US2792071A - Non-frosting heat exchanger - Google Patents

Description

May 14, 1957 N. A. PENNINGTON NoN-FRosTING HEAT EXCHANGER Filed May 25, 1953 ATTORNEY.

2,792,071 NON-FROSTHNG FEAT EXCHANGER Neal A. Pennington, Tucson, Ariz., assigner of one-fifth to Robert H. Henley, Tiptonville, Tenn., and one-fourth to Roger Sherman Hoar, South Milwaukee, Wis.

Application May 25, 1953, Serial No. 357,231

9 Claims. (Cl. 1553-2) My invention relates to a new and useful rotatable heat-exchanger, primarily for use in air-conditioning apparatus, for effecting heat-transfer between the air in two air-passages across both of which the heat-exchanger rotates.

More particularly my present invention relates to such a heat-exchanger, designed to greatly reduce the likelihood of frost gathering thereon, when one of the two air-streams is very humid and the other air-stream is very cold.

My present invention is an improvement, for use in specialized environments, over the heat-exchanger shown and described in my U. S. Patent No. 2,464,766, the rotary element of which is shown and described in my U. S. Patent No. 2,563,415, to both of which patents reference may be made for anything shown or described therein.

The reduction of likelihood of frosting is the principal object of this present invention..

In addition to this principal object, I have worked out a number of novel and useful details, which will be readily evident as the description progresses.

My invention consists of the novel parts and in combination and arrangement thereof, which are defined in the appended claims, and of which one embodiment is exemplified in the accompanying drawings, which are hereinafter particularly described and explained.

Throughout the description the same reference-number is applied to the same member or to Similar members.

Figure 1 is a vertical longitudinal section of my complete machine. M

Figure 2 is a vertical transverse section thereof, taken along the line 2 2 of Figure l.

Figure 3 is a horizontal transverse section thereof, taken along the line 3 3 of Figmre 2.

The details of my heat-exchanger will now be described, with particular reference to the drawings.

Referring now to Figure 1, we see that 11 is the main container of my invention, in which 12 is an air-inlet from outdoors. Centrifugal fan 13 impels this air into passage 14, thence through filter-pad 15, thence through rotating wheel-like element 16, and thence through louvres 17 into the space to be conditioned.

Outgoing air leaves this space through louvres 18, and passes into passage 19, thence through wheel-like heatexchange element 16, whence it is sucked by centrifugal fan 20, and is expelled through air-outlet 21.

Motor 22, through pulley 23, belt 24, and pulley 2S, drives shaft 26, on which both fans 13 and 20 are keyed. The speed of shaft 26 is such as to impel the air through passage 14 and sucks the air through passage 19 with a velocity of preferably about 600 feet per minute. Gear reduction 27, acting through shaft 23, and bevel-gears 29 and 30, drives shaft 31 at about 25 to 30 R. P. M. Wheel-like element 16 is keyed to shaft 31, and hence it too rotates at about 25 to 30 R. P. M.

Although this range is not absolutely critical, the speed should be of about that order or somewhat more, for

hired States Patent Pipice the following two reasons. First, as explained in my already-mentioned Patent No. 2,464,766, a speed of about that order is optimum for heat-transfer purposes. Secondly, as explained in my copending Patent No. 2,700,537, a speed of about that order is optimum to transfer moisture in the proper direction, inasmuch as under certain circumstances (as there explained) a speed materially less than that will transfer moisture in the opposite direction, under certain circumstances. The pertinency of this second criterion will be explained later here- 1n.

The details of my wheel-like element 16 will now be described. lt comprises a casing and packing.

