Electrical steam generator having adjustable electrodes for an air humidifier

The steam generator includes a cylindrical tank, a plurality of circumferentially-spaced electrical terminals extending through the tank top wall. To afford the capability of adjusting the horizontal distance between adjacent electrodes while maintaining the sides parallel and uniformly spaced, the underside of the tank top wall is provided with a radially extending row of radially-spaced bosses in conjunction with each terminal and each boss includes an aperture radially aligned with the corresponding terminal. The upper end of each electrode includes a radially-extending row of apertures which are adapted to receive the inner end of a terminal and are spaced so that, when a terminal is positioned in one of the electrode apertures, at least one other is in registration with a tank boss aperture to receive a metal screw or the like for anchoring the electrode on the tank. The electrodes each include a pair of vertical, generally flat, elongated perforated metal side members joined together in angular relationship along an inner edge to form a V-shaped cross-section and have an upper portion with vertical outer edges extending generally parallel to the tank side wall and a thicker lower portion having outer edges which extend at an incline downwardly and radially inwardly from the outer edges of the upper portion and terminate at the bottom in a generally horizontally extending edge.

BACKGROUND OF THE INVENTION 
This invention relates to air humidifiers employing an electrically 
operated steam generator and, more particularly, to the water tank and 
electrodes for such steam generators. 
Air humidifiers including an electrical steam generator for producing a 
stream of steam which is dispersed into the air distribution system for a 
building are well known. The steam generator includes a water tank which 
is partially filled with water and a plurality of electrodes immersed in 
the water. Electrical voltage is induced on the electrodes, current 
passing through the water causes it to boil, and a stream of steam is 
discharged through an opening in the top of the tank. Current flow between 
the electrodes is directly porportional to the surface area of the 
electrodes covered by the water. A control system controls the operation 
of a valve which admits water into the tank to maintain the water at a 
level necessary to produce steam at a rate required to obtain the desired 
humidification. The control system also periodically opens a drain valve 
for the purpose of removing contaminants from the tank. 
Tap water is normally used and the water hardness varies considerably from 
locale to locale. Minerals in the water, such as calcium carbonate, tend 
to deposit on the surface of the electrodes. These deposits act as an 
insulator and reduce the effectiveness of the electrodes. The hardness of 
the water affects its conductivity. Thus, the water level in the tank 
required to produce a predetermined amount of steam at a given voltage 
varies depending on the extent of mineral deposits on the electrodes and 
the conductivity of the water. During operation the water level must be 
gradually increased to compensate for the loss of effective electrode area 
from the mineral deposits. 
With initial water levels in the tank substantially below about 1/3 the 
electrode height, minerals tend to rapidly deposit on the immersed portion 
of the electrodes and these deposits build up to the point where a 
blockage is created in the bottom of the tank, preventing the inflow 
and/or drainage of water. This can occur with considerable unused 
electrode surface above the water level which means that the effective 
life of the steam generator is shorter than possible. Also, the electrodes 
can become completely uncovered from time to time during the drain cycle. 
This can adversely affect the electrical control system which operates on 
the basis of the amount of electrode immersion. 
With initial water levels over about 1/2 of the electrode height, the 
increasing water level required to compensate for mineral deposits during 
operation reaches a point where the volume above the water level is 
insufficient to produce the required steam within a shorter than optimum 
time period. Thus, it is desirable for the electrodes to be designed so 
they can produce the desired amount of steam at a given electrode voltage 
with about 1/3 of their height immersed in water at startup. 
The current passing through the electrodes varies as the circumferential 
spacing or horizontal distance between the electrode varies. Accordingly, 
the electrode mounting arrangement desirably should be arranged to permit 
convenient adjustment of the horizontal distance between electrodes when 
required to compensate for the conductivity of the particular water to be 
used. Adjustable electrode mounting arrangements are known; however, they 
are not designed to insure that adjacent electrodes are maintained in 
parallel relationship and uniformly spaced when adjustments in the 
horizontal distance are made. 
