Gas Pressure Measurement Research Articles

Enhancement of the accuracy of the ( P–ω) method through the implementation of a nonlinear robust observer

The ( P–ω) method is a model-based approach developed for determining the instantaneous friction torque in internal combustion engines. This scheme requires measurements of the cylinder gas pressure, the engine load torque, the crankshaft angular displacement and its time derivatives. The effects of the higher order dynamics of the crank-slider mechanism on the measured angular motion of the crankshaft have caused the ( P–ω) method to yield erroneous results, especially, at high engine speeds. To alleviate this problem, a nonlinear sliding mode observer has been developed herein to accurately estimate the rigid and flexible motions of the piston-assembly/connecting-rod/crankshaft mechanism of a single cylinder engine. The observer has been designed to yield a robust performance in the presence of disturbances and modeling imprecision. The digital simulation results, generated under transient conditions representing a decrease in the engine speed, have illustrated the rapid convergence of the estimated state variables to the actual ones in the presence of both structured and unstructured uncertainties. Moreover, this study has proven that the use of the estimated rather than the measured angular displacement of the crankshaft and its time derivatives can significantly improve the accuracy of the ( P–ω) method in determining the instantaneous engine friction torque.

A novel, wireless, automated system for measuring fermentation gas production kinetics of feeds and its application to feed characterization

This study describes a novel automated method of measuring fermentation gas production kinetics of feeds using sensors that intermittently measure the pressure arising from fermentation of feeds within culture bottles, and relays them to a server using a wireless radio frequency (RF) signal. Measurements can be downloaded from the server at any location that has internet access and saved in ASCII or Excel format. Consequently, once the measurement frequency is set, and the incubation commences, there is no need for attention to the system until the end of the fermentation. In order to validate the system, fermentation parameters of three 1 mm ground feeds (i.e., corn grain, dehydrated citrus pulp (DCP), Pensacola bahiagrass hay ( Paspalum notatum) were determined using the RF sensors and compared to those determined with a digital manometer. A second experiment used both pressure measuring devices to determine fermentation parameters of 1 mm ground bermudagrass hay ( Cynodon dactylon) treated with an esterase enzyme at 0, 1 and 2 g/100 g DM. Feed samples were incubated in buffered rumen fluid in quadruplicate (Experiment 1) or triplicate (Experiment 2) in 250 ml gas tight culture bottles at 39 °C. Each culture bottle was connected to a pressure sensor with a three-way Luer lock that was secured into a hole in the culture bottle cap. Pressure sensors made hourly pressure measurements to 96 h. A digital manometer was used to take pressure readings from the culture bottles after 0, 2, 4, 6, 8, 12, 24, 48, 60, 72 and 96 h of incubation, and an exponential model was fitted to fermentation gas production data from the sensors and the digital manometer. Fermentation parameters were compared using a factorial (Experiment 1) or completely randomized design (Experiment 2). In both experiments, method of gas pressure measurement did not affect fermentation parameters, and there was no method×feed interaction. In Experiment 1, corn grain and DCP had bigger ( P<0.001) gas pool sizes, faster fermentation rates and a longer lag phases than hay. Compared to DCP, corn had a longer ( P<0.05) lag phase, similar fermentation rate and a bigger ( P<0.01) gas pool size. In Experiment 2, increasing esterase enzyme levels did not affect fermentation rate, but increased ( P<0.05) the lag phase and tended ( P=0.063) to increase gas pool size. There was a good relationship between RF sensor and manometer-based estimates of gas pool size ( r 2 = 92), fermentation rate ( r 2 = 83), and lag phase ( r 2 = 60). Total measured gas volume correlated to in vitro digestibility ( r 2 = 0.60) and to stoichiometrically predicted total gas volumes ( r 2 = 0.74). This study demonstrates the potential of this RF sensor technique to differentiate fermentation kinetics among feeds.

