An ignition criterion for combustible solids integrating surface temperature and heating rate

2014 ◽  
Vol 39 (2) ◽  
pp. 139-152
Author(s):  
Ning Tian ◽  
Aixi Zhou
Keyword(s):  
Surface Temperature ◽  
Heating Rate ◽  
Ignition Criterion

Study on Temperature Change Rule of Sprayed Composite Powders in Flight

2011 ◽  
Vol 704-705 ◽  
pp. 375-381
Author(s):  
Hong Wei Liu ◽  
Jian Jiang Wang ◽  
Xiao Feng Sun ◽  
Ji Qiu
Keyword(s):  
Surface Temperature ◽  
Heat Release ◽  
Heating Rate ◽  
Temperature Change ◽  
Composite Powder ◽  
Exchange Process ◽  
The Self ◽  
Forming Process ◽  
Composite Powders ◽  
Eutectic Melting

The temperature change process of the single sprayed composite powder during the self-reactive spray forming process for preparing the Ti (C,N)-TiB2 ceramic preforms was numerically simulated by means of finite element analysis. The results show that after the sprayed composite powder with grain size of 50μm has entered the flame field for 0.35ms, the surface temperature of it will reach the igniting temperature and the self-propagating high-temperature synthesis (abbr. SHS) reaction will take place. The heating rate of the particle in this period is about 2.82×106°C/s. After the SHS reaction has taken place, the heating rate becomes quicker because of the double function of the flame and the reactive heat release. When the temperature of the sprayed particle is higher than that of the flame, the heat exchange process will turn into heat absorption from heat release, which leads to the great drop of the heating rate (about 1.20×106°C/s). The composite powder completes the reaction in 0.88ms and reaches the highest temperature of 2920°C, which makes it become a ceramic droplet. After the reaction has finished, the droplet cools down quickly from exterior to interior, and the surface temperature of it descends to the theoretic eutectic melting point of the composite ceramics (2620°C) after 0.34ms. Then the droplet begins to solidify at some degree of supercooling and becomes ceramic particle. The numerically simulated results before, during and after the reaction match the water-quenching experiments of the sprayed particle with particle size of 50μm during the corresponding period. It indicates the heat process of the sprayed composite powder on the whole, which is composed of being heated, heat releasing, cooling and solidifying.

scholarly journals Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

2009 ◽  
Vol 9 (18) ◽  
pp. 7143-7160 ◽  
Author(s):  
M. Mallet ◽  
P. Tulet ◽  
D. Serça ◽  
F. Solmon ◽  
O. Dubovik ◽  
...  
Keyword(s):  
West Africa ◽  
Surface Temperature ◽  
Heating Rate ◽  
Mineral Dust ◽  
Convective Available Potential Energy ◽  
Atmospheric Model ◽  
Heat Fluxes ◽  
Convective Activity ◽  
Sensible Heat ◽  
Dust Aerosols

Abstract. The present work analyses the effect of dust aerosols on the surface and top of atmosphere radiative budget, surface temperature, sensible heat fluxes, atmospheric heating rate and convective activity over West Africa. The study is focused on the regional impact of a major dust event over the period of 7–14 March 2006 through numerical simulations performed with the mesoscale, nonhydrostatic atmospheric model MesoNH. Due to its importance on radiative budgets, a specific attention has been paid to the representation of dust single scattering albedo (SSA) in MesoNH by using inversions of the AErosol RObotic NETwork (AERONET). The radiative impacts are estimated using two parallel simulations, one including radiative effects of dust and the other without them. The simulations of dust aerosol impacts on the radiative budget indicate remarkable instantaneous (at midday) decrease of surface shortwave (SW) radiations over land, with regional (9°–17° N, 10° W–20° E) mean of −137 W/m2 during the 9 to 12 March period. The surface dimming resulting from the presence of dust is shown to cause important reduction of both surface temperature (up to 4°C) and sensible heat fluxes (up to 100 W/m2), which is consistent with experimental observations. At the top of the atmosphere, the SW cooling (regional mean of −12.0 W/m2) induced by mineral dust is shown to dominate the total net (shortwave + longwave) effect. The maximum SW heating occurs within the dusty layer with values comprised between 4 and 7° K by day and LW effect results in a cooling of −0.10/−0.20° K by day. Finally, the simulations suggest the decrease of the convective available potential energy (CAPE) over the region in the presence of mineral dust.

