US3885125A - Method for electrically heating a heat transfer fluid - Google Patents

Abstract

A method of electrically heating a heat transfer fluid prior to circulation through a heat exchange system wherein the heat transfer liquid is circulated helically in a continuously swirling bodily flow through an elongated substantially unobstructed annular chamber. The helical flow is caused by the angle and position of entry of the fluid into the vessel. The swirling fluid is exposed to axially elongated heating elements that are disposed in the annular chamber and that are sufficiently small relative to the width of the annular chamber to transfer heat with the fluid while accommodating the continuously swirling bodily flow without turbulence.

Description

United States Patent Palm et al. May 20, 1975 [54] METHOD FOR ELECTRIC ALLY HEATING l,383,033 6/l92l Seimbille 219/309 X H R F R FL 1 2,325,722 8/[943 A EAT T ANS E U D 2,344,8l2 3/1944 [75] Inventors: Lewis J. Pa m; Ronald B- alm, 3,747,670 7 1973 Palm etal I65/l bmh Pulask" FOREIGN PATENTS OR APPLICATIONS [73] Assignee: llilugon Boiler Works, Inc., Pulaski, 665,045 4/l929 France 2l9/298 [22] Filed; Ju|y 3 1973 Primary Examiner-Av Bartis Attorney, Agent, or Firm-J. Patrick Cagney [2l] Appl. No.: 381,373

Related US. Application Data [57] ABSTRACT [62] Division of No. 77 20 OCL 5 1970 Pat No. A method Of electrically heating a heat transfer fluid 3 7 7 7 prior to circulation through a heat exchange system wherein the heat transfer liquid is circulated helically 52 US. (:1. 1. 219/298; l65/1; 165/157; in a continuously Swirling bodily flow through an elon- 219/299;2l9/306;2l9/3l6;2l9/368;2l9/382 gated substantially unobstructed annular chamber. [51 Int. Cl. H05b l/00; F24h l/lO The cal lo is Caused by the angle and position of 53 Fie|d f Search n 1 5 1 154 15 157; entry of the fluid into the vessel. The swirling fluid is 2 9 29 499 30 409 3 374 331 332 exposed to axially elongated heating elements that are 366468 disposed in the annular chamber and that are sufficiently small relative to the width of the annular 5 References Ci d chamber to transfer heat with the fluid while accom- UNITED STATES PATENTS modating the continuously swirling bodily flow without turbulence. 798,747 9/!905 OHamlon et al. 2l9/306 1,139,001 5/l9l5 Varvel 219/299 X 5 Claims, 9 Drawlng Figures SHEET 10? 4 ,TJEP-HEB HAY 2 0 58B SHEET 9 F HEAL sou 1 METHOD FOR ELECTRICALLY HEATING A HEAT TRANSFER FLUID RELATED APPLICATION This application is filed as a division of my copending application Ser. No. 77,820 filed Oct. 5, 1970, granted July 24, 1973 as US. Pat. No. 3,747,670 and is directed to the thermal fluid heater shown in FIGS. and 6 thereof.

BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to a method of heating or cooling thermal fluids for use in heat exchange systems. These systems operate by heating or cooling a fluid in a central location, i.e., in a heater or in refrigeration equipment and then moving the fluid through pipes to a point where the heat or cold of the fluid is utilized to perform a heat exchange function.

In accordance with the present invention, there is provided a method of indirectly exchanging heat with a thermal liquid having a boiling point higher than that of water along a substantially axially unobstructed elongated annular chamber that is bounded by inner and outer chamber walls that encircle a central axis, said method comprising the steps of: producing in a closed system a continuous bodily flow of said liquid continuously swirling about the central axis in a path of predetermined width and characterized by rotary and axial flow components cooperatively determining a flow that continuously fills and sweeps the entire chamber by introducing adjacent one end of the chamber a stream of said liquid along a direction that is tangent to the chamber periphery; electrically generating heat in axially elongated elements that are disposed within said annular chamber and that are sufficiently small relative to the width of said annular chamber to accommodate said continuously swirling bodily flow-without turbulence, conducting heat through said elements to said liquid as it sweeps said annular chamber; and withdrawing the liquid from adjacent the other end.