Combustion Reaction During Mechanical Alloying Synthesis of Ti3SiC2Ceramics from 3Ti/Si/2C Powder Mixture

Mechanical alloying (MA) synthesis of Ti3SiC2from a stoichiometric elemental powder mixture of Ti, Si, and C was conducted by using a planetary mill with a specially designed MA jar, which enables the real‐time measurement of temperature and gas pressure during the MA process. Sudden gas pressure and temperature rises were detected when the mixed powders were mechanically alloyed for a certain period, and consequently a large amount of Ti3SiC2particles was synthesized. Using the Ti–Si–C system as an example, the present study confirmed the combustion reaction triggered by the ball‐milling process for the first time.

Passive landfill gas emission – Influence of atmospheric pressure and implications for the operation of methane-oxidising biofilters

A passively vented landfill site in Northern Germany was monitored for gas emission dynamics through high resolution measurements of landfill gas pressure, flow rate and composition as well as atmospheric pressure and temperature. Landfill gas emission could be directly related to atmospheric pressure changes on all scales as induced by the autooscillation of air, diurnal variations and the passage of pressure highs and lows. Gas flux reversed every 20 h on average, with 50% of emission phases lasting only 10 h or less. During gas emission phases, methane loads fed to a connected methane oxidising biofiltration unit varied between near zero and 247 g CH 4 h −1 m −3 filter material. Emission dynamics not only influenced the amount of methane fed to the biofilter but also the establishment of gas composition profiles within the biofilter, thus being of high relevance for biofilter operation. The duration of the gas emission phase emerged as most significant variable for the distribution of landfill gas components within the biofilter.

Optimum design of the variable-volume gas pycnometer for determining the volume of solid particles

Little is known about optimum design of gas pycnometers, so that they can determine the volume of solid particles with the greatest accuracy. The purpose of this study was to investigate the optimum design of the ‘variable-volume’ gas pycnometer, because its ease of handling makes it a good candidate for widespread use. The law of propagation of uncertainty was used to derive a theoretical formula that relates the pycnometer's accuracy to the main sources of random uncertainty (gas-pressure measurements, pycnometer temperature, sample-chamber and piston-chamber volumes). The consequences of this formula in terms of optimizing the geometry and working conditions of the pycnometer are discussed. It was found that some gas pycnometers described in the literature may not have been used under the best conditions. As for the ‘constant-volume’ gas pycnometer, which was considered in a previous study, it seems possible to use commercially available components for constructing a variable-volume gas pycnometer that can determine the volume of solid particles with a relative standard uncertainty smaller than 0.25%. However, an accurately calibrated pressure transducer is required for the variable-volume gas pycnometer (instead, the only requirement for the constant-volume gas pycnometer is that the transducer's response varies linearly with pressure).

Characterization of local preform defects in resin transfer molding by the gas flow method and statistical analysis

An in situ gas flow method has been developed to determine the quality of fibrous preforms in resin transfer molding (RTM) prior to injection. Defects resulting from preform misplacement, accidental inclusions, etc., are quantified. Unintentional permeability variations can result in defective part production and excessive part scrapping. Pressure profiles generated during steady-state gas flow are affected by such variations. To determine defect location and severity, a multivariate statistical approach is applied to compare measured quantities from a test preform with quantities obtained from known groups. The tested preform is then classified into a defect free group or any one of several groups associated with specific types of defects. A specially designed mold, with multiple ports for gas injection and pressure measurement, was used to test various cases with and without defects. Application of this process has been accomplished on an unmodified industrial mold used to fabricate composite curved I-Beam stiffeners.

