This study investigates the impact of incorporating TiOsub.2 nanoparticles into two types of oils at different temperatures and with varying volume fractions: transformer oil (NYTRO LIBRA) and virgin ...coconut oil (manufactured by Govi Aruna Pvt. Ltd., Gampaha, Sri Lanka). The nanofluids were prepared using a two-step method by adding CTAB (cetyltrimethylammonium bromide) surfactant. To minimize nanoparticle agglomeration, this study employed relatively low-volume fractions. Thermal properties by means of thermal conductivity, thermal diffusivity, and volumetric heat capacity were measured in accordance with ASTM (American Society for Testing and Materials) standard methods using a multifunctional thermal conductivity meter (LAMBDA thermal conductivity meter). The measured thermal conductivity values were compared with theoretical models and previous research findings. It was confirmed that the modification of thermal properties was enhanced by doping TiOsub.2 nanoparticles with different volume fractions.
In this research, the effects of using nanofluid as a coolant on the thermal and electrical efficiencies of a PV/T (photovoltaic thermal unit) are experimentally studied. Coolant fluids in the ...experiments are pure water and silica (SiO2)/water nanofluid 1% and 3% by weight (wt%). A brief uncertainty analysis is performed which shows that the measurements are sufficiently accurate. By converting the output electrical energy of the PV/T system into an equivalent thermal energy, it is found that the overall energy efficiency for the case with a silica/water nanofluid of 1 wt% is increased by 3.6% compared to the case with pure water. When using the silica/water nanofluid of 3 wt%, however, the increase is 7.9%. The thermal efficiency of the PV/T collector for the two cases of 1 wt% and 3 wt% of silica/water nanofluids are increased by 7.6% and 12.8%, respectively. The total exergy of the PV/T system, with and without nanofluids, is also compared with that of the PV system with no collector. It is observed that by adding a thermal collector to a PV system, the total exergy for the three cases with pure water, 1 wt% silica/water nanofluid, and 3 wt% silica/water nanofluid is increased by 19.36%, 22.61% and 24.31%, respectively.
•The effects of adding nanofluids as a coolant on a PV/T system are investigated.•Experiments are performed on SiO2/water nanofluids (1 wt % and 3 wt %).•The system is analyzed from both energetic and exergetic viewpoints.•Adding nanofluids to the PV/T system increased overall efficiency up to 7.9%.•Total exergy of the PV/T system with nanofluids was increased up to 24.31%.
We report the temperature‐dependent Raman spectra of single‐ and few‐layer MoSe2 and WSe2 in the range 77–700 K. We observed linear variation in the peak positions and widths of the bands arising ...from contributions of anharmonicity and thermal expansion. After characterization using atomic force microscopy and high‐resolution transmission electron microscopy, the temperature coefficients of the Raman modes were determined. Interestingly, the temperature coefficient of the A22u mode is larger than that of the A1g mode, the latter being much smaller than the corresponding temperature coefficients of the same mode in single‐layer MoS2 and of the G band of graphene. The temperature coefficients of the two modes in single‐layer MoSe2 are larger than those of the same modes in single‐layer WSe2. We have estimated thermal expansion coefficients and temperature dependence of the vibrational frequencies of MoS2 and MoSe2 within a quasi‐harmonic approximation, with inputs from first‐principles calculations based on density functional theory. We show that the contrasting temperature dependence of the Raman‐active mode A1g in MoS2 and MoSe2 arises essentially from the difference in their strain–phonon coupling.
Special effects in 2D: The temperature‐dependent Raman spectra of single‐ and few‐layer MoSe2 and WSe2 in the 77–700 K range are reported. Linear variation is observed in the peak positions and widths of the bands arising from contributions of anharmonicity and thermal expansion.
Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays ...an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction.
The problem of natural convective boundary-layer flow of a nanofluid past a vertical plate is revisited. The model, which includes the effects of Brownian motion and thermophoresis, is revised so ...that the nanofluid particle fraction on the boundary is passively rather than actively controlled. In this respect the model is more realistic physically than that employed by previous authors.
•The problem of natural convective boundary-layer flow of a nanofluid past a vertical plate is revisited.•The model is revised so that the nanofluid particle fraction on the boundary is passively rather than actively controlled.•The model is more realistic physically than that employed by previous authors.
Heat transfer and fluid flow due to buoyancy forces in a partially heated enclosure using nanofluids is carried out using different types of nanoparticles. The flush mounted heater is located to the ...left vertical wall with a finite length. The temperature of the right vertical wall is lower than that of heater while other walls are insulated. The finite volume technique is used to solve the governing equations. Calculations were performed for Rayleigh number (10
3
⩽
Ra
⩽
5
×
10
5), height of heater (0.1
⩽
h
⩽
0.75), location of heater (0.25
⩽
y
p
⩽
0.75), aspect ratio (0.5
⩽
A
⩽
2) and volume fraction of nanoparticles (0
⩽
φ
⩽
0.2). Different types of nanoparticles were tested. An increase in mean Nusselt number was found with the volume fraction of nanoparticles for the whole range of Rayleigh number. Heat transfer also increases with increasing of height of heater. It was found that the heater location affects the flow and temperature fields when using nanofluids. It was found that the heat transfer enhancement, using nanofluids, is more pronounced at low aspect ratio than at high aspect ratio.
The boundary layer flow induced in a nanofluid due to a linearly stretching sheet is studied numerically. The transport equations include the effects of Brownian motion and thermophoresis. Unlike the ...commonly employed thermal conditions of constant temperature or constant heat flux, the present study uses a convective heating boundary condition. The solutions for the temperature and nanoparticle concentration distributions depend on five parameters, Prandtl number
Pr, Lewis number
Le, the Brownian motion parameter
Nb, the thermophoresis parameter
Nt, and convection Biot number
Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal and concentration boundary layers. The thermal boundary layer thickens with a rise in the local temperature as the Brownian motion, thermophoresis, and convective heating each intensify. The effect of Lewis number on the temperature distribution is minimal. With the other parameters fixed, the local concentration of nanoparticles increases as the convection Biot number increases but decreases as the Lewis number increases. For fixed
Pr,
Le, and
Bi, the reduced Nusselt number decreases but the reduced Sherwood number increases as the Brownian motion and thermophoresis effects become stronger.
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