Effect of crystal rotation on thermocapillary flow in a shallow molten silicon pool

In order to understand the effect of crystal rotation on thermocapillary flow, we conducted a series of unsteady three-dimensional numerical simulations of thermocapillary flow in a shallow molten silicon pool with Czochralski configuration. The crucible sidewall is maintained at constant temperature. Bottom and free surfaces are adiabatic. The temperature difference between the crucible and the crystal is 16 K and crystal rotation rate varies from ?10 and 10 rpm. The simulation results indicate that the spoken pattern rotates slowly with the crystal rotation at low rotation rate. When rotation rate exceeds a critical value, the spoken pattern becomes the hydrothermal waves. This transition exists hysteresis.     

The Effect of Fouling on Low Temperature Heat Exchangers Performance Based on Exergy Analysis

By analyzing heat and exergy transfer processes of heat exchangers operating below the surrounding temperature, the effect of fouling on the low temperature heat exchangers performance has been conducted. Taking the parallel flow, counter flow, and cross flow low temperature heat exchangers as examples, the effects of some non-dimensional parameters on the low temperature heat exchangers performance under the fouling condition are given by introducing exergy transfer units number.     

Global simulation of a silicon Czochralski furnace in an axial magnetic field

Control of melt flow in crystal growth process by application of the magnetic field is a practical technique for silicon single crystals. In order to understand the influence of axial magnetic field on the silicon melt flow and oxygen transport in a silicon Czochralski (Cz) furnace, a set of global numerical simulations was conducted using the finite-element method for the magnetic field strength from 0 to 0.3 T, the crystal rotation rates from 0 to 30 rpm and the crucible counter-rotation rates from 0 to −15 rpm. It was assumed that the flow was axisymmetric laminar in both the melt and the gas, the melt was incompressible and a constant temperature was imposed on the outer wall of the Cz furnace. The results indicate significantly different flow patterns, thermal and oxygen concentration fields in the melt pool when a uniform axial magnetic field is applied.     

Thermocapillary Convection in a Binary Mixture with Moderate Prandtl Number in a Shallow Annular Pool

This paper presented a series of numerical simulations on thermocapillary convection for mixed toluene/hexane solution with mass fraction of \(c_{0}=?26.27\)% in a shallow annular pool. The Prandtl number of the binary solution is 5.54. Results indicate that when the annular pool subjects to a radial temperature gradient, the solute shifts toward the inner wall under the Soret effect, which leads to a concentration gradient with the opposite direction to the temperature gradient. With the increase of surface heat dissipation, thermocapillary convection is enhanced and the flow is more prone to destabilization. Therefore, the critical thermocapillary Reynolds number of the flow destabilization and the corresponding critical oscillation frequency all decrease, but the critical wave number increases. After flow destabilization, the concentration fluctuation similar to the temperature fluctuation on the free surface appears. No matter the free surface is adiabatic or not, the flow always undergoes a transition from two-dimensional steady axisymmetric flow to the hydrothermal waves, and then to chaos with the increase of thermocapillary Reynolds number.     

Thermocapillary Convection Instability in Shallow Annular Pools by Linear Stability Analysis

The thermocapillary convection instability in shallow annular pools with Prandtl numbers (Pr) from 0.011 to 57.9, differentially heated at the outer wall and cooled at the inner wall, is investigated numerically. The critical Marangoni numbers (Ma _c ), critical azimuthal wave numbers (m _c ) and critical phase velocities (ω _c ) for the incipience of oscillatory flow are determined by linear stability analysis. The results indicate that the Ma _c increases steeply with increase of Pr number when Pr≤15.9, while it increases slightly with increase of Pr between Pr=23.9 and 57.9. The m _c and ω _c decrease with increase of Pr number.     

A parabolic dish/AMTEC solar thermal power system and its performance evaluation

This paper proposes a parabolic dish/AMTEC solar thermal power system and evaluates its overall thermal–electric conversion performance. The system is a combined system in which a parabolic dish solar collector is cascaded with an alkali metal thermal to electric converter (AMTEC) through a coupling heat exchanger. A separate type heat-pipe receiver is selected to isothermally transfer the solar energy from the collector to the AMTEC. To assess the system’s overall thermal–electric conversion performance, a theoretical analysis has been undertaken in conjunction with a parametric investigation by varying relevant parameters, i.e., the average operating temperature and performance parameters associate with the dish collector and the AMTEC. Results show that the overall conversion efficiency of parabolic dish/AMTEC system could reach up to 20.6% with a power output of 18.54 kW corresponding to an operating temperature of 1280 K. Moreover, it is found that the optimal condenser temperature, corresponding to the maximum overall efficiency, is around 600 K. This study indicates that the parabolic dish/AMTEC solar power system exhibits a great potential and competitiveness over other solar dish/engine systems, and the proposed system is a viable solar thermal power system.     

