Air Volume Flow Research Articles

Feasibility evaluation of the ventilation control mechanism drive of a large screen canopy

The study was carried out on how to enhance the effectiveness of solar energy and reduce technological risks connected with growing large-fruited tall tomato varieties in conditions of insuffi cient heat supply by using automatically controlled infl ow-and-exhaust ventilation. High probability of late recurring and early autumn frosts in Western Siberia poses a threat of complete harvest loss of thermophilic vegetable crops. Improvement of the heat supply during the growing period is possible due to the greenhouse effect occurring in canopies and greenhouses. In summer, additional energy creates the danger of overheating, which can be eliminated by an automatically controlled infl ow-and-exhaust ventilation. Laboratory experiments showed that the automatic device consistently maintains air temperature within 26-27°C, which meets biological requirements of plants, by changing the width of the exhaust air aperture. Opening of the infl ow air aperture increases the intensity of air fl ow inside the canopy. The hydraulic drive of the ventilation control mechanism consistently maintains the air temperature inside the canopy in the process of heating by means of automatic regulation of exhaust air aperture width, but it is ineffective in the cooling process due to high thermal inertia. Changing the height of the infl ow air aperture from 0 to 0.3 m makes the intensity of air exchange increase and the air temperature decrease.

Effects of various operating conditions on the performance of a CO2 air conditioning system for trains

This paper aims to investigate the effects of different operating parameters on the performance of a transcritical CO2 air conditioning system for trains. Similar designs of automotive CO2 air conditioning system are used in the train system such as internal heat exchanger (IHX) to improve the system efficiency. Experimental results are presented for the performance characteristics of the CO2 train air conditioning system with two independent circuits under different test conditions such as different refrigerant charge amount, compressor working frequency, indoor air volume flow rate and outdoor chamber temperature. Two different operating modes of the two circuits are also included in this research. For mode I while only one circuit is working, the test results show that the maximum cooling capacity and coefficient of performance (COP) is 24.3 kW and 2.7, during 55 Hz and 40 Hz compressor working frequency conditions respectively. Also, the cooling capacity and COP reach the minimum, 16.2 kW and 1.5, when the outdoor chamber temperature is 45 °C. For mode II while both two circuits are working, the results show that the cooling capacity and COP are 42.0 kW and 2.4, respectively. The system performance error between the test and numerical modeling which directs the design of the system is within ±5%. Furthermore, an optimum high pressure control algorithm for the transcritical CO2 cycle of the train AC system is also presented.

Fluid flow modulation in a domestic refrigerative dehumidifier with air-side gearing

Small refrigerative dehumidifiers have shown energy efficiency improvements when operating with air-side gearing. However, the geared domestic dehumidifier has not previously been investigated experimentally for a wide range of airflow settings typical of domestic dehumidifier operation, or with different throttling schemes, and the efficiency of these systems is not well understood under household conditions.In this work, we measure the performance of a commercial domestic dehumidifier, adapted for laboratory testing, in ungeared and geared modes at a wide range of airflows and with both capillary and thermostatic expansion valve throttling to understand how the system performance is effected, for air volume flow rates of 29 L/s - 48 L/s. The measurements show that both capillary and thermostatic expansion valve equipped domestic dehumidifiers can improve energy efficiency in the geared operation mode, but the capillary equipped system is more prone to frosting and wet compression, degrading performance.

Experimental research on four-stage cross flow humidification dehumidification (HDH) solar desalination system with direct contact dehumidifiers

A novel Four-stage cross flow humidification and dehumidification (HDH) solar desalination system with direct contact dehumidifiers was proposed in this paper. Firstly, the composition and operation principle of the system were introduced. Then, the heat and mass exchange models of main parts in the system were established, and some indexes to evaluate system performance were given. Next, an indoor experiment was set up and tested. Based on the experimental results, this paper analyzed the effects of seawater spraying temperature, spraying quantity and the air volume flow rate on freshwater production rate and the gain output ratio (GOR). Finally, the economic analysis and freshwater yield per unit volume of this system were discussed. The results show that when Ts1 = 83 °C, ms1 = 1.1 t/h and mc1 = 0.94 t/h, the water yields of the HDH system with 560 m2 total heat transfer area are 47 kg/h and 63 kg/h respectively under V·a = 0 m3/h and V·a = 300 m3/h. Compared with conventional systems, the current system has higher water yield per unit volume (34.1 kg/(m3·h)) and lower pure water yield cost (3.86 $/ton) when the investment cost of the whole solar desalination device with 42 m2 solar collectors is about $ 6563.

