U.S. patent application number 16/100930 was filed with the patent office on 2019-02-28 for geared gas turbine engine with oil deaerator.
The applicant listed for this patent is United Technologies Corporation. Invention is credited to William G. Sheridan.
Application Number | 20190063330 16/100930 |
Document ID | / |
Family ID | 53886821 |
Filed Date | 2019-02-28 |
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United States Patent
Application |
20190063330 |
Kind Code |
A1 |
Sheridan; William G. |
February 28, 2019 |
GEARED GAS TURBINE ENGINE WITH OIL DEAERATOR
Abstract
A gas turbine engine includes a fan section including a fan
rotor, a compressor section, a turbine section including a fan
drive turbine that drives the fan rotor through a gear reduction,
and a lubrication system that supplies oil to the gear reduction
and includes a lubricant pump that supplies a mixed air and oil to
an inlet of a deaerator during operation. The deaerator includes a
shell defining a cavity and a separator that separates the mixed
air and oil in the cavity, delivers separated air to an air outlet
of the deaerator and delivers separated oil back into an oil tank
during operation. A method of designing a gas turbine engine is
also disclosed.
Inventors: |
Sheridan; William G.;
(Southington, CT) |
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Applicant: |
Name |
City |
State |
Country |
Type |
United Technologies Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
53886821 |
Appl. No.: |
16/100930 |
Filed: |
August 10, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15873961 |
Jan 18, 2018 |
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16100930 |
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14737670 |
Jun 12, 2015 |
9976490 |
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15873961 |
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62019452 |
Jul 1, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02C 7/06 20130101; F01D
25/20 20130101; F02C 3/04 20130101; F05D 2260/98 20130101; F02C
7/36 20130101; Y02T 50/60 20130101; F05D 2260/608 20130101; F01M
2013/0427 20130101; F05D 2260/40311 20130101; F16N 39/002 20130101;
Y02T 50/671 20130101 |
International
Class: |
F02C 7/36 20060101
F02C007/36; F16N 39/00 20060101 F16N039/00; F01D 25/20 20060101
F01D025/20 |
Claims
1. A gas turbine engine comprising: a fan section including a fan
rotor; a compressor section; a turbine section including a fan
drive turbine that drives said fan rotor through a gear reduction;
a lubrication system that supplies oil to said gear reduction and
includes a lubricant pump that supplies a mixed air and oil to an
inlet of a deaerator during operation; wherein said deaerator
includes a shell defining a cavity and a separator that separates
the mixed air and oil in said cavity, delivers separated air to an
air outlet of said deaerator and delivers separated oil back into
an oil tank during operation.
2. The gas turbine engine as set forth in claim 1, wherein said
separator includes a member that splits the mixed air and oil into
lubricant flow paths on both of two opposed sides, said separator
includes a scroll spiraling from said inlet to an exit of said
deaerator, and said gear reduction includes a sun gear that drives
intermediate gears, and a ring gear.
3. The gas turbine engine as set forth in claim 2, wherein a gear
reduction ratio of said gear reduction is greater than 2.3:1.
4. The gas turbine engine as set forth in claim 3, wherein a dwell
time of oil in said oil tank as removed by said lubricant pump, on
average, is five seconds or less during operation.
5. The gas turbine engine as set forth in claim 4, wherein said
engine is rated greater than or equal to 15,000 and less than or
equal to 100,000 lbs in rated thrust at take-off.
6. The gas turbine engine as set forth in claim 4, wherein said
member of said separator is at an intermediate position in said
inlet.
7. The gas turbine engine as set forth in claim 6, wherein said
gear reduction includes oil baffles circumferentially between said
adjacent intermediate gears.
8. The gas turbine engine as set forth in claim 7, further
comprising: a bypass ratio of greater than or equal to 10; wherein
said fan section has a low fan pressure ratio of less than 1.45;
and wherein said fan drive turbine includes an inlet, an outlet and
a pressure ratio of greater than 5, the pressure ratio being
pressure measured prior to said inlet as related to pressure at
said outlet prior to an exhaust nozzle.
9. The gas turbine engine as set forth in claim 8, wherein said
deaerator is incorporated into said oil tank, and said exit
includes a plurality of oil outlets in a shell of said
deaerator.
