|Title of Invention||
A process for coating a substrate used in an energy exchange device
|Abstract||A process for coating a substrate for use in energy exchange device of the kind as herein described comprising : - applying to one side of the substrate a coating of desiccant/binder solution as herein described, - drying the said coated substrate in a drying chamber at a temperature of between 100-180ºC, - passing the opposite side of the said coated substrate over a surface coating wheel, so as to cause the desiccant solution to be applied onto the opposite side, - drying the said coated substrate in a drying chamber at a temperate of between 100-180ºC, - winding the said coated and dried substrate.|
|Full Text||The present invention relates to a process of coating a substrate for use in energy exchange device.
The invention relates to air-conditioning systems and more particularly to rotary air to air heat exchangers, also known as heat wheels.
"Heat wheels" are well known in the air-conditioning art for their ability to transfer heat, water vapor or both between two counter flowing air streams. The ability to transfer water vapor (Latent Energy) is of particular interest since it dehumidifies the outdoor air during the cooling season and humidities the outdoor air during heating season. This characteristic serves to reduce the energy demands required to condition outdoor air by as much as 95%. Known heat transfer devices have been described as falling into one of three types:
(1) those designed for the removal of sensible heat also known as "sensible wheels"
(2) those designed for the removal of latent heat also known as "dehumidification wheels" and
(3) those designed for the removal of both sensible and latent heat also known as "enthalpy wheels".
Diameters of these devices generally range from 250mm to 5000mm, depending on the volume of air to be treated.
The material usually consists of a substrate which is coated with a desiccant material. The substrate can be aluminum, metallic foil, plastic films organic and inorganic papers. The desiccant coating can be of alumina, silica gels, zeolites, various types of salts such as lithium chloride or combinations thereof.
Examples of sensible heat wheels are disclosed in US Patent Nos. 2,563,415 and 4,432,409. Examples of Latent heat wheels have been disclosed in US Patent Nos. 2,700,577 and 3,176,446. Enthalpy heat wheels are disclosed in US Patent Nos. 3,307,617; 3,664,095, 3,733,791; 4,172,164 and 4,255,171.
In prior art, the area of coating of desiccant mixtures on substrates is very rare because of lack of interest of energy exchanger manufacturers to undertake the necessary investment. For the most part, the coating of the substrate for this application is done by companies that perform coating services for others for a fee, also known as "Toll Coating" . As their equipment is designed primarily for a wide range of purposes , rather than specifically designed for this particular purpose, the unique problems associated with the coating of desiccants are not always addressed resulting in compromises in the product quality.
In the known art, the material to be coated called a web is coated only one side by feeding the web through an equipment that applies coating to one side of the web If coating is required on both the sides, then a second coating process is done whereby the other side is coated and dried.
Also, the problem encountered in the prior art was that the desiccant adhered to the substrate did not have a very high capacity to absorb vapor. In other words, the breathibilty of the desiccant was effected.
While coating the desiccant onto the substrate, it is important that the desiccant retains its ability to absorb water vapor. Therefore, the coating should allow the desiccant to adhere to the substrate without degrading the adsorption characteristics of the desiccant. This aspect has been discussed in my co-pending application No. 571 /Del/96.
Another aspect to the art is the need for a well metered coating applied to both sides of the substrate . Though sufficient means exist in coating to provide a well metered and measured coating, but coating both sides of the substrate pose some problems with conventional methods.
For energy exchange media using desiccants, the thickness of the coating generally ranges from 5gsm to.50gsm, preferably around 20 gsm.
The substrate preferably used is aluminium foil having a thickness of 15-150 micrometers, preferably 35 micrometers.This substrate is preferred for two
1. for enthalpy exchange media , the latent energy transfer potential and sensible energy transfer potential should be similar.
2. for cost considerations, the mass of aluminium in the substrate should be at the minimum needed for effective sensible heat transfer.
The web material is very fragile and subject to breakage during coating and rewinding. It is therefore desirable for the edges of the rewound web to be in alignment during processing, so that a flat coil of coated foil results. This is necessary to insure the quality of the subsequent forming processes performed in the fabrication of energy exchange matrix. If the coil is not wound flat or the edges are out of alignment, slitting of the web in another process may be necessary to correct, resulting in wasted material.
The current art of subjecting the web to unwinding , coating, drying and rewinding process twice causes unnecessary web breakage and material wastage which in the case of thin aluminium foil and desiccant materials represents an undesirable expense of manufacture.
The object of the present invention is to allow coating of substrate on both the sides simultaneously without causing unnecessary web breakage and material wastage which in the case of thin aluminium foil and desiccant materials represents an undesirable expense of manufacture.
Yet another object of the present invention is to minimize or eliminate the wastage and resulting extra cost associated with this processing material.
Yet still a further object of the present invention is to ensure that the coating on both the sides of the substrate have a uniform thickness of the desiccant without its breathibilty being compromised.
