Air Volume Flow Research Articles

Perturbations of the Depth of Liquid Penetration Into the Capillary During Bubble Departures

Abstract In the present paper, the influence of bubble size on liquid penetration into the capillary was experimentally and numerically studied. In the experiment, bubbles were generated from a glass capillary (with an inner diameter equal to 1 mm) in a glass tank containing distilled water, tap water or an aqueous solution of calcium carbonate. These liquids differ in the value of their surface tension, which influences the bubble size. During experimental investigations, air pressure fluctuations in the gas supply system were measured. Simultaneously, the videos showing the liquids’ penetration into the capillary were recorded. Based on the videos, the time series of liquid movements inside the capillary were recovered. The numerical models were used to study the influence of bubble size on the velocity of liquid flow above the capillary and the depth of liquid penetration into the capillary. It was shown that the air volume flow rate and the surface tension have the greatest impact on the changes of pressure during a single cycle of bubble departure (Δp). The changes in pressure during a single cycle of bubble departure determine the depth of liquid penetration into the capillary. Moreover, the values of Δp and, consequently, the depth of liquid penetration can be modified by perturbations in the liquid velocity above the capillary outlet.

Modeling of Passive and Forced Convection Heat Transfer in Channels with Rib Turbulators

The main goal of the research presented in this paper was the experimental and numerical analysis of heat enhancement and aerodynamic phenomena during air flow in a channel equipped with flow turbulators in the form of properly configured ribs. The use of ribs intensifies the heat transfer and at the same time increases not only the flow resistance but also the energy costs. Therefore, designing modern heat exchangers with optimal thermal and flow parameters requires the knowledge of the theory of heat exchangers as well as measurement methods and numerical calculations. Bearing in mind the above, the liquid crystal techniques (LCT), particle image velocimetry (PIV) and digital image processing (DIP) for temperature, velocity, friction factor and heat transfer coefficient measurements are presented herein. These three optical tools (using desktop computers) create an extremely powerful and advanced measuring technique that has not been available anywhere before. Brief histories of these measurement methods and techniques are discussed and some examples are presented. In order to assess and select the value of the measurement technique, local and average distributions of Nusselt numbers (in the measurement section) obtained by the transit analysis method on the inter-rib regions of a plate coated by thermochromics liquid crystal and heated by air as an alternative to the steady-state analysis. In the parallel, numerical calculation was performed with the use of the ANSYS Fluent software code and supported by laser anemometry-computed turbulence intensity of air flow. Comparison of the Nusselt number distributions was determined by three methods, i.e., steady state, the transient method and CFD simulation. Up to three-fold enhancement of the local heat transfer capability was observed. Failure to take into account the surface of the ribs in heat transfer causes differences in the obtained results of the Nusselt number depending on the method used. Apart from the heat transfer data, the pressure drop in the form of friction factors is also presented. On the basis of the conducted research, it can be stated that both qualitative and quantitative coherence was obtained between the experimental and computational studies.

The Impact of Cutting with a Shearer on the Conditions of Longwall Ventilation

In coal mines that are exploiting methane-saturated seams, high-level emission of methane is often the basic limitation for modern and high-efficiency longwall complexes. This paper presents selected observations and tests carried out in the Cw-4 longwall in seam 364/2 of the Budryk mine, which belongs to JSW SA. To observe the methane levels in the Cw-4 longwall, additional sensors were installed at the end section of the longwall from the side of the gobs, and the air velocity and methane concentration were registered in a multi-point system that were built in the selected longwall cross-section. The air parameters were recorded in the monitoring system. The use of multi-point simultaneous measurements of the local velocities and concentrations of methane in the longwall cross-section allowed for the precise determination of the air and methane volume flow using the velocity field method. This allowed us to perform a comparative analysis of the obtained records of the air parameters using special software to determine the distribution of the parameters in the cross-section of the excavation. An important element of the study was the simultaneous registration of the methane concentration in the longwall, information on the operating times, the direction of shearer operation, and the type of work being done (i.e., mining/cleaning).

