Solar-powered grain dryer and process for drying grain

A portable solar heating panel adapted for use in drying grain in the season thereof and for use for heating buildings or like heating purposes in the off season, is made of a double-glazed window spaced from an imperforate accumulator plate providing a dead air space which, in turn, is spaced from an insulating wall providing a circulating air space, characterized by the fact that all of the air to be heated is in heat-exchange with the rear surface only of the accumulator plate and by the fact that circulating air never comes into contact with the rear surface of the window. The accumulator plate is 5 millimeters or less in thickness, and is made of an aluminum alloy which, at that thickness, provides an isothermic plate which promotes uniform heat transfer and which has a coefficient of expansion which results in distortion of the surface plane of the plate to provide increased surface exposure, particularly during the early hours of the collection day, when the sun's rays are at less than a 90 degree angle.

FIELD OF INVENTION AND PRIOR ART 
The invention relates to a solar-powered grain dryer and process for drying 
grain and is particularly directed to an improved solar heating panel. 
Solar heating panels are well known in the art. See, for example, U.S. Pat. 
No. 3,863,621 and the patents cited therein. Such solar heating panels, 
however, have not been suited for drying grain because of the gross 
exposure to dust-laden air associated with such operations and because the 
limited period of usefulness hardly justified the cost of the solar 
panels. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a new and improved grain dryer 
and process for drying grain. It is a further object of the invention to 
provide a novel solar heating panel particularly suitable for use in a 
solar heating unit for drying grain. It is a further object of the 
invention to provide a solar heating panel which is insensitive to 
dust-laden or corrosive air. It is a further object of the invention to 
provide a portable solar heating unit which is interchangeable between 
drying grain and heating buildings, such as farm houses, barns, and the 
like. It is a further object of the invention to provide a solar heating 
panel having an improved accumulator or absorber. It is a further object 
of the invention to avoid the disadvantages of the prior art and to obtain 
such advantages as will appear as the description proceeds. 
BRIEF DESCRIPTION OF THE INVENTION 
The invention relates to a grain dryer and to a process for drying grain in 
which pre-heated ambient air is passed in contact with a mass of grain and 
in which the air is pre-heated, at least in part, by passage through a 
solar heating unit which comprises an accumulator or absorber, a 
transparent panel for passing radiant solar energy onto the accumulator 
panel and channeling means for channeling the ambient air into contact 
with the reverse side of the accumulator and keeping it out of contact 
with the inner surface of the transparent panel. 
In its broader aspects, the invention comprises a novel solar panel which 
comprises a transparent pane separated from the accumulator by a dead air 
space, in which there is no flow of air other than that induced by 
convection. In particular, the invention is directed to such solar heating 
panels in which the transparent panel is a multiplane panel with a vacuum 
between adjacent panes for reducing heat loss from the dead air space 
through convection. 
In the preferred form of the invention, the solar heating unit is portable 
so that it can be moved from the grain drying operation and hooked up to a 
building for heating the same during the season when it is not needed for 
drying grain and, to this end, is provided with means for channeling 
ambient air into the solar heating unit when it is used for drying grain 
and means for circulating air to and from said building when it is used 
for heating a building. 
In its further aspects, the invention is related to a solar heating panel 
per se, which is particularly adapted for use where dust-laden or 
corrosive air is passed in contact with the reverse side only of the 
accumulator and kept out of contact with the reverse side of the 
transparent pane. 
Advantageously, the accumulator plate is isothermic, so that uniform heat 
transfer from the obverse side to the reverse side is obtained. This is an 
important feature of the invention because the heat-transfer gas is heated 
exclusively by the reverse side of the accumulator plate. Preferably, the 
plate is made of a thin sheet of foil, say not more than 5 millimeters 
thick, made of aluminum alloy or any other suitable metal which can be 
processed into a foil of the desired thickness. An aluminum alloy which 
gives a foil having optimum isothermic properties and optimum tensile 
strength is one containing at least 99.45 percent aluminum; not more than 
0.55 percent silicon, 0.55 percent iron, and 0.05 percent manganese; not 
less than 0.05 percent copper; and not more than 0.03 percent other 
elements. 
An accumulator made of metallic foil of this thickness particularly when 
made of the particular alloy given above, has the further advantage that 
the coefficient of expansion is such that a distortion or crinkling of the 
foil takes place during the operation due to the differential temperature 
induced between the obverse and reverse surfaces thereof, which provides 
increased surface exposure and better collecting properties when the 
incident angle of the solar radiation is other than 90 degrees. 
Alternatively, a pre-crimped foil can be used with like advantage. In 
either case, the crinkling or crimping has the effect of promoting 
heat-transfer from the obverse face of the accumulator and to the air 
brought into contact therewith. 
The invention contemplates a marketable unit which comprises the 
transparent window and the accumulator supported in a suitable frame which 
can be built into any existing structure or any new structure, so as to 
provide a circulating air space between a wall of the building and the 
accumulator. Such a solar panel has the same advantage in keeping the 
reverse or inner surface of the window free of accumulation of dust or 
free from attack from corrosive chemicals. 
