Measurement Of Propagation Speed Research Articles

Combustion characteristics of skeleton polymer reinforced paraffin-wax fuel grain for applications in hybrid rocket motors

Paraffin-based fuel is a promising and low-cost alternative for hybrid rocket motor applications due to its advantage of high regression rate. Meanwhile, paraffin fuel alone has poor mechanical strength that cannot meet the requirements in practical applications. Embedding skeleton polymer into paraffin-wax fuel can effectively enhance the mechanical properties and keep the advantage of high regression rate. In this paper, the mechanical and combustion characteristics of different polymer materials were comprehensively evaluated by using SEM, TG, TDG, mechanical test and flame propagation speed measurement experiments. A type of polymer reinforced paraffin-wax fuel grain has been fabricated and tested using a newly-designed optically accessible solid fuel tubular combustor. Combustion efficiency of the polymer reinforced paraffin fuel grain was further measured using a lab-scaled hybrid rocket motor. As a result, ABS is a better candidate that can be used in polymer reinforced paraffin fuel grain in terms of favorable combustion and mechanical properties. The flame propagation speed of polymers printed by SLS technique are much higher than those printed by SLA technique due to its rougher surface. Moreover, Paraffin liquid droplets and columns were clearly observed during the combustion process of the new proposed polymer reinforced paraffin fuel due to the entrainment and shearing of oxidizer flow, leading to higher regression rate and better mixing efficiency, which turns in higher combustion efficiency in fuel rich conditions compared with literature results.

Reaction Monitoring by Ultrasounds in a Pseudohomogeneous Medium: Triglyceride Ethanolysis for Biodiesel Production

The sound propagation speed measurement us is used for monitoring triglyceride ethanolysis in a broad range of reaction conditions (mainly, temperature: 23–50 °C; ethanol/oil: from 6 to 24 mol/mol). Experimentally, us slightly increased with the reaction time in all cases as a result of the contribution of its dynamic mixture components. Nomoto’s expression for homogeneous mixtures offered suitable us estimation but with values notably higher than the experimental ones due to the resistance to sound propagation offered by the ethanol/oil interphase (non-homogeneous medium). Our strategy was based on both the comparison of the experimental us values and the theoretical ones correlated by means of triglyceride conversion and on the estimation of the sound speed of oil/ethanol that could emulate the resistance offered by the interphase. The evolution of the reactions was predicted quite well for all the experiments carried out with very different reaction rates. Nevertheless, at the beginning of the reaction, the estimated conversion (outside of industrial interests) showed important deviations. The presence of the intermediate reaction products, diglycerides, and monoglycerides could be responsible for those deviations.

Experimental characterization of ozone-enhanced n-decane cool flames and numerical investigation of equivalence ratio dependence

Low temperature combustion behavior is critical to understand for advanced combustor design and safety, but cool flames are challenging to study under chemistry-transport coupled conditions because of the generally transient nature of these flames. A series of studies have utilized a laminar flat flame Hencken burner platform and ozone enhancement at sub-atmospheric pressures to stabilize dimethyl ether, propane and heptane cool flames and measure flame characteristics such as propagation speed, flame temperature and product species. This work builds upon those prior studies to investigate n-decane, first through experimental characterization of ozone-enhanced n-decane cool flames, including measurement of propagation speeds and flame temperatures and imaging of formaldehyde planar laser induced fluorescence (CH2O PLIF) over a range of equivalence ratios and, second, through comparison of experimental results with one-dimensional cool flame simulations. Experimental findings showed moderate equivalence ratio dependence of cool flame propagation speeds and temperatures at lean equivalence ratios, and no significant equivalence ratio dependence for richer mixtures. Experimental CH2O profiles showed equivalence ratio dependence and no downstream consumption, as is characteristic of cool flames. Simulated n-decane cool flames showed significant dependence of propagation speeds and temperatures on equivalence ratio, as well as downstream consumption of CH2O, at the experimental conditions. Experimental and numerical discrepancies were first investigated by examining the influence of different ozone enhancement strategies on equivalence ratio dependence and the results indicate a minimal influence of ozone enhancement strategy for n-decane, while also providing insights to into equivalence ratio dependencies observed in previous ozone-enhanced and ozoneless cool flame studies. The effect of ozone concentration on simulated n-decane cool flames was then investigated, revealing a strong influence of ozone enhancement on equivalence ratio dependence. Simulated propagation speed and temperature dependence on equivalence ratio were shown to develop with increase in ozone enhancement levels. A kinetics analysis revealed enhancement of low temperature peroxy chemistry and other cool flame heat releasing reactions with ozone addition, increasing simulated flame temperatures and promoting the onset of early intermediate temperature chemistry (ITC), inducing equivalence ratio dependence which was not seen in experimental results. Finally, insights from this analysis were used to investigate reconciliation of differences in experimental and simulated cool flame temperatures and identify potential kinetics model discrepancies from experimental findings.

