U.S. patent number 3,792,594 [Application Number 05/182,236] was granted by the patent office on 1974-02-19 for suction line accumulator.
This patent grant is currently assigned to Kramer Trenton Company. Invention is credited to Daniel E. Kramer.
United States Patent |
3,792,594 |
Kramer |
February 19, 1974 |
SUCTION LINE ACCUMULATOR
Abstract
A refrigerant accumulator in the suction line of a closed
refrigeration system, provided with a controllably heated metering
tube between the bottom of the accumulator and a downstream point
in the suction line, to ensure at least adequate re-evaporation of
the refrigerant, to eliminate slugging and to return oil to the
compressor, particularly during the hot gas defrosting portion of
the refrigeration cycle, the heating being effected electrically or
by means of hot gas from the compressor.
Inventors: |
Kramer; Daniel E. (Yardley,
PA) |
Assignee: |
Kramer Trenton Company
(Trenton, NJ)
|
Family
ID: |
26877916 |
Appl.
No.: |
05/182,236 |
Filed: |
September 20, 1971 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
858749 |
Sep 17, 1969 |
3636723 |
Jan 25, 1972 |
|
|
Current U.S.
Class: |
62/503;
62/278 |
Current CPC
Class: |
F25B
43/006 (20130101); F25B 47/022 (20130101) |
Current International
Class: |
F25B
43/00 (20060101); F25B 47/02 (20060101); F25b
043/00 () |
Field of
Search: |
;62/196,278,503 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: O'Dea; William F.
Assistant Examiner: Ferguson; Peter D.
Attorney, Agent or Firm: Nolte, Jr.; Albert C. Hunter;
Edward B. Hamburg; C. Bruce
Parent Case Text
This is a divisional application of U.S. patent application Ser.
No. 858,749 of DANIEL E. KRAMER, filed Sept. 17, 1969 and entitled
REFRIGERATION SYSTEM WITH SUCTION LINE ACCUMULATOR, which
application has matured into U.S. Pat. No. 3,636,723, issued Jan.
25, 1972.
Claims
What is claimed is:
1. An accumulator for a refrigeration system comprising a tank, an
inlet connection, an outlet connection extending below the tank, a
conduit mechanically coupled to the bottom of the tank and the
outlet connection, extending only underneath the tank, constituting
a trap which has a first leg, descending from the tank, a second
leg rising to the outlet connection, heating means thermally
connected to said first leg, and separated heating means thermally
connected to said second leg.
2. An accumulator for a refrigeration system comprising a tank, an
inlet connection, an outlet connection extending below the tank, a
conduit mechanically coupled to the bottom of the tank and said
outlet connection and extending only underneath said tank, and a
heater thermally connected to said conduit, the outlet of the said
conduit extending into said outlet connection and being provided
with an opening facing upstream.
Description
Modern positive displacement refrigerant compressor technology has
generated designs which provide the maximum in capacity per unit,
weight, cost and power. In order to achieve these features the
compressors are generally designed for relatively high rotative
speeds and high bearing loads. Standard rotative speeds for
compressors are now 1,725 and 3,400 revolutions per minute. At
these speeds ingestion of liquids of any sort into the compressor
chamber can cause instantaneous mechanical failures. Liquid
entering the cylinders can stem from two sources; liquid oil can
enter the cylinders from foaming of the oil in the compressor
crankcase on start-up under conditions where liquid refrigerant has
condensed or dissolved in the oil during the off-cycle. The other
source of liquid is liquid refrigerant in relatively pure form
which can return under abnormal conditions through the suction line
from the evaporator.
If large quantities of liquid refrigerant enter the compressor,
much of the refrigerant will be entrained into the cylinders with
the vapor and will cause a condition known as slugging which is
accompanied by pounding and knocking sounds and frequently causes
instantaneous compressor damage.
