Note: Descriptions are shown in the official language in which they were submitted.
~l 1163S~
~ I BACKGROUND OF THE INVENTION
¦l Field of the Invention
! I The present invention relates to the structure of a
¦I b,ayonet tube heat exchanger and the method of use of such
I~ structure.
¦ Description of the Prior Art
The structure of the so-called bayonet tube heat exchanger
¦¦ has been found to have many uses in addition to merely
exchanging heat between two fluids having a heat differential.
~0 ¦ For example, the structure of the bayonet tube heat exchanger
has been found useful in the condensing of fluids, purifying
of fluids, and recovery of ~aluable chemicals from a fluid.
Some problems, however, ha~e de~eloped in the use of
the conventional structure of the bayonet tube heat exchanger
both in the traditional sense of pure heat exchange and in
more sophisticated uses. For example, in'the traditional
exchange o$ heat, non-condensible gases entrained in one of
the fluids in~ol~ed tend to accumulate in the exchanger and
to lower heat exchange efficiency.
20 jAnother problem is the tendency of the cooling fluid to
il be reheated in its progress through the exchanger, thus
lll reducing the efficiency of the exchanger. It is foreseen
; ', that the bayonet tube heat exchanger will find many new uses
j, if the problem of reheat can be satisfactorily resol~ed.
2~ ¦l One attempt at the solution of the problem of-reheating
in the bayonet tube heat exchanger-is disclosed in U.S.
~,¦ Patent No. 3,861,461. In this structure a complex double
,1l wall construction is utilized which materially increases the
cost of manu~acture of the exchanger.
. .. . .
.` 2 ~
` 11~3B27
SUMMARY OF THE INVENTION
It is, therefore, a principal object of this invention
to improve the efficiency of the structure of bayonet tube
heat exchangers.
It is another object of the invention to automatically
remove non-condensible gases from a bayonet tube heat
exchanger during a heat exchange operation.
It is a still further object of the invention to
provide a structure for a bayonet tube heat exchanger which
minimizes reheating of a fluid which i~ being cooled.
It is an ancillary object of the invention to improve
the apparatus for guiding a plurality of bayonet tubes into
multiple sheaths in forming or servicing bayonet tube heat
exchangers.
In accordance with an aspect of the invention
there is provided a bayonet tube heat exchanger comprising:
(a) a substantially horizontal outer shell having an
elongated center section, an inner end having a first tube
sheet closure and a closed distal end; (b) at least one
thin gauge tubular sheath having a closed end adjacent but
spaced from said closed distal end of said shell and an
open end facing said first tube sheet closure of said
shell; (c) means for forming a first fluid flow zone
between the outer surface of said sheath and said shell
wherein a first fluid is boiled; ~d) a bayonet tube
concentrically positioned in at least one of said sheaths,
said bayonet tube piercing said first tube sheet closure,
and having an outer portion extending at least through
said first tube sheet closure and an inner portion
terminating in an open end spaced from the closed end of
said sheath; and (e) means for forming a second fluid flow
zone between said bayonet tube and the inner surface of
said sheath wherein a second fluid is condensed.
" 1163627
Preferably the means for forming the first fluid flow
zone includes a second tube sheet closure joining the
outer surfaces of the open ends of the sheaths and the
inner surface of the outer shell and an inlet and outlet
into the first fluid flow zone. The means for forming a
second fluid flow zone preferably includes a plenum
between the second tube sheet closure, the first tube
sheet closure and the outer shell provided with at least
one inlet and one outlet for this zone.
The bayonet tube heat exchanger of this invention in
one preferred embodiment includes means for applying a
vacuum source to the outer portions of the bayonet tubes,
either directly to the end portions of the bayonet tubes
or by use of a vacuum chamber adjacent the first tube
sheet closure which is in fluid communication with a
vacuum source and with the open ends of the bayonet tubes.
In accordance with one aspect of the invention, the
means for forming a first fluid flow zone includes an
inlet and an outlet through the shell and the means for
2Q forming the second fluid flow zone includes an inlet
through each bayonet tube and an outlet through the shell.
In accordance with an aspect of the invention there is
provided a method for operating a bayonet tube heat
exchanger comprising: (a) forming a first fluid flow zone
between the inner surface of a shell having a closed end
and the outer surface of a tubular thin gauge sheath having
a closed end, the closed end of the sheath being spaced
from the closed end of the shell; ~b) forming a second
fluid flow zone between the inner surface of the sheath
and the outer surface of a bayonet tube concentrically
inserted into said sheath, the inner end of said bayonet
tube being open and spaced from the closed end of said
-4 ~
~163627
sheath, and the outer end of said bayonet tube extending
outside said second fluid flow zone; (c) causing a first
~Eluid to flow through said first fluid flow zone wherein
said first fluid is boiled; (d) causing a second fluid to
flow through said second fluid flow zone wherein said
second fluid is condensed; and (e) applying a vacuum to
the outer end of said bayonet tube for removing non-
condensible gases entrained in said second fluid and
accelerating fluid flow through said second fluid flow
zone.
