Abstract:
A gas mask and breathing equipment is provided with a circuit for breathing gas and with a heat exchanger ( 7 ) cooled by an evaporating agent. The evaporating agent is introduced from an evaporating agent container ( 8 ) into the heat exchanger ( 7 ) via at least one group of spraying elements ( 9 ) and a gas delivery means ( 11 ) allows a gas volume flow to flow through the heat exchanger ( 7 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2008 055 700.5 filed Nov. 3, 2008, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a device for cooling the breathing gas temperature in a respirator with a circuit for breathing gas and to a process for controlling the cooling of the respirator. 
       BACKGROUND OF THE INVENTION 
       [0003]    In respirators, especially in gas masks and breathing equipment, respiration takes place in a closed circuit to reduce the weight and to increase the use time, and only the amount of oxygen consumed is replaced from a pressurized gas reservoir and fed into the circuit. Enrichment of the carbon dioxide (CO 2 ) breathed out in the circuit to physiologically harmful levels in the circuit must be avoided. An absorber with an absorbent, which extracts the CO 2  from the breathing circuit, is present for this in the circuit. Prior-art absorbents consist of one or more alkali hydroxides and contain or consist especially of calcium hydroxide. The absorbents are contained in respirators in a breathing lime absorber, a so-called alkali cartridge used as a replaceable part. Heat and moisture are generated during the chemical reaction taking place between the CO 2  and the absorbent. The heat leads to a rise in the breathing gas temperature and may thus lead to a physical compromise for the person respirated by means of the respirator. Temperatures 25° C. above the ambient temperature were measured in experimental measurements in the breathing gas saturated with moisture at the outlet of the breathing lime absorber. 
         [0004]    One solution to eliminate this problem is to condition the breathing air in closed-circuit gas masks and breathing equipment, which are used for a use time of several hours, i.e., to both cool the breathing air and reduce the quantity of moisture in the circuit. 
         [0005]    The cooling of the breathing lime absorber with the use of paraffin or the use of a salt as a coolant for such respirators is disclosed in DE 879 851 B, where the evaporation or melt temperature is between 40° C. and 180° C. and the breathing lime absorber is surrounded by the coolant. The breathing lime absorber is used as a heat exchanger rather than the breathing gas being cooled directly. The use of a separate heat exchanger, in which the exchange of the amount of heat is brought about by the motion of the air generated by the breathing bag, is known from U.S. Pat. No. 4,635,629. The exchanged amount of heat is thus not adapted to the breathing gas temperature and cannot be influenced by a control circuit. Cooling of the breathing lime absorber with an evaporating agent by means of the external evaporative cooling via the housing of the lime absorber is known from DE 10304394 B4 (U.S. Pat. No. 6,990,979). The use of a fan is known from the same document DE 10304394 B4 to increase the amount of air and to improve as a consequence the heat exchange. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the present invention is to provide a respirator with a circuit for breathing gas with a regulated and improved conditioning for the breathing gas and to provide a process for regulating the respirator. 
         [0007]    According to the invention, a gas mask and breathing equipment is provided comprising a circuit for breathing gas as well as a heat exchanger connected to the circuit, the heat exchanger being cooled by an evaporating agent and including a first duct for the breathing gas and a second duct, the first duct of the heat exchanger being thermally and mechanically coupled with the second duct of the heat exchanger via a heat exchange surface. An evaporating agent container is provided with evaporating agent. A spraying element is provided for introducing the evaporating agent from the evaporating agent container into the second duct of the heat exchanger via the spraying element. A gas delivery means is provided to send a gas volume flow through the second duct of the heat exchanger, the first duct being located on an incoming flow side of a user of the gas mask and breathing equipment. 
         [0008]    According to another aspect of the invention, a process is provided for regulating a gas mask and breathing equipment. The process comprises the steps of providing a circuit for breathing gas and connecting a heat exchanger to the circuit. The heat exchanger is cooled by an evaporating agent and includes a first duct for the breathing gas and a second duct. The first duct of the heat exchanger is thermally and mechanically coupled with the second duct of the heat exchanger via a heat exchange surface. The process further includes providing an evaporating agent container with evaporating agent, providing a spraying element, introducing the evaporating agent from the evaporating agent container into the second duct of the heat exchanger via the spraying element and providing a gas delivery means. The gas delivery means sends a gas volume flow through the second duct of the heat exchanger with, the first duct being located on an incoming flow side of a user of the gas mask and breathing equipment. 