Experimental study and operation optimization of a parallel-loop heat pump for exhaust air recovery in residential buildings

The indoor space of residential building is limited, especially in building retrofit, to improve the indoor space utilization and the performance of exhaust air heat recovery system, a novel dual-cylinder rotary compressor with independent suction and discharge ports was designed to drive an inverter parallel-loop exhaust air heat pump. Through the experiments and analyzing the parallel-loop exhaust air heat pump system working characteristics under variable compressor frequency and different fresh air volume flow rate, the optimized method is proposed and verified experimentally. Finally, the annual energy efficient operation plan was proposed, and the seasonal performance factor and seasonal average input power under this operation plan in three typical countries/organization were calculated. Results show that the system COP can be greatly improved by applying a mixed air supply method during winter. When the fresh-air-to-return-air ratio is 1:1 and the outdoor temperature is −5 °C, the system COP reached 10.18, which is the highest comparing with the related studies. In summer, the system COP is increased by increasing the ventilation volume flow rate. When the operation of the parallel-loop exhaust air heat pump system follows the energy efficient operation plan to ensure the temperature effectiveness over 100% and the outdoor working condition complies with GB 21455–2013, the heating season performance factor, heating season average input power, cooling season performance factor, and cooling season average input power are 7.22, 0.6909 kW, 2.83, and 0.8167 kW, respectively. The work would provide guidance for the development of exhaust air heat recovery system in residential building.

Combustion instability control performance of an improved Helmholtz resonator in the presence of bias flow

Combustion instability may appear due to the interference between heat release rate and acoustically-driven flow perturbation in combustors. In the present study, we experimentally studied the effects of incident sound frequency, cavity depth, and sound pressure level on the sound absorption performance of a Helmholtz resonator (HR) with an optimized neck under bias flow. The greater the bias flow rate, the wider the sound absorption frequency band. The insertion of the honeycomb with minor porosity into the neck caused the central sound absorption frequency to shift to the low-frequency regime. The optimal cavity depth of the HR was also shortened, which is beneficial to save space. Moreover, a proper bias flow increased the maximum sound absorption coefficient of the resonator. When the modified HR was installed in the intake section of a swirl spray combustor, the pulsating pressure in the combustion chamber and plenum were reduced by 78% and 56%, respectively. The CH⁎ chemiluminescence intensity was reduced by 96%. Compared with traditional HR, the improved HR suppressed the pressure and heat release pulsation more effectively. Even if the primary air volume flow rate changed from 4.5 m3/h to 9.5 m3/h, the improved HR ensured that the pulsating pressure amplitude was reduced by about 82% on average.

Exergy analysis of two indirect evaporative cooling experimental prototypes

This paper deals with the exergy analysis of two experimental prototypes consisting of indirect evaporative cooling systems with different constructive characteristics. Both prototypes have been designed and manufactured in the Thermal Engineering Laboratory of the University of Valladolid. They are made of polycarbonate hollow panels of different cross section and connected into a heat recovery cycle. Each prototype has been tested at 4 levels of outdoor air volume flow (from 125 to 400 m3·h−1) and 4 levels of dry bulb temperature (from 25 to 40 °C). For each of the 16 different operating conditions the exergy destructed by each prototype has been calculated. Results show that the higher the dry bulb temperature at the primary air inlet, the higher the exergy destruction and the exergy losses. The exergy destruction increases when the wet bulb depression temperature of the secondary air inlet decreases, leading to more inefficient configurations. The value of the exergetic efficiency is in the order of 2–12 %. The optimum combination of operating conditions at any inlet temperature of the primary air can be proposed as: 300 m3h−1 and 200 m3h−1. for the wide and narrow plates prototype, respectively.

Simulation Study on Active Air Flow Distribution Characteristics of Closed Heat Pump Drying System with Waste Heat Recovery

A tridimensional turbulent flow model is established for a closed heat pump drying system with waste heat recovery to improve the drying air flow characteristics and reduce the energy consumption of air circulation. The active flow distribution mode is introduced to guide air flowing in the system’s drying cabinet, top air duct, mixing zone, and heat pump. It is found that the wind velocity in the cabinet’s supply channel is greater than that in the return channel, the velocity distribution in the top duct is uneven, and the outlet velocity of the bypass fan is high and a vortex forms. A partition panel added in the top duct and modulating fans in the drying cabinet are proposed to solve these problems. The simulation results show that removing the circulating fan, changing the volume flow of the bypass fan, adopting the alternative operation mode of the bypass fans, reducing the air volume flow of the supply fan, and reducing the total pressure of the fans can improve the dry air velocity uniformity in the drying cabinet and reduce the energy consumption of the fans. This paper analyzes the closed-loop drying air flow characteristics of the active flow distribution system in the heat pump drying system, which lays a foundation for the wind velocity, temperature, and humidity regulating of heat pump drying system with waste heat recovery.

