US3621909A

US3621909A - Heat exchange units and heating systems employing such units

Info

Publication number: US3621909A
Application number: US60855A
Authority: US
Inventors: Horace L Smith Jr
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-08-04
Filing date: 1970-08-04
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

Heat exchange units of the type in which a fluid heat transfer medium is circulated in counterflow relationship through independent flow paths. Heating systems employing such heat exchange units.

Description

llnited State Patent S mm T NW N U w mm d H mm mm m a m Tr m m A k w w m m mWS m a U99 NH 600 53 8 l m% w l 23 6 2 2 3 2 m V d n 0 m m m 3 m OH 5 Mm $5 3 mm 00 H36AN I 0. d m N m n n d w Whm .m AR? 1 ll] 2 25 W URN Primary ExaminerCharles Sukalo HEAT EXCHANGE UNITS AND HEATING All0rney-Strauch, Nolan, Neale, Nies & Kurz SYSTEMS EMPLOYING SUCH UNITS ABSTRACT: Heat exchange units of the type in which a fluid heat transfer medium is circulated in counterflow relationship through independent flow paths. Heating systems employing 5 82 7 mm d6 6 l 1 I F a a m .W "n" F mmm g "H" .m mmm mm." D mm 5 mmw muus lun .I h s h ZUImF ll] 2 0 555 PATENTEDuuv 23 Ian I v r lH H I I I I I HH H H Hl l l I lwlll ll llr I I V IH I'IHHHHHHHI HI IIHHHHHIHHHH SHEEI 1 UF 2 INVENTOR HORACE L. SMITH,JR.

ATTORNEYS HEAT EXCHANGE UNITS AND HEATING SYSTEMS EMPLOYING SUCH UNITS This invention relates to heat exchange. In one aspect this invention relates more specifically to novel, improved press platens or like devices. In another aspect the invention relates to novel systems for circulating a fluid heat transfer medium through such devices.

Press platens and similar heat exchangers are used in apparatus designed to dry or otherwise heat or cool a variety of materials such as veneers, wallboard and the like, laminates of various kinds, etc. Exemplary heat exchangers of the type with which the present invention is concerned are disclosed in U.S. Pat. Nos. 1,097,223 issued May 19, 1914; 1,754,853 issued Apr. 15, 1930; 1,828,477 issued Oct. 20, 1931; 2,217,652 issued Oct. 8, 1949; 2,572,972 issued Oct. 20, 1951; 1,627,290 issued Feb. 3, 1953; 2,699,325 issued Jan. 11, 1955; 3,055,642 issued Sept. 25, 1962; 3,064,363 issued Nov. 20, 1962; and 3,206,829 issued Sept. 21, 1965.

Another heat exchanger of this general type is disclosed in my U.S. Pat. No. 3,181,605 issued May 4, 1965. In the heat exchangers disclosed in that patent there is countercurrent flow of the heat exchange medium through two internested flow channels in the body of the device. Accordingly, such heat exchangers have a generally uniform temperature across their entire surface, which is a highly desirable attribute.

l have now invented novel heat exchangers such as press platens and the like which have the advantages of those disclosed in my earlier patent, but which have greater rigidity and even more uniform surface temperatures. In general, these novel heat exchangers consist of a body of heat-conductive material in which a series or row of parallel, spaced-apart conduits are formed. These conduits are blind-ended, and alternate conduits open onto opposite sides of the heat exchanger body. Dividers in the conduits, plugs in the open ends of the conduits, and longitudinal channels communicating with the conduits at their open ends cooperate with the conduits to provide two internested, serpentine flow paths in the body of the heat exchanger through which a heat exchange medium can be circulated in counterflow relationship.

Because of the relatively heavy sections of heat-conductive material around the flow conduits, excellent heat equilization is obtained by conduction in the novel heat exchangers of the present invention. Accordingly, such heat exchangers have highly uniform surface temperatures.

Also, because of this relatively massive construction, the heat exchangers of the present invention are extremely rigid and inflexible. This is very advantageous, especially in those applications requiring uniform pressure on the article or material being heated.

