U.S. patent application number 12/583474 was filed with the patent office on 2011-02-24 for multi tube-fins liquid-air heat exchanger and methods.
Invention is credited to John Yenkai Pun.
Application Number | 20110042037 12/583474 |
Document ID | / |
Family ID | 43604352 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110042037 |
Kind Code |
A1 |
Pun; John Yenkai |
February 24, 2011 |
Multi tube-fins liquid-air heat exchanger and methods
Abstract
A secondary refrigerant fluid is cooled or heated in the
operation of a multiple Tube-fins heat exchanger arranged in
parallel for fins to conduct heat transfer with air being propelled
by a multi-row bank of low profile brushless fans. Fluid is
controlled to ascend the bank of tubes in unison rate for high
efficiency heat transfer with air. Large temperature differential
exists between air and fluid when conditioned fluid travels through
the tubes for a relatively short distance. A system of components
is so arranged that the fluid flow rate to every heat exchanger is
preset and the "on" or "off" operation of any heat exchanger does
not affect the flow rate destined for other heat exchangers. Fluid
is not transported to a heat exchanger when it is not in operation
saving energy. Each heat exchanger is controlled by an integrated
thermostat so occupants can set the air conditioning operation
individually independent of all other heat exchangers.
Inventors: |
Pun; John Yenkai; (Coos Bay,
OR) |
Correspondence
Address: |
John Yenkai Pun
92955 Hill Grade Drive
Coos Bay
OR
97420
US
|
Family ID: |
43604352 |
Appl. No.: |
12/583474 |
Filed: |
August 20, 2009 |
Current U.S.
Class: |
165/50 ; 165/121;
165/182 |
Current CPC
Class: |
F24F 13/30 20130101;
F28D 1/05316 20130101; F28F 1/20 20130101; F24F 1/0007 20130101;
F24F 1/0033 20130101 |
Class at
Publication: |
165/50 ; 165/121;
165/182 |
International
Class: |
F24F 3/00 20060101
F24F003/00; F28F 1/18 20060101 F28F001/18; F28F 7/00 20060101
F28F007/00; F24F 13/30 20060101 F24F013/30 |
Claims
1. An apparatus for using cooled or heated fluid in a closed loop
system conducting heat transfer with air as heat exchanger for air
conditioning and refrigeration comprising: means for controlled
fluid flow rate shared by many tubes and ascending the tubes in
unison for a short distance conducting heat transfer with high
temperature differential between fluid and air; half diameter of
the tubes are soldered onto a groove formed longitudinally on the
fin to insure maximum heat transfer between tube and fin, a large
number of these tube fins are arranged in parallel close together
so air can conduct heat transfer intimately with fins, and rows of
fans propel air through the spaces between fins for heat
transfer.
2. The apparatus as in claim 1, wherein another fluid input tube
with multiple short tubes is connected to the primary input tube to
insure fluid is traveling through all tubes at uniform rate.
3. The apparatus as in claim 1, wherein the apparatus is installed
in every room and space needing air conditioning, and the heat
exchanger's operation is controlled by occupant independently from
other heat exchangers in an air conditioning system.
4. The apparatus is in claim 1, wherein each heat exchanger is
equipped with thermostat and optional relativity humidity
control.
5. The apparatus as in claim 1, wherein a heat exchanger can be
larger or smaller modules that fit needs of most size rooms.
6. The apparatus as in claim 5 that each heat exchanger is equipped
with manual valve for setting conditioned fluid flow rate to match
the module size in function.
7. The apparatus as claim 1 wherein the inclusion of temperature
sensors monitor temperature of input conditioned fluid and
temperature of processed fluid for heat exchanger operation.
8. The apparatus as in claim 7 wherein heat leakage of a room can
be monitored by the difference of temperatures of input and output
fluid to the heat exchanger at the same time keeping the room
temperature constant.
9. The apparatus as claim 1 wherein heat exchanger can be used for
reclaiming waste heat to for reuse.
10. A supporting system that includes air pressure generator, air
operated diaphragm pump, air storage tank(s), normally closed
solenoid valves, normally open solenoid valves, manual valve and
sensor/regulator for air pressure to operate in conjunction with
Tube-fins heat exchangers that offer functions that are previously
unattainable by prior arts.
