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Topic: Thermal diffusivity

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	Method and apparatus for measuring thermal diffusivity by ac joule-heating - Patent 5080495
		The method for measuring thermal diffusivity according to the non-steady state method is characterized in that the thermal diffusivity is determined by producing forcibly a thermally non-equilibrium state in a sample and measuring the temperature variation of the sample caused by the subsequent relaxation of the state.
		The heat energy is transmitted by thermal conduction, causing a periodic temperature oscillation in the gas in the sealed cell in contact with the opposite measurement surface and producing a periodic sound wave in agreement in phase with the temperature oscillation on the measurement surface of the sample.
		The thermal conductivity thus obtained has a peak in the vicinity of the glass transition temperature as in the case of the thermal diffusivity, and its whole behavior is also similar to that of the thermal diffusivity.
	www.freepatentsonline.com /5080495.html (5943 words)

	A20 (Site not responding. Last check: 2007-10-19)
		The thermal conductivity, or coefficient of thermal conductivity, is the quantity of heat in calories per second that passes through a 1 cm thick specimen of a cross sectional area of 1 cm
		Thermal diffusivity controls the time rate of temperature change as heat passes through a material.
		Therefore, both thermal conductivity and thermal diffusivity are important parameters in predicting the transfer of thermal energy through a material.
	nersp.nerdc.ufl.edu /~soderho/a20.htm (330 words)

	TPRL Flash Diffusivity
		The thermal diffusivity (alpha) is not only important in its own right, but it also offers a convenient, economical and accurate method of determining the thermal conductivity (lambda).
		Thermal diffusivity is the measure of the way heat flows through the material to the other side.
		Thermal Conductivity is a physical property of a substance and characterises the ability of the substance to transfer heat.
	www.tprl.com /flash.html (1281 words)

	Optimized method of thermal diffusivity determination of thin films by laser-induced dynamic gratings (Site not responding. Last check: 2007-10-19)
		The thermal diffusivity of a film is determined using the least deflection of measured temporal diffraction evolution in film-substrate structure from the theoretical curves that have been calculated for various thermal diffusivities of a film.
		On the condition that the thermal diffusivity of a substrate is known, the accuracy of thermal diffusivity determination of a film depends on an error of measurement of TDG time decay which is about 5%.
		The inexact knowledge of the thermal diffusivity of a substrate results in a increase of an error of the film thermal-diffusivity determination, even though the substrate contribution to the measured diffraction isn't essential on comparison with diffraction by thermal grating in a film (non-active substrate for diffraction).
	www.zae-bayern.de /ectp/abstracts/ivakin1.html (384 words)

	Double-beam optical method and apparatus for measuring thermal diffusivity and other molecular dynamic processes in ...
		A change in the index of refraction during the formation of the thermal lens is related to the molecular relaxation characteristics of the sample material, and the change in the index of refraction during dissipation of the thermal lens is related to the thermal diffusivity of the sample material.
		The dissipation time of the thermal lens is thus related to the thermal diffusivity of the sample material, the time being determined by measuring changes in the index of refraction of the sample material as indicated by changes in intensity of the probe light beam 12' monitored by the detector 14.
		By using the dye laser at an output wavelength of 380 nanometers, thermal diffusivity of PMMA using an apparatus according to the invention was calculated to be 1.0.times.10.sup.-3 cm.sup.2 sec.sup.-1 which is comparable to that obtained by the National Bureau of Standards which was 1.06.times.10.sup.-3 cm.sup.2 sec.sup.-1.
	www.freepatentsonline.com /4243327.html (4607 words)

	Abstract (Site not responding. Last check: 2007-10-19)
		Theoretical results indicate that the thermal conductivity in such systems is anisotropic, and support, analogous to the well-known stress-optic rule, the validity of a stress-thermal rule where the thermal conductivity and stress tensors are linearly related.
		Thermal diffusivity data are complemented by measurements of stress and birefringence so that evaluations of the stress-optic and stress-thermal rules can be made.
		Results show that the thermal diffusivity is enhanced in the flow (or stretch) direction compared to the equilibrium value and that the stress-thermal rule is valid for the modest deformations achieved in this study.
	www.chee.iit.edu /~schieber/Schieber_Publications18.html (196 words)