Modelling Lamb waves in the septal wall of the heart

Shear Wave Elastography (SWE) has been proposed to investigate cardiac health by non-invasively monitoring tissue stiffness. Previous work has shown that the plate-like geometry of the Interventricular Septum (IVS) may result in a dispersion similar to Lamb waves, complicating the link between shear wave speed and cardiac stiffness. However, the IVS is not a simple plate, e.g., its thickness tapers across its length. We have used 2-D Finite Element simulations to investigate the effects of tapering on Lamb waves. The model consists of an elastic slab immersed in water, with a thickness decreasing smoothly in space from 9 to 3 mm. Pulses with low (0–80 Hz) and high (0–700 Hz) frequency contents were used to excite natural and acoustic radiation force induced waves. The results show that, at the lower frequencies, propagation speed can decrease during propagation by ~20% due to the thickness reduction, producing a nonlinear space-time relation from which multiple speed values can be extracted. At higher frequencies, the main observation is a dependence of the dispersion behavior on the shape of the tapering (e.g., linear, concave, or convex). These results suggest that septal geometry is likely to play a role in deriving cardiac stiffness from propagation speed measurements.

Reproducibility of Natural Shear Wave Elastography Measurements

For the quantification of myocardial function, myocardial stiffness can potentially be measured non-invasively using shear wave elastography. Clinical diagnosis requires high precision. In 10 healthy volunteers, we studied the reproducibility of the measurement of propagation speeds of shear waves induced by aortic and mitral valve closure (AVC, MVC). Inter-scan was slightly higher but in similar ranges as intra-scan variability (AVC: 0.67 m/s (interquartile range [IQR]: 0.40–0.86 m/s) versus 0.38 m/s (IQR: 0.26–0.68 m/s), MVC: 0.61 m/s (IQR: 0.26–0.94 m/s) versus 0.26 m/s (IQR: 0.15–0.46 m/s)). For AVC, the propagation speeds obtained on different day were not statistically different (p = 0.13). We observed different propagation speeds between 2 systems (AVC: 3.23–4.25 m/s [Zonare ZS3] versus 1.82–4.76 m/s [Philips iE33]), p = 0.04). No statistical difference was observed between observers (AVC: p = 0.35). Our results suggest that measurement inaccuracies dominate the variabilities measured among healthy volunteers. Therefore, measurement precision can be improved by averaging over multiple heartbeats.

Selectively-deposited energetic materials: A feasibility study of the piezoelectric inkjet printing of nanothermites

This work investigated the utility of three piezoelectric inkjet printers as energetic material deposition systems, focusing on the ability of each system to achieve the seamless integration of energetic material into small-scale electronic devices. Aluminum copper (II) oxide nanothermite was deposited using the three deposition systems. The printers were evaluated based on their robustness to energetic ink solids loading, drop formation reliability, drop quality degradation over time, and the energetic performance of the deposited material. These metrics correlate to the feasibility of a deposition system to successfully achieve high sample throughput while maintaining the energetic performance of the printed material. After initial system testing, the PipeJet P9 500 μm pipe was used to demonstrate the successful deposition of nanothermite in varying geometric patterns with micrometer precision. From these samples, preliminary propagation speed measurements were obtained, which showed a correlation between the printed line widths and burning rates.