scholarly journals Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

2009 ◽  
Vol 9 (1) ◽  
pp. 2967-3006 ◽  
Author(s):  
M. Mallet ◽  
P. Tulet ◽  
D. Serça ◽  
F. Solmon ◽  
O. Dubovik ◽  
...  
Keyword(s):  
West Africa ◽  
Surface Temperature ◽  
Heating Rate ◽  
Mineral Dust ◽  
Cloud Microphysics ◽  
Heat Fluxes ◽  
Radiative Properties ◽  
Convective Activity ◽  
Sensible Heat ◽  
Dust Aerosols

Abstract. The present work analyzes the effect of dust aerosols on the surface and top of atmosphere radiative budget, surface temperature, sensible heat fluxes, atmospheric heating rate and convective activity over West Africa. The study is focused on the regional impact of a major dust event over the period of 9–13 March. Numerical simulations have been performed with the MesoNH model in which full interactions between radiation and dynamics are introduced, through various components representing size-resolved aerosol and cloud microphysics, radiative properties of particles and clouds, dynamics, and a surface model. Due to its importance on radiative budgets, a specific attention has been paid to the representation of dust SSA in MesoNH by using AERONET inversions. The radiative impacts are estimated using two parallel simulations, one including radiative effects of dust and the other without them. The simulations of dust aerosol impacts on the radiative budget indicate remarkable instantaneous decrease of shortwave (SW) radiations, with regional (09°–17° N, 10° W–20° E) mean of −160 W/m2 during the 9 to 13 March period. The surface dimming resulting from the presence of dust is shown to cause important reduction of both surface temperature (up to 4°C over regions where high AODs occur) and sensible heat fluxes (up to 100 W/m2), which is consistent with experimental observations performed over the same region. At the top of the atmosphere, the SW cooling (regional mean of −13.5 W/m2) induced by mineral dust, although moderated by the longwave (LW) warming (regional mean of +5 W/m2), dominates the total net (shortwave + longwave) effect. The maximum SW heating occurs within the dusty layer with values comprised between 4 and 7°K by day and LW effect results in strong cooling (−6 to −16°K by day) below the dust layer. Finally, the simulations suggest the decrease of the convective available potential energy (CAPE) over the region in the presence of mineral dust.

scholarly journals The Sensitivity of the Isentropic Slope in a Primitive Equation Dry Model

2008 ◽  
Vol 65 (1) ◽  
pp. 43-65 ◽  
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Surface Temperature ◽  
Heating Rate ◽  
Mass Flux ◽  
Time Scale ◽  
Diabatic Heating ◽  
Return Flow ◽  
Mean Flow ◽  
Primitive Equation ◽  
The Mean ◽  
Flow Changes

Abstract This paper discusses the sensitivity of the isentropic slope in a primitive equation dry model forced with Newtonian cooling when the heating is varied. This is done in two different ways, changing either the radiative equilibrium baroclinicity or the diabatic time scale for the zonal-mean flow. When the radiative equilibrium baroclinicity is changed, the isentropic slope remains insensitive against changes in the forcing, in agreement with previous results. However, the isentropic slope steepens when the diabatic heating rate is accelerated for the zonal-mean flow. Changes in the ratio between the interior and the boundary diffusivities as the diabatic heating rate is varied appear to be responsible for the violation of the constant criticality constraint in this model. Theoretical arguments are used to relate the sensitivity of the isentropic slope to that of the isentropic mass flux, which also remains constant when the radiative-equilibrium baroclinicity is changed. The sensitivity of the isentropic mass flux on the heating depends on how the gross stability changes. Bulk stabilities calculated from isobaric averages and gross stabilities estimated from isentropic diagnostics are not necessarily equivalent because a significant part of the return flow occurs at potential temperatures colder than the mean surface temperature.

