Abstract
Modulated heat transfer in air subject to pressures from 760 Torr to 10-4 Torr is experimentally studied by means of a thermal-wave resonant cavity placed in a vacuum chamber. This is done through the analysis of the amplitude and phase delay of the photothermal signal as a function of the cavity length and pressure through of the Knudsen’s number. The viscous, transitional, and free molecular regimes of heat transport are observed for pressures P>1.5 Torr, 25 mTorr<P<1.5 Torr, and P<25 mTorr; respectively. It is shown that the fingerprint of each regime is determined by the concavity of the amplitude decay in a length scan, which is concave upward for the viscous regime and concave downward in the free molecular one. Furthermore, the increase of the radiative contribution on both the amplitude and phase is also observed as the pressure reduces. The obtained results show that the proposed methodology can be used to study the molecular dynamics in gases supporting diffusive and ballistic heat transport.
Highlights
Diffusive-to-ballistic transition of heat transport in micro- and nanostructures is an active research area of increasing interest, because of its many potential implications on both fundamental and technological applications
The thermal-wave resonant cavity (TWRC) consists of three parallel layers: the first one is a thin film called heater, which is heated up with a laser beam of modulated intensity; while the second one is a fluid sample supporting the propagation of the temperature oscillations induces by the heater towards the pyroelectric detector that records the amplitude and phase delay of the thermal-wave signal, in the form of a voltage
For example l = 34μm, the heat transfer is in the transitional regime at L
Summary
Diffusive-to-ballistic transition of heat transport in micro- and nanostructures is an active research area of increasing interest, because of its many potential implications on both fundamental and technological applications. The TWRC consists of three parallel layers: the first one is a thin film called heater, which is heated up with a laser beam of modulated intensity; while the second one is a fluid sample supporting the propagation of the temperature oscillations induces by the heater towards the pyroelectric detector (third layer) that records the amplitude and phase delay of the thermal-wave signal, in the form of a voltage These two signals have been theoretically modeled taking into account the pure heat diffusion,[15,16] and the contribution of heat radiation from the heater to the detector.[17,18,19,20] Previous experimental works[22,23,24] reported that the thermal diffusivity
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