CHART Orca MicroBulk CO2 Series - Introduction; Theory of Operation; Terminology of Cryogenics; Cryogenic

9
Product Manual - Orca
™
CO
2
Series MicroBulk Delivery System
Theory of Operation
Although the Orca CO
2
Series system can have pressure
or pump delivery options, all units have the same general
functional operating characteristics. They have the ability to
be lled with liquid CO
2
and deliver that product to the end
customer safely and eciently.
Terminology of Cryogenics
Cryogenic
A product retaining a temperature of -238°F (-150°C) or
colder. Orca delivery systems maintain gases eciently in a
cryogenic liquid state. Gases can be most eciently stored
as liquids. Gases may be liqueed by compression or cooling
them until they liquefy. In order to be maintained in a liquid
state, each gas must be kept at or below their respective
boiling temperatures.
Though liquid CO
2
is very cold, it cannot exist below
-69.9°F. While it is technically not a cryogen, it is to be
handled as such.
Cryogenic Temperatures
The Orca CO
2
Series delivery systems employ near-
cryogenic temperatures to store the product in its liquid
state. CO
2
can exist as a liquid down to -69.9°F (60.4 psig
saturation). Below that, CO
2
becomes solid. CO
2
is typically
transported and stored above -20°F (200 psig saturation).
States of Matter
Matter can exist as a gas, liquid, or a solid. Two phase liquid
is a liquid with gas bubbles or slugs of gas due to lack of
pressure (subcool) to maintain equilibrium. Gas and liquid
can exist at a range of temperatures.
Saturation
Dened as the point at which liquid and vapor coexist at the
same pressure and temperature.
Liquid density, temperature, and equilibrium pressure change
with the saturation condition of the liquid. Saturation can
also be described as an energy state. Liquid molecules at a
higher energy state (warmer) take up more space, which is
often referred to as liquid growth.
Equilibrium
In a closed vessel the gas and liquid temperatures are the
same. If there is a temperature dierence between the gas
and liquid (with the tank closed), the gas and liquid will
change their temperatures until they are equal. In stationary
tanks, stratication can take place, creating a temperature
gradient across the liquid and vapor. However, the
temperature at the liquid-vapor interface is the same for both.
Saturation Pressure
Pressure (usually in psig) that is used to describe the current
saturation condition of a liquid and gas within a closed
container.
Subcool
Raising the vapor space pressure above the current boiling
pressure of a saturated liquid is called subcool. This
contributes to the Net Positive Suction Head (NPSH) to the
pump. The higher the subcool, the less susceptible the liquid
will be to two-phase ow and pump cavitation.
Two-Phase Liquid
The mix of liquid and gas due to the pressure dropping
below the saturation pressure of the liquid caused by the
lack of proper subcool. This can damage the pump and cause
meter inaccuracy.
Cavitation
Dened as the formation of vapor bubbles in a liquid, it
manifests as partial or full loss of pump prime due to the lack
of proper subcool. The pressure of the liquid owing to the
pump has dropped below the saturation pressure. Audible
changes in the pump often are an indication of partial loss
of prime. The pump will stop pumping during full loss of
prime. Cryogenic pumps will be damaged by cavitation.
Some CO
2
pumps can handle small amounts of cavitation,
however, cavitation should always be avoided.
Introduction