U.S. patent number 3,779,310 [Application Number 05/130,995] was granted by the patent office on 1973-12-18 for high efficiency heat transit system.
Invention is credited to George F. Russell.
United States Patent |
3,779,310 |
Russell |
December 18, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
HIGH EFFICIENCY HEAT TRANSIT SYSTEM
Abstract
A closed tube in substantially horizontal position and
approximately half filled with vaporizable liquid under very low
absolute pressure has one exterior portion of its length exposed to
hot fluid from which heat is extracted to vaporize liquid in the
tube and another exterior portion of its length exposed to a
relatively cool fluid which extracts heat from the vapor in the
tube and condenses it. Vapor formed in the portion of the tube
exposed to the hot fluid migrates to the portion of the tube
exposed to the cool fluid and the condensate resulting from such
cooling flows back to the tube portion exposed to hot fluid. The
major portion of the internal periphery of that portion of the tube
exposed to hot fluid is lined with wicking, but a gap is left
between ends of the arcuate liner below the surface of the liquid
in the tube for transmission of heat from the fluid externally of
the tube directly to liquid in the tube to expedite its
vaporization at that location.
Inventors: |
Russell; George F. (Tacoma,
WA) |
Family
ID: |
22447386 |
Appl.
No.: |
05/130,995 |
Filed: |
April 5, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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817483 |
Apr 18, 1969 |
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Current U.S.
Class: |
165/104.26;
122/33 |
Current CPC
Class: |
F28D
15/046 (20130101) |
Current International
Class: |
F28D
15/04 (20060101); F28d 015/00 () |
Field of
Search: |
;165/105,133 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Davis, Jr.; Albert W.
Parent Case Text
This application is a continuation-in-part of U.S. Pat. application
Ser. No. 817,483, filed Apr. 18, 1969 for Method of and Apparatus
for Heat Transit, now abandoned.
Claims
I claim:
1. In a heat transit device including a container having one
portion exposed to heat-supplying means and a different portion
exposed to heat-extracting means, the improvement comprising the
combination of wick liner means on the inner periphery of the
container portion exposed to the heat supply means, and the
container containing a body of free vaporizable heat transfer
liquid of substantial depth in the lower part of the container
portion exposed to the heat-supplying means, at least a portion of
the lower part of the inner periphery of the container below the
surface of said liquid body not being covered by said wick liner
means, and said liquid body also extending to the lower part of the
container portion exposed to the heat-extracting means whereby
bubbles resulting from the boiling of the liquid will saturate with
liquid a portion of said wick liner above said liquid body.
2. In the heat transit device defined in claim 1, the wick liner
means being interrupted for a portion of the peripheral extent of
the container wall beneath the surface of the body of heat transfer
liquid.
3. In the heat transit device defined in claim 2, the wick liner
means being interrupted along a generally horizontal band.
4. In the heat transit device defined in claim 3, the band along
which the wick liner means is interrupted being offset from the
central portion of the container bottom.
5. In the heat transit device defined in claim 1, the wick liner
means covering a portion of the inner periphery of the container
portion beneath the surface of the heat transfer liquid for direct
absorption of liquid by the wick liner means from the body of
liquid.
6. In the heat transit device defined in claim 1, the surface of
the body of heat transfer liquid in the container being
substantially midway between the top and bottom of the
container.
7. In the heat transit device defined in claim 1, the absolute
pressure in the space above the surface of the body of liquid being
less than atmospheric pressure.
8. The method of transferring heat from a heat-supplying location
to a heat-extracting location by a heat transfer fluid in a
container having a wick liner lining an upper portion of the
container and only part of the lower portion of the container,
which comprises placing in the container sufficient vaporizable
heat transfer fluid so that a substantial portion of the heat
transfer fluid is in the form of a free liquid body beneath the
portion of the wick liner lining the upper portion of the container
and above a portion of the wick in the lower portion of the
container and a portion of the free liquid body is located in the
heat-extracting portion of the container, heating a portion of the
container to effect nucleate boiling in the free liquid body for
promoting evaporation of the heat transfer fluid from its liquid
state to its vapor state and for moistening of the portion of wick
liner above the liquid body, also heating a portion of the
container upper portion lined with the wick liner for evaporating
heat transfer fluid from the wick liner, and cooling the container
at the heat-extracting location for condensing heat transfer fluid
vapor back into its liquid state to rejoin the free liquid body.
Description
A principal object of the present invention is to provide a device
for transferring heat from one fluid medium to another fluid medium
with high efficiency and which has large capacity.
A further object is to provide such a device which can effectively
transfer heat between such fluid mediums under widely different
temperature conditions.
Another object is to provide a heat transfer device which has one
portion exposed to hot fluid and such entire portion is maintained
at substantially uniform temperature to prevent local failure and
to provide maximum efficiency of operation.