10. The gas turbine engine as set forth in claim 9, wherein said
exit delivers oil into said oil tank at least 2 inches (5.08
centimeters) beneath a freestanding oil level within said tank
during operation.
11. The gas turbine engine as set forth in claim 9, further
comprising a gutter that surrounds said gear reduction such that
said gutter captures oil from said gear reduction during
operation.
12. The gas turbine engine as set forth in claim 11, wherein said
lubricant system includes a filter, an air/oil cooler and a
fuel/oil cooler arranged such that oil flows from said lubricant
pump to said filter, then flows to said air/oil cooler, and then
flows to said fuel/oil cooler, and then passes back to said oil
tank or said gear reduction during operation.
13. The gas turbine engine as set forth in claim 12, wherein oil
returning from said gutter passes back directly to said pump or
said oil tank during operation.
14. The gas turbine engine as set forth in claim 11, wherein an
inlet velocity to said deaerator is less than or equal to 14
feet/second, and an exit velocity from said deaerator of the
separated air is less than or equal to 14 feet/second during
operation.
15. The gas turbine engine as set forth in claim 14, wherein said
fan drive turbine drives a compressor rotor of said compressor
section, along with said fan rotor through said gear reduction, and
a low corrected fan tip speed of less than 1150 feet/second.
16. The gas turbine engine as set forth in claim 15, wherein a
dwell time of oil in said oil tank as removed by said lubricant
pump, on average, is three seconds or less during operation.
17. The gas turbine engine as set forth in claim 16, wherein said
intermediate gears engage and drive said ring gear to drive an
output shaft that drives said fan rotor.
18. The gas turbine engine as set forth in claim 17, wherein: said
oil tank may hold greater than or equal to 25 and less than or
equal to 35 quarts of oil; and wherein said oil tank is associated
with an engine having greater than or equal to 15,000 and less than
or equal to 35,000 lbs in rated thrust at take-off.
19. The gas turbine engine as set forth in claim 17, wherein: said
oil tank holds greater than or equal to 35 and less than or equal
to 50 quarts of oil; and wherein said oil tank is associated with
an engine having greater than or equal to 35,000 and less than or
equal to 100,000 lbs in rated thrust at take-off.
20. A method of designing a gas turbine engine comprising:
providing a fan drive turbine that drives a fan rotor through a
gear reduction; and providing a lubrication system that supplies
oil to said gear reduction, with an oil tank, said lubrication
system including a lubricant pump, said lubrication system
including a deaerator; supplying a mixed air and oil to an inlet of
said deaerator, said deaerator including a shell defining a cavity;
separating with said separator the mixed air and oil in said
cavity, delivering separated air to an air outlet of said
deaerator, and delivering separated oil from said deaerator back
into said oil tank.
21. The method as set forth in claim 20, wherein said step of
separating includes a member of said separator splitting the mixed
air and oil into lubricant flow paths on both of two opposed
sides.
22. The method as set forth in claim 21, wherein said separator
includes a scroll spiraling from said inlet to an exit of said
deaerator, and said step of separating includes causing oil to flow
downwardly along upper and lower paths of said scroll.
23. The method as set forth in claim 22, wherein: said gear
reduction includes a sun gear that drives intermediate gears, and a
ring gear; a dwell time of oil in said oil tank as removed by said
lubricant pump, on average, is five seconds or less; and said
deaerator is incorporated into said oil tank.
24. The method as set forth in claim 23, further comprising: a
bypass ratio of greater than or equal to 10; wherein a gear
reduction ratio of said gear reduction is greater than 2.3:1; and
wherein said fan drive turbine includes an inlet, an outlet and a
pressure ratio of greater than 5, the pressure ratio being pressure
measured prior to said inlet as related to pressure at said outlet
prior to an exhaust nozzle.
25. The method as set forth in claim 24, wherein said gear
reduction includes oil baffles circumferentially between said
adjacent intermediate gears.
26. The method as set forth in claim 25, wherein: an inlet velocity
to said deaerator is less than or equal to 14 feet/second; and an
exit velocity from said deaerator of the separated air into said
air outlet is less than or equal to 14 feet/second.
27. The method as set forth in claim 26, wherein: said oil tank may
hold greater than or equal to 25 and less than or equal to 50
quarts of oil; and wherein said oil tank is associated with an
engine having rated greater than or equal to 15,000 and less than
or equal to 100,000 lbs in rated thrust at take-off.