Use of zinc stearate to produce highly-hydrophobic adobe materials with extended durability to water and acid-rain

This paper presents a novel solution to increase the durability of adobe materials using zinc stearate at doses ranging from 0.25% to 2.00% w/w. Shrinkage, apparent density and ultrasonic propagation speed measurements were performed on the cured samples. In addition, water absorption and durability features were determined by capillary tests, Karsten tube measurements, immersion in water, hydrochloric acid (5% w/w) and sulphuric acid (5% w/w) solutions. The durability study was complemented by rain erosion and acid-rain erosion tests. The capillary water absorption was comparable to that of hydrophobic cement renders and the acid-rain erosion was negligible in samples containing 1.00–2.00% w/w zinc stearate. Besides, SEM examination confirmed the protective action of zinc stearate in front of acid-rain. To conclude, zinc stearate was found to be was an excellent choice to increase the durability of adobe materials.

Non-contact measurement of propagation speed in tissue-mimicking phantom using pass-through airborne ultrasound

The elastic properties of human tissues can be quantitatively evaluated from the ultrasonic propagation speed in tissues. To effectively propagate ultrasound in human tissues, ultrasonic transducers are typically brought into contact with tissue surfaces. In this study, the non-contact evaluation of human tissues using pass-through airborne ultrasound has been proposed. When airborne ultrasound propagates and passes through tissues, the pass-through wave is extremely attenuated. To detect the attenuated pass-through wave in the received signal, the signal-to-noise ratio (SNR) of the received signal is improved by pulse compression using a higher-order M-sequence in the proposed method. In this paper, the estimation of ultrasonic propagation speeds in tissue-mimicking phantoms is described. The urethane-rubber phantom and solutions of ethanol in water are used as the phantoms. The time of flight (TOF) of the pass-through wave in the phantom is determined from the wave front. The propagation speed in the phantom is estimated using the determined TOF. Propagation speeds in the urethane-rubber phantom and ethanol solutions can be estimated within errors of 3 and 2% in experiments.

Measurements of propagation speeds and flame instabilities in biomass derived gas–air premixed flames

Three biomass derived gases (BDGs, named GG-H, GG-L and GG-V), which are derived from industry facilities and can be useful for reducing CO 2 and the application to combustors, are studied and examined for some basic flame characteristics such as unstretched laminar burning velocity, Markstein length, and cell formation over the entire flame surface. Experiments were conducted in a constant volume combustion chamber using a schlieren system. A better agreement between the measured and predicted unstretched laminar burning velocities is obtained using a suggested reaction mechanism modified from the GRI-Mech 3.0 mechanism. Additionally, cell formations on flame surfaces of the three mixtures were also analyzed and compared using high-speed schlieren images. It is shown that the GG-H–air flames and the GG-L–air flames have similar flame wrinkled surfaces, while the GG-V–air flames shows a stronger cellularity behavior. The effects of each fuel component in mixtures to cellularity are also evaluated by varying the concentration of each fuel in the reactant mixtures. The cellular instability is promoted (diminished) with hydrogen enrichment (methane addition); meanwhile the similar behavior is obtained for carbon monoxide addition.

Experimental investigation of dynamics of premixed acetylene–air flames in a micro-combustor

This paper describes a detailed experimental study performed to investigate the flame propagation behaviour of premixed flames in micro-channels. A novel, modular, stackable micro-combustor was developed for this purpose. For a chosen planar channel geometry, the flow condition and the mixture equivalence ratio of premixed acetylene–air were varied to investigate various modes of operation. Three different modes of operation were observed; they were (i) stable periodic operation – consisting of ignition, flame propagation, flame extinction, and re-ignition, (ii) a-periodic operation, and (iii) anchored flame condition. The present work also aims to provide quantitative information on the dynamics of premixed acetylene–air flames propagating inside micro-channels. A novel measurement approach based on OH * chemiluminescence measurements employing a single photomultiplier unit was developed for this purpose. The data recorded were post processed using an in-house developed MATLAB code to evaluate the mean flame propagation speed measured between three different spatial locations along the length of the micro-channel. The results from the flame propagation speed measurements performed during ‘periodic’ mode of operation indicated that the flame travelled at higher propagation speed in the mid-length region of the channel compared to that at the initial entry point, suggesting flame acceleration. This flame acceleration could be attributed to a situation where the flame experienced different local equivalence ratio conditions at different upstream locations. The results suggest that after completion of a cycle of operation consisting of ignition, flame propagation and flame extinction, the fresh mixture that filled the channel was diluted with the exhaust gas from the previous cycle. This pocket of diluted mixture convected downstream with time, thus enabling the spatial variation in local equivalence ratio along the micro-channel.