In such a heat transfer device, it is an object to be able to
utilize any of various vaporizable liquids.
An additional object is to operate such a device under low pressure
conditions so that, if a failure should occur, minimal or no damage
will result.
FIG. 1 is a somewhat diagrammatic vertical section through a
representative heat transit device of the present invention.
FIG. 2 is a side elevation of a somewhat modified form of heat
transit device, parts being broken away, and FIG. 3 is a transverse
section through such device taken on line 3--3 of FIG. 2.
FIG. 4 and FIG. 5 are sections through heat transfer devices
corresponding to FIG. 3, but showing devices of the same type as in
FIG. 1, although of different size.
FIG. 6 is a top perspective of a section of a device shown in FIG.
1 with a portion broken away.
FIG. 7 and FIG. 8 are vertical sections through the heat transit
device corresponding to FIG. 1 but showing the device in different
attitudes, and FIG. 9 is a diagram comparing the relationship of
the attitudes of the device shown in FIGS. 1, 7 and 8.
Vaporizable liquid vapor has been used heretofore as a heat
transfer medium employing the latent heat of vaporization to
increase the heat transfer capacity. Where the liquid has been
evaporated from a wick at one location by absorption of heat and
such vapor has been condensed at a different location by extraction
of heat and the resulting liquid returned to the heat absorption
location by the capillary action of a wick, the apparatus
performing such operation has been designated a "heat pipe." Such a
device is disclosed in U.S. Pat. No. 3,229,759 and is discussed in
an article entitled, The Heat Pipe, by G. Yale Eastman in the
Scientific American for May, 1968, Volume 218, page 38. It is
pointed out in that article near the top of page 44 that the upper
limit to the power handling capacity of a given heat pipe is
determined by the ultimate pumping capacity of the wick.
The apparatus of the present invention also relies on the latent
heat of vaporization of a vaporizable liquid to transfer heat, but
it has advantages over a heat pipe and does not have some of the
disadvantages of the heat pipe. A principal difference of the
apparatus of the present invention over the heat pipe is that it
does not rely on the capillary action of a wick to return condensed
heat transfer liquid medium from a heat-extracting location to a
heat-absorbing location but utilizes a body of liquid for that
purpose.
As shown in FIG. 1, the heat transit device of the present
invention includes a tube 1 closed at both ends and having a
wicking liner 2 held in place on the inner periphery of the tube 1
by a perforated or reticulated wick retainer sheet 3. Such wick
retainer is sufficiently apertured to enable vapor to escape
readily through it from the wick into the hollow interior of the
tube 1 and to allow atomized liquid to pass readily from the
interior hollow of the tube through the wick retainer into the
wicking material.
The wicking material can be any of various types of more or less
rigid fibrous or foam material. If the wicking is of foam material,
it should be of the interconnected pore type. The wick retainer
sheet can be of perforated metal or plastic sheet or of metal or
plastic screen provided that it is strong enough to support the
material of wick 2 to provide an unobstructed hollow extending
axially of the tube 1. Also, the radial thickness of the wick is
not critical, although it should not be so thick as to restrict
unduly the hollow space extending axially of the tube.
A portion of the length of the tube 1 is exposed to heat-supplying
means such as extending through a portion of a duct 4 through which
heated fluid flows. Such duct, for example, may be a stack
conveying gaseous products of combustion. Another portion 5 of the
length of the tube 1 is exposed to heat-extracting means shown in
FIG. 1 in the form of a casing 6 surrounding the portion 5 of tube
1 and containing heat-absorbing fluid 7. Such fluid preferably is
liquid and can flow through the casing 6 by supplying cool liquid
through the supply pipe 8 and discharging heated liquid through the
discharge pipe 9. A baffle 10 projects from a wall of the casing 6
toward the heat transfer pipe end 5 between the cool-liquid supply
pipe 8 and the hot-liquid discharge pipe 9 to deter flow of liquid
from such supply pipe to such discharge pipe along a direct path
instead of flowing around the heat transfer pipe end 5.
The heat transit tube 1 contains free vaporizable liquid 11 of
substantial depth. Such liquid may be any of various types but
should have a reasonably high specific heat, quite a high latent
heat of vaporization and condensation and a boiling point which is
not excessively high or low. A further desirable characteristic of
such liquid is that it be economical and that it provide
substantial agitation under the condition of nucleate boiling. For
most installations, water has characteristics satisfactory for use
as the heat transfer medium.