28. The method as set forth in claim 27, further comprising
capturing oil from said gear reduction in a gutter that surrounds
said gear reduction.
29. The method as set forth in claim 28, wherein said member of
said separator is at an intermediate position in said inlet, and
said air outlet has a tube extending downwardly into a shell of
said deaerator.
30. The method as set forth in claim 29, further comprising:
supplying oil from said lubricant pump to a filter, then to an
air/oil cooler, and then to a fuel/oil cooler, and then passing the
oil back to said oil tank or said gear reduction; and delivering
oil from said exit into said oil tank at least 2 inches (5.08
centimeters) beneath a freestanding oil level within said oil tank.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/873,961, filed Jan. 18, 2018, which is a
continuation of U.S. patent application Ser. No. 14/737,670, filed
Jun. 12, 2015. U.S. patent application Ser. No. 14/737,670 claims
priority to U.S. Provisional Patent Application No. 62/019,452,
filed Jul. 1, 2014.
BACKGROUND OF THE INVENTION
[0002] This application relates to a gas turbine engine having a
gear reduction driving a fan wherein an oil tank has an improved
deaerator.
[0003] Gas turbine engines are known and, typically, include a fan
delivering air into a bypass duct as propulsion air. The fan also
delivers air into a core engine where it passes to a compressor.
The air is compressed in the compressor and delivered downstream
into a combustion section where it is mixed with fuel and ignited.
Products of this combustion pass downstream over turbine rotors
driving them to rotate.
[0004] Historically, the fan rotor and a fan drive turbine rotor
have been driven at the same speed. This placed a restriction on
the desirable speed of both the fan and the fan drive turbine.
[0005] More recently, it has been proposed to provide a gear
reduction between the fan drive turbine and the fan rotor.
[0006] The gear reduction is a source of increased heat loss. As an
example, a geared turbofan engine creates about twice as much heat
loss as a non-geared turbofan engine. In addition, the weight of
the engine increases due to the weight of the gear reduction.
[0007] It has typically been the case that a designer of a gas
turbine engine sizes an oil tank such that the oil can sit in the
oil tank long enough to de-aerate. On a normal turbofan engine,
this had been approximately at least ten seconds.
SUMMARY OF THE INVENTION
[0008] In a featured embodiment, a gas turbine engine comprises a
fan drive turbine for driving a gear reduction. The gear reduction
drives a fan rotor. A lubrication system supplies oil to the gear
reduction. The lubrication system includes a lubricant pump
supplying a mixed air and oil to a deaerator inlet. The deaerator
includes a separator that for separating oil, and delivering
separated air to an air outlet, and for delivering separated oil
back into an oil tank. The separator includes a member having
lubricant flow paths on both of two opposed sides.
[0009] In another embodiment according to the previous embodiment,
the separator has a splitter at an intermediate position in the
inlet.
[0010] In another embodiment according to any of the previous
embodiments, the air outlet has a tube extending downwardly into a
deaerator shell.
[0011] In another embodiment according to any of the previous
embodiments, an inlet velocity to the deaerator is less than or
equal to 14 feet/second, and an exit velocity from the deaerator of
the separated air is less than or equal to 14 feet/second.
[0012] In another embodiment according to any of the previous
embodiments, a deaerator exit delivers oil into the oil tank at
least 2 inches (5.08 centimeters) between a freestanding oil level
within the tank.
[0013] In another embodiment according to any of the previous
embodiments, a dwell time of oil in the tank as removed by the oil
pump, on average, is five seconds or less.
[0014] In another embodiment according to any of the previous
embodiments, the oil tank may hold greater than or equal to 25 and
less than or equal to 35 quarts of oil.
[0015] In another embodiment according to any of the previous
embodiments, the engine is rated greater than or equal to 15,000
and less than or equal to 35,000 lbs in rated thrust at
take-off.
[0016] In another embodiment according to any of the previous
embodiments, the oil tank holds greater than or equal to 35 and
less than or equal to 50 quarts of oil.
[0017] In another embodiment according to any of the previous
embodiments, the oil tank is associated with an engine having
greater than or equal to 35,000 and less than or equal to 100,000
lbs in rated thrust at take-off.
[0018] In another embodiment according to any of the previous
embodiments, the gear reduction includes a sun gear for driving
intermediate gears. Oil baffles are located circumferentially
between the intermediate gears.