U.S. Pat. No. 3,761,679 discloses the use of tapered electrodes having a 
complex geometric shape such that, as the water level increases, the 
surface of the electrodes covered by water increases geometrically and the 
horizontal distance between the electrodes decreases. With such an 
arrangement, the effect of differences between the conductivity of water 
is offset by relatively small increases in the water level which produces 
a substantial increase in the current flow due to the combined effect of 
the increased electrode area and the decreased horizontal distance between 
the electrodes and a proportional increase in the amount of steam 
generated. However, there is no provision for adjusting the horizontal 
distance between the electrodes as may be required for certain water 
conductivities in order to permit start up with an optimum initial wafer 
fill as discussed above. 
SUMMARY OF THE INVENTION 
One of the principal objects of the invention is to provide an electrical 
steam generator for an air humidifier including means for mounting the 
electrodes which affords convenient adjustment of horizontal distance 
between adjacent electrodes in a manner whereby the sides of the 
electrodes are maintained parallel to each other and uniformly spaced. 
Another of the principal objects of the invention is to provide an 
electrical generator for an air humidifier including electrodes which are 
arranged to give reliable control from start up through the effective life 
of the electrodes. 
A further of the principal objects of the invention is to provide an 
electrical generator for an air humidifier including electrodes which are 
arranged to permit higher initial water levels without reducing their 
overall effective life and to prevent rapid bridging of mineral deposit 
between the electrodes and the tank side wall. 
Other objects, aspects and advantages of the invention will become apparent 
to those skilled in the art upon reviewing the following description, 
drawings and the appended claims. 
The invention provides an electrical steam generator for an air humidifier 
including a generally cylindrical water tank including a top wall having a 
steam outlet, a bottom wall having a water inlet, and a generally vertical 
side wall, a plurality of circumferentially-spaced electrical terminals 
extending through the tank top wall at substantially equal intervals, and 
a plurality of electrodes having a pair of vertically extending, generally 
flat side members which diverge from each other in a direction toward the 
tank side wall and terminate in an outer edge spaced radially inwardly 
from the tank side wall. Each electrod is electrically connected to an 
electrical terminal and anchored to the underside of the tank top wall in 
uniformly spaced relationship in a manner whereby the side members of 
adjacent electrodes are generally parallel and the circumferential spacing 
between the side members of adjacent electrodes can be adjusted by 
movement of each electrode along a radial line to thereby maintain the 
side members of adjacent electrodes in a generally parallel relationship. 
Such an adjustment capability can be accomplished by providing, a 
radially-extending row of radially-spaced internal bosses on the underside 
of the tank top wall in conjunction with each of the terminals. Each of 
the internal bosses has an aperture radially aligned with the 
corresponding terminal and is adapted to receive means for anchoring the 
upper end of an electrode to the underside of the tank top wall. The upper 
end portion of each electrode is provided with a row of apertures which 
are adapted to receive a terminal and are spaced relative to the apertures 
in the tank bosses such that, when a terminal is positioned in any one of 
the electrodes apertures, at least one other of the electrode apertures is 
in registration with a tank boss aperture. The upper end of each of the 
electrodes is fastened to a terminal by a nut or the like threaded onto 
the inner end of the electrode projecting from the tank top wall and the 
upper end portion of each electrode is anchored to the underside of the 
tank top wall by a fastener located in an electrode aperture and a tank 
boss aperture which are in registration. 
The invention also provides electrodes for a steam generator having the 
above general configuration, each of the electrode side members including 
an upper portion having a vertical outer edge which extends generally 
parallel to the tank side wall and a lower portion having an outer edge 
which extends at an incline downwardly and radially inwardly from the 
outer edge of the upper portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Illustrated in FIG. 1 is an electrically-operated boiler or steam generator 
10 for an air humidifier. The steam generator 10 includes a generally 
cylindrical, upright tank 12 partially filled with water and a plurality 
(e.g. 6) of circumferentially-spaced electrodes 14 partially immersed in 
the water and connected to an electrical supply (not shown). 
The tank 12 is composed of two cylindrical halves, a bottom half 16 and a 
top half 18, preferably molded from a transluscent synthetic plastic 
material, such as polypropylene, so that the water level can be observed 
through the tank walls. The cylinder halves 16 and 18 having mating 
flanges 20 and 22 which are held together with a U-shaped band clamp 24 
including a threaded retainer 25. The bottom cylinder half 16 has a bottom 
wall 26 including a water inlet 28 through which water is introduced into 
and drained from the tank 12 in the usual manner during operation of the 
humidifier. The top cylinder half 18 has a top wall 30 including a steam 
outlet 32 through which a stream of steam is discharged and dispersed in 
the usual manner into the air distribution system (not shown) for a 
building or the like. The top and bottom cylinder halves 16 and 18 
cooperatively form a vertical side wall 33. 
