Patent Publication Number: US-9423179-B2

Title: System having a process chamber for workpieces

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the national stage of PCT/EP2013/058817, filed Apr. 26, 2013, designating the United States and claiming priority from German patent application no. 10 2012 207 312.4, filed May 2, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to an installation having a process chamber which has an inner space having a receiving region for workpieces and which has an opening for the supply or discharge of workpieces and which has a device for the introduction of gaseous fluid into the inner space, which device comprises at least one nozzle or aperture for the production of a fluid stream curtain between the opening and the receiving region for workpieces. 
     BACKGROUND OF THE INVENTION 
     Such an installation is known from WO 2010/122121 A1. 
     In production units for painting and coating vehicle bodyworks, drying installations are used for drying vehicle bodyworks which have been freshly painted or coated with corrosion protection. Those installations have a process chamber which is in the form of a drying tunnel and into which hot air is blown. There is a drying zone in the drying tunnel. The drying zone is a receiving region for workpieces in the form of vehicle bodyworks. In order to dry the vehicle bodyworks, they are moved on a conveying device through the drying tunnel. The coat of paint or coating of the vehicle bodyworks to be dried may be impaired by impurities, in particular particles of dust. Furthermore, gaseous fluid and with it heat from the inner space may be discharged through an opening for the supply of workpieces. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an installation having a process chamber which has an inner space which has a receiving region for workpieces and which can be opened at least partially, in which installation an efficient thermal separation of that inner space from the environment is possible with simple means and, at the same time, an adequate fresh air supply for the receiving region can be ensured. 
     This object is achieved by an installation of the type mentioned in the introduction which has a device for supplying fresh air into the process chamber, with which device fresh air can be introduced into the receiving region at a side of the fluid stream curtain, which side faces away from the opening. 
     The term “fresh air” is intended to be understood to be air which is in particular precompressed, heated and/or cleaned thermally and/or mechanically with a filter and/or dried and the status parameters of which are adjusted according to requirements. Fresh air may also be, for example, prepared exhaust air from a process chamber. Furthermore, fresh air may also be the exhaust gas from a heat engine or internal-combustion engine. With the supply of fresh air into the receiving region of the process chamber, it can be ensured that the solvent content of the air inside the process chamber does not exceed, when workpieces are dried, any threshold values above which drying processes are impaired and above which combustible solvents comprising dyes, paints, adhesives and/or coatings can bring about explosions because an explosion limit has been exceeded. 
     The invention is based on the notion that at least one air lock of a process chamber in a drying installation performs a dual function: fresh air which is supplied to the air locks and which produces a fresh air curtain can, on the one hand, be used to separate the inner space from the environment in technical flow terms and/or thermally. On the other hand, it is possible with the fresh air of the fresh air curtain for the solvent released during drying processes in the process chamber to be diluted sufficiently in that this fresh air is introduced into the process chamber. 
     Since the first function is charge-independent and the second function is charge-dependent, the inventors propose that this dual function of the air locks be separated. A volume flow which is directed into the process chamber is intended to be reduced or increased in terms of fluid in accordance with the charge of the process chamber. Fluids which may be considered include in particular fresh air and/or returned exhaust air. If a fresh air stream which is supplied to the process chamber of a drying installation is heated to a drying temperature, the adaptation of the fresh air volume stream to the charge allows a temporary reduction of the fresh air volume flow below its maximum value and consequently a reduction of the energy consumption. 
     The device preferably contains for the supply of fresh air in the installation at least one line which communicates with the receiving region and which has an opening for drawing in fresh air and which has a throughflow control device. The throughflow control device may comprise, for example, a throttle valve and/or an adjustable fan. 
     The installation may have in particular a device for agitating gaseous fluid in the receiving region by means of a circulating air line system which communicates with the receiving region and which is guided through a device for temperature control, in particular for heating gaseous fluid from the receiving region. The fresh air supplied to the process chamber can be supplied to the circulating air line system, for example, upstream or also downstream of a heat exchanger in the device for the temperature control. However, it is also possible to supply the fresh air in a line portion of the circulating air line system, by means of which line portion circulating air from the process chamber is directed to the device for temperature control or can be introduced into the process chamber by the circulating air which is temperature-controlled in the device for temperature control. 
     The installation may also contain a device for the supply of fresh air into the receiving region, which device has at least one line which has an opening for drawing in fresh air and which is connected to the circulating air line system. In this instance, a circulating air fan can be used in a cost-effective manner alternately or simultaneously to convey fresh air. A throughflow control device is optionally provided in the circulating air line system, the throughflow control device advantageously being arranged in a feed channel or a return channel of the circulating air line system. There are further optionally provided in the circulating air line system a heat exchanger and/or a heating device, the heat exchanger preferably transmitting heat from an exhaust gas flow into a fresh air flow within the device for supplying fresh air to the receiving region and a heating device preferably being connected, for example, to a solar thermal energy installation and/or a gas burner. 
     The line with the opening for drawing in fresh air may in particular open into a feed channel or return channel within the circulating air line system. 
     The installation may also contain a device for supplying fresh air to the receiving region, which device has at least one line which has an opening for drawing in fresh air and which is connected directly to the process chamber. 
     The throughflow control device is preferably part of a (superordinate) control or regulation circuit which supplies the receiving region with conditioned fluid, in particular with fresh air and optionally returned, prepared exhaust air. The throughflow control device may be connected directly or indirectly to a control or regulation circuit which contains a device for detecting a status parameter of the process chamber and which controls or regulates the quantity of fresh air which is introduced into the receiving region by means of the throughflow control device. 
     The process chamber in the installation may contain a device for monitoring operation of the process chamber, which device is configured for detecting a status parameter from the group set out below:
         i. carbon content and/or solvent content of the atmosphere in the receiving region;   ii. number and/or weight and/or type and/or size of the surface of workpieces which are arranged in the receiving region;   iii. number and/or weight and/or type and/or size of the surface of workpieces supplied to the receiving region per time unit;   iv. temperature of the exhaust air of a burner in a device for the temperature control of circulating air;   v. temperature difference of gaseous fluid which is removed from the receiving region and which is supplied to the receiving region again;   vi. temperature difference of gaseous fluid from the receiving region which is supplied to a combustion chamber of a burner in a device for the temperature control of circulating air, and of exhaust air from the combustion chamber of the burner;   vii. heat quantity per time unit which is supplied to the process chamber.       

     The process chamber in the installation can also be constructed with a receiving region which is subdivided into a first receiving region and an additional receiving region, the device for introducing gaseous fluid into the inner space producing a fluid stream curtain between the first receiving region and the additional receiving region. 
     The device for introducing gaseous fluid into the inner space of the process chamber contains at least one nozzle or at least one aperture for producing a fluid stream curtain between the opening and the receiving region for workpieces. The at least one nozzle or at least one aperture is preferably used as a discharge opening for air which has been heated above ambient temperature and/or air which is compressed above ambient pressure (or a correspondingly processed inert gas such as CO 2  or N 2 ). 
     The process chamber may contain, for example, gaseous fluid whose temperature T is above 100° C. and/or for which a temperature difference in relation to the environment of the process chamber is more than 50° C. In an embodiment, fluid is introduced approximately perpendicularly in a downward direction into the process chamber. In another preferred embodiment, the fluid introduced through the nozzle has a temperature which is higher or lower by more than 20° C. than the (approximately static) fluid contained in the process chamber. Reference is further made mainly to a rigid or adjustable nozzle geometry, the invention also being able to be carried out with one or more simple apertures, respectively. 
     The inner space of the process chamber is preferably constructed so as to be of tunnel-like form. It has a base and a cover. In that the at least one nozzle is in the form of a slot-type nozzle having a substantially rectangular discharge cross section, the gaseous fluid can be supplied via the cover of the inner space with a flow direction which is oblique in relation to the base so that a flow eddy which comprises air and which is at least partially mixed with introduced fluid is formed at the side of the fluid stream curtain, which side is directed toward the base or the inlet opening. 
     A notion of the invention is particularly that the fluid stream curtain can be produced with reduced energy consumption if the gaseous fluid which is introduced into the inner space via the at least one nozzle is guided by means of a guiding contour which projects into the inner space. It is particularly advantageous if that guiding contour can be pivoted. As a result, it is possible to adjust the fluid stream curtain in relation to the horizontal. An angle between 80° and 50° between the discharge direction and the horizontal is preferably adjusted. 
     If this angle between the discharge direction and the horizontal is adjusted, the fluid stream curtain produces a flow eddy at the lower side thereof when viewed in the flow direction, which side is directed toward the base or an opening. The fluid flow of the fluid stream curtain presses counter to the gaseous fluid which is located in the region of the base of the process chamber. The fluid flow of the fluid stream curtain overlaps and becomes mixed with fluid which leaves the process chamber in the region of the base. In particular, it is possible by the guiding contour being pivoted for workpieces not to be impaired during introduction into the process chamber or during discharge. 
