Heater

A heater having a planar metal sheet with a first and second surface. A metal oxide layer is formed on the first surface of the sheet and a combustion catalyst is impregnated into the metal oxide layer. A source of fuel and air is then supplied to the first side of the metal sheet resulting in catalytic combustion which heats the metal sheet. The metal sheet can serve as a cooking stove.

BACKGROUND

I. Field of Use

The present invention relates generally to heaters and, more particularly, to a heater using catalytic combustion and serving as a cooking stove.

II. Description of Related Art

Mobile cooking stoves are necessarily required by the military for use in field operations. The current cooking stove used by the military is the Modern Burner Unit which utilizes conventional combustion to heat the stovetop surface.

The Modern Burner Unit, however, suffers from a number of disadvantages. First, the Modern Burner Unit is loud and releases carbon monoxide in operation. As such, the stove must be properly ventilated in order to ensure the safety of those in proximity to the stove.

The Modern Burner Unit is also inefficient in operation. This inefficiency results from the use of conventional combustion to heat the stovetop surface.

SUMMARY

The present invention provides a heater which may be used as a cooking stove which overcomes the above mentioned disadvantages of the previously known devices.

In brief, the heater of the present invention comprises a metal sheet having a first and second surface. In embodiments, the sheet may, for example, be constructed of aluminum or titanium.

A thick metal oxide layer is formed on the first surface of the sheet. This thick metal oxide may be formed by anodization or cathodization to form a thick porous layer of the metal oxide, or alumina where the metal sheet is made of aluminum.

A combustion catalyst is impregnated within the metal oxide layer. The combustion catalyst preferably comprises platinum or rhodium although other types of combustion catalysts may be alternatively used.

A source of fuel as well as air is then supplied to the first surface of the sheet. The fuel, preferably JP-8 jet fuel, interacts with the catalyst in the metal oxide layer and undergoes catalytic combustion. Such catalytic combustion is highly efficient and reduces, or altogether eliminates, noxious oxide emissions such as carbon monoxide. In practice, the catalytic combustion generates sufficient heat so that the metal sheet can serve as a cooking stove.

With reference first toFIG. 1, a heater10in accordance with the present invention is illustrated. The heater10includes a housing12having an upper and generally circular housing top14supported by an elongated and vertically extending leg16. The housing12may be either of a one-piece or multi-piece construction and may be constructed of any suitable rigid material provided, however, that the housing top14be able to withstand relatively high temperatures of the type used in cooking food.

Preferably, however, the housing top14includes an upper ring15and lower ring17. The rings15and17are separated from each other by a plurality of annular spacers19(FIG. 1) which form a slot24for exhaust gases around the housing top14. A threaded fastener21(FIG. 1) extends through each spacer19and secures the rings15and17together.

A metal sheet18is supported in the housing top14in any conventional fashion and so that a chamber20is formed between the metal sheet18and a base22of the housing top14. The metal sheet18is preferably constructed of aluminum and includes a first side26which forms a top wall of the chamber20, and a second side28which is open exteriorly of the housing12. The first side26of the metal sheet is covered with a thick oxide layer of the same metal forming the sheet18. Thus, where the sheet18is constructed of aluminum, the oxide layer30is formed of alumina.

Any conventional means may be used to form the oxide layer30on the first side26of the metal sheet18. However, in the preferred form of the invention, the oxide layer30is formed by cathodization which produces not only a thick, but also a porous layer30of oxide. Other methods, such as anodization, may also be used to form the oxide layer30.

EXAMPLE

The aluminum6061wafers were obtained which have a 100 mm diameter and were cut from a 0.813 mm thick sheet. The wafers were obtained polished on one side with a #8 polish (roughness of 20 to 30 nm) and the other side bare. The polished side was either obtained with a type 2 anodization, or anodized or cathodized according to the variables below.

The wafers were prepped with a multi-step cleaning process (chemical polishing). First, they were sprayed with acetone, then iso-propanol alcohol. Next, they were soaked in 5% NaOH solution for two minutes and then in 25% HNO3solution for one minute (Raj & Mumjitha, 2014).

For in-house cathodization, the following parameters were kept constant. The electrolyte was 1.0 M oxalic acid (H2C2O4). The temperature was not controlled because it has almost no effect on the alumina pore density. Two variables were tested to find the effect on structural features. The times tested were 20, 40, 60, 80, and 100 minutes. The current densities were 1, 2, 3, 4, and 5 A/dm2. Current flowed into a strip of aluminum foil, then the aluminum wafer, next oxalic acid electrolyte, and into the gold wire; this process deposited a layer of porous aluminum oxide onto the aluminum wafer. In embodiments, the cathodization takes place at from about 2 to about 6 A/dm2 and for about 60 to 100 minutes.

For in-house anodization comparison, the wafer was anodized at 0.87 A/dm2and 80 minutes. The electrochemical circuit was just the opposite of that cathodization.

After anodization or cathodization, the samples were washed with deionized water. Next, the samples were impregnated with a platinum (IV) nitrate solution. The wafers were then put into the furnace at 500° C. to create a platinum (IV) oxide catalyst layer.

The oxide layer30is impregnated with a catalyst designed to form a catalytic combustion with hydrocarbon fuel. Any conventional catalyst such as platinum or rhodium may be used to impregnate the metal oxide layer30.

Referring again toFIG. 1, a fuel supply passageway32is formed through the housing support leg16so that an upper end of the fuel supply passageway32is open to the chamber20. The other end of the fuel passageway32is fluidly connected to a pressurized source36of hydrocarbon fuel, such as JP-8 jet fuel.

An annular air passageway38surrounds the fuel passageway32and fluidly communicates with ambient air through an air inlet41. Air flowing through the air inlet41and air passageway38intermixes with the vaporized fuel from the fuel source36in an alumina porous mixing foam42immediately below the chamber20. This construction ensures full intermixing of the air and the fuel as the air/fuel mixture enters into the chamber20and impinges against the metal oxide layer30.

A heating element40is attached to the housing leg16so that the heating tape40surrounds a portion of both the air passageway38and the fuel passageway32. This heating tape40preheats the air and vaporizes the fuel prior to the introduction of the fuel/air mixture into the chamber20and against the oxide layer30to a temperature sufficient to initiate catalytic combustion. Once catalytic combustion is initiated, the catalytic combustion heats the metal sheet18in the desired fashion while the exhaust products from the catalytic combustion exhaust through the exhaust passageways24in the housing top14. However, since the catalytic combustion is much more efficient than conventional hydrocarbon combustion, the emission of noxious gases, such as carbon monoxide, is either greatly reduced or eliminated altogether.

In practice, the heater10of the present invention may be used as a cooking stove and is particularly useful for applications such as mobile military use. Other applications for the heater10, however, are clearly within the scope of this invention. For example, the heater of the present invention could be in the form of a heated pot which is used for cooking.

From the foregoing, it can be seen that the present invention provides a heater, which is particularly useful as a mobile military stove, which is not only efficient in operation, but eliminates the noxious gases from the previously known mobile military stoves. Having described my invention, however, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.