11. System as in claim 10 wherein air pressure generator and air
tanks are used due to the need for a non-corrosive positive
displacement diaphragm pump that is in operation with compressed
air.
12. System as in claim 11 wherein a positive displacement pump is
essential in delivering a pre-set rate of fluid to each heat
exchanger without change or its output is not influenced by
operation of heat exchangers.
13. A system as in claim 10 wherein each heat exchanger can have
required rate of conditioned fluid being supplied pre-set for its
size and need.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to an apparatus and methods
that conduct controllable heat exchange between introduced air and
very small amount of cold or hot conditioned fluid.
[0002] Heat exchanger technology has long existed with two basic
heat transfer mechanisms. In one of the most common applications a
single long tube is bent back and forth with scores of thin heat
conductive fins in layers attached perpendicularly on the folded
long tube. In an attempt to increase heat conduction, an aluminum
fin is used with punched holes and tiny collars swaged onto the
coursing tube perpendicularly. Air is blown through the fin layers
effecting heat transfer between air and liquid inside the tubing.
Tubing contacts with the fins are small because the tube being
inserted perpendicularly to the fin with small temperature contact
area is characteristic of this practice. Purpose of this design is
obvious in allowing as much heat transfer possible as fluid courses
through the long tube. The fact remains that heat transfer rate
decreases as well as heat exchange efficiency as the fluid travels
through the tube. This is due to temperature of fluid approaching
that of air lowing the temperature differential between the two
media as it travels. This kind of heat exchanger typifies most
present day fluid air heat exchangers.
[0003] Some prior arts modify shape of the tube carrying fluid to
gain more tube surface in contact with the surrounding medium as
exemplified by U.S. Pat. No. 4,995,454. More commonly occurring is
the modification of fins and their attachments to the tubes. These
prior arts range from bending fins back and forth a short distance
with the bent portion touching the circumference of a tube, helical
spiral around the tube, modified fin shapes, to fin creating a
vortex air flow as exemplified in U.S. Pat. Nos. 5,398,752;
5,738,168; 6,035,927; 6,119,769; 6,167,950; 6,173,763; 6,349,761;
6,932,153; and 7,438,121. One prior art even uses wire substituting
for fins as shown in U.S. Pat. No. 6,192,976. Effectiveness of
increase in efficiency of heat transfer is questionable because
virtually all these prior arts show very small area of contact
between the fin and tube for good temperature conduction.
[0004] Tube-fins heat exchanger of this invention provides a very
large area of heat conduction path between tube and fin especially
the very large ratio between the small mass of fluid to surface
area of fin at a given length of tube.
[0005] The parallel placed short tubes with fins are designed to
achieve maximum heat transfer between air and fluid in a short time
interval while the fluid is traveling through the short tube taking
advantage of heat transfer is at its maximum when the differential
of temperature is greatest between air and fluid.
[0006] Rows of low profile DC brushless fans are used to provide
air flow for intimate efficient heat transfer between the parallel
fins. Each row of fans is individually controlled depending on need
of certain amount of heat transfer. Low profile of heat exchanger
also allows installation of module inside walls.
[0007] Heat exchanger is intended for function in every room and
space needing air conditioning. Very small tubings (instead of
large air ducts) are used in transport of very small amount of
heated and cooled fluid to be processed by the heat exchanger; heat
leakage during transport is virtually nonexistent with provision
similarly used in cryogenic fluid transport with vacuum. Heat
transfer can be accomplished with each heat exchanger at
destination needing air conditioning without energy waste.
[0008] A unique feature of the apparatus places a heat exchanger in
every room, allowing temperature setting for each room to be
independently accomplished by an occupant with an integrated
thermostat. Conditioned fluid for a heat exchanger not in operation
is prevented from being transported to the heat exchanger allowing
energy savings.
[0009] There are other applications for this heat exchanger besides
being used for air conditioning. It can used for measurement of
heat leakage of a room with provided temperature sensors measuring
input and processed conditioned fluid. Heat exchanger can also be
used in collecting waste heat.