.~_ -4a-
i~ 63627 ~`
l i
i! A bay~net tube heat exchanger having multiple tubes
¦ may be assembled by the use of a circular plate for positioning
bayonet tubes in sheaths. The circular plate has a diameter
I substantially equal to the inner diameter of the shell and
!1 a plurality of holes corresponding in number to the number
Il of sheaths and located in the plate in corresponding relation- !
ship to the sheaths. The holes in the positioning plate
have a diameter slightly larger than the bayonet tubes an~
I¦ en~ageable for sliding the open end of the bayonet tubes
lQ ¦¦ through the holes and into the sheaths.
¦ The present invention overcomes the problems of conven-
tional bayonet tube heat exchangers which have low heat
~ transfer efficiency and are of expensive construction. The
¦l present invention increases heat transfer rates and is a
15 ¦I si~ple and relatively inexpensive construction. In one
embodiment, by using an air lance or bayonet tube to remove
non-condensible gases from vapor condensing in a sheath between
the bayonet tube and an outer shell, it significantly
increases the efficiency of heat exchange. In another
` 20 l¦ embodiment, the invention increases heat transfer rates by
using a plastic bayonet tube to prevent reheat of the cooling
fluid. In this embodiment, the bayonet tube and sheath are
sized to allow only a small annulus between the bayonet tube
, and the sheath which creates more turbulent fluid flow, thus
1 providing higher heat transfer rates.
The invention described herein, as one of its applications,
can be used in a distiller/concentrator system which is
energy-efficient, reliable and which provides an effluent
which can be recirculated. In addition, it may be used to
recover high purity water for rinsing and valuable chemicals
,
for reuse. Other applications include use of the bayonet
-5-
1 1 6 3 6 2 7
! !
I; !
, tube heat exchanger in distillation systems, as a condenser,.
a flash e~aporator or with a freon heat pump as the heat
exchanger portion of the system.
,1. BRIEF DESCRIPTION OF THE DRAWINGS
5 'I FIG. 1, is a side view, partially in section, of a
single tube bayonet heat exchanger with an air lance in
` accordance with the invention;
,¦ FIG. 2 is a longitudinal cross-sectional view of a
`I multiple tube embodiment of the bayonet tube heat exchanger
of the invention, each tube having an air lance,
FIG. 3 is a schematic drawing of a vapor rPcompression
~1 evaporator in which the bayonet tube heat exchanger of
,1 either ~IG. '. or FIG. 2 can be utilized:
,I FIG. 4 is a longitudinal cross-sectional view of a
¦ single tube bayonet tube heat exchanger having a heavy
walled plastic bayonet tube;
~ F~G. 5 is an enlarged sectional view of the inner end
l~ of a multiple tube embodiment of the bayonet tube heat
,I exchanger of FIG. 4 ~ith a single pass arrangement;
i FIG. 6 is an enlaxged sectional view of the inner end
.~ of a multiple tube embodiment of the bayonet tube heat
exchanger of FI~. 4 with a two pass water box arrangement;
FIG. 7 is a general arrangement schematic of a domestic
hot water system utilizing the bayonet tube heat exchanger
, of FIG. 4;
FIG. 8 is an exploded view of a guidance plate for a
multiple bayonet tube heat exchanger with 2 set of bayonet
tubes partially inserted into the plate.
6- -
- 11636~7
i 'i
DESC~IPTION OF PREFERRED EMBODIMENTS
~' Reference will now be made in detail to the present
preferred embodiments of the apparatus and methods of the
ji in~ention, examples of which axe illustrated in the accom-
pænying drawings.
In accordance with the invention, the bayonet tube heat
;! `
exchanger as shown in FIG. 1 includes an outer shell 10 with
j an elongated center se~tion A, a tubular sheath 11 within
I' the shell and a bayonet tube or air lance 12 within the
1I sheath. Shell 10 is substantially horizontal and m~y be of
tubular shape. The shell has a distal end closed by an end
I, cap or, as shown in FIG. 1, by a permanently closed end portion
¦1 and i~ sealed at its inner end by a first tu~e sheet closure 20.
