Thermal Diffusivity Estimation in a Picosecond Photoreflectance Experiment

2006 ◽  
Vol 129 (6) ◽  
pp. 756-758 ◽  
Author(s):  
Jean-Luc Battaglia ◽  
Andrzej Kusiak ◽  
Jean-Christophe Batsale
Keyword(s):  
Heat Flux ◽  
Thermal Diffusivity ◽  
Impulse Response ◽  
Probe Beam ◽  
Pump Beam ◽  
Asymptotic Behaviors ◽  
Analytical Expression ◽  
Incident Heat Flux ◽  
Average Temperature

The aim of this work is to provide an analytical expression for the thermal diffusivity of a material in the configuration of the picosecond photoreflectance experiment. It is shown that the thermal diffusivity can be estimated from the absorption depth of the pump beam together with the probe beam as well as the time when the two asymptotic behaviors of the impulse response cross. Thereby, it is not required to measure absolute values of incident heat flux and average temperature on the aiming area.

Thermal Expansion-Recovery Microscopy (ThERM) for microstructural characterization

2013 ◽  
Vol 1526 ◽  
Author(s):  
Esteban A. Domené ◽  
Nélida Mingolo ◽  
Oscar E. Martínez
Keyword(s):  
Thermal Expansion ◽  
Thermal Diffusivity ◽  
Probe Beam ◽  
Pump Beam ◽  
Surface Deformation ◽  
Modulation Frequency ◽  
Microstructural Characterization ◽  
Sample Surface ◽  
Beam Size ◽  
Detection Schemes

ABSTRACTIn this work we compare two different detection schemes that are sensitive to the focus shift of a probe beam due to induced surface curvature. The technique on which both detection schemes are based is called ThERM (Thermal Expansion-Recovery Microscopy) and allows the retrieval of the thermal diffusivity at microscopic levels, hence mapping such magnitude over a sample surface. The induced thermal expansion defocuses the probe beam due to the surface deformation (curvature). The dependence of the defocusing with the pump modulation frequency yields the thermal diffusivity of the sample at the impinging location. The explored depth is controlled by the pump beam size. By scanning both beams, a complete map of the thermal diffusivity can be retrieved.

Pump-Probe Measurements Using Silicon Nanocrystal Waveguides

2003 ◽  
Vol 770 ◽  
Author(s):  
Nathanael Smith ◽  
Max J. Lederer ◽  
Marek Samoc ◽  
Barry Luther-Davies ◽  
Robert G. Elliman
Keyword(s):  
Probe Beam ◽  
Time Resolution ◽  
Pump Beam ◽  
Silicon Nanocrystals ◽  
Continuous Wave ◽  
Optical Gain ◽  
Optical Pump ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Measurements

AbstractOptical pump-probe measurements were performed on planar slab waveguides containing silicon nanocrystals in an attempt to measure optical gain from photo-excited silicon nanocrystals. Two experiments were performed, one with a continuous-wave probe beam and a pulsed pump beam, giving a time resolution of approximately 25 ns, and the other with a pulsed pump and probe beam, giving a time resolution of approximately 10 ps. In both cases the intensity of the probe beam was found to be attenuated by the pump beam, with the attenuation increasing monotonically with increasing pump power. Time-resolved measurements using the first experimental arrangement showed that the probe signal recovered its initial intensity on a time scale of 45-70 μs, a value comparable to the exciton lifetime in Si nanocrystals. These data are shown to be consistent with an induced absorption process such as confined carrier absorption. No evidence for optical gain was observed.

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

Autoignition of solid combustibles subjected to a uniform incident heat flux: The effect of distance from the radiation source

2011 ◽  
Vol 158 (5) ◽  
pp. 1015-1017 ◽  
Author(s):  
Yang Lizhong ◽  
Zhou Yupeng ◽  
Wang Yafei ◽  
Dai Jiakun ◽  
Deng Zhihua ◽  
...  
Keyword(s):  
Heat Flux ◽  
Radiation Source ◽  
Incident Heat Flux
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