Constant Temperature Region Research Articles

Discontinuity waves in temperature and diffusion models

We analyse shock wave behaviour in a hyperbolic diffusion system with a general forcing term which is qualitatively not dissimilar to a logistic growth term. The amplitude behaviour is interesting and depends critically on a parameter in the forcing term. We also develop a fully nonlinear acceleration wave analysis for a hyperbolic theory of diffusion coupled to temperature evolution. We consider a rigid body and we show that for three-dimensional waves there is a fast wave and a slow wave. The amplitude equation is derived exactly for a one-dimensional (plane) wave and the amplitude is found for a wave moving into a region of constant temperature and solute concentration. This analysis is generalized to allow for forcing terms of Selkov–Schnakenberg, or Al Ghoul-Eu cubic reaction type. We briefly consider a nonlinear acceleration wave in a heat conduction theory with two solutes present, resulting in a model with equations for temperature and each of two solute concentrations. Here it is shown that three waves may propagate.

Properties of off-axis helical long-period fiber gratings

In this paper, a new four-electrode arc discharge device with large constant temperature region is designed, which is used to prepared high-quality off-axis helical long-period fiber grating. The larger constant temperature heating area is more conducive to releasing the stress of optical fiber, so that the prepared device is less off-axis. In order to show that low off-axis is a key parameter of high-quality off-axis helical long-period fiber grating, the effects of single mode fiber on transmission spectrum of off-axis helical long-period fiber grating under different coupling lengths, pitches, core refractive indexes, cladding refractive indexes, core diameters, cladding diameters and off-axis quantity are simulated by using beam propagation method. Since traditional methods are difficult to measure the off-axis helical long-period fiber grating with small off-axis quantity, the off-axis quantity of the prepared device is estimated by using the method of spectral comparison and back-thrust off-axis quantity in this work. The off-axis helical long-period fiber grating is prepared by using the established processing device. The off-axis quantities of the prepared devices are about 0.12, 0.13 and 0.16 µm, respectively, according to the comparison between the simulated transmission spectrum and the actual spectrum. Finally, experiments on the torsional resistance and repeatability of the off-axis helical long-period fiber grating prepared by the device are carried out. The experimental results show that the prepared grating has certain torsional resistance and good spectral repeatability.

Study on the characteristics of four electrode wide constant temperature region for preparing high quality spiral fiber

Study on the characteristics of four electrode wide constant temperature region for preparing high quality spiral fiber

Experimental Study of Copper Wick Loop Heat Pipe with a Flat Plate Evaporator

This investigation examines the effect of the sintering temperature curve in manufactured copper powder capillary structure (wick) for a loop heat pipe (LHP). The production process of the copper powder capillary structure is composed of chose the type of copper powder, filled in the stainless steel mold, sintering temperature curve set up, Sintering air hydrogen into the mold, release from mold, and the copper structured wick. The sintering temperature curve is composed of a region of increasing temperature; a region of constant temperature and a region of declining temperature. The set up rang of the temperature ramp as best parameter for the sintering temperature curve is 9.8°C /min. The set up unit of the temperature for sintering is 550°C. The minutes of the constant temperature is 30 minutes. The stage of cooling down section is we keep the item cooling by radiation until the temperature dropped to its ambient temperature. The three main parameters that can be measured in the evaluation of a factory made wick are pore radius 8.5μm, porosity 66.8%, and permeability 2.5×10-13m2. The result of experiment test demonstrates that the heat transfer performance is optimal at 120W; the minimal total heat flux is 12W/cm2, thermal resistance is approximately 1.3°C/W.

Characterization of the thermal structure of six clustered microflames seeded with TaN particles through emission spectroscopy

The temperatures of TaN seed particles and electronically excited CH radicals (i.e. CH∗) emanating from a methane-air microflame burner were characterized using VIS-NIR emission spectra while varying fuel-air flow rates. The burner consisted of six micro-nozzles arranged in a circle surrounding a central nozzle through which air and TaN seed particles with sizes between 0.3 and 3 μm were injected. The temperature profiles of the particles at various heights above the base of the central nozzle, obtained by their VIS-NIR continuum emission, showed a well-defined constant temperature region that extended well beyond the actual flame front and changed as fuel and oxidizer flow rates were varied. High spectral resolution measurements were conducted to obtain CH∗ A2Δ-X2Π emission spectra which were then compared with theoretical CH∗ emission spectra from Lifbase simulations to determine rotational and vibrational temperatures. The CH∗ vibrational temperatures were clearly greater than the rotational temperatures, the difference of which was attributed to equilibration of the rotational temperature with the gas dynamic temperature and the excitation of vibrational states through chemical reactions. Analyses of the TaN particles before and after seeding using scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy with energy dispersive X-ray analysis (XPS/EDX) showed surface oxidation occurred in the flame. Comparing the shapes of the spectral emission with theoretical Planck emission corrected for TaN emissivity and Ta2O5 transmittance, the oxide layer was found to be clearly thinner than 100 nm in the high temperature regions. Our results show an ability to control the duration to which seed particles are subjected to high temperature reactions by adjusting fuel and oxidizer flow rates.

