CBE Interdisciplinary Glossary

ENGINEERING: The art of doing something well with one dollar what any idiot can do with two (or was it the other way around?).

Engineering

BIOCORROSION (see Microbially Influenced Corrosion–MIC)

CELL (Corrosion Eng./Electrochem.) Reactor used to assess the corrosion of metals, e.g. polarization cell.

CHALKING (Corrosion Eng.) The development of loose removable powder at or beneath a coating on metallic surfaces.

CHECKS (Corrosion Eng.) Slight microscopic breaks in a coating which do not penetrate to the underlying metal.

CORROSION A surface electrochemical phenomenon common to all base metals in aqueous or humid environments whereby metal ions are developed at an anodic site and the electrons associated with this dissolution accepted at a cathodic site.

EXFOLIATION (Corrosion Eng.) Scaling off of a surface in flakes or layers.

FLOW VELOCITY/FLOW RATE The distance traveled by a packet of fluid in a unit of time. The speed depends on where within the liquid the flow is measured. For example, the surface of a river will be flowing at the fastest speed, while at the very bottom of the river, it will not be flowing at all. Hence, a velocity gradient can be measured. In a closed pipe, liquid at the center of a pipe will be flowing the fastest, while at the edge of the pipe the velocity is zero. The average flow velocity can be calculated by dividing the flow rate by the cross sectional area.

FLUID VOLUMETRIC FLOW RATE The volume of fluid passing through a tube (or any geometric cross section) per unit time.

Table of Contents

Terms & Concepts by Discipline

Index

Mass transfer and momentum boundary layers are not necessarily the same, but are often closely related.

MICROBIAL TRANSPORT The movement of individual cells or aggregates of cells through a system. Often, this involves displacement of freely suspended microbes from the bulk aqueous phase to a surface and vice versa, allowing dissemination of progeny throughout the system.

MICROBIALLY INFLUENCED CORROSION (MIC)  The result of the presence and/or activities of surface-associated organisms that promotes deterioration of a metal or alloy, generally taking the form of localized attack on the surface.

NUTRIENT LOADING RATE This is simply the mass rate at which substrate or nutrient is delivered to a system. If the inlet concentration of substrate in S_in (mass/volume) and the fluid flow rate is F (volume/time), then the substrate loading is FS_in (mass/time). An average measure of the rate of nutrient or substrate provision in a system is expressed as mass substrate per biofilm area per time.

PICKLE (Corrosion Eng.) A solution or process used to remove corrosion products from the metals without affecting the base metal.

PROCESS ANALYSIS Simply a method of mathematically describing a complex phenomenon as the net result of a number of different processes. The rate concept more specifically assumes that the changes in the state of a system with time can be systematically treated as the sum of the rates of the individual processes acting on the system.

PROCESS ENGINEERING Engineering a sequence of individual processes or conversions to efficiently convert a raw material to a finished product. The processes involved can comprise physical, chemical, or biological changes in the raw material as it becomes a product. Physical processes change the shape, size, color, temperature, or concentration of a compound but do not alter its molecular structure. Chemical or biological reaction processes alter the very nature of a molecule, changing it to something different.

REACTOR ENGINEERING Concerned with the exploitation of a chemical, biological, or enzymatic reaction under a controlled set of conditions to affect either information about the reaction or to produce a product or products efficiently. Reactor design is that activity specifically directed toward setting the size and operating parameters of a reactor to affect some desired goal.

REYNOLDS NUMBER The Reynolds number is the ratio of inertial forces, as described by Newton's second law of motion, to viscous forces. If the Reynolds number is high, inertial forces dominate and turbulent flow exists. If it is low, viscous forces prevail, and laminar flow results. (See the book Biofilms, Characklis et al., pg. 273.)

Laminar vs. Turbulent Flow

SCALE DEPOSIT (Corrosion Eng.) Partially adherent layers of corrosion products on metals which generally develop in hard water and at high temperature.

SHEAR STRESS Shear stress in a flowing liquid is the force exerted as one layer moves past another.

FLUID SHEAR STRESS In flowing fluid all the molecules of the fluid "rub" against one another as they travel down the tube. Fluid molecules also exert a "rubbing" force on the walls of the tube. This rib or shear force can be calculated for flow in a tube if you know the fluid velocity, roughness of the tube, fluid properties, and diameter of the tube.

WALL SHEAR STRESS In biofilm studies we are normally concerned with wall shear stress. This is the shear stress at the wall caused by the liquid moving past it.

(PRODUCT) SOURING The result of the conversion of sulfate or other oxidized forms of sulfur-containing ions to hydrogen sulfide gas and sulfide ions through the respiratory activities of sulfur-reducing bacteria in an oil reservoir. In producing operations, the most significant detrimental effect of microbial souring is the generation of toxic and corrosive hydrogen sulfide that attacks vessels and pipeline and decreases the quality of the associated natural gas.  This may require expensive production equipment (rated for sour service) and gas sweetening operations to bring the gas back to export pipeline standards.

WATER ACTIVITY (Corrosion Eng.) A term used to classify aggressive nature of waters based on their chemical and physical parameters and their consequences on the corrosion of metals. Similar to corrosivity index of waters.