SUMMARY
[0010] The present invention relates to a modular apparatus and
methods for efficient controllable and measurable heat exchange
between ambient air and small amount of cold or hot conditioned
fluid. Contemporary air conditioners conduct heat exchange between
air in a building and refrigerant operating with a single heat
exchanger in one locale. Conditioned air must be distributed by an
air duct system to various rooms and spaces requiring air
conditioning. Air ducts carrying large volume of air consume space,
are expensive in components, cost a high amount in installation
labor, and waste over 20% electrical energy from heat leakage
(experimental conclusion published at Berkeley Lawrence National
Laboratory). Output of conditioned air is fixed in a traditional
system for delivery to all the rooms or spaces. Shutting
conditioned air off to any given room, air destined for that room
is distributed to the rest of the system. There is no energy
savings by shutting off air to one or more room(s).
[0011] Air is a poor conductor. The intermolecular distance is very
large so heat (molecular vibration) takes time in transmitting from
one molecule to another. Surface radiating heat also takes time to
transmit the heat to air molecules. Fluid like water with far
closer intermolecular distance transmits heat 24 times more
efficiently than air. This also means that heat can be transferred
much faster between water and a hot or cold metallic surface
besides being transmitted much faster between molecules. Even more
important is that water carries 3,716 times more heat than air;
only small amount of conditioned fluid needs be transported to each
room or space requiring air conditioning instead of very large air
ducts carrying large air volume. If we were to substitute a very
small tube in the order of 1/8 or 1/4% inch ID carrying hot or cold
fluid instead of 6.times.6 inch or larger air ducts to various
rooms or spaces, we can use a much better method of insulating heat
loss or gain that is far less expensive and endowed with
significant conservation of building space besides energy. Heat
exchange between fluid and air occurs in a room or space in this
invention. Besides the above mentioned advantages, this fluid to
air and vise versa heat transfer at destination of usage has far
more advantageous features.
[0012] Each room's operation of air conditioning can be
individually and independently set and controlled by the occupant.
People have different temperature preferences even between husband
and wife, and this feature is much sought. No conditioned fluid
will be processed in an unoccupied room so energy designated for
that room can be saved in the operation of the
compressor-condenser-evaporator.
[0013] The invention of the Tube-fins heat exchanger is also
essential in contributing energy and economic savings compared to
conventional central air conditioning systems. Virtually all
Tube-fins type heat exchangers being used in conditioning consist
of a single long tube bent back and forth with fins attached
mechanically perpendicular to the tube. The purpose is to conduct
heat transfer through the entire length of the long tube to extract
or absorb as much heat from fluid flowing through the tube as
possible with air flow over the fins. What is not considered is
that heat transfer rate is the greatest as fluid first flows
through the tube due to largest temperature differential between
fluid in tube and air. The tube temperature differential as well as
heat transfer efficiency is continuously lowered as fluid travels
through the long tube.
[0014] Since fluid like water carries 3,716 more heat than air,
only a very small amount of fluid per unit time is needed to cool
or heat a room or space. A heat exchanger having very high heat
transfer efficiency is needed to conduct heat transfer between this
small volume fluid and air. Instead of using a single tube, we use
many very small tubes so each tube carries only a very small amount
of conditioned fluid. Each tube is soldered along its length into a
groove formed on a strip of thin metal fin on half its diameter.
This method insures the fin making significant thermo-contact with
the fluid carrying tube. Assuming we have many of these tubes one
foot long and the fins are 1 inch wide by 11 inches long we can fit
47 tubes arranged in parallel in a 12 inch wide area. One foot long
1/8 inch diameter small copper tubing with tube ID 0.087 in is
commonly available. Eleven inches long and 1 inch wide with 0.004
inch thick copper sheeting strips are used for fins. In a 12 inch
wide area the fins possess 1034 in.sup.2 or 7.18 square feet of
surface area for heat transfer. Heat transfer capability of this
heat exchanger is more than enough for a large room. With an
electronically controlled pump set at 250 ml fluid being pumped to
the exchanger per minute, fluid fills the bank of parallel tubes
4.59 times per minute. Tests have been conducted within these
parameters and found heat transfer rate to be very satisfactory. If
% diameter tube is used or more 1/8 inch tubes are used air
conditioning in a much larger room can be accomplished with a
larger size heat exchanger module.
