The present invention relates to a heat exchanger and method for defrosting a heat exchanger, and more specifically to a novel mounting arrangement for electric resistance heating elements which are employed to defrost low temperature air-cooling heat exchangers.
Air-cooling heat exchangers are used in a variety of residential, commercial and industrial refrigeration applications where temperatures of a space are maintained below the freezing point of water (32° F.). When operating at these lower temperatures and in many environments, frost or ice will accumulate on the fins and tube surfaces of the heat exchangers. The frost or ice must be periodically removed from these surfaces in order to maintain the efficiency of the cooling system.
One common method of defrosting heat exchangers involves inserting electric resistance heating elements into vacant spaces which are adjacent to a heat exchanger fin bundle. Thereafter, these heating elements are occasionally and periodically energized to warm the fin and tube surfaces to a temperature which is sufficient to melt the accumulated frost or ice. The resulting water is then captured and removed from the space which is being refrigerated. After all the fin and tube surfaces have been freed of the accumulated frost and ice, the heating elements are deenergized, and the heat exchanger is again used to reduce the refrigerated space to the desired temperature. This periodic heating and cooling of the fin and tube surfaces to render the frost and ice free is sometimes referred to as a “defrost cycle.”
During a defrost cycle, melted frost or ice, in the form of liquid water, can sometimes make its way into the vacant tube spaces occupied by the heating element. As the heat exchanger begins to cool the refrigerated space after the defrost cycle, this liquid water conformally freezes and attaches, as ice, to the heating elements and to the sides of the vacant tube spaces in which the heating elements were placed. It should be understood that this same ice which forms around the heating element will temporarily anchor the heating element to the vacant tube spaces. Still further, and due to its coefficient of linear expansion, the metal sheath which typically encloses such heating elements will contract as the temperature of the heat exchanger drops. In the case of commercial and industrial heat exchangers, these heating elements can be as long as twenty feet or more. Consequently, the contraction which is experienced by these heating elements, when cooled, can be as much as one-half inch or more. When the heat exchanger is warmed during a subsequent defrost cycle, the same metal sheath of the heating element expands due the same coefficient of linear expansion. However, the ice that is anchoring the heating element to the vacant tube spaces does not immediately melt. Consequently, the resulting expansion of the heating element will cause it to move or creep outwardly from the heat exchanger tube bundle. Once the ice is dissipated, the heating element is left in an orientation where it is displaced outwardly relative to the heat exchanger by an amount which is equal to its linear expansion.
This movement of the heating element relative to the heat exchanger occurs, to some degree, during each defrost cycle. After repeated heating and cooling cycles, the heating element will essentially “creep” or “walk” out of the heat exchanger due to this repeated contraction and expansion. If this movement of the heating element remains unchecked, this relative movement of the heating elements may cause damage to the heating elements themselves, to the electrical wiring and circuits that feed the heating elements, or to neighboring equipment. To address this problem, a rigid mounting system was designed to restrain the heating element within the heat exchanger. It was discovered, however, that these mounting arrangements were often insufficient to counter the very strong forces resulting from the thermal expansion of the metal sheaths. More specifically, even if the chosen attachment device or method was strong enough, the repeated thermal expansion and contraction of the heating elements usually resulted in some internal damage to the heat exchanger tubes, fins, or casings.
A number of inventions have been disclosed which address the myriad of issues associated with the uneven expansion and contraction of components in heat exchanging devices, and which is caused by differences in temperatures of the component parts thereof. In U.S. Pat. No. 3,643,733 to Hall, for example, a spring is used to accommodate differences in expansion rates between tubes used to carry the different fluids in a fluid-to-fluid heat exchanger. Similar approaches have been used in cryogenic devices (U.S. Pat. No. 4,194,119 to MacKenzie) and fluid heaters (U.S. Pat. No. 5,117,482 to Hauber). None of these inventions, however, provide a solution to the problems associated with the expansion of an intermittently used heating element that is not directly involved with the normal heat exchange function.
Therefore, it has long been known that it would be desirable to provide a means of restraining electric resistance heating elements in such a way so as to accommodate limited movement of the heating elements during multiple defrost cycles while simultaneously preventing damage to the heating element and the associated heat exchanger. Further, it would be desirable to provide a means whereby the heating element could be returned to its proper position within the heat exchanger after each defrost cycle without causing damage to either the heating element itself, the heat exchanger, or associated equipment during their normal expected lifetime.
A novel mounting arrangement for electric resistance heating elements which avoids the shortcomings attendant with the prior art devices and practices utilized heretofore is the subject matter of the present application.
A first aspect of the present invention relates to a heat exchanger with a heating element which is positioned within a vacant space thereof, and which is further mounted in a resilient, longitudinally restrained orientation relative to the main body of the heat exchanger during the expansion or contraction of the heating element.
Another aspect of the present invention relates to a heat exchanger with a heating element and which further has a biasing member having a first end which is affixed to the first end of the heating element, and a second end which is affixed to a casing which encloses the heat exchanger.