¦I The sheath 11 has a closed distal end adjacent, but spaced
1~ from, the closed distal end of the shell 10 and an open end
facing the first tube sheet 20. ~nder the in~ention, means are
provided fox forming a first fluid flow zone within the
Il shell surrounding the sheath. As embodied herein, such means
- ! includ~ a second tube sheet 16 joining the outer surface of
1 sheath 11 and the inner surface of shell 10 to form a fluid
Il chamber 22 with an inlet 13 and an outlet 14 through the
shell at substantially opposite ends and opposite sides of
the center section A. The second tube sheet 16 forms a
fluid-tight seal between sheath 11 and the shell 10 such
that fluid entering chamber 22 through inlet 13 will flow
around the sheath 11 and exit through outlet 14.
The bayonet tube 12 is positioned concentrically within
the sheath 11. The tube 12 pierces the first tube sheet 20
and an inner portion of the bayonet tube extends substantially
the entire length of the sheath 11, terminating in an open
.~, ,, .~, . ,
--7--
;! 1 163627
end spaced from the closed distal end of the sheath. The
l bayonet tube 12 has an outer portion which extends at least
`I through the first tube sheet 20.
l In accordance with the invention, means are provided
1,! for forming a second fluid flow zone within the sheath of
iil FIG. 1. As embodied herein, such means include the second
¦I tube sheet 16, first tube sheet 20, a portion of the outer
shell 10 between the first and second tube sheets and the area
i~ between the sheath 11 and the bayonet tube 12. This arrange-
1 ment forms a fluid chamber 23 such that fluid entering inlet
15 through the portion of the shell 10 between the first and
¦ second tube sheets flows into the area between the bayonet
il tube and the sheath and, as described below, may exit either
¦I through an outlet 17 through the shell 10 or the bayonet
15 1 I tube 12, or through both.
When chamber 23,-the second fluid flow zone, has a
fluid, such ~s vapor or steam, introduced through inlet 15
¦ and a first Eluid, such as a cooling liquid circulating in
the first f~uid flow zone, i.e., chamber 22, the vapor in
1 chamber 23 will condense on the interior walls of chamber
23, especially within sheath 11 where there is maximum
¦¦ opportunity for heat transfer from the steam to the circulating
fluid in chamber 22. The condensed vapor collects within
~' sheath 11 and would interfere with heat transfer if not
~, removed.
In a preferred embodLment, the bayonet tube 12 of the
heat exchanger is operated under a vacuum. ~a~~uum increases
the infiltration of air into the heat exchanger system. Air,
howe~er, is a non-condensible gas under the operating conditions
3Q of these systems and tends to build up within sheath 11,
l~ creating a condition detrimental to transfer of heat through
the walls of the sheath.
--8--
1~l 1 163627 ~,
In order to make this system more efficient, the sheath
tube 11 is inclined downward toward the second tube sheet
16. The condensate collecting within sheath 11 drains into
i! the portion of chamber 23 adjacent drain outlet 17 from
5 il which the condensate exi.s .he heat ex~hanger.
Additionally, the bayonet tube or air lance 12 is of
considerably smaller diameter than the sheath 11 and is
! I connected to a vacuum source such as eductor 19 The air
~1 lance or bayonet tube 12 under vacuum removes the non-
¦I condensible gases which tend to concentrate at the distal
¦l end of the sheath 11 and thus inhibit heat transfer. The
¦¦ air lance 12, in addition, provides a positive fluid flow
drawing the steam, for example, into cham,ber 23 enabling
¦l hi~h~r flow rat~s of steam to be introduced into the exchanger.
~¦ In single tube heat exchangers, as depicted in Figure 1, the
;¦ bayonet or air lance 12, after piercing the first tube sheet
I 20, may be connected directly to the eductor as shown.
i Heat is transferred, for example, from high volume
l st~am condensing within the sheath 11 to circulating water
2a - I in chamber ~2. A small diameter bayonet tube, less than
one-quarter the diameter of the sheath, is used to remove
the relatively small volume of non-condensible gases and
entrapped condensate. The small surface area of the bayonet
I tube in relation to the sheath tube surfaoe area, i.e., less
than about one-sixteenth, minimizes reheat losses and more
importantly, provides complete evacuation of the non-condensible
gases in the condensing vapor.
_~_
~I 1163627
The condensate draining into outlet 17 can be evacuated
by a loop seal drain line 18 to a "T" connection 21 with the
li ~acuum line to the bayonet tube 12, as shown in Figure 1.
