GB2096483A - Catalytic heater - Google Patents

Abstract

A catalytic heater developed to reduce a significant amount of back radiation loss is provided with a radiation reflective surface between the rear portion of the back of the frame, and the back of the catalytic bed. The reflective surface may be a polished front face of the back of the frame, or an independent reflective surface positioned between the catalytic bed and the back of the frame. Optionally fiberglass or equivalent type of insulating material is positioned between the reflective surface and the back of the frame. When a reflective surface between the back of the frame and the back of the catalytic bed is employed, the reflective means reduces the temperature of the exterior portion of the back, and increases the temperature exteriorly of the catalytic bed. A comparison between a like kind of catalytic heater without the heat reflective surface demonstrates a definite temperature reduction on the back of the frame with like BTU output of the same heater.

Description

SPECIFICATION Catalytic heater The present invention relates to catalytic heaters of the type generally disclosed and described in U.S. patent 3,037,554. Such catalytic heaters burn LP gases such as propane and methane which are oxidized on the face at temperatures below the combustion temperature of the gas when employed in a flame-type heater.

As mentioned above, the prior art is exemplified by U.S. patent 3,037,554. Catalytic heaters have enjoyed increasing popularity in the United States, particularly for industrial usage. Examples of such usage include the heating of cargo trucks to prevent freezing of the contents in cold environments. In addition, catalytic heaters can be employed as "people heaters" for outdoor applications where, for example, a workman is involved in changing tire trucks, utility repairs, and the like.

Another increasingly important appliction of catalytic heaters relates to pig farming. It is a demonstrated fact that a brood sow may crush a good portion of her litter unintentionally in a farrowing pen. By utilizing a catalytic heater to warm a portion of the floor. The suckling pigs after nursing will then crawl over to the warm spot on the floor. They will thus sleep and rest away from the brood sow and when she rolls from time-to-time the likelihood of crushing the litter is significantly reduced. Also the warming of the sucklings promotes their rapid growth and ability of leaving the farrowing pen for other safer environment at an earlier age. Safety is promoted by using the catalytic heat in the farm environment of straw and other combustibles.

Catalytic heaters are also used to heat chick brooders.

Considering the desirability of catalytic heaters as directing their heat towards people, animals, and objects it therefore becomes important to maximize the unidirectional flow of the heat, as heat dissipating out of the back of the heater serves little or no useful purpose since the catalytic heaters are seldom employed in a closed room type environment.

Radiant heat is not basically unidirectional. The radiation from the combustion process wants to proceed in all directions from the source. In the traditional catalytic heater the insulating effect of the substrate material reduces the radiation from the combustion process towards the back of the heater. Nonetheiess, a portion does pass through the insulation provided by the substrate for the catalytic bed in a backward fashion, and heats the back of the frame of the heating element which directs heat from the back portion of the heater. The present invention is directed to minimizing the amount of heat in a catalytic heater passing through the back of the heater, and not in the direction desired for the "target" of the heater.

Summary The present invention stems from the discovery that a significant amount of back radiation loss in a catalytic heater can be reduced by providing a radiation reflective surface between the rear portion of the back of the frame, and the back of the catalytic bed. The reflective surface is a polished front face of the back of the frame, or an independent reflective surface positioned between the catalytic bed and the back of the frame. Optionally fiberglass or equivalent type of insulating material is positioned between the reflective surface and the back of the frame. When the method of the invention providing a reflective surface between the back of the frame and the back of the catalytic bed is employed, the reflective means reduces the temperature of the exterior portion of the back, and increases the temperature exteriorly of the catalytic bed.

A comparison between a like kind of cataytic heater without the heat reflective surface demonstrates a definite temperature reduction on the back of the frame with like BTU output of the same heater.

Objects of the invention A principal object of the present invention is to provide a reflective surface adjacent the rear portion of a catalytic heater frame back to thereby minimize the heat loss through the back of the heater, and reflect the same through the catalytic bed and forwardly to the intended "target" of the radiant heat.

A further object of the present invention is to upgrade the efficiency of a catalytic heater by directing the major portion of its radiated heat through the front.

Yet another object of the present invention is to provide a means and method for improving the radiation -characteristics of standard production catalytic heaters without major retooling to achieve the modification.

Yet another object of the present invention is to provide a cost effective means for reducing heat radiation off of the back of a catalytic heater, the modification cost of which will be recovered in a relatively short period of time and thereby offset the modest additional cost of producing such a heater.

