow to the glottis. Arytenoids approximation was maintained using a clamp under the distending laryngoscope. Acoustic and aerodynamic parameters were measured using synchronous signal collection system and analysis software. Vocal oscillation also was examined using stroboscope laryngeal imaging. For the nonstimulated in vivo phonation animal, the sound intensity and fundamental frequency were 78.3 ± 6.8 dB and 127.6 ± 29.2 Hz in the first experiment and 82.9 ± 6.6 dB and 175.2 ± 4.4 Hz 4 weeks later. The aerodynamic analysis revealed the mean subglottal phonation threshold pressure (PTP) and phonation threshold flow (PTF) were 8.5 ± 4.0 cmH20 and 683.0 ± 356.4 mL/s in the first experiment and 16.1 ± 8.6 cmH20 and 384.8.0 ± 230.6 mL/s in the second experiment 4 weeks later. Stroboscope image revealed sustained vocal vibration during great airflow delivery to glottis in the phonation animal model. We developed a survival nonstimulated in vivo phonation canine model that allows the study of long-term animal phonation study as its own control.

Design and Experimental Study of an Implemented Solar Air Heater Destined for Red Algae Drying

An experimental study is carried out on an affordable cost air heater with a constant volumetric air flow of 0.015 kg/s m 2 , under sunlight in a coastal area. It is a single pass solar air heater with glazing and corrugated sheet metal absorber locally manufactured and destined for red algae Gelidium sesquipedale drying. The heater is continuously maintained towards the sun in order to increase the absorbed energy. Solar irradiance, inlet and outlet air temperature of the solar heater, as well as the average temperature at the absorber surface are measured. Special care is taken to airflow measurements. The effect of collector tilt angle on its thermal and effective performances is characterized. For a tilt angle of 60° and under an average irradiance of 811 W/m² during 9 hours of exposure, 3 kWh/m 2 are harvested, with an efficiency of 41.2% and a temperature rise of 22 °C. The corresponding specific power is 337 W/m², which is about 14.7 times the power of the used draft fan. The outlet air temperature is in the range of 34 to 58°C which significantly reduces the drying time of red algae Gelidium sesquipedale compared to the traditional drying process at approximately 28°C.

Development and Quality Analysis of Protein Enriched Instant Soup Mix

The aim of the study was to develop protein enriched instant fish soup mix and analysis of the quality of various conditions. The study used a mechanical dryer for maintaining a constant air flow and temperature at its drying and dehydration stage. Powder was made after drying. An appropriate composition was used as an indicator. Various compositions like 75%, 65%, 55% and 45% fish powder were used as formulation 0, formulation 1, formulation 2, and formulation 3 respectively. Then these were reconstituted by boiled water for soup mix preparation. The result indicated that mixer 2 was the best composition. The finding suggested that 55% fish powder mix is the best composition for protein enriched instant soup mix. It will help to produce the instant soup mix and an alternative source of various costly animal and plant protein as a value-added material.

Influence of Drying on the Recoverable High-Value Products from Olive (cv. Arbequina) Waste Cake

Olive oil production in Chile has increased 900% in the last 10 years, resulting in a concomitant increase in waste products that need to be managed. In this study, drying assays were conducted in a convective hot-air dryer on Arbequina olive waste cakes between 40 and 90 °C and a constant airflow of 2 m/s. Proximate composition, dietary fiber, minerals, fatty acids, tocopherols, phytochemicals as well as antioxidant activity as DPPH, FRAP and ORAC values were determined. These six drying temperatures were found to have variable effects on general composition of the residues. Fatty acids were found in high concentration at low temperatures where oleic acid was the most abundant and α-tocopherol was the most prevalent form of vitamin E. The phytochemical content (total phenolics, flavonoids and flavanols) represented an average of 20.7% of the waste cake. Fresh cake showed the highest polyphenols and flavonoids content whereas flavanols content was higher at all drying temperatures. 3-Hydroxytyrosol was the most abundant phenolic compound, and found in higher abundance in samples dried at 90 °C. The antioxidant capacity measured by FRAP and DPPH assays decreased with drying or remained unchanged when measured by ORAC assay. Given the nutritional and commercial potential of waste cakes, a drying technology for the preservation of bioactive compounds from waste products is discussed.