The casing comprises a hub 32, spokes 33, and a rim 34. Although the spokes and rim are very thi-n, yet the hub, spokes, and rim are all of substantially the same considerable width in the direction parallel to the axis of rotation of the wheel. This, plus the fact that the packing completely fills each of the sec-tors, helps to hold the packing substantially in place in the casing, in spite of gravity, air-How, and rotation, and regardless of the plane of rotation. But the above-mentioned uniformity of width exists primarily for the purpose of preventing air-flow radially outwardly from the wheel, or Within the wheel from one to the other of the two air-passages. In order to prevent this undesired air-flow it is further necessary for the hub, spokes, and rim to be imperforate. These details of the casing of wheel-like element 16 are derived from my already-mentioned Patent No. 2,563,415.

Each of the sectors into which the spokes and rim divide the casing, is stuffed with two different layers of packing 35 and 36, which will be more particularly described later herein, these two different layers constituting the meat of my invention.

The packing can be held in the casing by any appropriate means, such as sectoral pieces of wire-mesh 37, these in turn being restrained by a spider-web of wires 38 threaded through holes 39 in spokes 33 near the edges of these spokes.

These details of the packing-holding means are derived from my already mentioned Patent No. 2,700,537.

The leakage of appreciable air from one passage to the other is prevented by partition 40, assisted by the above-described construction of the casing, by bridges 41 at each face of the wheel (these bridges being slightly Wider than one sector of the wheel-casing, and by two small plates 42 (see Figure 3) which lie in extension of the partition 40).

The leakage of appreciable air past the wheel in either passage is prevented by the cooperation of a shroud 43 (which projects inwardly from the container, completely around and almost touching the rim of the Wheel) and two felt rings 44 which surround the center of the rim 34 and are carried thereby.

These details of air-leakage prevention are derived from my already mentioned Patent No. 2,464,766, as improved upon in my already mentioned Patent No. 2,700,537.

And now finally to describe my two sorts of packing.

The packing of layer 3S should be some non-hygro scopic air-permeable non-rusting substance, highly heatabsorbent, such as metal wool, preferably aluminum wool, further as to which see my U. S. Patents Nos. 2,464,766 and 2,563,415, already mentioned earlier herein. These two patents, and the flies thereof, list as examples: silver wool, copper wool, aluminum wool, magnesium wool, zinc wool, and nickel Wool, and also refer generically to metal wool.

The packing of layer 36, by contrast, should be some rial, or corrugated asbestos paper or the like with the cori'gations extending axially, in either case impregnated with some appropriate hygroscopic liquid or with an appropriate solution of some appropriate hygroscopic salt,V all as described and'explained in my already mentioned Patent No. 2,700,537. That patent and Ser.'Nos. 231,445 and 765,554, both-now abandoned, incorporated by reference therein, list glycerine and the polyethylene glycols ('such as triethylene, and polyethylene 200 or 300), as examples of impregnating liquids; and calcium chloride, calcium bromide, lithium chloride, lithium bromide, potassium bromide, and combinations thereof, as examples of impregnatingsalts; and also refer generically to hyg'roscopic liquids, salts, and combinations of salts. For the present purpose, a high degree of hygroscopicity is not necessary, nor (inthe case of salts) is a high concentration necessary. But it ought preferably be one of substantially zero intrinsic vapor-pressure, so as not to require replenishing. Water solutions of the sorbents which have the above-listed characteristics, have a very low 4freezing-point, and this is essential to my present invention. I prefer calcium chloride.

Both layers of packing should bel rigidly but loosely stuffed into the sectors of my wheel 16.

My apparatus operates, as described in my U. S. PatentY No. 2,464,766, already mentioned, to transfer sensible heat from one of the two air-streams to the other. With eicient prevention of leakage of air from one air-stream to the other, and with a rotating wheel of axial thickness appropriate to the temperature-difference of the two air-streams, a 90% or even 95% temperature exchange is possible by means of the device of that patent. That is to say, if the incoming air enters the machine at degrees, and the outgoing air enters the machine at 100 degrees, then the incoming air should leave the machine at 95 degrees, and the outgoing air should be discharged at 5 degrees. In a case like that, the temperature of the indoorward level of the packing in the wheel would average 97.5 degrees, fluctuating but slightly from that ligure; and the temperature of the outdoorward level of the packing would average 2.5 degrees, fluctuating but slightly from that figure.

