Papers by Keyword: Fractal

Abstract: The porous materials are usually the sources or sinks of indoor volatile organic compounds (VOC). In order to predict the VOC emission rate and choose best adsorbents, reasonable estimation of the diffusion coefficients of porous materials is required. Porous materials were usually depicted as a random network of interconnected pores of unspecified sizes and shapes. It may generate deviation to assume the network as simple topological structures. This paper investigated the diffusion coefficients of porous mate­­rials with the fractal theory and derived their diffusion coefficients considering the pore size distribution of the materials. The calculated result was validated by published experimental data.

Abstract: In order to deeply investigate the contact stress state of two balls, a new fractal contact model of two ball’s surfaces is set up on the basic of traditional contact theory and new fractal contact model theory. It is proved to be true through the predicting result and the contact example respectively by using the traditional Hertz theory and the fractal theory. This model can generally reflect the infections of contact stress by the micro-factors and macro-factors of two balls, so it can ensure veracity and certainness of stress analysis. The establishment of the model supplies a basis and theory foundation for further practical application (such as contact stress calculation of rolling bearing and sliding bearing) and experimental research.

Abstract: For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

Abstract: The pore in the sinter is an important character. Because of multiphase and asymmetry in the sinter, the structure of the pore is very complex. To study the character of the pore effectively, the method of mercury intrusion porosimetry is applied to measure the pore in the sinter, and the results are dealt with by the fractal theory. The results prove that the pores in the sinter are actually fractal structure when the size of the pores is more than 204.5 nm because their curves in the log-log plot are linear, and some curves qualified with the linearity obviously possess of the segment linearity character. According to the calculation of the fractal D, the relationship of the strength and fractal D will be established.

Abstract: The sinter ore samples with different content of silica were prepared by the mini-sintering method so as to study the micro-mechanism of sinter. The fractal theory was also applied to analyze quantitatively the grain distribution in the samples’ two-dimensional microstructure. The study found that the grain distribution of the sinter shows the fractal characteristic, its fractal dimension is about 1.95, and the fractal dimension can be used to characterize uniformity of the grain distribution. With the increase of silica content, the fractal dimension of the samples shows a linear decreasing trend and it is the same trend in the comparing sintering-cup experiment when the fractal dimension of particle size distribution reduces, the silica content increases. In addition, the compressive strength of mini-sintering sinter sample was also measured. It shows that the compressive strength is the highest when the silica content is 3.8 wt%, which is correlative with the porosity, the content of calcium ferrite and glassiness in the sinter ore besides the fractal dimension.

Abstract: The raceway boundary is coarse and fragmentized, but all of previous studies are based on Euclidean geometry, which regard the dimension of raceway as an integer. In this paper, particle velocity contour has been developed to define the raceway boundary. The fractal method of calculating raceway size, which describe boundary with extremely un-regular or fragment characteristic, is brought forward in physical model. The result shows that the precise raceway boundary can be obtained by particle velocity contour, and the surface area of ellipsoidal raceway based on fractal is larger than that based on Euclidean.

Abstract: In order to find the distribution law of coal fragmentation, mathematic model of size distribution was built according to fractal theory. Based on this, the experiments of impactive crash were carried out under different impact rate and different Protodikonov's hardness. The comparison between Weibull distribution and fractal distribution was done so as to find the relationship between the influence parameters and the coal fragmentation characteristic index, the coal fragmentation degree coefficient and the fractal dimension. The results indicate that both two types of distribution functions are suitable for the distribution discipline of coal fragmentation, but the relationship of the coal fragmentation degree and impact parameter is not reacted correctly by the coal fragmentation characteristic index and coal fragmentation degree coefficient in the Weibull distribution while the coal fragmentation degree could be expressed by the fractal dimension in fractal distribution. The relationships between the fractal dimension and the rate, the Protodikonov's hardness of coal are linear.

Abstract: The fractal characteristic of microstructure in semisolid A356 alloy was researched by the calculating program written to calculate the fractal dimensions. The results indicated that the morphology of primary grain in semisolid A356 prepared by compound process is characterized by fractal dimension, and the morphology of primary grain at the different position of ingot had the different fractal dimensions, which reflected the effect of solidified conditions at different position in the same ingot on the morphology of semisolid primary grain.

Abstract: The aim of this study was to gather methodological clues in the scope of a fractal description of non-planar surfaces, which clues can be used for testing biomaterials. The fundamentals of a few most popular fractal methods of surface analysis are discussed here and two new methods are proposed by presenting their basic assumptions. On this basis, appropriate programs for numerical calculations have been developed, while simultaneously using measuring files from instruments which enable stereometric measurement of surfaces (profilographometers, confocal microscopes, etc.).

Abstract: According to frame concrete theory, Concrete was composed of mortar matrix, coarse aggregate, and transition zone between mortar matrix and coarse aggregate. Proper particle grading of fine aggregate can not only save cement, but also increase comprehensive properties of mortar matrix. Uniform design method was used to study the relationships between the grading of fine aggregate and workability, and the relationship with mechanic properties of mortar matrix and concrete. Based on fractal theory, the relationship between fractal dimension and modulus of fineness, and the relationship between fractal dimension and n value in Fuller equation were researched. It concluded that grading of fine aggregate affects the workability and mechanic properties of mortar matrix and concrete, significantly. There was a good linear relation between fractal dimension and n value in Fuller Equation, and fratatal dimension decreased with modulus of fineness increasing.