Principle Of Operation; Freezing Cycle - Bartscher B20 Manuel D'instructions

Page 6
How it works
In the ice makers the water used to make the ice
is kept constantly in circulation by a water pump
which primes it to the spray system nozzles from
where it is diverted into the inverted cup molds of
the evaporator (Fig. A).
A small quantity of the sprayed water freezes into
ice; the rest of it cascades by gravity into the
sump assembly below for recirculation.
FREEZING CYCLE (Fig. B)
The hot gas refrigerant discharged out from the
compressor reaches the condenser where, being
cooled down, condenses into liquid. Flowing into
the liquid line it passes through the drier/filter,
then it goes all the way through the capillary tube
where it looses its pressure.
Next the refrigerant enters into the evaporator
serpentine (which has a larger diameter then the
capillary tube) and starts to boil off; this reaction
is emphasized by the heat transferred by the
sprayed water.
The refrigerant then increases in volume and
changes entirely into vapor.
The vapor refrigerant then passes through the
suction accumulator (used to prevent that any
small amount of liquid refrigerant may reach the
compressor) and through the suction line. In both
the accumulator and the suction line it exchanges
heat with the refrigerant flowing into the capillary
tube (warmer), before to be sucked in the
compressor and to be recirculated as hot
compressed refrigerant gas.
The freezing cycle on B20 -B40 and B45 is
controlled by only the evaporator thermostat
which has its bulb in contact with the
evaporator serpentine while in B75 and B90
there is an second phase controlled by an
electronic timer.
The electrical components in operation during
the freezing cycle are:
COMPRESSOR
WATER PUMP
FAN MOTOR (in air cooled version)
On B20 air cooled versions (operating with
R134a) the refrigerant head pressure is
gradually reduced from the value of approx. 11
bar at beginning of the freezing cycle with the
machine at 21°C ambient temperature, to a
minimum value of approx. 7 bar just at the end of
the freezing cycle, few seconds before the starting
of the defrost cycle.
On B40, and B45 air cooled version operating
with R404A, the head pressure drops from
19,5 bar to 13 bar while on the other bigger
models (B75-B90) the refrigerant head
pressure is kept between two present values
(17-13,5 bar) by means of a fan pressure
control.

PRINCIPLE OF OPERATION

The declining of the pressure is relied to the
reduction of the evaporating pressure, caused
by the progressive growth of the ice thickness
into the inverted cup molds and to the flow of air
drown through the air cooled condenser by the
fan motor. The above values are in relation as
well to the ambient temperature of the ice maker
site and they are subject to rise with the increase
of this temperature. On B20 water cooled
versions
refrigerant head pressure ranges between 8,5
and 10 bar being controlled by an automatic hi
pressure control that energizes a water solenoid
valve located on the water line to the condenser,
which rates the cooling water to the condenser
while on models B40, and B45 water cooled
version operating with R404A, the head pressure
ranges between 12 and 17 bar. On B75 and
B90 water cooled version operating
R404A, the head pressure is constant at 15
bar controlled by a water regulating valve.
At starting of the freezing cycle the refrigerant
suction or lo-pressure lowers rapidly to 1,0 bar
(on B20) and to 2,5-3,0 bar on all other models
then it declines gradually – in relation with the
growing of the ice thickness – to reach, at the
end of the cycle, approx. 0-0,1 bar on B20 and
1,4-1,5 bar in the other models with the cubes
fully formed in the cup molds.
DEFROST OR HARVEST CYCLE (Fig. D)
On B20 - B40 and B45 the temperature of
the evaporator thermostat, in contact with the
evaporator serpentine, drops to a pre-set value
it changes its electrical contacts energizing the
herebelow shown components.(On B75 and
B90 when the electro-nic timer completes the
second portion of the freezing it changes
its electrical contacts energizing the same
components).
COMPRESSOR
WATER INLET SOLENOID VALVE
HOT GAS SOLENOID VALVE
The incoming water, passing through the water
inlet valve and the flow control, runs over the
evaporator platen and then flows by gravity
through the dribbler holes down into the sump/
reservoir (Fig. C).
The water filling the sump/reservoir forces part of
the surplus water from the previous freezing
cycle to go out to the waste through the overflow
pipe. This overflow limits the level of the sump
water which will be used to produce the next
batch of ice cubes.
Meanwhile the refrigerant, as hot gas discharged
from the compressor, flows through the hot gas
valve directly into the evaporator serpentine by-
passing the condenser.
(operating with R134a) the
with