	Details about Property Measurements
		Thermal properties of materials are established by experimentally establishing a heat flow boundary value problem, solving the theoretical equations, and then measuring necessary temperatures or heat fluxes to determine the thermal property by matching to the theoretical solution.
		The flash methods of measuring thermal diffusivity remove the steady state condition at the expense of measuring the temperature as a varying function of time.
		With the laser flash method the measurement of the thermal diffusivity of a material is usually carried out by rapidly heating one side of a sample and measuring the temperature rise curve on the opposite side (see schematic at right).
	www.calce.umd.edu /general/Facilities/laser_flash/details.htm (632 words)

	Bayerisches Geoinstitut - Annual Report 2002 - Thermal diffusivity of CaMgSi₂O₆ glass at high ... (Site not responding. Last check: 2007-10-19)
		Thermal diffusivity of a silicate melt is necessary to consider the convection of magma, because that is one of the terms in Prandtl and Rayleigh numbers.
		However, the measurement of thermal diffusivity of silicate melt is very rare mainly because of the technical difficulty.
		Thermal diffusivity was measured using the periodic temperature wave method (Ångström method).
	www.bgi.uni-bayreuth.de /annual_report/2002/c_78.phtml (343 words)

	Investigation of Thermal Diffusivity of Composite Material by Mirage Effect, by X (Site not responding. Last check: 2007-10-19)
		Thermal diffusivity is one of the important physical properties of composite materials.
		The thermal diffusivities for a series Copper/Carbon fiber composite (Cu-C), which containing 5 to 30 percent Carbon fiber homogeneously distributed in the composite, and Silver/Carbon fiber composite (AgC), which containing 3 percent Carbon are measured using the "Mirage Effect" technique.
		The "Mirage Effect" method is a useful NDE tool for determination of the thermal properties of metal-C fiber composite, and examination of the influence from the porosity and surface roughness of the composite materials.
	www.cnde.iastate.edu /QNDEDatabase/Vol.14A/p0467-0474.html (293 words)

	Thermal Transport Properties of Aluminum Metal Matrix Composites for Brake Applications
		Material properties such as thermal diffusivity, thermal conductivity and heat capacity are inputs to most finite element and analytical models for brakes.
		Thermal conductivity was calculated from K = a r Cp Thermal conductivity decreases with increasing temperature.
		Thermal diffusivity of all of the SiC Al-MMC's increases in response to aging.
	html.ornl.gov /tpuc/brakes.html (578 words)

	INSC: MatProp: UO2: Therm Cond
		If the assumption is made that the difference in thermal diffusivities between the thick and thin layers of UO in the experiment of Kim et al.
		If the thermal diffusivity was assumed to be constant, the thermal conductivity data of Tasman and the heat capacity of Ronchi et al.
		The uncertainty in the thermal conductivity and thermal diffusivity of liquid UO is approximately 40%, the uncertainty given by Tasman et al.
	www.insc.anl.gov /matprop/uo2/cond/liquid/wkliqm.php (3171 words)

	Bayerisches Geoinstitut - Annual Report 2000 Thermal diffusivity measurements of olivine and its polymorphs at high ...
		Thermal diffusivity measurements of olivine and its polymorphs at high pressure and temperature (Y.S. Xu, D.C. Rubie and F.
		Thermal diffusivity D increases with pressure and reciprocal thermal diffusivity is ordinarily proportional to temperature.
		However, the thermal diffusivity of ringwoodite might be similar to that of wadsleyite at the same pressure but so far we do not know pressure derivatives for either wadsleyite or ringwoodite.
	www.bgi.uni-bayreuth.de /annual_report/2000/c_22.phtml (474 words)

	The simultaneous measurement of thermal conductivity and thermal diffusivity. (Site not responding. Last check: 2007-10-19)
		The simultaneous measurement of thermal conductivity and thermal diffusivity.
		A fresh analysis of transient hot wire technique measure the thermal conductivity and thermal diffusivity of fluids is made.
		The reproducibility of the thermal conductivity data obtained is within 0.2% and the reproducibility is 2% for the thermal diffusivity.
	digitalcommons.hil.unb.ca /dissertations/AAINQ76362 (226 words)