Another advantage of the novel heat exchangers described herein is that they can be manufactured without welding. This permits the body to be made of materials such as gray cast iron which are extremely difficult to weld but have excellent rigidity and heat conduction and can be machined to the very close tolerances typically required in applications where press platens and the like are employed.

As pointed out in my issued patent U.S. Pat. No. 3,181,605, a number of advantages can be obtained by employing high boiling point liquids as the heat transfer media for press platens and the like rather than steam as is conventionally done. These include the elimination of superatmospheric pressures and the equipment required when such pressures are involved. Also, nonuniform heating is common when steam is employed in press platens and the like due to the presence of air in the steam and the uneven collection of condensate in the platen which can occur if the heat exchanger is not exactly level.

In another aspect the present invention relates to a novel system for supplying high boiling point liquids to heat exchangers of the type described herein. Another feature of this heating system is an arrangement by which the heat transfer liquid can be cooled and circulated through the heat exchanger where cooling or both heating and cooling are required.

One important and primary object of the present invention is the provision of novel, improved heat exchangers such as press platens and the like.

Another important and primary object of the present invention residesin the provision of heat exchangers which have the advantages of but are improvements over those disclosed in my issued patent U.S. Pat. No. 3,181 ,605.

Still other related and important but more specific objects of the invention reside in the provision of heat exchangers, which:

1. have highly uniform surface temperatures when heated.

2. are highly rigid and inflexible.

3. can be fabricated from materials which are difficult to weld, but otherwise have desirable properties.

4. have various combinations of the foregoing attributes.

Yet another important object of this invention resides in the provision of novel systems for heating and/or cooling and sup-. plying a liquid heat transfer medium to heat exchangers such as press platens and the like.

Other important objects and advantages and further novel features of the present invention will become apparent from the appended claims and as the ensuing detailed description and discussion of the invention proceeds in conjunction with the accompanying drawing in which:

FIG. 1 is a plan view of a press platen type heat exchanger constructed in accord with the principles of the present invention;

FIG. 2 is an end view of the heat exchanger;

FIG. 3 is a partial horizontal section through the heat exchanger;

FIG. 4 is a partial section through the heat exchanger taken substantially along line 4-4 of FIG. 3; and

FIG. 5 is a system in accord with the present invention for heating and/or cooling a liquid heat transfer medium and circulating it through a heat exchanger.

Referring now to the drawing, FIG. 1 depicts in schematic form an exemplary heating system 8 in accord with the present invention, which includes a heating unit 10, a cooling unit 12, a press platen l4 incorporating the principles of the present invention, and a closed system of conduits and controllers for circulating a liquid heat transfer medium at a specified temperature through platen 14.

Referring now to FIGS. 1-4, the novel press platen l4 referred to above includes a body 16 in which a row of laterally extending, parallel, spaced-apart conduits 18 extending generally from one side of body 16 to the other is formed as by rifle drilling. Body 16 will typically be formed from gray cast iron, which is a good heat conductor and has high strength and rigidity. The body 16 ofa typical press platen will be 8 feet long, 4 feet wide, and 2 inches thick. Conduits 18 will typically be on the order of 1 inch in diameter.

Referring now specifically to FIG. 1, each of the conduits 18 has an open end and a blind end. Alternate conduits open onto

opposite sides

20 and 22 of body 16.

As shown in FIG. 1, the lateral conduits 18 opening onto side 20 of body 16 communicate with a conduit 24 extending longitudinally through the body. The conduits 18 opening onto the opposite side 22 of the body similar communicate with a conduit 26 also extending longitudinally through the body 16 of press platen 24. The open ends of

conduits

24 and 26 are closed by plugs 27 threaded into or welded or otherwise fixed to the body 16 of press platen 14.

