Oxford Dictionary of Chemical Engineering by Schaschke Flashcards
(32 cards)
Another name for the *Weizmann process used for the production of acetone, butanol, and ethanol using the acid-resistant bacterium Clostridium acetobutylicum.
ABE fermentation
The removal of material by * erosion , * evaporation , or * chemical reaction . For short-term protection against high temperatures as a form of fire protection or fireproofing of process equipment, sacrificial materials are used such that during a fire there is resistance and protection to the equipment beneath for a sufficient period of time
ablation
The horizontal or x-coordinate in a two-dimensional Cartesian coordinate system such as a chart or graph. The * ordinate is the vertical or y-coordinate.
abscissa
Denoting a number or a measurement that does not rely on a standard reference value.
absolute
The mass per unit volume of a substance. It is the density of the actual substance and does not include any free space that may be between particles. The SI units are kg m –3 .
absolute density
The difference between a measured value and its true value.
absolute error
A type of filter used to remove all particles that may be present in the
flow of gas into or out of a process. Absolute filters are used for ensuring the sterile flow of
air or oxygen to biological reactors as well as for clean rooms and sterile cabinets used for
analytical work. Unlike an * air filter , the pore sizes are smaller than the expected particle
size. With a typical uniform pore size of 0.2 μm, the pressure drop is greater than that of air
filters made from fibrous materials.
absolute filter
The amount of water in air expressed as the mass of water vapour per unit mass of dry air for a particular temperature and pressure condition. The SI units are kg water kg air^–1
absolute humidity
The measurement of gas or air pressure relative to the pressure in a
total vacuum. In comparison, the * gauge pressure is measured above atmospheric pressure, which is variable.
absolute pressure
(Symbol ε) The roughness of a solid surface expressed as the average height of undulations and imperfections. It is measured using an instrument that draws stylus over the surface. The roughness of the inner surface of a pipe wall used to transport fluids with turbulent flow has the effect of increasing frictional pressure drop. Expressed as a ratio with internal pipe diameter, it is used in determining the friction factor of fluids flowing in pipes with turbulent flow. See relative roughness
absolute roughness
The lowest possible thermal energy state of a material. This corresponds to 0 K.
absolute zero
- A material that is capable of stopping ionizing radiation. * Alpha particles can be readily stopped by a sheet of paper whereas beta radiation can be resisted by a centimetre of aluminium. Gamma radiation is absorbed by materials with a high density, such as steel and concrete. Neutron absorbers include boron, hafnium, and cadmium and are used in the control rods in nuclear reactors.
- A shortened name for an * absorption tower
or column.
absorber
A mass transfer process in which one or more gases in a gaseous mixture is transferred into a liquid solvent or a solid. It is the most common form of separation of low molecular weight materials. Absorption is often used to remove gases from gas streams that may be harmful downstream or when released from the process. The absorption factor is used to determine the ease with which a component will absorb into the liquid phase and is based on liquid and vapour flow rates as well as the vapour liquid equilibrium for the component. For example, ammonia can be absorbed from a gas stream using water as the scrubbing liquid. Compare adsorption .
absorption
A tall vertical column containing a packing material in which a gas is absorbed by intimate contact with a liquid flowing downwards under the influence of gravity. The gas can be admitted either countercurrent or cocurrent to the flow of liquid in which one or more of the gaseous components are absorbed into the liquid. The minimum flow rate of scrubbing liquid required to achieve an absorption duty requires an infinite height of packing. In practice, a higher liquid rate is used to achieve a compromise between capital cost (i.e. height of column) and the operating cost (i.e. liquid flow rate). It is also known as a * scrubber.
absorption tower
The portion of radiant thermal energy falling on a surface which is converted to heat with the remainder being either reflected or transmitted. The absorptivity is dependent on the wavelength of the energy and the properties of the surface including colour. Compare reflectivity ; transmissivity .
absorptivity
A substance used to initiate and develop a fire. Flammable liquids are the most common form of accelerants.
accelerant
(Symbol a ) The rate of change of speed or velocity with respect to time. If the acceleration is constant then the final velocity, v , of a body that is initially moving with a velocity u after time t , is v u at = + . If the acceleration is not constant, then the acceleration can be found from:
a=(dv/dt) =[(d^2)s/dt^2]
where s is the distance moved by the body. In the case of motion in a circle, the acceleration is v^2/r and directed to the centre of the circle of radius r.
acceleration
(Symbol g) The acceleration experienced by a body due to the Earth’s gravitational field. The acceleration is normally taken as 9.806 65 m s ^(–2) although it does vary by small amounts over the Earth’s surface and with altitude.
acceleration due to gravity
The rapid growth of the culture of microorganisms in a bioreactor prior to the * log phase . After the medium within a bioreactor has been inoculated with a small population of microorganisms, there is an initial * lag phase of no growth in which they adjust to their new environment. Cell division then occurs at an increasing rate until the maximum growth rate is reached. The log or exponential phase corresponds to the rapid cell division such that the logarithm of the population increase with time is constant. As the substrate eventually becomes exhausted, this is then followed by a deceleration phase prior to the * stationary phase .
acceleration phase
A substance that alters the rate of a chemical reaction such as a * catalyst .
accelerator
A device used to smooth the rate of flow from a reciprocating pump and prevent the destructive effects of * water hammer from occurring. It consists of a vessel located on the pipe close to the pump with a * non-return valve preventing return flow back to the pump. The vessel contains a gas or a bladder bag although some use springs. As the pump discharges, some of the fluid enters the accumulator compressing the gas or spring. At the point of valve closure, the gas or spring expands allowing the accumulated volume to discharge through the pipe.
accumulator
A measure of the closeness or agreement of a numerical value to a true value. It is expressed as either * significant figures or decimal places depending on whether proportional or absolute accuracy is important. For example, a number written as 5.425 normally assumes that the four figures are meaningful. It would be incorrect to write the number to a precision of five significant figures unless the * error in the estimate is indicated such as 5.4250 ± 0.0005. Compare precision
accuracy
A parameter used in * equations of state to estimate physical and thermodynamic properties. It is used to characterize the acentricity of molecules in reduced-state correlations along with reduced pressure and reduced temperature.
acentric factor
A process for the production of cellulose fibres used for textiles. There are two methods: 1. The cellulose is obtained from wood pulp and dissolved in carbon disulphide and sodium hydroxide. The thick brown liquid that contains cellulose xanthate is forced through orifices into acid. The xanthate decomposes to leave a cellulose fibre known as viscose rayon. 2. The cellulose obtained from wood pulp and cellulose acetate is formed by dissolving in acetone. The solution is forced through orifices and the solvent is allowed to evaporate leaving a cellulose fibre of acetate rayon.
acetate process
