11.1 Principles Flashcards
Saturation temperature is…
When the number of molecules leaving the liquid surface is more than those re-entering, the water freely evaporates. At this point it has reached boiling point, or its saturation temperature, as it is saturated with heat energy.
Enthalpy is…
the amount of heat content used or released in a system at constant pressure.
A steam explosion is…
a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or heated by interaction with molten metals.
Condensation induced water hammer occurs when…
large quantities of condensate lying inside a pipe are pushed along the pipe at steam velocities. This can result in damage when the water impacts with an obstruction in the pipe, for example a control valve.
Mounded pressurised torpedoes offer a safer option and eliminate the possibility of
BLEVE
Refrigeration systems are designed around two key principles:
(1) Liquids absorb heat when changed from liquid to gas. (2) Gases give off heat when changed from gas to liquid.
A new, self-contained air compressor is to be installed in a workshop. Identify THREE protective devices that may be necessary to control the risk of over-pressurisation AND for EACH device outline its purpose. 6 marks
(a) Protective devices include: a pressure gauge to identify the receiver pressure a safety valve which would relieve excess pressure when the maximum safe working pressure of the receiver is attained a pressure cut-out or unloading device which cuts off the compressor when the working pressure is reached a fusible metal plug which prevents over-heating and in turn over pressurisation if external heat sources are applied by melting and thus again relieves the pressure.
PER divides pressure equipment into four major categories on the basis of two fundamental hazards:
(1) The degree of danger from failure of the equipment (expressed by the product of the pressure of the fluid and the volume of the equipment or DN value for piping products). (2) The degree of danger from the release of the fluid contained (based on classifications adopted in the directives on dangerous substances).
