Abstract:
This invention relates to a method for exchanging heat between one fluid and another fluid by using a heat exchanger, and circulating at least the one fluid through a fluid flow channel within a body made of a material which is a good heat conductor as well as a good conductor of electric current, so that the fluids become in heat exchange relationship through the walls of the body. The improvement includes insulating the body from electric current flow therethrough, so that, in use, the tendency for progressive precipitation of solid particles from the fluids onto the wetted surfaces of the body is substantially reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Reference to Related Applications 
     This application is a continuation-in-part of application Ser. No. 08/218,348 filed Mar. 28, 1994, now U.S. Pat. No. 5,379,603, which is a continuation-in-part of abandoned application Ser. No. 08/039,844, filed Mar. 30, 1993. 
    
    
     2. Field of the Invention 
     This invention generally relates to the art of exchanging heat between a heating fluid and a cooling fluid by using a heat exchanger body that is made of a material which is a good heat conductor as well as a good conductor of electric current. The heating fluid is circulated through the exchanger body while the cooling fluid surrounds the body inside a casing. 
     In a specific aspect, as described in our said patent, this invention relates to a novel heat exchanger for exchanging heat between the warm tap water flowing into an ice maker machine and the near freezing waste water ejected by it. 
     3. Description of the Prior Art 
     The prior art references in said patent incorporated herein by reference. 
     In an ice maker machine, pure water is initially normally frozen into ice, and the remainder near freezing surplus water contains a substantially higher mineral content that the tap water. Thus, at the end of one or more ice &#34;harvest&#34; cycles, a considerable volume of surplus 33°-34° F. cold waste water becomes available for dumping into the sewer together with its mineral content. While the cold energy within this waste water is beneficially utilized by our water prechiller, as described in our said patent, its mineral content, on the other hand, can become a serious handicap because a portion thereof becomes attracted to the walls of the heat exchanger&#39;s body, which is being cooled by the waste water as it flows from the ice machine to the drain through the heat exchanger casing. 
     Of course, the volume of this sediment content is larger when the tap water being prechilled itself contains solid particles typically lime. But the exact sediment content is unpredictable and can vary from region to region. 
     This mineral content makes the ice machine less energy efficient because its productivity is a function, among other things, of its ambient air temperature, of the temperature of the tap water used to make the ice, and of the volume of minerals deposoited on the heat exchanger&#39;s walls. The lower the tap water&#39;s temperature is, the higher will be the machine&#39;s ice yield during each ice &#34;harvest&#34;. Even if the air temperature remains the same, lowering the tap water&#39;s temperature by about 20° F. can considerably increase the machine&#39;s ice yield. In addition to boosting the ice yield, other tangible benefits will be obtained including: savings on the amount of required floor space for the ice maker, on its cost and installation, and on its operating and maintenance expenses. But, the efficiency of an ice machine, as well as that of our tap water prechiller, varies inversely with the volume of mineral buildup which occurs on their respective heat exchange surfaces. Periodically and regularly flushing and cleaning such heat exchange surfaces can somewhat alleviate but not eliminate the mineral buildup problem. But, for many reasons, such cleanouts are frequently not carried out by those in charge of the ice machine&#39;s maintenance. 
     Therefore, there has been a long lasting need in the heat exchanger art for an arrangement which would tend to reduce the progressive precipitation of sediments on the internal and external surfaces of a heat exchanger&#39;s wetted metallic surfaces. 
     When we filed our said application Ser. No. 08/218,348, which issued as said patent, we expected that the tap water prechiller described therein would in due course, like other heat exchangers, buildup an unavoidable and substantial hard mineral crust, especially if it is used in parts of the country where the warm tap water originates from water wells situated within lime formations. But, we have unexpectedly discovered that the heat exchanger body in our tap water prechiller exhibited a much lower attraction to minerals than we expected. Even after a relatively long time in service, the buildup of minerals on our heat exchanger body was substantially smaller than expected, even when used for prechilling &#34;hard&#34; tap waters originating from wells located in lime formations. 
     To find a cause and effect relationship, we carried out comparative studies which unexpectedly revealed that the particular type of non-conductor bulkhead union or connector used on our heat exchanger, which was shown on the drawings in both of our said prior patent applications, was responsible for the unexpected favorable results, i.e, for the much reduced rates of sediment buildups. 
