Although engineering turbulence modeling is a well-established field, there is room for new ideas. In the current work, the rate of Reynolds stress generation is considered the product of a probability coefficient dependent on the viscous effect over the inertia effect and an energetic parameter expressed in terms of velocity dependence. The rate of Reynolds stress dissipation is defined as a simple second-order power function; this function emphasizes the nature of the local interactions (molecular level at their origins) that are similar to those for the reaction. Hence, the current approach can be called a reaction engineering approach for turbulence. Examples analyzed with this approach are: 1) the Universal Law of the Wall; 2) diameter-wide axial velocity distribution of the circular pipe (internal flow); 3) bulk behavior of the axial velocity distribution for a turbulent planar jet (external flow); and 4) far-field axial velocity distribution for a planar jet with numerical simulations. These findings suggest the potential of this approach for future exploration.
The leaves of the Stevia rebaudiana Bertoni plant contain a variety of steviol glycosides used as natural high-intensity sweeteners. Rebaudioside D (RebD), a steviol glycoside, exhibits a sweetness profile similar to that of sugar but has very low aqueous solubility. In this study, we developed a method to dissolve RebD in a molten secondary component and prepared a solid-phase complex containing RebD. After screening, erythritol was selected as the optimal second component. For the erythritol/RebD complex, an aqueous solubility of 3000–4500 mg/L RebD was achieved, a 5- to 6-fold increase compared to saturation. The dissolution rate was also improved compared to RebD alone. Different cooling temperatures and rates were evaluated and found to affect the morphology and solubility of the complex. The solubility of RebD can be greatly improved by preparing binary complexes using the method proposed in this work.
Mal distribution and pressure drop are two important parameters for evaluating gas distributors, especially in vacuum towers. However, in many cases, the optimal results of these two parameters cannot be obtained simultaneously. To solve this problem, all the key geometric parameters of a two-direction vapor horn gas distributor were systematically analyzed in this study. These include the diameter of the column (D), inlet diameter (d), space between Inner sleeve and tower wall (H), height of inner sleeve (h), height of first vane (h′), radial slop angle (θ), number of vanes (N), inlet velocity in the column (v). The results showed that the pressure drop was mostly influenced by the space size at the inlet of the distributor, and the location of the high-speed zone of the gas was mainly affected by the gap between the inner sleeve and tower wall, height of the first vane, and number of vanes. Furthermore, an orthogonal experiment was conducted to obtain two correlation equations connecting the geometrically structured parameters with the pressure drop and mal distribution factor of the gas. This could help in predicting the gas distribution uniformity and pressure drop within the two-direction vapor horn gas distributor.
This study demonstrates the feasibility of a novel preparation method for positively charged nanofiltration membranes. First, the interfacial polymerization of piperazine with trimesoyl chloride was conducted to form a base polyamide layer on a polyethylene microfiltration membrane, followed by plasma graft polymerization of [2-(methacryloyloxy)ethyl]trimethylammonium chloride, containing a quaternary ammonium moiety, on the base membrane to fabricate a positively charged membrane surface. The novel nanofiltration membrane had a pure water permeability of 3.1×10−12 m3 m−2 s−1 Pa−1 and showed the highest rejection for magnesium chloride, followed by magnesium sulfate, sodium sulfate, and sodium chloride. This is a typical salt rejection trend for positively charged nanofiltration membranes as the rejection of salts containing divalent cations was higher. Finally, the monovalent/divalent ion separation performance was examined using a mixture of magnesium sulfate and sodium chloride, and the results showed that magnesium ion retention was the highest and sodium ion retention was the lowest even when the sodium chloride concentration was considerably high. Therefore, this novel nanofiltration membrane has potential applications in the recovery of divalent cations from desalinated seawater in electrodialysis processes for table salt production.
The dehydrogenation of isobutane in the presence of CO2 over NiO supported on γ-Al2O3 was investigated. For comparison, Cr2O3 supported on γ-Al2O3 was also investigated. Conventionally, catalysts used for the dehydrogenation of various alkanes suffer catalyst deactivation due to carbon deposition. In the present study, the yield of isobutene was significantly decreased with time-on-stream due to carbon deposition using Cr2O3(x)/γ-Al2O3, where x indicates the loading of a corresponding oxide by weight %. Carbon deposits were also evident on NiO(x)/γ-Al2O3; however, the yield of isobutene was enhanced with time-on-stream depending on the loading (x). This indicates that the contribution of the carbon deposition in the dehydrogenation on NiO(x)/γ-Al2O3 definitely differed from that on an ordinary catalyst system, such as Cr2O3(x)/γ-Al2O3. To confirm the advantageous effect of carbon deposition exerted on the yield of isobutene, NiO(x)/γ-Al2O3 was first treated with isobutane, following which its catalytic activity was examined. Predictably, it became clear that the carbon deposition during the pretreatment contributed to the enhancement of the isobutene yield. The presence of an Ni-carbide species together with the metallic Ni that was converted from NiO during the dehydrogenation definitely enhanced the yield of isobutene. Although carbon deposition is generally recognized as the main cause of catalyst deactivation, the results of the present study reveal that this is not necessarily the case.
The techniques used for encapsulating a hydrophilic molecule into a cyclodextrin-based metal–organic framework (CD-MOF) can be divided into either an adsorption method or a cocrystallization method. However, neither of these methods can be applied directly to water-insoluble hydrophobic molecules. In this study, it was found that tetrahydrofuran (THF) can be used as a suitable cosolvent for dissolving hydrophobic 1-pyrenemethylamine (PMA) in water during the cocrystallization of CD-MOF. PMA-loaded CD-MOF (PMA/CD-MOF) was crystallized in an aqueous solution of PMA containing THF via methanol vapor diffusion. PMA/CD-MOF crystal growth was achieved without methanol vapor diffusion, by a novel method in which the volatilization of THF led to a solubility change for γ-cyclodextrin (γ-CD) leading to crystallization.