Assessment of the Indoor Environment for Education

Indoor environment quality (IEQ) and its effect on well-being, productivity and performance are phenomena. Achieving suitable and comfortable indoor environment is a key factor in the creation and operation of the buildings in terms of basic principles of the sustainable development. The poor indoor environment is associated with the Sick Building Syndrome (SBS). The occurrence of pollutants in the indoor environment brings health problems to occupants as well as affects their productivity and performance. The main aim of the contribution is the study of indoor environment for educational purposes. The ordinary university classrooms located on the outskirts of the city České Budějovice (Czechia) are analysed. The classrooms are places, where the students reading, calculating, writing, and solving the assigned tasks. Achieving and satisfying the comfort in the indoor environment for education purposes is necessary for these student’s activities. For example, insufficient air exchange and the CO2 concentration above of 1000 ppm, cause fatigue and decreased concentration. The assessment of physical-chemical parameters includes analysis of indoor air temperature [°C], relative humidity [%], Carbon Dioxide (CO2) concentration [ppm], and illumination intensity [lx] in the university classrooms. The high-quality sensor for measuring air flow, temperature, humidity, pressure, heat radiation, CO2 concentration and illumination intensity Testo 480 with globe probe, IAQ probe, light probe and comfort level probe is used for measurement. The work is supported by the grant Specific University Research SVV 201802 Address identification and analysis of the determinants of the Indoor Environment Quality (IEQ).

К вопросу построения нейросетевой математической модели для оценки объемного расхода сжатого воздуха через пропорциональный клапан

The article describes an approach to neural network model design for simulating processes in shut-off and control pneumatic devices. This type of model can be used for a reasoned selection of components for multi-component pneumatic system configurations. As an example, the application of the proposed approach to the development of an artificial neural network to estimate the compressed air volume flow through a proportional valve is considered. The manufacturer’s catalog is used to obtain data samples. The structure of the proposed neural network model, data preprocessing for model configuration, and the selected learning algorithm are described. A computer program for compiling train and test data samples and the subsequent neural network training is developed. The results of measurements are simulated using additional, normally distributed noise with a standard deviation of 0.02. The results obtained using two mathematical models, the neural network model and the classical one, supplemented by empirical coefficients, are compared. The maximum deviation between the two models is less than 1.5 % of the maximum volume flow rate for a particular proportional valve model.

Investigating the effect of raising on the sound absorption behavior of polyester woven fabrics

This work presents the results of efforts focused on the development of sound absorptive woven fabrics by the raising process. Four woven fabrics with rib and basket weave patterns were produced for the raising process. Micro-fiber-based polyester weft yarns were used in one set of rib and basket weave fabrics, while weft yarns comprising regular polyester fibers were used in the other set. Fabrics were subjected to dyeing and heat setting prior to the raising process. Fabrics were then passed one to three times through the raising unit in order to obtain fabrics with different voluminous characteristics and different quantities of fiber ends on the fabric surface. The mass per unit area, thickness, air permeability, and sound absorption coefficient of the fabrics were measured and surface images of the fabrics were taken. The solid volume fraction and airflow resistivity of the fabrics decreased significantly after the first and second raising passes. Increasing the number of raising passes up to two passes resulted in higher sound absorption (average increment of 20% at 5 kHz) in the higher frequencies at the expense of that in the lower frequencies. Sound absorption change beyond two passes was insignificant, though. The results demonstrated that raised fabrics having a lower solid volume fraction and airflow resistivity had better acoustical properties in the higher frequency region.

CRSIDLab: A Toolbox for Multivariate Autonomic Nervous System Analysis Using Cardiorespiratory Identification.

