Rapid vapor generator

Details Rapid vapor generator Rapid vapor generator

1999-04-20

2001-01-02

Paik, Sang (Department: 3742)

Electric resistance heating devices

Heating devices

Vaporizer

C261S142000, C261S094000

Utility Patent

active

06169852

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to apparatus for the rapid vaporization of a subcooled liquid, and more specifically, to a rapid vapor generators, as may be used in humidity control, steam cooking, steam hair setting, steam skin therapy, steam iron, and the like.
BACKGROUND OF THE INVENTION
There are many circumstances in which, it is desirable to produce saturated or superheated steam instantaneously. For instance, the control of the humidity in an air-conditioned space usually requires a steam supply to have a fast startup and cut-off response. Other circumstances in which it is desirable to obtain steam instantaneously include steam body and skin therapy, steam cooking, steam hair setting, and steam iron. Further applications of high speed steam generators include steam boilers and vapor generators in other technological and engineering processes.
An electrically-energized steam generator is usually designed such that one or more electric heaters are immersed in a water container to heat up subcooled liquid to saturated or superheated vapor. One of the major drawbacks of such a design is that it takes a rather long time for subcooled water to be vaporized because the process of heating up a large volume of water in the whole container from the subcooled liquid state to the saturated state is usually slow. In order to generate steam instantaneously, in some applications the water in the container has to be maintained at the saturated state by heaters at all times. As will be apparent, this will cause an extra consumption of energy due to the heat losses to ambient.
A variety of techniques have been developed to speed up the vaporization of liquid in a vapor generator. The most relevant technique to the present invention is to use a porous body as the evaporating surface. Examples of the porous-media steam generators can be found U.S. Pat. No. 3,672,568, U.S. Pat. No. 4,020,321, U.S. Pat. No. 4,266,116, U.S. Pat. No. 4,748,314, U.S. Pat. No. 4,924,068, and U.S. Pat. No. 5,014,337. One prior art device (such as U.S. Pat. No. 3,672,568 and U.S. Pat. No. 4,924,068) consists of one or several electrical heaters housed in a porous body plunged wholly or partially in the liquid to be vaporized. When the liquid impregnated in the porous body is heated by the heaters to the boiling point, vapor is generated therein and, under the effect of capillary force developed in the porous body, migrates from the porous body to the vapor exit. Meanwhile, subcooled liquid is continuously pumped into the porous body. Another prior art device (U.S. Pat. No. 4,020,321, U.S. Pat. No. 4,266,116, U.S. Pat. No. 4,748,314, and U.S. Pat. No. 5,014,337) is the so-called electrode-type which comprises a pair of cylindrical or concentric prismatic electrodes connected to the terminals of an electrical energy source. A porous body, saturated with the saline solution, is clamped by two parallel electrode plates. The saline solution is directly heated by the electrical current passing through it. These two types of porous-media steam generator have a shorter period for the subcooled liquid to reach its boiling point as compared to the steam generator without a porous medium.
However, the reduction of vaporization time is still limited because the whole amount of liquid impregnated in the porous body is needed to be heated up before vaporization. For instance, for one prior art device (U.S. Pat. No. 5,014,337) having a 1.5 kW heating power, it takes 2 minutes for subcooled water at the room temperature to be vaporized. In addition, these two types of steam generators have a large heating surface, leading to a large heat losses to the ambient. Furthermore, the second type of the steam generators usually needs a special device (such as a pump) to impregnate liquid in the porous body. A special consideration is also needed for the problem of electrical insulation because the porous body and the liquid are energized directly. For these reasons, this type of steam generator usually has a rather complicated configuration.
SUMMARY OF THE INVENTION
According to the present invention there is provided a vapor generator comprising, a liquid reservoir, a porous medium in communication with said liquid reservoir, and heating means having a surface in contact with a surface of said porous medium, wherein the surface of said heating means in contact with said porous medium is provided with grooves to allow the escape of generated vapor.
In preferred embodiments of the invention the porous medium is contained within a housing and liquid is supplied to the medium from the reservoir at one end of the housing, and the heating means is supplied at an opposed end of the housing.
Preferably the housing is vertically arranged with the liquid being supplied at a lower end of the housing and the heating means being supplied at an upper end of the housing. In this way as liquid is vaporized at the contact between the porous medium and the heating element, liquid is drawn up through the porous medium and replenished at the bottom.
In a preferred form the heating means comprises a heating block formed with at least one electrical heating element, and wherein a surface of said block is in contact with the porous medium, the contacting surface being formed with a plurality of concentric grooves, and at least one radial groove interconnecting said concentric grooves, and the outermost of the concentric grooves being formed with a vapor discharge exit.
The heating element may be any form of suitable electrical heating element, such as for example a cartridge heating element or a film heating element. Means may be provided for controlling the power to the heating element so that at the start of operation it is run at a high power rating, and then subsequently at a lower power rating.
When the porous medium is disposed within a vertical housing, it may either extend not for the full height of the housing in which case a space will be defined beneath the porous medium for the supply of liquid, or it may extend for the full height of the housing and a liquid supply pipe may extend into the porous medium. In either case control means may be provided for maintaining the liquid level in the reservoir between predetermined upper and lower limits.
In another possible embodiment the vertical housing for the porous medium may be such that a lower end of the housing is located directly in the liquid reservoir.
In alternative embodiments of the invention the vapor generator may be tubular in construction. Either a tubular porous medium may be located within a tubular heating element, or conversely a tubular heating element may be located within a tubular porous medium. In either event the surface of the heating element contacting the porous medium is grooved to allow the escape and discharge of generated vapor, and preferably the grooves are axial such that vapor is discharged at an end of the vapor generator.


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