[0015] This invention is only interested in conducting heat
transfer when the temperature differential between air and fluid is
at or near maximum to gain the highest efficiency. It does not
matter what temperature the processed fluid has returning to the
reservoir to be cooled or heated again. If the temperature of the
returning fluid happens to be not overly different from the fluid
temperature setting less energy will be used and vise versa.
[0016] A vacuum assisted fluid transport system developed to
transport small amount of conditioned fluid without noticeable heat
leakage is under preparation for a separate patent application.
System energy savings is also the center focus. Traditional air
ducts have many joints and are not sealed against air leaks. A
large amount of insulation material is needed due to the thin
material (usually thin metal sheet) that comprises the air ducts;
occupation of a large amount of space is also required. ASHRAE
(American Society of Heating Air conditioning Engineers), a body
that makes recommendations for the air conditioning trade
recommends R6 insulation on air ducts due to the final large sizes
of insulated air ducts that is hardly adequate for stopping
significant amount of heat leakage and still on the average wastes
over 20% energy. A majority of existing air ducts in air
conditioned buildings do not even meet these inadequate ASHRAE
criteria. The other conventional air conditioning method, the split
system, has a similar problem using long small tubing to conduct
refrigerant with poor or no insulation to prevent heat leakage.
This problem can be acute because the surface (of the small tube)
to fluid mass ratio is very large; heat transfer rate between air
and fluid will also be large. However, small tubing can also be a
good thing; insulation can be accomplished with low expense and
energy consumption. Vacuum is used for insulation in transport of
cryogenic fluid very effectively. Without air there is no heat
conduction so vacuum is a good insulator. All needed is to place
the fluid transport tube inside another tube and pump the air out.
In order to insulate the air conditioning system's components
effectively, the invention uses vacuum insulating reservoir and
other components besides fluid transport tubes to prevent heat
leakage and conserve energy use.
[0017] In support of the Tube-fins heat exchanger, a unique method
is used to allow presetting flow rate to any heat exchanger that is
larger, smaller, or located on a different floor. Every heat
exchanger can be turned "on" or "off" and temperature of operation
set independently in every room and space; provision is also made
so that activities of any number of heat exchangers in operation do
not affect the flow rates preset for the remaining heat exchangers.
Energy is saved when any number of heat exchangers are not in
operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated and form a
part of this specification, illustrate embodiments of the invention
and together with the descriptions, serve to explain the principles
of the invention.
[0019] FIG. 1 is a side section view of the Tube-fins heat
exchanger showing a tube-fin and direction of secondary refrigerant
travel and its connections to refrigerant input and output tubes.
The drawing also displays 3 rows of DC brushless muffin fans that
blow room air through the Tube-fins heat exchanger and return the
air to the room through an air grill.
[0020] FIG. 2 is an enlarged view of how air from a room or space
is transported by fan(s) through the parallel openings of bank of
tube-fins to achieve heat transfer.
[0021] FIG. 2a is a detailed drawing of how a tube is soldered to a
stamped channel of a fin.
[0022] FIG. 3 is a front view of the Tube-fins heat exchanger FIG.
4 displays how a tube is fitted to the stamped longitudinal slot of
the fan.
[0023] FIG. 5 shows a frontal view of a Tube-fins heat exchanger
module and relationships of tubing connections.
[0024] FIG. 6 is a drawing of a wall inside mount module version
with narrow profile.
[0025] FIG. 7 is a wall mounted Tube-fins heat exchanger module
with control positions.
[0026] FIG. 8 is a diagram of system operating the heat exchangers
allowing each heat exchanger to receive secondary refrigerant
independently without changing other heat exchangers' conditioned
fluid flow.
[0027] FIG. 9 is a perspective view of a motorized recirculation of
fluid method through the fins of the evaporator(s).
[0028] FIG. 10 is the reservoir inside top view of FIG. 9 showing
fluid travel pattern during recirculation.
[0029] FIG. 11 is a side view of a dehumidifier module in line with
a heat exchanger showing fresh air intake and air travel path.
REFERENCE NUMERALS IN DRAWINGS
[0030] 1. Small diameter copper tubing [0031] 2. Thin copper fin
[0032] 3. Input copper tubing that connects all small copper tubes
at one end [0033] 4. Short interconnecting copper tube between
tubes 3 and 8 [0034] 5. DC brushless muffin fan [0035] 6. Output
copper tube that connects all the tubes at output end [0036] 7.