This paper presents the Cardiorespiratory System Identification Lab (CRSIDLab), a MATLAB-based software tool for multivariate autonomic nervous system (ANS) evaluation through heart rate variability (HRV) analysis and cardiorespiratory system identification. Based on a graphical user interface, CRSIDLab provides a complete set of tools including pre-processing cardiorespiratory data (electrocardiogram, continuous blood pressure, airflow, and instantaneous lung volume), power spectral density estimation, and multivariable cardiorespiratory system model identification. Parametrized multivariate models can assess both HRV and baroreflex sensitivity (BRS) by considering the causal relationship from respiration to heart rate (or its reciprocal, R-to-R interval - RRI) and from systolic blood pressure to RRI, for instance. The impulse response, estimated from the model, is used as a mathematical tool to effectively open the inherently closed-loop nature of the cardiorespiratory system, allowing the investigation of the dynamic response between pairs of cardiorespiratory variables. This system modeling approach provides information on gain and temporal behavior regarding dynamics, such as the baroreflex, complementing traditional HRV, and BRS indices. The toolbox is presented and used to investigate autonomic function in sleep apnea. The results show that, while traditional HRV indices were unable to differentiate between apneic and non-apneic subjects, the autonomic descriptors obtained from the multivariate system identification techniques were able to show vagal impairment in apneic compared to non-apneic subjects. Thus, CRSIDLab can help promote the use of cardiorespiratory system identification as a potentially more sensitive measure of ANS activity than classical HRV analysis.

도서관 전열교환기의 재실자수에 따른 기준 환기량 산정 및 수요기반제어

Purpose: Although ERV (Energy Recovery Ventilator) is operating during open hours all the time, students tend to be least satisfied with the indoor air quality of library. This discomfort is getting apparently observed while more students have seated longer time. This study aims to measure whether the supplied airflow rate per capita is sufficient against the law-enforced CO₂ concentration - 1,500 ppm in an actual university library. Also this study aims to perform a pilot test of the DCV (Demand Controlled Ventilation) based on number of occupants, as a compensation for the increased airflow rate that could be a recommended reaction after through measuring currently supplied airflow rates. Method: We first have fixed the supplied airflow rates while letting go off entering and leaving students as many as the number of students who usually visit the library, and then measured the marginal number of students at each flowrate, which makes CO₂ concentration under 1,500 ppm. Also we have fixed the 35 students and then measured the desired airflow rate that maintain CO₂ concentration under 1,500 ppm. Lastly, we have tested the occupant-based DCV for the ERV following combinations of the marginal number of students and the desired airflow rates. Result: It is observed that 1) more occupants require larger airflow rates, as expected. It should be noted that when occupants more than a certain number stay in the library, CO₂ concentration is increasing faster than it would do when there is smaller number of occupants; 2) when library is pretty much occupied, the law-enforced ventilation rate per capita may not be sufficient to meet CO₂ concentration under 1,500 ppm; 3) the occupant-based DCV well contains CO₂ concentration under 1,500 ppm upon varied number of occupants, while saving surplus airflow volumes and thus saving the electricity.

Development of trenchless technology of reconstruction of «pulling pig P» pipeline communications

The technology of trenchless reconstruction of pipeline communications has been developed by pulling a new polyethylene pipeline into a worn-out steel traction by the pig. The pig moves under the pressure of air supplied into the trans-pig space by the compressor. Mathematical and CFD modeling of the process of pulling the pipeline by a pig is performed. Formulas for calculating the resistance forces acting on the moving system, the pressure at the compressor outlet, at which the pig will extend a new polyethylene pipeline with the entire length of the reconstructed worn steel pipeline, are derived. The resistance forces acting on the moving system on horizontal sections of the route are: the force of mechanical friction of the pig cuffs against the walls of the steel pipeline; friction force of polyethylene pipe to steel; friction force of the polyethylene pipe in the ring cuffs of the sealing system. The results of CFD simulations are visualized in the postprocessor of the Ansys Fluent software package by drawing flow lines, speed vectors, pressure fields on the contours and in the longitudinal section of the annular and rotary space. The exact values of speed, pressure at various points of the annular and rotary space are determined. The structure of the air flow in the trans-pig and annular space is investigated. Places slowing down and accelerating the flow of air, falling and rising pressure are identified. The pressure losses in the annular space are determined. After performing experimental tests, it is found that the developed «Pulling pigP» technology can be used for the reconstruction of pipeline communications. According to the results of experimental measurements, graphs of changes in air pressure at the beginning of the pipeline in time are constructed when the pulling a polyethylene pipe into worn-out steel by the pig. The pressure at the beginning of the pipeline before the start of pulling increases, due to the force of static friction. After the start of pulling, the pressure decreases by a small amount, and during pulling, its slight increase occurs. The graphs of dependence of the pulling speed on the air volume flow and on the length of the pulled section of the polyethylene pipe are constructed. At the initial stage, the pulling speed increases dramatically and after such growth stabilizes

