This study adopts an alumina (Al2O3) and titania (TiO2) nano-coolant (NC) to enhance the heat dissipation performance of an air-cooled radiator. The two-step synthesis method is used to produce ...different concentrations of Al2O3 and TiO2/water (W) nanofluid by using a 0.2 wt.% chitosan dispersant, and the nanofluid is mixed with ethylene glycol (EG) at a 1:1 volume ratio to form NC1 to NC6. The experiments were conducted to measure the thermal conductivity, viscosity, and specific heat of the NC with different concentrations of nanoparticles and sample temperatures, and then the NC was used in an air-cooled radiator to evaluate its heat dissipation capacity, pressure drop, and pumping power under different volumetric flow rates and heating temperatures. Finally, this study evaluates the relationship of the heat dissipation capacity and pumping power by using the efficiency factor (EF). The experimental results show that the heat dissipation capacity and the EF of the NC are higher than EG/W, and that the TiO2 NC is higher than the Al2O3 NC according to most of the experimental data. The maximum enhanced ratios of the heat dissipation capacity, pressure drop, pumping power, and EF for all the experimental parameters are approximately 25.6%, 6.1%, 2.5%, and 27.2%, respectively, compared with EG/W. Overall, the NC improves the heat dissipation capacity and EF of the cooling system; however, the enhanced ratio of the pressure drop and pumping power is not obvious in this study.
•We employed oxide nano-coolant (NC) in air-cooled radiator for heat dissipation.•We produced the Al2O3 and TiO2 NC by the two-step synthesis method.•The heat dissipation capacity and the EF of the NC are higher than EG/W.•The enhanced ratio of the pressure drop and pumping power is not obvious.•The maximum enhanced ratios of EF for TiO2-NC6 was 27.2% compared with EG/W.
The creation of high-efficient MXene-based flame retardants to cope with the fire hazards of polymer composites remained an intractable challenge. Hence, this work explored a facile strategy to ...synthesize MXene-based nanohybrids (MXene@LDH) by in situ growth of layered double hydroxides (CoAl-LDH) on the surface of MXene in anticipation of constructing an efficient flame retardant system. The results indicated that the integration of LDH prevented the stacking of MXene nanosheets and enhanced the dispersion of MXene in EP matrix, endowing EP composites with excellent thermal properties and flame retardancy. With the addition of 2 wt% MXene@LDH, EP composites exhibited reduced the maximum mass loss rate (Rmax) of 28.5%, increased residual char and led to 25.3% reduction in PHRR and a drop of 24.4% in THR, compared to those of neat EP. Furthermore, EP/2 wt% MXene@LDH composites also demonstrated superior smoke suppression performance, mainly reflected by the 38.5%, 37.8%, 33.8% and 31.2% reduction in PSPR, TSP, PCO and PCO2, respectively, together with a 52.0% decline in smoke factor (SF), compared to those of pure EP. The improved fire safety of EP composites was attributed to the catalytic charring and attenuation effect of the transition metal oxides, coupled with the barrier effect of the nanosheets and the cooling effect, gas-phase dilution effect of LDH.
Adding conductive filler is an effective way to enhance the dielectric constant while usually also increases the dielectric loss of polymer. In this study, we demonstrated that polymer composites ...with much improved dielectric constant while maintaining ultra-low dielectric loss could be achieved via using hybrid filler and controlling the dispersion of conductive filler in polymer matrix. To do this, the graphene oxide was designed to be immobilized on the surface of large-sized insulating hexagonal boron nitride (h-BN) via electrostatic self-assembly, and afterwards introducing this hybrid filler into epoxy accompanied with chemical reduction. In this case, since the reduced graphene oxide (rGO) sheets were fixed on the surface of h-BN, rGO sheets were well separated from each other even at high loading. Hence not only significantly enhanced dielectric constant was observed, but also a very low dielectric loss comparable to that of neat epoxy was achieved. This low dielectric loss was believed to be ascribed to both embedded insulating network of h-BN to inhibit the mobility of charge carrier and well-separated rGO sheets via immobilization. In addition to obviously improved dielectric properties, the nanocomposites also exhibited good thermal conductivity. We believe that this special structure will provide a new thought for fabricating dielectric materials with much enhanced dielectric constant as well as well-suppressed dielectric loss.