Another aspect of the present invention relates to a heat exchanger which includes a casing which defines, at least in part, a vacant space; a fluid receiving conduit mounted on the casing and which defines, at least in part, the vacant space; a heat radiating fin mounted on the fluid receiving conduit, and extending outwardly relative thereto and into the vacant space; a heating element having a main body with opposite first and second ends, and wherein the main body is received within the vacant space, and disposed in juxtaposed, thermal transmitting relation relative to the fluid receiving conduit and heat radiating fin; and a biasing member having a first end which is affixed to the first end of the heating element, and a second end which is affixed to the casing.
Yet another aspect of the present invention relates to a heat exchanger with a casing defining at least one vacant space, and further including at least one aperture corresponding with the at least one vacant space; a plurality of fluid receiving conduits mounted on the casing; a plurality of heat radiating fins affixed to the plurality of fluid receiving conduits and extending substantially radially outwardly therefrom; a heating element having a main body with opposite first and second ends, and wherein the main body is received within the vacant space, and wherein the first end protrudes from the casing through the aperture, and wherein the heating element is disposed in juxtaposed, thermal transmitting relation relative to the fluid receiving conduit; and a flexing member with a first end, and an opposite second end; and wherein the first end of the flexing member is fixedly attached to the first end of the heating element, and wherein the second end of the flexing member is fixedly attached to the casing; and wherein the heating element is movable longitudinally relative to the vacant space to accommodate expansion and contraction of the heating element relative to the vacant space.
Still another aspect of the present invention relates to a method for defrosting an air cooling heat exchanger, and wherein the method includes the steps of providing a heating element; energizing the heating element to a temperature over 200° F., deenergizing the heating element; cooling the heat exchanger to a temperature below about 32° F.; and resiliently restraining the heating element relative to the casing so as to substantially oppose longitudinal movement of the heating element during the energizing and deenergizing of the heating element.
These and other aspects of the present invention will be described in greater detail hereinafter.
Preferred embodiments of the invention are described below with reference to the following accompanying drawings.
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).
Referring now to
The plurality of tubes 10 are arranged in spaced relation one relative to the others. As presently illustrated, a multiplicity of tubes 10 extend through the heat exchanger. In some arrangements, the tubes may be interconnected or continuous as seen in
Referring now to
Referring now to
Referring now to
In other embodiments of the present invention, the biasing member 30 may comprise at least one Belleville washer which is generally indicated by the numeral 32 (
In the event that the biasing member 30 is fabricated from an electrically conductive material, such as when a metal coil spring 31 is employed, the biasing member 30 will also act as a means to provide an electrical grounding path between the heat exchanger casing 12, and the metal sheath 24 of the heating element 20 (
Referring now to
The operation of the described embodiments of the present invention are believed to be readily apparent and are briefly summarized at this point.
During normal operation of the air-cooling heat exchanger 1, refrigerant (not shown) is pumped through the heat exchanger tubes 10 while fans (not shown) blow air across the radiant fins 11 so that the refrigerant may extract heat from same. In the operation of the heat exchanger 1, the heating element 20 is normally deenergized. During a subsequent defrost cycle, the following sequence of events typically occurs. As a first matter, the flow of refrigerant to the heat exchanger tubes 10 is stopped. Secondly, the air-cooling fans are turned off once most of the refrigerant has boiled off. Thirdly, the heating elements 20 are energized to a temperature which is normally above 200° F. The heat from the heating elements 20 is then thermally conducted or otherwise transmitted to the heat exchanger's refrigerant tubes 11 and radiating fins 12. During this stage, any frost or ice that has accumulated on these components is melted, and the liquid water is drained from the heat exchanger. Some water, however, inevitably finds its way into some of the regions adjacent to the vacant space tubes 14 in which the heating elements are placed. Fourthly, once all the frost and ice has melted, the heating elements 20 are deenergized. Fifthly, the flow of refrigerant through the heat exchanger tubes 10 is restored and the heat exchanger cools the refrigerant space down to the appropriate temperatures. Finally, in a sixth step, the air-cooling fans are reenergized.
When the heat exchanger begins to cool after the end of a defrost cycle, the water that accumulates, for example, in the vicinity of the vacant space tubes 14 where the heating elements 20 are located will freeze. The resulting ice will conformally and substantially rigidly affix at least a portion of the individual heating elements to the vacant space tube where they rest or are otherwise positioned. During a subsequently conducted defrost cycle, the heating element 20 will heat rapidly, and the metallic sheath 24 will expand as a function of its coefficient of linear expansion. This heating and expansion will typically occur before all the ice that has formed in the vacant spaces 13 and tubes 14 have melted. Since part of the heating element 20 is still anchored to the vacant space tube 14 by the remaining accumulating ice, the heating element will expand outwardly with respect to the heat exchanger casing 12. This outward expansion pressure will then be absorbed by the biasing member 30 without putting undue pressure on the clamp 40 or first and second members 41 and 42, respectively. More importantly, since the biasing member 30 is absorbing the linear expansion forces of the heating element, the heating element itself will not typically be damaged. Further, internal damage which might be caused to the heat exchanger tubes or fins by the expanding heat element 20 is substantially impeded.
Once the defrost cycle nears completion, the ice that has anchored the heating element 20 to the vacant space tube 14 eventually melts as well. As this anchoring ice melts, the biasing element 30 then returns the heating element 20 back to its original position, thus preventing the heating element from “creeping” or “walking” out of the heat exchanger 1. This, of course, further prevents damage to the heating element wiring and any neighboring equipment.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however; that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.