If the outgoing air were initially very humid, metal wool packing of enough below 32 degrees F. in its highest temperature would be apt to frost-up, thus reducing the efficiency of the machine, both by impairing the ability of the filaments to transfer heat, and by clogging the interstices between laments and thus impairing the air-permeability of the packing.

The heat of condensation is enough to otset not too`- far below 32 degrees F. initial temperature of the incoming air, and/ orV not too high initial humidity of the outgoing air; but would not prevent congealing if'the initial temperature of the incoming air were low enough, and the initial humidity of the outgoingk air were high enough.

This isv where my present invention comes into play.

As was seen in by already-mentioned Patent No. 2,700,537, a moisture-transferery such as there described, also transfers sensible heat from the air-stream of higher temperature to the air-stream of 'lower temperature. Also, at the speed of rotation about to30 R. P. M., or somewhat more) contemplated by my` present invention, such a moisture-transferer transfers moisture from the air-stream of greater vapor-pressure to the air-stream of lesser vapor- .ressure; regardless of the relative temperatures of the two streams. And all this will likewise be true of the hygroscopiolayer of the heat-exchange element of my present` invention.

For the ventilation of certain industrial processes, notably breweries, in which the indoor air is maintained at substantially 100% Rh, iii-winter operations `when the outdoor air is around zero or below, my invention, with the outer face of the wheel 'packedk with a proper. hygroscopic substance as described hereinabove, will prevent frosting.

The moisture incidentally transferred, along with the sensible heat, will not be a detriment, and in many of the uses of my present invention will be actually an advantage. The hygroscopic layer of my heat-transferer will, of course, not be quite so eicient in transferring sensible heat as the metal-wool layer, and so (to compensate) my wheel should be built slightly thicker than if it were packed with metal-wool clear through; but this slight disadvantage is more than offset by the non-frosting advantage.

The hygroscopic section of my heat-exchange element should not be any thicker than necessary. In even the most frigid climates encountered in this country, I have found that one-third or less of the total thickness is quite enough.

Having now described the various features and componcnts of my invention, I wish it to be understood that my .invention is not to be limited to the specific details herein described.

To facilitate the ready understanding of which layer of my packing is which, in reading the claims, the two faces of the heat-exchange element will be mnemonically termed the cold face and the warm face. In the normal use of the heat-transferer, cold outdoors air will enter through the cold face and will emerge warmed from the warm face, and warm indoors air will enter through the Warm face and will emerge cooled from the cold face. The hygroscopic frost-preventing layer Vwill lie adjacent the cold face, and the metal-wool layer willlie adjacent the warm face.

l' claim:-

`1. A heat-exchanger of the type comprising: two air- Apassages, parallel and adjacent; a wheel-like casing, having spokes, a hub, and a rim, all imperforate, and all of substantially the same width in an axial direction, said spokes dividing the casing into sectors; a packing of airpermeable material, said packing substantially lling each sector, and being packed into each sector with such compactness as to remain freely air-permeable and yet be so self-sustaining as to be substantially immovable with respect to the casing during the rotation of the casing even in a vertical plane; means secured to the casing at each face thereof to retain the packing therein; means for rotating the sectors of the casing successively across the two passages; and means for impelling cold air through o'nof the two passages, and warm air in countercurrent relationship through the other, whereby the face of the packing where the cold air enters will be cold and the face where the warm air enters will be warm; said heatcharacterized by the fact that the layer adjacent the warm face consists of Iine metallic filaments.

3. A heat-exchanger, according to claim 1, further characterized by the fact that the layer adjacent the warm 'face consists of ne aluminum wool.