     It is particularly advantageous if a wall which defines with the guiding contour a diffuser which contains a mixing chamber is arranged at the side of the guiding contour directed toward the opening. In relation to the central flow direction of the gaseous fluid from the at least one nozzle, the diffuser is constructed in an asymmetrical manner. The mixing chamber in the diffuser is arranged at the side of the fluid stream out of the nozzle, which side is directed downward when viewed in the flow direction. 
     The mixing chamber is positioned in the diffuser in such a manner that fluid at a side of the fluid stream curtain, which side is directed toward the opening (that is to say, outward from the inner space of the process chamber), is mixed with air from the region of the opening. In this instance, the air is drawn into the eddy by the gaseous fluid which flows through the nozzle or the aperture. 
     The wall may have one or more openings for the introduction of agitated air from the region of the opening. 
     In that an auxiliary chamber which acts as a “dead space” for gaseous fluid is formed at a side of the guiding contour directed away from the mixing chamber, it can be ensured that the stream of gaseous fluid being discharged from the nozzle or aperture is guided along the guiding contour without any flow breakdown. Preferably, lower flow speeds are present in the “dead space” than outside the dead space. As a result of the arrangement of an additional guiding wing in the mixing chamber, it is possible for large quantities of fluid to be guided back from the flow eddy into the fluid stream curtain. 
     In that a front wall which defines a retention space with the guiding contour is arranged at the side of the guiding wing directed toward the inlet opening, agitated air from the region of the inlet opening can be prevented from being discharged into the atmosphere, which air is redirected in the region of the guiding wing into an edge region of the inner space. 
     The front wall advantageously has one or more openings for the introduction of agitated air from the region of the inlet opening. The at least one nozzle may have a device for adjusting the flow quantity which is introduced through the nozzle for fluid. In that a plurality of nozzles having a device for adjusting the flow quantity which is introduced through the nozzle for fluid are provided, the fluid stream curtain can be adjusted in different manners in different portions between the inlet opening and the receiving region for workpieces. 
     The device for introducing gaseous fluid may have a heating device for heating the gaseous fluid. It is thereby possible for no condensate, for example, condensation water, to be produced in the region of openings of the process chamber. The process chamber is suitable for use in a drying and/or hardening installation. In particular, the process chamber may be integrated in a painting installation. 
     The fluid stream curtain is produced in the process chamber with gaseous fluid which is acted on with pressure and which is guided through a nozzle. Air from the region of an opening of the process chamber is added in the mixing chamber arranged adjacent to the nozzle to the gaseous fluid which flows out of the nozzle. The gaseous fluid which is guided through the nozzle is guided along a guiding contour which delimits the mixing chamber. That guiding contour separates the mixing chamber from an auxiliary chamber which is arranged adjacent thereto and which acts as a dead space for gaseous fluid. 
     The process chamber can be operated in particular in such a manner that a stream of gaseous fluid guided through a nozzle for producing a fluid stream curtain between the opening and the receiving region for workpieces is throttled or interrupted and/or wherein the direction of the fluid stream curtain is changed if a workpiece is moved through the opening. This ensures that the fluid stream curtain does not damage the surface of the coating of workpieces which are moved into and out of the process chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  shows a first drying installation for vehicle bodyworks; 
         FIG. 2  is a longitudinal section of a lock of the drying installation; 
         FIG. 3  is a three-dimensional view of the lock; 
         FIG. 4  shows the flow relationships for air in the region of the lock; 
         FIG. 5  is a longitudinal section of another lock for a drying installation; 
         FIG. 6  and  FIG. 7  and  FIG. 8  show portions of other longitudinal sections of alternative embodiments for locks in a drying installation; 
         FIG. 9  is a cross section of a drying tunnel in a drying installation; 
         FIG. 10  is a longitudinal section of another lock; 
         FIG. 11  shows a second drying installation for vehicle bodyworks; and, 
         FIGS. 12 to 19  show additional alternatively constructed installations for drying workpieces. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The installation  1  shown in  FIG. 1  for drying, for example, metal workpieces is configured in particular for vehicle bodyworks  3 . The installation  1  comprises a process chamber which is in the form of a drying tunnel  5 . The vehicle bodyworks  3  which are mounted on skids  7  can be moved through the drying tunnel  5  by means of a conveying device  9 . The conveying device has an electrical drive  10 . The drying tunnel  5  is lined with sheet metal. It has an inlet lock  11  having an inlet opening  12  and an outlet lock  13  having an outlet opening  14 . The drying tunnel  5  comprises a drying zone  15  which is located between the inlet lock  11  and the outlet lock  13 . The drying zone  15  is a receiving region for workpieces. The drying zone  15  is preferably configured in such a manner that approximately fifteen vehicle bodyworks  3  which are freshly coated with a substrate which contains paint and/or a solvent can be dried therein more or less at the same time. To this end, the drying portion  15  is configured, for example, with the length L=40 m, a clear width b of 1.40 m&lt;b&lt;2.70 m and a clear height h of 2.00 m&lt;h&lt;2.60 m. In a particularly preferred embodiment, for interval spacing of 5.2 m, thirty units per hour and 0.5 hours of dwell time, there is produced a tunnel length of 78 m (external width b: from 3 m to 4.6 m, external height h: from 2.8 m to 3.3 m). Fluid for drying is supplied to the drying portion  15  by means of a device  70  for providing conditioned gaseous fluid. 
     The device  70  preferably contains a circulating air line system  72  which communicates with the drying zone  15 . The circulating air line system  72  communicates with the receiving region  15  and has a feed channel  75  which acts as a circulating air recirculating channel and contains a return channel  77  which acts as a circulating air return channel for returning the circulating air. The circulating air line system  72  is guided through a heating device  63 . In the device  70 , there is a ventilator  61  with which the air for drying is introduced. With the device  70 , the air can be retained at a defined temperature in the drying zone  15  in a circulating air operating state. 
     The installation  1  further preferably contains a device  74  and alternatively or additionally a device  74 ′ for the supply of fluid in the form of fresh air, which may optionally also be conditioned. The device  74 ,  74 ′ has a line  76 ,  76 ′ having an opening  78 ,  78 ′ for drawing in fresh air. In the line  76 ,  76 ′ there is a throughflow control device  80 ,  80 ′ which is constructed as a throttle valve. The line  76 ,  76 ′ is advantageously connected to the circulating air line system  72 . 
     In order to direct away from the fluid atmosphere solvent which becomes volatilized in the drying tunnel  5  from paint, adhesives or coatings of the vehicle bodyworks  3 , there is in the installation  1  a line  65  or a plurality of lines for exhaust air, via which air charged with solvent can be supplied from the drying tunnel  5  to a cleaning reactor  67 . 
     In the inlet lock  11  and the outlet lock  13  of the drying tunnel  5  there is a nozzle  17 ,  19  for producing a fluid stream curtain  21 ,  23 . The nozzles  17 ,  19  are supplied with fresh air via a ventilator acting as a compressor for fresh air  25 ,  27  by a chamber  29 ,  31  which is arranged above the cover  6  of the drying tunnel  5 . The nozzles  17 ,  19  preferably have a narrow slot-like opening  33 ,  35  which extends substantially over the width of the drying tunnel  5  or over the width of the inlet or outlet openings  12 ,  14 . The slot-like opening  33 ,  35  of the nozzles  17 ,  19  opens in the inner space  39  of the drying tunnel  5 . The fluid being discharged from the nozzles  17 ,  19  is directed via a diffuser  16 ,  18  into the inner space of the drying tunnel  5 . The diffuser  16 ,  18  extends in front of the nozzles  17 ,  19  over the width of the inlet or outlet opening  12 ,  14 . The diffuser  16 ,  18  is constructed asymmetrically in relation to the direction of the fluid stream curtain  21 ,  23  and is delimited by a guiding plate having a guiding contour  211  and a front wall  215 . The fluid which flows out of the nozzles  17 ,  19  is directed into the inner space of the drying tunnel by means of the guiding contour  211  of the guiding plate. A temperature sensor  69 ,  71  is located on the guiding contour  211  for detecting in a manner which is advantageously possible the temperature T of the fluid which is supplied to the inner space  39  via the nozzles  17 ,  19 . 
     The fluid stream curtain  21 ,  23  preferably extends at an angle of 50°≦α≦80° with respect to the horizontal  37 . It is directed into the inner space  39  of the drying tunnel  5 . The fluid stream flowing out of the nozzles  17 ,  19  expands toward the base  41  of the drying tunnel  5 . With increasing distance from the opening  33 ,  35  of the nozzles  17 ,  19 , the speed of the flow of the fresh air which forms the fluid stream curtain  21 ,  23  as a gaseous fluid decreases. The fluid stream curtain  21 ,  23  separates the gas atmosphere in the inner space  39  of the drying tunnel  5  from the ambient air  42 . The fluid stream being discharged from the nozzles  17 ,  19  is adjusted to a predetermined shape by means of a control device  45 ,  47 . 
