21. Development of Zinc Oxide-Multi-Walled Carbon Nanotube hybrid nanofluid for energy-efficient heat transfer application: A thermal lens studyMohanachandran Nair Sindhu Swapna, 2021, original scientific article Abstract: This paper addresses the need for developing an energy-efficient hybrid nanofluid with zinc oxide–multi-walled carbon nanotube (ZnO-MWCNT) for overcoming the bottleneck of efficient heat transfer in thermal systems. The concentration-dependent thermal diffusivity modifications are analyzed using the highly sensitive mode mismatched thermal lens technique. The hybrid composite is prepared by the solid-state mixing and annealing of a pure multi-walled carbon nanotube (MWCNT) and zinc oxide (ZnO), synthesized by the solution combustion method. The composite formation is studied by structural, morphological, and optical characterization techniques. Among the three nanofluids ZnO, MWCNT, and ZnO-MWCNT, the composite exhibits a drastic enhancement in thermal diffusivity at a lower solid volume fraction of 0.047 mg/ml containing 0.009 mg/ml of MWCNT. All the nanofluids show an optimum concentration beyond which the thermal diffusivity decreases with the nanoparticle concentration. Thus, this study suggests the potential application of ZnO-MWCNT hybrid nanofluids in thermal system design to enhance internal combustion engines' efficiency during cold-start.
Keywords: Zinc Oxide, MWCNT, hybrid nanofluid, thermal lens, diffusivity, engine efficiency
Published in RUNG: 30.06.2022; Views: 2689; Downloads: 0
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22. Pharmacological application of thermal Lens technique - A thermal diffusivity studyMohanachandran Nair Sindhu Swapna, 2018, original scientific article Abstract: The photothermal phenomenon has emerged as a potential tool for the nondestructive evaluation of thermal and optical properties of materials. Thermal analysis of drugs is an unavoidable part of preformulation study, as temperature variations can induce structural changes of the constituents of drugs. Techniques based on photothermal phenomena are highly sensitive, as only the absorbed radiation contributes to the signal. Periodic illumination and subsequent nonradiative de-excitation generate thermal lens signals of various types within and around the sample. Variation of thermal diffusivity with a concentration of the commonly used drug terbutaline is studied through the single-beam thermal lens technique. The ultraviolet–visible spectrum of the drug shows strong absorption around 500 nm, which suggests the possible wavelengths that can be used for the study. It is found that concentration of the drug in liquid form decides its thermal stability, as its thermal diffusivity varies with concentration. The study gives information about the optimum value for the concentration of the drug noted above for which the chance of thermal stability is high.
Keywords: thermal lens, thermal diffusivity, pharmacology, drug
Published in RUNG: 30.06.2022; Views: 1949; Downloads: 0
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23. Weathering induced morphological modification on the thermal diffusivity of natural pyrrhotite : a thermal lens studyMohanachandran Nair Sindhu Swapna, Vijayakumar Gokul, Vimal Raj, R. Manu Raj, S. N. Kumar, Sankaranarayana Iyer Sankararaman, 2021, original scientific article Abstract: Natural pyrrhotites have gained significant attention due to
their interesting electronic, antimicrobial, and chemical
properties. The present work attempts to explore the
morphology-induced modifications in the thermal
characteristics of natural pyrrhotite due to ageing. The
morphological, elemental, structure, optical, and thermal
characterisations help in understanding the effect of
ageing. The effects of five years of ageing of the sample
are (i) Field Emission Scanning Electron Microscopic
analysis reveals a morphological transformation from flakes
to agglomerated powder, (ii) elemental analyses suggest
the ageing induced compositional modification (iii) the
Tauc plot analysis shows a bandgap energy modification
from 1.46 eV to 1.92 eV, (iv) X-ray Diffraction (XRD), Fourier
Transform Infrared, and X-ray photoelectron spectroscopic
studies affirm the formation of oxy-hydroxides (v) the XRD
data indicates an increase of dislocation density, and (vi)
Photoluminescence study shows a deep violet emission
evidenced through the CIE plot. The study by the thermal
lens technique shows a lowering of thermal diffusivity
study by 23%, due to the morphological modifications,
adsorbed/chemisorbed hydroxyl groups, and the formation
of secondary compounds due to oxidation and weathering.
The phonon boundary scattering, weathering induced
smaller grain size, reduced phonon mean free path, and
point defects also account for the lowering of the thermal
diffusivity value and thereby influencing its properties.
Keywords: pyrrhotite, thermal diffusivity, thermal lens, ageing, morphology
Published in RUNG: 30.06.2022; Views: 2102; Downloads: 7
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24. Investigations of the Thermal Parameters of Hybrid Sol–Gel Coatings Using Nondestructive Photothermal TechniquesŁukasz Chrobak, Dorota Korte, Hanna Budasheva, Miroslaw Malinski, Peter Rodič, Ingrid Milošev, Sylwia Janta-Lipińska, 2022, original scientific article Keywords: hybrid sol–gel coatings, non-destructive testing, photothermal radiometry, photothermal beam deflection spectrometry, thermal diffusivity, thermal conductivity
Published in RUNG: 03.06.2022; Views: 2901; Downloads: 36
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25. Through-plane and in-plane thermal diffusivity determination of graphene nanoplatelets by photothermal beam deflection spectrometryHumberto Cabrera, Dorota Korte, Hanna Budasheva, Behnaz Abbasgholi N. Asbaghi, Stefano Bellucci, 2021, original scientific article Abstract: In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding
sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry.
Two experimental methods were employed in order to observe the effect of load pressures
on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was
determined by the use of a slope method supported by a new theoretical model, whereas the
through-plane thermal diffusivity was determined by a frequency scan method in which the obtained
data were processed with a specifically developed least-squares data processing algorithm.
On the basis of the determined values, the in-plane and through-plane thermal conductivities and
their dependences on the values of thermal diffusivity were found. The results show a significant
difference in the character of thermal parameter dependence between the two methods. In the case
of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the
increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity
increases with an increase in thermal diffusivity for the whole range of the loading pressure used.
This behavior is due to the dependence of heat propagation on changes introduced in the graphene
nano-platelets structure by compression.
Keywords: graphene nanoplatelets, thermal diffusivity, thermal conductivity, photothermal spectrometry
Published in RUNG: 30.11.2021; Views: 3079; Downloads: 72
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