Advantageously, this sheet of aluminum alloy is surrounded by a rigid frame 
and is unitary therewith. The coefficient of expansion inherent in the 
alloy results in a distortion or crinkling of the foil, which provides 
increased surface exposure, which is particularly advantageous when the 
rays of radiant energy impinge on the sheet at more or less than a 90 
degree angle. 
In its use for drying grain, it is of advantage to have the inlet to the 
channeling means open to the ambient atmosphere; and, in its use for 
heating a building, to have the inlet of the channeling means in a closed 
cycle with the outlet thereof. Advantageously, means is provided whereby 
the channeling means is convertible from being open to the ambient 
atmosphere to a closed cycle in which the heated heat-transfer gas, after 
it has served its heating purpose, is recycled to the inlet of the 
channeling means. 
The channeling means is provided with baffles, as desired, to effect 
turbulence therein. Also, the dead air space can be provided with 
transparent baffles to isolate and minimize convection currents. 
The solar panel per se is a marketable unit which can be built into 
permanent buildings, in which case, a wall of the building can provide the 
insulated wall which is opposed to the accumulator to provide the 
circulating air space. When the solar heating panel per se is built into a 
livestock confinement building, especially one confining hogs, and the 
solar heating unit is used in connection therewith, it has the further 
advantage that the corrosive atmosphere which contains ammonia and sulfur 
which results from the excrement of the animals, does not come in contact 
with and corrode the reverse side of the transparent panel, but only in 
contact with the reverse side of the absorber. When this is composed of 
the aluminum alloy above-described, it has the further advantage of 
providing high corrosion resistance to these particular corrosive elements 
.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 there is shown a grain bin 10 having a solar heating unit 12 
hooked up thereto with the outlet pipe 14 of the solar unit 12 entering in 
the top of the bin 10. 
As shown in FIG. 2, ambient air enters the solar unit 12 through one or 
more apertures 16 at the bottom thereof and exits through an outlet dome 
18 at the top of the unit which connects with conduit 20, which is 
connected to the conduit 14 through an in-line blower 22. 
In FIG. 4, the inlet apertures 16 communicate with a manifold 24 which, in 
turn, communicates with an inlet conduit 26, which exits from the building 
28. The return air is thus fed through conduit 26 of the manifold 24 up 
through the solar unit 12, out through the top and down through conduit 30 
into the building. The air can pass directly into and out of the building 
or, through a heat-exchanger or air handler, not shown, for example, the 
cold air return of a hot air furnace. A closed circuit is thus formed. 
The solar unit 12 is mounted on skids, as seen in FIG. 5, so that it can 
readily be moved from one location to another. Thus, in the fall, when the 
solar unit is not needed to heat a building, but is needed for drying 
grain, it is hooked up as shown in FIG. 1. Later in the season, when the 
solar unit is no longer needed for drying grain, it is hooked up as shown 
in FIG. 4, where it can be used to supplement the heat in a home, as 
shown, or provide heat to some outbuilding on the farm. Thus, the seasonal 
down-time of the solar unit is minimized, so that the investment therein 
can be more easily justified. 
In FIG. 5, there is shown a solar unit according to the invention, in which 
32 is a framework having sealed in the forepart thereof, a multipane panel 
with a vacuum between adjacent or opposed panes, for example a 
double-glazed, low-iron, insulated, tempered glass panel 34, which admits 
radiant solar energy and yet insulates against the passage of other forms 
of heat. Faced inwardly from the window 34 is an accumulator or absorber 
36 structured of suitable material to absorb the radiant energy passing 
through the glazing 34. The accumulator 36 is spaced from the window 34 to 
provide a closed and sealed dead air space 38, the purpose of which will 
be presently described. At the rear of the accumulator 36 is a circulating 
air space 40, which is baffled (as shown at 41) to cause turbulence, which 
eliminates layering in the circulating air space, and communicates with 
inlet 16 and outlet 43. To the rear of the circulating air space 40 is an 
insulated wall panel 42. The window 34, the accumulator 36, and the 
insulating panel 42 are sealed in the frame 32 by suitable sealing 
material 44. To the bottom rear is the manifold 24 which communicates with 
the inlet apertures which constitutes the only access of ambient or 
circulated air into the unit 16. 
At the top of the frame 32 is an outlet chamber 46 having the outlet 43 
therein and apertures 48 at the bottom thereof communicating with a 
corresponding aperture in the frame 32, which communicates with the 
circulating air space 40. If desired, the outlet chamber 46 can be a 
manifold communicating with a plurality of outlet apertures 48 in order to 
distribute the flow of air to the circulating air space 40. The baffles 
41, which in some applications can be omitted, effect distribution of the 
air in the circulating air space and create turbulence therein to promote 
heat transfer from the accumulator plate 36 into the circulating air. This 
turbulence also minimizes the accumulation of dust on the reverse side of 
the accumulator panel 36. 
The space 50 in the double-glazed window is evacuated in accordance with 
the practice already known in the art, but the space 38 between the window 
34 and the accumulator 36 is not. 