         [0009]    The process further may include the steps of providing a temperature sensor, providing a pressure sensor, providing a control unit, detecting and analyzing signals of the temperature sensor and of the pressure sensor by the control unit and controlling the conditioning of the breathing gas. The control unit switches on the gas delivery means, for sending a gas volume flow, by means of an actuating signal based on breathing gas temperature exceeding a first temperature limit. The control unit controls an adjusting valve in terms of the duration of the opening time, for introducing the evaporating agent, by means of an actuating signal based on breathing gas temperature exceeding a second temperature limit of the breathing gas temperature. 
         [0010]    The first temperature limit of the breathing gas temperature may be preset in the range of 28° C. to 34° C. and the second temperature limit of the breathing gas temperature may be preset in the range of 31° C. to 37° C. The first temperature limit of the breathing gas temperature and the second temperature limit of the breathing gas temperature can be set as a function of the ambient temperature of the site of use. The first temperature limit of the breathing gas temperature and the second temperature limit of the breathing gas temperature can be set as a function of the humidity of the air at the site of use. 
         [0011]    An essential advantage of the present invention is the direct cooling of the breathing air in the breathing air duct of an air/air heat exchanger. As a result, cooling is more efficient than cooling via the outer surface of a lime absorber. The ergonomic requirements imposed on the closed-circuit gas mask and breathing equipment do not make it possible to use freely selectable geometric embodiments of the outer surface of the breathing lime absorber for the external cooling, so that an optimal thermal coupling of the largest possible number of breathing lime pellets in a narrow space with the outer surface of the breathing lime absorber is possible only conditionally. By contrast, nearly the entire amount of breathing gas circulating in a circuit can be cooled with a separate air/air heat exchanger. The air/air heat exchanger comprises a first inner duct for the breathing gas circuit and a second outer duct for the cooling gas circuit. The air in the cooling circuit is cooled down by means of the evaporative cooling by ambient air being caused to flow through the second duct by means of a gas delivery means and by a liquid evaporating agent being introduced into the second duct of the heat exchanger. The evaporating agent in the second duct is preferably introduced directly to the heat exchange surface between the first and second ducts. 
         [0012]    A material possessing good thermal conductivity, for example, a metal, is preferably used as the material for the heat exchange surface. 
         [0013]    The liquid evaporating agent is applied in the second duct directly onto the heat exchange surface by spray nozzles arranged in the second duct and is distributed there. As a result, the heat exchange surface is cooled directly, on the one hand, by the direct contact with the liquid evaporating agent, and, on the other hand, the air in the second duct of the air/air heat exchanger is cooled at a heat exchange surface due to the evaporation of the particles of evaporating agent. 
         [0014]    An electrically driven positive displacement blower designed as a fan, which delivers a gas volume flow of preferably 150 L to 250 L per minute uniformly along the second duct of the heat exchanger in order to achieve evaporation of the evaporating agent, especially water, an aqueous solution or a mixture with water, which cools the air in the second duct, is used as a gas delivery means to deliver the air in the second duct in the simplest case. The amount of heat generated in the breathing lime absorber and contained in the breathing gas is removed in this manner to the outside as a result. 
         [0015]    A gas volume flow of at least 150 L per minute has proved to be necessary to generate the amounts of convection air, which are different for the heat transport in the second duct. Both a parallel-flow heat exchanger and a counterflow heat exchanger may be used as the heat exchanger, the selection of the corresponding type being dependent on the dimensions in space of the closed-circuit gas mask and breathing equipment and the arrangement of the components gas delivery means, high-pressure oxygen cylinder, lime absorber, breathing bag and evaporating agent container in the closed-circuit gas mask and breathing equipment, which arrangement is dictated by the dimensions. 
         [0016]    The evaporating agent, preferably water, can be provided in an evaporating agent container. The pressure of the oxygen cylinder, 200 bar, is brought to a working pressure of 5 bar by means of a pressure reducer. The pressure is then reduced further by means of a dispensing nozzle, so that oxygen is introduced into the breathing circuit at a rate ranging from 1 L/minute to 2 L/minute. 
         [0017]    For a use time of 4 hours and with the user of the respirator having a respiratory minute volume of 30 L per minute, the amount of thermal energy generated in about 3 L of breathing lime is about 750 kJ. Conditioning improved according to the present invention can be achieved, while the limitations dictated by the weight and size of the closed-circuit gas mask and breathing equipment are taken into account at the same time, with the removal of a thermal energy of 450 kJ. 