SUMMARY OF THE INVENTION:
Accordingly the present invention provides a process for coating of a substrate of the kind as herein described for use in energy exchange matrix
comprising applying to one side of the substrate of the kind as herein described a coating of desiccant / binder solution as herein described, drying the said coated substrate in a drying chamber at a temperature of between 100 -180 °C , passing the opposite side of the said coated substrate over a surface coating wheel, so as to cause the desiccant solution to be applied onto the opposite side, drying the said coated substrate in a drying chamber at a temperature of between 100 -180 °C, winding the coated and dried substrate.
The coated substrate is preferably dried at a temperature of 140 ° C.
The heat may be supplied to the drying chamber by means of electric heating elements or by direct gas or oil burners.
The coating thickness is controlled by various means known to persons skilled in the art, and the time spent in the drying chamber depends upon a number of variables including web speed, coating thickness, type of coating, ambient conditions such as temperature and humidity, drying chamber temperature etc.
The substrate is selected from aluminium, plastic film, stainless steel,organic or inorganic paper and preferably aluminium. The thickness of the substrate is 15µ m to 150µm..
The coating consists of desiccant / binder, phenolic material, vinyl material, nitrocellulose material.
The invention specifically relates to a method for coating a substrate used in the manufacture of energy exchange matrix. The substrate is coated on both the sides and is subjected to heat in the drying chamber and is rewound into a coil in a single process.
The rewinding process occurs only one time, with the wastage due to edge break, edge damage etc virtually being eliminated.
The present invention will now be described with reference to the accompanying drawing:
Figure 1 .shows the manner in which the coating of the substrate is carried out.
Referring to figure 1, the substrate is unwound from a coil A, and is passed over a surface coating wheel which is moves at a pre-determined speed, said wheel being partially dipped into a tray of solution of the dessicant/binder mixture. The substrate moves over the said surface coating wheel and the coating is applied to its one side. Said one side coated substrate enters the drying chamber C wherein the said coated substrate is dried at a temperature between 100-180 ° C. The substrate exits the drying chamber to be coated onto the opposite side. Said one side coated substrate passes over a roller so that the opposite side may be coated, by means of another surface coating wheel D partially dipped in a solution of dessicant / binder moving at a predetermined speed and renters the drying chamber wherein the coating is cured and the substrate is thereafter rewound into a coil E.
In a preferred case, the rewind coil E is driven by either the center or the edge by a DC variable speed drive to allow adjustment of the substrate speed to ensure adequate time in the drying chamber. This drive if center driven may be synchronized by means of tachometer feedback to the DC drive controller to ensure constant web speed as the diameter of the rewound coil increases. In addition, the unwind coil A may be driven or free. The web tension or "draw" is then adjusted by an offset in the drive speed via the DC drive controller or by a simple friction clutch arrangement to adjust web draw.
The coating stations B and D are simplified renditions .Preferably surface coating wheel is a transfer roll which takes the coating mixture from the tray and deposits it onto the substrate. Just downstream from the transfer process, the coating is metered down to the desired thickness by using wire wound rods known as " Mayer bars" or "Supercoat rods".
In the figure, a minimum number of rollers is shown for clarity. Suffcient rolls may be provided in the path of the substrate to adequately support the substrate during the coating process.
The drying chamber is essentially a tunnel in which a hot air flow is maintained. Temperature of the said drying chamber is adjustable . Heat may be supplied by either electric heating elements or by direct or indirect gas or oil burners. It is preferred that blowers are arranged so that the air in the drying chamber is forced to circulate around the web as it travels through the chamber. A certain amount of air may be recirculated to decrease energy costs associated with the heating the chamber.,
1. A process for coating a substrate for use in energy exchange device of
the kind as herein described comprising:
-applying to one side of the substrate a coating of desiccant/binder solution as herein described,
-drying the said coated substrate in a drying chamber at a temperature of between 100-180 C,
-passing the opposite side of the said coated substrate over a surface coating wheel, so as to cause the desiccant solution to be applied onto the opposite side,
-drying the said coated substrate in a drying chamber at a temperate of between 100-180 C,
-winding the said coated and dried substrate.
2. A process as claimed in claim 1 wherein the coating of a substrate is dried at a temperature of 140 C.
3. A process as claimed in claim 1 wherein heat may be supplied to the drying chamber by providing electric heating elements or by direct gas or oil burners.
4. A process as claimed in claim 1 wherein the said substrate is aluminum, plastic film, stainless steel, organic or inorganic paper.
5. A process as claimed in claims 1 & 4 wherein the said substrate is aluminum.
6. A process as claimed in claim 1 wherein the thickness of the substrate is 15um to 150 um.
7. A process as claimed in claim 1 wherein the thickness ranges between 5-150 gsm.
8, A process as claimed in claim 1 wherein the coating consists of dessicant/binder,
9 A process as claimed in claim 1 wherein the coating consists of phenolic material, vinyl material, nitrocellulose material.
10. A process for coating a substrate substantially as herein described.
|Indian Patent Application Number||572/DEL/1996|
|PG Journal Number||37/2008|
|Date of Filing||18-Mar-1996|
|Name of Patentee||Deepak Pahwa|
|Applicant Address||20, Rajpur Road,|
|PCT International Classification Number||F 25 D 3/08|
|PCT International Application Number||N/A|
|PCT International Filing date|