Airflow Rate Measurements Research Articles

Development of Air Flow Rate Prediction Model Using Multiple Regression in VAV Terminal Unit

Accurate measurement of air flow rate is essential in automatic building control using the variable air volume (VAV) system. In order to solve the problems of the existing air flow measurement method and improve the accuracy of air flow control, this study developed a data-based multiple regression air flow prediction model. The independent variables used in the development of the predictive model were selected as the factors used for control and monitoring when operating with variable air flow rate in the existing air conditioning system. Data collection and correlation between independent variables and air flow rate of the terminal unit were analyzed. Using the IBM SPSS statistics version 25, an air flow rate prediction model was developed using multiple regression analysis. Reliability of model was evaluated by comparing the measured airflow. The relative error of −9.3% to 10.4% is shown when comparing the estimated air flow rate by the developed model with the measured air flow rate.

Constant Temperature Anemometer with Self-Calibration Closed Loop Circuit

In this paper, a Micro-Electro-Mechanical Systems (MEMS) calorimetric sensor with its measurement electronics is designed, fabricated, and tested. The idea is to apply a configurable voltage to the sensitive resistor and measure the current flowing through the heating resistor using a current mirror controlled by an analog feedback loop. In order to cancel the offset and errors of the amplifier, the constant temperature anemometer (CTA) circuit is periodically calibrated. This technique improves the accuracy of the measurement and allows high sensitivity and high bandwidth frequency. The CTA circuit is implemented in a CMOS FD-SOI 28 nm technology. The supply voltage is 1.2 V while the core area is 0.266 mm2. Experimental results demonstrate the feasibility of the MEMS calorimetric sensor for measuring airflow rate. The developed MEMS calorimetric sensor shows a maximum normalized sensitivity of 117 mV/(m/s)/mW with respect to the input heating power and a wide dynamic flow range of 0–26 m/s. The high sensitivity and wide dynamic range achieved by our MEMS flow sensor enable its deployment as a promising sensing node for direct wall shear stress measurement applications.

Effect of voicing and articulation manner on aerosol particle emission during human speech.

Previously, we demonstrated a strong correlation between the amplitude of human speech and the emission rate of micron-scale expiratory aerosol particles, which are believed to play a role in respiratory disease transmission. To further those findings, here we systematically investigate the effect of different 'phones' (the basic sound units of speech) on the emission of particles from the human respiratory tract during speech. We measured the respiratory particle emission rates of 56 healthy human volunteers voicing specific phones, both in isolation and in the context of a standard spoken text. We found that certain phones are associated with significantly higher particle production; for example, the vowel /i/ ("need," "sea") produces more particles than /ɑ/ ("saw," "hot") or /u/ ("blue," "mood"), while disyllabic words including voiced plosive consonants (e.g., /d/, /b/, /g/) yield more particles than words with voiceless fricatives (e.g., /s/, /h/, /f/). These trends for discrete phones and words were corroborated by the time-resolved particle emission rates as volunteers read aloud from a standard text passage that incorporates a broad range of the phones present in spoken English. Our measurements showed that particle emission rates were positively correlated with the vowel content of a phrase; conversely, particle emission decreased during phrases with a high fraction of voiceless fricatives. Our particle emission data is broadly consistent with prior measurements of the egressive airflow rate associated with the vocalization of various phones that differ in voicing and articulation. These results suggest that airborne transmission of respiratory pathogens via speech aerosol particles could be modulated by specific phonetic characteristics of the language spoken by a given human population, along with other, more frequently considered epidemiological variables.

СТАБІЛІЗАЦІЯ ТЕМПЕРАТУРНОГО РЕЖИМУ ПРИМІЩЕННЯ ЛАБОРАТОРІЇ ВИСОКОПРОДУКТИВНИХ ОБЧИСЛЕНЬ ДОННТУ

Purpose: to analyze the thermal load of the server cluster of the high-performance computing laboratory, stabilize the temperature regime of the room throughout the year, taking into account seasonal changes in the ambient temperature. Methodology: performing experimental studies using modern devices and analyzing experimental data to assess the heat load of server clusters at various degrees of their workload with calculations. Results: a thermal analysis of the work of the server cluster of a high-performance computing laboratory was carried out at various degrees of server load with calculations. Temperature measurements were carried out for various zones and elements of server racks, temperature changes were established when the servers were loaded with calculations. In the modern CFD system, the air flows of the server cooling system and the temperature regime of the server cluster and the server room are simulated, taking into account the location of the equipment and information about the measurements of temperatures and air flow rates. As a result, temperature distributions were obtained for different server loads. A comparison of the supply and exhaust ventilation options was carried out; equipment was selected to ensure the effectiveness of temperature stabilization in the server room at the required level. ISSN 2308-5312 Наукові праці ДонНТУ. Серія: «Машинобудування і машинознавство». No1(14)’2020 20 Scientific novelty: the assessment of heat dissipation during the operation of the server cluster was carried out, the temperature regime of the operation of the server room objects was simulated and the temperature distributions were obtained for different server loads. Practical significance: the design of the room with the location of equipment for supply and exhaust ventilation is proposed; the main parameters of equipment for effective ventilation to reduce the heat load of server racks are determined, recommendations for the use of heat laboratories of high-performance computing for partial heating of the educational building of the state higher educational institution