A TEM study of the influence of microstructure on the superplastic behavior of a U-5.8 wt.% Nb alloy

1986 ◽  
Vol 44 ◽  
pp. 568-569
Author(s):  
G. Mackiewicz Ludtka
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Phase Field ◽  
Single Phase ◽  
Superplastic Behavior ◽  
Two Phase ◽  
Single Phase Field

Historically, metals exhibit superplasticity only while forming in a two-phase field because a two-phase microstructure helps ensure a fine, stable grain size. In the U-5.8 Nb alloy, superplastici ty exists for up to 2 h in the single phase field (γ1) at 670°C. This is above the equilibrium monotectoid temperature of 647°C. Utilizing dilatometry, the superplastic (SP) U-5.8 Nb alloy requires superheating to 658°C to initiate the α+γ2 → γ1 transformation at a heating rate of 1.5°C/s. Hence, the U-5.8 Nb alloy exhibits an anomolous superplastic behavior.

Optimization of the time the chromatograph thermostats exit to a given temperature

2020 ◽  
pp. 40-45
Author(s):  
Nadezhda O. Vzduleva ◽  
Valery B. Gitlin
Keyword(s):  
Heating Rate ◽  
Entire Range ◽  
Gas Chromatograph ◽  
Heating And Cooling ◽  
Operating Temperatures ◽  
The Stability

The problems of ensuring the stability of the temperature of the chromatographic experiment carried out using a serial gas chromatograph LGH-3000 are considered. Limiting the permissible heating rate of the chromatograph thermostats does not allow a quick transition to the new conditions of the chromatographic experiment in accordance with the requirements of the technical conditions. The processes of heating and cooling the thermostat are analyzed. It is shown that the ratio of the duration of the interval equal to the sum of the durations of the heating and cooling intervals to the duration of the heating interval is inversely proportional to the temperature of the chromatographic experiment. Based on this situation, an empirical algorithm is proposed for heating the thermostat to a given temperature, which made it possible to reduce the time it takes to reach a given temperature in the entire range of operating temperatures.

Application of pyrometer and standard sample to determine surface temperature of studied materials

2019 ◽  
pp. 9-13
Author(s):  
V.Ya. Mendeleyev ◽  
V.A. Petrov ◽  
A.V. Yashin ◽  
A.I. Vangonen ◽  
O.K. Taganov
Keyword(s):  
Composite Material ◽  
Surface Temperature ◽  
Relative Error ◽  
Wavelength Range ◽  
Standard Sample ◽  
A Priori ◽  
Temperature Changes ◽  
Surface Temperatures ◽  
Relative Errors ◽  
Normal Emissivity

Determining the surface temperature of materials with unknown emissivity is studied. A method for determining the surface temperature using a standard sample of average spectral normal emissivity in the wavelength range of 1,65–1,80 μm and an industrially produced Metis M322 pyrometer operating in the same wavelength range. The surface temperature of studied samples of the composite material and platinum was determined experimentally from the temperature of a standard sample located on the studied surfaces. The relative error in determining the surface temperature of the studied materials, introduced by the proposed method, was calculated taking into account the temperatures of the platinum and the composite material, determined from the temperature of the standard sample located on the studied surfaces, and from the temperature of the studied surfaces in the absence of the standard sample. The relative errors thus obtained did not exceed 1,7 % for the composite material and 0,5% for the platinum at surface temperatures of about 973 K. It was also found that: the inaccuracy of a priori data on the emissivity of the standard sample in the range (–0,01; 0,01) relative to the average emissivity increases the relative error in determining the temperature of the composite material by 0,68 %, and the installation of a standard sample on the studied materials leads to temperature changes on the periphery of the surface not exceeding 0,47 % for composite material and 0,05 % for platinum.

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