Molded integrally in the top wall 30 of the top cylinder half 18 are a 
plurality (e.g., 6) of circumferentially-spaced electrical terminals 34 
including an outer end 36 projecting externally from circular bosses 37 on 
the top of the tank 12 and a threaded inner end portion 38 projecting 
inwardly beyond the underside of the top wall 30. 
As best shown in FIG. 5, each of the electrodes 14 includes a pair of 
vertically extending, generally flat, elongated side members 40 which are 
perforated and are connected together in angular relationship along an 
inner edge to form a V-shaped cross section. The side members 40 diverge 
from each other in a radial direction toward the tank side wall 33 and 
terminate in an outer edge 42 spaced radially inwardly from the tank side 
wall 33. 
Each side member 40 has a top or upper portion 44 including a substantially 
straight outer edge 42a which extends generally vertically and parallel to 
the tank side wall 33 and a bottom or lower portion 46 including an outer 
edge 42b which extends at an incline downwardly and radially inwardly from 
the outer edge 42a of the top portion 44 toward the central axis of the 
tank 12. While this incline can vary, it usually is in the order of about 
45.degree. relative to the tank axis. The juncture of the edges 42a and 
42b usually is located approximately at the horizontal medial plane 43 of 
the tank 12. 
The bottom end of the electrodes 14 is blunt, i.e., terminates in a short 
horizontally-extending bottom edge 48, rather than being pointed in order 
to minimize a tendency of electrical arcing and corona discharge. 
The electrodes 14 preferably are formed from a planar perforated plate 
which has the appropriate shape and is bent at the center to provide the 
desired V-shape. The lower portion 46 of the electrodes 14 preferably has 
a double thickness in order to minimize burnout from high density wattage 
when the water is at a level which covers only a relatively small portion 
of the electrode. This can be accomplished by welding to the lower portion 
46 an auxiliary perforated plate 50 having a shape generally corresponding 
to the lower portion 46. The auxiliary plate 50 can be welded onto the 
main plate prior to either being bent or welded to the main plate after 
both have been bent. 
A base plate 52 extending over the top edges of the electrode side members 
40 and spot welded or otherwise affixed thereto provides rigidity and 
serves as a support for connecting an electrode 14 to an electrical 
terminal 34 and for anchoring an electrode 14 to the top wall 30 of the 
tank 12 as described in more detail below. 
Affixed to the bottom end of each electrode 14 and depending therefrom is a 
threaded stud 54. The stud 54 fits through one of a plurality of apertures 
55 in a horizontally extending, electrically insulative, perforated plate 
member or disc 56. The disc 56 is fastened to the electrodes 14 by nuts 58 
threaded onto the studs 54 and serves to stabilize the bottom ends of the 
electrodes 14. The apertures 55 are radially spaced at equal intervals in 
radially extending rows to accommodate radial adjustment of the electrodes 
14 as described in more detail below. 
Means are provided for electrically connecting each electrode 14 to an 
electrical terminal 34 and for anchoring the electrodes on the top wall 30 
so that the side members 40 of adjacent electrodes 14 are located in 
uniformly-spaced, parallel relationship and are maintained in the parallel 
relationship when the horizontal distance or circumferential spacing 
between electrodes is adjusted to compensate for changes in the water 
conductivity under extreme conditions. In the specific construction 
illustrated, this is accomplished by providing a row 60 (FIG. 2) of 
circular bosses 62 and 64 on the underside of the top wall 30 of the top 
cylinder half 18 in conjunction and radially aligned with each electrical 
terminal 34. The bosses 62 and 64 respecively include central apertures 66 
and 68 which are radially spaced at equal intervals from the opposite 
sides of an electrical terminal 34 and are adapted to receive a sheet 
metal screw or the like. 