Synthesis temperature optimization of HgRe 1212 using an changed TBA

This work presents an improvement done in the thermobaric analysis (TBA) apparatus that allows the measurement of the total gas pressure in systems at constant volume while the sample temperature is varied. Two new thermocouples were included in order to observe the temperature variations between the sample and the reference, simulating a differential thermal system (DTA). In this way, the TBA, which already allowed to observe the temperatures at which the solid-gas reactions occur, now also permits the study of solid-solid reactions. This new technique was applied to optimize the synthesis of the ceramic superconductor Hg 0.82Re 0.18Ba 2CaCu 2O 6+ δ (HgRe1212). Using the temperatures determined by the differential thermal system, a new sample was synthesized at 781 °C during 48 h, which exhibited T c=120 K and presented a better magnetic shielding compared to the other synthesized samples.

Optimum design of the constant-volume gas pycnometer for determining the volume ofsolid particles

Gas pycnometry is based on Boyle–Mariotte’s law of volume–pressure relationships. Thismethod has been widely used to determine the volume (and thus the density) of rockfragments, soluble powders, light objects and even living beings. Surprisingly, little isknown about the optimum design of gas pycnometers. The purpose of this study was toinvestigate the optimum design of a gas pycnometer, so that it can determine the volume ofsolid particles with the greatest accuracy. The ‘constant-volume’ gas pycnometer wasconsidered because of its widespread use. The law of propagation of uncertainty was usedto derive a theoretical formula that relates the pycnometer’s accuracy to the main sourcesof random error (gas-pressure measurements, pycnometer temperature and sample-chambervolume). The consequences of this formula in terms of optimizing the geometry andworking conditions of the pycnometer are discussed. It was found that some gaspycnometers described in the literature may have not been used under the best conditions.Guidelines are given to design a gas pycnometer that can theoretically determine thevolume of solid particles with a relative standard uncertainty smaller than 0.2%.

Gas Pressure Measurements Inside an Aerated Hopper

A new technique, based on the determination of local gas pressure profiles, is proposed to characterize the flow properties of fine aerated powders. Gas pressure measurements were carried out in an aerated hopper discharging an aeratable powder (FCC) and a cohesive powder (corn starch). Solids discharge rates, gas pressure local time series and gas pressure profiles were determined. Experimental discharge rates confirm that the use of aeration promotes the motion of these powders. Pressure profiles and time series are analysed in order to discriminate between different mechanisms that were suggested for these kinds of powders and to elucidate the role of cohesive forces in the flow of fine powders. A classification of the regimes observed as a function of aeration and powder cohesion has been attempted. Pressure profiles were used to evaluate gas flow rates within the hopper during the discharge and to verify literature correlations on solids discharge rates. Some considerations on the relative significance of the gas rates during discharge allowed to obtain a simplified version of the De Jong and Hoelen (De Jong, J.A.H. and Hoelen, Q.E.J.J.M., 1975, Powder Technol ., 12: 201–208) equation which can be used in a predictive way with reasonable approximation.

Resonance gas oscillations in closed tubes: Numerical study and experiments

Periodic gas oscillations in closed tubes are investigated experimentally and numerically. At resonance, these oscillations are accompanied by shock waves traveling back and forth along the tube. Results of gas temperature and pressure measurements are reported. It is found that the gas temperature changes substantially along the tube. A two-dimensional numerical model of turbulent gas oscillations is developed and verified by a comparison with experiments. It is found that the experimental data of temperature and pressure inside the resonance tube are well correlated by the numerical model. Using the numerical model, turbulence and acoustic streaming at resonance are investigated. It is shown that the direction of gas streaming at resonance is opposite to that in nonresonant oscillations. A parametric investigation of resonant flow is performed in terms of the tube parameter ε, acoustic Reynolds number Rea and dimensionless tube length Λ. In particular, it is found that the normalized pressure amplitude, as well as other flow characteristics, are functions of a single parameter E=Rea1/3/Λ. Useful correlations for flow characteristics are proposed in terms of tube dimensionless parameters.

