The effect of sampling rate on interpretation of the temporal characteristics of radiative and convective heating in wildland flames

2013 ◽  
Vol 22 (2) ◽  
pp. 168 ◽  
Author(s):  
David Frankman ◽  
Brent W. Webb ◽  
Bret W. Butler ◽  
Daniel Jimenez ◽  
Michael Harrington
Keyword(s):  
Sampling Rate ◽  
Sampling Frequency ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Convective Heating ◽  
Moving Window ◽  
Prescribed Burn ◽  
Heating Rates ◽  
Time Resolved ◽  
The Difference

Time-resolved radiative and convective heating measurements were collected on a prescribed burn in coniferous fuels at a sampling frequency of 500 Hz. Evaluation of the data in the time and frequency domain indicate that this sampling rate was sufficient to capture the temporal fluctuations of radiative and convective heating. The convective heating signal contained significantly larger fluctuations in magnitude and frequency than did the radiative heating signal. The data were artificially down-sampled to 100, 50, 10, 5 and 1 Hz to explore the effect of sampling rate on peak heat fluxes, time-averaged heating and integrated heating. Results show that for sampling rates less than 5 Hz the difference between measured and actual peak radiative heating rates can be as great as 24%, and is on the order of 80% for 1-Hz sampling rates. Convective heating showed degradation in the signal for sampling rates less than 100 Hz. Heating rates averaged over a 2-s moving window, as well as integrated radiative and convective heating were insensitive to sampling rate across all ranges explored. The data suggest that peak radiative and convective heating magnitudes cannot be fully temporally resolved for sampling frequencies lower than 20 and 200 Hz.

Measurements of convective and radiative heating in wildland fires

2013 ◽  
Vol 22 (2) ◽  
pp. 157 ◽  
Author(s):  
David Frankman ◽  
Brent W. Webb ◽  
Bret W. Butler ◽  
Daniel Jimenez ◽  
Jason M. Forthofer ◽  
...  
Keyword(s):  
Fast Response ◽  
Radiative Heating ◽  
Radiative Energy ◽  
Convective Heating ◽  
Wildland Fires ◽  
Ambient Conditions ◽  
Heating Rates ◽  
Total Energy Release ◽  
Time Resolved ◽  
Relative Contribution

Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was much less variable in time, increasing nearly monotonically with the approach of the flame front and largely declining with its passage. Irradiance beneath two crown fires peaked at 200 and 300 kW m–2, peak irradiance associated with fires in surface fuels reached 100 kW m–2 and the peak for three instances of burning in shrub fuels was 132 kW m–2. The fire radiative energy accounted for 79% of the variance in fuel consumption. Convective heating at the sensor surface varied from 15% to values exceeding the radiative flux. Detailed measurements of convective and radiative heating rates in wildland fires are presented. Results indicate that the relative contribution of each to total energy release is dependent on fuel and environment.

scholarly journals Ignition of Slurry Fuel Droplets with Different Heating Conditions

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4553
Author(s):  
Timur Valiullin ◽  
Ksenia Vershinina ◽  
Pavel Strizhak
Keyword(s):  
Heat Fluxes ◽  
Radiative Heating ◽  
Convective Heating ◽  
Radiation Heating ◽  
Fuel Droplets ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Ignition And Combustion ◽  
Combustion Processes ◽  
Hot Surface

This paper describes modern research methods of the ignition and combustion processes of slurry fuel droplets. The experiments were carried out using a muffle furnace to ensure the conditions of radiation heating, the hot surface to reproduce the conditions of conductive heating, the high-temperature channel with convective heating, the chamber with the processes of soaring, i.e., a significant increase in the time of fuel residence in the combustion chamber. We identified the differences in combustion modes, threshold ignition temperatures, delay times and durations of combustion processes. We obtained the quantitative differences in the characteristics of the ignition and combustion processes for typical registration methods. It was found that for all heating schemes, the minimum ignition temperatures have comparable values. Minimum ignition delay times were recorded during convective heating. The maximum combustion temperatures were achieved with radiation heating. We determined the values of limiting heat fluxes, sufficient to initiate the combustion of slurries fuels during conductive, convective and radiative heating.