Il In order to provide for high heat transfer, relatively
" low cost and high corrosion resistance, the sheath 11 may be
constructed of a thin gauge corrosion-resistant metal such as
Il titanium or some known types of aluminum alloys. The second
- ,! tube sheet 16 between the sheath 11 and the shell 10 can be i
l! made of the same material. When this device is used in the
1I distillation of sea water or other corrosi~e media, use of
¦l corrosion-resistant metal is extremely important. The thin
~¦~ bayonet tube or air lance 12 can be constructed of pla-~tic,
copper or stainless steel since it contacts only pure steam
Il or condensate and is not subject to the same corrosive
15 1ll environment as the exterior of the sheath.
¦I The first tube she-et 20 for sealing the inner end of i
the shell 10 can be of plastic or carbon steel. If plastic
¦¦ is chosen, ~or the first tube sheet 20 or the bayonet tube
!¦ 12, poly~inylchloride (PVC), fiberglass reinforced PV~ or
chloropolyvinylchloride (CPVC) are examples of suitable
materials depending upon the operating temperature of the
¦ unit. Operational temperatures must be between approximately
30 F. and 180~. for use of PVC and CPVC. The operating
temperatures for a bayonet tube heat exchanger using metal
., .
.! bayonet tubes and sheaths can be considerably higher.
The bayonet tube heat exchanger of the embodiment of FTG.
l 1 of this invention is preferably operated under a vacuum, as
i stated above, and is designed to prevent formation of scale
which would precipitate at atmospheric boiling temperatures.
~ikewise it can pxevent the breakdown of heat sensitive
chemicals by operating at lower than atmospheric boiling
, ~ --10--
1163627
' temperatures. In one application of this invention, a heat
il exchanger is operated under a vacuum to distill sea water.
The sea water flows into chamber 22 and is ~eated by steam
I flowing in chamber 23. The s~eam has a velocity of 60-100
' feet per second tft/sec) as measured at the annulus area
between 11 and 12. Using this volume of steam and operating
under a vacuum of approximately 100 mm ~g absolute, the
j pressure differentials between chamber 22 and 23 are very
!! small and an extremely light gauge titanium sheath can be
I'j used. In this application, it is also essential to remove
¦ the non-condensible gases because of their detrimental
effect on heat transfer rates. This application has demonstrated
~¦ heat transfer rates of over 650 BTU/ft3/~. with a delta T
'il of only lO~F. compared to heat transfer rates of about 400
'l 3TU/ft3/~. for standard shell-and-tube type heat exchangers.
I ~IG. 2 depicts a multiple tube arrangement of the
bayonet tube heat exchanger of the type described in relation
il to FIG. 1. Common numerals have been used in ~IG. 2 to
I' designate corresponding elemPnts in FIG~ 1. The central
'i section of the outer shell is preferably constructed of two
parts 31 and 32. Each of these parts has a flange, respectively
designated as 33 and 34, for providing mating surfaces which
can be secured together to form a fluid tight seal as for
example by bolts (not shown) about the circumference of thè
flanges. The distal end of the exchanger is preferably
closed by an end head 30 which may contain a sight window
for observation of the interior of the exchanger. The inner
end of the exchanger is closed by another end head 35 which
may be secured to part 32 of the shell by screw threads on
the exterior end portion of the shell and on the interior
surface of the head which mate to form fluid tight seals.
`il '` 116362`~ i
A similar structure may be used for securing the e~.d head 30
ito the shell part 30.
'i In the multiple tube embodiment of FIG. ~, a plurality of
`sheaths are secured to each other and to the inner wall of the
shell by a second tube sheet 16a. This tube sheet may be of the
Isame material as the sheaths as described above and the edges of
,¦the tube sheet secured between flanges 33 and 34. The means for
~forming the first fluid flow zone in the embodiment of FIG. 2 com-
'prise the end head 30, shell part 31 and second tube sheet 16a to
Iform a chamber 22a fed by an inlet 13 on one side of shell part 31
and outlet 14 preferably on the other side of this shell part. A
con~entional tube support plate or preferably a lattice grid 9 is
used to ~provide even spacing of the bayonet sheaths at the distal i
end~ as required by TEMA (T~bular Exchanger Manufacturexs Associa- !
1~ 1 tion). Means for forming the second fluid flow zone in the embod-¦
iment of FIG. 2, such as chamber 23a, comprise first tube sheet
l'20a, second tube sheet 16a and shell part 32 with an inlet 15
.,j . .
and an outlet 17 through the shell part 32.