Aspectos tecnológicos na produção de farinha de polpa de pequi

<p>Objetivou-se avaliar o efeito da temperatura de secagem nas características nutricionais da farinha da polpa de pequi. A secagem da polpa de pequi foi realizada em um secador de bandejas com fluxo de ar constante a 0,5 m s<sup>-1</sup> em três temperaturas 55, 65 e 70 °C. As cinéticas de secagem foram avaliadas ajustando-se os dados experimentais através de sete modelos matemáticos por regressão não linear. Determinaram-se a difusividade efetiva e a energia de ativação requerida para a evaporação da umidade do produto. Os resultados mostraram redução do tempo de secagem com o aumento da temperatura do processo. Os ajustes dos modelos foram avaliados em função dos valores de R<sup>2</sup> e ERM. Todos os modelos apresentaram bons indicadores estatísticos, entretanto, o modelo que representou os melhores valores da cinética de secagem da polpa de pequi, para as condições estudadas, foi o de Page. Os valores da difusividade efetiva nas condições de temperatura estudadas estão entre 4,04 a 5,57 x 10<sup>-10 </sup>m<sup>2 </sup>s<sup>-1</sup> e a energia de ativação foi de 2,03 x 10<sup>4 </sup>J mol<sup>-1</sup>. O processo de secagem favoreceu na concentração de alguns nutrientes como carboidratos e proteínas. A desidratação a 55 ºC forneceu um produto com melhor aparência visual entre as temperaturas estudadas.</p>

Dynamic Characterization of a Ducted Inverse Diffusion Flame Using Recurrence Analysis

ABSTRACTNormal diffusion flame or partially premixed flame is used in many applications, such as aviation engines, tanks, ocean vessels, and industrial furnaces, because of its high flame stability and relatively low susceptibility to dynamic instabilities compared to lean premixed flames, which give lower emissions. However, associated with such flames are high NOx and soot emissions, which are particularly high for heavier hydrocarbon fuels. Increasingly stringent environmental norms have thus dictated the search for alternate approaches; one such being the inverse diffusion flame, which is currently being used in rocket motors, for staged combustion in gas turbine combustors, and furnaces. However, the dynamic response of such a flame, particularly in ducted applications where a coupling between unsteady heat release rate and duct acoustics may occur, is relatively less explored. The present work aims to plug that knowledge gap through an experimental investigation of a laboratory-scale ducted inverse diffusion flame. Two parametric variations of the flame were performed—variation of the flame position and variation of the air flow rate. Using tools of nonlinear dynamics, such as phase space reconstruction and recurrence quantification, several interesting dynamic characteristics were observed, such as limit cycles, intermittency, and homoclinic orbits. For a constant air flow rate, the system was observed to transition from a type-II intermittency regime to a limit cycle and then again to intermittent behavior as the position of the flame within the duct was varied. A similar trend was observed when the air flow rate was varied at a fixed flame position.

Energy Analysis of Solar Collector With perforated Absorber Plate

The thermal performance of three solar collectors with 3, 6 mm and without perforation absorber plate was assessed experimentally. The experimental tests were implemented in Baghdad during the January and February 2017. Five values of airflow rates range between 0.01 – 0.1 m3/s were used through the test with a constant airflow rate during the test day. The variation of the following parameters air temperature difference, useful energy, absorber plate temperature, and collector efficiency was recorded every 15 minutes. The experimental data reports that the increases the number of absorber plate perforations with a small diameter is more efficient rather than increasing the hole diameter of the absorber plate with decreasing the perforation numbers. Maximum air temperature difference throughout the solar collector with 3, 6 mm perforations and without perforations are 17, 15, and 12 oC, respectively. Also, it can be concluded that the energy gained from the solar collector with 3 mm perforation absorber plate is 28.2 % more than the energy gained from solar collector without holes per day for 0.1 m3/s airflow rate. The maximum values of the thermal performance curves are 0.67, 0.64, and 0.56 for the solar collector with 3, 6 mm, and without perforations, respectively.