Gas Flow Method for Detecting Local Preform Defects by Inverse Estimation of Space-Varying Permeability

A method using gas flow is proposed for testing the quality of fibrous preforms in the resin transfer molding process. The method is based on the idea that preform defects cause variation in permeability and deviation from Darcy's law. This paper presents a gradient-based inverse method that estimate space-varying permeability by examining the consistency between computed and measured pressures at various locations in the mold during steady-state gas flow through the enclosed preform. Such consistency is achieved by the conjugate gradient method. The computed pressures are obtained by the control volume finite element method (CVFEM). The proposed method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement, and testing for various cases with and without defects.

Absolute cross sections for single and double charge-exchange in Feq+impacting on He

We report measured absolute single and double charge-exchange cross sections (CSs) for Feq+ions with He at the ion impact energy of 7.0 × q keV forq = 5–13.The range of ion velocities is 350 km s−1 forq = 5, to 560 km s−1for q = 13,comparable to typical solar wind velocities. A retarding-field method is used forcharge-state analysis of the ion beam after traversing the stationary target gascell. The CSs are determined from absolute measurements of the ion currents andHe target gas pressure.

Detection of Local Preform Defects by Gas Flow Method and Statistical Analysis

A method for testing the quality of fibrous preforms using gas flow is proposed. The method detects defects caused while placing the fibre preform in the mould by checking the deviations of measured pressures from the reference expected value at various locations in the mould during steady state gas flow through the enclosed preform. A statistical method is employed to classify the test preform into a normal group or any one of several groups associated with specific types of defects. To implement this method experimentally, a specially designed mould with multiple ports for gas injection and pressure measurement was used. Results obtained for various cases with and without preform defects were compared and analysed.

Influence of fibrolytic enzymes on the hydrolysis and fermentation of pure cellulose and xylan by mixed ruminal microorganisms in vitro.

A series of in vitro studies was conducted to determine the effects of adding a commercial enzyme product on the hydrolysis and fermentation of cellulose, xylan, and a mixture (1:1 wt/wt) of both. The enzyme product (Liquicell 2500, Specialty Enzymes and Biochemicals, Fresno, CA) was derived from Trichoderma reesei and contained mainly xylanase and cellulase activities. Addition of enzyme (0.5, 2.55 and 5.1 microL/g of DM) in the absence of ruminal fluid increased (P < 0.001) the release of reducing sugars from xylan and the mixture after 20 h of incubation at 20 degrees C. Incubations with ruminal fluid showed that enzyme (0.5 and 2.55 microL/g of DM) increased (P < 0.05) the initial (up to 6 h) xylanase, endoglucanase, and beta-D-glucosidase activities in the liquid fraction by an average of 85%. Xylanase and endoglucanase activities in the solid fraction also were increased (P < 0.05) by enzyme addition, indicating an increase in fibrolytic activity due to ruminal microbes. Gas production over 96 h of incubation was determined using a gas pressure measurement technique. Incremental levels of enzyme increased (P < 0.05) the rate of gas production of all substrates, suggesting that fermentation of cellulose and xylan was enzyme-limited. However, adding the enzyme at levels higher than 2.55 microL/g of DM failed to further increase the rate of gas production, indicating that the maximal level of stimulation was already achieved at lower enzyme concentrations. It was concluded that enzymes enhanced the fermentation of cellulose and xylan by a combination of pre- and postincubation effects (i.e., an increase in the release of reducing sugars during the pretreatment phase and an increase in the hydrolytic activity of the liquid and solid fractions of the ruminal fluid), which was reflected in a higher rate of fermentation.

Determination of in‐plane permeability of fiber preforms by the gas flow method using pressure measurements

AbstractA method is described for measuring the in‐plane permeability of orthotropic fibrous preforms using gas flow. The method is based on an optimization process between computed and measured pressures at various locations in the mold during steady state gas flow through the enclosed preform. The computed pressure is obtained by the control volume finite element method (CVFEM). This method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement and it was shown that it can be implemented easily and yields consistent and reliable results.