     Using our novel tap water prechiller, less cleanings thereof are required, thereby reducing maintenance costs; less damage is sustained by its internal parts, thereby considerably prolonging the operational life thereof, and allowing the ice machine&#39;s bin to fill up faster with ice during periods of peak demand. 
     SUMMARY OF THE INVENTION 
     The method involves exchanging heat between one fluid and another fluid by using a heat exchanger body and circulating at least said one fluid through a fluid flow channel within the body made of a material which is a good heat conductor as well as a good conductor of electric current, so that the fluids become in heat exchange relationship through the walls of the heat exchanger&#39;s body. The improvement of this invention includes insulating the heat exchanger&#39;s body from electric current flow therethrough, so that, in use, the tendency for progressive precipitation of solid particles from the two fluids, that are in heat exchange relationship, onto the wetted surfaces of the heat exchanger&#39;s body is substantially reduced. 
     In a specific aspect of the invention, at least one end of the fluid flow channel within the heat exchanger&#39;s body includes a pipe connector or coupler made of a material exhibiting a high resistivity to the flow of electric current, thereby insulating the body from electric current flow therethrough, so that the tendency for progressive precipitation of minerals on the heat exchanger&#39;s body is substantially reduced, even when the tap water flowing therethrough originates from wells located in lime formations. The preferred pipe coupler is a bulkhead connector made of a non-conductor material, which is typically a plastic material for ease of fabrication. It serves a double purpose: it detachably and sealingly interconnects the heat exchanger&#39;s body to a fluid carrying metal pipe, and it prevents electric current flow through the heat exchanger&#39;s body. 
     In our said water prechiller, the heat exchanger&#39;s body is a copper coil having a plurality of spiral turns followed by a substantially straight copper tube portion within and surrounded by the coil turns. The one fluid is the warm tap water being prechilled for use by an ice maker machine to make ice cubes and the like, and the other fluid is the near freezing waste water ejected by it as a result of the ice making process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of the prechiller of the present invention; 
     FIG. 2 is a sectional view of the prechiller taken on line 2--2 of FIG. 1; 
     FIG. 3 is a sectional view on line 3--3 of FIG. 2 of the long tubing from which the heat exchanger is made up; 
     FIG. 4 is a schematic view of the prechiller with the preferred non-conductor bulkhead connectors; 
     FIG. 5 is an elevational sectional view of the non-conductor bulkhead connector taken on line 5--5 of FIG. 4; 
     FIG. 6 is a sectional view of a simplified but less desirable pipe connector, which is made of a non-conductor material, and which therefore could alleviate the mineral buildup problem; and 
     FIG. 7 is a schematic view of the prechiller using less desirable metal bulkhead connectors, which allow electric current flow therethrough, and which therefore do not alleviate the mineral buildup problem. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1-3 of the drawings use the same reference characters as are used in our said prior patent applications. In particular, the non-conductor bulkhead connectors were generally designated as 22 and 26, but the description thereof only dealt with their ability to detachably and sealingly interconnect the pipes leading to and out of the heat exchanger&#39;s body 40, and not with their additional ability also to prevent electric current flow through the heat exchanger. 
     In the drawings, numeral 10 generally designates an apparatus 10 for prechilling the warm tap water, fed into an ice maker machine 30 to make ice cubes and the like, with the near freezing mineral contaminated waste water 54 ejected by the machine as a result of the ice making process. 
     In its preferred embodiment and with reference to FIGS. 1-2, prechiller 10 has an elongated casing 12, preferably upright, which encloses a reservoir 14. Casing 12 can be a cylindrical pipe section having a bottom cap 16 and a top cap 18. It is entirely covered with a layer of thermal insulation 20. 
     Within reservoir 14 is a heat exchanger body 40 having a first stage 42 and a second stage 44, both sharing a single continuous tubing 46 of great length compared to the length of casing 12. Tubing 46 is made of a good thermal conductor preferably copper which is also a good conductor of electricity. 
