Surface decondensation system

Abstract

The invention relates to a system for decondensing a surface. According to the invention, the system comprises at least one light source capable of emitting infrared radiation of a given wavelength, to locally heat said surface in order to prevent the formation of condensation or to cause its disappearance. Figure for the abstract: Fig. 3

Description

Title of the invention: Surface decondensation system

[0001] The present invention relates to a surface decondensation system. Such a system is particularly but not exclusively suitable for the decondensation of certain surfaces of a motor vehicle, subject to condensation, such as, for example, the transparent glass of lighting parts. Condensation is a natural phenomenon that occurs when warm air laden with moisture comes into contact with a cold surface. This surface locally cools the air in contact with it. However, cold air is capable of transporting less moisture than warm air. As a result, the air deposits its excess water on the cold surface, causing the formation of micro droplets of liquid water, or even the formation of a film of liquid water.

[0003] Automotive lighting parts with their transparent glass, which is a very fashionable design trend at the moment, are subject to this phenomenon. However, the presence of these water droplets on the lighting parts gives the impression that these parts have a manufacturing defect and contributes to degrading their visual appearance. As a result, customers may be put off by the idea of ​​acquiring a vehicle whose lighting parts are covered in condensation.

[0004] In the past, vehicle lighting devices involved bulbs operating from a filament. The passage of electric current in the filament caused the said filament to heat up, which then behaved like a gray body. This local heating had the consequence of generating a lot of heat and therefore rapidly heating the air in the lighting device, reducing or even preventing the formation of condensation in said lighting device. This solution is certainly effective but results in high electricity consumption.

[0005] Since the 1990s, lighting devices in motor vehicles have gradually been switching to LEDs as light sources, to the detriment of bulbs. However, since LEDs heat up much less than bulbs, the phenomenon of condensation in lighting devices remains present if no special measures are taken to prevent its formation.

[0006] A solution currently used to prevent the formation of condensation is the application of a specific anti-condensation varnish to transparent parts subject to condensation deposits, and for which condensation is problematic. These varnishes act on the surface tension of the water so that the latter forms a continuous film in thickness on the surface, thus making the condensation invisible. These varnishes can be divided into two categories: - Yes, they are very effective but their high surface tension causes in case heat their agglomeration and the formation of whitish deposits or unsightly drips, - Either their surface tension is not optimal to avoid this problem, but their effect dissipates over time, after a few years. This solution gives the customer a feeling of being cheated, with the appearance of a breakdown after the warranty period.

[0007] A decondensation system according to the invention makes it possible to prevent the formation of condensation or to eliminate it quickly when it has already formed, while being barely visible to the consumer, consuming little energy, quick to implement and adaptable to a large number of configurations.

[0008] The invention relates to a system for decondensing a surface to be decondensed.

[0009] According to the invention, the system comprises at least one light source capable of emitting infrared radiation having a given wavelength, in order to locally heat said surface and prevent the formation of condensation or cause it to disappear. Such a method thus makes it possible to prevent the formation of condensation on the surface of an object which is subject to the deposition of condensation or to quickly remove condensation which may have been deposited on said surface. The term "rapidly" means "in a few seconds". The principle of a method according to the invention consists of the use of at least one light source capable of emitting infrared radiation, in order to locally heat the surface on which it is desired to prevent the formation of condensation or cause it to disappear.The idea is not to heat the entire volume of air or the entire thickness of transparent material, but to locally heat the water formed by condensation and / or the surface of the material on which condensation is likely to occur, so that the air placed near said surface is also heated. This results in an increase in its dew point, and therefore by equilibrium of local partial vapors, the air will absorb part of the water or not have to discharge part of its humidity at the location where the decondensation system is located. In the case where condensation has already deposited on the surface, the wavelength of the infrared radiation is chosen to generate maximum absorption so that a maximum of light passing through the film of liquid water is absorbed and therefore it absorbs a maximum of energy for maximum efficiency.To maximize the operation of the decondensation system according to the invention in terms of speed and energy efficiency, it is essential to carefully choose the wavelength to be used. The light source capable of emitting infrared radiation may, for example, consist of at least one LED, or a laser, or at least one SLED.