More particularly, in the method of this invention, the bodily flow of thermal liquid moves in a path having a width between I and inches, the thermal liquid being introduced adjacent the lower end of the chamber and withdrawn adjacent the upper end at a temperature in excess of 250F.

It is conventional to heat these thermal fluids in heaters of the coil or tube type. Such heaters include a myriad of tubes or coils located in a heat transfer vessel. In the conventional tube or coil type heater, thermal fluid enters a tube bundle and passes through these tubes which are in contact with the heat or flame. The fluid is heated as it moves through the coil. The tubes and coils in a heater of this type tend to restrict the flow of the fluid, such restriction results in overheating at certain points and inefficiency in heat transfer resulting from the uneven heating. Further inefficiency results because tube heaters cannot maximize the contact of heat transfer fluid with the heating means.

Tube-type heaters also present a maintenance problem because of the tendency of the tubes to burn out. Such heaters are also difficult to clean because of the irregular tube surfaces.

In accordance with the present invention, the thermal fluid enters a substantially unobstructed annular heat transfer vessel with a spinning or helical flow caused by its angle and position of entry into the vessel, this helical flow is carefully maintained as fluid moves through the vessel. The fluid vessel can be either vertically or horizontally positioned without affecting the critical flow relationship necessary for effective heat transfer. The pressure and flow rate is controlled to induce and maintain the swirling action and to keep the fluid from being overheated. This helical motion enables the thermal fluid to have maximum and uniform contact with the heating means employed.

The heating system disclosed in the present invention is of the type having a tubeless or coilless construction. This system has a greater thermal efflciency and allows a more even flow of fluid than a tube or coil heater. The thermal fluid passes through the tubeless annular heat transfer vessel which is designed to receive heat from the heating medium in such a way that the continuous helical flow of the fluid is not impaired.

Other features and advantages of the invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which show structure embodying preferred features of the present invention and the principles thereof, and what is now considered to be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming a part of the specification, and in which like numerals are employed to designate like parts throughout the same:

FIG. 1 is a system diagram showing the heater unit operatively connected to the various external components that complete a practical operating embodiment.

FIG. 2 is a fragmentary perspective view showing the flow relationships occurring within the heater.

FIG. 2A is a transverse sectional of the perspective of FIG. 2.

FIG. 3 is a transverse sectional view through the heater take along line 33 of FIG. 2, better showing its physical arrangement and, in particular, showing the tangential entry path of the thermal fluid.

FIG. 4 is an elevational view of another embodiment of this invention.

FIG. 4A is a top plan view of the embodiment of FIG. 4.

FIG. 5 is a fragmentary perspective view of another embodiment of this invention; FIG. 6 is a top view of same; and FIG. 7 is a transverse sectional view similar to FIG. 3 and showing the electrical heater embodi ment of FIG. 5 the section being taken along line 7-7 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the system shown generally in FIG. 1, thermal fluids, particularly liquids other than water, such as, min eral oils; diphenyl-diphenyloxide mixtures; chlorinated biphenyls; silicones, silates and silanes; polyglycols; and polyphenyl ethers and esters are pumped by a circulating pump 10 into a fluid vessel 11. This vessel is made of heat conductive material and consists of an inner annular shell 12 concentric with and surrounded by an outer annular shell 13. The outer shell 13 is of larger diameter than the inner shell 12, therefore, a space or path is defined through which the fluid is to flow. The cold fluid enters the fluid vessel through an inlet 14 placed at the bottom of the vessel 11. The pressure created by the circulating pump forces the fluid to flow upward through the annular vessel until it reaches a fluid outlet at the top of the vessel. The thermal fluid is heated to the desired temperature as it passes through the annular vessel.

The annular fluid vessel 11 is contained within the heating unit 16. The unit includes an outer steel jacket 17 and an inner steel jacket 18 with an insulation layer 19 between them. There is a space left between the inner jacket 18 and the outer annular shell 13 of the heat transfer vessel 11. The fluid vessel is attached to the base of the heating unit by angle supports 20 (only one shown). Heat is transferred to the moving fluid by hot gases ignited at the top of the heating unit 16.