4. A heat-exchanger, according to claim l, further characterized by the fact that the layer adjacent the cold face consists of an inert sorbent carrier, impregnated with a hygroscopic impregnant having a very low intrinsic vapor-pressure and being such that Waterv solutions thereof have a very low freezing-point.

5. A heat-exchanger, according to claim 1, further characterized by the fact that the layer adjacent the warm faeeconsists of tine metallic laments, and that the layer adjacent the cold face consists of an inert sorbent carrier, impregnated with` a hygroscopic impregnant having a very low intrinsic Vapor-pressure `and being I such that water solutions thereof have a very low freezing point.

6. A heat-exchanger, according to claim 5, furtherl characterized by the fact that the carrier is excelsior.

7. A heat-exchanger, according to` claim 1, further characterized by the fact that the layer adjacent the cold face consists of an inert sorbent carrier, impregnated with a hygroscopic impregnant having a very low intrinsic vapor-pressure and being such that water solutions thereof have a very low freezing point; and being still further characterized by the fact that the carrier is corrugated asbestos paper, the corrugations of which run axially of the rotable element.

8. A heat-exchanger of the type comprising: two airpassages, parallel and adjacent; a wheel-like casing, having spokes, a hub, and a rim, all imperforate, and all of substantially the sarne width in an axial direction, said spokes dividing the casing into sectors; a packing of airpermeable material, said packing substantially filling each sector, and being packed into each sector with such cornpactness as to remain freely air-permeable and yet be so self-sustaining as to be substantially immovable with respect to the casing during the rotation of the casing even in a vertical plane; means secured to the casing at each face thereof to retain the packing therein; means for rotating the sectors of the casing successively across the two passages; and means for impelling cold air through one of the two passages, and Warm air in countercurrent relationship through the other, whereby the face of the packing where the cold air enters will be cold and the face where the warm air enters will be warm; said heatexchanger being characterized by the fact that the packing consists of two axially successive layers, of which the layer adjacent the cold face constitutes hygroscopic means for imparting a very low freezing point to the water which it absorbs, and the layer adjacent the warm face constitutes non-hygroscopic means for absorbing sensible heat from atmosphere of higher temperature and giving up sensible heat to atmosphere f lower temperature.

9. A heat-exchanger of the type comprising: an incoming air-passage and an outgoing air-passage, parallel and adjacent; means for impelling air through each of these two passages, in countercurrent relationship; a wheel-like casing, having spokes, a hub, and 4a rim, all imperforate, and all of substantially the same width in an axial direction, said spokes dividing the casing into sectors; a packing of air-permeable material, said packing substantially filling each sector, and being packed into each sector with such compactness as to remain freely airpermeable and yet be so self-sustaining as to he substantially immovable with respect to the casing during the rotation of the casing even in a vertical plane; means secured to the casing at each face thereof to retain the packing therein; and means for rotating the sectors of the casing successively across the two passages; and means for preventing appreciable leakage of air past the casing in either passage, or from one passage to the other; said heat-exchanger being characterized by the fact that the packing consists of two axially successive layers, of which the outdoorward layer constitutes hygroscopic means for imparting a very low freezing point to the water which it absorbs, and the indoorward layer constitutes non-hygroscopic means for absorbing sensible heat from atmosphere of higher temperature and giving up sensible heat to atmosphere of lower temperature; and by having means for rotating the casing at such |a speed that the heat-transfer thereby from the air-stream of higher temperature to the air-stream of lower temperature will be efficient, and that the outdoorward layer will transfer moisture from the air-stream of greater vaporpressure to the air-stream of lesser vapor-pressure, regardless of the relative temperatures of the two streams.

References Cited in the tile of this patent UNITED STATES PATENTS 1,762,320 Wood June 10, 1930 2,302,807 Shoeld Nov. 24, 1942 2,563,415 Pennington Aug. 7, 1951 2,566,366 Pennington Sept. 4, 1951 2,680,492 Kopp lune 8, 1954

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