	Libor Vozár and Tatiana Srámková: STEP HEATING METHOD FOR THERMAL DIFFUSIVITY MEASUREMENT
		The main advantage of the method is in insensitivity of the thermal diffusivity calculation on the temperature level before the step heating application (base line) and in independency of results on the disturbing of the data by a linearly rising or falling signal.
		The received values of thermal diffusivity gained using the OLS and LM together with the values given by NIST [8,9] are given in the table 1.
		The measurement of a temperature rise response curves in several different positions on rear face increases the precision of the radial thermal diffusivity estimation, which is in general strongly dependent on the knowledge of exact detector position, difficult to measure precisely.
	www.tpl.ukf.sk /engl_vers/imeko97/imeko97.htm (1939 words)

	MACSFR -- Report on Thermal Diffusivity of Tire Bales
		In order to model the effective measure of diffusivity for this non-homogeneous composite material, accurate accounts of thermal properties for both air and rubber, as well as the ratios of air and rubber in a generalized tire bale are necessary.
		Once thermal property values for the elements in the tires were found, conclusions were made about the effective thermal conductivity and specific heat of a tire.
		The thermal properties found for tires were then combined with the thermal properties of air in a ratio expression to evaluate effective thermal properties for the tire bale.
	www.mines.edu /Academic/courses/math_cs/macs370/FinalReports/tirebale (5386 words)

	The effect of fluids on thermal diffusivity of some magmatic rocks (Site not responding. Last check: 2007-10-19)
		Thermal transport properties of rocks are strongly affected by the presence or absence of a fluid phase.
		A new transient technique is described to measure thermal diffusivity of fluid bearing rocks.
		The observed increase in thermal transport properties by water in the examined samples varies between 100% (conductive transport) and 200% (convective/advective transport).
	www.gfz-potsdam.de /pb4/pg1/people/schillingabstracts/theeffect.html (84 words)

	[No title] (Site not responding. Last check: 2007-10-19)
		A pulsed heat source obtained by flash lamps was used to heat one side of the sample, while the temperature response of the opposite surface was monitored by an infrared camera.
		The diffusivity evaluation is corrected based on FEA results, due to that the brakes have two steps in axial direction.
		The resulting through-thickness thermal diffusivity value is then compared with the value measured by conventional method carried out on the samples cut from the same brake pad.
	www.sem.org /APP-CONF-AC-List2-Abstract.asp?PaperNo=195 (200 words)

	A Transient Technique to Measure Thermal Diffusivity at Elevated Temperatures (Site not responding. Last check: 2007-10-19)
		A transient technique is presented to measure the thermal diffusivity of different solid materials between room temperature and 1000°C. A temperature signal is transferred from a filament to the front surface of the sample and detected with a thermocouple near the front surface.
		With given thermal diffusivities hypothetical curves are calculated with a finite-difference scheme.
		The thermal diffusivity of the finite-difference scheme is varied systematically to obtain an optimum fit between hypothetical and measured equilibration behavior.
	www.gfz-potsdam.de /pb4/pg1/people/schillingabstracts/transtech.html (233 words)

	Thermal diffusivity
		Thermal diffusivity is the thermal response of material derived from transient heat flow conditions.
		The thermal diffusivity may be determined knowing the density and specific heat.
		The initial temperature of the specimen is accurately controlled and a thermocouple or similar temperature measuring device attached to the rear face of the specimen or an infrared sensor measures the resulting rear face temperature rise after a thermal flash.
	www.rapra.net /vircon/4_2_6.asp (156 words)

	Measurement of Thermal Diffusivity by Lock-in Thermography (Site not responding. Last check: 2007-10-19)
		One-dimensional or multi-dimensional diffusivity values are recovered, by means of experimental data processing in time or frequency domain.
		Because average temperature of the surface is equal to the environment, a permanent thermal regime is reached very soon.
		A matematical simulation of the thermal process is a tool for a deeper investigation of the testing techniques in order to apply it in situ.
	www.univ-reims.fr /Labos/LEO/Qirt_2000/docs/1-4Bison.htm (407 words)

