Synthesis of zeolitic imidazolate framework-8 and gold nanoparticles in a sustained out-of-equilibrium state

The design and synthesis of crystalline materials are challenging due to the proper control over the size and polydispersity of the samples, which determine their physical and chemical properties and thus applicability. Metal − organic frameworks (MOFs) are promising materials in many applications due to their unique structure. MOFs have been predominantly synthesized by bulk methods, where the concentration of the reagents gradually decreased, which affected the further nucleation and crystal growth. Here we show an out-of-equilibrium method for the generation of zeolitic imidazolate framework-8 (ZIF-8) crystals, where the non-equilibrium crystal growth is maintained by a continuous two-side feed of the reagents in a hydrogel matrix. The size and the polydispersity of the crystals are controlled by the fixed and antagonistic constant mass fluxes of the reagents and by the reaction time. We also present that our approach can be extended to synthesize gold nanoparticles in a redox process.

A Method for Predicting Efficiency of Perforated Muzzle Brakes

This paper presents a method for predicting a value of a gasdynamic efficiency coefficient for perforated muzzle brakes. The method is based on the interior ballistics modelling for determining gasdynamic flow parameters at the brake inlet and 2D modelling the processes inside the brake with treating vents as circumferential slots. The modelling provides information about the mass flux time changes at the inlet and at the outlet of the brake. Using this information, the mass partition coefficient values and the gasdynamic efficiency coefficient values are calculated. It has been shown that the mass partition coefficient establishes very quickly and it is determined only by the geometry of the brake. The gasdynamic efficiency coefficient establishes after a relatively long time, what demands carrying out calculations for a relatively long time period. However, it has been shown that this problem can be solved by making use of the established ratio of mass fluxes at the outlet and the inlet. So, flow parameters’ values at the inlet are sufficient for determining the gasdynamic efficiency coefficient to the moment of attaining the final value. It has been shown that this value depends on the ballistics and on the vents inclination angle.

Distribution and Potential Sources of OCPs and PAHs in Waters from the Danshui River Basin in Yichang, China

To investigate the concentrations, spatial distribution, potential sources and mass fluxes of organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in waters from the Danshui River Basin, a total of 20 water samples were collected and analyzed from a karstic river in Western Hubei of Central China. The average concentrations of total OCPs and PAHs in the river water were 4719 pg·L−1 and 26.2 ng·L−1, respectively. The characteristic ratios of different isomers and the composition analysis of individual OCPs and PAHs revealed that HCHs originated from a mixed input of technical HCHs and Lindane, DDTs were mainly from technical DDTs, and PAHs mainly originated from biomass and coal combustion. The mass flux analysis showed that PAHs had a higher emission and heavier burden than OCPs in the Danshui River Basin. OCPs and PAHs emitted from agricultural or other human activities could enter the groundwater and then be transported to the surface/river water in the karst area. The adsorption of OCPs and PAHs by particles and the sedimentation of particles could be the primary processes to intercept these pollutants in the water of the karstic river system.

Thermo-diffusion impacts on the flow of an elastico-viscous fluid over an inclined heated plane with magnetized wall

The focus is in this article is to scrutinize the simultaneous significances of magnetic diffusion, thermo-diffusion and angular location on the hydromagnetic flow of an elastico-viscous fluid over an inclined heated plane with magnetized wall. The flow medium is considered to be uniformly permeable (Darcy-Brinkman porous medium) and the flow of the fluid is considerably affected due to the appearance of a strong magnetic field in the direction normal to the flow surface. The significances of Hall current, induced magnetic field and Coriolis force on flow nature is also included in the study. The leading non-dimensionalized equations are explored by regular perturbation analysis. Ultimately, the expressions for velocity field, induced magnetic field, temperature and concentration are obtained. We further derived the surface skin friction, surface current density, heat and mass fluxes. The computation of results is performed with the aid of Mathematica software and results are presented in graphical and tabular forms for distinct flow impacting parameters. Numerical simulation explores that mass diffusion factor brings growth in the fluid velocity, temperature and normal induced magnetic field while it reduces the main induced magnetic field. Magnetic diffusion develops the primary flow and primary induced magnetic field and lessens the normal flow and normal induced magnetic field. Inclination angle of the heated plane upgrades primary induced magnetic field while downgrading normal induced magnetic field.