Input air to the Tube-fins heat exchanger [0037] 8. Output air to
room or space after heat transfer [0038] 9. Diffuser [0039] 9a.
Wall board at back of heat exchanger [0040] 9b. Outer wall board
surface in room [0041] 10. Temperature thermostat [0042] 11.
Optional relative humidity controller [0043] 12. Infrared sensor
for remote control [0044] 13. Room air intake grill [0045] 14.
Dehumidifier module [0046] 15. Air compressor [0047] 16. Hose
transporting compressed air [0048] 17. Compressed air operated
volumetric diaphragm pump [0049] 18. Secondary refrigerant plenum
[0050] 19. Secondary reservoir containing evaporator(s) and
immersed heater(s) [0051] 20. Fluid plenum collecting secondary
refrigerant from valve(s) 19 [0052] 21. Bank of normally open
solenoid valves [0053] 22. Connecting tube(s) from 21 to 23 [0054]
23. Bank of manual adjusting valves [0055] 23a. Individual manual
operating valves(s) [0056] 24. Tube(s) connecting 23 and 20 [0057]
25. Bank of normally closed solenoid valve(s) [0058] 26. Motorized
cylinder with paddles for fluid circulation [0059] 27. Secondary
refrigerant [0060] 28. Evaporator(s) [0061] 29. Immersed heater
[0062] 30. Direction(s) of travel of circulating fluid [0063] 31.
Direction(s) of travel of returning fluid to the circulator [0064]
32. Tube-fins heat exchanger [0065] 33. Dehumidifier [0066] 34.
Fresh air intake
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] Reference will now be made in detail to the preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. While the invention will be described in
conjunction with the preferred embodiments, it will be understood
that they are not intended to limit the invention to those
embodiments. On the contrary, the invention is intended to cover
alternatives, modifications and equivalents, which may be included
within the spirit and scope of the invention as defined by the
appended claims.
[0068] As described above, the present invention provides an
apparatus and methods for fluid and heat exchange in the
application of air conditioning of rooms and spaces in structures
or dwellings. More particularly, the apparatus distributes small
amount of conditioned (hot or cold) fluid into large number of
small tubes each attached lengthwise with thin metal fins and
oriented in the same direction FIG. 1, FIG. 2, FIG. 3 and FIG. 4;
1, 2 (47 tubes in a square foot wide area as an example) with the
amount of fluid travelling as uniformly as possible from one end to
the other end of tubes for conduction of heat transfer with air
within a room or space where the heat exchanger is located. The
tube is soldered onto a longitudinal groove formed in the fin FIG.
4; 1 and 2. The fin has good temperature conduction with half the
diameter of the tube soldered along its entire length. Thin profile
brushless DC fans (9 arranged in three rows within a square foot)
FIG. 1, FIG. 5, and FIG. 6; 5 mounted on one side of the of tube
bank suck in room air and blow the air through the bank of tubes
with fins carrying out heat transfer and returning the conditioned
air to the room 7 and 8. Processed fluid FIGS. 1 and 6; 6 is
returned to a reservoir FIG. 8; 19 that contains an evaporator and
submersible electric resistance heaters for reheating or re-cooling
processed fluid.
[0069] In one embodiment, this invention relates to air
conditioning fluid that is cooled or heated instead of air as in
traditional systems. Water, for instance, holds 3,716 times more
heat that equal volume of air. Large air ducts in central air
conditioning can be replaced by small tubes FIG. 8 22a which
transport conditioned fluid to rooms or spaces needing air
conditioning supplying heat exchangers for heat transfer with room
air. Small tubes are easier to insulate from heat leaks that waste
electrical energy over 20% for a large air duct system in
transporting conditioned air. In our systems, a large number of
rooms and spaces are air conditioned by an equal number of heat
exchangers supplied with their own thermostats. This invention
differs from traditional air conditioner's single thermostat
control for the whole system.
[0070] Moreover, each heat exchanger can be turned "on" or "off"
independently with its own thermostat FIG. 7; 10 and 12 without
affecting others' operations. This invention includes another
embodiment that, regardless how many heat exchangers are in
operating mode, the conditioned fluid flow rate and pressure remain
constant going to every heat exchanger. This operational feature is
controlled by novel use of matching solenoid valves combined with
manual set valve for definitive flow control FIG. 8; 21, 23, 23a
and 25. One set is incorporated with each heat exchanger so desired
amount of conditioned fluid flow is predetermined and preset FIG.