         [0018]    The quantity of water needed as an evaporating agent to cool the thermal energy of 450 kJ is 0.25 L, which is provided in the evaporating agent container for injection into the second duct of the heat exchanger under a pressure of 2 bar to 6 bar. The heat exchanger is designed for cooling the thermal energy of 450 kJ to a thermal output of 30 W. A pressure in the range of 2 bar to 6 bar is set via a reducing nozzle at the outlet of the evaporating agent container for operating the spraying elements. The spraying elements spray the evaporating agent by means of an adjusting valve onto the heat exchange surface of the heat exchanger. A control unit sends a control signal to the adjusting valve. The adjusting valve is opened and closed cyclically in a cycled manner. 
         [0019]    To measure the breathing gas temperature, a temperature sensor is arranged in the breathing gas circuit in the first duct of the heat exchanger at the breathing gas outlet to the user of the gas mask and breathing equipment and is electrically connected to the control unit. 
         [0020]    To spray the evaporating agent into the second duct, a pressure must be admitted to the evaporating agent. In a preferred embodiment, this pressure can be made available by the oxygen cylinder present in the closed-circuit gas mask and breathing equipment. 
         [0021]    In an optional embodiment, the evaporating agent may be maintained under a pressure already in the evaporating agent container itself, in which case the evaporating agent container is introduced into the gas mask and breathing equipment as a consumable agent for the operation, for example, in the form of a cartridge. The necessary pressure in the range of 2 bar to 6 bar is admitted now to the evaporating agent by a propellant gas reservoir arranged in the evaporating agent container. 
         [0022]    In another preferred embodiment, the evaporating agent container is a consumable part, in which case the evaporating agent container is designed as a cartridge that is under pressure. 
         [0023]    In another embodiment according to the present invention, the spraying elements are arranged in the duct of the air/air heat exchanger at different angles in relation to the heat exchange surface of the heat exchanger in order to achieve distribution of the evaporating liquid over the entire area on the heat exchange surface. The preferred angle range of the array of spraying elements is in an angle range of 30° to 90° in relation to the heat exchange surface. 
         [0024]    The cooling of the breathing gas by means of the gas volume flow in the second duct of the heat exchanger, the quantity of evaporating agent sprayed in via the group of spraying elements, and the operating pressure set on the evaporating agent container are regulated in the following manner: the gas delivery means is activated above a predetermined first breathing gas temperature of 30° C., the spraying elements are activated when a second, predetermined breathing gas temperature of 35° C. is exceeded, and they spray quantities of evaporating agent into the second duct in a cycled manner. The first and second breathing gas temperatures are preset by a presetting means within the temperature limits of 28° C. to 34° C. for the first breathing gas temperature and within the temperature limits of 31° C. to 37° C. for the second. In a special embodiment of the process according to the present invention, the temperature limits are adapted to the needs in the use of the gas mask and breathing equipment. The ambient temperature and humidity of the air at the site of use are parameters that make changes in the predefined first and second breathing gas temperatures necessary. 
         [0025]    An exemplary embodiment of the present invention will be explained below on the basis of the schematic figure. 
         [0026]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    In the drawings: 
           [0028]      FIG. 1  is a schematic diagram of a closed-circuit gas mask and breathing equipment according to the invention with the components necessary for cooling the breathing air; and 
           [0029]      FIG. 2  is a schematic view of the arrangement of the components necessary for regulating the cooling of a closed-circuit gas mask and breathing equipment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring to the drawings in particular,  FIG. 1  shows a respirator housing  10 , in which a breathing lime absorber  5 , an air/air heat exchanger  7 , an evaporating agent container  8 , nonreturn valves  2 ,  3 , a breathing bag  6 , a group of spraying elements  9 , a fan  11 , an adjusting valve  12 , a drain valve  13 , a high-pressure oxygen cylinder  14 , a pressure reducer  15 , a dispensing nozzle  16 , delivery lines  17 ,  18 , and a temperature sensor  26  are arranged. 
         [0031]    The expired air of the respirator user is released via the expiration breathing tube  4   a  and the nonreturn valve  2  to the breathing lime absorber  5 . The user of the gas mask and breathing equipment again inspires via an inspiration breathing tube  4   b  and the nonreturn valve  3 . The user inspires through the first duct  20  of the air/air heat exchanger from the breathing bag  6 , which is connected to the breathing lime absorber  5 . The circuit for the breathing gas is thus closed. 