Sounding-Based Thermodynamic Budgets for DYNAMO

2015 ◽  
Vol 72 (2) ◽  
pp. 598-622 ◽  
Author(s):  
Richard H. Johnson ◽  
Paul E. Ciesielski ◽  
James H. Ruppert ◽  
Masaki Katsumata
Keyword(s):  
Radiative Forcing ◽  
Deep Convection ◽  
Active Phase ◽  
Life Cycles ◽  
Radiative Heating ◽  
Convective Heating ◽  
Madden Julian Oscillation ◽  
Heating Rates ◽  
Gross Moist Stability ◽  
Cumulus Congestus

Abstract The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden–Julian oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the special observing period in October and November. Data from a northern and a southern sounding array (NSA and SSA, respectively) have been used to investigate the apparent heat sources and sinks (Q1 and Q2) and radiative heating rates QR throughout the life cycles of the two MJO events. The MJO signal was far stronger in the NSA than the SSA. Time series of Q1, Q2, and the vertical eddy flux of moist static energy reveal an evolution of cloud systems for both MJOs consistent with prior studies: shallow, nonprecipitating cumulus during the suppressed phase, followed by cumulus congestus, then deep convection during the active phase, and finally stratiform precipitation. However, the duration of these phases was shorter for the November MJO than for the October event. The profiles of Q1 and Q2 for the two arrays indicate a greater stratiform rain fraction for the NSA than the SSA—a finding supported by TRMM measurements. Surface rainfall rates and net tropospheric QR determined as residuals from the budgets show good agreement with satellite-based estimates. The cloud radiative forcing was approximately 20% of the column-integrated convective heating and of the same amplitude as the normalized gross moist stability, leaving open the possibility of radiative–convective instability for the two MJOs.

scholarly journals Local Balance and Variability of Atmospheric Heat Budget over Oceans: Observation and Reanalysis-Based Estimates

2014 ◽  
Vol 27 (2) ◽  
pp. 893-913 ◽  
Author(s):  
Sun Wong ◽  
Tristan S. L’Ecuyer ◽  
William S. Olson ◽  
Xianan Jiang ◽  
Eric J. Fetzer
Keyword(s):  
Heat Budget ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Latent Heating ◽  
Heating Rates ◽  
Cooling Rates ◽  
Atmospheric Heating ◽  
Atmospheric Heat

Abstract The authors quantify systematic differences between modern observation- and reanalysis-based estimates of atmospheric heating rates and identify dominant variability modes over tropical oceans. Convergence of heat fluxes between the top of the atmosphere and the surface are calculated over the oceans using satellite-based radiative and sensible heat fluxes and latent heating from precipitation estimates. The convergence is then compared with column-integrated atmospheric heating based on Tropical Rainfall Measuring Mission data as well as the heating calculated using temperatures from the Atmospheric Infrared Sounder and wind fields from the Modern-Era Retrospective Analysis for Research and Applications (MERRA). Corresponding calculations using MERRA and the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis heating rates and heat fluxes are also performed. The geographical patterns of atmospheric heating rates show heating regimes over the intertropical convergence zone and summertime monsoons and cooling regimes over subsidence areas in the subtropical oceans. Compared to observation-based datasets, the reanalyses have larger atmospheric heating rates in heating regimes and smaller cooling rates in cooling regimes. For the averaged heating rates over the oceans in 40°S–40°N, the observation-based datasets have net atmospheric cooling rates (from −15 to −22 W m−2) compared to the reanalyses net warming rates (5.0–5.2 W m−2). This discrepancy implies different pictures of atmospheric heat transport. Wavelet spectra of atmospheric heating rates show distinct maxima of variability in annual, semiannual, and/or intraseasonal time scales. In regimes where deep convection frequently occurs, variability is mainly driven by latent heating. In the subtropical subsidence areas, variability in radiative heating is comparable to that in latent heating.

scholarly journals A diffusion anisotropy descriptor links morphology effects of H-ZSM-5 zeolites to their catalytic cracking performance

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Xiaoliang Liu ◽  
Jing Shi ◽  
Guang Yang ◽  
Jian Zhou ◽  
Chuanming Wang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Catalytic Cracking ◽  
Catalytic Performance ◽  
Zeolite Catalysts ◽  
Time Resolved ◽  
Cracking Performance ◽  
Morphology Effect ◽  
Ft Ir ◽  
The Difference ◽  
Dynamics Simulations

AbstractZeolite morphology is crucial in determining their catalytic activity, selectivity and stability, but quantitative descriptors of such a morphology effect are challenging to define. Here we introduce a descriptor that accounts for the morphology effect in the catalytic performances of H-ZSM-5 zeolite for C4 olefin catalytic cracking. A series of H-ZSM-5 zeolites with similar sheet-like morphology but different c-axis lengths were synthesized. We found that the catalytic activity and stability is improved in samples with longer c-axis. Combining time-resolved in-situ FT-IR spectroscopy with molecular dynamics simulations, we show that the difference in catalytic performance can be attributed to the anisotropy of the intracrystalline diffusive propensity of the olefins in different channels. Our descriptor offers mechanistic insight for the design of highly effective zeolite catalysts for olefin cracking.

scholarly journals Overheating In Silicon During Pulsed-Laser Irradiation?