Analysis of Natural Ventilation Performance Gap between Design Stage and Actual Operation of Office Buildings

Suitable natural ventilation in office buildings can not only reduce energy consumption of air conditioning, but also improve indoor air quality. In the architectural design stage, the effect of natural ventilation design is mainly simulated by CFD simulation software for indoor air speed, pressure, and age of air, etc.. However, during the actual building operation, the indoor natural ventilation effect will be affected by many factors, such as surrounding buildings, indoor layout, window position and open-close status, human behavior, etc., and the natural ventilation performance between design stage and actual operation is often different. In this paper, a typical office building was selected and FloVENT software was used to quantitatively analyse the influence of surrounding buildings, indoor layout, door/window opening conditions on indoor natural ventilation. Field measurement of indoor air flow rates in typical positions in office were carried out under different circumstances. In order to reduce the instantiate influence of outdoor wind speeds, a new index named Wind Speed Ratio(WSR) is put forward.Through comparative analysis of simulated data and measured data. the gap degree in natural ventilation performance between design stage and operation operation is discussed, and results show that the relative errors of the WSR, which could be considered to reflect the performance gap, are about 78.0%, 28.7% and 150% respectively, under corresponding condition settings of surrounding buildings, indoor layout, and door/window opening.

Development of Virtual Air Flow Sensor Using In-Situ Damper Performance Curve in VAV Terminal Unit

In this study, we developed a virtual air flow sensor using an in-situ damper performance curve to secure the stability of control of the variable air volume (VAV) terminal unit, and also established the in-situ measurement procedure. The minimum air flow rate of the VAV terminal unit was related to the energy consumption, it was important to determine the minimum air flow rate suitable for the situation of each room in terms of energy saving. However, it was difficult to set the minimum air flow rate low setpoint due to the low accuracy of the air flow sensor of the VAV terminal unit. This paper suggested a virtual air flow sensing method using an in-situ damper performance curve in the VAV terminal unit. The input factors of the virtual sensor were developed on the basis of the supply fan speed and damper opening ratio, which could be easily obtained from the existing control system. In addition, the in-situ measurement procedure of the virtual air flow sensor was developed by dividing the procedure into five steps. Finally, reliability of the virtual air flow sensor was evaluated through uncertainty analysis of input variables and relative error analysis, in comparison with the conventional air flow rate measurement method. The developed virtual air flow sensor was found to have an uncertainty of up to 8.8%, and it was also found that the closer to the maximum the values of the input variables, the lower the uncertainty. In addition, verification of relative error with respect to the measured values by the hot-wire anemometer was conducted by varying operation conditions to a total of 12 cases, and as a result, relative error was found to be up to 5.6%. In addition, the results of long-term experiment showed that relative error was within about 9.5%, and thus, the feasibility for field application and control was confirmed.

Assessment of the air flowrate measurement in altitude engine tests by the national measurement standards system

The air flowrate in the engine inlet is an important parameter used to calculate common performance metrics such as the thrust and specific fuel consumption of a gas turbine engine. In the Korea Aerospace Research Institute (KARI) altitude engine test facility, air flowrates are calculated by measuring the static pressure, total pressure and temperature in an engine inlet duct. In the present study, in order to verify the air flowrate measurements at the engine inlet duct of the KARI altitude engine test facility, inlet flow measurement devices which are a total pressure rake, total temperature rake, and boundary layer rake were tested in the national measurement standards system for high pressure gas flow of the Korea Research Institute of Standards and Science (KRISS). Sonic nozzles, calibrated for flows rate up to 10000 m3/h and pressure range up to 50 bar (with an uncertainty = 0.18 %), were used as reference meters. We compared the air flowrates obtained by the area-weighted average duct Mach number in the inlet flow measurement devices of the KARI engine inlet duct to the reference flowrates of sonic nozzles at KRISS up to a Mach number of 0.15.

