The
conversion of layered transition metal carbides and/or nitrides
(MXenes) into zero-dimensional structures with thicknesses and lateral
dimensions of a few nanometers allows these recently discovered materials
with exceptional electronic properties to exploit the additional benefits
of quantum confinement, edge effects, and large surface area. Conventional
methods for the conversion of MXene nanosheets and quantum dots, however,
involve extreme conditions such as high temperatures and/or harsh
chemicals that, among other disadvantages, lead to significant degradation
of the material as a consequence of their oxidation. Herein, we show
that the large surface accelerationon the order of 10 million g’sproduced by high-frequency (10 MHz) nanometer-order
electromechanical vibrations on a chip-scale piezoelectric substrate
is capable of efficiently nebulizing, and consequently dimensionally
reducing, a suspension of multilayer Ti3C2T
z
(MXene) into predominantly monolayer nanosheets
and quantum dots while, importantly, preserving the material from
any appreciable oxidation. As an example application, we show that
the high-purity MXene quantum dots produced using this room-temperature
chemical-free synthesis method exhibit superior performance as electrode
materials for electrochemical sensing of hydrogen peroxide compared
to the highly oxidized samples obtained through conventional hydrothermal
synthesis. The ability to detect concentrations as low as 5 nM is
a 10-fold improvement to the best reported performance of Ti3C2T
z
MXene electrochemical
sensors to date.
h i g h l i g h t s Three performance indicators used including a newly defined heat pipe effectiveness. Optimum operation is discussed based on existence/absence of dryout in the grooves. Near optimum, dryout tendency increases with increasing groove density and heat flux. Effectiveness increases with groove density, and drops with increasing heat flux.
The highly viscous property of heavy oil often causes problems in its transportation in pipelines. Mixing heavy oil with light oil as well as ultrasound treatment are viable solutions to this problem. In this study, extra heavy crude oil samples were first diluted with 0, 0.05, 0.1, and 0.15 mL/mL (0, 5, 10, and 15 vol%) of a light crude oil; then the mixture was irradiated by ultrasonic waves for 0, 5, 10, 15, and 20 min; finally the viscous shear functions of all mixtures was measured at different values of shear rate at different temperature levels. The results revealed that the minimum viscosity of the diluted extra heavy crude oil samples was obtained at 10 min of ultrasonic irradiation. Moreover, the viscosity reduction rate in relation to temperature decreases as temperature increases. In other words, the maximum viscosity reduction rate occurred at 0.05 mL/mL (5 vol%) of light crude oil. Using the experimental data, the parameters of common rheological models were obtained and a new modified Power Law model was presented to calculate the effect of shear rate and temperature simultaneously.
The thermal characterization of aluminum flat grooved heat pipes is performed experimentally for different groove dimensions. Three heat pipes with groove widths of 0.2 mm, 0.4 mm, and 1.5 mm are used in the experiments. The effect of the amount of the working fluid is extensively studied for each groove width. The results reveal that, although all three succeed in dissipating the heat input through the phase change of the working fluid by continuous evaporation and condensation, the effectiveness of the heat transfer increases with reduced groove width. Furthermore, it is observed that there exists an optimum operating point, where the temperature difference between the heating and cooling sections is at a minimum, and the magnitude of this temperature difference is a strong function of the groove width. To the best of the authors' knowledge, the combined effects of groove dimensions and the amount of the working fluid, from fully flooded to dry, is reported for the first time for aluminum flat grooved heat pipes.
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