On the statistical detection of propagating waves in polar coronal holes

Context. Waves are important to the study of dynamical processes in coronal holes and the acceleration of the fast solar wind. A spectral time series was taken with the SUMER spectrometer on-board SoHO on 20 October 1996. The observations were obtained in the N iv 765 A transition region line and the Ne viii 770 A line of the low corona. Aims. We detect the presence of waves and study their characteristic properties in terms of their propagation speeds and direction. Previous statistical studies, undertaken with data from the CDS spectrometer, report the presence of waves in these regions.We extend this analysis using SUMER observations. Methods. Using Fourier techniques, we measured the phase delays between intensity oscillations, as well as between velocity oscillations, in our two lines over the full range of available frequencies. From this, we were able to measure the travel time of the propagating oscillations, hence the propagation speeds of the waves that produce the oscillations. Results. We detect the long period oscillations in polar coronal holes on the disc. For network bright locations within coronal holes, our results indicate the presence of compressional waves with a dominant period of ≈25 min. However, we also find power at many other different frequencies, so we are able to study oscillations over a full range of frequencies. We find evidence of propagating waves with a fixed time delay in the coronal hole.We find, moreover, that there is a difference in the nature of the wave propagation in the bright (“network”), as opposed to the dark (“internetwork”) regions, with the latter sometimes showing evidence of downwardly propagating waves that are not seen in the former. From a measurement of propagation speeds, we find that all measured waves are subsonic in nature. Conclusions. Waves with different characteristics are found to be present at different locations in the observed coronal hole. The measured propagation speeds are subsonic, indicating that the majority of them are slow magneto-acoustic in nature. These waves, measured in the lower atmosphere, could accelerate farther at higher altitudes and may be important for the acceleration of the fast solar wind.

Measurement of propagation speeds in adiabatic cellular premixed flames of CH 4 + O 2 + CO 2

Experimental measurements of the propagation speed of adiabatic flames of methane + oxygen + carbon dioxide are presented. The oxygen content O 2/(O 2 + CO 2) in the artificial air was 31.55% and 35%. Non-stretched flames were stabilized on a perforated plate burner at atmospheric pressure. A heat flux method was used to determine propagation speeds under conditions when the net heat loss of the flame is zero. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Measurements in cellular flames are presented and compared with those for laminar flat flames. Cellularity disappeared when the flames became only slightly sub-adiabatic. Visual and photographic observations of the flames were performed to quantify their cellular structure. Increasing the oxygen content in the artificial air and increasing the temperature of the burner plate led to increase of the number of cells observed.

Measurement of propagation speeds in adiabatic flat and cellular premixed flames of C2H6+O2+CO2

Adiabatic burning velocities of premixed flat flames and propagation speeds of adiabatic cellular flames of mixtures of ethane+oxygen+carbon dioxide are reported. The oxygen content O2/(O2+CO2) in the artificial air was varied from 26 to 35%. Nonstretched flames were stabilized on a perforated plate burner at 1 atm. A heat flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. Measurements in cellular flames are presented and compared with those for laminar flat flames and also with qualitative predictions of a theoretical model. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Cellularity disappears when the flames become only slightly subadiabatic.

Oscillations above sunspots: Evidence for propagating waves?

