Brochure

Catalog CIC-2003-1/US
Accumulators, Receivers, Tanks and Mufflers
Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
59
Accum'tors,
Receivers, Tanks
& Mufflers
The prime function of a suction line accumulator in a heat
pump or refrigeration system is to catch and hold any unused
portion of the system charge. It must also prevent liquid slug-
ging of the compressor and excessive refrigerant dilution of the
compressor oil.
The accumulator must return refrigerant and oil to the
compressor at a sufficient rate to maintain both system
operating efficiency and proper crankcase oil level. To make
sure these tasks are accomplished, system designers must
consider the following items:
• The accumulator must have sufficient internal
volume.
• A properly sized and protected oil return orifice is
required to ensure positive oil (and refrigerant) return
to the compressor.
• The pressure drop across the accumulator should be
as low as possible for given inlet and outlet fitting sizes.
Oil return at minimum flow rate is controlled by the outlet U-
tube size. Refrigerant and oil will be returned to the compressor
by pressure drop across the orifice metering area and the liquid
head above the orifice. Other design requirements include:
• Safe working and burst pressures.
• Agency approvals.
• Salt spray, moisture, and corrosion resistance.
Figure 1 shows a typical accumulator with an inlet deflector.
The shape of the deflector directs the inlet flow in a slightly
downward tangential direction.
The inlet to the U tube is located behind the inlet deflector to
prevent liquid carry-over and is bell-shaped to reduce the
sudden contraction loss of the high-velocity gas. The U-tube
diameter is selected to minimize pressure drop at high flow
rates yet provide adequate oil return at low flow rates.
A 50 x 60 mesh screen is installed to protect the small diameter
oil return orifice.
An anti-siphon hole, provided near the outlet of the U tube,
prevents liquid from siphoning into the outlet tubing and com-
pressor during an off cycle.
A fusible alloy plug is generally a U.L. requirement. It is a safety
device to protect against excessive pressures in the event of a
fire.
Accumulator Fine Tuning
Accumulator selection can be fine tuned for best performance.
This involves the sizing of the accumulator, and the sizing of the
orifice. The controlling factor for both is the type of metering de-
vice used on the system, either a fixed orifice or a thermostatic
expansion valve.
In systems using a fixed orifice in the heating
mode, the accumulator holding capacity should
be about 70% of the system charge. This
should provide adequate holding capacity
during operation with blocked or fouled heat
exchanger coils. The resulting high discharge/
low suction pressure condition will push much
of the system charge into the accumulator. The
oil return orifice size should be small to prevent
excess liquid refrigerant being returned to the
compressor. This would excessively reduce the
compressor discharge temperature, lowering
heating performance. Parker recommends a
0.040 inch diameter orifice as a good starting
point for these systems.
In systems using an expansion valve, the
accumulator holding capacity should be about
50% of the system charge. At startup and after
defrost, the bulb of the expansion valve is
warm. This causes flooding of the evaporator
and brings the accumulator into play until the
valve regains control. The accumulator must
also deal with off cycle refrigerant migration.
At shut down, the accumulator is the coldest
component in the system. This results in
migration of liquid refrigerant to the lower
temperature accumulator. This type of system
needs to get the refrigerant returned to circula-
tion more quickly than the fixed orifice system.
Parker recommends a 0.055 inch diameter
orifice to allow quick return of liquid refrigerant.
The recommended sizes of the orifices can be
further tested for optimum results. Parker has
the ability to provide orifices in sizes smaller
and larger to satisfy the characteristics
required by the customer.
Figure 1 - Typical accumulator with inlet deflector
baffle.
Introduction to Accumulators
Introduction to Accumulators Accumulators