Airflow Rate Measurements Research Articles

Single phase through-plane permeability of carbon paper gas diffusion layers

Effects of mechanical compression and PTFE content on the through-plane gas permeability of gas diffusion layers (GDLs) of PEM fuel cells are investigated both experimentally and theoretically. A new test bed is designed and built which allows pressure drop and air flow rate measurement for various GDL samples. The measured values are used to calculate the through-plane permeability. Various GDLs are obtained and tested over a wide range of PTFE content and compression ratio. The experimental data show a reverse relationship between the through-plane permeability and both PTFE content and mechanical compression. An existing model for through-plane permeability of planar fibrous structures is revisited to develop a model that accommodates effects of PTFE content and mechanical compression. The proposed model captures the trends of the experimental data for the through-plane permeability, measured in the present study or reported by others.

Experiment Research on Air Flow Rate Measurement Using Tracer Gas Method

Experiment research on the air flow rate measurement using tracer gas method in a 300mm internal diameter and 90° elbow duct are presented, which CO and air are selected as tracer gas and gas stream. Results show that the relative errors between the flow rate measured by tracer gas method and turbine flowmeter are varied in the range of -2.15%~1.69% when the injection point is upstream of the elbow on 7D~13D (D is the internal diameter of the duct), and the sampling point is downstream of the elbow on 10D~14D. The further distances of the injection point and sampling point are apart, the less relative errors of the gas flow rate measured by tracer gas method and turbine flowmeter are made. The injection flow rate of tracer gas should be matched with the gas flow rate in the duct. It is a simple and effective method that gas flowmeter online calibration with tracer gas method on the large diameter industrial gas pipeline transportation.

Comparing Two-Zone Models of Dust Exposure

The selection and application of mathematical models to work tasks is challenging. Previously, we developed and evaluated a semi-empirical two-zone model that predicts time-weighted average (TWA) concentrations (Ctwa) of dust emitted during the sanding of drywall joint compound. Here, we fit the emission rate and random air speed variables of a mechanistic two-zone model to testing event data and apply and evaluate the model using data from two field studies. We found that the fitted random air speed values and emission rate were sensitive to (i) the size of the near-field and (ii) the objective function used for fitting, but this did not substantially impact predicted dust Ctwa. The mechanistic model predictions were lower than the semi-empirical model predictions and measured respirable dust Ctwa at Site A but were within an acceptable range. At Site B, a 10.5 m3 room, the mechanistic model did not capture the observed difference between PBZ and area Ctwa. The model predicted uniform mixing and predicted dust Ctwa up to an order of magnitude greater than was measured. We suggest that applications of the mechanistic model be limited to contexts where the near-field volume is very small relative to the far-field volume. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a PDF file containing tables giving data for fitted emission rates and random air speeds for testing events with measured airflow rates for both near- and far-field zones and near-field zone only, and figures showing fitted random air speed varies with near-filed geometry when fitted with objective functions 1 and 2.]

Operational characteristics of residential and light-commercial air-conditioning systems in a hot and humid climate zone

Forced-air space-conditioning systems are ubiquitous in U.S. residential and light-commercial buildings, yet gaps exist in our knowledge of how they operate in real environments. This investigation strengthens the knowledge base of smaller air-conditioning systems by characterizing a variety of operational characteristics measured in 17 existing residential and light-commercial air-conditioning systems operating in the cooling mode in Austin, Texas. Some key findings include: measured airflow rates were outside of the range recommended by most manufacturers for almost every system; actual measured cooling capacities were less than two-thirds of rated cooling capacities on average; hourly fractional operation times increased approximately 6% for every °C increase in indoor–outdoor temperature difference; and lower mean indoor surrogate thermostat settings and higher supply duct leakage fractions were most associated with longer operation times. The operational characteristics and parameters detailed herein provide insight into the magnitude of the effects of HVAC systems on both energy consumption and indoor air quality (IAQ) in residential and light-commercial buildings.

Simple and efficient control of CHO cell cultures

Cell cultures must tightly be kept under control in order to guarantee a sufficiently small variability in the protein product quality. A simple and efficient technique for CHO-cell cultures is presented that allows keeping the viable cell count Xv and the specific growth rate μ of the cells on predefined trajectories. As Xv and μ cannot directly be measured online, they are controlled indirectly via the total mass of oxygen consumed. Online values of the latter can precisely be estimated from off gas analysis, i.e. from the O2 volume ratio measured in the vent line and air flow rate measurements. In glutamine-limited fed-batch cultivations, the glutamine feed rate can be manipulated in such a way that the viable cell density and the specific growth rate are kept on predefined profiles for nearly the entire cultivation time. The viability of the cells is not affected by the closed loop control actions. The technique was validated with CHO-cells cultured in a 2.5-L fully instrumented stirred tank bioreactor. It is shown that the controller is able to run the process exactly on predefined tracks with a high batch-to-batch reproducibility. By means of six fed-batch cultivations of CHO cells it was shown that a remarkable reproducibility of viable cell concentration could be achieved throughout 140h cultivation time.