     Top cap 18 has a non-conductor bulkhead connector 22 for receiving tap water from line 24, and a non-conductor bulkhead connector 26 through which the prechilled tap water flows out into line 28 of ice machine 30, such as an ice cube maker used in restaurants, bars, hotels, schools, hospitals, etc. 
     The bulkhead connectors 22 and 26 insulate the tap water copper feed line 28 from the copper heat exchanger 40 so that no electric current can flow therebetween. For that purpose, only one bulkhead connector either 22 or 26 could be sufficient, because each is made of a non-conductor material which is typically a plastic material for ease of fabrication. Such a material exhibits a high resistivity to the flow of electric current therethrough. 
     The inlet end 48 of tubing 46 is removably and sealingly coupled to connector 22 (FIGS. 1, 4 and 5) and the outlet end 49 of tubing 46 is removably and sealingly coupled to connector 26. Hence, each connector 22 or 26 serves a double purpose. For example, connector 22 (1) detachably and sealingly interconnects pipes 24 and 48 together, and (2) prevents electric current flow between tap water copper feed line 28 and copper heat exchanger 40. 
     Tubing 46 in first stage 42 is wound into a coil 50 having spiral turns 52 that are near to the inner wall of casing 12 (FIG. 2), thereby substantially increasing the length of the path of travel for the tap water within the casing. 
     In such coiling, the tube&#39;s sectional area is purposely altered from circular to substantially rectangular or oval (FIG. 3). It is believed that such an alteration favorably alters the heat exchange surface area relative to the volume of tap water contained within tubing 46. 
     The portion of tubing 46, in second heat exchanger stage 44, is substantially straight and upright and hereinafter will be also designated by the numeral 44. Straight tube 44 is inside of and completely surrounded by turns 52. The bottom end of tube 44 merges smoothly with the lowest turn 52&#39;. 
     In the preferred embodiment, along substantially its entire length, tube 44 is surrounded by a concentric upright conduit 58, having an open end 59 and a closed off top end 60. Conduit 58 is made of a poor thermal conductor material. In a less preferred embodiment (not shown), tube 44 can be outside of and parallel to conduit 58. 
     The side wall of top cap 18 has a socket 32 that receives from machine 30 ice cold waste water 54 on line 34, and a socket 36 which allows excess waste water 54 to escape to drain line 38. 
     The space between tube 44 and the inner wall of conduit 58 forms an elongated chamber 64 for receiving the waste water 54 from socket 32 through a coupling 62. 
     In the first ice harvest cycle, from line 34 of ice maker 30, ice cold waste water 54 flows downwardly through along and around straight tube 44, through open bottom end 59 of chamber 64, which is also the bottom of reservoir 14, and then flows upwardly towards the top of reservoir 14 along and around the coil&#39;s turns 52. 
     Conduit 58 thermally isolates the colder waste water 54 in chamber 64 from the warmer waste water 54 within the rest of reservoir 14. 
     The inlet 48 of tubing 46 receives from line 24 tap water under pressure which circulates downwardly through turns 52. The tap water flows spirally toward the lowest turn 52&#39;, thence upwardly within straight tube 44, and through its tap water outlet 49 into feed line 28 of machine 30 for making ice. 
     The waste water 54 in reservoir 14 cools the downwardly circulating tap water to progressively lower temperature levels. 
     The same tap water is further cooled to progressively lower temperature levels as it flows upwardly in straight tube 44 from the lowest turn 52&#39; of coil 50, because the arriving counter flowing coldest waste water 54 from machine 30 maximally lowers the temperature of the tap water in tube 44 before it flows out through outlet 49 into feed line 28. 
     In chamber 64 the waste water&#39;s temperature progressively increases from its top to the bottom of reservoir 14. In reservoir 14 the waste water&#39;s temperature progressively increases from its bottom to its top, thereby resulting in a progressive rise in the temperature of the waste water surrounding tubing 46 from inlet socket 32 to to outlet socket 36, whereat it has its highest temperature, while the tap water has its lowest temperature within tube 44 at the level of socket 32. 
     As a result, the temperature of the tap water within the entire length of tubing 46 is progressively and continuously lowered from its inlet end 48 to its outlet end 49. 
