Article ID Journal Published Year Pages File Type
668699 International Journal of Thermal Sciences 2014 12 Pages PDF
Abstract

•The damping of the thermal waves was studied quantitatively.•The damping level and damping factor were defined to evaluate the damping.•The damping factor is a characteristic number for the damping process.•The damping level of the heat flux is a good evaluation for the damping.•The damping process satisfies the exponential relationship in most situations.

The damping levels of the temperature and heat flux (ɛT, ɛq) and the damping factor (ξ) were defined for evaluating and determining the damping of the thermal waves predicted by the Cattaneo–Vernotte (CV), dual-phase-lagging (DPL), and thermomass (TM) models. Numerical analyses were performed in terms of the three models. The damping level of the heat flux, instead of the temperature, is found to be a better evaluation factor because the heat flux is directly related to the energy transported by the thermal wave while the temperature can be also affected by the thermal properties. The damping factor ξ  (L/ατ) represents the ratio of the time that the thermal wave needs to travel the distance L   to the relaxation time, or 3 times of the reciprocal of the Knudsen number, where L is the travelling distance of the thermal wave, α is the thermal diffusivity, and τ is the relaxation time. For the sharp thermal waves predicted by the CV and simplified TM models, the damping factors ξCV and ξTM can be the characteristic numbers that has a decisive impact on the damping level of the heat flux. But if both including the sharp and blunt thermal waves, the increase of overdamped cases under the blunt thermal wave situation will lead to the deviation for the characteristic numbers. For the sharp thermal waves predicted by the DPL and TM models, the damping factors ξDPL and ξTM cannot be the characteristic numbers, which is due to the impacts on the propagation speed of the thermal wave and its heat diffusion caused by the inertia term of the temperature gradient to time for the DPL model, and the inertia term of the temperature to time and nonlocal terms for the TM model, respectively. For the thermal waves predicted by the CV and simplified TM models, their propagation processes satisfy the exponential damping relationship in most situations, with the deviation occurring only when the overdamped cases play a major role and the thermal waves stay at the primary stage. Besides, the sharp and blunt thermal waves predict different slopes of −ln(1 − ɛq) to the damping factor ξ. If the thermal wave is sharper, the overdamped cases are fewer, and therefore the corresponding slope of −ln(1 − ɛq) to ξ is closer to 0.5. The studies are expected to help not only understand the thermal wave behaviours but also carry out experimental investigations and engineering evaluations.

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Related Topics
Physical Sciences and Engineering Chemical Engineering Fluid Flow and Transfer Processes
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