! I In the operation of the multiple tube embodiment, the bayo-
~ `Inet t~b~s extending into each sheath pass through the first tubesheet 20a. However, rather than having indi~idual connections to
,la vacuum source, means are included for applying a vàcuum source
to the outer portion of the plurality of vacuum tubes. As embod-
ied herein this means, as illustrated, includes a vacuum chamber
24 formed by the first tube sheet 20a, end head 35, and the por-
tion of shell 32 between .he tube sheet and the end head, the
chamber having an outlet 25 adaptable for fluid communication
with a vacuum source. In this arrangement the vacuum chamber 24
provides a vacuum to `the multiple bayonet tubes, each of which
3~ passes through the first tube sheet 20a and opens into the
~ ~ vacuum ch~mber.
I :
- FIG. 3 depicts an application of the bayonet tube heat
--12--
3 6 2 7
exchanger o~ FIG~ 2 in a vapor recompression evaporator designed
or high vacuum operation. This arrangement prevènts the forma-
tion of scale which is precipitated at atmospheric boiling temp-
eratures and is also useful in preventing t~e breakdown of heat
; sensitive chemicals. In this applic~tion, ~he bayonet tube heat
exchanger 40 is fed from feed tank 41 through fluid line 42 and
l inlet 13 into the heat exchanger. (The same reference numerals
i, as used in FIGS. 1 and 2 are used in F~G. 3 where appropriàte.)
I` After flowing through the first fluid flow zone, i.e.,
chamber 22, surrounding the sheaths, tube, the fluid feed exits
the heat exchanger 40 in a heated condition via outlets 14 and is
l,l conducted by wet vapor uptakes 43 into vapor separator 44. The
¦1 ~a~or separator has a series of mesh demistors 45 to entrain
liquid droplets which drain to the bottom of the separator 44 and
are returned to the feed tank 41 via fluid communication line 46
11 and pump 47 or taken of as concentrate via fluid communication
! ¦ line 48. The vapor separator is connected by outlet 49 at its
upper end to suction vapor delivery line 50 and then to a vapor
i
compressor 51. This vapor compressor 51 pressurizes the ~apor
~0 , and the pressurized vapor, exiting the compressor at its lower
end, is delivered to inlet 15 of the heat exchanger 40 via.pipe
l, 52. The pressurized vapor flows into the second fluid flow zone
; I! i.e., chamber 23a of the embodiment of the heat exchanger, as de-
picted in FIG. 2. The flow rate of Yapor is from about 60-100
ft/sec, as measured at the area of the combined annuli. The
v por condenses in sheaths 11 as heat is transferred through the
sheath walls to the cooler feed fluid flowing through chamber 23a
The vapor sweeps non-condensible gases (e.g., air) to the distal
end of the sheaths 11 where the bayonet tubes 12, connected via
vacuum chamber 24 and outlet 25 to a vacuum line, continuously
., ~.. ~........ ...
- -13-
`i ' 1 163627 ` i
siphon the non-condensible gases off. As the vapor condenses
,~, in sheaths 11, the condensate drains individually from each
sheath by the pitch of the sheaths toward the first tube
sheet 20a. Thus, the condensate does not drop down and
l, build up on the lower tube banks to form films of condensate
,, which would blanket the tubes and decrease the heat transfer
. .
efficiency.
The condensate drains from the heat exchanger through
, drain line 18 which joins the vacuum line exiting from the
, vacuum chamber 24 at a "T" junction 21. The condensate is
then pumped to the distillate tank 53 through fluid line 54
il running from the eductor 19 to the dis~illate tank.
The vapor compression e~aporator, as described above,
,~ can operate under low temperature and high ~acuum conditions.
'I This permits the use of CPVC for piping, evaporator and
,i condensor shells. In addition to reducing construction
costs, CPV~ is immune to the corrosive effects of salt water
and other mediums such as chromic acid solutions formed in
', electroplating wastes.
20 ',' Another embodiment of the in~ention, as depicted FIG. 4,
has a thi~k walled insulating bayonet tube within a thin
walled sheath. This embodiment permits the transfer of
heat from boiling fluids to circulating hot water or from
condensing steam to circulating cooling water with high
~5 efficiency. The bayonet tube heat exchanger 60 of FIG. 4 has an
outer shell 61 with an elongated center section A, a tubular
sheath 6~ within the shell and a bayonet tube 66 within the
sheath. Shell 60 is substantially horizontal and as depicted,
is of tubular shape. The shell has a distal end 61 which may be
closed by an end head as described abo~e in relation to FIG.
,` :
-14-
I' 1163S27
il 2 or by a permanently closed end portion as shown in FIG. 4.