Effect of Sintering Temperature and Time in Nickel Wick for Loop Heat Pipe with Flat Evaporator

This paper specifically addresses the effect of changing the constant temperature region of the sintering temperature curve in manufacturing nickel powder capillary structure (wick) on the performance of a flat loop heat pipe (FLHP). The sintering temperature curve is composed of three regions: a region of increasing temperature, a region of constant temperature, and a region of decreasing temperature, with the sintering time and temperature in the region of constant temperature having significant effect on the permeability of the wick. In this study, for wick manufacturing the temperatures in this region tested range from 550°C to 650°C and the time from 30 minutes to 60 minutes. The properties and internal parameters of the wick are measured, and the wick is placed into FLHP for performance testing. Experimental results show that at sintering temperature of 550°C and lasting about 45 minutes, maximum heat load is 200W, minimum thermal resistance is 0.32°C/W, permeability is , porosity is 66%, effective porosity is 3.8and heat flux is around 21W/cm2; related literatures have only reported maximum heat load increase of 25%.

Effect of Sintering Temperature Curve in Wick Manufactured for Loop Heat Pipe with Flat Evaporator

This paper specifically addresses the effect of the sintering temperature curve in manufacturing nickel powder capillary structure (wick) for a loop heat pipe (LHP) with flat evaporator. The sintering temperature curve is composed of three regions: a region of increasing temperature, a region of constant temperature, and a region of decreasing temperature. The most important region is the increasing temperature region, as the rate of temperature increase directly affects the performance of the wick.When the slope of the region of increasing temperature is 0.8 (equivalent to 8OC/min), the structure of the manufactured wick is complete, with the best heat transfer performance result. Experimental resultsshowed that the optimal heat transfer performance is 160W, the minimal total thermal resistance is approximately 0.43OC/W, and the heat flux is 17W/cm2; the optimal wick manufactured has an effective pore radius of 5.2 μm, a permeability of 5.9×10-13m2, and a porosity of 64%.

Direct Imaging of Thermally Driven Domain Wall Motion in Magnetic Insulators

Thermally induced domain wall motion in a magnetic insulator was observed using spatiotemporally resolved polar magneto-optical Kerr effect microscopy. The following results were found: (i)the domain wall moves towards hot regime; (ii)a threshold temperature gradient (5 K/mm), i.e., a minimal temperature gradient required to induce domain wall motion; (iii)a finite domain wall velocity outside of the region with a temperature gradient, slowly decreasing as a function of distance, which is interpreted to result from the penetration of a magnonic current into the constant temperature region; and (iv)a linear dependence of the average domain wall velocity on temperature gradient, beyond a threshold thermal bias. Our observations can be qualitatively explained using a magnonic spin transfer torque mechanism, which suggests the utility of magnonic spin transfer torque for controlling magnetization dynamics.

Boundary treatment effects on molecular dynamics simulations of interface thermal resistance

Molecular Dynamics simulations of heat conduction in liquid Argon confined in Silver nano-channels are performed subject to three different thermal conditions. Particularly, different surface temperatures are imposed on Silver domains using a thermostat in all and limited number of solid layers, resulting in heat flux in the liquid domain. Alternatively, energy is injected and extracted from solid layers to create a NVE liquid Argon system, which corresponds to heat flux specification. Imposition of a constant temperature region in the solid domain results in an unphysical temperature jump, indicating the presence of an artificial thermal resistance induced by the thermostat. Thermal resistance analyses for the components of each case are performed to distinguish the artificial and interface thermal resistance effects. Constant wall temperature simulations are shown to exhibit superposition of the artificial and interface thermal resistance values at the liquid/solid interface, while applying thermostat on wall layers sufficiently away from the liquid/solid interface results in consistent predictions of the interface thermal resistance. Injecting and extracting energy from each solid layer eliminates the artificial resistance. However, the method cannot directly specify a desired temperature difference between the two solid domains.