Air is taken in through the inlets 21 in a blower as sembly 22 and mixed with a gaseous ignition fuel in the burner assembly 23. The mixture is deflected downward through the air blast tube 24 and the funnel shaped air deflector 25. After passing the deflector 25, the gas-air mixture is ignited and combusts in the inner annular shell 12 of the heating vessel 11. The burner assembly 23 shown in FIG. 1 is located at the top of the heating unit 16; alternative construction would be to locate the burner at the bottom or in the middle of the unit.

As the hot blend goes downward through the interior of the inner annular shell 12, it gives up some of its heat into the shell. The hot gases are forced downward under the vessel 11.

As shown in FIG. 1, and in greater detail in FIG. 3, the hot gas after passing under the fluid vessel travels upward through a secondary flue pass. The secondary flue pass consists of the annular opening between the external shell 13 of the fluid vessel 11 and the inner jacket 18 of the insulation layer 19. Equally-spaced vertical ribs or fins 26 are joined to the circumference of the outer shell 13 of the fluid vessel 11. These ribs or fins 26 are effective in absorbing the heat from the gases rising through the secondary pass. The hot gases pass up through the secondary flue and give their remaining heat into the conductive outer annular shell 13 of the fluid vessel 11. Therefore, both sides of the fluid vessel are heated. The upward rising hot gases or products of combustion leave the system through a flue outlet 27. When the heated fluid reaches the top of the fluid vessel, it is forced through an outlet 15 into the external heating system.

The heated thermal fluid is circulated to the external system and then is recirculated from the external system through the pump 10 and inlet 14 after it performs its heating function. A pressure indicator and pressure fluctuation reliever 28 is provided on the return path of the fluid to the heating unit.

In accordance with the present invention, as shown in FIGS. 2 and 2A, improved efficiency and evenness of heat exchange are produced by the flow relationships occurring within the heater. The thermal fluid to be heated is pumped into the annular fluid heating vessel 11 through an inlet 14 which is tangential to the fluid flow path defined by the annular vessel 11 and at a 90 angle to the vertical axis of the annular vessel. This tangential entry path causes the thermal fluid to come into and flow through the fluid vessel with a spinning or swirling motion. The entire volume of fluid ro tates and mixes around the vessel. The fluid is therefore induced to spin around and between the annular shells 12,13 of the fluid vessel 11 in a helical path. To heat the fluid, the burner assembly gives a circular or whirling movement to the gaseous heat exchange medium as it passes downwardly of the interior of the inner annular shell 12 of the heating vessel 11. The circular movement of the gas plus the natural tendency for heat to rise, slows the downward movement of the flame; thereby, efficiently heating the inner annular shell 12. When the hot gas reaches the bottom of the interior of the annular heating vessel, it turns upward to make a complete second pass around the exterior of the outer shell of the heating vessel, thereby, transmitting additional heat to the outer annular shell and consequently to the fluid. The flow relationship shown in FIGS. 2 and 2A produces maximum heat transfer because of the smoothness of flow of the thermal fluid through the annular path and also because of the length of flow through the vessel caused by the rotational movement. This ideal fluid flow is exposed to double pass heat which takes maximum advantage of the heating ability of the gaseous medium.

The design of the heating vessel is ideal for heating thermal fluids due to the even distribution of two pass heat and the minimal restriction of the moving fluidv The minimal restriction of the fluid in the heating vessel results in a low pressure drop. The annular vessel can be constructed with the following dimensions de pending on the heating system required: (1] length of the vessel, 24 to 96 inches; (2) outer diameter of the vessel, l2 to 48 inches; (3) distance between the inner and outer walls of the vessel, 1 to [0 inches; and (4) inlet diameter, 1% to 3 inches.

The flow rate of the fluid is controllable through the vessel, and as such is dependent upon the distance between the inner and outer walls of the vessel. In addi tion, the flow rate must be kept above a minimum level in order to keep the thermal fluid from burning or scorching. This heater will operate at a minimum flow rate of one foot per second and can be adjusted to a maximum of 10 or 15 feet per second. This feature allows the thermal fluid heater to be used for a wide variety of applications.

The construction shown in FIGS. 4 and 4A makes use of multiple inlets and outlets. Five inlets 30, 31, 32, 33, 34 are shown all feeding fluid into a tangential path for helical flow. As shown in FIGS. 4 and 4A, the fluid inlets can be placed at locations other than the bottom of the heating vessel. This construction uses two outlets 35,36 to send heated fluid into the system.