	Thermal diffusivity
		The thermal diffusion is expected to play an important role in determining the crystal growth morphology and the nature of crystalline defects, which may be generated by thermal stress during growth.
		The measurements for the thermal diffusivity a will investigate the anisotropy and explore the temperature dependence for crystal.
		Measurement for thermal diffusivity was performed on single crystal samples using the flash pulse method.
	www.fisk.edu /~aburger/Published03_06/Measurement_/Thermal/Thermal_diffusivity/thermal_diffusivity.html (207 words)

	Technical Note 68: Thermal Diffusivity by the Flash Method
		The higher the thermal diffusivity, the faster the heat propagation.
		The thermal diffusivity is related to the thermal conductivity
		The thermal diffusivity is then determined from this thermogram.
	www.anter.com /TN68.htm (483 words)

	Physics Department, Trinity College Dublin, PhD Theses
		Parameters such as the thermal diffusivity, melt threshold and reflectivity are important for understanding the thermal processes that occur when a sample is irradiated by a pulsed laser.
		Using the flash method for determining the the thermal diffusivity, measurements were performed on samples both at room temperature and at elevated temperatures.
		At elevated temperatures the diffusivity is observed to decrease with increasing temperature in both types of samples.
	www.tcd.ie /Physics/Research/Mag/mmclough.html (607 words)

	Thermal diffusivity -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-19)
		Thermal diffusivity -- Facts, Info, and Encyclopedia article
		In (Click link for more info and facts about heat transfer) heat transfer analysis, thermal diffusivity (symbol:) is the ratio of (Click link for more info and facts about thermal conductivity) thermal conductivity to (Click link for more info and facts about heat capacity) heat capacity.
		Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their thermal 'bulk'.
	www.absoluteastronomy.com /encyclopedia/t/th/thermal_diffusivity.htm (79 words)

	[No title]
		Background Thermal and molecular diffusivity measure the rates by which heat and particles, respectively, are conducted or dispersed through a convective medium.
		In the trials for determination of molecular diffusivity, the tube of smallest diameter, Tube 3, showed the most accurate data for D. This, however, was not the case for the thermal trials that data for which can be seen in Table 7.
		The standard deviations for both thermal and molecular diffusivity, however, are greater than their respective means, indicating a wide spread of data that yielded inconclusive results.
	www.seas.upenn.edu /courses/belab/LabProjects/2000/be310s00m2.doc (5005 words)

	3.2 Validation of Methods
		In order to test the methods for inverse determination of the soil apparent thermal diffusivity, idealised temperature data are generated for a period of 20 days.
		Experiment 1 and 2 both suggest that the DPM1 and DNM are not suitable for determination of apparent thermal diffusivities of the soil.
		The apparent thermal diffusivity of the soil affects the amount of damping and phase shifting with depth of diurnal temperature waves.
	www.iac.ethz.ch /staff/fuhrer/publ/dipl/node13.html (2443 words)

	Diamond Burs and Dentin Thickness Effects on Dentin Thermal Diffusivity (Site not responding. Last check: 2007-10-19)
		Objective: The objective of this study was to evaluate the effect of bur type and remaining dentin thickness (DT) on thermal diffusivity of dentinal tissues during high-speed tooth preparation.
		Bur type, DT and thermal diffusivity (Joules/sec) were applied to least-squares estimation.
		Thermal diffusivity caused by burs is shown in table.
	iadr.confex.com /iadr/2005Balt/techprogram/abstract_59956.htm (324 words)

	Thermal diffusivity - Wikipedia, the free encyclopedia
		In heat transfer analysis, thermal diffusivity (symbol: α) is the ratio of thermal conductivity to volumetric heat capacity.
		k is thermal conductivity (SI units: watts per metre-kelvin)
		The SI units for thermal diffusivity are square metres per second or m²/s.
	www.wikipedia.org /wiki/Diffusivity (107 words)

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