Influence of Airway Secretion on Airflow Dynamics of Mechanical Ventilated Respiratory System.

Secretions in the airways of mechanical ventilated patients are extremely dangerous to patients' health. In recent studies, the continuous constant airflow is adopted, however, it is not consistent with a clinical situation. To study respiratory airflow dynamic characteristics with secretion in the airways, a mathematical model based on clinical mechanical ventilation is established in this paper. To illustrate the secretion's influence on the airflow dynamics of mechanical ventilated respiratory system, three key parameters which are cross section area ratio of secretion/ pipe, air-secretion contact area, and secretion viscosity are involved in the study. Through the experimental study, the accuracy and dependability of the model are confirmed. By the simulation study, we find that: based on the model which combines two airways and two model lungs, when one of the airways was covered with secretion, the maximum pressure of the model lung which is attached to the end of this airway maintains constant when the cross section area ratio is less than 66 percent, and then it tends to decline sharply with the ratio increasing, but it remains constant with the augment of air-secretion contact area, the maximum flow declines both with the increasing of cross section area ratio and air-secretion contact area. Furthermore, as for the other airway, the maximum pressure of the model lung has no significant changes with the augment of area ratio and air-secretion contact area, however, along with the increasing of area ratio and air-secretion contact area, the maximum flow rises up. Moreover, the secretion viscosity has barely any influence on airflow dynamics. According to our analysis results, we conclude that the cross section area ratio of secretion/pipe has bigger influence on airflow dynamic characteristics than air-secretion contact area and secretion viscosity. This paper lays the foundation for the further study of efficacy and safety in mechanical ventilation and the secretion clearance of mechanical ventilated patients. In addition, the mathematical model proposed in this paper can also be referred to study on the secretion movement in human airways.

Numerical investigation of turbulent airflow and microparticle deposition in a realistic model of human upper airway using LES

The Large Eddy Simulation (LES) technique was used to study the turbulent airflow field in a realistic model of human upper airways from nostril to the end of trachea. The Lagrangian approach was used to calculate the trajectories and deposition of micro-particles for the breathing rates of 30 and 60 l/min. While the LES is inherently unsteady, the cases of inhalation breathing with a constant mean airflow velocity were simulated.The present LES results are compared with those obtained from the earlier RANS model study. In the RANS model the effect of airflow turbulence velocity fluctuations on particle trajectories was modeled using the Continuous Random Walk (CRW) stochastic model. It was found that the results obtained by the LES method for the total depositions of micro-particles are comparable with those of the RANS model. The regional particle deposition, however, showed marked differences. In addition, significant differences were found in the predicted airflow characteristics.

The influence of personally controlled desk fan on comfort and energy consumption in hot and humid environments

Human beings' comfort is critical for health and work performance of occupants in modern buildings. The main objective of this study was to investigate the influence of a type of energy-efficient desk fan on subjective evaluation of thermal comfort in hot and humid environment. A series of experiments was conducted in an experimental room in Hunan University, China during summer. In total, 24 subjects were invited to participate in the experiments and they experienced the environments which were set at 26, 28, and 30 °C with fixed or free-controlled local airflow by desk fan, respectively. The subjects reported their thermal sensation, thermal comfort, and perceived air quality during the tests. The obtained results indicate that the use of desk fan significantly improved the subjects' thermal comfort and perceived air quality. When subjects were allowed to freely control the desk fan, they considered the hot-humid environment more comfortable; moreover, they thought indoor air was fresher than when they were under the influence of constant local airflow by desk fan. Furthermore, only a little energy was consumed by desk fan (maximum power was merely 3 W) to maintain a comfortable environment for subjects, thus making personally controlled desk fan a very energy-efficient way to deliver comfort in hot-humid environment.

