Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
2001-03-07
2002-05-21
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C392S471000
Reexamination Certificate
active
06393212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to steam generators and more particularly, relates to a compact, small volume steam generating system.
2. Background Information
Portable steam generating systems are used for steam cleaning in restaurant kitchens, hotel/motel bathrooms, public bathrooms, rest homes, hospitals, dental offices and related human services facilities. They are also used in industry for cleaning dirty and contaminated surfaces of oil and grease, and also for steam cleaning vehicle engines. Steam generating systems are also used for the removal of paint, wallpaper, graffiti, etc.
Heavy duty steam cleaning equipment has been available for many years for heavy and medium cleaning. However, a lengthy and in-depth study revealed almost a complete lack of small, portable, lightweight, low capacity steam cleaning equipment for small items and limited surface areas in confined spaces. To date, only a few foreign and United States companies supply such equipment.
The only U.S. producer of a low capacity steam cleaner was found to be a system that has a small tank (≈500 in
3
), having a 1,500 to 2,500 watt heater with a fill valve and a steam discharge valve as shown in FIG.
1
. The system also includes a pressure relief valve and a low water liquid level cut-off switch for safety purposes. The operating parameters provide a pressure up to 200 PSI, and a temperature up to 350° F. Generally, the water tank shown in
FIG. 1
has a capacity of approximately three quarts. The steam flow provided is in the range of about 0.005 to 0.007 gallons per minute (GPM). A problem with this type of system is that it can take up to thirty minutes from a cold start to reach operating temperature and pressure. Since the system is made to be portable, the water supply is intermittent at about three quarts per filling for a run time per filling of one to three hours.
This type of small, light weight and low capacity system has a number of operational limitations and one very serious safety problem. The system is limited by it's low water volume since only three quarts of water can be used at any one time, then the system must be powered down, pressure reduced to atmospheric and then refilled with fresh water. It also suffers with the problem of a long heat-up time; typically thirty minutes before any steam is generated. The steam tank, being a substantial size and having a water capacity of only three quarts, has a large, heavy, thick-walled and expensive certified steam pressure vessel.
The serious safety problem is because the super-heated steam/hot water combination can explode to a substantial volume if a tank failure occurs. Generally, the steam explosion can be on the order of 200 times the tank volume. A typical commercial unit, as shown in
FIG. 1
, has a 7″×13″ cylindrical tank with a volume of 500 cubic inches, which could produce a steam plume of approximately 100,000 cubic inches (expansion ratio of 200) which is of sufficient size to injure anyone within 4 to 5 feet of the tank wall. A 7″×13″ tank with a standard wall thickness of 0.034 inches, 304 type stainless steel has a Barlow burst pressure of approximately 2,400 pounds per square inch (PSI) and a safety factor of approximately twelve (12). Using a flat welded end of the pressure tank can reduce the safety factor to below 3.
The end result of a study of existing small portable steam cleaners is as follows: 1) All units are heavy and bulky. 2) Have severely limited water supplies. 3) Units must be shutdown, depressurized and cooled to replace the water supply. 4) Units must use expensive heavy wall tanks to contain super-heated steam. 5) Have lengthy (≈30 minute) start-up times. 6) Require tank certification to steam boiler codes. 7) Contain from three quarts or one to 6 pounds of super-heated steam during operation. 8) Have operating energy potential to expand explosively if ruptured with concomitant injury to operating personnel and nearby persons.
Therefore, it is one object of the present invention to provide an efficient steam generator that is small in size and has an extremely low (≈2×10
−6
Gal or 2×10
−5
lbs) super-heated steam volume in the boiler at any given time during operation.
Still another object of the present invention is to provide a steam generating system that can be light in weight, yet provide unlimited continuous supply of steam.
Yet another object of the present invention is to provide a steam generating system that has an extremely short transient heat-up time. For example, a steam generating time of three to five minutes from a cold start.
Yet another advantageous object of the invention is to provide a light weight, low capacity steam generating system that can be refilled while in use, thus providing continuous steam supply.
Yet another object of the present invention is to provide a light weight, low volume steam generator that has a design that is inherently fail safe because it has a cylinder rupture safety factor many times larger (S.F. ≈39) than that of present systems.
Still another object of the present invention is to provide a light weight, low capacity steam generator system that has a reduction in operating super-heated steam weight by a factor of approximately 0.5 million.
Still another object of the present invention is to provide a light weight, low capacity steam generating system that has the important major inherent safety design feature of a continuous open ended flow from the water supply to the steam generator to the outside world.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system that includes a method of preventing water droplets from being ejected with the steam from the system.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system that includes an extension at the outlet that minimizes ejection of water droplets into the steam.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system having an end formed on the extension that minimizes the injection of water droplets into the steam.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a method of maintaining the temperature and pressure of the super-heated steam from the steam generator outlet to a cleaning tool.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a special coaxial output hose configured to substantially reduce steam heat loss to the atmosphere during transportation of steam from the steam generating cylinder to an application tool or brush.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system having an insulation plastic tube over a smaller diameter Teflon tube as a thermal insulator to physically shield and protect against abrasion during use.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a small diameter, output tube wound around a steam generating cylinder to maintain the temperature of the super-heated steam and increase the thermal conductivity from the outlet to the application tool or brush.
BRIEF DESCRIPTION OF THE INVENTION
The purpose of the present invention is to provide a light weight, low capacity steam generating system that is very portable and safe to use. The present invention addresses and solves all eight deficiencies of current small portable production steam cleaning units listed above.
The invention described uses two different applications based upon a single approach to efficiently and rapidly transfer heat energy from a hot source to a body of water or related type fluid. The hot source is normally a resistive wire (nichrome, etc.) coil or hot gas such as a methane gas heater flame. While the disclosure is focused upon electric
Campbell Thor
Harwil Corporation
O'Reilly David
Walberg Teresa
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