A Manometric Method of Measuring the Apparent Density of Granular Materials

Abstract

Materials in the form of heterogeneous gas–solid systems are widely used in modern industrial production and agriculture. In order to assure a high level of performance of technological processes when such materials are used, it is necessary to know their thermophysical properties, such as density, thermal conductivity, thermal capacity, and thermal diffusivity [1O 3]. The density of granular material is determined by measuring its mass and volume. Different methods and devices are used to measure mass [4]. The mass of the hardest particles or the mass of the particles together with the air between them may be measured. Because of the great difference between the density of a gas and that of particles, the error of such measurements will be insignifi cant. The problem of measuring the volume of granular material does not have a unique solution. Depending on the relationship between the solid and gas phase in a volume that is being monitored, we distinguish the packed, volume, apparent, and effective density of granular material [1, 2]. By the volume density is understood the average density of the particles of a material in the volume of which there are closed and open pores. The defi nition of the apparent density in a volume of particles does not include open pores. The effective density is the density of the matter of the solid particles. For porous materials, some of these types of density may coincide, depending on the structure of these materials. The volume density and apparent density are measured by the methods of liquid and gas substitution. Methods of liquid substitution suffer from a number of drawbacks as compared to gas substitution, for example, the need to remove gas bubbles through heating or other means; interaction of the liquid with solid matter, leading to a variation in the solid volume and the fact that the liquid cannot be reused; the need to take into account the molecular volume of the liquid to assure it can percolate through open pores [2]; and the need to dry the material and the measurement tank. The methods used to measure density with gas substitution are based on the variation of the pressure in the measurement tank containing the test substance. Nondestructive methods of gas substitution are sometimes classifi ed as noncontact methods, since in the course of compressing the gas, which is a constituent part of granular material, no other medium comes into contact with the solid particles.