Page 326 - Mechanical Engineer's Data Handbook

314 MECHANICAL ENGINEER’S DATA HANDBOOK
combined stress A state of stress combining tensile conservation of matter Matter is neither created nor
(or compressive), shear, and bending stresses. destroyed during any physical or chemical change.
combustion equations Chemical equations used in conservation of momentum In a closed system the
the study of combustion of fuels for engines, boilers, sum of the momenta Zmu, is constant, where:
etc. m= mass, u = velocity.
combustion products Chemical products resulting constant-pressure cycle (Diesel cycle) An ideal engine
from the combustion of fuels in air. cycle in which combustion is assumed to take place at
complex number A number of the form (a+ib) constant pressure.
having a ‘real’ part a and an imaginary part ib where constant volume cycle (Otto cycle) An ideal cycle in
i = J-1. The symbol j is also used. which combustion is assumed to take place at constant
composite A material consisting of a mixture of two volume. The basis for the petrol engine cycle.
or more materials, e.g. glass or carbon fibres in a contact stresses The localized stress between contact-
plastic matrix. ing curved surfaces and between a curved and a flat
compressibility The reciprocal of ‘bulk modulus’. surface, such as occurs in ball and roller bearings.
compression ignition engine An engine in which igni- continuous beam A beam supported on three or more
tion takes place as the result of temperature rise in the supports.
air/fuel mixture due to compression. continuous casting A process in which an ingot, billet
compression ratio In an internal combustion engine, or tube is produced continuously.
the ratio of the total volume in a cylinder at outer dead convection of beat The transfer of heat from one part
centre to the clearance volume. In powder metallurgy, of a fluid to another due to ‘convection currents’ often
the ratio of the volume of loose powder to the volume due to gravity (natural convection) or by induced flow
of the ‘compact’ made from it. (forced convection).
compressive strength The maximum compressive convergent-divergent nozzle A nozzle for fluid flow
stress a material will withstand, based on the original which decreases in area to a throat and then increases
cross-sectional area. in area to the exit; the flow may be supersonicat outlet.
compressive stress Compressive force divided by convergent nozzle A nozzle for fluid flow which
area of cross-section. decreases in area to a ‘throat’ at outlet.
compressor A rotary or reciprocating machine which core A formed object inserted into a mould to shape
compresses air or other gases. an internal cavity.
condenser A heat exchanger in which a vapour, e.g. core box In casting, a box in which cores are formed
steam, is condensed, usually by water flowing in tubes in sand, etc.
over which the vapour passes. corrosion The deterioration of a metal by chemical or
conductance The property of a substance which electrochemical reaction with its environment.
makes it conduct electricity. The unit is the ‘siemens’ cosine rule A mathematical rule for solving triangles:
(symbol G). The reciprocal of resistance. a’ = b2 + c2 - 2bc cos A, where a, b, c = lengths of the
conduction of heat Heat transferred from one part of sides, A =angle opposite side a.
a medium to another without motion, the heat being counterboring Drilling or boring a flat-bottomed
passed from one molecule to another. hole, often concentric with other holes.
conductivity (electrical) Conduction (reciprocal of counterflow heat exchanger A heat exchanger in
resistance) between opposite faces of a 1 m cube at a which the two fluids flow in opposite directions.
specified temperature. The unit is the ‘ohm metre’ countersinking Forming a conical depression at the
(symbol a-m). entrance to a hole for deburring, and for countersunk
conductivity (thermal) A measure of the rate at which screw heads.
heat flows through a wall by conduction. The unit is couple Two equal and opposite forces parallel to one
watt per metre per kelvin (W m-I K- ’). another. The distance between them is the ‘arm’. Its
conservation of angular momentum In a closed sys- magnitude is the product of one force and the arm.
tem the sum ofthe angular momenta ZZw is aconstant, crank An arm on a shaft with a pin used to produce
where Z = moment of inertia, w = angular velocity. reciprocating motion with a connecting rod.
conservation of energy The energy in a closed system crankshaft A shaft carrying several cranks, usually at
cannot be changed but only interchanged, e.g. poten- different angular positions, to which connecting rods
tial to kinetic energy. are fitted in an engine, reciprocating pump, etc.