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Effect of duty cycle on photothermal phenomenon – a thermal lens study
Mohanachandran Nair Sindhu Swapna, 2019, izvirni znanstveni članek

Ključne besede: Photothermal phenomena Thermal lens technique Optical chopper Duty cycle variation
Objavljeno v RUNG: 05.07.2022; Ogledov: 1367; Prenosov: 0
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Time series analysis of duty cycle induced randomness in thermal lens system
Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: The present work employs time series analysis, a proven powerful mathematical tool, for investigating the complex molecular dynamics of the thermal lens (TL) system induced by the duty cycle (C) variation. For intensity modulation, TL spectroscopy commonly uses optical choppers. The TL formation involves complex molecular dynamics that vary with the input photothermal energy, which is implemented by varying the duty cycle of the chopper. The molecular dynamics is studied from the fractal dimension (D), phase portrait, sample entropy (S), and Hurst exponent (H) for different duty cycles. The increasing value of C is found to increase D and S, indicating that the system is becoming complex and less deterministic, as evidenced by the phase portrait analysis. The value of H less than 0.5 conforms the evolution of the TL system to more anti-persistent nature with C. The increasing value of C increases the enthalpy of the system that appears as an increase in full width at half maximum of the refractive index profile. Thus the study establishes that the sample entropy and thermodynamic entropy are directly related.
Ključne besede: Time series analysis Fractal analysis Photothermal lens spectroscopy Fractal dimension Hurst exponent Sample entropy
Objavljeno v RUNG: 05.07.2022; Ogledov: 1498; Prenosov: 0
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17.
Thermal diffusivity downscaling of molybdenum oxide thin film through annealing temperature-induced nano-lamelle formation: a photothermal beam deflection study
S. Soumya, Vimal Raj, Mohanachandran Nair Sindhu Swapna, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek

Opis: The present work proposes a method of downscaling the thermal diffusivity (α) of MoO3 thin films through annealing temperature-induced nano-lamelle formation. The thermal diffusivity modification of the MoO3 films, prepared by the doctor blade method, is investigated by the sensitive transverse photothermal beam deflection technique. The X-ray diffraction analysis confirms the structural phase transformation from monoclinic to orthorhombic in the films annealed from 300 to 450 °C. The thermal induced anisotropy of the film is evident from the variation of the morphology index and texture coefficient. The field emission scanning electron microscopic analysis unveils the morphology modifications from blocks to the nano-lamelle structure with layers of average thickness ~ 77 nm. The thermal diffusivity measurement reveals a 53% reduction upon annealing the film to 450 °C. The drastic reduction is achieved through the annealing temperature-induced nano-lamelle formation and the phase transformation from monoclinic to orthorhombic in the MoO3 films.
Ključne besede: thermal diffusivity, molybdenum oxide, thin film, nano-lamelle, photothermal beam deflection
Objavljeno v RUNG: 04.07.2022; Ogledov: 1421; Prenosov: 26
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18.
Thermal diffusivity of molybdenum oxide nanowire film: a photothermal beam deflection study
Mohanachandran Nair Sindhu Swapna, 2021, izvirni znanstveni članek

Opis: The paper reports the preparation of thin film with MoO3 nanowires (NWs) by the doctor blade method and the study of its thermal diffusivity (α) by the sensitive photothermal beam deflection (PTD) method. When the Field Emission Scanning Electron Microscopic and Atomic Force Microscopic analysis unveil its morphology as NW bundles, the X-ray diffraction analysis reveals the structure to be orthorhombic. The NWs formed are of diameter ~ 20 nm and length up to 5 μm. The standardization of the transverse PTD setup is done by determining the value of α of iron, which agrees well with literature reports. The thermal diffusivity of MoO3 NW film is obtained as 0.0036 cm2 /s, which is 9.48% of its bulk counterpart. The reduction in the thermal diffusivity of NW makes it a suitable candidate for thermoelectric applications.
Ključne besede: Nanowires Molybdenum oxide Photothermal beam deflection Thermal diffusivity
Objavljeno v RUNG: 04.07.2022; Ogledov: 1501; Prenosov: 0
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Soot effected sample entropy minimization in nanofluid for thermal system design : a thermal lens study
Mohanachandran Nair Sindhu Swapna, Vimal Raj, K. Satheesh Kumar, Sankaranarayana Iyer Sankararaman, 2020, izvirni znanstveni članek

Opis: The present work suggests a method of improving the thermal system efficiency, through entropy minimisation, and unveils the mechanism involved by analysing the molecular/particle dynamics in soot nanofluids (SNFs) using the time series, power spectrum, and wavelet analyses of the thermal lens signal (TLS). The photothermal energy deposition in the SNF lowers the refractive index due to the temperature rise. It triggers the particle dynamics that are investigated by segmenting the TLS and analysing the refractive index, phase portrait, fractal dimension (D), Hurst exponent (H), and sample entropy (SampEn). The wavelet analysis gives information about the relation between the entropy and the frequency components. When the phase portrait analysis reflects the complex dynamics from region 1 to 2 for all the samples, the SampEn analysis supports it. The decreasing value of D (from 1.59 of the base fluid to 1.55 and 1.52) and the SampEn (from 1.11 of the base fluid to 0.385 and 0.699) with the incorporation of diesel and camphor soot, indicate its ability to lower the complexity, randomness, and entropy. The increase of SampEn with photothermal energy deposition suggests its relation to the thermodynamic entropy (S). The lowering of thermal diffusivity value of the base fluid from 1.4 × 10−7 m2/s to 1.1 × 10−7 and 0.5 × 10−7 m2 /s upon diesel and camphor soot incorporation suggests the heat-trapping and reduced molecular dynamics in heat dissipation.
Ključne besede: soot, entropy, thermal system, photothermal, time series, nanofluid, fractal
Objavljeno v RUNG: 30.06.2022; Ogledov: 1485; Prenosov: 0
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