The magnetic suspension balance in high pressure measurements of pure gases

In the present work the supercritical fluids argon, methane, nitrogen, carbon dioxide, ethane, ethylene and propane were picked out as examples, and the results of analysis concerning the adsorption of these fluids at activated carbon Norit R1 (Norit Company, Germany) and SCS-3 (ISPE, Kiev) at different temperatures up to a pressure of 50 MPa are presented and discussed in this paper. The principle of working of the measuring device is described in this context as well. A three-parameter isothermal equation is used to represent the adsorption equilibrium. The isothermal equation is based on a physical model concept which has already been used for the modelling of adsorption processes with a pressure up to 15 MPa.

Influence of Several Process Parameters on Sourdough Fermentation

AbstractThe influence of several process parameters (starter, sourdough refreshment, dough yield, ingredients) on sourdough fermentation was investigated. This was realised by online measurement of both pH and gas pressure in sourdough in a closed air‐tight reactor. Firstly, the effect of sourdough refreshment on both gas pressure and acidification was evaluated and shown to be accompanied by an increase in both acidification and gas pressure evolution rates. Secondly, two commercial starters (BRS and BIO) differing in their microflora were compared as regards to their gassing power and acidifying properties. BRS exhibited faster acidification but less gassing power. Moreover, the variation of sourdough yield for BRS starter induced a different evolution of the acidification profile. Sourdough fermentation varied also depending on the presence of NaCl. 2% of NaCl induced a lower gassing power in sourdough by inhibiting the yeasts.

DETERMINATION OF PERMEABILITY OF FIBROUS MEDIUM CONSIDERING INERTIAL EFFECTS

A method is described for measuring the Reynolds number dependent permeability in order to consider the inertial effects of the flow through porous media. A nonlinear correction term is introduced and the corresponding coefficients are determined by inverse analysis. The method is based on an optimization process between computed and measured pressures at various locations in the mold and flow rates at the gate during steady state gas flow through the enclosed fiber preform. The computed pressure is obtained by the control volume finite element method (CVFEM). The proposed method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement

Simple resonating microstructures for gas pressure measurement

The resonance characteristics of an oscillating microcantilever are modified due to the changing damping effects as the ambient air pressure varies, and the device is used as an absolute pressure sensor. Three variations of the microcantilever device were designed, fabricated, and tested for changes in resonant frequency, quality factor, amplitude of oscillation, and actuating current required to maintain the amplitude of oscillation constant as the ambient pressure was varied from 15 to 1450 Torr. The device has been analyzed and a relationship has been derived to aid in the prediction of device behavior. Values for precision comparable to commercial pressure sensors are also presented for each method of detection.

In situ determination of oxygen and nitrogen dynamics in the upper ocean

Total gas pressure, oxygen, temperature and salinity were measured at 50 m on a mooring at the Hawaii Ocean Time series (HOT) station from January through September of 1997 and 1998 using a gas tension device (GTD) and a conductivity temperature depth and oxygen (CTD-O 2) sensor (GTD–CTD-O 2 instrument package). Our goal was to evaluate the precision and accuracy of the in situ total gas and oxygen measurements and to assess their utility for remotely determining net biological oxygen production in the euphotic zone. By calibrating the oxygen sensor approximately every month during periodic visits to the mooring it was possible to remotely measure the time history of the partial pressures of nitrogen and oxygen to within ±0.5% accuracy as assessed by independent determination of nitrogen concentration. Oxygen changed at 50 m by 2–4% in a series of episodes with durations of 1–3 months, indicating the discontinuous nature of net O 2 production and the probable decoupling of oxygen production and respiration in the euphotic zone. The GTD and oxygen measurements together can be used to distinguish the effects of physical processes and net biological oxygen production on the oxygen concentrations. The largest uncertainty in the coupled O 2 and total gas pressure measurements is the drift of the oxygen sensor, making frequent calibration presently a necessity. With more complete vertical coverage in the upper ocean it should be possible to use this approach to determine depth-integrated net oxygen production in the euphotic zone and upper thermocline respiration.