[0010] According to a possible characteristic of the invention, the wavelength of the radiation infrared emitted by said at least one light source is centered on 1.45pm and / or 3pm.

[0011] Another subject of the invention is an assembly comprising a decondensation system according to the invention and a surface to be decondensed.

[0012] According to the invention, the surface to be decondensed belongs to a wall made of a material having good resistance to infrared radiation over time and maximum absorption for the chosen wavelength. In this way, the infrared light emitted by the light source will heat the material of the wall in order to prevent the formation of condensation or cause it to disappear if the condensation has already deposited on the surface. The heating of the wall will be added to the direct local heating generated by the light source capable of emitting infrared radiation, to prevent the formation of condensation or cause it to disappear.

[0013] According to a possible characteristic of the invention, the material of the wall is a polycarbonate to which at least one colorant has been added to make it more absorbent for the chosen wavelength. Indeed, the polycarbonate may have undergone a treatment to increase its capacity to be heated more easily by the infrared radiation emitted by the light source.

[0014] According to a possible characteristic of the invention, the material of the wall is a polycarbonate to which at least one additive has been added to make it more absorbent for the chosen wavelength. This additive may for example be chosen from the following elements: LaB6, NdB6, PrB6, CeB6, GdB6, TbB6, DyB6, HoB6, YB6, SmB6, EuB6, LaB6, TmB6, YbB6, LuB6, SrB6, TiB2, ZrB2, HfB2, VB2, TaB2, CrB, CrB2, MoB2, Mo2B5, MoB, W2B5, K(WO3)3, Rb(WO3)3, Cs(WO3)3, Tl(WO3)3. This additive will have effects similar to those caused by coloring the polycarbonate, in terms of the temperature rise of said polycarbonate under the effect of infrared radiation.

[0015] According to a possible characteristic of the invention, the wall delimits an enclosed space, in which said at least one light source capable of emitting infrared radiation is placed. This enclosed space may for example be constituted by the internal space of a lighting part of a vehicle.

[0016] According to a possible characteristic of the invention, the assembly constitutes a lighting device for a vehicle, at least one LED capable of emitting white light being placed in the enclosed space delimited by the wall. In this way, the light source capable of emitting infrared radiation can be positioned next to the LED capable of emitting white light or can be embedded among several LEDs capable of emitting white light.

[0017] According to a possible characteristic of the invention, an optical system is inserted between the light source emitting infrared radiation and the surface to be decondensed in order to modify the orientation of said radiation, its intensity as well as its geometry. This system may for example comprise at least one element to be chosen from an optical lens and a mirror.

[0018] Another subject of the invention is a method for decondensing a surface by means of a decondensation system according to the invention.

[0019] According to the invention, the method comprises the following steps: -A step of placing at least one light source capable of emitting infrared radiation near an area of ​​the surface to be decondensed, -A step of activating the light source, -A step of decondensation of said zone.

[0020] For such a method, said at least one light source capable of emitting infrared radiation is oriented as precisely as possible in order to direct said radiation towards the area of ​​the surface to be decondensed. Such a method aims either to prevent the formation of condensation on the surface of a wall which would be subject to a potential deposit of condensation, or to cause the disappearance of condensation if it had already been deposited on said surface.

[0021] A decondensation system according to the invention has the advantage of not requiring a significant energy source to power the light source intended to emit the infrared radiation, since very often this light source will be constituted by an LED. It also has the advantage of being particularly effective because it makes it possible to heat the surface of a wall in a few seconds to prevent the formation of condensation, or to cause the disappearance of condensation which would have deposited on said surface. A method according to the invention has the advantage of being simple to implement by limiting the number of parts involved, and of not requiring any particular clearance space, due to the reduced dimensions of the light source capable of emitting infrared radiation.