[0019] In another embodiment according to any of the previous
embodiments, an oil capture gutter surrounds the gear
reduction.
[0020] In another embodiment according to any of the previous
embodiments, an oil capture gutter surrounds the gear
reduction.
[0021] In another embodiment according to any of the previous
embodiments, the separator includes a scroll spiraling from the
inlet to a deaerator exit.
[0022] In another embodiment according to any of the previous
embodiments, the exit includes a plurality of holes in a shell.
[0023] In another featured embodiment, method of designing a gas
turbine engine includes providing a fan drive turbine for driving a
gear reduction. The gear reduction drives a fan rotor. A
lubrication system is provided to supply oil to the gear reduction,
with an oil tank, the lubrication system including a lubricant
pump. Mixed air and oil are delivered to a deaerator inlet, the
deaerator including a separator for separating oil, and delivering
separated air to an air outlet, and delivering separated oil back
into an oil tank. The lubricant separator includes a member having
lubricant flow paths on both of two opposed sides.
[0024] In another embodiment according to the previous embodiment,
the separator is at an intermediate position in the inlet.
[0025] In another embodiment according to any of the previous
embodiments, the air outlet has a tube extending downwardly into a
deaerator shell.
[0026] In another embodiment according to any of the previous
embodiments, the flow separator includes a scroll spiraling from
the inlet to a deaerator exit.
[0027] In another embodiment according to any of the previous
embodiments, the separator is at an intermediate position in the
inlet.
[0028] These and other features may be best understood from the
following drawings and specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic view of a gas turbine engine.
[0030] FIG. 2 shows a portion of a cross-section of a gear
reduction.
[0031] FIG. 3 shows another portion of a gear reduction.
[0032] FIG. 4 shows a lubrication system.
[0033] FIG. 5 shows a deaerator.
[0034] FIG. 6 shows internal structure of the deaerator.
[0035] FIG. 7 shows additional internal structure of the
deaerator.
DETAILED DESCRIPTION
[0036] FIG. 1 schematically illustrates a gas turbine engine 20.
The gas turbine engine 20 is disclosed herein as a two-spool
turbofan that generally incorporates a fan section 22, a compressor
section 24, a combustor section 26 and a turbine section 28.
Alternative engines might include an augmentor section (not shown)
among other systems or features. The fan section 22 drives air
along a bypass flow path B in a bypass duct defined within a
nacelle 15, while the compressor section 24 drives air along a core
flow path C for compression and communication into the combustor
section 26 then expansion through the turbine section 28. Although
depicted as a two-spool turbofan gas turbine engine in the
disclosed non-limiting embodiment, it should be understood that the
concepts described herein are not limited to use with two-spool
turbofans as the teachings may be applied to other types of turbine
engines including three-spool architectures.
[0037] The exemplary engine 20 generally includes a low speed spool
30 and a high speed spool 32 mounted for rotation about an engine
central longitudinal axis A relative to an engine static structure
36 via several bearing systems 38. It should be understood that
various bearing systems 38 at various locations may alternatively
or additionally be provided, and the location of bearing systems 38
may be varied as appropriate to the application.
[0038] The low speed spool 30 generally includes an inner shaft 40
that interconnects a fan 42, a first (or low) pressure compressor
44 and a first (or low) pressure turbine 46. The inner shaft 40 is
connected to the fan 42 through a speed change mechanism, which in
exemplary gas turbine engine 20 is illustrated as a geared
architecture 48 to drive the fan 42 at a lower speed than the low
speed spool 30. The high speed spool 32 includes an outer shaft 50
that interconnects a second (or high) pressure compressor 52 and a
second (or high) pressure turbine 54. A combustor 56 is arranged in
exemplary gas turbine 20 between the high pressure compressor 52
and the high pressure turbine 54. A mid-turbine frame 57 of the
engine static structure 36 is arranged generally between the high
pressure turbine 54 and the low pressure turbine 46. The
mid-turbine frame 57 further supports bearing systems 38 in the
turbine section 28. The inner shaft 40 and the outer shaft 50 are
concentric and rotate via bearing systems 38 about the engine
central longitudinal axis A which is collinear with their
longitudinal axes.