     A solvent sensor  73  is arranged in the drying zone  15  for detecting the concentration of solvent in the gas atmosphere of the drying tunnel  5 . Alternatively or additionally, such a solvent sensor may be arranged in the exhaust air channel  65 . The gaseous fluid in the form of air supplied to the nozzles  17 ,  19  is preheated in a heating device  43 ,  44  to a desired process temperature T soll  which is preferably in a temperature range of 160° C.≦T soll ≦250° C. In that the fluid stream curtain  21 ,  23  comprises fresh air, it can be ensured that a lower explosion limit for organic solvents in the drying zone  15  of the drying tunnel  5  is not exceeded. The preheating of the supplied fluid causes condensate not to occur in the inlet lock  11  and the outlet lock  13  of the drying tunnel  5 . 
     In order to ensure that the explosion limit in the drying zone  15  is complied with, fresh air can be introduced into the drying portion  15  where applicable via the device  74  or  74 ′. 
     The control device  45  is connected to the throughflow control device  80  for adjusting the quantity of the fresh air supplied to the drying tunnel  5  via the device  74  or  74 ′. With the control device  45 , the fresh air supplied via the line  76  or  76 ′ is adjusted to a predetermined value. The adjustment of the fresh air supply is carried out in accordance with the number detected by means of a sensor  49 ,  51  as process chamber operating state parameters in respect of the vehicle bodyworks moved per time unit through the drying zone  15  of the drying tunnel  5  and/or on the basis of the signals of the temperature sensors  69 ,  71  and/or the solvent sensor  73  and/or one or more other process chamber operating state parameters which allow statements concerning the composition of the gas atmosphere in the drying tunnel  5  and therefore the establishment of the fresh air requirement when the drying tunnel  5  is operated. The fresh air supply is adjusted in such a manner that, when the installation  1  is operated, the so-called lower explosion limit of the composition of the gas atmosphere in the drying tunnel  5  is not exceeded. 
     In order to detect process chamber operating state parameters, in a modified embodiment of the installation  1 , there may also be provided as an alternative to the sensor  49  a photoelectric barrier for establishing the number of vehicle bodyworks moved per time unit through the drying tunnel  5 . Alternatively or additionally to the sensor  49 , it is also possible for this purpose to provide the installation with a measurement device with which the weight of the vehicle bodyworks  3  supplied to the drying tunnel  5  can be established and/or to provide a device with which the size of the surface of the vehicle bodyworks  3  provided with a surface coating can be detected. Furthermore, the installation  1  may also be provided with a device for detecting a digital code which is fitted to workpieces, for example, the vehicle bodyworks  3  or a skid  7 , for example, a bar code which contains digital information concerning the size and quality of a surface coating which is applied to a workpiece, for example, to a vehicle bodywork  3 , or a specific workpiece type. 
     In an installation according to the invention, the establishment of the fresh air requirement of the process chamber, in particular a drying tunnel for motor vehicle bodyworks, may be carried out through, for example, as follows on the basis of a predefined type of workpiece: 
     The mass and number of workpieces which are present in the process chamber or which are on the way into the process chamber is established by means of a mass detection device and a batch number detection device. For each measurement value of the mass of a workpiece taking into consideration variations to be anticipated, which is taken into consideration as a result of the workpieces to be processed in the installation, a workpiece type is stored in the control device  45 . In the control device  45 , a conclusion can then be drawn from the type of workpiece established in the control device  45  with regard to the size of the painted surface of that workpiece. From the relevant value for the size of the surface, a fresh air requirement of the process chamber can then be determined via the solvent quantity discharged from this surface, which requirement is necessary so that, for example, the proportion of combustible solvent in the gas atmosphere of the process chamber  15  remains below the explosion limit. 
     According to the invention, therefore, in the installation a conclusion is drawn with regard to a specific workpiece, that is to say, a specific workpiece type, in particular from the mass of a workpiece established with the mass detection device. For the specific workpiece, a quantity of paint or coating applied thereto is then assumed and, from that assumed quantity of paint or coating, a conclusion is then drawn with regard to a solvent quantity taken up in the paint applied to the workpiece or the coating arranged thereon. 
     In combination with the batch number of the relevant workpieces in the process chamber, it is then possible to establish a total solvent quantity which is introduced into the process chamber during the drying of workpieces. The fresh air requirement for the process chamber can then be established therefrom in order to operate the chamber below the explosion limit. 
     It may be noted that a device for detecting the mass and batch number of workpieces may be formed according to the invention, for example, as a weighing device, with which the number of weighing operations is detected. 
     In order to take into account the thermal inertia of the entire system, it is advantageous to fit a device for detecting a workpiece parameter upstream of the process chamber. In the remaining time until the introduction of a workpiece into the process chamber, a desired process temperature and/or a desired composition of the gas atmosphere can then be adjusted in the process chamber, for example, by means of the quantity of fresh air introduced into the process chamber. 
     It should also be noted that the thermal inertia of an above-described installation is substantially determined by the thermal capacity of the process chamber and the magnitude of the air quantities supplied thereto and discharged therefrom. 
     In that the above-mentioned devices are connected to the control device  45 , it is possible to control or to regulate the composition of the gas atmosphere by adjusting the fresh air supply in accordance with the requirements of the vehicle bodyworks  3  which are arranged in the drying tunnel  5  in particular taking into consideration the solvent content in the surface coating of the vehicle bodyworks  3 . 
     The installation  1  can therefore be operated, for example, in the following operating states: 
     Operating State 1: 
     With the fluid stream curtain  21 ,  23 , a constant fresh air volume flow is supplied into the inlet or outlet locks  11 ,  13  and ensures not only adequate sealing of the inner space  39  but also adequate dilution of a solvent content in the atmosphere of the drying zone  15 . The drying tunnel  5  is acted on here in a charge-independent manner with the volume flow which is necessary for the solvent quantity supplied in the case of full loading. 
     Operating State 2: 
     With the fluid stream curtain  21 ,  23 , a constant fresh air volume flow is supplied into the inlet or outlet locks  11 ,  13  and ensures adequate sealing of the inner space  39 . In order to ensure adequate dilution of the solvent content in the atmosphere of the drying zone  15 , additional fresh air is supplied by means of the device  74 . The quantity of fresh air supplied with the device  74  is adjusted with the control device  45  and changes with the charging of the installation  1 . If fresh air is supplied to the drying zone  15  in an increased manner, a corresponding quantity of exhaust air must simultaneously be removed from the drying tunnel  5  via the line  65  so that the installation  1  is in equilibrium and no over-pressures or under-pressures are produced in the drying tunnel  5 . 
       FIG. 2  is a sectioned view of the inlet lock  11  of the drying installation  1  from  FIG. 1 . The nozzle  17  in the inlet lock  11  is a slot-type nozzle. The fresh air heated in the heating device  44  is supplied to the nozzle  17  via a pipeline  201 . The pipeline  201  opens in a chamber  203 . In the chamber  203 , the fresh air is directed to the nozzle  17  via air filters  205  and an obliquely arranged housing plate  206 . There is a guiding plate  207  in the lock  11 . The guiding plate  207  is securely connected to the housing plate  206 . The guiding plate  207  and the housing plate  206  can be pivoted in the lock  11  about a rotation axis  208  in the direction of the arrow  214 . The pivoting of the guiding plate  207  with the housing plate  206  affords access to the filter  205  so that maintenance operations can be carried out there. The nozzle  17  has a slot-like opening  209 . The slot-like opening  209  of the nozzle  17  is arranged so as to be recessed with respect to the cover  6  of the drying tunnel  5 . This makes it possible for impairments and damage of an as-yet-non-dried coating of vehicle bodyworks, which are being moved through the inlet lock  11  into the drying tunnel  5 , to be able to be avoided even at high flow speeds of a fluid stream being discharged from the nozzle  17 . The important aspect for preventing such damage is a comparatively large spacing of the opening  209  of the nozzle  17  from the base  41  of the drying tunnel  5 . This can be achieved by a recessed arrangement of the nozzle  17  in the drying tunnel  5 . This ensures that the impulse of the gaseous fluid flowing out of the nozzle  17  is already weakened at the center of the drying tunnel to such an extent that corresponding coatings of vehicle bodyworks  3  cannot be damaged by the fluid stream curtain  21 . 
     The fluid stream  210  being discharged from the opening  209  of the nozzle  17  is guided into the interior of the drying tunnel  5  along the contour  211  of a guiding plate  207  acting as a guiding wing. The length L of the contour  211  of the guiding plate  207  preferably corresponds to from 20 times to 40 times the slot width B of the nozzle opening  209 . 
     At the side of the contour  211  directed toward the inlet opening  213  of the drying tunnel  5 , there is a front wall  215 . The front wall  215  extends over the width of the lock  11 . The front wall  215  delimits the diffuser  16  with the contour  211 , a ridge element  212  and the contour  211  of the guiding plate  207 . The diffuser  16  is constructed in an asymmetric manner in relation to the main flow plane  202  of the fluid which flows out of the nozzle  17 . The main flow plane  202  and the contour of the guiding plate  211  are at an angle φ relative to each other. The portion of the diffuser  16  which is at the side directed toward the front wall  215  in respect of the plane  204  which is symmetrical to the contour of the guiding plate  211  in relation to the main flow plane  202  and which encloses the angle 2φ with the contour of the guiding plate  211 , acts as a mixing chamber  217  for gaseous fluid  219 . The mixing chamber  217  is arranged so as to be recessed in relation to the cover  6  of the drying tunnel  5 . The diffuser  16  with the mixing chamber  217  is in the lock  11  above the inlet opening  213 . The mixing chamber  217  is adjacent to the inlet opening  213 . The guiding plate with the contour  211  separates the mixing chamber  217  from an auxiliary chamber  216 . The auxiliary chamber  216  opens in the interior  39  of the drying tunnel  5 . The auxiliary chamber  216  forms a dead space for air from the drying tunnel  5 . The auxiliary chamber formed at the rear of the guiding plate with the guiding contour  211  causes the fluid stream  210  to be guided on the guiding contour  211  as a result of the Coanda effect without any flow breakdown. 
       FIG. 3  is a three-dimensional view of the inlet lock  11  from  FIG. 2 . The slot-like opening  209  of the nozzle  17  extends over the entire width of the inlet opening  213  of the drying tunnel  5 . The slot-like opening  209  of the nozzle  17  is so narrow that the fluid stream being discharged from the nozzle  17  forms a fluid stream curtain over a wide flow range with different discharge speeds. That fluid stream particularly prevents an introduction of dirt particles  301  from the environment of the drying installation  1  shown in  FIG. 1  into the interior of the drying tunnel  5 . 
       FIG. 4  shows with arrows the flow relationships for air in the inlet lock  11  in the plane of a longitudinal section of the drying tunnel  5  from  FIG. 1 . The fresh air which is supplied to the drying tunnel  5  via the slot-like nozzle  17  brings about a fluid stream curtain  401  at the outlet side of the nozzle  17 . From the opening  209  of the nozzle  17 , the fluid stream curtain  401  comprising fresh air flowing in the direction of the arrows  402  extends in the form of a bent leg  403  relative to the base  41  of the inlet lock  11 . The leg  403  has, at the height H of the center of the inlet lock  11 , a thickness D which is determined by the width B of the opening  209  of the nozzle  17 . At the side of the fluid stream curtain  401  directed toward the inlet opening  213  of the drying tunnel  5 , the fresh air flowing out of the nozzle  17  produces a flow eddy  407  of air. In the flow eddy  407 , the air flows with a flow direction which is indicated by the arrows  406  about a center  409 . The air in the region of the center  409  is substantially not moved. The air agitated in the flow eddy  407  is mixed at least partially with the fresh air which is introduced via the nozzle  17 . The flow eddy  407  extends from the base  41  as far as the cover  6  of the inlet lock  11 . 
     A diffuser  16  is formed by the guiding plate  211 , on the one hand, and the front plate  215  which is arranged at the side of the guiding plate  211  directed toward the inlet opening  213 , on the other hand. The diffuser  16  preferably takes up a portion of the air agitated in the flow eddy  407  inside the mixing chamber  217  thereof. In the mixing chamber  217 , this air is carried and added to a portion of the gaseous fluid which flows out of the opening  209  of the nozzle  17  in the manner of a Venturi effect. This increases the volume flow of the fluid stream curtain  401  in the region of the arrows  402 . The volume flow of the fluid stream curtain  401  may thus comprise a level of 30% or more of gaseous fluid which is supplied to the fluid stream which flows from the nozzle  17  via the mixing chamber  217 . This results in a fluid stream curtain  401  which extends as far as the base  41  of the drying tunnel  5  also being able to be produced with a comparatively small quantity of introduced fresh air. 
     The air from the mixing chamber  217  is thereby supplied to the flow eddy  407  again. This process results in only a small proportion of the gaseous fluid which is supplied via the nozzle  17  into the inner space  39  of the drying tunnel  5  leaving through the opening  213  of the lock  11  of the drying tunnel  5  again. The gaseous fluid which flows out of the nozzle  17  therefore reaches the interior of the drying tunnel  5  in accordance with the direction of the arrows  408  for the most part. A barrier with air agitated in the flow eddy  407  is produced in the region of the opening  213  of the lock  11  by means of the gaseous fluid which flows out of the nozzle  17 . This barrier brings about a thermal separation of the inner space  39  of the drying tunnel  5  from the outer region. Furthermore, that barrier also prevents the introduction of dust and dirt particles into the inner space  39  of the drying tunnel  5 . 
       FIG. 5  shows a modified embodiment of a lock  501  for a drying installation. The lock  501  has a nozzle  503  for the supply of fresh air with a nozzle geometry which is modified in comparison with the lock  11  from  FIG. 1 . The nozzle  503  is a double-chamber nozzle. The nozzle  503  has a slot-like nozzle opening  505  and a slot-like nozzle opening  507  which extends over the entire width of the cover  509  of the inlet lock  501 . The nozzle  503  comprises a pivotable control valve  511 . The control valve  511  can be moved by means of a spindle drive which is not shown in greater detail. However, an adjustment mechanism having a shaft or a cable control is also suitable for moving the control valve. By pivoting the control valve  511 , the fresh air supplied to the nozzle  503  via the chamber  513  may optionally be directed through the nozzle opening  507 , the nozzle opening  509  or through the nozzle openings  507 ,  509  simultaneously. This allows the air stream which is discharged from the nozzle openings  507 ,  509  to be metered. For example, it is possible by means of the control valve  511  to vary the air stream from the nozzle  503  in accordance with the position of vehicle bodyworks in the region of the inlet opening of a drying tunnel. It is thereby possible for a paint coating which is applied to a vehicle bodywork not to become impaired by the fluid stream which is formed with fresh air from the nozzle  503 . Furthermore, it is possible by means of the control valve  511  to adjust the thickness D of the fluid stream curtain and therefore the quantity and/or the speed of the fresh air which is supplied to the interior of the drying tunnel. 
     In a modified embodiment of the inlet lock  501 , it is also possible to provide a nozzle having a plurality of nozzle openings and having a plurality of control valves in order to adjust a fresh air stream for a drying tunnel. 
       FIG. 6  shows a portion of an alternative embodiment for a lock  601  having a nozzle  603  in order to construct an air curtain in the inlet or outlet region of a drying installation. 
     A preferably pivotably arranged guiding plate  605  which acts as a guiding wing is associated with the nozzle  603  in the lock  601 . The guiding plate optionally has an outer contour, which is at least partially curved. In particular, it extends over the entire width of the nozzle  603 . The pivotable guiding plate  605  in the case of the opening  607  of the nozzle  603  is pivotably supported on the cover  608  of the lock  601  on a rotary joint  615 . The pivotable guiding plate  605  projects into the interior  611  of the lock  601 . 
     The length L of the contour of the guiding plate  605  substantially corresponds to from 20 times to 40 times the slot width B of the nozzle opening. A front wall  609  is again arranged in the lock  601  opposite the pivotable guiding plate  605 . In this instance, the pivotable guiding plate  605  and the front wall  609  also define together with a ridge element  612  a diffuser with a mixing chamber  613 . As a result of the pivotability of the guiding plate  605 , the geometry of the diffuser and the mixing chamber  613  can be changed in the case of the lock  601 . 
     For the pivoting action, an actuating drive which is not illustrated in greater detail is associated with the guiding plate  605 . By pivoting the guiding plate  605  in accordance with the double-headed arrow  617 , it is possible to adjust an angle of incidence β in relation to the horizontal  616  and therefore the direction of a fluid stream curtain which is produced with gaseous fluid from the nozzle  603  in the lock  601 . The guiding plate  605 , on which the gaseous fluid which flows out of the nozzle  607  is guided, is displaced by the pivoting action. The shape of the flow eddy can thereby be changed, which shape is formed as a result of the fluid which flows out of the nozzle  603  at the side of the guiding plate  605  directed toward the opening  619  of the lock  601 . By the guiding plate  605  being pivoted toward the cover  608  of the lock  601 , it is possible to bring about a comparatively planar introduction of gaseous fluid into the lock. By the guiding plate  605  being moved upward and downward, the flow direction of the fluid flowing out of the nozzle can be adapted to the position and geometry of vehicle bodyworks which are moved by the lock  601  into the interior of the drying tunnel. Thus, it is possible for the fluid which flows out of the nozzle not to be redirected by the vehicle bodyworks toward the opening  619  and a paint coating which is applied to vehicle bodyworks and which is intended to be dried in the drying tunnel not to be dispersed or to suffer damage in the drying tunnel. 
       FIG. 7  shows a portion of another alternative embodiment for a lock  701  having a nozzle  703  in order to form an air curtain in the inlet region or outlet region of a drying installation. The nozzle  703  opens into a diffuser portion which adjoins the narrowed cross section of the nozzle and thus expands the cross section of flow for the fluid. The nozzle  703  with adjoining diffuser portion thus has a flow channel  704  whose cross section extends toward the interior  711  of the lock  701  into a volume which acts as a diffuser and in which a mixing chamber  713  is located. 
     The structure of the lock  701  further corresponds to that of the lock  601  from  FIG. 6 . Mutually corresponding subassemblies of the lock  601  and  701  are therefore indicated in  FIG. 7  with reference numerals which are increased by 100 in comparison with  FIG. 6 . Unlike the front wall  609  of the lock  601  in  FIG. 6 , the lock  701  has a front wall  709  having one or more inlet openings for ambient air. The front wall  709  preferably has openings in the form of a sieve-like perforation. That measure also allows air to be drawn from an upper region  721  of the environment of the lock  701 . The air which is drawn into the lock  701  in this manner is preferably mixed with air from a flow eddy which is formed at the opening of the lock. The drawn air and a portion of the air from the flow eddy are subsequently added to the fluid flow which is discharged from the diffuser. 
       FIG. 8  shows a portion of another alternative embodiment for a lock  801  having an aperture  803  which has an opening  804  in order to form an air curtain in the inlet or outlet region of a drying installation. The structure of the lock  801  corresponds to that of the lock  701  from  FIG. 7 . Mutually corresponding subassemblies of the lock  701  and  801  are therefore indicated in  FIG. 8  with reference numerals which are increased by 100 in comparison with  FIG. 7 . The front wall  809 , the ridge element  812  and the guiding plate  805  here also delimit a diffuser which comprises a mixing chamber. Unlike the front wall  709  of the lock  701  in  FIG. 7 , the front wall  809  of the lock  801  is constructed so as to have a recess  816 . That measure also allows air to be received from an upper region  821  of the environment of the lock  801  into the flow eddy which is produced by means of the aperture  803  at the opening of the lock. 
       FIG. 9  shows a cross section of an inlet or outlet lock  901  of a drying tunnel  900  in a drying installation having a vehicle bodywork  912 . The lock  901  has slot-like nozzles  903 ,  905 ,  907  which are located on the cover  910  of the lock  901 . The nozzles  903 ,  905 ,  907  can be acted on by means of a device which is not illustrated in greater detail for supplying fresh air with a fresh air stream  909 . In the lock  901 , there are control valves by means of which the fresh air stream  909  can be divided between different channels  911 ,  913  and  915  for acting separately on the nozzles  903 ,  905  and  907  with fresh air. 
     This measure allows the adjustment of a fluid stream curtain  917  at the openings of a drying tunnel which can be adjusted differently in accordance with the passage of workpieces, for example, vehicle bodyworks over the width B of the opening. 
       FIG. 10  is a longitudinal section of another lock  1011  for a drying tunnel in an installation for drying metal workpieces. In accordance with  FIG. 4 , the flow relationships for air in the lock  1011  are also indicated with arrows in this instance. The fresh air which is supplied to the drying tunnel via the slot-like nozzle  1017  brings about a fluid stream curtain  1401  at the outlet side of the nozzle  1017 . 
     On the basis of an opening  1209  of the nozzle  1017 , the fluid stream curtain  1401  (preferably comprising fresh air which flows in the direction of the arrows  1402 ) extends in the form of a leg  1403  which is bent to a greater or lesser extent in the direction of a base  1041  of the lock  1011 . At a side of the fluid stream curtain  1401  directed toward the inlet opening  1213  of the lock  1011 , the fresh air which flows out of the nozzle  1017  produces a flow eddy  1407  of air. In the flow eddy  1407 , the air flows with a flow direction which is indicated by the arrows  1406  about a center  1409 . The air in the region of the center  1409  is substantially not moved. The air which is agitated in the flow eddy  1407  is at least partially mixed with the fresh air which is introduced via the nozzle  1017 . The flow eddy  1407  extends from the base  1041  as far as the cover  1006  of the inlet lock  1011 . 
     The lock  1011  has a curved ridge wall  1215  at the side of a guiding plate  1211  which has a guiding contour which side is directed toward the inlet opening  1213 . The guiding plate  1211  and the ridge wall  1215  delimit and surround partially a diffuser  1210  with a downwardly open mixing chamber  1217 . In the embodiment according to  FIG. 10 , a flow guiding element  1218  in the form of a “flow wing”, which preferably extends over the entire width of the lock  1011  similarly to the opening  1009  of the nozzle  1017 , is positioned in the diffuser  1210 . The guiding plate  1211  separates the diffuser  1210  from an auxiliary chamber  1216 . The auxiliary chamber  1216  acts as a dead space for air, in which lower flow speeds than in the remaining lock are present (except for the actually negligible rotation center  1409  of the flow eddy). 
     A silhouette wall  1220  is arranged at the base  1041  of the lock  1011  in the region of the opening  1213 . The silhouette wall  1220  acts in particular as a flow barrier or as a flow guiding element at the base side. The silhouette wall  1220  preferably comprises a spring steel or other temperature-resistant and/or corrosion-resistant steels. The silhouette wall  1220  can be pivoted or folded about a (horizontal) axis  1222  in accordance with the arrow  1224 . 
     According to the invention, the mixing chamber  1217  takes up a small portion of the air agitated in the flow eddy  1407 . In the mixing chamber  1217 , this air is redirected with the flow wing  1218  as a result of a Venturi effect to the gaseous fluid which flows out of the opening  1209  of the nozzle  17 . It is carried along by the gaseous fluid. That increases the volume flow of the fluid stream curtain  1401  in the region of the arrows  1402 . The volume flow of the fluid stream curtain  1401  can thus comprise to a large degree gaseous fluid which is supplied to the fluid stream from the nozzle  1017  via the mixing chamber  1217 . That results in a fluid stream curtain  1401  which extends as far as the base  1041  of the drying tunnel also being able to be produced with a comparatively small quantity of fresh air being introduced. 
     The air from the mixing chamber  1217  is thereby supplied to the flow eddy  1407  again. That process results in only a small portion of the gaseous fluid which is supplied via the nozzle  1017  to the inner space  1039  of the drying tunnel leaving again through the opening  1213  of the lock  1011  of the drying tunnel. The gaseous fluid which flows out of the nozzle  1017  is therefore introduced into the interior of the drying tunnel for the most part in accordance with the direction of the arrows  1408 . By means of the gaseous fluid which flows out of the nozzle  1017 , there is produced in the region of the opening  1213  of the lock  1011  a barrier with air which is agitated in the flow eddy  1407  and which thermally separates the inner space  1039  of the drying tunnel from the outer region and furthermore also prevents an introduction of dust and dirt particles into the drying tunnel. The silhouette wall  1220  at the base  1041  of the lock  1011  causes the flow eddy  1407  to be comparatively narrow. Only if a workpiece is moved into the drying tunnel does the silhouette wall in accordance with the arrow  1220  become folded briefly in the direction of the base  1041 . It should be noted that, alternatively or additionally, a foldable silhouette wall which corresponds to the silhouette wall  1220  can also be arranged in the upper region of the inlet opening. 
     The installation  2001  shown in  FIG. 11  for drying vehicle bodyworks  2003  has a process chamber in the form of a drying tunnel  2005 . The drying tunnel  2005  is constructed so as to have an inlet lock  2011 , an intermediate lock  2012  and an outlet lock  2013 . In the drying tunnel  2005 , the intermediate lock  2012  separates a first drying portion  2015   a  from an additional drying portion  2015   b  as receiving regions for the motor vehicle bodyworks, which a retention zone  2016  which acts as an additional receiving region for motor vehicle bodyworks and which is arranged upstream of the outlet lock  2013  adjoins. 
     The structure of the locks  2011  and  2013  corresponds to the structure of the inlet and outlet lock  11 ,  13  in the installation  1  shown in  FIG. 1  for drying. In at least one lock  2011 ,  2013 , there is a nozzle  2014  for producing a fluid stream curtain  2021  which comprises fresh air and which is directed obliquely into the interior of the drying tunnel  2005 . One or more nozzles  2014  are combined with a diffuser  2018 , in particular the diffuser is arranged adjacent to the nozzle outlet and constructed asymmetrically relative to a main flow plane through the associated nozzle. By means of an asymmetrical diffuser at the nozzles of the inlet and outlet locks  2011 ,  2013 , it is possible to produce, at a side of the fluid stream curtain directed toward the opening  2015 ,  2017  of the drying tunnel  2005 , a flow eddy which comprises air and which comprises, on the one hand, fluid which is introduced through a line  2019  via the nozzles  2014  and ambient air at the openings  2015 ,  2017 . The intermediate lock  2012  has a nozzle  2009  which produces a fluid stream curtain  2020 . 
     A modified embodiment of the installation  2001  may also be constructed without any asymmetrical diffusers in the nozzles, for instance, if reduced demands are placed upon the tightness of the locks. For example, a mechanical closing of the corresponding locks may also be provided. 