The Error Analysis of a Steady-State Thermal Conductivity Measurement Method With Single Constant Temperature Region

Abstract A method for steady-state thermal conductivity measurement with single constant temperature region has been developed. To better understand the accuracy of the method a numerical model is devised and verified by experimental results. The ratios of thermal conductivity derived from the temperature distribution solutions to that given in the numerical model are obtained and shown. They can be used to correct the systematic error of measurement introduced by the one-dimensional approximation. Finally, the measurement uncertainty due to misalignment of the temperature sensors and the limitation of sensing devices is also investigated. The numerical model is suitable for estimating the range of confidence in practical measurements.

The effects of chromatic dispersion on temperature measurement in the laser-heated diamond anvil cell

We have developed numerical simulations of spectroradiometric temperature measurement for refractive optical systems used in laser-heated diamond anvil cell (LHDAC) experiments. Chromatic dispersion in refractive optics is quantified by the wavelength-dependent radial displacement function. Results show that a combination of high peak temperature, steep temperature gradient, high spatial resolution, and large radial displacement can cause extreme errors in temperature, on the order of hundreds to thousands of degrees of Kelvin. Increasing detector bin size can dampen the magnitude of the error in peak temperature, but the average temperature produced in this way is still likely to be erroneous. Accurate peak temperature can be measured if the radial displacement is less than the radius of a region of constant temperature. Errors in accuracy can be reduced by locating the wavelength range that produces a minimum and symmetrical radial displacement. The precision of the fitted blackbody function is correlated positively with accuracy so that the optimal wavelength range can be located by minimizing the error in the blackbody fit. Modern spectroradiometric systems that utilize refractive optics are capable of accurate temperature measurement if proper steps are taken to identify and mitigate the effects of chromatic dispersion.

The effects of chromatic dispersion on temperature measurement in the laser-heated diamond anvil cell

We have developed numerical simulations of spectroradiometric temperature measurement for refractive optical systems used in laser-heated diamond anvil cell (LHDAC) experiments. Chromatic dispersion in refractive optics is quantified by the wavelength-dependent radial displacement function. Results show that a combination of high peak temperature, steep temperature gradient, high spatial resolution, and large radial displacement can cause extreme errors in temperature, on the order of hundreds to thousands of degrees of Kelvin. Increasing detector bin size can dampen the magnitude of the error in peak temperature, but the average temperature produced in this way is still likely to be erroneous. Accurate peak temperature can be measured if the radial displacement is less than the radius of a region of constant temperature. Errors in accuracy can be reduced by locating the wavelength range that produces a minimum and symmetrical radial displacement. The precision of the fitted blackbody function is correlated positively with accuracy so that the optimal wavelength range can be located by minimizing the error in the blackbody fit. Modern spectroradiometric systems that utilize refractive optics are capable of accurate temperature measurement if proper steps are taken to identify and mitigate the effects of chromatic dispersion.

Mathematical modeling of thermal decomposition of coal

Pyrolysis, as a first step in all thermochemical coal conversion processes, has been investigated in detail over the years in order to evaluate the kinetic data and to establish reliable models for the complex reaction scheme. Since coal pyrolysis is not a single reaction but rather a multiplicity in different time intervals for isothermal pyrolysis, or in different time and temperature intervals for the case of heat-up, any set of parameters cannot be expected to represent data accurately over a wide range of conditions. In this study, different kinetic models were used to model the decomposition of coal in the variable and constant temperature regions of pyrolysis. In the variable temperature region, the selected mechanism takes into account the order of reaction as a variable and uses data obtained; in different types of equipment, using different types of coal and a range of heating rate values. In the constant temperature region, a fixed-bed reactor data was used. Various models have been examined and the model which takes into account the dependence of the apparent activation energy on time, total conversion and the volatile matter in coal; gave the best correlation. Various numerical and analytical techniques were utilized to find the kinetic constants of the equations.

Small-angle X-ray studies of soot inception and growth

The high spectral intensity of X-rays produced by the undulator at the Basic Energy Sciences Synchrotron Radiation Center of Argonne's Advanced Photon Source has allowed us to perform small-angle X-ray scattering (SAXS) studies of the initial distribution of soot particles formed by various fuels. SAXS provides an in situ probe of the morphology of soot in the region between 1 and 100 nm and complements the ex situ technique of electron microscopy. The basic aspects of SAXS and its potential are illustrated with measurement on a laminar flame of acetylene in air. The more complex fuel toluene has been studied in a flat-flame burner that supports a CH4/H2/air or CO/H2/air diffusion flame stabilized by N2 co-flow. This burner produces a nearly constant temperature region above the flame where the pyrolysis and combustion of the heavier fuels occurs. Kinetic information is obtained by performing measurements of the scattered intensity profile as a function of the height above the burner. These profiles have been reduced to give the mean radius and dispersion of a distribution of spherical particles. Mean radii between 0.8 and 18 nm have been observed. The smallest of these is a factor of ten smaller than previously detected with Lorentz-Mie scattering. Near 1550 K, the soot distribution found in toluene shows a distinct step behavior that is consistent with model calculations.