[0039] The core airflow is compressed by the low pressure
compressor 44 then the high pressure compressor 52, mixed and
burned with fuel in the combustor 56, then expanded over the high
pressure turbine 54 and low pressure turbine 46. The mid-turbine
frame 57 includes airfoils 59 which are in the core airflow path C.
The turbines 46, 54 rotationally drive the respective low speed
spool 30 and high speed spool 32 in response to the expansion. It
will be appreciated that each of the positions of the fan section
22, compressor section 24, combustor section 26, turbine section
28, and fan drive gear system 48 may be varied. For example, gear
system 48 may be located aft of combustor section 26 or even aft of
turbine section 28, and fan section 22 may be positioned forward or
aft of the location of gear system 48.
[0040] The engine 20 in one example is a high-bypass geared
aircraft engine. In a further example, the engine 20 bypass ratio
is greater than or equal to about six (6), with an example
embodiment being greater than about ten (10), the geared
architecture 48 is an epicyclic gear train, such as a planetary
gear system or other gear system, with a gear reduction ratio of
greater than about 2.3 and the low pressure turbine 46 has a
pressure ratio that is greater than about five. In one disclosed
embodiment, the engine 20 bypass ratio is greater than or equal to
about ten (10:1), the fan diameter is significantly larger than
that of the low pressure compressor 44, and the low pressure
turbine 46 has a pressure ratio that is greater than about five
5:1. Low pressure turbine 46 pressure ratio is pressure measured
prior to inlet of low pressure turbine 46 as related to the
pressure at the outlet of the low pressure turbine 46 prior to an
exhaust nozzle. The geared architecture 48 may be an epicycle gear
train, such as a planetary gear system or other gear system, with a
gear reduction ratio of greater than about 2.3:1. It should be
understood, however, that the above parameters are only exemplary
of one embodiment of a geared architecture engine and that the
present invention is applicable to other gas turbine engines
including direct drive turbofans.
[0041] A significant amount of thrust is provided by the bypass
flow B due to the high bypass ratio. The fan section 22 of the
engine 20 is designed for a particular flight condition--typically
cruise at about 0.8 Mach and about 35,000 feet. The flight
condition of 0.8 Mach and 35,000 ft, with the engine at its best
fuel consumption--also known as "bucket cruise Thrust Specific Fuel
Consumption (`TSFC`)"--is the industry standard parameter of lbm of
fuel being burned divided by lbf of thrust the engine produces at
that minimum point. "Low fan pressure ratio" is the pressure ratio
across the fan blade alone, without a Fan Exit Guide Vane ("FEGV")
system. The low fan pressure ratio as disclosed herein according to
one non-limiting embodiment is less than about 1.45. "Low corrected
fan tip speed" is the actual fan tip speed in ft/sec divided by an
industry standard temperature correction of .left brkt-bot.(Tram
.degree. R)/(518.7.degree. R).right brkt-bot..sup.0.5. The "Low
corrected fan tip speed" as disclosed herein according to one
non-limiting embodiment is less than about 1150 ft/second.
[0042] As shown in FIG. 2, a flexible shaft 99, which is driven by
the turbine 46, drives a sun gear 101 which, in turn, engages and
drives intermediate gears 102. In some embodiments, the
intermediate gears 102 may be planet gears of a planetary epicyclic
gear system. In other embodiments, the intermediate gears 102 may
be star gears of a star epicyclic gear system. The intermediate
gears 102 engage and drive a ring gear 103 to, in turn, drive an
output shaft 106, which then drives the fan rotor 42. In other
embodiments, a planetary gear carrier (not shown) driven by
planetary gears may drive the fan shaft. Lubricant is supplied to a
journal pin 108, to the intermediate gears 102 and to other
locations within the gear reduction 48.
[0043] FIG. 3 shows baffles 100 which are placed circumferentially
between adjacent planet gears 102.
[0044] A gutter 104 surrounds the gear reduction 48 and captures
oil that has left the gear reduction. Oil from the gear reduction
48 is returned to a pump 72 (See FIG. 4) or a tank 90 as shown
schematically in FIG. 4. As shown, a lubricant system 70 includes
the gear reduction 48 which may be structured as shown in FIGS. 2
and 3. Notably, complete details of the operation of the baffle,
the gutter and the other portions of the gear reduction may be as
disclosed in U.S. Pat. No. 6,223,616, the disclosure of which with
regard to the operation of the gear reduction is incorporated by
reference.