8; 25 and 23a. The other set is located immediately after the
volumetric pump, and its flow is immediately returned to the
reservoir FIG. 8' 21 and 23. The setting of the flow matches that
of a heat exchanger. In an "off" mode of a particular heat
exchanger, the solenoid valve will be shut. The matching solenoid
valve and manual flow valve for that particular heat exchanger will
be open returning fluid to the reservoir. When this heat exchanger
is turned "on", conditioned fluid flows into the heat exchanger for
conduction of heat transfer; the corresponding solenoid valve by
the pump will be shut "off" preventing conditioned fluid flowing
back to the reservoir. This novel arrangement allows conditioned
fluid flowing to all other heat exchangers to remain the same.
[0071] Another significance of the above arrangement is clear; if a
heat exchanger is not turned "on", conditioned fluid designated for
that particular heat exchanger is not transported. No heat leakage
occurs when the conditioned fluid has to travel such a short
distance back to the reservoir. Energy is only expended when a heat
exchanger is in operation. Fluid returning to reservoir at the same
or near the temperature as fluid inside reservoir does not use
additional energy in cooling or heating. Energy savings due to this
feature can be significant.
[0072] Computer control and sensors integrated with the system,
especially those associated with the Tube-fins heat exchanger,
offer automated air conditioning temperature setting on a room to
room basis that not only saves energy but provides user comfort
previously unattainable. Traditional air conditioners' cooling and
heating is a simple "on" or "off" operation without gradation
control. Once the set temperature from a single thermostat for
rooms and spaces is reached, the air conditioner is turned "off".
Depending on the manufacturer, the air conditioner is turned back
"on" when the single thermostat measures the temperature to be so
many degrees in deviation from preset value. It is not uncommon
that one or more rooms have temperatures far different from that
measured by a single thermostat in one location causing occupant
discomfort and waste of energy.
[0073] Rooms of a house have different orientations to the sun,
exposures to wind, or lack thereof. Insulation of walls, and number
and sizes of windows also play prominent roles in degree and rate
of heat leakage. None of these important factors are taken into
consideration by existing manufacturers.
[0074] Fresh air intake control previously unavailable in domestic
air conditioners is included in this invention (FIG. 11). This
feature is incorporated especially well into to the wall mounted
heat exchangers. Since our Tube-fins heat exchanger is designed to
fit into walls constructed with 2 by 4 lumber, and most rooms in a
house have one wall facing outside, it is logical to incorporate
such an important part of air conditioning function as
incorporating outside air with heat exchanger of this invention and
dehumidifier (in another invention). Virtually all building codes
in US require commercial installations have fresh air intake of
10%. Newer homes have far better insulation than older ones in
eliminating air leaks. It is obvious the advancement of insulation
methods and materials contribute to build up of carbon dioxide in a
house. Dilution of inside air with outdoor air appears to be the
simplest economical solution to counter the carbon dioxide problem.
This invention again utilizes the basic heat exchanger (or an
inline dehumidifier of another invention) for operation of an
adjustable air intake to obtain desirable amount of outside air to
be incorporated with inside air of that room housing the heat
exchanger. Two types of adjusting devices will be used since they
can be controlled electronically via a computer and a remote. A
screw drive with a stepping motor is one and a rotation device
similar to a model airplane control is the other. A remote control
can be used to set percentage of fresh air needed, and the computer
drives these electronically controlled devices to open or close the
vent to the outdoors to preset amount.
[0075] FIG. 8 and FIG. 10 depict an optional design for a reservoir
19 with a built-in fluid circulation through the heating 29
(immersed electrical resistance heaters) and cooling 28
(evaporator) components. The stirrer is of paddled and slotted
cylindrical construction and is motorized 26. Rotating paddles
propel the fluid outward from the stirrer to conduct heat transfer
with the evaporator or heating elements 30. Fluid inside the
rotating stirrer exits the slots to replace the moving fluid. Fluid
31 is also returned through the bottom of the stirrer to replace
fluid exiting the slots.
* * * * *