1985 ◽  
Vol 51 ◽  
Author(s):  
B. C. Larson ◽  
J. Z. Tischler ◽  
D. M. Mills
Keyword(s):  
Laser Irradiation ◽  
Thermal Strain ◽  
Pulsed Laser ◽  
Interface Velocity ◽  
High Energy ◽  
Time Resolved ◽  
Synchrotron Source ◽  
Zero Velocity ◽  
The Difference ◽  
Pulsed Laser Irradiation

ABSTRACTNanosecond resolution time-resolved x-ray diffraction measurements of thermal strain have been used to measure the interface temperatures in silicon during pulsed-laser irradiation. The pulsed-time-structure of the Cornell High Energy Synchrotron Source (CHESS) was used to measure the temperature of the liquid-solid interface of <111> silicon during melting with an interface velocity of 11 m/s, at a time of near zero velocity, and at a regrowth velocity of 6 m/s. The results of these measurements indicate 110 K difference between the temperature of the interface during melting and regrowth, and the measurement at zero velocity shows that most of the difference is associated with undercooling during the regrowth phase.

scholarly journals Mechanisms of Jet Formation on the Giant Planets

2010 ◽  
Vol 67 (11) ◽  
pp. 3652-3672 ◽  
Author(s):  
Junjun Liu ◽  
Tapio Schneider
Keyword(s):  
Angular Momentum ◽  
Rossby Wave ◽  
Momentum Flux ◽  
Wave Generation ◽  
Heat Fluxes ◽  
Giant Planets ◽  
Radiative Heating ◽  
Flux Divergence ◽  
Low Latitude ◽  
Flow Configurations

Abstract The giant planet atmospheres exhibit alternating prograde (eastward) and retrograde (westward) jets of different speeds and widths, with an equatorial jet that is prograde on Jupiter and Saturn and retrograde on Uranus and Neptune. The jets are variously thought to be driven by differential radiative heating of the upper atmosphere or by intrinsic heat fluxes emanating from the deep interior. However, existing models cannot account for the different flow configurations on the giant planets in an energetically consistent manner. Here a three-dimensional general circulation model is used to show that the different flow configurations can be reproduced by mechanisms universal across the giant planets if differences in their radiative heating and intrinsic heat fluxes are taken into account. Whether the equatorial jet is prograde or retrograde depends on whether the deep intrinsic heat fluxes are strong enough that convection penetrates into the upper troposphere and generates strong equatorial Rossby waves there. Prograde equatorial jets result if convective Rossby wave generation is strong and low-latitude angular momentum flux divergence owing to baroclinic eddies generated off the equator is sufficiently weak (Jupiter and Saturn). Retrograde equatorial jets result if either convective Rossby wave generation is weak or absent (Uranus) or low-latitude angular momentum flux divergence owing to baroclinic eddies is sufficiently strong (Neptune). The different speeds and widths of the off-equatorial jets depend, among other factors, on the differential radiative heating of the atmosphere and the altitude of the jets, which are vertically sheared. The simulations have closed energy and angular momentum balances that are consistent with observations of the giant planets. They exhibit temperature structures closely resembling those observed and make predictions about as yet unobserved aspects of flow and temperature structures.

The influence of sampling frequency and interpolation on the bit error rate of GMSK signal

2021 ◽  
pp. 108-114
Author(s):  
D.D. Privalov
Keyword(s):  
Signal Detection ◽  
Bit Error Rate ◽  
Error Rate ◽  
Clock Synchronization ◽  
Additive White Gaussian Noise ◽  
Sampling Rate ◽  
Digital Signal ◽  
Sampling Frequency ◽  
Synchronization Error ◽  
Minimum Number

The sampling rate at a given bit rate is a requirement for the speed of digital signal processors. In this regard, it is necessary to strive to reduce it in the development of electronic devices, especially portable ones. However, this can lead to an increase in the bit error rate during signal detection. Therefore, it is important to determine the degradation of signal detection with decreasing sampling frequency and to develop practical recommendations to ensure the specified quality of communication. The aim of the article is to study the influence of sampling frequency and interpolation on the bit error rate of GMSK Signal. The article considers the incoherent detection of a GMSK signal in a channel with additive white Gaussian noise, taking into account the influence of the clock synchronization error. Numerical results are presented that characterize an increase in the bit error rate with a decrease in the signal sampling frequency. It is shown that when using the cubic Farrow interpolator, there is no significant degradation in the bit error probability. The minimum number of samples per symbol is determined, at which the bit error rate is close to the theoretical values in the absence of synchronization error. The presented results can be used in development of wireless data transmission systems.