Use of external nasal strip influences alveolar cell population of horses after exercise

ABSTRACT The nasal strip is widely used in horses during exercise, but effects of using a nasal strip are controversial and little is known about its effect on horses undergoing endurance events. The aim of this study was to determine whether the use of nasal strips influences alveolar cell population assessed by bronchoalveolar lavage (BAL), tidal volume, and nasal airflow rate. Six Arabian horses were subjected to two low intensity tests on a treadmill, with and without application of a commercial external nasal strip. Tidal volumes and airflow rates were measured during the test; two hours after the test, BAL was performed to assess cytology of pulmonary secretions. The lavage fluid showed increased neutrophil count after exercise in animals with the nasal strip (P<0.05). This suggests that turbulence of airflow through the nasal cavity may have diminished with nasal strip use, thus allowing larger particles to be deposited more distally in the respiratory system, inducing a more intense neutrophilic response. No differences in tidal volumes or airflow rates were observed between groups (with or without nasal strips) during the test (P>0.05). The use of nasal strips seems to influence alveolar cell population during and after exercise in horses after low intensity exercise tests. Further studies are needed to verify whether alveolar cell population is related to poor exercise performance in horses.

Acoustic features of palatalized consonants in Nasa Yuwe

Nasa Yuwe a Colombian language spoken in the Cauca presents complex features of palatalization [1,2]. Stops and affricates can be palatalized, aspirated and palatalized-aspirated at all places of articulation while prenasalized consonants and fricatives can only be palatalized. Data for this study were recorded from an acoustic recording session and by combining, in a second phase, synchronized acoustic, EGG and oral airflow recordings from 6 speakers (3 female and 3 male). Results show that all palatalized stops are characterized by a short frication noise at the end and a F3/F4 pole at the start of the following vowel. Aspirated stops have a greater frication noise duration and an open glottis. Palatalized-aspirated stops and affricates are produced with frication noise, a F3/F4 pole at the start of the following vowel and an open glottis. Palatalized-aspirated consonants have two phases: a short and intense frication noise accounting for the palatalization, followed by a lower intensity aspiration noise. Both phases can be distinguished by their FFT spectra and oral airflow volume velocity. Prenasalized consonants behave as palatalized stops but without the aspiration feature. Palatalized fricatives have a resonance during the frication, reflecting a tongue movement towards the palatal place. [1] E. Dias, El Habla Nasa (paez) de Munchique: Nuevos Acercamientos a Su Sociolingüistica, Fonologia y Morfosintaxis (Université Lumière Lyon 2, 2019). [2] T. Rojas, La Lengua Paez (Ministerio de Cultura, Bogota, 1998).

Study of the flame flow and combustion characteristics of pool fires around a bluff body in the ship engine room

In the development of a fire, all kinds of equipment in ship cabins cause flames to flow around them, which greatly affects the combustion characteristics of the flames. Experimental studies were conducted on a pool of 80 cm × 6 cm × 5 cm containing a bluff body with a diameter of 2 cm and a height of 15 cm. Using diesel fuel as an ignition source, the flame flow around the bluff body propagating as a crosswind at speeds of 0.8–2.4 m/s was studied. The results showed that the fluctuation of the mass loss in a rising period decreased. A new flame spreading phenomenon of “continuous-flow around-broken-retract” appeared. The average spreading rate affected by the bluff body had a quadratic nonlinear relationship with the intensity of airflow. A prediction model of the flame drag length for the rectangular pool containing a bluff body was established. In addition, there were two vortices near a bluff body that were symmetrical and flowed in opposite directions. The temperature at the standing vortices reached a maximum of approximately 260 °C. At the same time, the vortices presented the characteristics of periodic formation and shedding with an interval of approximately 3.6 s.

