View:

decibel

decibel   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...decibel ( G ) A logarithmic measure of the ratio of two variables, V 1 and V 2 say, defined by G (dB) = 20log 10 ( V 1 / V 2 ). By choosing a suitable reference value for V 2 the decibel can be used as a measure of a variable V 1 , rather than of the ratio between variables. For example, sound pressure level ( SPL ) is expressed in decibel by SPL (dB) = 20log 10 ( p/p REF ) where p is the sound pressure and p REF a reference pressure, normally taken as 20 μ ‎Pa. Because decibels are a logarithmic measure, they are additive when two variables...

gain margin

gain margin   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...amount by which the gain of the system, at the frequency at which the phase shift is 180°, would have to be increased to reach unity. It is thus a measure of how much the gain could be increased before instability occurs. In decibels, it is: G a i n M a r g i n = − 20 log 10 | G ( i ω ) | ϕ = 180 where G(i ω ‎) is the gain at frequency ω ‎ , i = − 1 and ϕ ‎ = 180 indicates that the gain is measured at the frequency where the phase shift ϕ ‎ is 180°. See also Bode plot ; Nyquist diagram...

incompressible

incompressible   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...incompressible A substance for which the specific volume (or density) does not change with increasing or decreasing pressure, is incompressible, and has an infinite speed of sound . Liquids are practically incompressible and have high sound speeds, e.g. 1 482 m/s for water at 20 o C. See also compressibility ; inviscid fluid...

solidification range

solidification range   Quick reference

A Dictionary of Construction, Surveying and Civil Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2020

...range The temperature range between the liquid and solid state for a material on cooling from the liquid state. Many solids (especially metals) do not have a specific or single melting point; indeed, melting occurs over a range, e.g. 20°C, this is the solidification range. When a metal or material is heated and enters this range, it undergoes incipient...

stokes

stokes   Quick reference

A Dictionary of Chemical Engineering

Reference type:
Subject Reference
Current Version:
2014
Subject:
Science and technology, Engineering and Technology
Length:
74 words
Illustration(s):
1

...stokes (Symbol St) A c.g.s. unit of measure of the kinematic viscosity of a fluid expressed as the ratio of the viscosity, μ , in poise divided by the density, ρ , in grams per cubic centimetre: The units of centistokes, cSt, are more commonly used where 1 cSt is equal to 10 −6 m 2 s −1 . The kinematic viscosity of water is exactly 1 cSt at 20.2 º C. ...

standard state

standard state   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...STP ) defined by IUPAC as 273.15 K (or 0°C) and 10 5 Pa (or 1 bar). Until 1982 the standard pressure was defined as exactly 1 atm (or 1.013 25 × 10 5 Pa). Property values at the reference state are often indicated by the superscript o , e.g. h o and u o . The standard temperature is sometimes taken as 20 or 15°C. See also Normal Temperature and Pressure...

brick

brick   Quick reference

A Dictionary of Construction, Surveying and Civil Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2020

...municipal buildings, and produced in a regular block form for building walls. Bricks are usually made from clay and calcium silicate, although other types are also used, e.g. concrete. Bricks are porous materials with up to 25% free volume with compressive strengths up to 100 MPa (N/mm 2 ) with common UK dimensions of 215 × 102.5 × 65 mm. A common house brick is normally within a range of 20–40...

hypereutectic alloy

hypereutectic alloy   Quick reference

A Dictionary of Construction, Surveying and Civil Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2020

...the eutectic composition. If two metals are mixed together, a binary alloy phase system is obtained. At any mix of the two metals, the alloy will not have a definite melting point; instead, it will melt over a temperature range (e.g. over 20 o C). Only at one specific mix between the two alloys (assuming alloy A and alloy B), e.g. 50% A and 50% B, will the alloy have one specific melting point. This unique composition whereby a two-metal alloy system has one specific melting point is the eutectic composition . Thus assuming the eutectic composition to be 50%...

cone penetrometer

cone penetrometer   Quick reference

A Dictionary of Construction, Surveying and Civil Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2020

...apparatus consists of a polished stainless steel cone, with a mass of 80 g having an angle of 30 o and a dial gauge calibrated to 0.1 mm. In the cone penetration test the cone is allowed to penetrate a soil sample, at a range of different moisture contents, confined within a tin 55 mm in diameter and 40 mm high. Penetration values are plotted against moisture content values and a best-fit line is drawn. The liquid limit of the sample is taken as the moisture content corresponding to 20 mm...

plasma

plasma   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...plasma An inert gas heated, e.g. by an electric arc, to a sufficiently high temperature (10 000 to 20 000 K is typical) for it to ionize. A plasma is created in the gas (typically sulfur hexafluoride) within a high-voltage circuit breaker when the contacts separate. Among the processes using a plasma to modify the physical and chemical properties of a material’s surface is plasma spraying in which a consumable in powder form is melted and propelled through a nozzle (a plasma torch ) on to a substrate to form a coating. The consumables are fed into a plasma...

International System of Units

International System of Units   Quick reference

A Dictionary of Mechanical Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...came into effect on 20 May 2019 . Minor adjustments were also made to the values of these constants. In addition to the base units, there are 22 coherent derived units , including radian (rad) for plane angle, steradian (sr) for solid angle, hertz (Hz) for frequency, newton (N) for force, pascal (Pa) for pressure, joule (J) for energy, work, and amount of heat, and watt (W) for power and radiant flux . Recommended practice is to avoid combinations such as N/mm 2 , MN/m 2 being preferred. The SI system also specifies 20 prefixes for the...

jar test

jar test   Quick reference

A Dictionary of Construction, Surveying and Civil Engineering (2 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Engineering and Technology
Length:
274 words
Illustration(s):
1

...four or six 1000 ml beakers with raw water. Different dosages of the coagulant (e.g. alum ) is then added to each beaker—the coagulant is normally added from a stock solution. The beakers are then placed on the jar test equipment, where paddles are inserted into the beakers. The paddles are initially rotated for a short time at high speeds (say, 200 rpm for 60 seconds) to ensure uniform dispersion of the coagulant. After which the speed of the paddles is reduced (say, 20 rpm for 15–30 minutes) to aid the formation of floc . The paddles are then stopped...

carbon intensity

carbon intensity   Quick reference

A Dictionary of Energy Science

Reference type:
Subject Reference
Current Version:
2017

...for biofuels it includes emissions associated with land-use change. Examples, in units of g CO 2 -eq/MJ, are: petrol ( US gasoline) ~95; corn starch ethanol ~65–90; sugar cane ethanol ~45–70. When applied to power stations, the carbon intensity is the amount of emissions per unit of electricity generated. Typical values, in units of kg CO 2 -eq/MWh e , are: coal-fired ~1000; gas-fired ( combined cycle gas turbine ) ~500; solar photovoltaic farm ~50; onshore wind farm ~20. When applied to a country, the carbon intensity is the amount of emissions per unit of ...

biomass

biomass   Quick reference

A Dictionary of Energy Science

Reference type:
Subject Reference
Current Version:
2017

...corn, straw, logs, dung, and crop residues that are used either directly or indirectly to produce heat, electricity, or fuels ( biofuels ). The burning of biomass provides about 10 per cent of the world’s energy requirements. Biomass production per unit area per year is typically ~20 t/ha/y, corresponding to ~1 MWth/km 2 , which necessitates large areas of land for significant power production (NB: algae biofuels can have a significantly higher yield). As a source of energy, it is potentially low-carbon, since the carbon dioxide released on combustion was...

View: