Method and device for vaporizing a liquid reactant in manufacturing a glass preform

Field of the Invention

The The present invention relates to a method and an apparatus for evaporation of a liquid Reactant in an intermediate step of a process for Manufacturing an optical fiber, in particular in the step of producing a glass soot preform, drawn hereinafter to an optical fiber. To the glass soot preform manufacture, the vapor is Reactant to a burner for generating a stream of glass soot supplied to the is deposited on a deposition target.

State of the art

Optical fibers for telecommunications are usually high purity silica-based glass fibers drawn from glass preforms were, the preforms with different glass deposition techniques produced can be.

Some of these deposition techniques, including of the axial vapor deposition (Vapor deposition axially, VAD) and outside vapor deposition (Outside vapor deposition, OVD) require the use of a burner to produce the glass soot, which are deposited. This burner is usually a silica precursor such as eg SiCl₄, Together with combustion gases fed so that a fine glass particles (ie SiO₂) forming flux is produced at high temperature. This river is on a rotating target for growing a glass soot preform that directed, which has been consolidated thereafter to a glass preform to obtain. Optionally, the burner also a dopant such as GeCl₄ are supplied to the index of refraction the glass suited to change.

The different gases to the burner using a gas delivery system provided, includes what gas sources and pipe connections. It is important, a source of a glass precursor material to have, which is capable of the precursor material at a controlled Rate and without undesirable to generate temporal fluctuations.

Several Types of Gaszuführsystemen and gas sources are known in the art for such a purpose.

The <patcit><text>US-A-4,314,837</text></patcit> concerns a method for feeding of vaporous Starting materials in an oxidizing reaction flame or the like. Each component (eg SiO₂, GeO₂and B₂O₃) is in liquefied Form in a sealed container maintained, which is provided with a heater to raise the temperature of the liquid raise to a value which is sufficient to provide in the reservoir provide a predetermined vapor pressure. The resulting fumes are using individually controlled dosing devices transfer and appropriate conduits to the reaction device. Oxygen, the vapor-leading Line or added directly to the steam-using apparatus will. The reservoirs can commercially available pressure vessel be. The pressure in the reservoir is monitored and the thus obtained Information is used to control the operation of the heater. Mass flow control devices are provided in the different lines, so that the mass flow (Masssendurchsatz) vapors can be controlled.

Of the Applicant has verified that such a vaporizer has the drawback of non-desired Pressure fluctuations to subject. The Applicant has also observed, that the presence of these reservoirs in the laboratories in where researchers and technicians have to work, be dangerous because of Ausströmungsrisikos can. About that also noted the applicant, that the described system, the use of Mass flow control devices requires that expensive and fragile devices are and what along the vapor flow lines, ie used on hot points of the system be where it errors and faults are subjected. The Applicant also notes that these containers a relatively large Amount of liquid must contain and therefore are bulky.

The <patcit><text>US-A-5,707,415</text></patcit> disclosed an evaporator (thin film evaporator) for halide-free Silicon-containing liquid Reactants that are used to manufacture preforms. The evaporator contains a plurality of packed-bed columns, surround a central tube. A mixture of liquid reactants, such as Oktamethylzyklotetrasiloxan, and gas, such as oxygen, is a set of spray nozzles the tops of the columns sprayed. The liquid Reactants and the gas to flow downward together through the columns and are heated by hot oil, around the walls of the the columns around &lt;?page 3?&gt;flows. The liquid Reactant evaporates into the gas phase until the dew point temperature is reached at which the entire liquid reactant in vapor will be converted. The vapor / gas mixture exits the bottom the columns from where its flow direction changes from downward to upward. These Change of flow direction separates species with higher Molecular weight of the vapor / gas mixture. The vapor / gas mixture leaves the evaporator through a central tube and is generating the soot fed burners, where it is used to manufacture preforms.

The <patcit><text>US-A-5,078,092</text></patcit> refers to a system for delivering a liquid reactant at high Flow rates to an oxidation or flame used Glasrußabscheidungsstelle. A first liquid Reactants (TiCl₄) Is one on an inner surface Throttle steam chamber (flash evaporation chamber) performed to a thin film form, and is mixed after the evaporation of oxygen. additional vaporous Reactants (SiCl₄) Then the evaporated first liquid mixed, before they are fed to an oxidation / flame hydrolysis burner, order on a soot preform an outer cladding layer form of glass soot.

The inner surface the throttle steam chamber is formed by a heating element, whose Temperature is kept below the temperature at which a nucleate or film boiling of the liquid occurs.

The <patcit><text>US-A-5,356,451</text></patcit> concerns a method and apparatus for providing reaction vapors in an implementation body. The device comprises an evaporation chamber, of an upper and a lower wall, side walls and is enclosed by a first and second end wall. The first End wall is increased with respect to the second end wall. The reactant is in liquid Form supplied to a flow distributor, the liquid that leads to that part of the bottom wall near the first end wall. Of the Angle at which the bottom wall is inclined in relation to the horizontal is, is sufficient for the liquid, the bottom wall having flow down a rate can sufficient to form a film whose thickness is less than those thickness with which form during heating the film bubbles could (ie, no boiling occurs). The surface is heated to a temperature heated, as the larger the boiling point of the liquid is, whereby the liquid Reactant is converted into steam, the vapor is led to the place of use.

A Object of the present invention is to provide an alternative way provide from the evaporator, which ensures high evaporation rates, which is safe and has the reduced dimensions.

Summary of the Invention

Of the Applicant has found that it is possible to use a evaporation to obtain at a high rate in a small space by a liquid Reactant onto a heated surface along a limited by edges, predetermined path flow leaves, wherein the temperature of the surface, the height the edges and the flow rate of the liquid are such that evaporation in the region of Bläschensiedens or the film boiling takes place. The film and Bläschensiedebereiche are two of the possible boiling ranges a liquid, As is known from the prior art and will be explained later in greater detail. The technique for the evaporation of liquids in the present Invention may advantageously in a process with high Deposition rate the production of a glass soot preform are used, which consolidates and then to an optical Fiber can be drawn.

The Evaporation device that forms a the heated surface Evaporation plate and the evaporation plate covering cap for the includes collecting the vapor, can advantageously in another provided space than the liquid container , whereby the risks for the people working in the area of ​​the vaporization device technician be avoided.

According to a first aspect, the present invention thus relates to an A method for vaporizing liquid Reactants in a process for producing a glass soot preform, comprising forming a continuous stream of liquid reactant with a thickness to generate steam under film or Bläschensiedebedingungen sufficient; and heating the stream of liquid reactant at a temperature for generating steam under film or Bläschensiedebedingungen sufficient.

Of the Step of forming a continuous stream of liquid reactant preferably comprises continuously flowing the liquid reactant in a channel, the side walls limited &lt;?page 4?&gt;is the amount at least equal to the said thickness.

Furthermore comprises heating the flow the liquid Reactant comprises heating a surface delimiting said channel.

Advantageously, the method further comprises the steps of collecting the vapor, so as to achieve a predetermined pressure, and under this Pressure to perform stationary steam to a steam recovery point.

the The method may further the flowing the stream of liquid Reactant comprise in another channel on a positioned lower level with respect to said channel is.

According to a second aspect, the present invention relates to a Process for producing a preform glass comprising evaporating a liquid Reactant to generate a vapor reactant, the supply the vapor reactant to a burner for forming glass soot particles and depositing the glass soot particles on a deposition target to draw the glass preform, the step of vaporizing a liquid reactant according to the above performed procedures described is.

In a further aspect, the present invention relates to an evaporation plate for vaporizing a liquid reactant comprising an upper portion defining a vaporization surface and a plurality of walls, extending on the evaporation surface, comprising in order a liquid flow channel limiting, and another portion with a heating system to heat on the evaporation surface transferred to.

Prefers have the walls a height greater than the minimum thickness of SiCl₄ is that necessary is to generate vapor under film or Bläschensiedebedingungen.

Prefers is the evaporation plate, a metallic, disc-like Plate.

In a first embodiment includes the plurality of walls a plurality of concentric annular walls of a plurality Channel sectors limit, each of said annular walls having an opening, a liquid passage to allow from one channel sector to the other. In this embodiment, comprises the plurality of annular walls preferably at least a pair of annular walls having the respective openings, the diametrically opposite are positioned.

In Alternatively, possesses the channel has a spiral section.

Of the further portion suitable for connection to a heating system, is, can a seat (recording) form, adapted to receive a metal wire suitable is.

Of the Channel, at least one depression (a depression) in an end portion which have to remain remaining liquid collect, and the sink can with a respective liquid sensor keep in touch.

In a further aspect, the invention relates to a device for vaporizing a liquid reactant, comprising as described above, positioned horizontally Vaporizing plate for receiving the liquid reactant and to form a flow thereof, and a heating system connected to the evaporation plate and is for heating the liquid Reactant over a is suitable minimum temperature which is necessary to steam under Film or Bläschensiedebedingungen to create.

Prefers the apparatus further comprises a Flüssigkeitszuführer to supply the liquid Reactant to an evaporation surface of the evaporation plate, an over the surface positioned Cover for forming a vaporization chamber, the appropriate is to collect the vapor, and an outlet channel for the vapor for discharging from the evaporation chamber.

Of the includes Flüssigkeitszuführer preferably a liquid flow line, which is provided with a flow control valve.

&lt;?page 5?&gt;

The Device can advantageously have a in the vaporization chamber positioned pressure sensor and a control circuit comprising, around the Operation of the flow control valve according to a signal of the pressure sensor to regulate.

The Apparatus may also include at least a further vaporizing plate include, as described above, under the evaporating plate is positioned to a residual part of the flow of the liquid reactant from the evaporation plate to take, and at least one other comprise heating system connected to the further vaporizing plate is.

Brief Description of Drawings

<figref idrefs="S30">1</figref> is a schematic representation of a Glasrußabscheidungsvorrichtung that for producing a glass soot preform is used;

<figref idrefs="S30">2</figref> is a detailed illustration of the apparatus of <figref idrefs="S30">1</figref>;

<figref idrefs="S31">3</figref> shows an evaporator according to the present Invention;

<figref idrefs="S32">4</figref> is a top view of a vaporizing plate, which is part of the evaporator the <figref idrefs="S31">3</figref> is;

<figref idrefs="S32">5</figref> is a bottom view of the evaporating plate <figref idrefs="S32">4</figref>;

<figref idrefs="S33">6</figref> is a graph showing the different boiling ranges of a liquid shows;

<figref idrefs="S33">7</figref> shows another embodiment the vaporizing plate; and

<figref idrefs="S34">8th</figref> shows another embodiment of the evaporator.

description Preferred Embodiments Regarding <figref idrefs="S30">1</figref> is by reference numeral <figref>1</figref> as Whole a Glasrußabscheidungsvorrichtung refers to that in a method for producing a glass soot preform is used, the consolidated and then to an optical Fiber is drawn.

The deposition apparatus <figref>1</figref> comprises a pressure vessel <figref>2</figref>. which is suitable for a liquid Reactants (in particular a glass precursor material) to evaporate take, an evaporation unit <figref>3</figref> to evaporate the liquid Reactant and a burner <figref>4</figref> for receiving the vaporous Reactant from the evaporation unit <figref>3</figref> and Generating a stream of glass soot particles. Particularly the burner <figref>4</figref> adapted to produce a flame in which the vaporous Reactant is transformed into particles, which particles on a rotating target to grow the glass soot preform be deposited.

With in reference to <figref idrefs="S30">2</figref>That the deposition apparatus <figref>1</figref> detailed represents, comprises the evaporation unit <figref>3</figref> an evaporator <figref>7</figref>. for receiving the liquid of the Reactant through a first conduit <figref>5</figref> to the container <figref>2</figref> in liquid compound stands. Preferably, a flow control valve<figref>6</figref>, especially a mass flow meter (Mass flow meter (MFM)) along the line <figref>5</figref> positioned to control the flow of the captured liquid reactant to regulate. A valve<figref>11a</figref> can also on the line <figref>5</figref> at the End of the container <figref>2</figref> positioned be to the channel of the line <figref>5</figref> to open or close. The management <figref>5</figref> is preferably provided with two further valves <figref>11b</figref> and <figref>11c</figref> provided, at the input of the evaporation unit <figref>3</figref> downstream of the Flow Control Valve <figref>6</figref> or at the input of the evaporator <figref>7</figref> positioned are.

A second line <figref>8th</figref> connects the evaporator <figref>7</figref> With the burner <figref>4</figref> to the feed of the evaporator <figref>7</figref> exiting Vapor to the burner <figref>4</figref> to allow. The administration<figref>8th</figref> can at the evaporator outlet <figref>7</figref> with a valve <figref>11d</figref> provided be, which allows the vapor pressure in the evaporator <figref>7</figref> to regulate. About that addition, the second line is <figref>8th</figref> advantageously at a predetermined temperature (eg 100 ° C) is heated and preferably with a temperature sensor (not shown) for temperature control provided.

The Evaporation unit <figref>3</figref> preferably comprises a housing <figref>9</figref> With a first compartment <figref>9a</figref> for receiving the evaporator <figref>7</figref> and a second compartment <figref>9b</figref> for receiving the end portion of the with the evaporator <figref>7</figref> and the corresponding flow control valves jointed pipes, including the end of the line <figref>5</figref> and the valve <figref>6</figref>, The first and the second compartment<figref>9a</figref>. <figref>9b</figref> will preferably maintained at different temperatures, for example 90 ° C in the first subject <figref>9a</figref> and room temperature in the second compartment <figref>9b</figref>. and are connected to respective &lt;?page 6?&gt;blowers <figref>10</figref> provided, order to control the temperature therein.

Of the Flüssigkeitszuführtank <figref>2</figref> is advantageously in a different room from the housing <figref>9</figref> located, so in case of leakage from the tank <figref>2</figref> to avoid risks for the technicians. The burner <figref>4</figref> is typically located in a deposition chamber, which in the same room as the housing <figref>9</figref> or in a another room may be located.

Prefers comprises the evaporation unit <figref>3</figref> further a hydraulic rinse cycle for flushing the evaporator <figref>7</figref> and the various conduits of the deposition apparatus <figref>1</figref> after their use. The hydraulic flushing circuit comprises a source <figref>13</figref> with purge gas, such as N₂, And the source <figref>13</figref> With the line <figref>5</figref> connecting line <figref>14</figref>, The administration<figref>14</figref> can with a valve <figref>11e</figref> be provided that in the second compartment <figref>9b</figref> of housing <figref>9</figref> positioned is. Another line<figref>15</figref>Associated with the conduit <figref>14</figref> a associated T-Connector is communicating with the evaporator <figref>7</figref> in conjunction and is advantageously with a valve <figref>11f</figref> provided that in the second compartment <figref>9b</figref> of housing <figref>9</figref> positioned is. The evaporator<figref>7</figref> is also preferably using a drain pipe <figref>12</figref> connected to a drain line for draining operations (emptying processes). especially is the outlet pipe <figref>12</figref> having a first inlet of a two-way valve <figref>11g</figref> connected, the outlet of which is connected to the drain line and whose second inlet the passage of purge gas is that, for example, from the source <figref>13</figref> comes.

all Parts of the apparatus <figref>1</figref>Associated with the reaction partner, either in liquid or vapor form, can come into contact, are preferably made of electro polished stainless steel to To avoid entrainment of particles and corrosion.

With in reference to <figref idrefs="S31">3</figref> includes the evaporator <figref>7</figref> prefers a base support <figref>20</figref>. is suitable in a known manner (for example using bolts) on a horizontal wall <figref>29</figref> the housing <figref>9</figref> secured to be, a vaporizing plate <figref>21</figref>That above the base support <figref>20</figref> positioned is a feed <figref>22</figref> for liquid reactants, to the liquid Reactant to the vaporization plate <figref>21</figref> lead, and a bell-like Hood <figref>23</figref>To the vaporizing plate of the <figref>21</figref> generated to gather steam. The space between the hood<figref>23</figref> and the base support <figref>20</figref> defined the evaporation chamber <figref>30</figref>, The evaporator<figref>7</figref> includes preferably a temperature sensor <figref>31</figref> and a pressure sensor <figref>32</figref> known Type, which in the evaporation chamber <figref>30</figref> are positioned, the temperature and pressure during the process to be observed. The hood <figref>23</figref> has a steam output <figref>24</figref>, Via a management <figref>8th</figref> with the burner <figref>4</figref> communicates.

Prefers is the evaporation plate <figref>21</figref> a disc-like Element of metal, for example made of electro polished stainless steel, and two sides to form in use a top side <figref>21</figref> for liquid evaporation and a lower side <figref>21b</figref>That on the base support <figref>20</figref> positioned is. The top<figref>21a</figref> has a substantially flat and horizontal vaporization surface <figref>45</figref> and a plurality walls <figref>46</figref>. the fluid flow channel limit, which extends substantially on the entire top surface <figref>21a</figref> extends. In particular, the surface defining <figref>45</figref> and the walls <figref>46</figref> the Bed or the side edges of the Channel. The channel is open at the top to increase steam up allow. As shown in the plan view of the<figref idrefs="S32">4</figref> better it can be seen the flow channel defines a tortuous way for the liquid, of here with a dashed line and with the reference numbers <figref>48</figref> designated is. In the particular embodiment shown here defines a plurality of concentric annular edge <figref>46a</figref> to <figref>46g</figref> a plurality of annular channel sectors or annular surface areas <figref>45b</figref> to <figref>45g</figref>, Each edge <figref>46</figref> has a respective opening <figref>47</figref>, to the Passage of liquid by an annular to allow other area. The flow path<figref>48</figref> extends wound from the center of the evaporation plate <figref>21</figref> to the Edge.

On mean surface area <figref>45a</figref> the top <figref>21a</figref>Which from a central edge <figref>46a</figref> is limited, is below the feed <figref>22</figref> of liquid Reactant positioned to receive the liquid flow. The average edge <figref>46a</figref> has an opening <figref>47</figref>, to the Passage of liquid a first annular surface area <figref>45b</figref> to allow, in turn, externally from a second edge <figref>46b</figref> is limited. The second edge<figref>46b</figref> has an opening <figref>47</figref> at a position that the opening the first edge <figref>46a</figref> diametrically opposite, so that fluid to force the entire surface the first annular surface area <figref>45b</figref> to cover before in a second annular surface area <figref>45c</figref> flows, the outside the first is.

The particular embodiment the <figref idrefs="S32">4</figref> owns next to the central region <figref>45a</figref> and the central edge <figref>46a</figref> six annular surface areas <figref>45b</figref> to <figref>45g</figref> and six more annular edge <figref>46b</figref> to <figref>46g</figref>, The four edges<figref>46b</figref> to <figref>46e</figref> are thinner than the average edge and each of them has an opening &lt;?page 7?&gt;over that the previous edge. The penultimate edge<figref>46f</figref> has a Plurality of equally spaced openings <figref>47</figref>To it the liquid allow for, in the outer annular surface area <figref>45g</figref> at several to flow points. The outer surface area <figref>45g</figref> can a plurality of wells <figref>49</figref> have to remove the excess liquid collect (ie, the liquid, is not evaporated). Each sink<figref>49</figref> can a Liquid level sensor <figref>55</figref>. for example, be an infrared sensor is provided, which is suitable, the presence of liquid in the respective sink <figref>49</figref> to eat. The outer edge<figref>46g</figref> limited externally the outer surface portion <figref>45g</figref> and is preferably thicker and higher than the edges <figref>46b</figref> to <figref>46g</figref>,

The edge <figref>46a</figref> to <figref>46g</figref> to an altitude hold, greater than the minimum thickness of liquid reactant is necessary to vapor under film or Bläschensiedebedingungen to generate, with the range of film boiling and Bläschensiedens two possible Boiling ranges of liquid are, how later explained in more detail is. Specifically, the levels the edges <figref>46a</figref>-<figref>46g</figref> greater than the diameter of the Bases in the boiling liquid be. In particular, for a general liquid the bubble diameter (in meters) given by: <img img-content="cf" img-format="tif" he="12" wi="36" file="00140001.tif" />wherein the surface tension σ of the liquid (In N / m), g is the acceleration of gravity (9.81 m / s²) is ρ₁ the density of the liquid phase in kg / m³ is and ρ_v the density of the vapor phase in kg / m³ is. For SiCl₄ the diameter of the bubbles about 1.8 mm. Therefore, should the case of SiCl₄ the height of edge <figref>46a</figref>-<figref>46g</figref> be greater than 1.8 mm.

As in the bottom view of the <figref idrefs="S32">5</figref> shown, has the evaporating plate <figref>21</figref> a lower portion, which is adapted to be connected to a heating system. In particular, defines the lower side <figref>21b</figref> a seat <figref>50</figref> in Form of a continuous groove around a metal wire <figref>51</figref> take, the part of the heating system is. The groove<figref>50</figref> extends like a serpentine to substantially the entire surface of the plate <figref>21</figref> cover. The metal wire <figref>51</figref> is connected to a circuit, in particular a generator <figref>52</figref> an electric current, so as to be capable of the plate <figref>21</figref> to a predetermined Operating heating T, when it is flowed through by electric current. In the particular, example shown here has the groove <figref>50</figref> a plurality of linear and parallel sections, identified by a variety of circular be connected sections, allowing easy positioning of the wire <figref>51</figref> allowed.

The Vaporizing plate <figref>21</figref> is preferably provided with a (not shown) Temperature sensor provided to the temperature of the heated surface <figref>45</figref> to measure. The operating temperature T, which for complete evaporation the liquid on the plate <figref>21</figref> needed will depend on the type of liquid Reactant and the liquid flow rate from. If the flow rate increase is higher Temperature necessary to the higher Amount of liquid vaporize. The temperature may advantageously during Process vary. The temperature T should be above the minimum temperature are, on the one nucleate the liquid occurs, and preferably above the minimum temperature at which film boiling of the liquid occurs. In the case of SiCl₄ the minimum temperature for the nucleate 80 ° C, and the minimum temperature, to obtain a film boiling is about 100 ° C.

The various possible Siedemodalitäten (Or areas) are in the graph of <figref idrefs="S33">6</figref> shown. Roman Sections I, II, III and IV denote the modes of the free Convection, the formation of bubbles, the transition and film boiling. The x-axis denotes the multi-temperature .DELTA.T_eTo the difference between the surface temperature T_s and the saturation temperature T_sat corresponds to, and the ordinate axis denotes heat flow.

Point A separates free convection, wherein there is insufficient vapor with the liquid Phase in contact is to boiling at the saturation temperature to effect, by the bubble forming Mode, in which bubbles the bubble forming form points (evaporation germs) and separate from the surface and in which the steam with further increase in temperature as a beam or columns escapes.

Of the Boiling range between the points B and C, the transition boiling, unstable Boiling or partial film boiling is called, is a portion, wherein the blisters so quickly happens that a vapor film or vapor coating itself on the surface train starts. At each point of the surface, conditions may between Film boiling and nucleate oscillate, however, takes the film be from&lt;?page 8?&gt;Covered percentage of total area with increasing .DELTA.T_e to.

Point C, which indicates the start of the film mode, is also known as the Leidenfrost point known. Film boiling exists for .DELTA.T_e ≥ .DELTA.T_{e, C,} wherein .DELTA.T_{e, C} the More temperature at the Leidenfrost point (C). At point C, the heat flux q minimal and the heated surface is complete with a vapor coating covered. Heat transfer from the surface on the liquid is done through conduction through the vapor. When the surface temperature increases, the radiation travels through the vapor film in importance and the heat flux decreases with increasing .DELTA.T_e to. For a comprehensive description of the different Boiling ranges can in the book "Fundamentals of heat and mass transfer "of Incropera and De Witt, John Wiley &amp; Sons, are found. The Filmsiederegime is also in the article "Film Boiling Heat Transfer From a Horizontal Surface ", PJ Berenson, Journal of Heat Transfer, August 1961 describes.

As previously mentioned is the evaporation process of the present invention in vesicles or film boiling conducted preferably in the film boiling. For purposes of the present invention with "vesicle or Film boiling "a meant area Bläschensiedebereich the, the film boiling or the transition region between the Bläschensiedebereich and the film boiling corresponds, in which the behavior of partially that of Bläschensiedebereichs and partly that is the Filmsiedebereichs as previously described has been.

The Working conditions of the process previously described, are therefore different from those in the <patcit><text>US-A-5,356,451</text></patcit> have been described, in which the blisters is prevented (no boiling) and from those in the <patcit><text>US-A-5,078,092</text></patcit> described were, in which the temperature of the heating element below the Temperature is maintained at the vesicle or film boiling of the liquid occurs.

in the Use, in particular during a deposition process, the deposition apparatus operates <figref>1</figref> With open valves <figref>11a</figref>. <figref>11b</figref>. <figref>11c</figref> and <figref>11d</figref> and closed valves <figref>11e</figref>. <figref>11f</figref> and <figref>11g</figref>, Hence flows the liquid Reactant from the tank <figref>2</figref> to the evaporator <figref>7</figref> by the administration <figref>5</figref>, Passes through the valves <figref>11a</figref>. <figref>11b</figref>. <figref>11c</figref> and the flow control valve <figref>6</figref>, The liquid reactant enters in the vaporization chamber <figref>30</figref> the evaporator <figref>7</figref> about the feed <figref>22</figref> on and flows to the central region <figref>45a</figref> the upper surface <figref>45</figref> the Vaporizing plate <figref>21</figref>, The steady flow forces the liquid to be on the outer annular surface areas <figref>45b</figref>-<figref>45g</figref> along the fluid path <figref>48</figref> to move by through openings <figref>47</figref> the edge <figref>46</figref> passes. The front of the liquid moves forward, until the full Evaporation has reached energy required.

The Flow rate of the liquid Reactant is such that the liquid is a film having a thickness forms, which is lower than the level of edges <figref>46</figref>. However, higher than the diameter of a bubble in the liquid when the liquid boils, ie than the minimum thickness required to produce a vesicle or Film boiling to obtain. Before the liquid flows, is the temperature of the evaporating plate <figref>21</figref> on the above specified Temperature T is raised (that is, a temperature at which nucleate and preferably film boiling of the liquid occurs), by electrical current in the wire <figref>51</figref> cleverly is. The operating temperature, the full for evaporation on the evaporation plate <figref>21</figref> is needed depends on the type of liquid Reactant from.

the Film boiling requires a higher Plate temperature than the nucleate boiling, but can be advantageously carried out at a higher liquid flow rate, so a higher to obtain steam flow rate.

During the Procedure the temperature and pressure sensors are continuously monitored, To verify that No adverse changes the operating conditions occur. If no change or only a slight change the steam flow rate is necessary, the temperature set point of the Vaporizing plate <figref>21</figref> while the process can be kept constant, as well as the set point the liquid flow rate. Small changes the steam flow rate can be obtained by simply changing the liquid flow rate through the Flow control valve <figref>6</figref> varies when the plate temperature is. A change in the Liquid flow rate resulting in Indeed, a change the extent of the wetted area on the evaporation plate <figref>21</figref>, As far as the edge of the plate. It is therefore preferred to use an evaporation plate <figref>21</figref> to have, not fully with liquid filled is so small changes the liquid flow rate allow and so appropriate changes the steam flow rate to produce, without acting on the plate temperature. The pressure sensor <figref>22</figref> is advantageously observed to the Betriebseinstellpunkt the flow control valve <figref>6</figref> to control and so the pressure in the evaporation chamber <figref>30</figref> on the desired value to keep. In particular, a control circuit<figref>56</figref>, Of the pressure sensor <figref>32</figref> with the flow control valve <figref>6</figref> verbin&lt;?page 9?&gt;det, appropriate to the signal from the pressure sensor <figref>32</figref> take, the difference between the measured pressure and a reference pressure and to determine the fluid flow rate through the valve <figref>6</figref> to change so that this difference is minimized.

Around major changes to generate the steam flow rate, preferably, both the liquid flow rate and changing the drive temperature so a larger amount of liquid vaporize. Again, the signal of the pressure sensor<figref>32</figref> in a control loop used to the new set points for the plate temperature and the liquid flow rate to determine.

Furthermore be during the method, the level sensors, within the recesses <figref>49</figref> are positioned observed to the presence of liquid to discover it. If liquid within the recesses <figref>49</figref> exists, the efficiency Remove the process because some of the liquid is not vaporized. To overcome the problem, the temperature of the vaporizing plate <figref>21</figref> raised are, to the wells <figref>49</figref> are emptied.

Of the in the evaporation chamber <figref>30</figref> Steam generated is from a Hood <figref>23</figref> with the desired pressure collected and leaves the chamber <figref>30</figref> through the exit <figref>24</figref>, Then, the steam flows through line <figref>8th</figref> (, Passing through the valve <figref>11d</figref>) and reaches the burner <figref>4</figref> together with other gases, in particular at least with a combustible gas and a combustion- -sustaining gas. For example, the burner<figref>4</figref> with SiCl₄, With N₂ as the internal Shielding gas, with O₂ as the outer shield gas and a mixture from CH₄ and O₂ charged will. About that addition, the vaporous Reactants or glass precursor material A carrier, preferably O₂are mixed before he supplied to the burner is.

in the Burner produces a flame and it will rise to a reaction, which the vaporous Reactants in glass soot particles converts. The flame is on a deposition target (such as a Bar) directed, so that the soot can be deposited and a glass soot preform can grow.

If over the process is, the valves <figref>11a</figref>. <figref>11b</figref>. <figref>11c</figref> and <figref>11d</figref> closed. At predetermined times, the deposition apparatus <figref>1</figref> be flushed in order to avoid accumulation of substances. The rinsing is carried out by that first residues of the reactant via the drain pipe <figref>12</figref> out the evaporator <figref>7</figref> be drained and then into the various Lines of the evaporation unit <figref>3</figref> and in the evaporator <figref>7</figref> gradual Nitrogen (N₂) Is introduced. More specifically, draining characterized performed that all the valves of the vaporizing unit are closed, except for the two-way valve <figref>11g</figref>. which is switched so that it is the discharge pipe <figref>12</figref> With the drain line connects, thereby allowing vapor residues in the evaporation chamber <figref>30</figref> be drained. While the valves <figref>11a</figref> and <figref>11d</figref> are kept closed, then the valves <figref>11b</figref>. <figref>11c</figref>. <figref>11e</figref> and <figref>11f</figref> opened and the Two-way valve <figref>11g</figref> is switched so that the purge gas source connects with the drain line. As a result, flows north₂ in the line <figref>14</figref> and in the end portion the line <figref>5</figref>, This occurs through the valve <figref>11b</figref>. the flow control valve <figref>6</figref> and the valve <figref>11c</figref>and then enters the evaporation chamber <figref>30</figref> on. simultaneously flows N₂ in the line <figref>15</figref>, Occurs through the valve <figref>11f</figref>, And occurs again in the evaporation chamber <figref>30</figref> on. N₂ the evaporation chamber <figref>30</figref> about the management <figref>8th</figref> or the line <figref>12</figref> leaving.

<figref idrefs="S33">7</figref> shows an alternative embodiment of the evaporation plate with here <figref>21 '</figref> is designated. The evaporation plate<figref>21 '</figref> defines a spiral Away <figref>48 '</figref> for the liquid, the edges <figref>46 '</figref> limited is. The spiral Away <figref>48 '</figref> starts at a central surface portion <figref>45'a</figref>, extends along a spiral surface portion <figref>45'b</figref> and ends in an outer annular surface portion <figref>45 ° C.</figref>, The outer annular surface portion<figref>45 ° C.</figref> has a Plurality of wells <figref>49 '</figref>. the same function as in the embodiment of <figref idrefs="S32">4</figref> have. The lower portion of the evaporation plate can that the plate <figref>21</figref> identical be. For the height the edges <figref>46 '</figref> be valid the same considerations as for the edges <figref>46</figref> the plate <figref>21</figref>,

It is to be understood that the embodiments the <figref idrefs="S32">4</figref> and <figref idrefs="S33">7</figref> only illustrative examples and that different evaporation plates with different Kinds of ways according to the teaching of the present invention can be realized.

<figref idrefs="S34">8th</figref> provides an alternative embodiment of the evaporator represents the present invention, the here <figref>7 '</figref> designated is and can be used advantageously when higher steam flow rates necessary are. The evaporator<figref>7 '</figref> differs from evaporator <figref>7</figref> the <figref idrefs="S31">3</figref> therein, he two superimposed includes mounted evaporative plates, in particular an upper evaporation plate <figref>210</figref> and a lower evaporation plate <figref>211</figref>That are substantially have the same shape and the same dimensions &lt;?page 10?&gt;can or may be different from each other. The upper evaporation plate <figref>210</figref>Provided with a not shown support device is provided, is below the output of the liquid supply <figref>22</figref> positioned to receive the liquid as in its central region, however, unlike the vaporizing plate <figref>21</figref> has it in its outer region instead of the wells for at least one through hole <figref>54</figref>. so as to cause that the liquid Reactant which is not evaporated before reaching that region is, on the lower evaporation plate <figref>211</figref> transpires. The lower evaporation plate <figref>211</figref> is adapted to that of the upper evaporation plate <figref>210</figref> at its outer portion percolating liquid take and as a result of the shape of the path on its surface to its flow towards the center allow. In its central region, the lower evaporation plate<figref>211</figref> a Depression (not shown) for collecting the remaining liquid have, which is preferably provided with a temperature sensor.

The plates <figref>210</figref> and <figref>211</figref> may both be the same type, For example, the in <figref idrefs="S32">4</figref> or in <figref idrefs="S33">7</figref> disclosed Art, or another form. In addition, a different number of plates in the evaporation chamber <figref>30</figref> arranged are dependentof the amount of liquid Reactant which has to be evaporated.

It It will be apparent to the skilled person that various modifications and changes in the disclosed embodiment, the present invention can be made without departing from the scope or spirit of the invention departing. For example, the upper surface of the Vaporizing plate a slight own inclination, in particular a negative slope in the direction the flow of fluid to it the liquid allow to to flow easily to her. In addition, here can top described vaporization plate by a metal body of a any shape can be replaced, provided that at its top surface a way for the liquid defined, the sufficient formation of a liquid film Thickness allowed, and provided that it is connected with a heating system may be, which is located in it, heating the body to a temperature which is sufficient to obtain at least one nucleate boiling, and preferably a temperature which is sufficient to provide a film boiling to obtain. Another (not shown) embodiment of the deposition apparatus may also include a plurality of vaporizing units of the above-described include type, each with its own vapor exit line are provided. Those lines can are connected so that the different vapor flows before Feeding the burner are admixed.

It is to be understood that the evaporator of the present invention has very small dimensions and that it is possible, large amounts of of liquid thereby evaporating that more evaporation plates superimposed are placed, the entire assembly is still very compact is maintained. As previously mentioned, is about also possible the liquid tank position in another room in order in the case of the spillage risks To avoid the technicians. Another advantage of the arrangement of the the present invention is that they have no mass flow control devices in hot Regions of the device requires, since the only mass flow controller, ie the valve <figref>6</figref>That the liquid flow to the evaporator <figref>7</figref> regulates, operates at room temperature.

Experimental tests

Of the Applicant has performed a series of experimental tests to the effectiveness the deposition apparatus of the present invention in the generation to verify a stable flow of glass precursor material for one Glasrußabscheidungsvorgang suitable is.

A Vaporizing plate as the evaporating plate <figref>21</figref> the <figref idrefs="S31">3</figref>. <figref idrefs="S32">4</figref> and <figref idrefs="S32">5</figref> has been used and possessed the following dimensions: <ul><li>- Outer diameter: 230 mm;</li><li>- Height: 12 mm;</li><li>- width the annular surface areas <figref>45b</figref>-<figref>45g</figref>: 10 mm;</li><li>- diameter the average surface area <figref>45a</figref>: 35 mm;</li><li>- width the first annular edge <figref>46a</figref>: 10 mm;</li><li>- width the annular edge <figref>46b</figref>-<figref>46f</figref>: 2.5 mm;</li><li>- Height of the annular edge <figref>46a</figref>-<figref>46f</figref>: 2.5 mm;</li><li>- Height of the annular edge <figref>46g</figref>: 4.6mm;</li><li>- Nut <figref>50</figref>: ten linear and parallel sections, 20 mm apart, the circular grooves of nine be connected to 26 mm diameter;</li></ul>

The Experiments were carried out under the following operating conditions: &lt;?page 11?&gt;<ul><li>- Liquid reactant: SiCl₄;</li><li>- temperature the evaporating plate <figref>21</figref>: 145 ° C;</li><li>- temperature in the upper compartment <figref>9a</figref> the housing <figref>9</figref>: 90 ° C.</li></ul>

These Conditions, together with the liquid flow rates indicated below, were sufficient for boiling of the liquid under the Filmsiederegime.

The Experiments were performed 420 minutes long using three different flow rates of the liquid reactant, namely 30, 45 and 55 g / min. The vapor pressure in the evaporation chamber<figref>30</figref> has been in time intervals measured 30 min. The following table gives the values ​​of the measured pressures expressed in mbar again. <tables><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colname="1" colwidth="1*" /><colspec colname="2" colwidth="1*" /><colspec colname="3" colwidth="1*" /><colspec colname="4" colwidth="1*" /><tbody><row><entry morerows="1">Time (min)</entry><entry namest="2" nameend="4">Liquid flow rate</entry></row><row><entry colname="2">30 (G / min)</entry><entry colname="3">45 (G / min)</entry><entry colname="4">55 (G / min)</entry></row><row><entry colname="1">30</entry><entry colname="2">1073 (Mbar)</entry><entry colname="3">1102</entry><entry colname="4">1355</entry></row><row><entry colname="1">60</entry><entry colname="2">1075</entry><entry colname="3">1104</entry><entry colname="4">1357</entry></row><row><entry colname="1">90</entry><entry colname="2">1076</entry><entry colname="3">1105</entry><entry colname="4">1358</entry></row><row><entry colname="1">120</entry><entry colname="2">1077</entry><entry colname="3">1106</entry><entry colname="4">1358</entry></row><row><entry colname="1">150</entry><entry colname="2">1077</entry><entry colname="3">1106</entry><entry colname="4">1356</entry></row><row><entry colname="1">180</entry><entry colname="2">1076</entry><entry colname="3">1105</entry><entry colname="4">1359</entry></row><row><entry colname="1">210</entry><entry colname="2">1077</entry><entry colname="3">1104</entry><entry colname="4">1357</entry></row><row><entry colname="1">240</entry><entry colname="2">1078</entry><entry colname="3">1104</entry><entry colname="4">1358</entry></row><row><entry colname="1">270</entry><entry colname="2">1076</entry><entry colname="3">1106</entry><entry colname="4">1355</entry></row><row><entry colname="1">300</entry><entry colname="2">1076</entry><entry colname="3">1105</entry><entry colname="4">1356</entry></row><row><entry colname="1">330</entry><entry colname="2">1077</entry><entry colname="3">1107</entry><entry colname="4">1355</entry></row><row><entry colname="1">360</entry><entry colname="2">1078</entry><entry colname="3">1104</entry><entry colname="4">1356</entry></row><row><entry colname="1">390</entry><entry colname="2">1076</entry><entry colname="3">1103</entry><entry colname="4">1356</entry></row><row><entry colname="1">420</entry><entry colname="2">1076</entry><entry colname="3">1103</entry><entry colname="4">1353</entry></row></tbody></tgroup></table></tables>

It is to be understood that the method according to the present invention allows vapor pressures to obtained that the requirements of current Glasrußabscheidungsverfahren fulfill and are particularly stable. In particular, it can be observed that under the test conditions described hereinabove, the pressure variations less than 5% and more particularly less than about 0.46% be.