Observational study on boundary-layer moist static energy budget over the tropical western Pacific and its variability associated with boreal summer intraseasonal oscillation

Moist static energy (MSE) in the atmospheric boundary layer (BL) is one of the essential parameters determining convective activity over tropical oceanic areas. It is thus important to quantitatively understand BL MSE budget processes and their variability. Among these processes, only few studies have evaluated contributions of entrainment across the BL top and convective downdraft. This study aims to estimate these contributions by analyzing upper-air and surface meteorological observations obtained using Research Vessel Mirai over the tropical western Pacific in June 2008. Daily-mean downward mass fluxes due to the two processes are calculated using BL dry static energy and moisture budget equations under the BL quasi-equilibrium approximation. Estimated mass fluxes are consistent with convective activity observed by a shipborne weather radar and a ceilometer. This study further examines how the mass fluxes and budget processes are modulated when a convectively active phase of boreal summer intraseasonal oscillation arrives at the observation area in the second half of the month. It is found that, while the contribution of the entrainment does not change significantly, the convective downdraft mass flux and the resultant BL MSE export increase 5 times and 3 times, respectively, in the convectively active period compared with those in the pre-active period. Furthermore, ~1/4 of the increase in the convective downdraft mass flux is attributable to the increase in MSE of convective downdraft air associated with mid-tropospheric moistening.

Stratosphere-Mesosphere exchange: Long term changes and drivers

<p>The meridional overturning mass circulation in the middle atmosphere, i.e. the Brewer-Dobson circulation (BDC), was first discovered before decades based on the distribution of trace gases and a basic analytical concept of BDC has been derived using the transformed Eulerian mean equations. Since then, BDC is usually defined as consisting of a diffusive part, and an advective, residual mean circulation. In the vertical, BDC is separated into two branches – a shallow branch in the lower stratosphere and a deep branch higher in the middle atmosphere.<br />Climate model simulations robustly show that the advective BDC part accelerates in connection to the greenhouse gas-induced climate change and this acceleration dominates the middle atmospheric changes in climate model projections. A prominent quantity that is being studied as a proxy for advective BDC changes is the net tropical upwelling across the tropopause, which measures the amount of mass advected by residual circulation from the troposphere to the stratosphere per unit of time. The upper BDC branch received considerably less research attention than its shallow part, but features some striking phenomenon in the terrestrial atmosphere. It couples the stratosphere and mesosphere and is also responsible for a large portion of interhemispheric transport and coupling in the middle atmosphere.<br />In our research, for the first time, we produce a conceptual study of the advective stratosphere-mesosphere exchange. The analysis of advective exchange of mass between the stratosphere and mesosphere, i.e. the advective mass transport across the stratopause represents another step towards a better understanding of the structure of the upper BDC part and at the same time provides valuable insights into the relatively little-explored stratopause region. We investigate the variability and trends in mass fluxes from the stratosphere to the mesosphere and vice versa based on data from the EMAC-L90 model CCMI-1 simulation for the period 1960-2100. We develop an analytical method that allows us to attribute the changes of transport to causative factors such as acceleration of residual circulation, variable height of the stratopause, change of a geometric shape of the stratopause and changes in width of the upwelling and downwelling regions. The main driver of the increasing mass exchange between the stratosphere and the mesosphere is the faster circulation, however, the other terms are not negligible. The derived methodology offers the possibility of using an analogous procedure also for the tropopause in the future.</p>

Numerical Dimensioning of a Pre-Cooler for sCO2 Power Cycles to Utilize Industrial Waste Heat

The annual waste heat available from industry in the European Union is more than 2700 PJ. Consequently, the utilization of the unexploited thermal energy will decisively contribute to a reduced overall power consumption and lower greenhouse gas emissions. In the present investigation, a cycle layout, based on supercritical carbon dioxide (sCO2), was applied for a certain waste heat source, a gas compressor station. The boundary conditions determined by the cycle were used by the numerical code ANSYS CFX to design a pre-cooler. Subsequently, this printed circuit heat exchanger was examined for sCO2 mass fluxes between 100 kg/m²s and 900 kg/m²s. The heat transfer and pressure drop increase as the flow channel diameter is reduced. As the pressure drop of the coolant channel is more sensitive to the diameter, a larger coolant channel diameter is selected to maintain a reasonably low pressure drop. The optimum pre-cooler design consists of a 0.5 mm and 0.8 mm channel diameter for the sCO2 and coolant channel. Based on these results, internal fins were applied and optimized, to improve the heat transfer performance. An internal fin height of 4 mm was found to achieve the optimum thermal-flow performance for the pre-cooler.

Evaluation of Pressure Drop of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

Various experiments on the pressure drop of a two-phase flow boiling in a mini channel tube have been carried out. This study is aimed at characteristics of the pressure drop of a two-phase flow boiling using a refrigerant R290. The experiment uses a horizontal, stainless steel, 2-m-long mini-channel tube with a 3-mm inner diameter. The experiment has been carried out using various data with the vapor qualities ranging from 0.1 to 0.9, the mass fluxes ranging 50 kg/m2s to 180 kg/m2s, and the heat fluxes ranging from 5 kW/m2 to 20 kW/m2. Furthermore, several homogeneous and separated methods were used to predict the experimental data. Li and Hibiki’s correlation give the best overall deviation pressure drop value is the most accurate with its deviation amounting 19.47%.