Air Preheater

Air Preheater (external heat source type):   Air preheaters that utilize low temperature heat from an external source (e.g. low pressure steam) to improve heater or boiler efficiency.

Air Preheater (direct exchange type):   Air preheaters that exchange heat directly between flue gas and air.  These air preheaters often require an external heat source air preheater to increase the air inlet temperature to prevent cold end corrosion.

Air Preheater (indirect exchange type):   Air preheaters that use water or hot oil to cool the flue gas.  The heated water is used to heat up the air.  Cold end corrosion is prevented by keeping the water or hot oil is kept above the dewpoint temperature. 
 

Allotropy

Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, known as allotropes of these elements. An allotropy is polymorphism of metals.

Ferrite, Cementite, Pearlite & Austenite

alpha-Iron is Ferrite
Fe3C - Cementite
Ferrite + Cementite is Pearlite
Gamma-phase Iron is Austenite

Actuary

An actuary is a business professional who applies mathematical and statistical methods to deal with the financial impact of risk and uncertainty in the field of insurance, investment etc.

Appositive

An appositive is a word, phrase, or clause in apposition – that is, it is a word placed next to another word so that the second explains the first.

Adiabatic Process

An adiabatic process is one in which there is no heat transfer into or out of the system. The system can be considered to be perfectly insulated.

Attemperator

An apparatus for reducing and controlling the temperature of a superheated steam.

Arch

A flat or sloped portion of the heater radiant section opposite the floor.

Applicable code

The code, code section or other recognized and generally accepted engineering standard or practice to which the system/equipment was built or which is deemed most appropriate for the situation.

Anchor

A metallic or refractory device that holds the refractory or insulation in place.

API Gravity

An arbitrary scale expressing the gravity or density of liquid petroleum products. The measuring scale is calibrated in terms of degrees API; it is calculated as follows:
                Degrees API = (141.5 / (sp. gr. 60ºF / 60ºF)) - 131.5

The higher the API gravity, the lighter the compound. Light crudes generally exceed 38 degrees API and heavy crudes are commonly labeled as all crudes with an API gravity of 22 degrees or below. Intermediate crudes fall in the range of 22 degrees to 38 degrees API gravity.

Absolute Pressure & Gauge Pressure

When pressure is measured relative to a perfect vacuum, it is called absolute pressure (psia).

When pressure is measured relative to atmospheric pressure (14.7 psi), it is called gauge pressure (psig).

Absolute humidity

Absolute humidity is the mass of water vapor divided by a unit volume of air (grams of water/cm3 of air)

Air Craft

"All man made contrivances which fly, that is to say which are kept in the air by forces produced by the air are called aircraft".
Eg: balloons, kites, aeroplanes etc.

There are two kinds of air crafts, those which are lighter than air and those which heavier than air. The lighter than means their weight by volume is less than that of air. Heavier than means the weight by volume is heavier than that of air. The former includes balloons, airships etc. and the later comprises kites and aero planes.

Acute angled triangle

A triangle in which all the three angles are acute is called an acute angled triangle.

Adverb clause

An adverb clause is a group of words which contains a subject and a predicate of its own and does the work of an adverb.

Adjective Clause

An adjective clause is a group of which contains a subject and a predicate of its own and does the work of an adjective

Adverb phrase

An adverb phrase is a group of words that does the work of an adverb

Adjective Phrase

An adjective phrase is a group of words that does the work of an adjective

Active Voice

A verb is in the active voice when its form shows that the person or thing denoted by the subject does something