Measuring airflow through the portable high-efficiency air filtration (PHEAF) device to assess reliability of instrument and sample location

ABSTRACT The portable high-efficiency air filtration (PHEAF) device is an engineering control common to the environmental remediation industry. Damage to the high-efficiency particulate air (HEPA) filter (e.g., filtration media, gasket), improper installation of the filter into the mounting frame, or defects in the filtration housing affect the capture efficiency of the device. PHEAF devices operating at less than marketed efficiencies justify periodic leak testing of the PHEAF device, especially when the filtered air is exhausted into occupied spaces. A leak test is accomplished by injecting a known concentration of aerosol upstream of the HEPA filter and measuring the percentage of aerosol penetrating through the filtration system. The test protocol scripted for stationary systems (i.e., biological safety cabinets) states that upstream concentrations can be empirically determined using the aerosol photometer to measure particulate matter (PM) in the airstream. This practice requires a homogenous mixture of the aerosol challenge agent within the airstream. However, design of the PHEAF device does not include a validated induction point for the aerosol. Absent of an acceptable means to achieve a homogenous mixture for upstream measurement, the aerosol concentration is mathematically derived based on the measured air volume passing through the PHEAF equipment. In this study, intake volume and exhaust volume for each PHEAF device were measured by either the balometer or the hot wire anemometer. Variability of measurements was examined by instrument and sample location (intake vs. exhaust) to understand which combination would be most consistent for measuring airflow volume. From this study, the authors conclude that the balometer is preferred compared with the hot wire anemometer for measuring airflow through the PHEAF device. Exhaust measurement by balometer seems more reliable than intake measurements by hot wire anemometer. Implications: Although testing of PHEAF devices is recommended by various public health authorities, no nationally recognized test protocol has been published in the United States. In support of measuring the performance of the PHEAF device in a field setting, this study evaluated the hot wire anemometer and balometer techniques and sample locations (intake vs. exhaust) to reliably measure airflow through the PHEAF device. Since accuracy of the particle measurement is associated with airflow volume, it is essential to obtain a true airflow reading. This study suggests that the balometer was more consistent in measuring airflow through the PHEAF device.

Enhancing the exergetic performance of a pilot-scale convective dryer by exhaust air recirculation

In this study, an air recirculating pilot-scale convective dryer operating at various exhaust air recycle fractions was exergetically investigated in detail. Two drying air temperatures (55–70 °C), two air volume flow rates (360–450 m3/h), and six exhaust air recycle fractions (0–100%) were considered for drying of poplar wood chips. The effects of drying variables were studied on the exergetic efficiencies of drying system and drying chamber. The total exergy of air exhausting from drying chamber was also fractionated into thermophysical and wet exergies for further evaluating the effect of recycle fraction. The universal exergetic efficiency of drying chamber ranged from 41.84% to 98.07%, while the average overall functional exergetic efficiency of drying system varied from 1.32% to 4.01%. Exhaust air recirculation profoundly improved the overall functional exergetic efficiency of drying system as a decision-making parameter up to over two times. Although the recycle fraction of 100% showed the highest improvement in the overall functional exergetic efficiency of drying system, the drying time drastically increased at this condition as expected. Overall, a compromise should be made between drying time and exergetic improvement in order to select a proper recycle fraction for recovering exergy from outflow air.