If the liquid refrigerant returns to the compressor in small
quantities, but over a long period of time, this liquid refrigerant
tends to dilute the oil, reducing its lubricity and generating a
condition of rapid bearing wear under those designed conditions of
high rotative speeds and high bearing loads to which the compressor
is ordinarily exposed. To help guard compressors against either
immediate or long range damage caused by the return of liquid
refrigerant through the suction line to the compressor, more and
more compressor manufacturers are presently recommending the use of
so-called surge drums or suction accumulators whose purpose is to
catch the liquid refrigerant returning in large or small quantities
and prevent this potentially harmful liquid refrigerant from
reaching the compressor. Because of the new requirements for
suction line protection against liquid return to the compressor,
many manufacturers have begun listing for sale suction accumulators
with various refrigerant holding capacities and various inlet and
outlet line sizes supposedly designed to fit a wide range of
systems and refrigerant charges.
Manufacturers of accumulators are faced with the problem of
providing positive means for the oil, which normally circulates
with the refrigerant in refrigeration systems, to be returned to
the compressor. If this oil is not returned but is caught or
trapped in the suction accumulator, the compressor may run out of
oil or the accumulator's potential for holding liquid refrigerant
will be diminished.
According to the present invention, there is provided an external
bleeder tube between the accumulator and the suction line together
with one or more heaters so positioned, constructed, selected and
controlled that liquid refrigerant flowing through the bleeder tube
is completely re-evaporated before it reaches the suction line.
Practical embodiments of the invention are shown in the
accompanying drawings, wherein:
FIG. 1 represents a vertical section of a known type of suction
line accumulator;
FIG. 2 represents an elevation of another known type of
accumulator, parts being broken away;
FIG. 3 is a diagrammatic view of a refrigerating system embodying
the apparatus of the present invention;
FIG. 4 represents a vertical section of a first form of accumulator
embodying the invention;
FIG. 5 represents an elevation of a second form of accumulator;
FIG. 6 is a diagrammatic view of a portion of a refrigeration
system showing an alternative means for heating the bleed tube;
FIG. 7 is a diagrammatic view of a refrigeration system having
means for heating both the bleed tube and the suction line;
FIG. 8 is a diagrammatic view of a portion of a refrigeration
system showing the use of a thermostatic control for the bleed tube
heater, and
FIG. 9 is a detail diagram showing means for ensuring
discriminating functioning of the thermostatic control of FIG.
8.
According to FIG. 1, the accumulator 10 is a vertically disposed
cylinder having an inlet 11 from the evaporator, opening at 12 into
the upper part of the cylinder, and an outlet 13 leading to the
compressor, the outlet being connected to a U-shaped trap 14 open
at its free end 15 to receive evaporated refrigerant and provided
with a metering orifice bleed hole 16 adjacent its bottom.
Since the bleed hole is built-in it must be made large enough to
return the maximum flow of oil that might be expected.
Unfortunately, experience has shown that if the bleed hole is made
large enough to return the largest quantities of oil which might be
pumped by any compressor, the hole is then so large that excessive
amounts of refrigerant are allowed to return to the compressor when
the accumulator is partially filled with liquid refrigerant. In
addition, laboratory tests and experience have shown that the
return of refrigerant and oil flow through the bleed hole is
related to the vapor velocity passing through the accumulator.
Although this effect would not at first appear to be obvious, the
effect was positively determined by quantitative laboratory tests.
An investigation of the cause of this increase in refrigerant flow
through the bleed hole showed that it is caused by the pressure at
the inside of the tube in which the bleed hole is located being
much lower than the pressure on the outside. The pressure is lower
inside the tube not only by virtue of the frictional pressure drop
loss in the outlet tube, but also the much greater pressure
reduction caused by the Bernoulli effect, i.e., the higher the
fluid velocity, the lower the pressure in that fluid.
All constructions of suction accumulators observed to this date are
affected by this problem which means that the rate of refrigerant
flow from the body of liquid accumulated in the accumulator into
the suction line is not a constant but a variable.