[0022] A detailed description of a preferred embodiment of a method according to the invention is given below with reference to the following figures:

[0023] [Fig.l] represents a diagram of the absorbed humidity as a function of the temperature,

[0024] [Fig.2] represents a diagram of the absorption of water as a function of the wavelength of the emitted radiation,

[0025] [Fig.3] represents the percentage of radiation transmitted through a thickness of polycarbonate as a function of the wavelength,

[0026] [Fig.4] represents the percentage of radiation transmitted through a 3mm thickness of plexiglass as a function of the wavelength,

[0027] In a motor vehicle, certain parts are subject to the deposit of condensation. As a reminder, condensation is a natural phenomenon which occurs when warm air laden with moisture comes into contact with a cold surface of a wall of an object. This surface locally cools the air in contact with it. However, cold air is able to carry less moisture than warm air. As a result, the air deposits its excess water on the cold surface, generating the formation of micro water droplets, or even a film of liquid water.

[0028] Automotive lighting parts with their transparent glass are subject to this phenomenon. However, the presence of these water droplets on the lighting parts gives the impression that these parts have a manufacturing defect and contributes to degrading their visual appearance. As a result, customers may be put off by the idea of ​​acquiring a vehicle whose lighting parts are covered in condensation.

[0029] A decondensation system according to the invention makes it possible either to prevent the formation of condensation on a wall of an object, or to remove this condensation, which would have inadvertently deposited on this wall. To allow this decondensation, a system according to the invention comprises at least one light source capable of emitting invisible infrared radiation towards an area of ​​a wall of an object, which would be subject to the deposition of condensation. This light source can for example be constituted by at least one LED, by a laser or by at least one SLED.

[0030] For the remainder of the description, we will consider that the light source capable of emitting infrared radiation is represented by an LED.

[0031] Referring to [Fig.2], it is preferable to choose an invisible wavelength for regulatory compatibility reasons, either in the ultraviolet or infrared. The choice fell on infrared, because it causes less problems with plastic materials, and it is less dangerous for human health than ultraviolet which can cause skin cancer. In addition, the manufacture of infrared LEDs is more common.

[0032] In the context of a vehicle lighting device, delimited at least partially by a transparent wall, the LED capable of emitting in the infrared is placed inside the transparent wall, being either placed next to an LED capable of emitting white light, or embedded in the middle of a plurality of LEDs capable of emitting white light.

[0033] The use of infrared light sources makes it possible to locally heat the surface on which we want to prevent condensation from forming or disappearing. The idea is not to heat the entire volume of air or the entire thickness of transparent material. By using infrared, we can heat the water from the condensation and / or the surface of the wall material on which condensation is likely to be deposited, so that the air near said wall is also heated. This has the consequence of increasing its dew point, and therefore by balancing the local partial vapors, the air will absorb some of the water or not have to discharge some of its moisture at the location of the decondensation system.

[0034] To maximize the efficiency of the decondensation system, it is essential to carefully choose the wavelength at which the infrared LED will emit.

[0035] The wavelength is chosen to correspond to a maximum absorption so that a maximum of light passing through the water film is absorbed. For the wall whose surface is subject to the formation of condensation, a material transparent in the visible is also chosen so that it too has good resistance to infrared radiation over time, and that it generates a maximum absorption for the chosen wavelength. In this way, the infrared radiation will heat the surface where condensation is likely to be deposited, in order to prevent the formation of condensation. In the case where a water film has already been deposited on the wall, the IR radiation produced by the LED will be absorbed by said film and contribute to its disappearance. Part of the IR radiation will also be transmitted to the wall, which will then locally heat up by absorbing said radiation.The combined effects of the heating generated directly by the radiation on the water film and the heating by conduction generated by the wall on said film, will make it possible to make said water film disappear quickly and completely.

[0036] Referring to Figures 3 and 4, a material commonly used to constitute the transparent wall of an automobile headlight is polycarbonate or PMMA (polymethyl methacrylate) also called PLEXIGLAS. However, it is realized that for radiation having a wavelength of 1.45 pm corresponding to a water absorption peak, the transmission of the radiation by these materials is of the order of 80%, demonstrating that these materials are not very absorbent and are therefore quite ineffective with regard to the formation of condensation or with respect to its disappearance. In order to improve the absorption performance of these materials with regard to infrared radiation, dyes or additives can be added to them to reduce the transmission of the radiation and bring it back to a low value, for example less than 20%.

