Thermal diflusivity

The Prandtl number is the ratio of the kinematic viscosity (i.e., the momentum diffusivity) to the thermal diflusivity. Because the Schmidt number is analogous to the Prandtl number, one would expect that Sc is the ratio of the momentum diffusivity (i.e., the kinematic viscosity), v, tothe mass diffusivity Dab- Indeed, this is true ... 

When a temperature difference is to be equalized inside a body, its heat capacity is another property which affects the process. This quantity is included in the so-called thermal diflusivity a which has the dimension (cm s ) ... 

The theoretical anatysis is performed two-dimensionafly, assuming that the acoustic wave is not infliKnced by the finite length of the sample cell (see Fig, 2). Another simplification results from the fact that the thermal diflusion can be neglected. 

Prandtl number (iV) - A dimensionless quantity used in fluid mechanics, defined by Pr = T /pa, where T is viscosity, p is density, and a is thermal diflusivity. [2]... 

B. Weidenfeller, M. Hofer, F.R. Schilling, Thermal conductivity, thermal diflusivity, and specific heat capacity of particle filled polypropylene. Compos. Part A Appl. Sci. Manuf. 35, 423-29 (2004)... 

Thermal diflusivity is a measure of the rate at which a material changes temperature when the temperature of its surroundings changes. The thermal diflusivity, h, is the ratio of thermal conductivity, k, and the product of specific heat, c, and density,... 

S. B. Lang, Tbehnique for the raeasuremcot of thermal diflusivity based on the laser intensity modulation method (UMM). Fenoelectrics 93 87 (1969X... 

The so called pulse and/or stepwise transient methods [622,623] are found beneficial where the thermophysical parameters can be jointly found from the temperature function and the temperature response upon the thermal disturbance applied to the measured sample. The specimen consists of three parts, see Fig. 79, where the planar heat source is clamped between the first and the second parts. The heat pulse is produced by the Joule heat effect in a planar electrical resistor and the temperature response is scanned by thermocouples to distinguish the transient temperature, T(h,t) where h is the sample separating distance and t is the observation time. The standard one-point evaluation procedure considers a maximum of the temperature response for calculation of the thermophysical parameters involved, namely, the specific heat, Cp = Q/V(2jrephTm), thermal diflusivity, q = h /2tm and thermal conductivity, A = Qh/(2V 2jietmT,n where Tm is the maximum of temperature response at the allied time tm and e denotes the Euler number and p density. A simplified but useful industrial modification is called the hot ball method [623] and is based on the combined generation of the heat flux (within the ball skeleton attached to the measured specimen) from an interior point-heat-source upon a simultaneous sensing the temperature by a thermometer placed parallel in the center of the heat source. 

The infrared absorption coefficient and thermal wave decay coefficients, a(v) and flj, respectively, determine the magnitude of the photoacoustic signal. The term ot( exp —[a( +fls]x in the expression for temperature oscillation leads to a linear PA signal dependence on infrared absorption when a( thermal wave decay length, L, although it is sometimes referred to as the sampling depth, penetration depth, or thermal diflusion depth. The sample layer extending a distance L beneath the surface contributes... 

It is most probable that the crystallization proceeds in the quenching period from temperature of melt to the pre-determined Tc for Tc < 100° C before the isothemial temperature is reached. The liquid with hi er thermal diflusivity e.g. water cools the sample more rapidly than the liquid with lower diffiisivity e.g. silicon oil. Consequently the difference between the actual and pre-determined Tc for samples quenched in water is lower than that for samples quenched in silicon oil. It is clear from Fig. 1 that a rapid decrease of the K value with decreasing Tc started at 80° C for samples quenched in water. Considering the results of Varga the estimated lower critical temperature limit lies between 80 and 100°C. 

Specific heat Thermal conductivity Thermal diflusivity Solubility parameter Polymer-Solvent interaction parameter (25-30°C)... 

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