We present results of an analysis of time series data observed in sunspot umbral regions. The data were obtained in the context of the SOHO Joint Observing Program (JOP) 97 in September 2000. This JOP included the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imaging (MDI) instrument, both part of SOHO, the TRACE satellite and various ground based observatories. The data was analysed by using both Fourier and wavelet time series analysis techniques. We find that oscillations are present in the umbra at all temperatures investigated, from the temperature minimum as measured by TRACE 1700 A up to the upper corona as measured by CDS $\ion{Fe}{xvi}$ 335 A ($\log T=6.4$ K). Oscillations are found to be present with frequencies in the range of 5.4 mHz (185 s) to 8.9 mHz (112 s). Using the techniques of cross-spectral analysis time delays were found between low and high temperature emission suggesting the possibility of both upward and downward wave propagation. It is found that there is typically a good correlation between the oscillations measured at the different emission temperatures, once the time delays are taken into account. We find umbral oscillations both inside and outside of sunspot plume locations which indicates that umbral oscillations can be present irrespective of the presence of these sunspot plumes. We find that a number of oscillation frequencies can exist co-spatially and simultaneously i.e. for one pixel location three different frequencies at 5.40, 7.65 and 8.85 mHz were measured. We investigate the variation of the relative amplitudes of oscillation with temperature and find that there is a tendency for the amplitudes to reach a maximum at the temperature of $\ion{O}{iii}$ (and less typically $\ion{O}{v}$ and $\ion{Mg}{ix}$) and then to decrease to reach a minimum at the temperature of $\ion{Mg}{x}$ ($\log T=6.0$ K), before increasing again at the temperature of $\ion{Fe}{xvi}$. We discuss a number of possible theoretical scenarios that might explain these results. From a measurement of propagation speeds we suggest that the oscillations we observe are due to slow magnetoacoustic waves propagating up along the magnetic field lines.

Photographic measurements of propagation speeds of the conducting zone in polyaniline films during electrochemical switching

In order to observe the propagation of a conducting zone of a polyaniline film in response to anodic switching, propagation perpendicular to the film surface was simulated by propagation along the film by mounting the film on an insulated plate. A polyaniline film electrochemically deposited on an indium tin oxide (ITO) electrode was reinforced by casting polymethylmethacrylate solution on the film. It was peeled off the ITO, chemically reduced and then potentiostatically oxidized at one end in 1 mol dm −3 H 2SO 4 solution. Dynamic growth of the conducting zone was observed through an optical microscope. A well-defined boundary between the conducting zone and the insulating zone was seen. The contrast of the boundary did not vary with the electrolysis time, the growth length or the applied potential. The growth rate decreased slightly with the electrolysis time as a result of IR drop across the film. A differential equation for growth rate involving the effect of the IR drop was presented and solved to give more accurate values of the rate. The logarithmic growth ratio exhibited a linear relation with the applied potential, indicating a charge-transfer rate of the Tafel type. The anodic transfer coefficient was 0.2 and the rate constant was 5 × 10 −5 m s −1. The propagation on a molecular scale was discussed on the basis of the experimental results.

超音波伝ぱ速度に基づく弾性率の特異性

The comparison of the modulus Ep evaluated from the ultrasonic propagation speed measurements with the static modulus Es from the tensile tests and the examination of change in Ep with tensile deformation for polyethylene terephthalate (PET) fibers and glass beads filled polystyrene composites revealed the following peculiarities in Ep.(1) Ep was not linearly dependent upon the crystallinity but dependent upon the cube root of crystallinity, while Es was directly dependent upon the crystallinity. In the case of PET fibers, the moduli, Ep and Es, were satisfactorily described by a parallel two-phase structure model with crystalline and amorphous regions.(2) The two-phase structure model also enabled to be applied to composite materials. Ep of the glass beads filled polystyrene composites was not linearly dependent upon the volume fraction of fillers but was dependent upon the cube root of volume fraction of fillers. In the case of glass beads filled polystyrene composites in which the adhesion between fillers and matrix was improved by silan-treating, the modulus Es was described by the series model. In the case of untreated composites, Es was constant.(3) In the case of low oriented PET fiber, Ep decreased by drawing in spite of an increase in birefringence. It is suggested that the disorder of secondary bonds are closely related to the ultrasonic propagation mechanism.(4) Ep for PET fibers increased in stress relaxation after a small deformation but decreased in stress relaxation after a large deformation.

Acoustic measurements in rubberlike polymers during compressive deformation

Problems associated with the method of measurement of acoustical properties of viscoelastic materials and the influence of various external factors (temperature, pressure) on these materials have been examined. The results of measurements of propagation speeds and damping coefficients of waves of the sonic and ultrasonic regions in resins are given for discrete excitation frequencies and during simultaneous static action on the specimen. It is shown that uniaxial compression of the resin results in the appearance of dispersion of the dynamic elastic modulus. A possible explanation of this phenomenon is suggested.