An effort by the present applicant to solve this problem is shown
in FIG. 2, wherein the horizontally disposed accumulator 17, having
an inlet 18 and outlet 19 (corresponding to inlet 11 and outlet
13-15 in FIG. 1) is provided with an external bleeder tube 20,
running from a point 21 at the bottom of the accumulator to a point
22 in the suction line 19. This external bleeder tube 20 is so
designed and constructed that it can be removed and exchanged for a
bleeder of a different diameter.
In addition, the easily serviceable design means that the bleed
tube can be more closely sized to the actual requirements without
any concern that dirt might plug the bleed tube and permanently
destroy the usefulness of the accumulator.
Instead of the bleeder having to be made sufficiently large for the
worst situation, the bleeder can be made with an internal bore
which exactly matches the system requirement. Even if an error is
made in initially sizing the bleeder its replacability makes a size
adjustment an easy matter.
Even though the development of the suction accumulator with
external and replaceable bleed tube constituted a tremendous
advancement over the best previously available accumulators, and
although the application of this accumulator has been satisfactory,
all these accumulators had certain application limitations. All
accumulators had, generally, to be installed so that a relatively
long run of suction line existed between the outlet of the
accumulator and the compressor inlet. In addition, the suction line
had to be exposed to an ambient 32.degree.F or higher. The purpose
of requiring this length of suction line is maintained at a
relatively high ambient was to insure that even the limited amount
of liquid refrigerant that flowed through the calibrated bleeder
tube into the suction line under conditions when floodback into the
accumulator occurred, was completely evaporated to dryness so that
no liquid refrigerant at all entered the compressor. Under the
conditions where the accumulator was placed very close to the
compressor and/or where a very short suction line was employed, or
the suction line was exposed to cold winter ambients, for example
-10.degree.F or 20.degree.F, reevaporation of even the small amount
of liquid refrigerant bled through the bleeder tube could not occur
and this liquid refrigerant entered the compressor causing oil
dilution and excessive bearing wear leading to early compressor
failure.
In order to make sure that no liquid refrigerant returns to the
compressor, even where the suction line is short and cold as, for
instance, where the accumulator is mounted directly on the
compressor chassis, either of two solutions can be employed. A
first possible solution is the provision of a heat exchanger in the
suction line between the accumulator outlet and the compressor
using, for instance, the heat available from the hot gas leaving
the compressor discharge to warm the suction vapor leaving the
accumulator and evaporate the liquid mixed with that vapor. This
system has the drawback that the normally cold suction vapor is
heated not only when the ambient surrounding the system is low, as
in the winter, but also when the weather is very hot. Then the
suction heat exchanger aggravates potential compressor overheating
and reduces compressor capacity by warming the suction vapor
entering the compressor which makes the vapor less dense and allows
the compressor to pump less with each rotation of its
crankshaft.
As illustrated in FIG. 3, a refrigeration system in which the
present invention may be embodied includes the evaporator 30
supplied with liquid refrigerant from the condenser 31 and receiver
32 under the control of the expansion valve 33. The compressor 34
supplies gaseous refrigerant under compression through the line 35
to the condenser, during refrigeration, or through the hot gas
defrosting line 36, controlled by solenoid valve 37, directly to
the evaporator 30 during defrosting.
The accumulator 38 is similar to that shown in FIG. 2, receiving
refrigerant from the evaporator through the line 39 and having an
outlet 40 opening into the upper part of the accumulator and
connecting with the suction line 41 to the compressor. An external
bleeder tube 42, similar to tube 20, leads from the bottom of the
accumulator to the suction line and there is also provided,
according to the invention, a heater 43 so positioned and
controlled that liquid refrigerant flowing through the bleed tube
is completely reevaporated before it reaches the suction line. This
construction has the advantage that even strong heating of the
bleed tube will have essentially no effect on the temperature of
the vapor entering the compressor. The heater therefore becomes
discriminating in that it only heats liquid refrigerant or perhaps
oil leaving the accumulator via the bleed tube but does not exert
any heating effect on the suction vapor transversing the
accumulator itself.