Critical Distillation Experiments in a Region near the Homogeneous Ternary Azeotrope in the System Ethyl Acetate−Ethanol−Water

A nine-tray distillation column has been used to critically examine a constant-temperature region near the ternary homogeneous azeotrope in the system ethyl acetate-ethanol-water. Liquid samples withdrawn from the trays show an almost constant ethanol composition for a specific charge to the reboiler. An examination of the experimental discrete distillation lines on a portion of the ternary phase diagram showed that the constant-temperature region had been covered and an indication of a different location of the ternary homogeneous azeotrope. Process simulation studies could be expected to be difficult with existing parameters in thermodynamic models, under these conditions.

Temperature and energy partition in fragmentation

We study fragmentation of small atomistic clusters via molecular dynamics. We calculate the time scales related to fragment formation and emission. We also show that some degree of thermalization is achieved during the expansion process, which allows the determination of a local temperature. In this way we can calculate the break-up temperature as a function of excitation energy, i.e. the fragmentation caloric curve. Fragmentation appears as a rather constant temperature region of the caloric curve. Furthermore, we show that different definitions of temperature, related to different degrees of freedom, yield very similar values.

Caloric curve in fragmentation

We study phase transitions of small two-dimensional Lennard-Jones drops via microcanonical molecular dynamics in a broad energy range. We found that the caloric curve can be extended to high energies to comprehend high evaporation rates and highly nonequilibrium phenomena such as multifragmentation. Multifragmentation appears as a constant temperature region in the caloric curve like the solid-liquid phase transition.

AKINETIC STUDY OF LOW-TEMPERATURE LIGNITE CARBONIZATION

Abstract Seyilömer and Tunçbilck lignite samples have been carbonized in a fixed-bed reactor under various temperature and time conditions in a nitrogen atmosphere. The total conversion, tar and gas yields have been calculated as functions of temperature and time. The results were grouped as those obtained in the constant-heating-rate regime and those obtained at the constant stable temperature. Different kinetic models were applied to these “increasing” and “constant” temperature regimes. In the increasing temperature regime the degree of the reaction was deduced through the proposed kinetic model. In the constant temperature regime the reaction degree was presumed at the beginning and the gaseous products were identified as primary and secondary. Various models have been examined for lignite carbonization process for comparison of experimental findings. Parameter estimating analysis were carried out on the results and the rate constants have been found. Then, multiple linear regression analysis were used to deduce activation energies and frequency factors. The kinetic rate constants (k1=0.00002 and k2=0.00106 min−1 at 600°C) that were found for tar and primary gas are lower with respect to the corresponding values in the constant temperature region. The secondary gas decomposition rate is observed to be higher than production rate.

Change in Microbial Numbers during Thermophilic Composting of Sewage Sludge with Reference to CO 2 Evolution Rate

Dewatered sewage sludge was composted in a laboratory-scale autothermal reactor in which a constant temperature of 60 degrees C was kept as long as possible by regulating the air feed rate. The change in CO(2) evolution rate was measured continuously from the start up through the cessation of compositing. The succession of mesophilic bacteria, thermophilic bacteria, and thermophilic actinomycetes was also observed during the composting. Specific CO(2) evolution rates of thermophilic bacteria and actinomycetes in the constant-temperature region of 60 degrees C were assessed quantitatively. It was found that the CO(2) evolution rate was attributed to thermophilic bacteria at the initial stage of 60 degrees C and to thermophilic actinomycetes at the later stage of 60 degrees C.

Free convection boundary layers in a saturated porous medium with lateral mass flux

The effects of uniform lateral mass flux on the free convection boundary layer on a vertical wall in a saturated porous medium are considered. A series valid near the leading edge is derived and this is extended by a numerical solution of the full equations. Asymptotic expansions, valid at large distances along the plate, are derived in both the cases of withdrawal and injection of fluid. In the former case the boundary layer has constant thickness, while in the latter case there is a region of constant temperature next to the wall made up of fluid that has been injected through the wall, with an outer region where thermal diffusion is important.