     The installation  2001  contains a heating device  2023  which is in the form of a device for the thermal cleaning of exhaust air and which has a line  2025  for supplying hot clean gas from the drying tunnel  2005  and a heat exchanger  2027  which is used for heating exhaust air from the drying tunnel  2005 . The exhaust air which is heated in the heat exchanger  2027  from the drying tunnel  2005  can be burnt in a combustion chamber  2029  of the heating device  2023  with or without the addition of additional fuel. 
     The heating device  2023  supplies heat to a plurality of heat transfer devices  2031 ,  2033 ,  2035 ,  2037  through a hot gas line  2036  which acts as a clean gas line. The heat transfer devices  2031 ,  2033  and  2035  are connected to the hot gas line  2036  in a row one behind the other. The heat transfer devices  2031 ,  2033 ,  2035  are preferably constructed substantially in the same manner. The device  2037  contains an air/air heat exchanger and is connected as the last of the heat transfer devices to the hot gas line  2036 . The device  2037  is used for the temperature control of the fresh air which is guided to the nozzles  2014  for producing the fluid stream curtain  2021  comprising fresh air. The devices  2031 ,  2033  and  2035  each contain a heat exchanger  2039  which is connected with a hot gas line  2038  to the hot gas line  2036  and are configured for agitating circulation air in the drying portions  2015   a ,  2015   b  and in the retention zone  2016 . The circulating air, which is guided by a circulating air line system  2041  which communicates with the receiving regions  2015   a ,  2015   b  and  2016  and which has a circulating air recirculating channel  2041   a  for removing circulating air from the drying tunnel  2005  and a circulating air supply channel  2041   b  for the introduction of circulating air into the drying tunnel  2005 , is temperature-controlled in the heat exchangers  2039 . 
     In the installation  2001 , there are devices  2043  for the supply of additional fresh air into the receiving regions of the drying tunnel  2005 . The devices  2043  have lines  2045  which communicate with a receiving region in the drying tunnel  2005  and which contain a throughflow control device  2047  which is in the form of a throttle valve. 
     It should be noted that the throughflow control device  2047  may also be provided alternatively or additionally with a fan. Fresh air is directed via the lines  2045  into the circulating air line system  2041  of the devices  2031 ,  2033 ,  2035  if the fresh air supplied through the nozzles  2014  to the drying tunnel  2005  is not sufficient to meet the fresh air requirement inside the drying tunnel. 
     The installation  2001  contains a control device  2046 . The control device  2046  is connected to a first device  2051  for detecting a status parameter of the drying tunnel  2005  acting as a process chamber in the installation  2001 . In the device  2051 , an adjustment of the throttle valves  2052 ,  2055  in the lines  2038  for guiding hot gas through the heat exchangers  2039  and an adjustment of the throttle valves  2047  in the lines  2045  for supplying fresh air are detected by means of potentiometers or limit switches. It is possible to establish therefrom a fluid quantity which is supplied to the drying tunnel  2005  per time unit with the devices  2031 ,  2033 ,  2035  and  2037 . As a result, it is again optionally possible to establish a thermal quantity which is supplied with the fluid if the fluid temperatures are measured via temperature sensors which are associated with the lines of a circulating air line system  2041  and a line  2045 . 
     Furthermore, the control device  2046  is connected to a second device  2053  for detecting a status parameter of the drying tunnel  2005  which acts as a process chamber in the installation  2001 . The device  2053  is in the form of a bodywork counting device, with which the number of motor vehicle bodyworks  2003  moved per time unit into the drying tunnel  2005  and therefore the quantity of motor vehicle bodyworks  2003  which are arranged in the drying tunnel  2005  can be determined. 
     The control device  2046  is also connected to a temperature sensor  2007  for detecting the hot gas temperature TA in the hot gas line  2036 . The temperature sensor  2007  is used for measuring the temperature of the hot gas which flows through the hot gas line  2036  at the outlet side of the heat transfer device  2037 , with which the hot gas from the installation  2001  is released to the environment as a clean gas (clean gas over roof temperature). 
     The control circuit  2046  is connected to a control module  2056  for adjusting the speed of a ventilator  2057  which is arranged in the line  2025  and an additional control module  2059  for adjusting the speed of a ventilator  2061  which is used to draw fresh air into the line  2019  to the nozzles  2009  which produce a fluid stream curtain  2021  in the drying tunnel  2005 . 
     The throughflow control devices  2047  in the devices  2043  for supplying fresh air and the speed of the ventilator  2057  are then adjusted by means of the control circuit  2046  in accordance with the value established by means of the device  2051  for the heat quantity supplied to the drying tunnel  2005  per time unit and the number established by means of the device  2053  in respect of bodyworks  2003  arranged inside the drying tunnel  2005 . 
     So much fresh air is supplied into the line  2019  by means of the ventilator  2061  that the locks  2011 ,  2012  and  2013  are sealed by means of the fluid stream curtain  2021  produced with the nozzles  2009 . 
     It should be noted that the control device  2046  can in principle also be in the form of a control circuit. It should further be noted that the fresh air supply by the heat transfer devices  2031 ,  2033 ,  2035  in the drying tunnel  2005  can also be controlled or regulated with a control device  2046 , to which one or more of the subsequently set out measurement variables are supplied as process chamber operating state parameters for the installation  2001 : 
     solvent introduction into the atmosphere in the receiving regions of the drying tunnel  2005 ; 
     total carbon content in the receiving regions of the drying tunnel  2005 ; 
     number of bodyworks arranged in the receiving regions of the drying tunnel; 
     temperature of the hot gas produced with the heating device  2023  in the hot gas line  2036  downstream of the device  2037  upstream of an exhaust air chimney; 
     temperature difference of the circulating air before and after the devices  2031 ,  2033  and  2035 ; 
     temperature difference of the exhaust air from the drying tunnel which is supplied to an exhaust gas cleaning installation and exhaust air which leaves the exhaust gas cleaning installation through an exhaust air chimney; 
     weight of a bodywork or size of a bodywork surface acted on with paint in order to conclude a solvent quantity therefrom. 
     It is advantageous if a plurality of measurement variables are combined in the control device  2046  as status parameters (process chamber operating state parameters). Thus, for example, a “clean gas over roof temperature” detected by means of the temperature sensor  2007  may also be detected as a primary measurement variable and an adjustment of the throttle valves  2052 ,  2055  for adjusting the hot gas flow in the hot gas lines  2036 ,  2038  (clean gas valve position) as a secondary measurement variable. The primary measurement variable is used to establish a fresh air/exhaust air volume flow and the secondary measurement variable is used for verifying, confirming and/or optionally correcting that fresh air/exhaust air volume flow. 
     After the fresh air/exhaust air volume flow is established by means of the “clean gas over roof temperature”, for example, a verification of that flow is carried out on the basis of the secondary measurement variable. For example, the variable fresh air volume flow is kept constant or increased until the positions of all the clean gas valve positions are again below a previously fixed value, if the position of the clean gas valve positions exceeds the said fixed value which is dependent on the overall system and which may be between 50% and 100% of the opening degree. Such a combination of a plurality of measurement variables can particularly ensure that a sufficient thermal quantity is contained in the drying tunnel  2005  of the installation  2001 . 
     The installation  2001  may be operated in particular as follows: 
     In a first operating mode which corresponds to a charging state A of the installation  2001  of, for example, A≦50% in relation to the maximum possible capacity of workpieces in the process chamber in the form of a drying tunnel, a constant fresh air volume flow is supplied via the locks  2011 ,  2012  and/or  2013 . An additional fresh air supply via the lines  2045  into the process chamber does not necessarily have to be carried out here. 
     In a second operating mode which corresponds to a charging state A of the installation  2001  of, for example, 51%≦A≦90% in relation to the maximum possible capacity of workpieces in the process chamber in the form of a drying tunnel, a constant fresh air volume flow is supplied via the locks  2011 ,  2012  and/or  2013 . At the same time, additional fresh air is introduced into the process chamber by opening throughflow control devices  2047  in the form of throttle valves in the lines  2045  via the heat exchanger devices  2031 ,  2033 ,  2035  and/or  2037 . 
     In a third operating mode which corresponds to a charging state of the installation  2001  of, for example, 91%≦A≦100% in relation to the maximum possible capacity of workpieces in the process chamber in the form of a drying tunnel, a constant fresh air volume flow is supplied via the locks  2011 ,  2012  and/or  2013  and the stream of the additional fresh air which is supplied to the heat transfer devices  2013 ,  2033 ,  2035  and/or  2037  is further increased by additional opening of the throughflow control devices  2047  in relation to the second operating mode. 
     It should be noted that the installation  2001  can also be operated in additional operating modes in which the throughflow control devices  2047  in the lines  2045  have a different opening position in relation to the above-mentioned operating modes. In particular, in principle it is also possible to change the operating mode of the installation  2001  in a stepless manner. 