Design and Characterization of a Novel Upward Flow Reactor for the Study of High-Temperature Thermal Reduction for Solar-Driven Processes

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
H. Evan Bush ◽  
Karl-Philipp Schlichting ◽  
Robert J. Gill ◽  
Sheldon M. Jeter ◽  
Peter G. Loutzenhiser
Keyword(s):  
High Temperature ◽  
Flow Reactor ◽  
Thermal Reduction ◽  
Heat Fluxes ◽  
O2 Evolution ◽  
Transfer Model ◽  
Upward Flow ◽  
Heating Rates ◽  
Solar Simulator

The design and characterization of an upward flow reactor (UFR) coupled to a high flux solar simulator (HFSS) under vacuum is presented. The UFR was designed to rapidly heat solid samples with concentrated irradiation to temperatures greater than 1000 °C at heating rates in excess of 50 K/s. Such conditions are ideal for examining high-temperature thermal reduction kinetics of reduction/oxidation-active materials by temporally monitoring O2 evolution. A steady-state, computational fluid dynamics (CFD) model was employed in the design to minimize the formation of eddies and recirculation, and lag and dispersion were characterized through a suite of O2 tracer experiments using deconvolution and the continuously stirred tank reactors (CSTR) in series models. A transient, CFD and heat transfer model of the UFR was combined with Monte Carlo ray tracing (MCRT) to determine radiative heat fluxes on the sample from the HFSS to model spatial and temporal sample temperatures. The modeled temperatures were compared with those measured within the sample during an experiment in which Co3O4 was thermally reduced to CoO and O2. The measured temperatures within the bed were bounded by the average top and bottom modeled bed temperatures for the duration of the experiment. Small variances in the shape of the modeled versus experimental temperatures were due to contact resistance between the thermocouple and particles in the bed and changes in the spectral absorptivity and emissivity as the Co3O4 was reduced to CoO and O2.

scholarly journals Quantifying the Radiative Impact of Clouds on Tropopause Layer Cooling in Tropical Cyclones

2020 ◽  
Vol 33 (15) ◽  
pp. 5527-5542
Author(s):  
Louis Rivoire ◽  
Thomas Birner ◽  
John A. Knaff ◽  
Natalie Tourville
Keyword(s):  
Tropical Cyclones ◽  
Spatial Scales ◽  
Radiative Heating ◽  
Orthogonal Polarization ◽  
Heating Rates ◽  
Tropical Tropopause Layer ◽  
Convective Clouds ◽  
Tropical Tropopause ◽  
Convective Region ◽  
Order Of Magnitude

AbstractA ubiquitous cold signal near the tropopause, here called “tropopause layer cooling” (TLC), has been documented in deep convective regions such as tropical cyclones (TCs). Temperature retrievals from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) reveal cooling of order 0.1–1 K day−1 on spatial scales of order 1000 km above TCs. Data from the Cloud Profiling Radar (onboard CloudSat) and from the Cloud–Aerosol Lidar with Orthogonal Polarization [onboard the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)] are used to analyze cloud distributions associated with TCs. Evidence is found that convective clouds within TCs reach the upper part of the tropical tropopause layer (TTL) more frequently than do convective clouds outside TCs, raising the possibility that convective clouds within TCs and associated cirrus clouds modulate TLC. The contribution of clouds to radiative heating rates is then quantified using the CloudSat and CALIPSO datasets: in the lower TTL (below the tropopause), clouds produce longwave cooling of order 0.1–1 K day−1 inside the TC main convective region, and longwave warming of order 0.01–0.1 K day−1 outside; in the upper TTL (near and above the tropopause), clouds produce longwave cooling of the same order as TLC inside the TC main convective region, and up to one order of magnitude smaller outside. Considering that clouds also produce shortwave warming, it is suggested that cloud radiative effects inside and outside TCs only explain modest amounts of TLC while other processes must provide the remaining cooling.

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