VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 27, through Friday, November 29. We will resume normal operations on Monday, December 2. Thank you for your patience.

Browsing by Author "Dabak, Turgay"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Coal resource characterization using the theory of coregionalized variables
    Unal, Ahmet (Virginia Polytechnic Institute and State University, 1986)
    A typical coal resource characterization study calls for estimating thickness, density, and quality parameters over a block or node simultaneously. Traditionally, estimation has been done for each variable independent of the other variables. The methods range from the well known polygonal and distance weighting methods to the geostatistical method of kriging. None of these methods takes the correlations between the variables into account explicitly. A comprehensive study has been undertaken to determine whether the joint estimation technique of cokriging may be used to utilize intervariable correlations in increasing the accuracy of estimation. Seam thickness, density, ash, calorific value, and sulphur have been studied to determine whether they are cross-correlated. Significant cross-correlations have been found to exist between ash content, density, and calorific value, where the rank of the coal is stable. A survey and a case study indicated that seam thickness may also be cross-correlated with ash content and density. Subsequently, separate kriging and cokriging results have been subjected to comparison via a cross-validation procedure. After normalization, cokriging has provided substantial improvements over kriging in estimating thickness, density, and ash content. Moreover, cokriging performed well in replicating the correlation schemes where kriging occasionally failed. In this study, geostatistical methods have been found to produce results in compliance with their probabilistic premises. A general purpose geostatistics software package has been written to carry out modeling and part of the research on a personal computer. This package has been designed to provide many advantages over the existing costly and black-box type software.
  • Thumbnail Image
    Formulation of the particle size distribution effects on the rheology and hydraulics of highly-concentrated suspensions
    Dabak, Turgay (Virginia Polytechnic Institute and State University, 1986)
    A formulation was developed for the rheological characterization of highly concentrated suspensions, accounting for the physical effects of particle size distribution. A number of dimensionless parameters were developed signifying the physical characteristics of the solids and the vehicle fluid, and functionally related to the yield-stress and a flow parameter. Each of these expressions of the formulation contains an empirical dimensionless coefficient accounting for the interparticle and fluid/solid interactions that are not explained by the physical parameters involved. A formulation and a methodology were also developed for predicting the shear viscosity behavior of highly concentrated suspensions at low and high shear-rates through the use of three parameters signifying effects of particle size distribution. A number of applications were made using various non-coal and limited coal-liquid mixture data reported in the literature to demonstrate the general validity of the formulations. A methodology was proposed for the analysis of the particle size distribution effects on the overall optimum energy efficiency during hydraulic transportation and particle size reduction. The computer model developed for this purpose was employed to evaluate the transportation energy consumption and the energy consumed in the grinding process to prepare the slurry, in pipes of various sizes and lengths for a coal slurry of various specified particle size distributions and concentrations. Correlations obtained indicated the sensitivity of transportation energy efficiency to various parameters including the maximum packing concentration, relative concentration, specific surface area of particles, surface area mean size, pipe size and length, and annual mixture throughput. The results of combined energy calculations have shown that the particle size distribution and related physical parameters can significantly affect the energy efficiency due to both grinding and transportation, and the delivered cost of slurry fuels.