多孔建材中VOC扩散系数的两尺度模型

基于对建材微观结构的分析和压汞实验,提出了预测建材中有机挥发物(VOC)扩散系数的宏观一介观两尺度模型.和传统的从压汞实验计算扩散系数方法不同的是,本模型不仅考虑了孔隙率,还对孔的尺度分布和孔的连接方式进行了研究和分析.三种不同中密度板中VOC的散发实验表明,采用新模型计算的扩散系数比文献中的传统模型更好地吻合实验数据.     

渤海近岸水体后向散射系数反演模型

水体后向散射系数bb是重要的海洋光学参数,在以悬浮物为主要组分的浑浊二类水体中,其对于水体光学性质起着决定性的作用,该参数的遥感反演对于海洋光学与水色遥感研究具有重要意义.利用2005年渤海近岸水体实测数据集,建立了基于水体遥感反射率光谱数据的后向散射系数bb(λ)经验反演模型(λ=442 nm,488 nm,532 nm,589 nm,676 nm),经实测数据检验,bb(442)和bb(589)反演平均相对误差约为30%;bb(488)和bb(676)反演半均相对误差优于40%;bb(532)反演半均相埘误差约为57%.通过分析模型对于输入误差的敏感性发现,当输入端引入±5%的误差时,模型反演值的误差波动在绝大多数情形下可控制在±10%以内,模型足稳定可靠的.模型适用于渤海近岸浑浊水体,可用丁水体光学参数的时空分布特征分析以及基丁固有光学参数的水色组分遥感反演.     

Boundary coupled dual-equation numerical simulation on mass transfer in the Process of laser cladding

The coupled numerical simulation on fluid flow, heat transfer, and mass transfer in the process of laser cladding is undertaken on the basis of the continuum model.In the simulation of mass transfer in the laser molten pool, the concentration distribution in the regions on different sides of the interface between cladding layer and substrate is calculated separately and coupled at the co-boundary.The non-equilibrium solute partition coefficient is obtained from equilibrium solute partition coefficient according to the Sobolev model.By using the developed software which is based on the commercial software PHOENICS 1.4, the distribution of Fe in laser molten pool in an experiment of cladding Stellite 6 on 12CrMoV is calculated.The obtained results well coincide with the experimental ones.     

The effect of magnetic field heat treatment on magnetostriction of Terfenol-D 2-2 composites

Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d₃₃ of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10⁻⁶ at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10⁻⁶ without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10⁻⁶. The dynamic magnetostrictive coefficient d₃₃ of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d₃₃ of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment.     

The relation between composition in laser absorption region and ambient pressure

In this paper, the compositions in a laser absorption region can be determined from the experiment of laser impulse coupling. When the ambient pressure varies from 9325 to 33325Pa, the compositions are vapour and plasma; while from 35325 to 101325Pa, they are ambient air and plasma. By analysing the relation between the degree of compression and the ambient pressure, the compositions can be determined and the variation of plasma can be explained.     

Electronic transport study of PbSe pellets prepared from self-assembled 2D-PbSe nanostructures

This work presents a study of the electronic transport properties of PbSe pellets fabricated starting of PbSe nanostructures that exhibited a flake-like 2D morphology, which were synthesized by the co-precipitation method. Seebeck coefficient measurements revealed that the PbSe sample displays n-type conductivity, a maximum Seebeck coefficient of −512.6 μV/K around 380 K, and that the carriers scattering is dominated by acoustic and optical phonons. The Fermi level dependence on the temperature and the band gap energy are also reported. Interestingly, size-dependent confinement effects due probably to the reminiscent PbSe 2D character could be evidenced.     

Experimental and numerical analysis of cylindrical turbulators in a double pipe heat exchanger under turbulent flow conditions

In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor.     

Scattering coefficients for a sphere in a visco-acoustic medium for arbitrary partial wave order

Analytical solutions are reported for the scattering coefficients of a solid elastic sphere suspended in a viscous fluid for arbitrary partial wave order. Expressions are derived for incident compressional and shear wave modes, taking into account the viscosity of the surrounding fluid and resultant wave mode conversion. The long compressional wavelength limit is employed to simplify the derivation, whereas no restriction is placed on the shear wavelength in the fluid compared to the particle dimension. The analytical approximations are compared with numerical results obtained from matrix inversion of the boundary equations and agree within the validity domain of the solutions.     

Side Information Generation Scheme Based on Coefficient Matrix Improvement Model in Transform Domain Distributed Video Coding

In order to effectively improve the quality of side information in distributed video coding, we propose a side information generation scheme based on a coefficient matrix improvement model. The discrete cosine transform coefficient bands of the Wyner–Ziv frame at the encoder side are divided into entropy coding coefficient bands and distributed video coding coefficient bands, and then the coefficients of entropy coding coefficient bands are sampled, which are divided into sampled coefficients and unsampled coefficients. For sampled coefficients, an adaptive arithmetic encoder is used for lossless compression. For unsampled coefficients and the coefficients of distributed video coding coefficient bands, the low density parity check accumulate encoder is used to calculate the parity bits, which are stored in the buffer and transmitted in small amount upon decoder request. At the decoder side, the optical flow method is used to generate the initial side information, and the initial side information is improved according to the sampled coefficients by using the coefficient matrix improvement model. The experimental results demonstrate that the proposed side information generation scheme based on the coefficient matrix improvement model can effectively improve the quality of side information, and the quality of the generated side information is improved by about 0.2–0.4 dB, thereby improving the overall performance of the distributed video coding system.     

An experimental investigation on heat transfer enhancement in circular jet impingement on hot surfaces by using Al2O3/water nano-fluids and aqueous high-alcohol surfactant solution

The present article reports the heat transfer characteristics of a vertical stainless steel foil of 0.15 mm thickness (SS304) by circular impinging jets of various fluids such as pure water, nano-fluids (Al₂O₃-water, ф = 0.15%, 0.6%), and aqueous high-alcohol surfactant (HAS, i.e., 2-ethyl-hexanol, 100–400 ppm) studied using an infrared thermal imaging camera (A655sc, FLIR System). The enhancement in the heat transfer rates for Al₂O₃-water nano-fluids with ф = 0.15%, ф = 0.60%, and aqueous surfactant solution (150ppm) is found to be 140%, 207%, and 117% higher compared to pure water results, respectively. The surface characteristics of the foil after jet impingement by various fluids are also studied using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and surface wettability.