Dimensionless modeling for convective drying of tuberous crop (Solanum tuberosum) by considering shrinkage

The shrinkage of biological materials (agri-food), is a common phenomenon developed during a drying operation that directly affects the product quality. In this work a dimensionless mathematical model including the reduction at the interface of a high moisture content food (tuber) in 1D geometry was developed. The mass and heat conservation equations coupled to the Leibniz-Reynolds Transport Theorem (LRTT) at the interface of a high moisture content food were solved. The system of nonlinear unsteady state equations was solved by using a multi-frontal massively parallel sparse direct Solver. In order to validate this model, tuberous crop slices were dried at three temperatures: 40, 50 and 60 °C, relative humidity of 25% and a constant airflow of 1.5 m/s. Drying kinetics and the evolution of temperature within the product were logged. The model is able to simulate the moisture loss and predict the highest thickness change. The simulations show a good agreement with the experimental drying kinetics, as well as for the evolution of temperature. Simulations show 1-D shrinkage is not linear and the model improves its prediction when the drying temperature is higher (intensive mass flux).

Temperature influence on the response at low airflow of a variable orifice flowmeter.

In mechanical ventilation, in particular when neonates are ventilated, it is crucial to accurately control the amount of the gas delivered to the patients. Mechanical ventilators are equipped with one of more flowmeters. The signal of the flowmeter is used as feedback to control the amount of gas delivered to the patients. Therefore, the accuracy of the flowmeter plays a crucial role in the accurate adjustment of the gas amount delivered by the ventilator. Among several solutions, variable area orifice meters (VAOMs) have several valuable features (e.g., good accuracy, and adequate frequency response), moreover they have the main advantage, with respect to orifice meters, related to the linearity of the response. Despite of their spread in this field, there are not studies focused on the analysis of the air temperature influence on VAOMs response. This study focuses on this topic by investigating the gas temperature influence on the response of a commercial VAOM. Experiments have been performed at low airflow (up to 1.5 L·min-1) and at four different temperatures (i.e., from 22°C to 38°C) covering the range of interest in the field of artificial ventilation. Results show that the response of the VAOM under test is sensitive to temperature: at constant airflow the higher the temperature the higher the sensor output. This analysis may be useful to add correction to sensor output in order to reject the influence of temperature, so to minimize the measurement error due to this factor.

Numerical investigation of transient transport and deposition of microparticles under unsteady inspiratory flow in human upper airways

In the present study, unsteady airflow patterns and particle deposition in healthy human upper airways were simulated. A realistic 3-D computational model of the upper airways including the vestibule to the end of the trachea was developed using a series of CT scan images of a healthy human. Unsteady simulations of the inhaled and exhaled airflow fields in the upper airway passages were performed by solving the Navier-Stokes and continuity equations for low breathing rates corresponding to low and moderate activities. The Lagrangian trajectory analysis approach was utilized to investigate the transient particle transport and deposition under cyclic breathing condition. Particles were released uniformly at the nostrils’ entrance during the inhalation phase, and the total and regional depositions for various micro-particle sizes were evaluated. The transient particle deposition fractions for various regions of the human upper airways were compared with those obtained from the equivalent steady flow condition. The presented results revealed that the equivalent constant airflow simulation can approximately predict the total particle deposition during cyclic breathing in human upper airways. While the trends of steady and unsteady model predictions for local deposition were similar, there were noticeable differences in the predicted amount of deposition. In addition, it was shown that a steady simulation cannot properly predict some critical parameters, such as the penetration fraction. Finally, the presented results showed that using a detached nasal cavity (commonly used in earlier studies) for evaluation of total deposition fraction of particles in the nasal cavity was reasonably accurate for the steady flow simulations. However, in transient simulation for predicting the deposition fraction in a specific region, such as the nasal cavity, using the full airway system geometry becomes necessary.