A Novel Non-Intrusive Vibration Energy Harvesting Method for Air Conditioning Compressor Unit

The purpose of harvesting vibration energy is to obtain clean and sustainable energy by converting vibration energy from ambient sources into a voltage output. In this work, a piezoelectric sensor, PZT-5H is attached to a 3D printed and custom-made mounting to be placed at an air conditioning condenser unit, to harvest vibration energy. The configuration of the harvester is non-intrusive, in which the harvester did not intrude into compressor unit operation. Temperature (20 °C, 22 °C, and 24 °C) and air volume flow rates (3 levels of air volume flow rate at 245 L/second, 274 L/second, and 297 L/second) were taken into consideration in this investigation. An accelerometer was first used to investigate the optimum vibration frequency in Hertz, and six locations were identified. Next, the piezoelectric sensor was mounted at these six locations, and the output root-mean-square (RMS) voltage from the piezoelectric sensor was obtained. The analysis of variance (ANOVA) indicated that temperature and air volume flow rates factors were significant. It was found that the location identified with the highest amount of vibration at 830.2 Hz from accelerometer measurement, was also the highest amount of RMS voltage, at 510.82 mV, harvested by the piezoelectric, from the temperature of 20 °C and air volume flow rates at high level (air flow volume flow rate at 297 L/second). From this work, it is feasible to utilize this novel method of harvesting waste vibration energy from the air conditioning compressor unit.

Optimization Study of Guide Vanes for the Intake Fan-Duct Connection Using CFD

The connection between an intake fan and a ventilation shaft must be designed in such a way that it minimizes the energy waste due to singularity losses. As a result, the questions of which radius of curvature to use and if guide vanes have to be included need to be answered. In that case, the variables such as the number, upstream and downstream penetration length, radius of curvature, and width of the vanes, need to be defined. Although this work is oriented to mine ventilation, these questions are usually valid in other engineering applications as well. The objective of this study is to define the previously mentioned variables to determine the optimal design combination for the radius/diameter relationship (r/D). Computational fluid dynamics was used to determine the shock loss factor of seven elbow curvature ratios for a 3 m diameter duct and fan, with and without guide vanes to estimate the best performing configuration and, therefore, to maximize the fan airflow volume. The methodology used consisted of initially developing models in 2D geometries, to optimize the meshing and the CPU use, and studying separately the number of vanes, upstream and downstream penetration, radius of curvature, and width of the vanes for each curvature ratio (r/D). Then, the best-performing variable combinations for each curvature ratio were selected to be simulated and studied with the 3D geometries. The application of the guide vane designs for three-dimensional simulated geometries is presented, first without and then with guide vanes, including the shock loss factors obtained. The methodology and obtained results allowed quantifying the energy savings and to reduce the CFD simulations steps required to optimize the design of the elbow and guide vanes. The results obtained cannot be used with elbows in exhaust fans, because fluid dynamics phenomena are different.

Research on the control law of dust in the main ventilation system in excavated tunnels for cleaner production

This study was based on computational fluid dynamics (CFD) and field measurement verification. First, we researched and analyzed the main ventilation system, when closed or opened, of a tunnel boring machine (TBM), to demonstrate that the main ventilation system had the ability to control dust. Then, summarized the theory of pressure airflow dust control in an excavated tunnel. Next, the airflow volume (QM) of the main ventilation system was modified based on different excavation lengths and by adjusting the values of QM from 5 m3/s to 40 m3/s. We found that when QM = 25–30 m3/s, the dust could be effectively controlled, the dust in the working area was effectively controlled within 45.5–55.6 m, and the dust concentration was reduced to less than 9.59–10.50 mg/m3. The accuracy of the CFD results was verified through field measurement, which also showed that the dust concentration was effectively reduced. In conclusion, that the main ventilation system functioned to both supply oxygen and control dust, helping to protect the health of tunnel workers.