Description of drawings Further objects and advantages of the present invention will become apparent as the following description of an illustrative embodiment proceeds, taken in conjunction with the accompanying drawings, in which: Figure 1 diagrammatically illustrates the front portion of a catalytic heater; Figure 2 is an enlarged transverse sectional view, partially diagrammatic, taken along section line 2-2 of Figure 1; and Figure 3 is a back view of the catalytic heater shown in Figure 1 and diagrammaticlly indicating the points where temperatures were taken to demonstrate the difference between the method in the catalytic heater of the present invention, and the prior art.

Description ofpreferred emobodiment Atypical catalytic heater 10 is shown in Figure 1 in which a frame 11 surrounds and secures a retainer 12 which in turn is the outer face of a heater bed 15 (the latter being shown in greater detail in Figure 2). The heater bed includes a catalyst 16 on the outer face, and a fibrous back 18. Traditionally, the useful with the present invention, the catalyst portion 16 of the heater bed 15 is impregnated with a small portion of platinum. The fibrous back or substrate is a mineral-type insulator which is sufficiently permeable to LPG to distribute the fuel over the catalytic face 16 of the heater bed 15.

The plenum chamber 20, in turn is fed LPG through inlet 21 and then into a manifold 22 which has a plurality of orifices 24. Safety shut-off valves, and control systems for intitially igniting the catalytic heater are well-known in the art, essentially as exemplified in U.S. patent 3,037,554 and are not shown in detail or described in this application since the present invention may be employed with a wide variety of controls and distribution systems as well as start-up and shut-off equipment.

A reflector 25 is provided between the frame back 19, and the heater bed 15. In the preferred embodiment, the reflector is a sheet of heavy-duty aluminium foil such as purchased for barbecuing, and cooking activity.

Such aluminium foil has a highly polished surface on one face, and by way of contrast, the other face is somewhat dull. The highly polished face is oriented to be directly opposed to the catalytic heater bed 15. An alternative embodiment of the reflector results when the frame 11 is aluminium, and the interior back face is polished. Other frames may be plated with a reflective surface, but the cost of polishing the aluminium or plating the surface normally exceeds that of providing a sheet of aluminium foil on the interior portion of the frame back 19 as shown. Optionally, irrespective of the type of reflector 25 employed, fiberglass insulation or other equivalent insulating material is positioned between the reflective surface 25 and the back of the frame 19. In one commercial embodiment, a 1/4 inch thick pad of fiberglass was employed with improved results.

Normally, in such catalytic heaters 10, there is a bed of fiberglass 15 or comparable non-woven material positioned behind the catalyst 16 and directly against the gas dispersion member, such as exemplified by the manifold 22 disclosed here. There remains a space behind the gas-dispersion unit or manifold. In one of the embodiments disclosed, the reflective surface of aluminium is backed by fiberglass mat 26 having a thickness of 1/8 to 1/4", and secured to the back pan 19 ofthe frame 11. The thickness of the reflector 25 has no major factor in the reflectivity, other than the reflector should be thick enough to structurally present a reflective surface.It is further desirable to provide a gap between the external edges of the reflector 25 and the side of the back frame 11 to avoid conductive heat losses, thereby further maximizing the reflectivity of the target area.

In actual experience, a 12,000 BTU catalytic heater furnished by Societe Lyonaise des applications Catalyiques, a company of France was assembled utilizing the aluminium foil, and the 1/4 inch fiberglass insulation. After temperatures had stabilized, two separate thermometers were independently positioned on 9 different temperature reading sites (T1-T9). By using two separate thermometers, errors in each thermometer were averaged. By using 9 sites, an average of the temperature of the back of the catalytic heater could be fairly well determined. The same heater was then tested, but in its original commercial form without any reflective surface 25 such as just described above. The basic results were that the average back temperature of the unit without employing the method of the present invention in an average ambient temperature of 70 degrees F utilizing 120 minutes for warming resulted in an average temperature of 178.2 degrees F With the reflector and 1/4 inch fiberglass insulation, the average temperature at the back of the frame 11 was 163"F. When the 1/4 inch fiberglass insulation was not employed, the average back temperature rose slightly, but the temperature reduction from the unmodified 12,000 BTU standard heater still was at least more than 10 degrees. Set forth below, noting sites T1-T9 where the temperatures actually obtain from first the prior art, and then the unit modified in accordance with with the present invention.