[0045] Oil flows from an oil pump 72 to a filter 74 through a
pressure relief valve 76 to an air/oil cooler 78 and then to a
fuel/oil cooler 80. The oil may pass through an oil pressure trim
orifice 82 and back to the tank 90. Alternatively, the oil may pass
through a strainer 84 and then to the gear reduction 48. Oil
returning from the gear reduction and, in particular, from the
gutter, may pass back directly to the pump 72 or to the tank 90.
This is a simplification of the overall lubricant system and, as
appreciated, there may be other components.
[0046] Applicant has recognized that by utilizing baffles 100 and a
gutter 104 on the gear reduction 48, which may be generally as
disclosed in the above-mentioned U.S. patent, the oil need not sit
in the oil tank for ten seconds in order to de-aerate. Thus, the
size of the tank 90 may be made much smaller.
[0047] Conventional turbofans allow the oil to dwell in an oil tank
for approximately seven to ten seconds. The dwell time allows air
bubbles to separate from the oil to prevent foaming. With the move
to a geared gas turbine engine, the oil flow volumes may
effectively double. This would require a much larger oil tank, and
as much as twice as large if the same dwell time is allowed. Thus,
it becomes important to reduce dwell time.
[0048] Applicant has discovered that oil is de-aerated by the
baffles 100 and gutter system and that a dwell time in the oil tank
to remove air bubbles may be less than five seconds. More
preferably, it may be less than or equal to about 3.0 seconds. This
allows the use of oil tank 90 to be of a size roughly equivalent to
the size utilized in prior non-geared gas turbine engines. A
deaerator 88 is shown incorporated into the oil tank 90.
[0049] The better the deaeration before the oil reaches the tank,
the shorter the dwell time that can be achieved. The disclosed
deaerator achieves these very low dwell times.
[0050] As an example, an oil tank that holds 25 to 35 quarts of oil
may be utilized on a geared gas turbine engine with 15,000 to
35,000 lbs in rated thrust at take-off. Further, an oil tank may be
35 quarts to 50 quarts of oil for an engine with 35,000 to 100,000
lbs in rated thrust at take-off.
[0051] FIG. 5 shows a deaerator embodiment 188. A line 190 receives
an air/oil mixture such as from the pump 72. Air leaves through an
air outlet 192, as shown in FIG. 4.
[0052] A plurality of oil outlets 194 are shown in an outer shell
195 of the deaerator. An oil level 196 is shown schematically, and
would be the oil level within the oil tank 90 of FIG. 4.
[0053] As shown in FIG. 6, a flow splitter or separator 200 is
provided inline to the inlet 190 and serves to split the air/oil
flow into two paths, and at an intermediate location in inlet 190.
This will hasten the deaeration of the mixed oil and air from the
inlet 190. The air will be at the radially outer locations, and
will pass through a tube 193 into the air outlet 192. As shown, air
outlet 192 has an end 300 extending into a shell 302 of deaerator
188.
[0054] As shown in FIG. 7, the oil will flow downwardly along an
upper path 202 of a scroll or spiral, and along a lower path 204.
Although shown as vertically upper and lower sides, other opposed
side orientations may be used. The inventive deaerator more quickly
removes the oil, and thus facilitates the dwell times as mentioned
above.
[0055] A deaerator exit 194 delivers oil into the oil tank 90 at
least 2 inches (5.08 centimeters) between a freestanding oil level
196 within the tank 90. An inlet velocity to the deaerator 188 may
be less than or equal to 14 feet/second. An exit velocity from the
deaerator 188 into the air outlet 192 may be less than or equal to
14 feet/second.
[0056] Applicant has found that introducing the oil and air mixture
into an oil tank is much "quieter," resulting in less re-aeration
when it is delivered at least two inches below a free surface. As
an example, if the oil were sprayed into the free surface, this
could cause splashing and foaming.
[0057] As to the velocity, high velocity oil and air mixtures
entering the tank may cause re-aeration. The 14 feet/second is a
very good goal to reduce the chances of re-aeration.
[0058] Although an embodiment of this invention has been disclosed,
a worker of ordinary skill in this art would recognize that certain
modifications would come within the scope of this invention. For
that reason, the following claims should be studied to determine
the true scope and content of this invention.
* * * * *