Parametric analysis of an air-based radiative cooling system coupled to a thermal storage wall for a low-income household

Research on natural cooling of buildings has produced an extensive scientific bibliography since 1980s. Nevertheless, few examples of complete experimental systems are registered, and rigorous procedures for their dimensioning are currently not available. This work analyses the performance of an air-based low energy radiative cooling system in Chile. The system is composed of a series of specialized radiative air collectors, a mechanical ventilation system, and a thermal storage wall, which is part of the indoor environment. The design has been tested in an experimental prototype where external and internal environmental conditions have been monitored during a full week in midsummer conditions. The data obtained is used to validate an analytical model designed to study the behavior of each component and the system’s performance. This work studies the relationship between the radiator surface, the air volume flow rate, and the thermal storage wall volume that serves to neutralize the thermal loads, maintaining comfortable temperature conditions throughout the day. Comparison of the simulations with and without thermal conditioning has been conducted. In term of the system sizing, a thermal wall of 2.55 m3 and a total air flow rate of 48 m3/h is required to reach the optimal operating point of the first floor of the house. A sensibility analysis indicated that increasing the number of collectors slightly reduces the wall’s size. Based on these conditions, the work concludes with the proposal of a simple procedure for the sizing of passive cooling systems installed in social housing developments.

Theoretical analysis and experimental investigation of flame trajectory of horizontal subsonic jet diesel spray under sub-atmospheric pressure

The safety of a horizontal spray combustion flame and the design of a heating device for a low-pressure area of a plateau have both been widely examined. The shape equation and length of a flame’s trajectory are the two most important indexes. Regardless of the atomization and evaporation process of fuel, the analytical formula of trajectory for a horizontal spray flame supplied by forced swirling air is derived, and the numerical solution is obtained. The variation in flame trajectory and its uplifted characteristics with atmospheric pressure are analyzed theoretically and verified experimentally. The flame trajectory length and its coincidence degree at 0.05 and 0.08 MPa of atmospheric pressure are compared. The results show that the flame trajectories coincide when the rated volume air flow is maintained under different atmospheric pressures. Keeping the same equivalence ratio, the slope of the uplifted trajectory is proportional to the atmospheric pressure. If flame trajectories coincide at any two atmospheric pressures, the ratio of equivalence is the inverse ratio of air density. Finally, based on the air entrainment theory, the flame trajectory length equations for different atmospheric pressures and equivalence ratios are unified. This study is of great theoretical significance to research into low-pressure spray flames and the design of a high-altitude oil burner.

종합병원 외래진료부내 내원자수 변화에 따른 실별 공기감염균수 분석

Recently, infectious airborne pathogens of foreign origin have increased, causing individual and group infections of the respiratory tract. In particular, the indoor spread of airborne bacteria must be prevented because they spread rapidly and are difficult to contain owing to the effects of air currents. A subject space was selected in an outpatient department of a general hospital to measure the number of visiting patients, airflow volumes of the supply and exhaust systems, and differential pressures between rooms. The number of visiting patients was used in a machine learning (ML) algorithm to generate a “predicted visiting schedule of outpatients” and produce an “airborne bacteria generation prediction data” by applying human CO₂ emissions and behavior variables. Furthermore, after conducting an airflow analysis simulation, we evaluated the distribution of airborne bacteria in each room of the outpatient department. The results of this study show that it is necessary to predict the changes in the number of visiting patients in a hospital such that real-time air conditioning control methods can be employed to ensure adequate air quality. Furthermore, we obtained the basic data for predictive air-conditioning control to prevent the spread of airborne diseases in general hospitals.

호기성 미생물을 이용한 슬러지 감량 최적조건 연구

This study focused on the optimum temperature and airflow volume for the operation of sludge reduction under the aerobic condition with the microbe s. This d e vice was installed in the sewage treatment plant in the B city with a 5 ton/day capacity. The medium of microbes was the mixture of sludge, microbes, and sawdust. Air was supplied to the air hole of the agitators. The moisture content o f t he input sludge was 8 0-82 %. The reduction rate of the sewage was more than 66.7 %, and the reduction time was operated from 16 to 29 hours, but it was found that the moisture content was reduced to less than 25 %. The correlation between the reduction rate, the amount of air flow, and the internal temperature of the reactor was derived. The air flow was about 4.9 to 5.3 m3/min to meet the aerobic condition. In the case of the internal temperature, it was found that when the temperature was above 50℃, the reduction rate was maintained at 90 % or more. The optimum reduction rate was achieved when it was maintained at least 40℃.