Such an accumulator, with heated bleed tube, can be mounted at or
near the compressor, will allow free return of oil which is trapped
in the accumulator, and yet effects the complete evaporation of
liquid refrigerant traversing the oil flow passage without any
heating effect on the suction vapor entering the compressor. This
system can be used for defrosting of evaporators even when the
compressor, accumulator and other high side components are located
in ambients as low as 0 F or -10.degree.F.
An additional improvement in accumulator design is a modification,
shown in FIG. 4, which at least partially offsets the variation in
refrigerant flow through the bleeder which occurs with various
vapor velocities. This improvement constitutes extending the outlet
of the bleed tube 44 into the outlet tube 45 and bending this
outlet, as indicated at 46, upwards so that a pilot tube effect is
generated. With this construction the impact pressure of the vapor
on the end of the bleed tube opposes the increased pressure
difference which higher vapor velocities generate.
An additional refinement in the design of the bleed tube involves
the application of heat in such a way as to sharply decrease the
rate of flow which occurs through the bleed tube even when the
bleed tube is of a large diameter. FIGS. 3 and 4 show the basic
bleed tube arrangement of this invention which pitches uniformly
from the bottom of the accumulator to the outlet tube with or
without the pilot effect.
FIG. 5 shows the bleed tube 47 at one end thereof removably and
interchangeably connected to the bottom of accumulator tank 40, by
tube connector fitting 47A, and similarly connected, at the other
end of the tube, to the tank outlet tube 45 by connector 47B. The
figure also shows the tube modified in the form of a trap 48. Heat
is applied at 49 on the downward flowing side of the trap and
separately at 50 on the upward flowing side of the trap. The
application of heat on the downward flowing side of the trap
generates bubbles whose buoyancy tends to offset the pressure
differential generated by the vapor flow and by the the head of
liquid in the accumulator. By the correct application of the heat
at this point the flow of liquid refrigerant in the bleed tube can
be adjusted as required so that the heater 50 on the outward
upflowing leg of the bleed tube can completely evaporate the liquid
refrigerant which succeeds in traversing the downflowing leg.
Together the division of heat between the downflowing leg and the
upflowing leg constitutes means for externally changing the
effective flow capacity of the bleed tube without actually
modifying its internal construction or diameter by an interchange
of tubes with the aid of the fittings 47A, 47B.
The bubbling of the refrigerant in the trap is comparable to the
"vapor lock" effect obtainable in any small tube, including the
tube 44 in FIG. 4. When liquid refrigerant moves through a
relatively small tube in the form of a solid column of liquid under
a given head the flow of that liquid is sharply impeded when the
stream is heated and thereby assumes the quality of a mixture of
vapor bubbles plus liquid. This impediment caused by vapor bubbles
in a refrigerant liquid stream moving in a small bore tube is
called vapor lock, and when an adequate amount of heat is applied
to the metering tube it could practically cut off most of the flow
of liquid through it. While the application of heat to the metering
tube creates the condition called vapor lock in a refrigerant
liquid stream, the application of heat to the metering tube while
oil is moving through it during normal operation has practically a
zero effect on the flow of the oil returning to the compressor
during normal operation except that the oil becomes warmer and
correspondingly less viscous.
Heating of the bleeder tube, as described above, is of particular
importance during defrosting, when some of the refrigerant from the
evaporator is most likely to be in liquid form. However, the
heaters 43, 49, 50 may be kept on continuously, if desired, in
order to avoid the necessity for providing special controls. A
suitable setting can be determined for any given installation and
adjustments, if any, may then be on a seasonal basis. During normal
operation of the system, for refrigeration, with little or no
liquid entering the accumulator, the heating of the small amounts
of vapor passing through the bleeder tube has a negligible effect
on the refrigerant gas flowing to the compressor, but whenever any
liquid does enter the accumulator -- during defrosting or for any
reason during refrigeration -- it is rendered harmless by the use
of this invention.
