Civil Engineering Reference
In-Depth Information
12
Facilities: Cooling Systems
12.1
Introduction
Refrigeration systems for process application and air conditioning convert work
into a flow of heat from a process source or from a refrigerated space to an
environmental sink. The main types can be described as vapor compression,
absorption, and Brayton cycles.
Vapor compression systems are the commonest; for heat transfer they use the
condensation and evaporation of a volatile medium (refrigerant or coolant) such as
ammonia, light hydrocarbon, or fluorocarbon. The compressor driver supplies the
input power. The basic principles of compressor operation have been discussed in
Chap.
11
.
Absorption systems need a high-temperature source as main power input and
mechanical power only as additional power to drive a pump. Ammonia-water and
lithium bromide-water systems are generally used.
Brayton cycles are used for gas refrigeration systems, where a change in phase
does not occur. They are chosen to achieve very low temperatures for the liquefac-
tion of air and other gases and for specialized applications such as aircraft-cabin
cooling.
12.2
Basic Principles of Vapor-Compression Systems
Figure
12.1
shows the basic scheme of a vapor-compression refrigeration system,
where power flows and heat transfers are also pointed out (they are positive in the
direction of the arrows).