Pengaruh Ventilasi Alami Terhadap Sick Building Syndrome

<p><em>The number of buildings that use air conditioner (AC), causing a lack of air change rate from the outside into the room or vice versa that can reduce indoor air quality. A bad indoor air quality is often give rise to complaints on its occupants called the "Sick Building Syndrome" (SBS). The presence of ventilation is expected to improve air quality and increase user comfort and wellness rooms. Therefore, the research on the influence of natural ventilation against sick building syndrome (SBS) is needed. This research was conducted with quantitative-descriptive methods with direct measurements of temperature, humidity and vloumetric air flow rate on samples of objects namely RSND clinic waiting room on the 2nd floor. As for analysis is carried out descriptively based on recommended standards. The purpose of doing this research is to know the influence of natural ventilation to the indoor air quality towards sick buiding syndrome. The result of this research show that the temperature, humidity and the clean air needs of the room doesn’t meet the standarts, meanwhile the air change per hour meet the standarts on some spots. So, there is some influence of the use of natural ventilation that can improve the indoor air quality which is relating to sick building syndrome.</em></p>

Techniques for airflow measurements to determine the real efficiency of heat recovery in ventilation systems

Heat recovery in ventilation is essential to reduce energy use and thus mitigate greenhouse gas emissions from the building sector. Heat recovery efficiency of at least 80 % in new buildings is required according to Norwegian standards. However, measurements show that the real heat recovery efficiency during operation is commonly 10-20 % lower. Measuring heat recovery efficiency in buildings is challenging, mainly due to difficulties measuring airflow rates close to the air handling unit (AHU). This study assesses the following duct airflow measurement techniques and equipment: pressure differential, velocity traversal technique, ultrasound and tracer gas. The pressure differential method can provide accurate flow rates and thus it is used as the reference measurement. However, it is not suitable for duct flow measurements due to its high pressure penalty and long straight duct requirement. Velocity traverse and tracer gas methods introduce less disturbance to the flow. Nevertheless, both methods require intensive labour work and cannot track quick changes of the airflow with time. The application of ultrasound to measure airflow is relatively novel and it can automatically measure constant and fluctuating airflows with low pressure drop and acceptable accuracy when the proper installation and minimum straight duct are provided.

Road Tunnel Axial Fan Performance In Situ Test: Taking Qinling Zhongnan Mountain Highway Tunnel as an Example

Axial fans play a pivotal role in the road tunnel ventilation system. Qualified performance of the axial fan is important for both safety and air quality maintenance reasons. Axial fans performance in situ test of Qinling Zhongnan Mountain highway tunnel, the second longest road tunnel in the world, is presented in this research. Performance test items and the qualification criterion, as well as a general framework for the road tunnel axial fan assessment, are recommended. Log-Tchebycheff method is suggested to confirm the location for the measuring lines and points. The precision of the log-Tchebycheff method in air flow rate measuring is verified by comparing with the biharmonic spline interpolation fitting result. The research shows that the log-Tchebycheff method has high precision and good efficiency in the air flow rate measurement of the road tunnel air duct. What is more, the biharmonic spline interpolation fitting method can be applied to obtain a more accurate result. The number of interpolation points of the biharmonic spline interpolation fitting method should be bigger than 2000 to provide quality results.

A Fully-Integrated, Single-Element CMOS Anemometer

Miniaturized flow rate sensors are increasingly utilized for in situ gas and liquid sensing, where small size, low cost, and robust operation are critical. Many flow rate sensors utilize two sensor elements, a heater, and a downstream temperature sensor, for measurement of mass flow rate. In this article, a single-element flow rate sensor architecture is presented, in which the sensor element and measurement electronics are integrated into a silicon complementary metal-oxide semiconductor (CMOS) integrated circuit (IC) substrate. The architecture uses a single, resistive transducer element defined in top-metal CMOS layers, which requires no postfabrication or postprocessing. The design is implemented in a general purpose 0.18 $\mu$ m CMOS process, and a two-phase control and measurement scheme is used to alternately heat and cool the sensor. Experimental results demonstrate the feasibility of the fully integrated CMOS anemometer for measuring air flow rate, and the complete sensor occupies less than 0.065 mm $^2$ IC chip area.

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.

