This invention relates generally to the field of powder technology and, more particularly, to a method and apparatus for measuring the cohesive forces in aggregates of particulate matter.
The tensile, or cohesive, strength of dust aggregates affects the reentrainment of dust in electrostatic precipitators and the removal of dust cakes from fabric filters, but it is a very difficult quantity to measure directly. Conventional methods are based on the application of forces on particulate samples by mechanical means. Such techniques for measuring tensile strength can be ineffective or inaccurate because the forces holding particles together are very small. The problems that arise in using a mechanical approach, include friction and inertia in the apparatus, and the difficulties of attaching the apparatus to a sample. The problem is also complicated by the heterogeneity of inter-particle forces that arises from the range of particle sizes in most applications of interest.
The cohesive forces among particles are often described in terms of measured values of reactions to shear stresses. Several methods have been used, ranging from the simple split-ring Jenike cell to the complex ring shear device. The advantages of the relatively simple design of the Jenike cell are offset by lengthy test procedures and a strong dependence on preparation of the sample. In contrast, characterizations of cohesive forces performed with ring shear devices are quicker and less operator-dependent. However, these devices are quite expensive. Methods and equipment are also presently available for the direct measurement of the tensile strength of powders. The procedures and equipment used in these methods are also relatively complex, due to the difficulties inherent in mechanically applying and measuring tensile stresses. Thus, the instant invention provides a novel approach to the measurement of a quantity that is important to various aspects of flue gas clean up and fine powder handling.