     It should be particularly noted that the supply of fresh air into the drying tunnel  2005  in the installation  2001  can also be carried out at locations other than those shown in  FIG. 11 : 
     In an alternative configuration of the installation  2001 , for example, there may be provision for circulating air and/or fresh air to be supplied to the receiving regions  2015   a ,  2015   b ,  2016  of the drying tunnel  2005  via openings in the wall, in the cover and/or in the base of the drying tunnel  2005 . The supply of fresh air to the circulating air line system  2041  may also be carried out in principle in an installation  2001  described above with respect to the flow direction of the circulating air upstream or downstream of a heat exchanger  2039  in a heat transfer device  2031 ,  2033 ,  2035 . It should further be noted that the supply of fresh air is possible both inside a heat transfer device  2031 ,  2033 ,  2035  and outside a heat transfer device  2031 ,  2033 ,  2035  to a circulating air recirculating channel  2041   a  or circulating air return channel of a circulating air line system  2041 . 
     In order to adjust a defined volume flow for the fresh air, a ventilator can also be arranged in the line  2045  for fresh air. It is further possible for the fresh air to be supplied in a lock  2011 ,  2013 ,  2015  of the installation  2001  at the side of a fluid stream curtain  2021  directed into the interior of the drying tunnel  2005 . 
     In order to explain the alternative configurations of the installation  2001  as set out above, additional installations according to the invention for drying are described below with reference to  FIG. 12  to  FIG. 19 : 
       FIG. 12  shows an additional installation  2001 ′ which is for drying vehicle bodyworks  2003  and which corresponds in principle to the installation  2001  from  FIG. 11  in terms of its construction. If the subassemblies in the installation  2001  from  FIG. 11  and in the installation  2001 ′ from  FIG. 12  are identical, they have the same reference numerals in  FIG. 11  and  FIG. 12 . In the installation  2001 ′, the line  2045  for supplying fresh air to the circulating air line system  2041  is connected via a line branch  2045   a  and a line branch  2045   b  in the heat transfer device  2037  to the line  2019  for supplying fresh air to the nozzles  2009 . As a result of the line branch  2045   a , it is possible to supply fresh air which is drawn in by means of the ventilator  2061  into the line  2045  which has been heated in the heat exchanger  2039  of the heat transfer device  2031  with heat from the clean gas which is guided in the hot gas line  2036 . 
     Alternatively or additionally, it is also possible to convey fresh air through the line branch  2045   b  in the heat transfer device  2037  into the line  2019  by means of the ventilator  2061  into the line  2045 . In this instance, the fresh air conveyed by means of the ventilator  2061  is not then guided or only partially guided through the heat exchanger  2039  in the heat transfer device  2037 . 
     The fresh air guided in the line  2019  is introduced in the installation  2001 ′ in the heat transfer devices  2031 ,  2033  and  2035  in such a manner that it is introduced into the drying tunnel  2005  via the heat exchanger which is arranged in the heat transfer devices  2031 ,  2033  and  2035 . 
     The fresh air introduced into the heat transfer devices  2031 ,  2033  and  2035  from the line  2045  can therefore be heated with heat from the clean gas which is guided in the hot gas line  2036 . 
     A throughflow measurement device  2062  is arranged in the line portion  2019   a  of the installation  2001 ′. The throughflow measurement device  2062  controls an actuating member in a throughflow control device  2048 . As a result, it can be ensured in the installation  2001 ′ that for different speeds of the ventilator  2061  the nozzles  2009 ,  2014  for producing a fluid stream curtain  2020 ,  2021  are supplied with a constant fresh air stream. A throughflow measurement device  2063  is arranged in the line  2045 . The throughflow measurement device  2063  is used to establish the quantity of fresh air supplied to the line  2045  by means of the ventilator  2061 . 
     In the installation  2001 ′, a fresh air stream supplied into the line  2045  is adjusted by means of the throughflow control device  2048  in accordance with the number of bodyworks  2003  arranged inside the drying tunnel  2005 , which number is established with the device  2053 . 
     The throughflow measurement devices  2062 ,  2063  determine the quantity of fresh air supplied to the line  2019 ,  2045  by means of the ventilator  2061  by detecting the pressure decrease at an aperture which is arranged in the line portion with the throughflow measurement device  2062 ,  2063 . It should be noted that the throughflow measurement device  2062 ,  2063  for detecting the flow of fresh air can contain, as an alternative thereto, a magnetically inductive sensor, an ultrasound measurement unit or an impeller. 
       FIG. 13  shows another installation  2001 ″ for drying, whose construction is substantially identical to the construction of the above-described installation  2001 ′. If the subassemblies in the installations shown in  FIG. 12  and  FIG. 13  are functionally identical, they have the same numerals in  FIG. 12  and  FIG. 13  as reference numerals. 
     Unlike in the installation  2001 ′ from  FIG. 12 , in the installation  2001 ″ the fresh air is supplied to the circulating air line system  2041  at the outlet side with respect to the heat exchanger  2039  through the line  2045  for supplying fresh air to the heat transfer devices  2031 ,  2033  and  2035 . In a heat exchanger  2039  of a heat transfer device  2031 ,  2033 ,  2035 , only the circulating air supplied through a supply channel  2041   a  from the drying tunnel  2005  is then heated. 
       FIGS. 14 and 15  show additional installations  2001 ′″ and  2001 ″″ for drying whose construction corresponds to the construction of the installation described with reference to  FIG. 12  and  FIG. 13 . Functionally identical subassemblies in those installations again have here the same reference numerals as the corresponding subassemblies of the installations from  FIG. 12  and  FIG. 13 . In the installation  2001 ′″, fresh air is introduced via the line  2045  outside the heat transfer devices  2031 ,  2033  and  2035  into the circulating air return channel  2041   b  of the line system. In the installation  2001 ″″, the line  2045  for supplying fresh air to the drying tunnel  2005  is connected to a circulating air recirculating channel  2041   a  of the line system  2041 , through which channel the circulating air from the drying tunnel  2005  is directed into a heat transfer device  2031 ,  2033  and  2035 . 
     It should be noted that in a modified embodiment of the installation  2001 ′″ from  FIG. 14 or 2001 ″″ from  FIG. 15 , there may also be provision for fresh air to be supplied from a line  2045  both to a circulating air recirculating channel  2041   a  and to a circulating air return channel  2041   b  of a circulating air line system  2041 . If the fresh air is supplied to a circulating air return channel  2041   b , however, it must be ensured that the relevant fresh air is warmed. 
     The installation  3001  shown in  FIG. 16  for drying vehicle bodyworks  3003  has a plurality of temperature sensors  3070 ,  3072 ,  3074  and  3076  as a device for detecting a status parameter of a drying tunnel  3005  which acts as a process chamber. If the subassemblies in the installation  3001  functionally correspond to the subassemblies in the installation  2001  from  FIG. 11 , they are indicated in  FIG. 12  with numerals which are increased by 1000 in relation to  FIG. 11  as reference numerals. 
     The temperature sensors  3070 ,  3072 ,  3074  and  3076  are connected to the control device  3046 . The temperature sensor  3070  is arranged in the hot gas line  3026  between the heating device  3023  and the heat transfer device  3031 . The temperature sensor  3072  is located in an end portion of the hot gas line  3026 , from which the clean gas which flows through the hot gas line  3026  is introduced into the ambient atmosphere. The temperature sensors  3070 ,  3072  are used for establishing the heat which is discharged into the drying tunnel  3005  by the clean gas flowing through the hot gas line  3026  by establishing the difference of the temperatures measured by means of those temperature sensors ΔT H =T 1 −T 2 . With the temperature sensors  3074  and  3076 , there is established the difference of the temperatures ΔT U : =T 3 −T 4  of circulating air which flows from the drying tunnel  3005  in the circulating air recirculating channel  3041   a  and circulating air which is mixed with fresh air and which is directed through the circulating air supply channel  3041   b  into the drying tunnel  3005 . 
     The control device  3046  controls the speed of the ventilator  3057  in the line  3025  and the adjustment of the throughflow control devices  3047  for adjusting the quantity of fresh air supplied to the line system  3041  in accordance with the temperature difference ΔT H , ΔT U  detected by means of the temperature sensors  3070 ,  3072 ,  3074  and  3076 . Alternatively, the control device  3046  may also be constructed as a control circuit which controls the speed of the ventilator  3057  in the line  3025  and the adjustment of the throughflow control device  3047  on the basis of the signal of the temperature sensors  3070 ,  3072 ,  3074  and  3076 . 
     The installation  4001  shown in  FIG. 17  for drying vehicle bodyworks  4003  has as a device for detecting a status parameter of a drying tunnel  4005  which acts as a process chamber a balance  4078  for establishing the mass of vehicle bodyworks  4003  supplied to the drying tunnel  4005 . If the subassemblies in the installation  4001  functionally correspond to the subassemblies in the installation  2001  from  FIG. 11 , they are indicated in  FIG. 13  with numerals which are increased by 2000 in relation to  FIG. 11  as reference numerals. 