Thermal performance characterisation of a reverse-flow energy recovery ventilator for a residential building application

The European Union’s 2020 and 2030 sustainable energy policies seek significant reductions in both energy consumption and carbon emissions. These policies demand a greater use of energy efficient technologies and a transition away from fossil fuels. This paper studies one such technology, an indoor climate control system with a reverse-flow enthalpy recovery ventilator, capable of recovering both sensible and latent heat. The thermal performance characteristics are established using an experimental facility and calculation methods defined by European Standard EN 13141-7:2010. This involves measurement of temperature, humidity, pressure and volumetric air flow rates over a range of operating conditions. Total thermal energy recovery rates ranged from 0.63 kW to 2.2 kW, with energy recovery efficiency of 72.8 % to 88.6 %. The recovery efficiency ratio, which reflects the capacity of the indoor climate control system to recover thermal energy relative to its power consumption ranged between 6.87 to 19.97. Due to the unique reverse-flow defrost function, the system demonstrates operation down to -7 °C without frost formation. These results highlight the potential that this system can make towards the EU goals of reducing energy consumption, operating costs and carbon emissions associated with indoor climate control.

Integrity Assessment of Open-Circuit Respiration Chambers for Ruminant Animal Indirect Calorimetry

Abstract. Open-circuit chambers have been widely applied to gas exchange measurement for indirect calorimetry and greenhouse gas emission. The reliability of these systems is crucial and is commonly evaluated through recovery tests. These tests simulate gas exchanges of animals through the injection or consumption of known quantities of gases, while monitoring the gas flux with the measurement system, and then comparing the difference between the known mass and the measured mass to assess the system integrity. Although the recovery test approach is widely accepted, the method of how to choose recovery tests has rarely been documented, and no single source has been found that summarizes a complete process for evaluating a system and correcting post-evaluation systematic errors. In this study, three recovery methods were applied: (1) the alcohol combustion method (ACM) burns a known amount of pure ethanol to simulate both consumption (O2) and production (CO2); (2) the gravimetric gas injection method (GRAV) directly measures the weight change of a compressed CO2 gas cylinder during the injection process; and (3) the constant gas injection method (CGIM) steadily injects sulfur hexafluoride (SF6) gas into the chamber. An experiment was conducted that included eight repeated trials for each of the three methods in six identical chambers (144 total tests) of the Ruminant Emission Measurement System (REMS) at the Beef Cattle and Sheep Field Laboratory at the University of Illinois in Urbana-Champaign. The recovery percentages of the respiratory quotient for the six ACM chambers varied from 72.58% to 77.76%, indicating that measurement and calculation errors occurred in the system. The CGIM and GRAV methods were used for identifying the errors from ventilation measurement and calculation of exhaust airflow rate. Correction factors were generated from the results and proved effective, as recovery percentages were improved to an acceptable level (100% ±5%) for all chambers. This approach can be applied to other studies and other systems to assist in selecting appropriate integrity tests and applying correction methods. Keywords: Cattle, Emissions, Gas exchange, Metabolism, Recovery method, Tracer gas measurement.

Qualification of channels produced by laser powder bed fusion: Analysis of cleaning methods, flow rate and melt pool monitoring data

Laser powder bed fusion, is an additive manufacturing technology that is used in industry for rapid prototyping and manufacturing of aftermarket products, molds and special machine parts. Quality assurance and process stability still require improvement until this technology is ready for large scale serial production. Scan strategies and parameter sets for manufacturing are often fixed when certification processes are finished. Thus, it is important to test the manufacturability of specific design features such as inner channels. In the following we will present the qualification of inner channels in different test parts for the aluminum alloy AlSi10Mg and the stainless steel 1.4542. The testing includes different cleaning methods and air flow rate measurements. Additionally, we will compare such parts and LPBF specific problems to observations with a coaxial melt pool monitoring system.

From Instrument to Architecture: Environmental Models as Design Tools

This paper revisits a case study in the history of technology, Étienne-Jules Marey’s 1900–1902 wind tunnel prototypes, and makes links between Marey’s wind tunnel and the prototyping of physical environmental models as environmental design tools today. Using historiographic research and physical prototypes, the research asks: What insights about airflow do Marey’s wind tunnel and contemporary iterations of it offer architectural designers today? Insights are explored in relation to three measures: Marey’s wind tunnel photographs measure air flow rates; the wind tunnel measures the material sensitivity of air; in the author’s prototypes, air and water flows reveal constructional measures, suggesting a tectonic approach to architecture. The significance of the research lies in situating a technique exemplified by Marey within a contemporary environmentally-responsive architectural design context.