A Gray-Box Based Virtual SCFM Meter in Rooftop Air-Conditioning Units

Knowledge of supply airflow rate (SCFM) measurement in packaged rooftop air-conditioning units (RTUs) is vital for improving energy management and indoor air quality and facilitating real-time automated control and fault detection and diagnosis. Despite the importance of SCFM measurement in RTUs, the conventional SCFM metering devices are very vulnerable. The credibility of SCFM measurement would be compromised dramatically after a long-term use in adverse duct work surroundings. Moreover, application of conventional SCFM meters in RTUs is very costly in regard to procurement, installation, and periodic maintenance. A cost-effective and accurate nonconventional first principles based SCFM meter in RTUs was proposed previously to virtually monitor SCFM measurement. In order to overcome the deficiencies of the first principles based virtual SCFM meter in model implementation and fault diagnostics, experiments with a wider combination and coverage are investigated in this study. It is found that a gray-box based virtual SCFM meter can be obtained with available system information (outside air damper status) and low-cost temperature measurements (direct measurement of a manufacturer-installed supply air temperature sensor (SATmfr,meas) and outside air temperature). Further experiment evaluations demonstrate that the gray-box based virtual SCFM meter could predict the true value of SCFM very accurately (the uncertainty is ±5.9%) with significantly enhanced applicability in model implementation and capability in fault diagnostics. Additionally, the gray-box based virtual SCFM meter also inherits good characteristics of the first principles based virtual SCFM meter, such as high cost-effectiveness, good robustness against variations in multivariable operating conditions, and applicability to similar RTUs. This innovative virtual meter could serve as a permanent monitoring tool to indicate real-time SCFM measurement and/or to automatically detect and diagnose an improper quantity of SCFM for RTUs.

Cycle-to-Cycle Flow Rate Measurement on Reciprocating HCCI Engine Using Fast-Response Laminar Flow Meter

In recent years, higher thermal efficiency and lower emissions are required on a reciprocating engine development and therefore cycle-to-cycle combustion control is necessary. Especially it is a key factor to control HCCI combustion engine. In HCCI engine, one of the most promising combustion methods to achieve high thermal efficiency, the ignition timing strongly depends on the mass-averaged temperature of charged gas and residual gas and very precise combustion phase control is required. Therefore it is important to detect the changes of cycle-to-cycle intake air flow rate, EGR gas flow rate and as well as residual gas in each cycle. The traditional laminar flow meter has too low responsivity to measure cycle-to-cycle flow rate. In this study, the fast-response laminar flow meter was developed in order to measure cycle-to-cycle dynamical flow rate. The availability of the fast-response laminar flow meter for cycle-to-cycle intake air flow rate measurement of the HCCI engine is shown in this paper.

Imaging based optofluidic air flow meter with polymer interferometers defined by soft lithography

We present an optofluidic chip with integrated polymer interferometers for measuring both the microfluidic air pressure and flow rate. The chip contains a microfluidic circuit and optical cavities on a polymer which was defined by soft lithography. The pressure can be read out by imaging the interference patterns of the cavities. The air flow rate was then calculated from the differential pressure across a microfluidic Venturi circuit. Air flow rate measurement in the range of 0-2mg/second was demonstrated. This device provides a simple and versatile way for in situ measuring the microscale air pressure and flow on chip.

Testing and thermal modeling of radiant panels systems as commissioning tool

This paper presents the results of a study performed to develop a thermal modeling of radiant panels systems to be used in situ, as diagnosis tool in commissioning processes to determine the main operating conditions of the system in cooling or heating mode. The model considers the radiant panels as a finned heat exchanger in dry regime. By using as inputs the ceiling and room dimensions, the radiant ceiling material properties and the measurements of air and water mass flow rates and temperatures, the model is able to calculate the radiant ceiling capacity, ceiling surface average temperature, water exhaust temperature and resultant temperature as a comfort indicator. The modeling proposed considers combined convection, perforation effect and a detailed radiative heat exchange method for radiant ceiling systems. An example of each system considered in this study is shown, illustrating the validation of the model. A sensitive analysis of the model is performed.