Turning now to FIGS. 1 and 3, the open ends oflaterally extending conduits 18 are closed by plugs 28. Extending from each plug 28 through the associated conduit 18 and terminating short of the blind end 30 of the conduit is a divider 32. As shown in FIGS. 1, 3 and 4, dividers 32 divide each of the flow conduits 18 into two adjacent flow paths 34aand 34b, which communicate at the blind end 30 of the conduit.

Referring now specifically to FIG. 1, the flow path 34a in each of the conduits 30 communicates with the flow path 34b in the next conduit opening onto the same side of press platen body 16 through the

longitudinal conduit

24 or 26 with which these conduits l8 communicate.

The arrangement just described provides in body 16 two serpentine,

internested flow paths

36 and 38 extending generally from end-to-end of press platen body 16 with the legs of the flow paths substantially spanning the platen body.

The liquid heat transfer medium is circulated in counterflow relationship through

flow paths

36 and 38. This is accomplished by introducing the heat transfer medium into flow path 36 through inlet 40 and discharging it through outlet 42 while introducing the heat transfer medium into flow path 38 through inlet 44 and discharging it through outlet 46.

One of the novel features of the present invention resides in employing a high boiling point liquid as the circulating medium, permitting it to be circulated at extremely high temperatures in liquid form. Consequently, the using units may be heated to high temperatures and yet the system components need be designed to withstand only very low pressures. Suitable heat transfer liquids include Aroclor 1248 a chlorinated bi-phenyl) and lsopropyl Santowax (a polyphenyl alkyl), which are produced by Monsanto Chemical Co., and XFl-014 (an aryl oryloxy silone manufactured by Dow Chemical Company). Aroclor 1248 liquid may be heated to temperatures on the order of 550-570 F. without boiling and without exceeding a permissive rate of decomposition rate of slightly less than 0.00l percent per hour of operation. Since a buildup of decomposition products of approximately 20 percent can be tolerated before pumping costs become excessive, the same liquid may be used for about 3 years without replacement (a system of the type to which the present invention relates normally operates on the order of 7,000 hours per year).

If the medium is to be heated to higher temperatures, lsopropyl Santowax or XFl-l84 may be employed. lsopropyl Santowax liquid can safely be heated to temperatures of about 700 F. At 700 F., this liquid has substantially the same rate of decomposition that Aroclor 1248 has at 550 F. XFl-l84 can be used at temperatures up to about 800 F. At 700 F. XFl- 0l84 has substantially the same rate of decomposition as lsopropyl Santowax at the same temperature.

Referring now to FIG. 5, the heat transfer liquid is introduced into the closed circulating system from a storage tank 47 which is connected by conduit 48 to return conduit 50 of the main circulating system. A reversible pump 52 is interposed in conduit 48 to force the liquid into the return conduit and to return it to storage tank 47 if it becomes necessary to drain the system, A manual valve 54 in conduit 48 may be opened to allow the liquid to be pumped from storage tank 47 into the system and closed to prevent discharge of the liquid back into the storage tank after the system is filled. A drain valve 55 will also typically be provided so that system 8 can be drained when necessary.

The main circulating pump 56 interposed in return conduit 50 pumps the liquid through the return conduit into heating unit 10. Pump 56 can be isolated by closing

valves

57a and 57b in main return conduit 50,

An expansion tank 86 is connected into main return conduit 50 by a branch conduit 88. This tank 86 accommodates expansion of liquid in the closed system, preventing abnormal pressure conditions from bursting conduits or other system components, and maintains a gravity head on the system.

In the expansion tank is a valve (not shown) operated by a float 90, which controls flow through an outlet line 92. If, under some abnormal operating condition, the level of the liquid in expansion tank 86 should rise to a dangerous level, float 90 will open the valve, allowing excess liquid to be discharged through outlet line 92 to prevent rupture or bursting of system components.

An indication of the pressure in the circulation system is furnished by

pressure gages

58 and 60 interposed in main return conduit 50 on the inlet and discharge sides of the main circulating pump 56.

Pressure gages

58 and 60 provide a ready indication of conditions detrimental to circulation such as blockage ofa flow conduit or the like.