A further embodiment of this invention is illustrated in FIGS. 5, 6, and 7. In this embodiment thermal fluids of the type previously described are pumped into a fluid vessel 40. This vessel consists of an inner annular shall 41 concentric with and surrounded by an outer annular shell 42 so that a space or path is defined through which the fluid is to flow. Cold fluid enters the fluid vessel through an inlet 43 placed at the bottom of the vessel 40. Fluid is forced to flow upward of the vessel by pressure created by a circulating pump (not shown). The thermal fluid is heated to the desired temperature as it passes through the annular vessel. The fluid vessel 40 is contained within a heating unit and is circulated to the external system substantially, as described in conjunction with the previous embodiment. Heat is transferred to the moving fluid by thin electrical resistance elements 44 extending vertically the length of the vessel.

These resistance elements are grouped in sets of live, each set 45 forming a resistance heating zone. Four sets of elements are arranged equally spaced 90 apart from each other. These sets of elements each create an elevated temperature Zone within the annular vessel 40.

As in the previously described embodiment the thermal fluid to be heated is pumped into the annular fluid heating vessel 40 through an inlet 43 which is tangential to the fluid flow path defined by the annular vessel 40 and at a 90 angle to the vertical axis of the vessel. The tangential entry path causes the thermal fluid to come into and flow through the fluid vessel 40 with a spinning or swirling motion and causes the entire vol ume offluid to rotate and mix around the vessel. As the fluid rotates about the flow path defined by the annular vessel, it passes through the elevated temperature zones defined by the sets of resistance elements 45. Heat is conducted to the moving liquid as it swirls about its flow path and through the elevated temperature Zones.

The resistance elements 44 are constructed out of thin members so as to leave the thermal fluid flow path substantially unobstructed. In this manner. the swirling flow of the thermal fluid is not substantially impaired.

Thus, while preferred constructional features of the invention are embodied in the structure illustrated herein. it is to be understood that changes and variations may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

We claim:

1. A method of indirectly exchanging heat with a thermal liquid having a boiling point higher than that of water along a substantially axially unobstructed elongated annular chamber that is bounded by inner and outer chamber walls that encircle a central axis. said method comprising the steps of: producing in a closed system a continuous bodily flow of said liquid continuously swirling about the central axis in a path of predetermined width and characterized by rotary and axial flow components cooperatively determining a flow that continuously fills and sweeps the entire chamber by introducing adjacent one end of the chamber a stream of said liquid along a direction that is tangent to the chamber periphery; electrically generating heat in axially elongated elements that are disposed within said annular chamber and that are sufficiently small relative to the width of said annular chamber to accommodate said continuously swirling bodily flow without turbulence. conducting heat through said elements to said liquid as it sweeps said annular chamber; and withdrawing the liquid from adjacent the other end.

2. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of one inch width.

3. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of ten inches width.

4. A method as in claim 1 wherein said bodily How is in a vertical direction and said thermal liquid is intro duced adjacent the lower end of the chamber and withdrawn adjacent the upper end.

5. A method as in claim 1 wherein said liquid is with drawn at a temperature in excess of 250 F.

Claims (5)

1. A method of indirectly exchanging heat with a thermal liquid having a boiling point higher than that of water along a substantially axially unobstructed elongated annular chamber that is bounded by inner and outer chamber walls that encircle a central axis, said method comprising the steps of: producing in a closed system a continuous bodily flow of said liquid continuously swirling about the central axis in a path of predetermined width and characterized by rotary and axial flow components cooperatively determining a flow that continuously fills and sweeps the entire chamber by introducing adjacent one end of the chamber a stream of said liquid along a direction that is tangent to the chamber periphery; electrically generating heat in axially elongated elements that are disposed within said annular chamber and that are sufficiently small relative to the width of said annular chamber to accommodate said continuously swirling bodily flow without turbulence, conducting heat through said elements to said liquid as it sweeps said annular chamber; and withdrawing the liquid from adjacent the other end.

2. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of one inch width.

3. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of ten inches width.

4. A method as in claim 1 wherein said bodily flow is in a vertical direction and said thermal liquid is introduced adjacent the lower end of the chamber and withdrawn adjacent the upper end.

5. A method as in claim 1 wherein said liquid is withdrawn at a temperature in excess of 250* F.

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