Measurement of Ventilation Airflow Rates of 39 Houses by Three Different Methods

This paper reports on the measurement results of ventilation rates in existing occupied houses in the northern region of Japan. A total of 61 measurements were made over a period of 4 years on 39 houses. Some houses were measured once a year over the four years investigation period. The ventilation systems equipped in some of the investigated houses were improved during the course of this investigation period. The effect of the improvement on ventilation airflow volume was reported. The ventilation rates were measured by three different methods, namely constant concentration method, measurement of airflow rate at inlets/outlets and passive homogeneous emission method. Through this investigation, the measurement results indicated that the ventilation rate was insufficient in many houses and some of the ventilation systems were not operated properly. In addition, the amount of air leakage in the house envelope and the amount of air change due to occupant behaviour were also determined.

Painting problem solver: The trick to measuring air flow rates and velocity in spray booths

Painting problem solver: The trick to measuring air flow rates and velocity in spray booths

Buoyancy Driven Natural Ventilation through Horizontal Openings

An experimental study of the phenomenon of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. The measurements were made for opening ratios L/D ranging from 0.027 to 4.455, where L and D are the length of the opening and the diameter of the opening, respectively. The basic nature of airflow through single-sided openings, including airflow rate, air velocity, temperature difference between the rooms and the dimensions of the horizontal openings, were measured. A bi-directional airflow rate was measured using the constant injection tracer gas technique. Smoke visualizations showed that the airflow patterns are highly transient and unstable, and that the airflow rate oscillates with time. Correlations between the Froude (Archimedes) number Fr (Ar) and the L/D ratio are presented. In some cases the measured airflow rates fit quite well with the Epstein’s formula but in other cases the measured data show clear deviations from the Epstein’s formula. Thus, revised formulas for natural ventilation are proposed.

Laboratory Testing of Downhole Gas Separators

Summary This paper provides insights on the design of downhole gas separators based on the laboratory study of various separator designs. A downhole gas separator, also known as a gas anchor, may be installed below the pump to separate free gas from the produced liquid. The free gas-produced downhole is usually separated through the casing-tubing annulus (the casing-tubing annulus acts as a natural gravity separator) while the liquid is produced through the tubing. However, inefficient gas anchor designs are widespread and an acceptable guide for their optimum design does not currently exist. Laboratory testing of downhole gas separators has been ongoing since January 2005 at The University of Texas at Austin Petroleum Production Engineering Facility (UTAPPEF) using an instrumented full-scale model of a wellbore and separator constructed with clear acrylic pipe to visualize the fluid mechanics of the separation process. An air and water mixture is injected through the well's perforations. The air and water flow rate measurements are used to measure and define a performance plot of each separator design. The separator designs tested differed in entry-port configuration, size of dip tube, and the relative position of the separator-fluid entry ports with respect to the well's perforations. Based on the results of the tests, a new separator design that includes the effect of centrifugal forces to separate the gas and liquid phases was developed. The results show that, for the conditions in the laboratory, 100% separation was achieved whenever the entry ports were located 1- to 2-feet (ft) below the bottom-most casing perforation thereby dispelling the predominant industry-held opinion that more distance is required between the separator-fluid entry ports and the bottom-most casing perforation. Similarly, laboratory results equally show that an optimum dip tube length of 5.5 ft is sufficient for the optimal separation of free gas from the produced liquid by the separator. This clearly runs contrary to the accepted industry practice, as many industry models employed for the estimation of dip-tube length were found to over-estimate the dip-tube length, and this subsequently results in the undesirable increased pressure drop across the separator. Lastly, the entry port geometry does not appear to have a significant impact on the separator performance as long as sufficient flow area is present. The efficiency of all gravity-driven separators was limited by the liquid velocity inside the separator annulus. When the liquid velocity inside the separator averaged approximately 6 in. per second or less, an almost-to-complete gas separation was achieved. On the other hand, the centrifugal separator had a liquid capacity 70% greater than any of the gravity-driven, static-downhole gas separators.

Online prediction of mass flow rate of solids in dilute phase pneumatic conveying systems using multivariate calibration

Pneumatic conveying systems are used extensively in a wide range of industrial applications. Mass flow rate is one of the most important parameters in this kind of system since it is fundamental for the control of this process and to improve its operation efficiency. A method to predict the mass flow rate of solids in dilute phase conveying is presented in this article. The method uses pressure and air flow rate measurements as variables to calibrate a Partial Least Squares (PLS) regression model, which can be used to predict the mass flow rate of solids from new pressure and air flow rate measurements. Pneumatic conveying tests were carried out with dextrose monohydrate in dilute phase conditions. Independent experimental data from the tests was used to validate the model. The model was successfully validated for a range of different conditions of blow tank pressure and air flow rate. Good agreement with the experimental data was obtained when predicting mass flow rate with all the sensors available in the pneumatic conveying test rig. When using only the air flow rate measurements and two pressure sensors the accuracy of prediction was not affected. The latest suggests the possibility of industrial application, since air flow meters and pressure transmitters are commonly used in industrial settings.

