Viking Pump TSM420: HL-LL 4925 - Manual (Page 17)

SECTION TSM 420 ISSUE E PAGE 17 OF 18
WATER COOLING PIPES
CONDENSER (5)
ACCumuLATOR
(6)
RECEIvER (1)
EvAPORATOR (3)
(REfRIGERATOR)
COmPRESSOR (4)
(86°f., 154 PSIG)
ExPANSION
vALvE (2)
(210°f., 154 PSIG)
(5°f., 19 PSIG)
(5°f., 19 PSIG)
vIkING REfRIGERATION AmmONIA
PumPS uSED IN ThIS PORTION
Of SySTEm TO WIThDRAW LIquID
AmmONIA fROm ThE ACCumuLATOR
SEE fIGuRES 2 & 3
(86°f., 154 PSIG)
figure 23 is a schematic of a simple Vapor Ammonia
Refrigeration System with the major pieces of equipment
named and numbered Each piece of equipment is described
briefly and its function in the system discussed in the following
paragraphs To illustrate temperatures and pressures that
would exist in a actual illustration there is given with the
discussion of each piece of equipment the actual temperature
and pressure for a system operating with a condenser
temperature of 86°F and an evaporator temperature of 5°F
1. RECEIVER - A storage tank for ammonia and ambient
temperatures The receiver “receives” the liquid
ammonia as it comes from the condenser The pressure
in the receiver will correspond to the vapor pressure of
the ammonia at the
temperature of the cooling medium used in the condenser
In this case with an 86°F condenser temperature the
ammonia pressure would be 154 PSI (the saturation
pressure corresponding to a temperature of 86°F )
2. EXPANSION VALVE - A throttling valve that controls the
amount of liquid that flows into the evaporator It cannot
be controlled manually or by thermostats located in the
evaporator The temperature and pressure of the liquid
on the inlet side of the expansion valve is the same as
that in the receiver (86°F and PSI); the pressure on the
outlet side of the extension valve is that maintained in
the evaporator by the compressor; (the compressor
would have to pull down and hold the pressure in the
evaporator at 19 PSIG to maintain the evaporator
temperature at 5°F ; this is the saturation temperature
corresponding to 19 PSIG)
3. EVAPORATOR - The evaporator is the main purpose for
the existence of the refrigeration system It is through the
evaporator that heat is picked up by the ammonia The
temperature in the evaporator area will be “pulled down”
to the saturation temperature of ammonia at the pressure
maintained by the compressor The ammonia enters as
a liquid at the temperature in the receiver; it leaves as
a vapor (gas) at the saturation temperature (For the
system being considered the pressure in the evaporator
would have to be maintained at 19 PSIG This is the
pressure corresponding to a saturation temperature of
5°F )
fIgURE 23
Schematic of a Simple Vapor-Compression Ammonia Refrigeration System
4. COMPRESSOR - The compressor pulls the ammonia
vapors from the evaporator The pressure or vacuum
pulled in the evaporator by the compressor will
determine the pressure at which the evaporator works
The compressor compresses the ammonia gas to the
pressure corresponding to the saturation pressure of
the ammonia at the temperature maintained in the
condenser The compressed ammonia gas as it leaves
the compressor is hot and is in a super heated vapor
state (The vapor pulled into the compressor is at 5°F ,
the vapor as it leaves is at a temperature of approximately
210°F and a pressure of 154 PSIG The pressure of 154
PSIG is the saturation pressure of the ammonia at the
86°F condenser temperature)
5. CONDENSER - The condenser cages the super heated
ammonia vapors back to liquid ammonia It does this
by transferring the heat from the ammonia to a cooling
liquid, such as water flowing through the condenser
tubes The pressure that the compressor must develop
is determined by the saturation pressure of the ammonia
at the temperature maintained in the condenser (The
temperature maintained in the condenser by the cooling
medium is 86°F ; the saturation at the temperature
pressure is 154 PSIG which is the pressure that must
be maintained in the condenser to change the ammonia
vapor back to liquid) The liquid ammonia coming from
the condenser is stored in the receiver From here it is
ready to start the cycle over again
6. ACCUMULATOR - The accumulator or low pressure
receiver is not one of the essential pieces of equipment
in the simple system, but in practice it serves a very
important function For the proper operation of the
compressor it is important that no liquid ammonia can be
carried over from the evaporator The accumulator serves
as a trap to keep liquid ammonia from being entered with
the ammonia vapors that are pulled from the evaporator
by the compressor (The temperature and pressures are
the same as they are in the evaporator) As the liquid is
collected or accumulated in the accumulator it must be
removed THE REMOVAL Of THE LIQUID AMMONIA
fROM THE ACCUMULATOR IS WHERE THE VIKINg
REfRIgERATION AMMONIA PUMP IS USED.