     The changes in the temperature in the waste water 54 per unit of vertical height enhances the heat transfer from the tap water flowing through tubing 46 to the surrounding waste water 54. It is believed that the substantially rectangular sectional area of tubing 46 tends to improve the amount of heat transferred in a unit of time across a unit of surface area of heat exchanger 40, and in a unit of length of tubing 46. 
     In summary, the heat exchanger&#39;s first stage 42 first prechills the fresh tap water with warmed up waste water 54 received from second stage 44, which further prechills the tap water received from first stage 42 with fresh ice cold waste water 54 received from line 34 into chamber 64. 
     Hence, the cooling energy within the waste water 54 discharged from ice machine 30, which would otherwise be wasted, is optimally reclaimed by heat exchanger 40 which removes heat energy from the tap water prior to injecting it into the ice making section of machine 30. 
     After a relatively long time in use, we discovered that the buildup of minerals on heat exchanger 40 was substantially smaller than expected. To find a cause and effect relationship, we carried out comparative studies which revealed that the non-conductor bulkhead connectors 22 and 26, which we used and have shown in FIGS. 1-3 of our said prior applications, were responsible for the unexpected favorable results, i.e, for the much reduced rates of mineral buildups. 
     We have discovered that the tendency for progressive precipitation of minerals from the waste water 54 flowing externally of the heat exchanger 40, and from the tap water flowing internally of the heat exchanger, onto the wetted surfaces thereof is substantially reduced, even when the tap water flowing therethrough originates from wells located in lime formations. 
     Since bulkhead connectors 22 and 26 are identical, FIGS. 4 and 5 show only non-conductor bulkhead connector 22 in detail. Inlet end 48 of tubing 46 is removably and sealingly coupled to bulkhead connector 22 which has a main hollow body 66 that defines a threaded external cylindrical wall portion 65, which is loosely inserted through an orifice 19 in top cap 18. Two circular top and bottom openings are provided in body 66 from which outwardly extend tubular anchoring sleeves 68 and 69, respectively. A radially-extending inner annular lip 70 maintains metal tubes 24 and 48 in spaced apart relationship. 
     Sleeves 68, 69 have fingers 71, 72, respectively, that are free to slide to a very limited extent on tapered walls 73&#39;, 74&#39;, respectively, which are extensions of cylindrical walls 73, 74, respectively. Fingers 71, 72 carry in a horizontal plane a plurality of radially-extending anchoring metal inserts 71&#39; and 72&#39;, respectively. A cap 76 threadedly engages the threaded cylindrical wall portion 65, thereby clampingly securing body 66 and compressing an external seal ring 78. The internal fluid tightness of body 66 is maintained by a top inner O-ring 80 and by a bottom inner O-ring 82. 
     In use, pipe 24 is inserted through metal inserts 71&#39; and O-ring 80, and pipe 48 is inserted through metal inserts 72&#39; and O-ring 82. Pipes 24 and 48 become anchored to body 66 by slightly pulling out sleeves 68 and 69, respectively. Conversely, pipes 24 and 48 become freed by pushing in sleeves 68 and 69, respectively. Thus, sleeves 68 and 69 accept for quick connect/disconnect the end portions of pipes 24 and 48, without the need for soldered connections, and hold them together against downward movements while allowing them rotational movements. 
     Hence, bulkhead connectors 22,26 allow prechiller unit 10 to become simply and easily connected to or removed from ice machine 30. 
     Body 66 and sleeves 68, 69 are made of non-conductor materials, such as plastics, exhibiting a very high resistivity to the flow of electric current therethrough, so that no appreciable electric current can flow either directly between pipes 24 and 48 or through body 66, thereby effectively electrically insulating tubing 46 which forms heat exchanger 40. 
     We believe that the non-conductor material of main body 66, which effectively prevents electric current flow between pipes 24 and 48, is responsible for maintaining the wetted surfaces of tubing 46 substantially free of mineral accumulation, even when the tap water flowing therethrough originates from wells situated in lime formations. 
     Thus, in accordance with this invention, each bulkhead connector 22 or 26 has a dual purpose: to operatively and detachably couple in a leakproof manner heat exchanger 40 to a source of tap water feeding the heat exchanger, and to provide a high resistance to the flow of electric current between the heat exchanger&#39;s copper tubing 46, ice machine 30, and ground. 