The end of main return conduit 50 is connected to the inlet of heating unit 10. As illustrated, heating unit includes sinuous heating tubes 62 (one of which is shown) through which the circulating medium flows and over which hot gases generated by combustion units 64 pass. Heating tubes 62 and combustion units 64 are housed in an outer shell 66 of conventional construction which is preferably lined with an appropriate refractory (not shown) to radiate heat to heating tubes 62. The combustion units 64 may be either gas or oil burners or, if heating unit 10 is of larger capacity, may be coal fired.

Fuel flows to combustion units 62 through an inlet line 68 in which is interposed an automatically controlled valve 70. Valve 70 is preferably controlled by a conventional temperature-responsive controller 72 responsive to the temperature of the circulating medium discharged from the heating tubes 62 in heating unit 10 to insure that the circulating medium discharged from the heating unit is at the correct temperature.

The outlets of heating tubes 62 are connected to the main' supply conduit 73. The heated circulating medium flows through this conduit to heat using unit 14* or, if there is no demand for heat, from this conduit directly through conduit 74 and normally closed valve 76 into main return conduit 50. mmber of heating using units will be supplied from a single heating unit 10. Only one heat using unit is shown for the sake of clarity.

When there is a requirement for heat in heat exchange unit 14, valve 78 is opened; valve 76 is closed; and the heated liquid is pumped through main supply conduit 73 to

branch supply conduits

79 and 80. Branch supply conduit 79 is connected to the inlet 40 to flow path 36 through press platen l4, and branch supply conduit 80 is connected to the inlet 44 to flow path 38.

The outlet 42 from flow path 36 is connected to a branch return conduit 82, and the outlet 46 from flow path 38 is connected to a branch return conduit 84. These branch return conduits are in turn connected to main return conduit 50. Thus, when there is a demand for heat, heated liquid is circulated from heating unit 10 through main supply conduit 73 and

branch supply conduits

79 and 80 to the heat-using unit 14, through the

flow paths

36 and 38 in that unit, and then through

branch return conduits

82 and 84 and main return conduit 50 back to the heating unit.

Notwithstanding the variation in demand for heat transfer liquid at press platen 14, a reasonably constant high-velocity flow, preferably on the order of about 8 feet per second, must be maintained through the main circulating system for, ifconstant circulation is not maintained, the medium in the heating tubes 62 of heater 10 will be overheated and will polymerize, forming a thick sludge which will adversely affect the performance of the system when heat transfer liquids such as those described above are employed.

In order to maintain this flow substantially constant, a valve 94 is connected in main return conduit 50. Valve 94 is controlled by a pressure controller 96 responsive to the pressure in main return conduit 50. Valve 94 functions as follows: if the circulating medium is diverted from main supply conduit 73 into the heat-using unit 14 in the manner described above, this diversion of circulating medium from the main supply conduit will be detected by the sensing element of pressure controller 96 which will open valve 94 more widely, increasing the flow area through it to compensate for the diversion of circulating medium into the unit when the demand for additional heat exists. As the demand for additional heat by the heat-using unit is satisfied, less of the circulating medium will be diverted through it. This condition will be detected by pressure controller 96 which will decrease the flow area through valve 94 to compensate for the diminishing diversion of the circulating liquid to the heat-using unit. Thus, by taking advantage of the known flow law that quantity of flow is directly proportional to the flow area and the pressure drop through a closed circulating system, pressure regulated valve 94 maintains substantially constant flow through the main circulating system.

Notwithstanding the precautions taken to insure constant flow through the main circulating system, stoppage in the supply or branch conduits may occur, decreasing or even completely blocking flow through the main system and leading to overheating and polymerization of the circulating medium. To prevent a flow stoppage in the main circulating system form having this adverse effect, a novel bypass circuit arrangement, including a bypass conduit 98 connected between main supply conduit 73 adjacent the discharge end of heating unit and to main return conduit 50 on the inlet side of main circulating pump 56, is provided. Flow through bypass conduit 98 is controlled by a valve 100 which, in turn, is regulated by a differential pressure controller 102, the two bellows-type sensing elements of which (not shown) are connected by

leads

104 and 106 to the discharge and inlet sides of main circulating pump 56. Differential pressure controller 102, which may be of any conventional construction such as the Differential Pressuretrol manufactured by Minneapolis Honeywell Regulator Co., takes advantage of the well-known fact that, if a constant differential is maintained between the suction and discharge pressures of a pump, the volume of liquid circulated by the pump will remain constant.

