Thermal waves in materials with inhomogeneous thermal conductivity: An analytical approach

1996 ◽  
Vol 79 (5) ◽  
pp. 2225-2228 ◽  
Author(s):  
J. Fivez ◽  
J. Thoen
Keyword(s):  
Thermal Conductivity ◽  
Analytical Approach ◽  
Thermal Waves

Steady State Heat Transfer Within a Nanoscale Spatial Domain

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Kirill V. Poletkin ◽  
Vladimir Kulish
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Spatial Domain ◽  
Thermal Waves ◽  
Steady State Heat ◽  
Steady State Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper, we study the steady state heat transfer process within a spatial domain of the transporting medium whose length is of the same order as the distance traveled by thermal waves. In this study, the thermal conductivity is defined as a function of a spatial variable. This is achieved by analyzing an effective thermal diffusivity that is used to match the transient temperature behavior in the case of heat wave propagation by the result obtained from the Fourier theory. Then, combining the defined size-dependent thermal conductivity with Fourier’s law allows us to study the behavior of the heat flux at nanoscale and predict that a decrease of the size of the transporting medium leads to an increase of the heat transfer coefficient which reaches its finite maximal value, contrary to the infinite value predicted by the classical theory. The upper limit value of the heat transfer coefficient is proportional to the ratio of the bulk value of the thermal conductivity to the characteristic length of thermal waves in the transporting medium.

The Effect of Thermal Waves on Heat Transfer Enhancement in Nanofluid Suspensions

2008 ◽  
Author(s):  
Johnathan J. Vadasz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Transfer Enhancement ◽  
Hyperbolic Heat Conduction ◽  
Thermal Waves ◽  
Transfer Enhancement ◽  
Scale Level ◽  
Macro Scale ◽  
Wave Effects

The spectacular heat transfer enhancement revealed experimentally in nanofluids suspensions is being investigated theoretically at the macro-scale level aiming at explaining the possible mechanisms that lead to such impressive experimental results. In particular, the anticipation that thermal wave effects via hyperbolic heat conduction could have been the source of the excessively improved effective thermal conductivity of the suspension is shown to be impossible.

scholarly journals Structure Function Analysis of Temperature-Dependent Thermal Properties of Nm-Thin Nb2O5

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 610
Author(s):  
Lisa Mitterhuber ◽  
Elke Kraker ◽  
Stefan Defregger
Keyword(s):  
Thermal Conductivity ◽  
Structure Function ◽  
Time Domain ◽  
Analytical Approach ◽  
Function Analysis ◽  
Numerical Approach ◽  
Probe Laser ◽  
Laser Technique ◽  
Ambient Temperatures ◽  
Thermal Transients

A 166-nm-thick amorphous Niobium pentoxide layer (Nb2O5) on a silicon substrate was investigated by using time domain thermoreflectance at ambient temperatures from 25 °C to 500 °C. In the time domain thermoreflectance measurements, thermal transients with a time resolution in (sub-)nanoseconds can be obtained by a pump-probe laser technique. The analysis of the thermal transient was carried out via the established analytical approach, but also by a numerical approach. The analytical approach showed a thermal diffusivity and thermal conductivity from 0.43 mm2/s to 0.74 mm2/s and from 1.0 W/mK to 2.3 W/mK, respectively to temperature. The used numerical approach was the structure function approach to map the measured heat path in terms of a RthCth-network. The structure function showed a decrease of Rth with increasing temperature according to the increasing thermal conductivity of Nb2O5. The combination of both approaches contributes to an in-depth thermal analysis of Nb2O5 film.

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