Natural Convection of Water Near its Density Maximum around a Cylinder Inside an Elliptical Enclosure along Slender Orientation

A numerical investigation of natural convection of water near its density maximum around a cylinder inside the concentric elliptical enclosure along slender orientation was carried out. The effects of the aspect ratio, the elliptical ratio, the density inversion parameter, and the Rayleigh number were investigated. The typical flow and thermal fields were exhibited by means of streamlines and isotherms, respectively. Variations of the local and average Nusselt numbers were obtained and discussed with the details of both flow and thermal fields. The mechanism of oscillation was also analyzed when the stable flow transits to the unstable flow. Based on the simulation results, the heat transfer correlation has been proposed.     

Biodegradable Nanoparticles of mPEG-PLGA-PLL Triblock Copolymers as Novel Non-Viral Vectors for Improving siRNA Delivery and Gene Silencing

Degradation of mRNA by RNA interference is one of the most powerful and specific mechanisms for gene silencing. However, insufficient cellular uptake and poor stability have limited its usefulness. Here, we report efficient delivery of siRNA via the use of biodegradable nanoparticles (NPs) made from monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly-l-lysine (mPEG-PLGA-PLL) triblock copolymers. Various physicochemical properties of mPEG-PLGA-PLL NPs, including morphology, size, surface charge, siRNA encapsulation efficiency, and in vitro release profile of siRNA from NPs, were characterized by scanning electron microscope, particle size and zeta potential analyzer, and high performance liquid chromatography. The levels of siRNA uptake and targeted gene inhibition were detected in human lung cancer SPC-A1-GFP cells stably expressing green fluorescent protein. Examination of the cultured SPC-A1-GFP cells with fluorescent microscope and flow cytometry showed NPs loading Cy3-labeled siRNA had much higher intracellular siRNA delivery efficiencies than siRNA alone and Lipofectamine-siRNA complexes. The gene silencing efficiency of mPEG-PLGA-PLL NPs was higher than that of commercially available transfecting agent Lipofectamine while showing no cytotoxicity. Thus, the current study demonstrates that biodegradable NPs of mPEG-PLGA-PLL triblock copolymers can be potentially applied as novel non-viral vectors for improving siRNA delivery and gene silencing.     

Exergo-economic analysis of finned tube for waste heat recovery including phase change heat transfer

In this paper, an exergo-economic criterion, i.e. the net profit per unit transferred heat load, is established from the perspective of exergy recovery to evaluate the performance of finned tube used in waste heat recovery. Also, the dimensionless exergy change number is introduced to investigate the effect of the flow (mechanical) exergy loss rate on the recovered thermal exergy. Selecting R245fa as a working fluid and exhaust flue gas as a heat source, the effects of the internal Reynolds number Re _i, the external Reynolds number Re _o, the unit cost of thermal exergy ? _q, the geometric parameter of finned tube η _o β and the phase change temperature T _v etc. on the performance of finned tube are discussed in detail. The results show that the higher T _v and η _o β, and lower Re _i may lead to the negligible flow (mechanical) exergy loss rate. There exists an optimal value of Re _i where the net profit per unit transferred heat load peaks, while the variations of Re _o, ? _q and T _v cause monotonic change of the net profit per unit transferred heat load. The phase change temperature exerts relatively greater influence on the exergo-economic performance of finned tube in comparison with other parameters. And there exists a critical phase change temperature, where the net profit per unit transferred heat load is equal to zero.     

磷酸钙陶瓷在不同动物的模拟体液中类骨磷灰石的形成研究

根据人、狗、猪、猴和兔五种动物体液的钙离子浓度和pH值的差异,配制了不同组分的模拟体液,将孔壁致密和有微孔的多孔磷酸钙陶瓷分别浸泡在这些模拟体液中,研究陶瓷孔隙表面类骨磷灰石的形成情况.结果表明:在模拟体液中浸泡14天后,孔壁致密的材料未见有类骨磷灰石层形成;有微孔的多孔磷酸钙陶瓷,材料孔壁表面(包括陶瓷表面较深孔隙)有类骨磷灰石层的形成,这与体内植入实验观察到的类骨磷灰石层形成和诱导成骨情况相似,可以推论类骨磷灰石层的形成的确是骨诱导的先决条件.随着钙离子浓度的增加,其孔壁表面类骨磷灰石层的形成也更为均匀,但类骨磷灰石生长快慢顺序与动物组织学观察到的骨诱导性高低的次序不完全一致.