Performance of a new type of solar air collector with transparent-vacuum glass tube based on micro-heat pipe arrays

In this study, a novel solar air collector with transparent-vacuum glass tube is designed and investigated through experiment and numerical simulation. The collector consists of micro-heat pipe arrays (MHPA), selective absorption film and transparent-vacuum glass tube. The absorption film is directly pasted on the MHPA by using heat-conducting glue, which is then placed into transparent-vacuum glass tube. The efficient heat conduction of MHPA and good thermal insulation of the transparent-vacuum glass tube contribute to the high efficiency and low pressure loss of the collector. The collector average efficiency can reach 82.7% and the pressure loss is less than 20 Pa. This collector form for heating spaces and drying crops is new and effective. Increasing the air volume flow rate can considerably improve the collecting efficiency. The ambient temperature in winter results in a higher efficiency than that in summer. Furthermore, a calculation numerical model, which is used to develop 20 collecting units, is established and verified for validity. This model can obtain temperature increase in each collecting unit. Considering the temperature increase in each collecting unit and the thermal efficiency, the proposed maximum collecting unit quantity is 20. Study results provide a theoretical guidance for designing MHPA solar air collector.

Bioinspired Hairy Skin Electronics for Detecting the Direction and Incident Angle of Airflow.

The human skin has inspired multimodal detection using smart devices or systems in fields including biomedical engineering, robotics, and artificial intelligence. Hairs of a high aspect ratio (AR) connected to follicles, in particular, detect subtle structural displacements by airflow or ultralight touch above the skin. Here, hairy skin electronics assembled with an array of graphene sensors (16 pixels) and artificial microhairs for multimodal detection of tactile stimuli and details of airflows (e.g., intensity, direction, and incident angle) are presented. Composed of percolation networks of graphene nanoplatelet sheets, the sensor array can simultaneously detect pressure, temperature, and vibration, all of which correspond to the sensing range of human tactile perceptions with ultrahigh response time (<0.5 ms, 2 kHz) for restoration. The device covered with microhairs (50 μm diameter and 300 μm height, AR = 6, hexagonal layout, and ∼4400/cm2) exhibits mapping of electrical signals induced by noncontact airflow and identifying the direction, incident angle, and intensity of wind to the sensor. For potential applications, we implement the hairy electronics to a sailing robot and demonstrate changes in locomotion and speed by detecting the direction and intensity of airflow.

A new multicopter-based unmanned aerial system for pollen and spores collection in the atmospheric boundary layer

Abstract. The application of a new particle collection system (PCS) developed in-house and operated on board a commercially available multicopter unmanned aerial vehicle (UAV) is presented as a new unmanned aerial system (UAS) approach for in situ measurement of the concentration of aerosol particles such as pollen grains and spores in the atmospheric boundary layer (ABL). A newly developed impactor is used for high-efficiency particle extraction on board the multicopter UAV. An airflow volume of 0.2 m3 min−1 through the impactor is provided by a battery-powered blower and measured with an on-board mass flow sensor. A bell-mouth-shaped air inlet of the PCS is arranged and oriented on the multicopter UAV to provide substantial isokinetic sampling conditions by advantageously using the airflow pattern generated by the propellers of the multicopter UAV. More than 30 aerosol particle collection flights were carried out near Tübingen in March 2017 at altitudes of up to 300 m above ground level (a.g.l.), each with a sampled air volume of 2 m3. Pollen grains and spores of various genera, as well as large (&gt;20 µm) opaque particles and fine dust particles, were collected, and specific concentrations of up to 100 particles per m3 were determined by visual microscopic analysis. The pollen concentration values measured with the new UAS match well with the pollen concentration data published by the Stiftung Deutscher Polleninformationsdienst (PID) and by MeteoSwiss. A major advantage of the new multicopter-based UAS is the possibility of the identification of collected aerosol particles and the measurement of their concentration with high temporal and spatial resolutions, which can be used inter alia to improve the database for modelling the propagation of aerosol particles in the ABL.