In operation it is desirable for the portion of the wick 2 in the
portion of the tube 1 exposed to the source of heat supply to be
completely saturated with vaporizable liquid. Such saturation will
prevent the occurrence of localized areas of higher temperature or
hot spots which could deteriorate the wicking material of some
types and in any case would reduce the differential in temperature
between that of the wicking and the temperature of the
heat-supplying fluid. Such reduction in temperature differential
results in a reduction of heat transfer efficiency between the
heat-supplying fluid and the vaporizable liquid. Also, complete
saturation of the wick 2 will insure that there is always adequate
heat transfer liquid available for evaporation from the wicking by
heat absorbed from the heat-supplying fluid in duct 4.
That portion of the heat transfer liquid 11 which is evaporated
both from the wicking and directly from the liquid body in the
portion of the tube 1 exposed to the heat-supplying fluid will flow
into the interior hollow of the tube 1 and fill the portion 5 of
such tube which is exposed to the heat-extracting means. Heat
extracted from such vaporized heat transfer fluid by the liquid 7
will result in condensation of the heat transfer fluid in the
portion 5 of the tube 1 so that such liquid joins the body of
liquid in the tube and can flow to the left as seen in FIG. 1 from
the condenser section of tube 1 into the vaporizer section of such
tube.
An expedient for insuring that the wick liner 2 is always
completely saturated with vaporizable heat transfer liquid is to
provide a construction which will produce nucleate boiling of the
liquid body of the heat transfer fluid in the fluid-vaporizing
section of the tube 1. Such nucleate boiling is accomplished by
interrupting the continuity of the wick 2 over portions of the
vaporizing section of the tube 1.
In FIGS. 3, 4, 5 and 6, the wick liner is shown as having arcuate
ends 12 and 13 spaced apart circumferentially of tube 1 to leave a
gap 14 in which the heat transfer fluid 11 in liquid form is in
direct contact with the wall of the tube. In this gap the heat
transfer liquid is not insulated from the heat-conducting wall of
the tube by the wick liner 2 so that at this location, heat will be
absorbed from the heat-supplying fluid more readily by the heat
transfer liquid than at the locations where the tube wall is
covered by the wick.
The result of such concentrated heat absorption by the heat
transfer liquid in the gap 14 is to cause localized vaporization of
the liquid below the surface of the liquid to produce vapor bubbles
15 within the body of the liquid which rise to the surface. During
such nucleate boiling of the liquid, the liquid body surface will
be greatly agitated and bubbles will rise from the surface a
greater or lesser distance and burst so as to provide both vapor
and unevaporated atomized liquid in the space above the surface of
the liquid body. Such atomized liquid will pass through the
apertured wick retainer sheet 3 to supply liquid directly for
absorption by the upper portion of the wicking above the liquid
body instead of relying solely on the capillary action of the
wicking to maintain such wicking in fully-saturated condition by
osmosis from the portion of the wicking submerged in the liquid to
the upper portion of the wicking above the liquid body.
A further expedient is used to increase the boiling action and to
promote vaporization of the heat transfer liquid. Such expedient is
to provide a very low absolute pressure within the tube 1 instead
of such pressure being equal to or greater than atmospheric
pressure. Such low pressure is produced in the pipe 1 without a
pumping operation simply by heating the tube to promote vigorous
boiling of the liquid in it when it is sealed. Such boiling will
insure that the space above the liquid body is filled with vapor of
the heat transfer liquid instead of air. When the tube is cooled,
whatever portion of the vaporized liquid is condensed will reduce
the pressure within the sealed tube 1 correspondingly.
Absorption of heat from the heat-supplying fluid by the heat
transfer fluid absorbed by the wick 2 to vaporize such fluid from
the wick can be increased to some extent by increasing the
effective heat transfer area of the surface of pipe 1. Such
increase in heat transfer surface area may be accomplished by
providing annular fins 16 in axial spaced relationship on the
external periphery of the tube as shown in FIGS. 2 and 3. Except
for such fins, the construction of the heat transit tube of FIGS. 2
and 3 is the same as that shown in FIGS. 1, 4, 5 and 6. Also, the
tube 1 of FIGS. 2 and 3 is shown as being of the same size as the
tube of FIGS. 1 and 6 which may, for example, be 21/2 inches or 3
inches in outside diameter.
The heat transit tube 1 of FIGS. 1, 2 and 3 is shown as being
approximately half filled with heat transfer fluid in liquid form.
If a heat transit tube 1 of a considerably larger diameter, such as
shown in FIG. 4, is used, which may have an outside diameter of 4
or 5 inches, the depth of heat transfer fluid in liquid form 11a
should be greater than the depth of such liquid in the smaller tube
so that the space above the surface of the liquid into which the
bubbles 15a rise and in which they burst will be approximately the
same distance from the upper portion of the wick liner 2a held in
place by the wick retainer sheet 3a.
On the other hand, if the heat transit pipe is of a diameter much
smaller than that shown in FIGS. 1, 2 and 3, such as shown in FIG.
