余核飞行与ΔE—E望远镜双鉴别系统

设计和测试了一套在重离子熔合反应中同时测量蒸发剩余核的质量和电荷的飞行时间谱仪和ΔE-E望远镜双鉴别系统。实验结果表明,该系统对粒子的鉴别能力,Z分辨率好于25,质量分辨可达45。     

Feed water cooler to increase evaporation range in MSF plants

Multistage flash (MSF) desalination is the most widely used process to provide potable water. In MSF plants, water starts to evaporate in the top stage at a temperature set by the scale prevention techniques and stops at the bottom stage whose temperature is controlled by the feed water conditions. Increasing the difference between these two temperatures elongates the span along which evaporation occurs (evaporation range) and therefore increases the mass of the fresh water produced. This paper suggests installing a cooling system at the seawater intake in order to reduce the feed water temperature, and hence the temperature of the last stage. This technique leads to increasing the evaporation range without exceeding the conventional limits of top brine temperature and eliminates the effects of seasonal climatic changes. Moreover, the proposed scheme is a suitable arrangement to improve the water production from dual-purpose plants since the power needed to operate the cooling system is available on the same site. An improvement in the yield by 1.4–1.84% for every 1 °C reduction in the feed temperature can be achieved at the expense of a less than 0.2% of the power produced by the expansion of the heating steam.     

Predictions of turbulent flow and heat transfer in gas–droplets flow downstream of a sudden pipe expansion

Droplets-laden turbulent flow downstream of a sudden pipe expansion has been investigated by using Euler/Euler two-fluid model for the gaseous and dispersed phases. Significant increase of heat transfer in separated flow at the adding of evaporating droplets has been demonstrated (more than 2 times compare with one-phase flow at the value of mass concentration of droplets M_L1  0.05). Addition of dispersed phase to the turbulent gas flow results in insignificant increase of the reattachment length. Low-inertia droplets (d₁  50 μm) are well entrained into the circulation flow and present over the whole pipe section. Large particles (d₁ ≈ 100 μm) go through the shear layer not getting into the detached area. Comparison with experimental data on separated gas–droplets flows behind the plane backward-facing step has been carried out.     

燃料液滴超临界蒸发综述

从常压液滴蒸发的传热传质过程出发,建立了常压液滴蒸发的数学模型。通过比较液滴超临界蒸发和常压蒸发的差异,研究液滴超临界蒸发所涉及的关键问题。以二甲基醚(DME)在氮气介质中超临界蒸发为例,介绍了状态方程法计算DME-N2体系的高压气液相平衡,在相关文献的基础上,总结了流体热物性和输运参数的变化特性。     

卤水蒸发过程中的四元水盐体系相图分析及计算

以四元水盐体系相图理论做指导，对几种不同区域的卤水进行等温蒸发，给出了析出钾石盐或含钠光卤石较为理想的蒸发终止点。     

Coupled effects of flow field geometry and diffusion media material structure on evaporative water removal from polymer electrolyte fuel cells

In this work, the coupled effects of flow field geometry and diffusion media (DM) material structure on evaporative water removal during gas purge are investigated with the ex-situ test methods developed in previous works 31 and 32. Three different flow field structures with various land to channel width ratios (L/C) were utilized with paper and cloth-type DM to understand the impact of L/C and DM properties on evaporative water removal rate, water distribution in DM, purge efficiency, and irreducible saturation. In the capillary flow dominant regime, it was determined that evaporative water removal is not significantly affected by L/C or DM properties, and can be semi-empirically correlated with critical purge time. The cloth-type DM was found to be superior to paper-type to mitigate the in-plane impedance of the land on water removal. In addition to the ex-situ evaporative tests, neutron radiography was utilized to visualize the in-situ water removal behavior. Results validate a novel purge protocol suggested by the authors in a previous study to achieve a more efficient and durable gas purge that preserves membrane durability.     