Average Ambient Temp. - 70 F 120 minutes warm-up Back View Standard French 12,000 B.T.U./Hr. (No Reflector) Element Site T1 Site T2 Site T3 176"-T-1 164"-T-1 174"-T-1 172"-T-2 158"-T-1 1680-T-2 Average 174 161 171 Total Temp. 1604.5 Hi-Temp: 192.5 Lo-Temp: 161 Site T4 Site T5 Site T6 Avg.Temp: 178.2 183"-T-1 177 -T-1 1800-T-1 1800-T-2 172 -T-2 174 -T-2 Average 181.5 174.5 177 Site T7 Site T8 Site T9 1940-T-1 1900-T-1 189 -T-1 191 -T-2 182 -T-2 184 -T-2 Average 192.5 186.5 186.5 French 12,000 B.T.U./Hr.

Element with Reflector and 1/4" fiberglass Site T1 Site T2 Site T3 insulation 164 -T-1 1500-T-1 1700-T- 156 -T-2 143 -T-2 166"-T- Average 1600 146.5 168 Total Temp: 1467 SiteT4 Sites SiteT6 Hi-Temp: 171.5 162 -T-1 156 -T-1 1700-T- LoTemp: 146.5 158 -T-1 154 -T-2 166"-T- Avg. Temp: 1630 Average 1600 155 168 Average Temp.Site T7 Site T8 Site T9 differential comprises 175 -T-1 1700-T-1 172 -T-T 178.2 F-163 F=1 5.2 F 168 -T-2 164 -T-2 170"-T- Average 171.5 167 171 When the same heater with a reflective surface but without the fiberglass was tested, the average temperature was 167.2 F leaving a temperature differential with the non-reflective heater of 1 1"F. In each instance the reflector was aluminium foil.

To further confirm the above results, tests were conducted with a standard Simpson 389-3-L potentiometer. One of the leads measured the ambient temperature. The other two leads were connected to flat black sensors hung precisely under each of the two configurations of the heaters, the one the standard unit, and the other exemplary of the present invention. The standard heater had a temperature increase of 35.2 F, taken from the front, but the heater with the reflecting surface of the present invention had an increase of 39,65"F. This is in the range of approximately a 13% increase. When the data in the two tables above is applied, and the ambient temperature subtracted, it will be noted that the temperature differential of 15.2 F works out to approximately a 15% reduction in back radiation.This corresponds to the 13% increase in frontal radiation just described.

Not to be overlooked is the fact that the ordinary user of a heater employing the method and apparatus of the present invention will not have to be retrained since he will be utilizing the same controls, the same fixtures, and the same gas souces as with the prior art unmodified catalytic heaters. The only modification required by the heater user may be in calculating a reduction in the capacity of the size heater needed for a given application in view of the upgraded efficiency of radiation from the frontal portion of the heater to the intended target.

Although particular embodiments of the invention have been shown and described in full here, there is no intention to thereby limit the invention to the details of such embodiments. On the contrary, the intention is to cover all modifications, alternatives, embodiments, usages and equivalents of the subject invention as fall within the spirit and scope of the invention, specification, and the appended claims.

Claims (10)

1. A catalytic heater comprising, in combination, - a frame having sides and a back - a catalytic bed secured by said frame sides in spaced relationship to the back and defining a plenum therebetween, - a gas dispersion means in said plenum, - heat reflective means between the interior portion of the back and said catalytic bed whereby the heat reflective means reduces the temperature of the exterior portion of the back and increases the temperature on the exterior of the catalytic bed when compared to a catalytic heater of the like kind without the heat reflective means.

2. A catalytic heater according to claim 1, in which - said reflective means is a polished interior surface of said back.

3. A catalytic heater according to claim 1, in which - said heat reflective means in an independent element between the interior of the back and the catalytic bed.

4. A catalytic heater according to claim 1, in which - said heat reflective means is a sheet of aluminium foil with its polished face opposing the catalytic bed.

5. A catalytic heater according to claims 3 or 4, in which - an insulative layer is positioned between said heat reflective means and the interior surface of the back.

6. The method of increasing the frontal heat radiation of a catalytic heater having a frame with sides and a catalytic bed secured to the frame sides and defining a plenum between the back and the catalytic bed, and a gas dispersing means within said plenum, comprising the step of - providing a heat reflective surface between the back of the frame and the catalytic bed whereby more heat is radiated from the front of the catalytic bed than the rear of the back of the frame when compared with a like catalytic heater without such a heat reflective surface.

7. In the method of claim 6, the additional step of - providing an independent element with a heat reflective surface.

8. In the method of claim 7, the additional step of - providing an insulative layer between the reflective surface and the interior portion of the back of the frame.

9. In the method of claim 8, the additional step of - selecting an aluminium foil sheet for the heat reflective surface.

10. In the method of claims 7,8 or 9, the additional step of - selecting an insulative layer to position between the heat reflective surface and the interior of the back of the frame which is fiberglass insulation.