Experimental study on bituminous coal blending in a down‐fired boiler with anthracite combustion system under low load

AbstractThe industrial experiments were carried out to study the bituminous coal blending in a 660‐MWe supercritical down‐fired boiler with anthracite combustion system under low load. The influence of the bituminous coal ratio on the boiler thermal efficiency, flue gas temperature, flue gas species, and heat transfer of various heating surfaces was analyzed in detail. The ignition distances of three experimental coals were measured, and the influence mechanism of bituminous coal blending on the combustion, heat transfer, and NOx emission in the furnace was proposed. The results show that increasing the bituminous coal blending ratio is beneficial to reduce NOx emissions. However, it leads to the rise of the exhaust gas temperature and the decrease of the boiler efficiency, which can be ascribed to the large amount of the cold primary air sent into the pulverizing system to control the air pulverized coal flow temperature at the mill outlet. The ignition distances of three experimental coals are different. The ignition distance from short to long follows the following order, that is, bituminous coal, lean coal, and anthracite. The earlier ignition of the bituminous coal leads to a sharp rise in the temperature of the airflow at the burner nozzle outlet, a rapid expansion of the airflow volume, and a sharp attenuation of the airflow rigidity, resulting in a short flame downward penetration depth and the upward movement of the flame center in the furnace. As the bituminous coal is blended, the change of the flame center and the flame fullness in the furnace affects the flue gas temperature distribution. Similarly, the change of the radiant heat transfer intensity and the convective heat transfer intensity affects the heat absorption distribution of the heating surface in the furnace.

Modeling and simulation of temperature control system in plant factory using energy balance

Closed production systems, such as plant factories and vertical farms, have emerged to ensure a sustainable supply of fresh food, to cope with the increasing consumption of natural resource for the growing population. In a plant factory, a microclimate model is one of the direct control components of a whole system. In order to better realize the dynamic regulation for the microclimate model, energy-saving and consumption reduction, it is necessary to optimize the environmental parameters in the plant factory, and thereby to determine the influencing factors of atmosphere control systems. Therefore, this study aims to identify accurate microclimate models, and further to predict temperature change based on the experimental data, using the classification and regression trees (CART) algorithm. A random forest theory was used to represent the temperature control system. A mechanism model of the temperature control system was proposed to improve the performance of the plant factories. In terms of energy efficiency, the main influencing factors on temperature change in the plant factories were obtained, including the temperature and air volume flow of the temperature control device, as well as the internal relative humidity. The generalization error of the prediction model can reach 0.0907. The results demonstrated that the proposed model can present the quantitative relationship and prediction function. This study can provide a reference for the design of high-precision environmental control systems in plant factories. Keywords: plant factory, temperature control system, mechanism simulation, random forest, cart model, generalization error DOI: 10.25165/j.ijabe.20211403.6114 Citation: Zhang M Q, Zhang W, Chen X Y, Wang F, Wang H, Zhang J S, et al. Modeling and simulation of temperature control system in plant factory using energy balance. Int J Agric & Biol Eng, 2021; 14(3): 66–75.

Aerodynamics Analysis of the Impact of Nasal Surgery on Patients with Obstructive Sleep Apnea and Nasal Obstruction

Objective: The purpose of this study was to evaluate the effects of nasal surgery on airflow characteristics in patients with obstructive sleep apnea (OSA) by comparing the alterations of airflow characteristics within the nasal and palatopharyngeal cavities. Methods: Thirty patients with OSA and nasal obstruction who underwent nasal surgery were enrolled. A pre- and postoperative 3-dimensional model was constructed, and alterations of airflow characteristics were assessed using the method of computational fluid dynamics. The other subjective and objective clinical indices were also assessed. Results: By comparison with the preoperative value, all postoperative subjective symptoms statistically improved (p < 0.05), while the Apnea-Hypopnea Index (AHI) changed little (p = 0.492); the postoperative airflow velocity and pressure in both nasal and palatopharyngeal cavities, nasal and palatopharyngeal pressure differences, and total upper airway resistance statistically decreased (all p < 0.01). A significant difference was derived for correlation between the alteration of simulation metrics with subjective improvements (p < 0.05), except with the AHI (p > 0.05). Conclusion: Nasal surgery can decrease the total resistance of the upper airway and increase the nasal airflow volume and subjective sleep quality in patients with OSA and nasal obstruction. The altered airflow characteristics might contribute to the postoperative reduction of pharyngeal collapse in a subset of OSA patients.