The electrode base plate 52 (FIG. 5) is provided with a radially extending 
row of apertures 70, 72 and 74 which are adapted to receive the inner end 
portion 38 of an electrical terminal 34 and are radially spaced at equal 
intervals so that, when an electrical terminal 34 is positioned in one of 
the apertures 70, 72 and 74, at least one other of these apertures is in 
registration with boss apertures 62 or 64. As shown in FIG. 2, the 
electrical terminals 34 are positioned in the base plate apertures 72 and 
the base plate apertures 70 are in registration with the boss apertures 
66. 
The electrodes 14 are electrically connected to the electrical terminals 34 
by a nut 76 which is threaded onto the inner end portion 38 projecting 
through the base plate aperture 72. The electrodes 14 are anchored onto 
the top wall 30 by a sheet metal screw 78 extending through the base plate 
aperture 70 and tapped into the boss aperture 66. 
The horizontal distance between the electrodes 14 can be adjusted to 
compensate for extreme water conditions by removing the nut 76 and the 
screw 78, positioning the electrical terminal 34 in the appropriate base 
plate aperture, threading the nut 76 back onto the inner end portion 38 of 
the electrical terminal 34 and screwing the metal screw 78 into the boss 
aperture in registration with the base plate aperture. Since the boss 
apertures extend in a row radially aligned with the electrical terminals 
and the base plate apertures are also radially aligned, the electrodes 34 
are moved along a radial line and the side members 40 of adjacent 
electrodes are maintained in parallel relationship during the adjustment 
as shown by the dashed line in FIG. 2. 
The base plate apertures 70, 72 and 74 are identified by indicia on the 
base plate 52 such as by numerals 1, 2 and 3. This indicia serves as 
reference for insuring that all the electrodes are mounted at the same 
position, and therefore uniformly spaced, during initial assembly or 
subsequent adjustment. 
A screen 80 covering the water inlet 28 is fastened to the bottom wall 26 
of the cylinder half 16 by sheet metal screws 82 tapped into apertures 84 
in circular bosses 86 provided on the bottom wall 26. The screen 80 serves 
as a strainer for preventing particulate contaminants from passing out of 
the tank 12 during the drain cycle. 
During operation, the tank 12 is initially filled to a level which provides 
the necessary electrode coverage to obtain the current draw required at a 
given voltage to produce the desired amount of steam. Since the lower 
portions 46 of the electrode side members 40 are inclined or tapered, the 
water level initially must be somewhat higher than that would be the case 
for straight-sided electrodes in order to obtain coverage of the same 
surface area. This higher water level minimizes the chances of the 
electrodes becoming completely uncovered during the drain cycle when 
higher conductive water is being used as discussed above. The increased 
distance between the tapered lower portions of the electrode side members 
and the tank side wall 33 increases the time period for mineral deposits 
to form a bridge between electrodes 14 and the tank side wall 33 and 
thereby block or impede the flow of water into and out of the tank. 
With the tapered lower portions 46, the electrodes 14 can accommodate a 
wider range of water conductivities even though a higher initial water 
level is used. That is, the amount of electrode surface area covered, and 
thus the current flow, increases geometrically as the water level rises 
instead of directly proportional as is the case with straight-sided 
electrodes. For example, with an electrode having a 45.degree. taper, the 
current draw would be two times that of a straight-sided electrode for the 
same increase in water level. After the initial fill, the current draw for 
a given voltage can be increased to compensate for mineral deposits and/or 
changes in water conductivity with smaller increases in the water level, 
thereby minimizing the chances of the water level rising to a point where 
there is insufficient volume above the water to generate the required 
amount of steam even though the electrodes have remaining effective life. 
Thus, the tapered electrodes, in addition to minimizing premature mineral 
deposit blockage, provide reliable control from start up throughout the 
effective life of the electrodes, particularly for higher conductive 
water. 
At start up, the tank is usually filled with water to a level where 
approximately the lower 1/3, but less than the lower 1/2, of the 
electrodes 14 is covered in order to maximize the effective life of the 
electrodes and yet prevent them from becoming uncovered during the drain 
cycle. 
From the foregoing description, one skilled in the art could easily 
ascertain the essential characteristics of the invention and, without 
departing from the spirit and scope thereof, make various changes and 
modifications to adapt it to various usages.