Real-Time Airflow Rate Measurements from Mechanically Ventilated Animal Buildings

This paper describes techniques used to determine airflow rate in multiple emission point applications typical of animal housing. An accurate measurement of building airflow rate is critical to accurate emission rate estimates. Animal housing facilities rely almost exclusively on ventilation to control inside climate at desired conditions. This strategy results in building airflow rates that range from about three fresh-air changes per hour in cold weather to more than 100 fresh-air changes per hour in hot weather. Airflow rate measurement techniques used in a comprehensive six-state study could be classified in three general categories: fan indication methods, fan rotational methods, and airspeed measurement methods. Each technique is discussed and implementation plans are noted. A detailed error analysis is included that estimated the uncertainty in airflow rate between ±5 and ±6.1% of reading at a building operating static pressure, air temperature, relative humidity, and barometric pressure of 20 Pa, 25 °C, 50%, and 97,700 Pa, respectively.

Influence of the air distribution elements in the pneumatic hammer with an elastic valve on the energy carrier rate

The authors describe a measurement complex and experimental measurement of air flow rates for some pneumatic hammers. Based on the experimental results, the air flow rate range has been determined.

Technical Note: Upstream vs. Downstream Placement of FANS Device to Determine Ventilation Fan Performance in Situ

Accurate ventilation rate (VR) data are essential to maximizing the quality of aerial emission measurements. The Fan Assessment Numeration System (FANS) has been widely used by U.S. researchers in measuring aerial emissions from mechanically ventilated livestock and poultry facilities. The FANS device is used to measure airflow rates of ventilation fans in situ, thereby developing fan performance curves under field conditions. The FANS device was originally intended to be placed upstream of the fan to be calibrated. However, certain field situations make it impractical to apply the FANS device as such. This study was conducted to assess use of the FANS device downstream of a ventilation fan, with the gaps between the FANS device and the discharge cone of the exhaust fan sealed using a non-permeable fabric. Nine exhaust fans (1.22 or 1.32 m diameter) in laying hen and turkey houses were tested with the FANS device placed upstream and downstream for a building static pressure range of 10 to 40 Pa. The results revealed that downstream placement of the FANS device yielded 0.6% 0.4% to 4.0% 0.9 % (mean SE) higher but not significantly different (P > 0.28) VR values as compared to upstream placement for the exhaust fans tested. This magnitude of discrepancy is considered acceptable for in situ measurement of fan performance.

Experimental investigations of a chimney-dependent solar crop dryer

An experimental investigation into the performance of a solar crop dryer with solar chimney and no air preheating is described. Tests were first performed on the cabinet dryer, using a normal chimney. The trials were repeated with a solar chimney. Still with the solar chimney, further trials were carried out with the roof of the drying chamber inclined further to form a tent dryer. The described tests include no-load tests for airflow rate measurements and drying tests, with cassava as the crop. Air velocities, temperatures, ambient relative humidity and the drop in crop moisture contents at different stages of the drying process are also presented. The effects of the various configurations described above on the drying process are deduced and discussed while comparing the experimental results with one another. In addition, the performance of the dryer in relation to other natural convection dryers is discussed. The results show that the solar chimney can increase the airflow rate of a direct-mode dryer especially when it is well designed with the appropriate angle of drying-chamber roof. However, the increase in flow rate only increases the drying rate when the relative humidity (RH) of the ambient air is below a certain mark (60% for cassava).

エアコン吹き出し風量の現場測定方法に関する検討

In order to calculate cooling or heating capacity of air conditioner, airflow rate and difference of enthalpy between supply and exhaust airflow are required. However, there is no adequate technique to measure airflow rate of air conditioner. Therefore, in this paper, 3 field measuring techniques for supply airflow of air-conditioner are validated in an experimental house.

A test bed for evaluation of energy efficiency of residential exhaust fans

A test bed has been designed and constructed for measurement of air flow rate, and Ventilation Efficiency Ratio (VER) of residential exhaust fans. The test bed can provide accurate measurement of air flow rate, fan energy efficiency, and other air flow parameters. The test bed described here will also be useful for improvement of design of residential exhaust fans constructed in the country. Presently, the test bed is being used in an on going project for compilation of standards for consumption and energy labeling of fans in Iran.