ABSOLUTE VACUUM: Refers to a pressure or vacuum gauge that compensates for (subtract) the actual barometric reading. PSIA = pounds per square inch absolute; PSIG = pounds per square inch gauge (more common).

AGGLOMERATION: Adherence of particles into a small mass due to moisture, static charge, or chemical or mechanical binding.

BULK DENSITY: The weight per unit volume for solid materials. Expressed as pounds per cubic foot or grams per cubic centimeter. Untapped bulk density is the lowest attainable density. Tapped bulk density is the highest attainable density for a sample without compression.

CAPILLARY FLOW: The flow of liquid by liquid-solid molecular attraction through the material. As liquid is removed from the exterior of the particle, the equilibrium is shifted and the interior liquid is induced to move to the surface.

CONDUCTION: Transfer of heat from one part of a body to another part or to another body with which it is in contact.

DIFFUSION: Movement of internal liquid or vapor from the interior of a solid to the surface.

EXPANSION: All gases expand and contract at the same rate of 1/273 per degree Celsius (ref. gas law).

FRIABILITY: The tendency for materials to break down into smaller sizes due to handling.

HEAT CAPACITY: The amount of energy a mass can store for each degree of temperature difference with its surroundings. Defines the quantity of energy required to increase the average temperature of a mass. Common units are Btu/lb. or Joules/Kg.

INDIRECT CONTACT: The heating medium and product do not intermingle. Heat transfer is by conduction though a body such as a steel shell.

NATURAL REGAIN: The moisture that a material acquires from surrounding air.

RADIATION: Heat transfer by infrared radiation through space (air or vacuum) from a warmer mass to a cooler mass.

SEGREGATION: Separation of particles differing in size, shape, and density. Small, smooth, and dense particle will tend to sink through large, rough, light particles.

TIP SPEED: Refers to the speed of a point (as on an agitator) on the outermost radius in feet per minute. Used for expressing and comparing the speed of various diameter-rotating bodies, including agitator elements.

UNBOUND MOISTURE: The liquid on the exterior of the material or on exterior cells or fibers. Unbound moisture has the same vapor pressure as the liquid in the absence of the solid material at a given temperature. All water in a non-hygroscopic material is unbound.

The terms and definitions for this issue’s Word Search come from a glossary of terms compiled by the Paul O. Abbé (www.pauloabbe.com), a provider of engineered solutions for drying, blending, mixing, or grinding applications.