Impact of demand controlled ventilation on system performance and energy use

Demand-controlled-ventilation (DCV) refers to a ventilation system with controlled air flow rate based on indoor air quality. DCV operates at reduced air flow rates during most of the operation time. Therefore, less energy is required for fan operation, compared to a constant-air-volume (CAV) ventilation system.Typically, DCV has a two-layer control with variable-air-volume (VAV) valves, and a fan speed control to maintain a constant-static-pressure in the duct system based on a pressure set point.However, this nominal design based fan pressure setpoint is higher than required when all VAV-valves are closed to a certain extent. Therefore, advanced pressure-reset (PR) control - resetting the pressure set point - potentially reduces fan energy use even further.This paper assesses the impact of fan control on both fan energy use and ventilation performance in DCV system of a densely occupied office. Results of a simulation model and realistic measurement setup are compared. The PR control, using air flow rate and VAV-valve position measurements as feedback, causes significantly reduction on fan energy use. These reductions compared to conventional DCV and CAV respectively, are approximately 10% and 72% in case of high occupancy and 50% and 93% in case of low occupancy. Largely, DCV with PR control is strongly considered, especially when occupancy is often expected to deviate significantly from the nominal conditions. Moreover, both simulations and measurements show that there is a clear trade-off between air flow rate deficit and fan energy use, when the fan energy use is lower, the air flow rate deficit is higher and vice versa. Furthermore, the results show that VAV-valve accuracy, characteristics and its lower operational limit hamper the ventilation system in achieving the predicted performance as in the simulation.

Response of Tisochrysis lutea [Prymnesiophycidae] to aeration conditions in a bench-scale photobioreactor

The effects of superficial gas velocity (Ugr), gas entrance velocity (ν), and bubble size on the growth of Tisochrysis lutea was investigated in 600-mL photobioreactors operated with airlift pumps. Superficial gas velocities, calculated from measured air flow rates, ranging from 7 to 93 mm s−1 were created using a 1.6-mm diameter syringe. We tested the effects of sparger velocity over a range of 2.48 to 73.4 m s−1 and the effects of bubble size by using two styles of air stones and an open glass pipette, which created a bubble sizes in the range of 0.5 to 5 mm. We calculated oxygen mass transfer coefficient, kLa, values for all experimental conditions. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicated that smaller bubble size leads to some initial cell damage, but after time, the increased gas transfer as reflected by the kLa value produced higher growth than larger bubbles. Two mechanisms were observed to correlate with cell damage in T. lutea: increasing velocity at the sparger tip and bubble bursting at the surface. These results demonstrate a method to test sensitivity of T. lutea to aeration, which is important for the design of airlift systems.

Accuracy analysis of air torque position dampers based on blade profiles and damper locations

The primary concern of this paper is a single-blade air torque position damper used for the indirect measurement of volumetric air-flow rates by measuring the moment of airstream force exerted on the blade and the damper position. The purpose of the paper is to analyze the accuracy of the air velocity measurements and the adequacy of the damper mathematical model on the basis of the blade profile and the damper location in a duct system. The analysis was performed on the basis of the experimentally obtained results. Four different blade profiles (flat, V-groove, symmetrical airfoil, and non-symmetrical airfoil blades) were taken into account, as well as three different damper locations in the duct system (at the duct entrance, within the duct, and at the duct exit). Two blade orientations at the duct entrance were examined relative to the direction of air-flow (with front and rear mounting flanges). It was determined that the blade profile and particularly the damper location in the duct system affect the measurement accuracy and the adequacy of the damper mathematical model provided the blade angle of attack is less than or equal to 30?, i. e. within the range of a more open damper.

Perception and Respiratory Responses of the Upper Airway Mechanism to Added Resistance With Aging.

ObjectivesTo assess breathing behaviors and perception of added respiratory loads in young compared to old individuals, and to determine whether aging affects the perception and response to changes in nasal airway resistance.Study designIn a clinical study, 40 young (11–20 years) and 40 older (59–82 years) subjects were evaluated during rest breathing and during the application of added airway resistance loads.MethodsThe pressure‐flow technique was used to measure airflow rate (mL/s) and oral‐nasal pressures (cmH2O) to calculate nasal resistance (cmH2O/L/s). To create calibrated resistance loads for the test conditions, we used a device modified from a precision iris diaphragm.ResultsDuring rest breathing airflow rate was significantly lower for the younger group compared to older group. Using the loading device, 11–20‐year‐olds detected increased resistance at the level of 2.26 cmH2O/L/s compared to 4.55 cmH2O/L/s in 59–82‐year‐olds. In contrast to the younger group, mean airflow rate was higher during expiration than during inspiration among 59–82‐year‐olds except at rest breathing.ConclusionsThe data revealed that the perception and respiratory response to increased airway resistance changed with aging. Younger subjects were more sensitive to changes within the airway. In both groups, subjects responded to increased airway resistance by decreasing airflow rate. However, expiratory phase became more active than inspiratory phase only in the older group.Level of EvidenceN/A