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This application claims the benefit of and priority from U.S. Provisional Patent Application Ser. No. 61/031,182, filed Feb. 25, 2008, and entitled: Electric Heater Bracket Arrangement.
This invention relates generally to refrigeration systems and, more particularly, to a bracket for attaching a heater to an evaporator coil thereof.
In transport refrigeration systems, an evaporator coil is provided to cool the air that is circulated within a cargo space to be cooled. Since such an evaporator coil has a tendency to frost up during certain environmental conditions, and since there are periods in which heating of the cargo space is required rather than cooling, one common approach has been to provide an electrical resistance heater at or near the evaporator coil for either or both of those purposes. One such design is shown in U.S. Pat. No. 6,298,680 granted on Oct. 9, 2001 and assigned to the assignee of the present invention. In that design, a plurality of heater rods are individually nested in grooves formed in one face of the evaporator coil, and a plurality of brackets are then placed over the individual rods to thereby secure them in place. With this approach, the individual rods are firmly pressed and held in close contact to the coil such that any expansion or contraction along their longitudinal axes tends to cause thermal stress therein, as well as frictional wear on the rods. Also, since the lead wires going to the terminals are attached at one end of the heater rods, the wires can be damaged by that end of the heater rod contacting a surface which is perpendicular to the longitudinal direction of the heater rod, such as a tube sheet for the coil.
In accordance with one embodiment of the invention, a plurality of heater rods are preassembled by insertion against the sides of a plurality of brackets, with a retainer member then being secured on the other side of the rods to hold them in place. This subassembly can then be easily attached to one side of an evaporator coil, with the heater rods being free to expand or contract within their subassembly.
By another aspect of the invention, the terminal ends of the heater rods pass by each other in a paperclip manner at the nominal center of the heater rod and are turned up at some angle. This angle occurs on either side of the central bracket such that heater rods are not constrained in the longitudinal direction and can be moved freely.
FIG. 1 is a perspective view of the present invention as installed on an evaporator coil.
FIG. 2 is a front view of the assembled subassembly in accordance with the present invention.
FIG. 3 is a partial exploded view thereof.
FIG. 4 is a partial section view showing the ends portions of the heater rods in accordance with the present invention.
The invention is shown generally at 10 in FIG. 1 wherein a subassembly 11 is attached by its plurality of brackets 12, 13 and 14 to the respective tabs 16, 17 and 18 protruding from intermediate tube sheets of an evaporator coil 19.
As will be seen in FIG. 2, the subassembly includes, in addition to the brackets 12, 13 and 14 a plurality of heater rods 21, 22, 23, 24, 26 and 27. The heater rods are aligned normally with respect to the brackets 12, 13 and 14 and in mutual side-by-side, parallel relationship as shown. As will be seen in FIG. 3, which shows only the bracket 12 but is representative of all the brackets, a plurality of scallops 28 are formed in one edge 29 of the brackets to supportably receive the respective heater rods 21-27 therein. A retainer member 31 with a plurality of scallops 32, corresponding to the scallops 28 in the edge 29 and to the associated installed heater rods, is provided to fit over the other side of the heater rods, with the retainer 31 then being secured at its ends to the bracket 12 by fasteners or the like.
The completed subassembly, which includes the three brackets 12, 13 and 14, the six heater rods 21-27 and the three retainer members 31, can then be installed as a unit to the one side of the evaporator coil 19 as shown in FIG. 1.
Referring again to FIG. 2 and also to FIG. 4, it will be seen that each of the individual heater rods is formed of a continuous member which extends in a loop from one end 33, in a first direction (i.e. to the left) to a return bend 34, in the opposite direction (i.e. to the right) to another return bend 36 and then back in the first direction to the other end 37, with the one end 33 and the other end 37 overlapping on either side of a central position on the heater rod 21 in which the bracket 13 resides. Further, as shown in FIG. 4, the rods are bent at oblique angles A and B such that the ends 33 and 37 are easily accessible for attachment to their respective leads. The angles A and B are offset from the bracket 13 as shown so that the bracket does not restrict the longitudinal movement of the rod. This arrangement allows for the ends 33 and 37 to be attached to appropriate electrical leads in such a way that they will not be forced into engagement with other surfaces when the heater rods tend to expand or contract with changes in temperature.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.