[0037] More generally, water absorption peaks are observed for radiation having wavelengths equal to 1.45 pm, 2.0 pm and 3.0 pm.

[0038] To obtain radiation with a wavelength of 1.45pm, Er: Glass (Erbium laser) or InGaAs-based technologies can be used, or in a combination of the two.

[0039] To obtain radiation with a wavelength of 3.0pm, technologies based on Er:YAG lasers used by dentists for their wavelengths absorbed by water can be used. When pumped at 980nm, Er:YAG has a greater tendency to emit around 1.5pm and 3.0pm, and its use is common in telecommunications.

[0040] Once the source has been chosen to emit radiation having a given wavelength, a polycarbonate transparent in the visible is selected to which an additive is added to make it absorbent at wavelengths greater than 1.2 pm and especially at the wavelengths of the Er:YAG laser.

[0041] Between the LED capable of emitting IR radiation and the wall, one of the surfaces of which is affected by a potential condensation deposit, optical systems such as, for example, mirrors, deflectors or lenses may be interposed in order to adjust the intensity of the emitted radiation and its orientation in space.

[0042] Referring to [Fig.l], we can calculate the power which is necessary to remove condensation which may have deposited on the surface of a wall.

[0043] According to the graph, for a 10°C increase in ambient temperature between +5°C and +15°C, the air's capacity to contain moisture increases from 5gr / kg to 10gr / kg. However, the glass of a projector has an approximate surface area of ​​200cm2 and the water film is 5pm. The mass of water present on the projector's glass is therefore 1gr.

[0044] It therefore takes 10 calories to raise the temperature by 10°C, or 42 Joules.

[0045] Water has an absorption of 104 / m at 1.5pm and 106 / m at 3.0pm. Via Beer's law- Lambert we obtain that at 1.5pm, 90% of the light is transmitted by the water film, and that at 3.0pm only 4.5 per ten thousandths are transmitted.

[0046] If we impose the constraint that the increase must be done in 10s, we then have

[0047] At 1.5pm: 42[J] / 0.1[%] / 10[s] = 42W.

[0048] So with an efficiency of 85% of the reflector, 50W of optical power is needed for 10 seconds to raise the water film by 10°C.

[0049] At 3.0pm: 45[J] / 1[%] / 10[s]= 4.5W.

[0050] On the same principle, it is necessary to count 5W optical for 10 seconds to raise the water film by 10°C.

[0051] We will therefore select a source for these values ​​at 3.0pm and we can estimate that the system will consume 15W for 10 seconds to make the condensation disappear and then switch to a mode which simply maintains the temperature while the motor and the LEDs have sufficiently heated the air in the lighting room.

Claims

Claims

1. Assembly comprising a decondensation system and a surface to be decondensed, said system comprising at least one light source capable of emitting infrared radiation having a given wavelength, in order to locally heat said surface and prevent the formation of condensation or cause it to disappear, the surface to be decondensed belonging to a wall made of a material having good resistance to infrared radiation over time and maximum absorption for the chosen wavelength, characterized in that the material of the wall is a polycarbonate to which at least one colorant has been added to make it more absorbent for the chosen wavelength.

2. Decondensation assembly according to claim 1, characterized in that the wavelength of the infrared radiation emitted by said at least one light source is centered on 1.45pm or 3pm.

3. Decondensation assembly according to any one of claims 1 or 2, characterized in that the light source is to be chosen from at least one LED, a laser and at least one SLED.

4. Assembly according to any one of claims 1 to 3, characterized in that the material of the wall is a polycarbonate to which at least one additive has been added to make it more absorbent for the chosen wavelength.

5. Assembly according to any one of claims 1 to 4, characterized in that the wall delimits an enclosed space, in which said at least one light source capable of emitting infrared radiation is placed.

6. Assembly according to claim 5, characterized in that it constitutes a lighting device for a vehicle, at least one LED capable of emitting white light being placed in the enclosed space delimited by the wall.

7. Assembly according to any one of claims 1 to 6, characterized in that an optical system is inserted between the source emitting infrared radiation and the surface to be decondensed in order to modify the orientation of said radiation, its intensity as well as its geometry.

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