The shell is sealed at its inner end by first tube sheet
68. Sheath 65 has a closed dlstal end adjacent, but spaced
¦ from, the closed distal end of shell 61 and an open end
!11 facing first tube sheet 68. In accordance with the in~ention,
means are pro~ided for forming a first fluid flow zone
within the shell surrounding the sheath. Such means, as
¦' embodied herein, include a tube sheet 78 joining the outer
Ij surface of sheath 65 to the inner surface of shell 60 to
1I form a fluid chamber 64 with at least one inlet 62 through
Il the shell and at least one outlet 63 through the shell, both
¦I being between the tube sheet 78 and the distal end of the
I shell. The tube sheet 78 forms a fluid tight seal at the
¦ inner end of chamber 64 such that fluid entering inlet 62
15 ¦I flows around sheath 65 and exits through outlet 63.
The bayonet tube 66 is positioned concentrically within ',
the sheath 65. The bayone~ tube 66 pierces the tube sheet
68 and an inner portion of the bayonet tube extends substan-
¦ tially the entire length of the sheath 65, terminating in an
20 -¦ open end spaced from the closed distal end of thr sheath. `,
The bayonet tube 65 has an outer portion which extends
¦I through first tube sheet 68. In the single tube embodiment
shown in FIG. 4, the bayonet tube is threaded into the
Il interior portion of a double tapped bushing 67 which extends
I through tube sheet 68 and which is suitable for fluid tight
connection to a fluid source at its exterior portion.
In accordance with the in~ention, means are also provided
for forming a second fluid flow zone within the sheath 65.
Such means, as embodied herein, include second tube sheet
78, first tube sheet 68 and a portion of the outer shell 60
. ~.~ ,, ,.. ~.. . .
~ -15-
, -
1163627
between the first and second tube sheets, as well as the
~ area between the sheath 65 and the bayonet tube 66. These
'i elements define a fluid chamber 71 such that fluid entering
i through bayonet tube 66 flows along the length of the bayonet
I tube to the distal end of sheath 65 and flows through the
I annulus between the bayonet tube and the sheath and exits at
,1 outlet 72 located in shell 61 between tube sheet 78 and tube
`¦ sheet 68.
~, In order to minimize reheat of the fluid in the second
, fluid flow zone, the bayonet tube in this embodimet is
'¦ constructed of an insulating material such as plastic. Both
,¦ PVC and CPVC have been ~ound to be suitable materials due to
,I their low cost and the ease with which they may be worked.
tl The sheath 65 and the tube sheet 78 may be made of
'¦ light gauge titanium or other corrosion resistant metal as
described in relation to FIGS. 1 and 2.
In order to position the bayonet 66 within the sheath 65,
the invention, means are pro~ided such that a relatively
~ uniform annular passage surrounds the bayonet. It is preferred
20 I to affix metal wires or pins 90 extending radially from the~ i
~¦ bayonet ~ube at equal distance spacings (about 120 àpart~around
¦ the circumference of the bayonet tube. These pins 90 extend
from at least the outer surface of the bayonet tube for a
' dîstance as necessary to contact the inner surface of the
, sheath 65. Pins 90 may be spaced at one or more locations
along bayonet tube 65 depending upon the length of the
, bayonet tube.
In order to reduce entrance drag at the end of the
bayonet tube 66 where the fluid flows from the bayonet tubes
into the small annular passage between the bayonet tube 66 and
.
the sheath 65, it is preferred to bevel the outer surface of
- the end of the bayonet tube as best shown in FIG. 4.
` `` 1 163627
,
The plastic bayonet tube of the invention effectively
pre~ents reheating by its insulating quality. The optimum
, parameters found for this embodiment of the in~ention uses a
I one-inch OD (outer diameter) tube of 0.035 wall thickness
, for the sheath and a 1/2 inch ips (iron pipe size) (0.84
inch OD) Schedule 80 (0.147 inch) PVC or CPVC tube for the
~, bayonet tube. The preferred inside cross-sectional area of
I the sheath is 0.679 square inches and the outside cross-sectional
, area of the bayonet is 0.554 square inches lea~ing an annular
j passage surrounding the bayonet of 0.125 square inches in
,I cross-section or about 18 percent of the total area inside
of the sheath. A flow rate through each such bayonet tube
,~-of two ~allons of liquid per minute provides a velocity of
¦ 5.1 feet per second through the annular passage surrounding
I the bayonet. This smali annular passage and the relatively
l high flow velocity creates a high turbulence in the fluid in
¦ the annular passage which promotes overall heat transfer
'I rates of 600-800 Btu/cf/F. at the high vacuums at which
I these h~at exchanges are operated. The sheath preferably may
I range in OD from 75" to 1.5" and the bayonet tube from 0.5~
to 1.25~" The wall thicknesses of the sheath and the bayonet
tube can be determined by the intended application but it is
preferred that an annular passage with an area of about 18
; percent of the total area within the sheath be maintained
for the most effective heat transfer rates.