     The preferred embodiment for optimum thermal efficiency and adapted for use in most ice maker installations, utilized refrigeration grade copper tubing having a 3/8&#34; outside diameter (OD) and a wall thickness of 0.035&#34;. Casing 12 had a 4&#34; OD, a height of 26&#34;, and a reservoir 14 whose volume was 1.44 gallons. For smaller machines, four feet of copper tubing per linear foot of casing 12 is adequate. 
     However, for use on a wide range of ice makers from small to large sizes and for optimum thermal efficiency, about 23 feet of copper tubing per linear foot of casing 12 is preferred. In this case, the total length of tubing 46 is 48 feet yielding 54 coil turns 52, an outside diameter of coil 50 of 3.6&#34;, an inside diameter of coil 50 of 2.9&#34;, and a length of straight tube 44 of 25.5&#34;. Thus, in the universal 4&#34; OD cylindrical casing 12, the coil should use between 4 and 23 feet of copper tubing per linear foot of casing 12. The volume of reservoir 14, with the tubing 46 inside, is about 1.13 gallons for about 23 feet of tubing per linear foot of casing 12 having about 4&#34; outside diameter and about 26&#34; in length. 
     Other preferred dimensions include: 
     caps 16 and 18: 4&#34; diameter 
     hollow member 46: 1&#34; OD, 23&#34; length 
     bulkhead connectors 22, 26: 3/8&#34; to 3/8&#34; 
     These non-conductor bulkhead unions or connectors 22, 26 were purchased from Cole-Parmer Instrument Company, P.O. Box 48898, Niles, Ill. 60714-0898 under Catalog No.L-06372-61. The manufacturer of connectors 22, 26 is John Guest Southern Ltd., believed to have an office in Middlesex England. 
     The present invention may be carried out in various ways and is not limited to the specific way described above, which is at present the best mode contemplated for accomplishing the objectives previously enumerated, as well as other objectives which will become apparent to those skilled in the art. 
     For example, while it is preferred for casing 12 to remain upright, in use, the prechiller 10 will function with the casing 12 in an inclined or horizontal position but at a sacrifice in thermal heat exchange efficiency between the warm tap water and the cold waste water 54. 
     Instead of the desired bulkhead connector 22, a less desired straight pipe coupler 83 (FIG. 6) can be employed. It has an inwardly and radially extending shoulder 84 at the center thereof, thereby defining top and bottom sockets 86, 88 for receiving the free ends 24 and 48, which are physically separated from each other by the annular shoulder 84. 
     Coupler 83 is also made of a non-conductor material, such as plastic, exhibiting a very high resistivity to the flow of electric current therethrough, so that no appreciable electric current can flow either directly between pipes 24 and 48 or through the body of coupler 83, thereby effectively preventing the flow of electric current between the heat exchanger&#39;s copper tubing 46, ice machine 30 and ground. 
     In use, however, because pipe 24 needs to be fixedly secured to socket 86 and pipe 48 to socket 88, coupler 83 lacks the very important quick connect/disconnect advantage offered by bulkhead connectors 22 and 26. 
     Instead of the desired non-conductor bulkhead connectors 22, 26, less desired identical bulkhead connectors 90 and 92 can be employed as shown in FIG. 7. The main difference between bulkhead connectors 90, 92, and 22, 26 is that the body of bulkhead connector 90 is made of metal and not of a non-conductor material. Otherwise, the construction of each metal bulkhead connector 90 or 92 is identical to that of bulkhead connector 22. Thus, because the heat exchanger 40 will not become electrically insulated as desired, it will provide a continuous low electric resistivity path from ice machine 30 to ground. As a result, bulkhead connector 90 will encourage the undesired tendency of mineral accumulation on and around heat exchanger 40. 
     In sum, while metallic bulkhead connectors 90 and 92 cannot serve the purpose of electrically isolating heat exchanger 40, they can be used for providing quick connect/disconnect of pipe ends 24 and 48. 
     It will be readily apparent that our novel tap water prechiller 10 offers a very simple, practical, unique and inexpensive approach to a very difficult sediment precipitation problem, which, although recognized by others in the heat exchanger art, had not been heretofore effectively addressed.