     In this instance, the control device  4046  controls the speed of the ventilator  4057  in the line  4025  and the adjustment of the throughflow control devices  4047  for adjusting the quantity of fresh air supplied to the line system  4041  in accordance with the mass of the vehicle bodyworks  4003  supplied to the drying tunnel  4005 , which mass is detected by means of the balance  4078 . 
       FIG. 18  shows an installation  5001  for drying vehicle bodyworks  5003 . If the subassemblies in the installation  5001  functionally correspond to the subassemblies in the installation  2001  from  FIG. 11 , they are indicated in  FIG. 17  with numerals which are increased by 3000 in relation to  FIG. 11  as reference numerals. In the installation  5001 , the line  5045  for the supply of fresh air in the heat transfer device  5037  receives fresh air which can be heated by means of the heat exchanger  5039  with heat from the clean gas guided in the hot gas line  5026 . The fresh air from the line  5045  is introduced into the locks  5011 ,  5012  and  5013  of the drying tunnel in the installation  5005 . 
       FIG. 19  shows an installation  6001  for drying vehicle bodyworks  6003 . If the subassemblies in the installation  6001  functionally correspond to the subassemblies in the installation  5001  from  FIG. 18 , they are indicated in  FIG. 19  with numerals which are increased by 1000 in relation to  FIG. 18  as reference numerals. In the installation  6001 , the fresh air from the line  6045  is introduced into the drying portions  6015   a ,  6015   b  and the retention zone  6016  of the drying tunnel  6005 . 
     Additional modifications and developments of an installation according to the invention may result inter alia from a combination of different features of the above-described advantageous embodiments. 
     In conclusion, the following preferred features of the invention should be emphasized: A process chamber  5 ,  2005  has an inner space  39  having a receiving region  15 ,  2015   a ,  2015   b ,  2016  for workpieces  3 ,  2003 . The process chamber  5 ,  2005  has an opening  12 ,  14 ,  2015 ,  2017  for the supply or discharge of workpieces  3 ,  2003 . The process chamber  5 ,  2005  is constructed so as to have a device  17 ,  19 ,  25 ,  29 ,  33 ,  37 ,  35 ,  2014  for introducing gaseous fluid into the inner space  39 , which device has at least one nozzle  17 ,  19 ,  2014  or aperture  803  for producing a fluid stream curtain  21 ,  23 ,  2021  between the opening  12 ,  14 ,  2015 ,  2017  and the receiving region  15 ,  2015   a ,  2015   b  for workpieces  3 ,  2003 . The process chamber  5 ,  2005  has a device  74 ,  2043  for supplying fresh air with which fresh air can be introduced into the receiving region  15 ,  2015   a ,  2015   b  at a side of the fluid stream curtain  21 ,  23 ,  2021  facing away from the opening  12 ,  14 ,  2015 ,  2017 . 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Installation 
           3  Vehicle bodywork 
           5  Drying tunnel, process chamber 
           6  Cover 
           7  Skid 
           9  Conveying device 
           10  Drive 
           11  Inlet lock 
           12  Inlet opening 
           13  Outlet lock 
           14  Outlet opening 
           15  Drying portion, drying zone 
           16 ,  18  Diffuser 
           17 ,  19  Nozzle 
           17 ,  19 ,  25 ,  29 , 
           33 ,  37 ,  35  Device 
           21 ,  23  Fluid stream curtain 
           25 ,  27  Fresh air 
           29 ,  31  Chamber 
           33 ,  35  Opening 
           37  Horizontal 
           39  Inner space 
           41  Base 
           42  Ambient air 
           43 ,  44  Heating device 
           45 ,  47  Control device 
           49 ,  51  Sensor 
           61  Ventilator 
           74 ,  74 ′ Device 
           63  Heating device 
           69 ,  71  Temperature sensor 
           70  Device 
           72  Circulating air line system 
           73  Solvent sensor 
           74  Device 
           75  Feed channel 
           76 ,  76 ′ Line 
           77  Return channel 
           78 ,  78 ′ Opening 
           80 ,  80 ′ Throughflow control device 
           201  Pipeline 
           202  Main flow plane 
           203  Chamber 
           204  Plane 
           205  Air filter 
           206  Housing plate 
           207  Guiding plate 
           208  Rotation axis 
           209  Opening 
           210  Fluid stream 
           211  Guiding contour, contour, guiding plate 
           213  Inlet opening 
           215  Front wall, front plate 
           216  Auxiliary chamber 
           217  Mixing chamber 
           219  Fluid 
           401  Fluid stream curtain 
           402  Arrow 
           403  Leg 
           406  Arrow 
           407  Flow eddy 
           408  Arrow 
           409  Center 
           501  Lock, inlet lock 
           503  Nozzle 
           505  Nozzle opening 
           507  Nozzle opening 
           509  Cover 
           507 ,  509  Nozzle openings 
           511  Control valve 
           601  Lock 
           603  Nozzle 
           605  Guiding plate 
           607  Opening, nozzle 
           608  Cover 
           609  Front wall 
           611  The interior 
           612  Ridge element 
           613  Mixing chamber 
           615  Rotary joint 
           616  Horizontal 
           617  Double-headed arrow 
           619  Opening 
           701  Lock 
           703  Nozzle 
           704  Flow channel 
           709  Front wall 
           711  The interior 
           713  Mixing chamber 
           721  Region 
           801  Lock 
           803  Aperture 
           804  Opening 
           805  Guiding plate 
           809  Front wall 
           812  Ridge element 
           816  Recess 
           821  Region 
           900  Drying tunnels 
           901  Lock, outlet lock 
           903 ,  905 ,  907  Nozzle 
           909  Fresh air flow 
           910  Cover 
           911 ,  913 ,  915  Channel 
           917  Fluid stream curtain 
           1006  Cover 
           1009  Opening 
           1011  Lock, inlet lock 
           1017  Nozzle 
           1039  Inner space 
           1041  Base 
           1209  Opening 
           1210  Diffuser 
           1211  Guiding plate 
           1213  Opening, inlet opening 
           1215  Ridge wall 
           1216  Auxiliary chamber 
           1217  Mixing chamber 
           1218  Flow guiding element, flow wing 
           1220  Silhouette wall, arrow 
           1222  Axis 
           1224  Arrow 
           1401  Fluid stream curtain 
           1402  Arrow 
           1403  Leg 
           1406  Arrow 
           1407  Flow eddy 
           1408  Arrow 
           1409  Center, rotation center 
           2001 ,  2001 ′, 
           2001 ″,  2001 ′″, 
           2001 ″″ Installation 
           2003  Vehicle bodywork, workpiece 
           2005  Drying tunnel, process chamber 
           2007  Temperature sensor 
           2009  Nozzle 
           2011 ,  2012 , 
           2013 ,  2015  Lock 
           2014  Nozzle 
           2015   a ,  2015   b  Drying portion, receiving region 
           2015 ,  2017  Opening 
           2016  Retention zone 
           2018  Diffuser 
           2019  Line 
           2019   a  Line portion 
           2020  Fluid stream curtain 
           2021  Fluid stream curtain 
           2023  Heating device 
           2025  Line 
           2027  Heat exchanger 
           2029  Combustion chamber 
           2031 ,  2033 , 
           2035  Heat transfer device 
           2036 ,  2038  Hot gas line 
           2037  Heat transfer device 
           2039  Heat exchanger 
           2041  Circulating air line system 
           2041   a  Circulating air recirculating channel 
           2041   b  Circulating air supply channel 
           2043  Device 
           2045  Line 
           2045   a ,  2045   b  Line branch 
           2046  Control device 
           2047 ,  2048  Throughflow control device 
           2049  Control circuit 
           2051 ,  2053  Device 
           2052 ,  2055  Throttle valve 
           2056 ,  2059  Control module 
           2057 ,  2061  Ventilator 
           2062 ,  2063  Throughflow measurement device 
           3001  Installation 
           3003  Vehicle bodywork, workpiece 
           3005  Drying tunnel, process chamber 
           3023  Heating device 
           3025 ,  3045  Line 
           3026  Hot gas line 
           3031  Heat transfer device 
           3041  Line system 
           3041   a  Circulating air recirculating channel 
           3041   b  Circulating air supply channel 
           3046  Control device 
           3047  Throttle valves 
           3057  Ventilator 
           3070 ,  3072 , 
           3074  and  3076  Temperature sensor 
           4001  Installation 
           4003  Vehicle bodywork, workpiece 
           4005  Drying tunnel, process chamber 
           4025 ,  4045  Line 
           4041  Line system 
           4046  Control device 
           4047  Throttle valve 
           4057  Ventilator 
           4078  Balance 
           5001  Installation 
           5003  Vehicle bodywork, workpiece 
           5011 ,  5012  and 
           5013  Lock 
           5036  Hot gas line 
           5037  Heat transfer device 
           5039  Heat exchanger 
           5041  Line system 
           5041   a  Circulating air recirculating channel 
           5045  Line 
           6001  Installation 
           6005  Drying tunnel 
           6015   a ,  6015   b  Drying portion 
           6045  Line