In a multiple tube heat exchanger as shown in FIG. 5,
the plastic bayonet tubes 66 may be adhered to plastic tube
sheet 69 while a metal tube sheet 78 is used to seal the
sheath tubes 65 to each other and to the outer shell. In
3n this embodiment, the tube sheet 78 is sealed between flanges
11 75 and 76 of outer shell sections 73 and 74 respectively.
-17-
1163627 ``
Il ~n inlet fluid plenum 70 is formed by a portion of outer
i! shell section 74 between tube sheet 69 and an end head 77.
Fluid enters the plenum 70 through inlet 79 positioned in
Il the wall of shell section 74 between tube sheet 69 and end
i head 77. A similar inlet plenum is unnecessary in the
il single tube embodiment of FIG. 4 since the bayonet tube 66
¦ extends into a bushing 67 through tube sheet 68 providing a
¦¦ direct connection to a fluid supply line.
The embodiment of FIG. 5 of a bayonet tube heat exchanger
¦ of the invention in addition to providing high heat transfer
rates, cost effectiveness in construction and operation and
compact arrangement performs functions which would be impossible `
or quit,e expensive in standard heat exch~nger constructions.
I For example, a "U" tube design would not be able to use the
1 light gauge corrosion resistant metals found in this invention
¦¦ since such materials are al st impossible to bend to a
l short radius. Further, sm~ller tube diameters ha~e to be
! used in conventional construction to provide necessary tube
l ~elocities for good heat transfer rates. The use of 0.5~ to
i 1.25" OD bayonet tubes and 0.75" to 1.5" OD sheaths in this
¦l invention, in addition to being economical tube sizes, also
l! pro~ides optimum water flow velocities without use of much
smaller tubes and attendant increase in the number of dri
holes and construction costs.
25 ,l A further preferred embodiment of a multiple bayonet
tube heat exchanger is depicted in Fig. 6. This embodiment
has a two-pass water box -rrangement wherein one or more
bayonet tubes 83 and one or more bayonet tubes 87 rather
than connecting to a single plenum 71 as in FIG. 5, connect
, to two plenums 80 and 31. Thus, the second fluid flow zone
.: .~ .~.. . .
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has fluid entering plenum 80 through inlet 82 through a tube
sheel 91 from which it enters at least one bayonet tube 83 which
is in fluid com~unication with plenum 80. This fluid travels
,l the length of the ~ayonet tube 83 and returns through annular
5 li passage 84 between the bayonet tube and its sheath 89 into
1'1 chamber 85. Fluid entering chamber 85 r which is formed by
li tube sheet 78a, tube sheet 69a and shell section 74a, then
travels into annular passage 86 surrounding bayonet tube 87
Il and exits down at least one bayonet tube 87 which is in
ll fluid communication with plenum 81 and exits through outlet
~¦ 88. This arrangement increases the water velocities through
the heat exchanger. Such velocities may be further increased
¦ by adding additional passes.
¦¦ FIG. 7 pro~ides an illustration of one application of
1¦ the embodiment of the bayonet tube heat exchanger described
in relation to FIG. 4. The heat exchanger can be coupled
with a domestic hot-water heater to produce low cost potable
water from contaminated well water. Water from the hot
I water ~ank 100, e., a first fluid, is supplied via fluid
I line 114 to the inlet 62 feeding the first fluid flow zone
of bayonet tube heat exchanger 101 to be further heated. 1,
i! Additional water from tank 100 is supplied via ~luid line '
~l 115 and pump 116 to inlet 67 feeding the second fluid flow
~l~ zone of bayonet tube heat exchanger 102. A second fluid
~' in~roduced through inlet 67 feeding the second fluid flow
zone of heat exchanger 101 is heated by an auxiliary electric
heater 104 in heater loop 103 serviced by pump 117. The
heated fluid entering inlet 67 from loop 103 exits the heat
1 exchanger 101 at outlet 72 and recirculates thro~gh the
, heater loop after giving up its heat to the water in the
first fluid flow zone.
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The heated water and water Yapor from the first fluid
~lo~ zone exits from outlet 63 and flows through pipe 105 to
~apor separator 106. The liquid water in the separator 106,
' which contains concentrated pollutants, drains through
.5 outlet 107 to drain line 108 and is pumped away by pump 118.