The rational lifetime-tuning strategy of ultralong organic phosphorescence is extraordinarily important but seldom reported. Herein, a series of multi-host/guest ultralong organic phosphorescence ...materials with dynamic lifetime-tuning properties were reported. By doping a non-room-temperature phosphorescence emitter into various solid host matrices with continuously reduced triplet energy levels, a wide-range lifetime (from 3.9 ms gradually to 376.9 ms) phosphorescence with unchangeable afterglow colors were realized. Further studies revealed that the host matrices were employed to afford rigid environment and proper energy levels to generate and stabilize the long-live triplet excitons. Meanwhile, these multi-host/guest ultralong organic phosphorescence materials also exhibited excitation-dependent phosphorescence and temperature-controlled afterglow on/off switching properties, according to the virtue of various photophysical and thermal properties of the host matrices. This work provides a guiding strategy to realize lifetime-tuning ultralong organic phosphorescence with lifetime-order encoding characteristic towards widespread applications in time-resolved information displaying, higher-level security protection, and dynamic multi-dimensional anti-counterfeiting.
By using nonequilibrium molecular dynamics simulations, we demonstrated that thermal conductivity of germanium nanowires can be reduced more than 25% at room temperature by atomistic coating. There ...is a critical coating thickness beyond which thermal conductivity of the coated nanowire is larger than that of the host nanowire. The diameter-dependent critical coating thickness and minimum thermal conductivity are explored. Moreover, we found that interface roughness can induce further reduction of thermal conductivity in coated nanowires. From the vibrational eigenmode analysis, it is found that coating induces localization for low-frequency phonons, while interface roughness localizes the high-frequency phonons. Our results provide an available approach to tune thermal conductivity of nanowires by atomic layer coating.
In this paper, the problem of boundary layer flow of a nanofluid past a stretching sheet has been investigated analytically by using the Homotopy Analysis Method. Both the effects of Brownian motion ...and thermophoresis are considered simultaneously. An analytical solution is presented which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb and thermophoresis number Nt. The results show that the reduced Nusselt number is a decreasing function of each dimensionless number, while the reduced Sherwood number is an increasing function of higher Pr and a decreasing function of lower Pr number for each Le, Nb and Nt numbers like the results presented by Khan and Pop. Contrary the results presented by Khan and Pop, It is found that the reduced Nusselt number decreases with the increase in Pr for many Nb numbers. However for a special Nb, there are conversely interesting results that are clearly discussed in this paper.
Recently there have been many research breakthroughs in two-dimensional (2D) materials including graphene, boron nitride (h-BN), black phosphors (BPs), and transition-metal dichalcogenides (TMDCs). ...The unique electrical, optical, and thermal properties in 2D materials are associated with their strictly defined low dimensionalities. These materials provide a wide range of basic building blocks for next-generation electronics. The chemical vapor deposition (CVD) technique has shown great promise to generate high-quality TMDC layers with scalable size, controllable thickness, and excellent electronic properties suitable for both technological applications and fundamental sciences. The capability to precisely engineer 2D materials by chemical approaches has also given rise to fascinating new physics, which could lead to exciting new applications. In this Review, we introduce the latest development of TMDC synthesis by CVD approaches and provide further insight for the controllable and reliable synthesis of atomically thin TMDCs. Understanding of the vapor-phase growth mechanism of 2D TMDCs could benefit the formation of complicated heterostructures and novel artificial 2D lattices.
•Thermophysical properties of TiO2/water nanofluids were measured experimentally.•Thermal performance of tilted mesh heat pipe using TiO2/water nanofluid was studied.•The study focused on the effect ...of vol. fraction,% fill charge ratio and tilt angle.•Results show that utilization of nanofluid enhanced thermal performance of heat pipes.•An inclination angle 45° and 60% fill charge ratio give the best thermal performance.
In recent study, the transport properties, namely the thermal conductivity and viscosity were studied experimentally for titanium dioxide nanoparticle dispersed in distilled water. The data are collected for particle volumetric concentration up to 1.0% and the temperature range of the measurements was from 10 to 60°C. The results showed that the thermal conductivity increased with increasing volumetric concentration and also with increasing temperature. The data obtained from the measurements were compared with several existing theoretical models. However, our data do not reveal a good agreement with the classical as well as Brownian motion theoretical model. Furthermore, the effect of nanofluid on the thermal performance of heat pipes is investigated experimentally. The wall temperature distribution and the thermal resistance between evaporation and condensation section are measured and compared with those for the heat pipes using distilled water. The influence of% charge volume ratio of working fluid, inclination angle of the heat pipe and% amount of nanoparticles dispersed in distilled water on thermal performance of heat pipes are considered. It is found that the inclination of 45° and 60% charge volume ratio of working fluid corresponds to the best thermal performance of heat pipe using distilled water as well as titanium dioxide nanofluids.
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