5, in which the tube 1b may have an outer diameter of 1 to 11/2
inches, the level of the heat transfer fluid in liquid form 11b
will be lower than that shown in FIGS. 1, 2 and 3. Again, the
height of the space between the surface of the liquid in the tube
and the upper portion of the wick layer 2b, held in place by the
wick retainer 3b, should be about the same as in the tubes of FIGS.
1, 2, 3 and 4. Under these circumstances the bubbles 15b will have
approximately the same distance to travel between the surface of
the liquid and the wick liner as in the other instances.
Particularly if the heat-supplying fluid is flowing through the
duct 4 and one side of that portion of the tube 1 exposed to the
heat-supplying fluid faces upstream, it is desirable for the gap 14
in the wick liner to be on the upstream side of the heat transit
tube. Thus, the gap 14 between the arcuate ends 12 and 13 of the
wick liner, as shown in FIG. 3, the gap 14a between the arcuate
ends 12a and 13a of the wick liner 2a shown in FIG. 4 and the gap
14b between the arcuate ends 12b and 13b of the wick liner 2b shown
in FIG. 5 should be on the upstream side of the heat transit tube
while still being well below the surface of the liquid body of heat
transfer fluid in the heat transit tube.
The heat transit tube 1 should be disposed substantially horizontal
in order to accomplish the desired operation, and, in any case,
should not be tilted more than five degrees in either direction as
indicated by the lines in FIG. 9. The line S1--C1 designating the
heat source and the condenser is horizontal corresponding to the
position of FIG. 1. The line S7--C7 of FIG. 9 indicates the
situation shown in FIG. 7 in which the condenser end of the heat
transit tube is lower than the heat source end and the tube is
inclined downward at an angle of 5.degree.. The line S8--C8 of FIG.
9 indicates the situation of the heat transit tube in FIG. 8 in
which the condenser end is higher than the heat source end and the
inclination of the tube is 5.degree..
When the heat transit tube is in the horizontal position shown in
FIGS. 1 and 2, the heating of the liquid in the gap 14 will produce
vigorous bubbling of the nucleate boiling liquid, which bubbling
will be substantially uniform throughout the length of the portion
of the heat transit tube exposed to the heat source 4 if the
temperature of such heat source is approximately the same across
the width of the duct.
When the heat transit pipe slopes downward toward the condenser, as
shown in FIG. 7, however, the liquid will not be sufficiently deep
at the opposite end to provide bubbling which will be effective to
insure that the wick in the upper part of this lengthwise portion
of the tube will be completely saturated at all times. Also, it
will be observed at the right end of FIG. 7 that the passage for
vapor from the heated portion of the heat transit tube to the
condenser end of the tube is greatly constricted, if not completely
blocked, so that the vapor of the heat transfer liquid cannot pass
readily to the condenser. Also, the volume of the condenser
occupied by vapor is extremely small so that the condenser cannot
operate effectively. As vapor is condensed in the condenser,
however, additional vapor may pass to the condenser in a surge
causing undesirable violent periodic agitation in the transit
tube.
On the other hand, if the condenser end of the heat transit tube is
substantially higher than the heated end portion of the tube, the
wick may not be wetted adequately adjacent to the condenser and
insufficient space may be provided for effective vaporization of
liquid from the wick adjacent to the opposite end of the tube so
that the operating efficiency of the evaporator section of the tube
is decreased. Also, the boiling liquid may block a portion of the
tube spaced from the left end to trap vapor in the left end which
will escape periodically through the liquid block to the condenser,
thus causing periodic surging more violent than when the tube is
sloped toward the condenser as shown in FIG. 7. It is therefore
important that the heat transit tube be disposed substantially
horizontally in order to obtain the most efficient heat transfer
operation.
Because the heat transit tube 1 is sealed when the heat transfer
liquid is heated to boiling temperature, at least most of the air
in the upper portion of the heat transit tube 1 will be displaced
by vapor of the heat transfer fluid at the time of sealing.
Consequently, during normal operation, the absolute gas pressure in
the space above the liquid will be less than atmospheric pressure.
Even if the heat transit tube is heated excessively, the pressure
in the space above the liquid will not be increased greatly over
atmospheric pressure, and, consequently, such gas pressure will not
have any great tendency to rupture the tube. Even if severly
overheated, therefore, the tendency of the sealed heat transit tube
1 to explode is negligible providing an important safety feature.
The reduction in the latent heat of vaporization of the heat
transfer liquid resulting from this operation under low pressure,
however, is quite small.
As has been mentioned above, water is a satisfactory heat transfer
fluid for most operations. Some heat transfer fluids have the
disadvantage that during nucleate boiling the bubbles liberated do
not produce agitation in the body of liquid as vigorous as is
desirable.
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