As conventional energy sources like fossil fuels are getting rare, cost of energy production has become higher as well as the concern of environmental pollution by burning of fossil fuels among the ...developed and developing nations. Solar energy is the most vastly available energy and very effective in terms of energy conversion. The most common solar thermal collector used is the black surface as radiant absorber but the thermal energy efficiency is low. In this study, the effect of nanofluid has been analyzed by using as working fluid for direct solar collector. The extinction coefficient of water based aluminum nanofluid has been investigated and evaluated by varying nanoparticle size and volume fraction. The particle size has minimal influence on the optical properties of nanofluid. On the other hand, the extinction coefficient is linearly proportionate to volume fraction. The improvement is promising within 1.0% volume fraction and the nanofluid is almost opaque to light wave.
Five bioactive glasses based on 49.5SiO
2–1.1P
2O
5–(23.0(1
−
x))CaO–
xMgO–26.4Na
2O
mol.% were synthesised where CaO was replaced progressively on a molar basis by MgO (where 0
⩽
x
⩽
1). The glasses ...were characterised by
31P and
29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dilatometry, differential thermal analysis (DTA) and density measurements with the aim of gaining a comprehensive understanding of the structure–property relationships.
The
31P NMR spectra of the glasses exhibited well-defined resonances at
ca. 9–14
ppm, corresponding to a Q
0 orthophosphate environment. Full substitution of MgO caused a downfield shift of
ca. 5
ppm, implying the preferential association of sodium with the orthophosphate species. The
29Si NMR spectra exhibited a peak at
ca. −79
ppm, indicating a Q
2 silicon species, along with a shoulder at
ca. −90
ppm, corresponding to a Q
3 species. On addition of MgO, the Q
3 shoulder was seen to progressively increase in magnitude. These results suggest that MgO, rather than depolymerising the silicate network by acting as a network modifier, is behaving in part, as an intermediate oxide. Deconvolution of the
29Si NMR peaks suggest that, although 86% of the magnesium oxide is acting traditionally as a network modifying cation, up to 14% of the magnesium oxide is entering the silicate network as tetrahedral, MgO
4, removing network modifying ions for charge compensation and resulting in the observed polymerisation of the silicate network. Correspondingly, both the glass transition temperature and dilatometric softening point values were seen to decrease whilst the thermal expansion coefficient values rose, with increasing MgO content. This was due to the significantly lower bond strength, of Mg–O compared to Si–O, weakening the glass network.
We have used molecular dynamics to calculate the thermal conductivity of symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in size (up to approximately 4 nm wide and ...approximately 10 nm long). For symmetric nanoribbons, the calculated thermal conductivity (e.g., approximately 2000 W/m-K at 400 K for a 1.5 nm x 5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally measured value for graphene. We have investigated the effects of edge chirality and found that nanoribbons with zigzag edges have appreciably larger thermal conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons, we have found significant thermal rectification. Among various triangularly shaped GNRs we investigated, the GNR with armchair bottom edge and a vertex angle of 30 degrees gives the maximal thermal rectification. We also studied the effect of defects and found that vacancies and edge roughness in the nanoribbons can significantly decrease the thermal conductivity. However, substantial thermal rectification is observed even in the presence of edge roughness.
In this research work, first-principles computational study is performed on the structural, elastic, thermal, magnetic, electronic, and thermoelectric properties of the ternary Heusler compound ...Co.sub.2MnGe in its cubic phase. For this purpose, the "full potential linearized augmented plane-wave FP-L(APW + lo)" approach realized in the WIEN2k code is employed. To determine total energy, the exchange-correlation energy/potential part is treated within the "Perdew-Burke-Ernzerhof (PBE)" parameterized approach of "generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ)" schemes. The magnetic phase stability was predicted via quantum mechanically total energy calculations for both non-magnetic and magnetic phases. Our obtained results for total energy show that the title material is stable in the ferromagnetic phase. The analysis of the profile of density of states (DOS), band structure plots, and the calculations of spin magnetic moment endorse the semi-metallic nature of the title compound. Calculations of the elastic constants, C.sub.ij, and results of the elastic moduli, such as bulk modulus (B), shear modulus (G), Young modulus (E), Poisson ratio (nu), and ratio B/G, are reported and analyzed as well. Gibbs computational code based on the "quasi-harmonic Debye model" is used to explore thermal properties, whereas parameters to understand the thermoelectric behavior, BoltzTrap code based on Boltzmann theory for transport properties is applied. Besides that, the chemical potential effect on the Seebeck coefficient and power factor is also analyzed at temperatures 300, 600, and 900 K. The results of thermoelectric parameters of the title Heusler compound, for the spin-down channel, are found good; hence, the obtained results highlight the title compound as a potential candidate for thermoelectric devices.