         [0032]    The gas from the high-pressure oxygen cylinder  14  is reduced to a working pressure  7   a  of 5 bar in the closed-circuit gas mask and breathing equipment  10  with a pressure reducer  15  and reduced to the breathing pressure  6   a  via a first pressure line  17  and a dispensing nozzle  16  and fed into the circuit, and the oxygen consumed is replaced. The working pressure  7   a  of 5 bar is admitted to the evaporating agent container  5  from the outlet of the pressure reducer  15  via a second pressure line  18 . The evaporating agent is fed under the operating pressure  8   a  to the group of spraying elements  9  via an adjusting valve  12  and the feed line  27 . The spraying elements  9  are arranged such that they are directed towards the heat exchange surface  19  in the second duct  21  in the air/air heat exchanger  7  and can spray the full area of the heat exchange surface  19  with evaporating agent. The arrangement of the individual spraying elements  9  may be selected to be at right angles to the heat exchange surface  19 , but it is also advantageous for achieving wetting of the heat exchange surface  19  over a large area to direct the spraying elements at an angle differently from one another in an angle range of 30° C. to 90° C. in relation to the heat exchange surface  19 . The size of the evaporating agent container  8  is selected to be such that it stores a sufficient amount of evaporating agent for the duration of use by the user of the respirator or the respirator. In case of water, 250 mL to 450 mL are sufficient for a use time of four hours. 
         [0033]    The ambient air is drawn in the direction of the first arrow  22  of the air inlet opening  24  and is discharged on the opposite side in the direction of the second arrow  23  through an outlet opening  25 . The air now sweeps over the second duct  21  of the air/air heat exchanger  7  and removes the evaporated evaporating agent, especially water, with the air being delivered into the environment. The group of spraying elements  9  comprises at least one spraying element. In the arrangement shown in  FIG. 1 , four spraying elements  9  are shown as an example, but a smaller or greater number of spraying elements  9  is also covered by the solution according to the present invention. The spraying elements  9  are activated in a control circuit with inclusion of the breathing gas temperature. The breathing gas temperature is detected via a temperature sensor  28  at the outlet of the first duct  20  of the air/air heat exchanger  7 . 
         [0034]    A drain valve  13 , via which the liquid collected in the circuit can be drawn off into the environment, is arranged at the breathing bag  6 . 
         [0035]      FIG. 2  shows a control unit  30 , to which the temperature sensor  26  and the pressure sensor  28  are connected. 
         [0036]    The control unit  30  is designed to control the amount of air of the fan  11  by means of an actuating signal F indicated by reference symbol  11   a . The amount of air can be adjusted in the simplest manner by varying the speed of fan  11 . Furthermore, the control unit  30  is designed to open and close the adjusting valve  12  by means of an actuating signal E indicated by reference symbol  12   a . The quantity of evaporating agent flowing through the adjusting valve  12  in a cycled manner is obtained from the particular opening angles of the spraying elements  9  and the operating pressure  8   a  of the evaporating agent present at the adjusting valve  12 . The control unit  30  is designed for this to derive the opening cycle time for the adjusting valve  12  from the signal and to correspondingly actuate the adjusting valve  12  by means of the actuating signal E. The control unit  30  is designed, furthermore, to determine the working pressure  7   a  from the signal of the pressure sensor  28  and to include it in the setting of the opening cycle time for the adjusting valve  12 . 
         [0037]    While specific embodiments of the invention have been described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
       APPENDIX 
     List of Reference Numbers 
       [0000]    
       
           1  User of gas mask and breathing equipment 
           2  First nonreturn valve 
           3  Second nonreturn valve 
           4   a  Expiration breathing tube 
           4   b  Inspiration breathing tube 
           5  Breathing lime absorber 
           5   b  Breathing lime pellets 
           6  Breathing bag 
           6   a  Breathing pressure 
           7  Air/air heat exchanger 
           7   a  Working pressure 
           8  Evaporating agent container 
           8   a  Operating pressure 
           9  Group of spraying elements 
           10  Respirator housing 
           11  Gas delivery means, fan 
           11   a  Actuating signal E for the fan 
           13  Adjusting valve 
           12   a  Actuating signal F for the adjusting valve 
           13  Drain valve 
           14  High-pressure oxygen cylinder 
           15  Pressure reducer 
           16  Dispensing nozzle 
           17  First delivery line 
           18  Second delivery line 
           19  Heat exchange surface 
           20  First duct in the air/air heat exchanger 
           21  Second duct in the air/air heat exchanger 
           22  Direction of first arrow of air flow 
           23  Direction of second arrow of air flow 
           24  Air inlet opening 
           25  Air outlet opening 
           26  Temperature sensor 
           27  Feed line 
           28  Pressure sensor 
           30  Control unit