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11.
Flow resistivity, tortuosity, viscous characteristic length and thermal characteristic length of three melamine foam and two glass wool samples have been measured. It has been found that a melamine foam sample with a bulk density 10.3 kg m−3 and a glass wool sample with a bulk density 28.0 kg m−3 have almost the same flow resistivity, however, the bulk density is as much as three times different. The cross-sectional pore shape factors, which are deduced with the non-acoustical parameters in the Johnson-Allard model, of the melamine foam are smaller than those of the glass wool. This paper also discusses a new relationship between the flow resistivity, the fibre equivalent diameter and the bulk density in melamine foam. 相似文献
12.
Takahiro Ohkubo 《Transport in Porous Media》2008,72(3):339-350
The diffusion of fluids in porous media, composed of regularly aligned plate-like obstacles, was studied by Monte Carlo simulation.
The diffusion coefficients and all diagonal components of the diffusion tensor were estimated for these media. The calculated
tortuosities were modeled as a function of porosity by using the Koponen’s equation related to percolation threshold. These
results indicated that a media with a homogeneous porosity has a heterogeneous tortuosity, is affected by the alignments of
the plate-like obstacles. Furthermore, the calculation results were compared with the experimental results for fixed perpendicular
plates of Comiti and Renaud as a function of porosity. The results for tortuosity compared well for porosity larger than 0.86. 相似文献
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14.
Quantification of water compartmentation in cell suspensions by diffusion-weighted and T(2)-weighted MRI 总被引:1,自引:0,他引:1
Roth Y Ocherashvilli A Daniels D Ruiz-Cabello J Maier SE Orenstein A Mardor Y 《Magnetic resonance imaging》2008,26(1):88-102
When studying water diffusion in biological systems, any specific signal attenuation curve may be reproduced by a broad range of mathematical functions. Our goals were to quantify the diffusion and T2 relaxation properties of water in a simple biological system and to study the changes that occur in osmotically stressed cells. 相似文献
15.
Evaluation of acoustical and non-acoustical properties of sound absorbing materials made of polyester fibres of various cross-sectional shapes 总被引:1,自引:0,他引:1
Four types of fibrous material samples made of polyester fibres of various cross-sections, i.e. circle, hollow, flat and triangle, have been prepared. The surface impedance and the non-acoustical parameters of them have been measured.The effect of the variation in the cross-sections on the acoustical properties and the non-acoustical parameters of the polyester fibre samples have been examined. The effects of the ‘circle’ and the ‘hollow’ samples are almost the same. However, for the ‘flat’ and the ‘triangle’ samples, the effects different from the ‘circle’ sample are found in the measured flow resistivity and the two characteristic lengths. This paper also discusses the equivalent diameters of the materials made of non-circular cross-sections. 相似文献
16.
The aim of the present work has been to develop a methodology which accurately predicts the acoustic behavior of a material without having to manufacture large panels and testing them in reverberation room. Moreover, it can be predicted the sound absorbing performance at normal and random incidence of the sound wave on a material for different thicknesses and multilayer configurations, dramatically reducing the number of experimental tests. This methodology might decrease the cost of the investigation, which is particularly important when dealing with recycled materials that must compete with commercial products used in the same application. 相似文献