Therefore, should a condition arise tending to resist the flow through the system, the differential between the suction and discharge pressures will increase. In this circumstance, differential pressure controller 102 will open bypass valve 100, allowing the circulating medium to flow from main supply conduit 73 through bypass conduit 98 into main return conduit 50, maintaining the flow of liquid through heating unit 10 constant and thereby preventing the circulating medium from overheating.

When the resistance to the flow of fluid through the main circulating system is removed, the differential between the pump suction and discharge pressures will decrease. Differential pressure controller 102 will then close bypass valve 100, decreasing the flow of liquid through bypass conduit 98 and increasing the flow through the main circulating system.

Another important function is also served by the bypass arrangement just described. When the system is started up, it is preferable to bring the circulating medium to operating temperature as quickly as possible. in this circumstance, differential pressure controller 102 is set to open bypass valve 100 so that a substantial portion of the liquid in the circulating system will flow directly through bypass conduit 98 back into heating unit 10, quickly raising the circulating medium to operating temperature.

As mentioned above, provision is also preferably made in heating system 8 for cooling the heat exchange liquid before it is circulated to press platen 14 so that the platen can be used for cooling as well as heating, The components provided for this purpose include cooling unit 12, which is a conventional heat exchanger having tubes 108 (only one of which is shown), through which the heat exchange liquid flows, and a shell 109 through which a coolant is circulated. The heat exchanger is connected by supply and return

conduits

110 and 112 to main supply and return

conduits

73 and 50. A pump 1 14 is provided to circulate the heat exchange liquid through a closed path including heat exchanger 12,

supply conduits

110, 73, and 79 and 80, press platen 14, and return

conduits

82 and 84, 50, and 112.

Pressure gages

116 and 118 on opposite sides of pump 114 provide an indication of flow conditions in the closed circulation path just described.

When there is a demand for a reduced temperature at press platen 14, valves 78 and 94 in main supply and return

conduits

73 and 50 are closed,

valves

120 and 122 in the

conduits

110 and 112 connecting heat exchanger 12 to the main supply and return conduits are opened, and pump 114 is started to circulate the heat transfer liquid through the path described above. As the heat transfer liquid flows through the tubes 108 of heat exchanger 12, its temperature is reduced by water or other coolant which flows to the heat exchanger through conduit 124, circulates through the shell 109 of the heat exchanger, and discharges through conduit 126, the flow being controlled by a valve 127 in conduit 124. The lower temperature liquid then flows to press platen 14 to reduce its temperature.

in the operational mode of heating system 8 just described, expansion tank 86 is isolated from the circulation system. Ac-

cordingly, a second expansion tank 128 equipped with an outlet line 130 and a float-controlled valve (not shown) is preferably connected to conduit 112 through a conduit 134. This arrangement functions in the same manner as that described above and is provided for the same reasons.

Heating systems of the type just described will typically have other components such as systems for pumping the heat transfer liquids at a different rate through each of a plurality of heat exchangers and an arrangement for preventing overheating of the heating unit when the system is shut down. These and other system components are described in my US. Pat. No. 3,236,292, which is hereby incorporated herein.