The vapor at about 165~. from the upper end of separator
106 is introduced via fluid line 119 into the inlet 62 feeding
the first fluid flow zone of bayonet tube heat exchanger
' 102. The water entering heat exchanger 102 from tank 100
, through inlet 67 feeding the second fluid flow zone of exchanger j
'll 102 causes the ~apor in the first fluid flow zone to condense~
i Distilled water is taken off through outlet 109 which communi- i1
cates with the first fluid flow zone. The distillate is pumped
11 via fluid line 110 connected to a wet vacuum pump 111.
1l The water exiting heat exchanger 102 through outlet 72
Il is at a t~mperature of 120-140F. and returns via fluid line
- l, 112 to a valve 113 which directs it through the household
hot water system or returns it to the hot water tank 100. With
', this system, using single tube bayonet tube heat exchangers of
2~ . the type depicted in FIG. 4, for every twelve gallons of
, water raised 80F~, one gallon of distilled water can be
,~ produced for less than 1/8 of a KW for pumping costs. This
application can also be used for a small electroplating set
up to concentrate and recover plating wastes. The ganged
pumping system used is described in U.S. Patent No. 3,358,609.
In order to assemble the multiple tube bayonet tube
heat exchangers, as depicted in FIG. 2, especially when
there are dozens or hundreds of bayonet tubes involved, a
guidance means is provided to permit the bayonet tubes to be
aligned with their corresponding sheath tubes. As depicted
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in FIG. 8, a circùlar plate 120 is provided with holes
121. The number of holes at least equals the number of
bayonet tubes used in the heat exchanger in which such
guidance plate is employed. The plate may be of plastic
or metal depending upon the operating temperature range of
the heat exchanger in which it is used. The holes 121 are
positioned to correspond with the openings of the sheaths
in the second tube sheet 16a. As depicted in FIG. 2, the
plate 1~0 is dimensioned to fit within the outer shell of
the heat exchanger and is held a distance away from tube
sheet 16a by positioning rods 122. The holes in plate 120
are slightly larger than the diameter of the bayonets in
order to enable the bayonets to slide freely through the
positioning holes and into the sheath tubes.
In operation, the free ends of the bayonet tubes are
inserted into holes 121 in plate 120 and the plate is
aligned with the sheath tubes 11. Then, by pushing the
bayonet tube sheet, the bayonet tubes slide through the
plate 120 and along the length of sheath tubes 11 until
the positioning rods 122 contact the sheath tube sheet 16a.
This plate enables the proper positioning of the bayonets
upon insertion and maintains them in proper spaced
relationship upon removal of the bayonet tubes from the
heat exchanger.
Other applications and modifications of this invention
will be obvious to one skilled in the art of heat
exchangers. Such applications may include the use of the
bayonet tube heat exchanger with a climbing film evaporator
in conjuction with a Freon (trade mark) heat pump with
secondary heat transfer loops using distilled water to
prevent transfer of radioactivity from the concentration
of radioactive wastes. Reference to
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1 16362~
Williamson U.S. Patent Nos. 3,248,305; 3,399,118; 3,420,747
will furnish further details as to applications particularly
as they would apply of a freon pump.
The freon condenser of the heat pump can employ the
bayonet tube heat exchanger ~sing enhanced tubing for the
sheath. Finned or twisted tubes similar to those described
in U.S. Patent No. 3,533,267 can be used to condense the
freon vapors on the outside of the sheath and transfer heat
to distilled water, or other liquid to be heated~ in the
annulus between the sheath and the insulating bayonet.
The bayonet tube heat exchanger may be used with a long
tube flash evaporator of the type depicted in Williamson
U.S. Patent No. 3,186,924 and would be particularly
advantageous. The bayonet tube heat exchanger could replace
the condenser portion identified as 22 in the 3,186,924
patent and would reduce the length of the heat recovery
condenser in half and eliminate any problem with expansion
stresses. For example, a long tube flash evaporator
requiring 1/2" O~ tubes in order to acquire optimum tube
velocity could use 1" OD bayonet sheaths and insulating
bayonet t~bes providing the small annuli area which would
require half the length heat transfer tube in order to
acquire the same square feet of heat transfer surfaces with
the same tube velocities. The number of tube holes to be
drilled would be greatly reduced and save in tubing and
fabrication costs. The division plates 45 in the patent
3,186,924 can be part of the new removable bayonet tube
bundle and would eliminate the need for flanging sections 41.
It is intended that modifications and variations of
the above embodiments can be made within the scope of this
invention as defined by the appended claims and their
equivalents.
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