Simulation of transient Rayleigh-Bénard-Marangoni convection induced by evaporation

Numerical simulation of thermal convection induced by solvent evaporation in an initially isothermal fluid is considered. Both thermocapillarity and buoyancy driving forces are taken into account, and a criterium based on the Peclet number is used to analyze the stability of this transient problem. Critical Marangoni and Rayleigh numbers are obtained for a large range of Biot and Prandtl numbers. Results of the non-linear simulations are compared with a previous linear transient stability analysis based on a non-normal approach and with visualizations performed during polyisobutylene (PIB)/toluene solutions drying experiments. A scaling analysis is developed for the Marangoni problem and correlations are derived to predict the order of magnitude of temperature and velocity as a function of Bi, Ma and Pr numbers.     

A molecular dynamics simulation investigation of fuel droplet in evolving ambient conditions

Molecular dynamics simulations are applied to model fuel droplet surrounded by air in a spatially and temporally evolving environment. A numerical procedure is developed to include chemical reactions into molecular dynamics. The model reaction is chosen to allow investigation of the position of chemical reactions (gas phase, surface, liquid phase) and the behavior of typical products (alcohols and aldehydes). A liquid droplet at molecular scale is seen as a network of fuel molecules interacting with oxygen, nitrogen, and products of chemical fuel breakdown. A molecule is evaporating when it loosens from the network and diffuses into the air. Naturally, fuel molecules from the gas phase, oxygen and nitrogen molecules can also be adsorbed in the reverse process into the liquid phase. Thus, in the presented simulations the time and length scales of transport processes – oxygen adsorption, diffusion, and fuel evaporation are directly determined by molecular level processes and not by model constants. In addition, using ab initio calculations it is proven that the reaction barriers in liquid and gas phases are similar.     

Porous multiphase approach for baking process – Explicit formulation of evaporation rate

A multiphase model for simultaneous heat and mass transfer in porous medium was developed to simulate the baking process of a bread product. The model was based on Fourier’s law for conductive heat transfer and Darcy’s and Fick’s laws for mass transfer of liquid (water) and gas (water vapour and CO₂) phases. Explicit formulation was adopted for the evaporation rate allowing direct solution of the system of equations. The use of the non equilibrium approach, allowed the implementation of the model in commercial software. Numerical Finite Element Method (FEM) scheme was used to solve the equations. The model was compared with experimental results reported in literature. Results show a good agreement between experimental and numerical results. Sensitivity analysis of the effect of the evaporation rate constant and process operating conditions on the temperature and moisture content were conducted and showed that the baking process was affected mainly by the convective heat transfer and the product initial moisture characteristics.     

Modelling of biofuel droplets dispersion and evaporation

Alternative renewable fuels are more and more important due to increasing oil prices, environmental concerns and their potential to preserve the agricultural activity. For the case of biofuels derived from agricultural crops, several possibilities can be considered, such as raw oil, oil-derived methyl esters, bioethanol or mixtures with conventional fuels (diesel fuel or gasoline). The straight use of vegetable oils and their derivates poses some problems on the mixture formation process and droplet evaporation, that are essentially derived from their much higher viscosity (up to five times the viscosity of the diesel fuel) and higher boiling temperature. The present paper presents a numerical study on evaporating biofuel droplets injected through a turbulent cross-stream. This study uses an Eulerian/Lagragian approach to account for turbulent transport, dispersion, evaporation and coupling between both processes in practical spray injection systems, which usually include air flows in the combustion chamber-like swirl, tumble and squish in I.C. engines or cross-flow in boilers and gas turbines. An array of evaporating biofuel droplets through a cross-flow is studied, and a comparison of the droplet fuel dispersion and evaporation with conventional fuels is performed. The results obtained with DF-2 and RME showed that an homogeneous mixture can only be obtained with very high levels of pre-heating, and the use of ethanol (obtained from sugar or starch crops) may be a better alternative in ignition-assisted combustion systems, while RME can be successfully used as an alternative fuel in applications that utilize diffusion flames.