Electric resistance heating devices – Heating devices – Vaporizer
Reexamination Certificate
1999-10-08
2002-01-15
Paik, Sang (Department: 3742)
Electric resistance heating devices
Heating devices
Vaporizer
C269S139000
Reexamination Certificate
active
06339678
ABSTRACT:
The invention relates to a method for vaporising and super-heating a sterilising agent, in which the sterilising agent is brought to a first temperature and vaporised with the aid of a heated surface, and the vapour is subsequently to brought a second, higher temperature and super-heated by heating elements.
The invention also relates to a device of this type, which is provided with a vaporising chamber and a heater with super-heating channels and heating elements connected after said vaporising chamber.
It is known to vaporise and to super-heat liquids, and in particular water, for many purposes. With this, moist vapour is produced in a first container or boiler by heating the liquid. The vapour is subsequently conducted into a second container or boiler which, without increasing pressure, super-heats the vapour, that is to say heats it above the boiling point of the liquid, so that the vapour leaving this boiler is super-heated and can be described as dry vapour.
There are various liquids similar to water which can be subjected to such methods, as required. For example, it is desirable from time to time to super-heat sterilising agent in order to apply it as super-heated vapour to surfaces to be sterilised. The known methods and devices for producing super-heated sterilising vapours have the disadvantage that they are expensive, require a relatively large amount of heat and can only be produced in devices which take up a large amount of space.
The object of the invention is therefore to simplify the known methods and make them more effective, and to use technically more simple and more compact components for the device.
With respect to the method, the solution of the object according to the invention is in that
a) the sterilising agent is sprayed onto the heated surface, which is heated to a first temperature,
b) which is lower than the surface temperature at which film boiling begins,
c) the first temperature of the heated surface is sensed and converted into signals for controlling the heating elements for super-heating, and
d) the sterilising agent vapour is heated in a counter flow such that the first temperature is kept substantially constant by means of the second, higher temperature and by means of a flow of heat directed in the opposite direction to the flow of vapour.
While with the known methods and devices for producing super-heated sterilising agents, the heated surface can be said to be the internal surface of the container in which the liquid is boiled, or, in the case of a boiler, is the internal surface of pipes on or in which the liquid to be heated and vaporised lies, in accordance with the invention, the sterilising agent is brought into contact with the heated surface by means of sprays. The solid mass of liquid therefore does not come into contact with the heated surface, but instead only a mist of sterilising agent, that is to say a large member of finely distributed droplets. In this way the active surface of the flowable sterilising agent is significantly increased, and the heat transfer from the heated surface to the respective liquid droplets is improved.
When the first temperature described of this heated surface is now lower than the surface temperature at which film boiling of the sterilising agent concerned begins, the total thermal balance is particularly advantageous for reasons which will be explained hereinafter. According to the method in accordance with the invention, a significantly smaller quantity of heat is needed for vaporising and super-heating the sterilising agent, and in this way energy can be saved. Because the temperature of the so-called heated surface is kept within the range described, a high thermal gradient is guaranteed and thereby a large flow of heat to the heated surface from the heater deliberately arranged at a distance from the heated surface.
This heating can be advantageously controlled and used for regulating the method according to the invention when a temperature sensor produces signals corresponding to the first temperature of the heated surface, with which the heating elements can be regulated for super-heating. In other words, a quantity of heat is constantly produced by the heating elements such that it flows towards the heated surface and keeps it at the temperature previously described.
The many small droplets of the initially flowable sterilising agent are vaporised on the heated surface, and this vapour flows, influenced by the pressure differential, in a direction which is counter to the direction of the flow of heat. In this way, the sterilising agent vapour is heated in a counter-flow by means of the novel method. Advantageously, the first temperature of the heated surface is maintained at the correct level by means of a second, higher temperature in the downstream area of the method, because the heat flow is produced counter to the direction of the flow of vapour. In this way the heated surface can be kept at the desired first temperature.
By means of the method according to the invention, the optimum temperature of the heated surface is obtained for vaporising the mist droplets of sterilising agent. It is very important to find the correct temperature of the heated surface, to set it and to keep it at the correct value during operation. From a diagram which will be explained hereinafter, it is evident that theoretically, given the optimum temperature of the heated surface, a relatively large amount of heat can be transferred from the heated surface to the mist droplets of sterilising agent. In operation, the applicant has previously carried out other experiments with other heating methods, and for example, attempted vaporisation and super-heating by means of hot air with different temperatures. The degree of effectiveness of such methods remains far below that according to the method according to the invention, however.
If now, by following the teaching according to the invention, a high degree of heat emission is obtained on the up-stream heated surface, large quantities of flowable sterilising agent can be vaporised per unit time. With correct adjustment of the heating elements, that is to say with a correct temperature of the super-heated vapour in the down-stream area of the method, a significantly lower heat flow into the vapour is obtained so that the amount of heat produced by the heating elements flows towards the heated surface in the opposite direction of flow to the flowing vapour. In this way the optimum temperature can be established and maintained in a very simple manner.
When, in an advantageous embodiment of the invention, the sterilising agent is hydrogen peroxide, the vaporisation method can be carried out under conditions similar to those for water to good effect. Clearly, hydrogen peroxide at different concentrations can be used. Hydrogen peroxide has similar characteristics to water with respect to temperature, vaporisation and super-heating properties.
It has been shown advantageous for carrying out the method according to the invention when, in a preferred embodiment, the first temperature of the heated surface is kept in the range of 100° C. to 150° C., preferably in the range of 120° C. to 140° C.
If the amount of heat which can be derived from the surface of the sterilising agent, measured in watts per square meter, is plotted on a diagram above a temperature difference formed from the current temperature minus the boiling point of the sterilising agent, measured in degrees Celsius, a first maximum is found for water at a current temperature of approximately 130° C. At this temperature the maximum amount of heat can thus be transferred from the heated surface to the sterilising agent.
The relationships are quite different at temperatures of, for example, 200° C. If the sterilising agent vapour is super-heated to such a temperature using the method according to the invention, that is to say by the action of the heating element, the diagram shows a greatly reduced amount of heat which can be transferred to the sterilising agent. The amount of heat produced by the heating ele
Paik Sang
Tetra Laval Holdings & Finance S.A.
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