For applications where temperatures higher than those obtainable by the heat transfer liquids described above may be advantageously utilized, eutectic mixtures of organic salts such as HTS may be employed as the heat transfer medium. In this case modifications such as those described in my US. Pat Nos. 3,258,204 issued June 28, 1966 and 3,329,344 issued July 4, 1967, may be made in the exemplary press platen or heating system described above or in both of the foregoing.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent 1s:

1. A heat exchange unit such as a press platen or the like, comprising a body of heat-conductive material; a row of parallel, spaced-apart, lateral passages formed in said body, said passages extending generally from one side of said body to the other side thereof and each of said lateral passages having an open end and a blind end with alternate passages having their open ends at opposite sides of said body; divider means in and extending generally the length of each lateral passage but terminating short of the blind end thereof for dividing the passage into two connected flow channels; a longitudinally extending passage formed in said body at each side thereof, those lateral passages having their open ends at one side of said body all communicating at said open ends with one of said longitudinally extending passages, the remainder of said lateral passages all communicating at their open ends with the other of said longitudinally extending passages, and the longitudinally extending passages cooperating with the divider means to so provide fluid communication between the flow channels in the lateral passages opening onto one side of said body as to provide a first serpentine flow path extending generally from end to end of the press platen body and between the lateral passages opening onto the other side of said body to provide a second serpentine flow path internested with the first flow path; and means for effecting flow of a fluid heat transfer medium in counterflow relationship through said first and second flow paths to thereby change the temperature of the press platen body.

2. A heat exchange unit such as a press platen or the like, comprising a body of heat-conductive material; a row of parallel, spaced-apart, lateral conduits formed in said body, said row of conduits extending generally from one side of said body to the other side thereof and each of said lateral conduits having an open end and a blind end with alternate conduits opening onto opposite sides of said body; plugs fitted in the open ends of said conduits to prevent the escape of fluid therefrom; divider means in each of said lateral conduits for dividing the conduit into two connected flow channels, said divider means being fixed at one end thereof to the plugs in the same lateral conduits to prevent short circuiting of the heat exchange medium between the lateral conduits and the opposite ends of said divider means terminating short of the blind ends of the conduits in which they are disposed to provide the fluid communication between the two flow channels in each of said conthe sides of the body, each of said longitudinal conduits communicating with the lateral conduits opening onto the side of the body in which the longitudinal conduit is formed; and means for effecting flow of a fluid heat transfer medium in counterflow relationship through said first and second flow paths to thereby change the temperature of the press platen body.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 I 909 Dated November 23 1971 Inventor(s) Horace L. Smith, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 16, change "1,627,290" to --2,627,290--.

Column 2, line 61, change "24" (first occurrence) to --l4.

Column 5, line 3, change "form" to --from--.

Patent should have issued in the name of SMITHERM INDUSTRIES,

INC. Assignment recorded 4/29/71, Reel 2733,

Frame 326.

Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM O-1 50 -6 USCUMM-I/(I WINE-P61:

u S LOVEIINMFNY vwmnm mull Win1- 101, an

Claims

2. A heat exchange unit such as a press platen or the like, comprising a body of heat-conductive material; a row of parallel, spaced-apart, lateral conduits formed in said body, said row of conduits extending generally from one side of said body to the other side thereof and each of said lateral conduits having an open end and a blind end with alternate conduits opening onto opposite sides of said body; plugs fitted in the open ends of said conduits to prevent the escape of fluid therefrom; divider means in each of said lateral conduits for dividing the conduit into two connected flow channels, said divider means being fixed at one end thereof to the plugs in the same lateral conduits to prevent short circuiting of the heat exchange medium between the lateral conduits and the opposite ends of said divider means terminating short of the blind ends of the conduits in which they are disposed to provide the fluid communication between the two flow channels in each of said conduits; means providing fluid communication between the flow channels in adjacent ones of the conduits opening onto one side of said body to provide a first serpentine flow path extending generally from end to end of the press platen body and between the conduits opening onto the other side of said body to provide a second serpentine flow path internested with the first flow path, the means providing communication between the flow channels in adjacent conduits comprising longitudinal conduits formed in said body which extend along and adjacent the sides of the body, each of said longitudinal conduits communicating with the lateral conduits opening onto the side of the body in which the longitudinal conduit is formed; and means for effecting flow of a fluid heat transfer medium in counterflow relationship through said first and second flow paths to thereby change the temperature of the press platen body.