As a practical alternative, heat from the compressor discharge may
be used to ensure vaporizing temperatures in the bleed tube. FIG. 6
shows an arrangement in which the accumulator 51 has an outlet 52
communicating with the suction line 53 to the compressor 54. The
bleed tube 55 (similar to the tubes 42 or 44) is heated by close
association with the line 56 through which flows a portion of the
hot gas which is by-passed around a throttling device 58 in the
discharge line 57. The line 56 and tube 55 may be strapped or
soldered together to ensure heat transfer contact. All parts of the
suction line normally tend, with varying degrees of effectiveness,
to vaporize liquid refrigerant passing therethrough. If the
distance from the evaporator to the compressor or from the
accumulator to the compressor is short, there would be more need
for heat in the bleed tube and/or in the suction line than there
would if such distances were longer. Since the discharge line
carries much more heat than is needed for ensuring complete
vaporization in the suction line, the line 56 in FIG. 6 may be
relatively small and the throttling device 58 may be either a hand
valve, for adjustment as required, or an orifice of selected size,
to ensure an adequate diversion of hot gas through the line 56,
while permitting most of said gas to follow its normal course to
the condenser.
If the refrigeration system includes provision for hot gas
defrosting, the hot gas line can be routed adjacent to the suction
line, as shown in FIG. 7, where the accumulator 59 with inlet 60,
outlet 61 and bleed tube 62 is associated with hot gas lines for
heating both the bleed tube and the suction line 63. The compressor
discharge line 64 includes a portion 65 in heat transfer contact
with the bleed tube 62 (as in FIG. 6) while the hot gas defrost
line 66, controlled by solenoid valve 67, is similarly in heat
exchange relation to the suction line 63 throughout a sufficient
length of said outlet line for the accumulator, to evaporate liquid
returning during defrost. This supplementary heating would provide
a safety factor in case of excess liquid return from the evaporator
to the accumulator, above the vaporizing capacity of the metering
tube. Such heating of the suction line would not have the harmful
effects of continuous heating, mentioned above, since the heating
takes place only during defrosting and the suction line is not
heated during normal refrigeration.
Where electric heaters are used they may be arranged to turn on
when the compressor starts and to turn off when the compressor
stops, as by means of a relay indicated conventionally at 70, in
FIG. 3, associated with the compressor motor circuit. If
consumption of electric power must be controlled carefully a
thermostat may be provided on the suction line near the compressor
inlet to turn on the heater or heaters when the suction line
becomes cold, implying the presence of liquid refrigerant. This
would mean that electric heaters might remain de-energized for long
periods of time, for instance, during warm weather when the
accumulator, bleed tube and suction line cooperate inherently to
perform their re-evaporating function. In colder weather, however,
when the ambient around the suction line is such that liquid
flowing through the bleed tube is not re-evaporated, the heater
would be turned on.
In FIG. 8 is shown a portion of a system similar to that of FIG. 3
but having thermostat 71, with bulb 72 adjacent suction line 73
arranged to open and close the switch 74 in the circuit of heater
75 (corresponding to heater 43).
The use of a thermostat detecting only the suction line
temperature, as a means for ascertaining the presence or absence of
liquid, is not always reliable since liquid refrigerant at a
temperature higher than the thermostat setting could, under certain
circumstances, be present and could return to the compressor
without detection by the thermostat. As an added refrinement, to
eliminate the possibility just mentioned, a small cartridge heater
76 (FIG. 9) may be added to the suction line 77 adjacent the
thermostat bulb 78, or to said bulb itself, in order to ensure that
the thermostat will react only to the presence of liquid, assuming
a setting higher than the temperature of any returning liquid. The
cooling ability of liquid refrigerant is about 100 times better
than that of vapor refrigerant. With liquid refrigerant in the
suction line of the bulb of the thermostat is effectively cooled
despite the presence of the small heater 76, tripping the
thermostat and energizing the relatively high voltage heater on the
bleed tube. If there is only cold vapor in the line, its cooling
effectiveness is insufficient to overcome the heating of the bulb
by the heater 76 and the bleed tube heater is not energized. The
arrangement just described constitutes a positive means for
detecting the presence of liquid refrigerant in the suction line
without putting a sensor directly in the flow stream.
* * * * *