Performance Study of Water Harvesting Unit Working Under Iraqi Conditions

The scarcity of water facing the world is one of the biggest challenges of this century. This challenge requires research plans in the field of water desalination that is not suitable for human use or the harvesting of water from the air. In this work, the performance of the water harvesting unit from the ambient air is studied. For this purpose, a vapor compression system is designed and built, a 372[Formula: see text]W reciprocating compressor is selected depending on the use of a small family consisting of four persons. The components of the vapor compression system are designed depending on the compressor power. The unit evaporator is modified to condensate the water vapor associated with the air instead of cooling the air. The effect of volume flow rate of air across the evaporator is studied. The range of air volume flow rate is from 224 to 244[Formula: see text]m3/h, as well as the operation mode of the unit which either continues to condensate or freeze the water vapor on the evaporator is also studied. The result showed that the water harvesting unit can work at a relative humidity as low as about 20%. The maximum water production for the unit is 7.9[Formula: see text]l/day with a power consumption of 1.76[Formula: see text]kW-h/l at the volume flow rate of air is 230[Formula: see text]m3/h. When an evaporative cooler is turned on in the test chamber, the amount of water production increases to about 13.11[Formula: see text]l/day with a power consumption of 1.068[Formula: see text]kW-h/l, for the same volume flow rate of air mentioned above.

Effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing

This paper studies the effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing with four degrees of freedom (4-DOF). A clearance function is used to describe the film thickness of air journal bearings with angular misalignment along two perpendicular directions. The finite different method (FDM) and an iterative procedure are applied to solve the Reynolds equation and obtain the air film pressure distribution. Various eccentricity ratios and rotating speeds are taken into considerations for the comparisons of static performances of the air journal bearing under different tilt angles. The results show that the air film thickness, load capacity, stiffness, load moment, attitude angle and volume flow rate are affected greatly by the angular misalignment.

Generation and control of helium-filled soap bubbles for PIV

The operating regimes of an orifice-type helium-filled soap bubbles (HFSB) generator are investigated for several combinations of air, helium and soap flow rates to establish the properties of the production process and the resulting tracers. The geometrical properties of the bubbles, the production regimes and the production rates are studied with high-speed shadowgraphy. The results show that the bubble volume is directly proportional to the ratio of helium and air volume flow rates, and that the bubble production rate varies approximately linearly with the air flow rate. The bubble slip velocity is measured along the stagnation streamline ahead of a cylinder via particle image velocimetry (PIV), yielding the particle time response from which the neutral buoyancy condition for HFSB is inferred. The HFSB tracing capability approaches that of an ideal tracer (i.e., minimum slip and shortest response time) when the volume flow rate of helium is approximately one thousandfold the soap flow rate. This study provides guidelines for operating HFSB generation systems, intended for PIV experiments.Graphical abstract

Flat bed desiccant dehumidification: A predictive model for desiccant transient characterisation using a species transport model within CFD

As opposed to steady state characteristics which have been, in the past, estensively investigated, the transient dehumidification characteristics of silica gel under different flat bed configurations, has not been studied in detail with respect to varying mass and air flow rates. Such data is essential in the design of systems employing this method of dehumidification. Moreover, numerical models of the performance of flat bed desiccant configurations generally take the form of fundamental studies with explicit modelling of the desiccant particle geometries. The primary objective of this work aims is to generate dehumidification characteristics in high humidity environments. Secondly, a more simplified and practical approach is proposed here on the basis of experimental calibration. The methodology consists of two main approaches: (i) the development of a test rig for the experimental determination of the transient dehumidification characteristics and, (ii) the development of a Computational Fluid Dynamics (CFD) model using experimental data as input to provide easy extrapolation of experimental data. This paper presents detailed dehumidification results for varying air volume flow rate and desiccant mass. The numerical model, on the other hand, successfully predicts the dehumidification performance of varying silica gel masses by using only a single experimental test case. This proves the validity of using such a model to extrapolate on experimental data.

A Study on In-Cylinder Flow of Small Engine Using Steady-State Flow Benches

In-cylinder air flow structures are known to strongly impact on the performance and combustion of internal combustion engines (ICE). Therefore, the aim of this paper is to experimentally study an IC engine in-cylinder flow under steady-state conditions. Steady-state flow bench methods can be used to characterize the in-cylinder flow engine. The experiments were carried out on the small cylinder head with pressure difference across the inlet valves of 100 to 300 mmH2O. The experimental results are presented in terms of the measured air flow rate, flow coefficient and discharge coefficient. Moreover, the CFD used to illustrate the evolution of tumble motion in-cylinder engine. The results show that air volume flow rate and flow coefficient increased as the valve lift increases but the coefficient of discharge decrease if valve lift increase. The higher the pressure drop the higher the mass flow rate value. However, the higher the pressure drop the lower the value of flow coefficient and discharge coefficient.