One purpose of the dead air space 38 is to protect the inner face 52 from 
exposure to dust-laden or corrosive ambient air which is encountered 
around a farm, and provides near zero velocity at the glazing surface, 
thus reducing the loss via convection. For this purpose, the accumulator 
36 is a solid, imperforate sheet, so that no transfer of air from the 
circulating air space 40 to the dead air space 38 is possible. If desired, 
a molecular sieve desiccant can be included in the dead air space 38 to 
eliminate any possibility of fogging. Also, if desired, transparent 
baffles, not shown, can be included therein to minimize convection 
currents. The solar unit 12 is mounted on skids 54 at an angle to the 
vertical so that it will be at a proper angle to receive the sun's rays. 
Suitable braces or struts 56 can be provided to hold the panel at the 
desired angle. 
In the operation of the solar unit, in connection with a corn crib, grain 
bin, or flat storage, or the like, as shown in FIGS. 1 and 2, the manifold 
24 can be taken off in order to provide free and unrestricted flow of 
ambient air to the circulating air space 40. Any suitable blower, such as 
the in-line blower 22 can be used to effect this circulation. Thus, no 
matter how dust-laden the ambient air is, none of it contacts the inner or 
reverse surface 52 of the window 34. This is an important feature of the 
invention, since it makes possible the use of the solar unit efficiently 
in an environment where dust-laden air is encountered, without the 
necessity of filtering the air or providing removable windows so that they 
can be removed for cleaning purposes. 
In the application shown in FIG. 4, the air flow is in a closed cycle 
comprising the building, the manifold 24, the outlet header 46, and 
connecting pipes 26 and 30. 
The same advantage is obtained in case the solar panel is incorporated in a 
livestock confinement building, as the corrosive air is kept out of 
contact with the reverse surface 52 of the window 34 and confined to 
contact with the interior surfaces only of the circulating air space 40. 
If desired, the conduit 20 can be connected to the inlet side of the solar 
unit, in which case, the blower 22 is reversed, thus making it possible to 
have either a negative or positive air flow through the solar unit. 
The size of the in-line blower 22 is chosen to provide an air velocity 
suitable for drying grain, it being taken into account that excessively 
high temperatures can cause degredation of the grain. For practical 
purposes, it has been found that a blower which effects a circulation of 
between about twenty-five to about thirty cubic feet per minute per square 
foot of collector exposed thereto, will produce a temperature which is not 
excessive. If desired, the in-line blower 22 can be made variable, so that 
the flow can be adjusted to the particular kind of grain being dried, and 
to the particular conditions obtaining at the time. 
In the application of the invention to heating buildings, a considerably 
lower flow rate through the solar unit is desirable in order to produce a 
higher temperature effluent. 
Thus, the invention provides a simple and effective solar unit which, 
during the harvest season, can be utilized to dry grain and has the 
advantage for this purpose that the grain is not exposed to temperatures 
so high as to alter its food value or its keeping qualities. Also, unlike 
the grain driers heretofore in use, which have only seasonal usefulness, 
the solar unit of the invention has multi-seasonal uses, so that the 
initial cost and upkeep is not borne solely by the grain operation. 
The effectiveness of the solar unit of the invention is greatly increased 
by making the accumulator 36 of isothermic material, that is to say, of a 
material having uniform heat-transfer characteristics throughout its 
expanse. This desideratum is accomplished most effectively by using a thin 
sheet of foil, say about 5 millimeters in thickness, or less, made of an 
aluminum alloy or any other suitable metal which can be processed into a 
foil of the desired thickness. An aluminum alloy which gives a foil having 
optimum isothermic properties and optimum tensile strength is one 
containing 99.45 percent aluminum, not less than 0.05 percent copper, not 
more than 0.55 percent silicon and iron, not more than 0.05 percent 
manganese, and not more than 0.03 percent unspecified elements. 
An accumulator made of metallic foil of this thickness, particularly when 
made of the particular alloy given above, has the further advantage that 
the coefficient of expansion is such that a distortion or crinkling of the 
foil takes place during the operation due to the differential temperature 
induced between the obverse and reverse surfaces thereof, which provides 
increased surface exposure and better collecting properties when the 
incident angle of the solar radiation is other than 90 degrees. 
Alternatively, a pre-crimped foil can be used with like advantage. In 
either case, the crinkling or crimping has the effect of promoting 
heat-transfer from the obverse face of the accumulator and to the air 
brought in contact therewith. 
The invention contemplates a marketable unit which comprises the 
transparent window 34 and the accumulator 36 supported in a suitable frame 
which can be built into any existing structure or any new structure, so as 
to provide a circulating air space between a wall of the structure and the 
accumulator 36. Such a solar panel has the same advantages in keeping the 
reverse or inner surface 52 of the window 34 free of accumulation of dust 
or free from attack from corrosive chemicals. 
It is to be understood that the invention is not to be limited to the exact 
details of operation or structure shown and described, as obvious 
modifications and equivalents will be apparent to one skilled in the art.