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•Surface functionalized and stabilized HyNC dispersed in fluid without surfactant.•Convective heat transfer coefficient increased by 52% for hybrid nanofluids.•Particulate thermal ...diffusion rate influenced by fluid density and flow viscosity.•Heat transfer rate reduced at higher flow frictional pressure drop of nanofluids.•Enhanced heat exchanger performance is possible at lower particulate fractions.
An experimental study has been carried out to investigate the heat transfer potential and rheological characteristics of copper–titania hybrid nanofluids (HyNF) using a tube in the tube type counter flow heat exchanger. The nanofluids were prepared by dispersing the surface functionalized and crystalline copper–titania hybrid nanocomposite (HyNC) in the base fluid, with volume concentrations ranging from 0.1% to 2.0%. The Heat transfer and rheological characteristics of nanofluids containing HyNC of an averaged size of 55nm were experimentally investigated. The test results reveal that the convective heat transfer coefficient, Nusselt number and overall heat transfer coefficient were increased by 52%, 49% and 68% respectively, up to 1.0% volume concentration of HyNC. Beyond the volume concentration of 1.0% and up to 2.0%, the reduction in the convective heat transfer potential and the Nusselt number were marginal, which signified the effective thermal conductivity enhancement in HyNF. The functionalized structure and crystalline nature of HyNC acted as extended surfaces within the fluid medium, thereby creating more thermal interfaces for achieving improved thermal conductivity and the heat transfer potential of HyNF. The friction factor and pressure drop of HyNF for 2.0% volume concentration were expected to be 1.7% and 14.9% respectively, which implies a penalty in the pumping capacity. However, the enhancement in the heat transfer characteristics and acceptable variations in rheological aspects of HyNF, would help to reduce the consumption of higher volume concentration of metallic or metal oxide nanostructures, to be dispersed in the fluid medium. In order to validate the experimental measurements, a new correlation was developed, which predicted the experimental data with a maximum deviation of +7% and −4% for all the volume concentrations of HyNF. The present correlation was in good agreement with the experiments and can be helpful in predicting the heat transfer potential of HyNF.
Endoglucanase (EG) is a key enzyme during enzymatic preparation of cellulose nanocrystals (CNCs). Myceliophthora thermophila is a thermophilic fungus that has thermal properties and a high secretion ...of endoglucanases (EGs), and could serve as potential sources of EGs for the preparation of CNCs. In this work, four different GH families (GH5, GH7, GH12, and GH45) of EGs from M. thermophila were expressed and purified, and their enzymatic characteristics and feasibility of application in CNC preparation were investigated. It was shown that the MtEG5A from M. thermophila has good potential in the enzymatic preparation of CNCs using eucalyptus dissolving pulp as feedstock. It was also observed that there was a synergistic effect between the MtEG5A and other MtEGs in the preparation of CNCs, which improved the yield and properties of CNCs obtained by enzymatic hydrolysis. This study provides a reference for understanding the enzymatic characteristics of different families of EGs from M. thermophile and their potential application in nanocellulose production.
A superhydrophobic surface with stability against moderate drop impact was quickly created with only a candle. There was no further need for any additional solvent, further surface treatment, drying ...process or post-treatment process. The fabrication is very simple. A surface is coated with a candle paraffin wax and then sooted with a candle flame. The paraffin wax was used to fix the fragile candle soot. This paraffin wax-fixed candle soot (PFCS) coating showed improved drop impact durability by up to a factor of 50, compared to a bare soot coating without a paraffin wax treatment. Thermal stability, compression tolerance, and pH tolerance of the PFCS coating were tested. The mechanism behind the PFCS coating and durability enhancement of the coating is explained. The simple PFCS coating method can be applied to various surfaces, such as metal, ceramic, wood, plastic and even paper. We provide proof-of-concept demonstrations in the application of this PFCS coating method. We foresee PFCS coating as opening up a new avenue for the development of an inexpensive and quick process for the fabrication of superhydrophobic surfaces.
Ultrathin (0.3-3 nm) metal dichalcogenides exhibit confinement of carriers, evolution of band-structure and photophysical properties with thickness, high on/off rectification (in MoS2, WS2, and so ...forth) and high thermal absorption. Here, we leverage the stable sulfur/nobel-metal binding to incorporate highly capacitive gold nanoparticles (Au NPs) onto MoS2 to raise the effective gate-voltage by an order of magnitude. Functionalization is achieved via both diffusion limited aggregation and instantaneous reaction arresting (using microwaves) with selective deposition on crystallographic edges (with 60° displacement). The electrical, thermal, and Raman studies show a highly capacitive interaction between Au NP and MoS2 flakes (CAu-MoS2 = 2.17 μF/cm(2)), a low Schottky barrier (14.52 meV), a reduced carrier-transport thermal-barrier (253 to 44.18 meV after Au NP functionalization), and increased thermal conductivity (from 15 to 23 W/mK post NP deposition). The process could be employed to attach electrodes to heterostructures of graphene and MoS2, where a gold film could be grown to act as an electron-tunneling gate-electrode connected to MoS2.
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