Patent Publication Number: US-6905659-B2

Title: Ozonizer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat plate laminate ozone generating apparatus including a plurality of laminated plate-shaped high voltage electrodes and low voltage electrodes between which an alternating voltage is applied to produce a discharge and generate ozone gas, and in particular, to an ozonizer which is an essential portion of the flat plate laminate ozone generating apparatus and which includes the high voltage electrodes and low voltage electrodes and to which oxygen is supplied to generate ozone gas. 
     2. Description of the Related Art 
       FIG. 25  is a cross sectional drawing of a conventional ozonizer described in, for example, Japanese Patent Publication No. 3113885 “Discharge Cell for Ozone Generator”. In a conventional ozonizer, as shown in  FIG. 25 , a plurality of low voltage electrodes  7  composed of approximately flat plate-shaped rigid bodies sandwich a pair of block(s)  25  on both sides and are superposed in a thickness direction of the plates to construct a number of electrode module laminated bodies. The electrode module laminated bodies are secured between an electrode presser plate  22  and a base  24  by means of a plurality of fastening bolts  21  passing through both side portions thereof in the laminating direction. 
     Each electrode module comprises a pair of upper and lower low voltage electrodes  7 , a pair of bilateral blocks  25  sandwiched between the low voltage electrodes  7 ,  7 , dielectric unit(s)  30  disposed between the low voltage electrodes  7 ,  7  and situated at an inner side of the blocks  25 ,  25  and a plurality of elastic spacers  26  for forming a plurality of discharge gaps provided for forming discharge gap(s)  6  at both sides of the dielectric unit(s)  30 . The elastic spacers  26  constitute rod-shapes of a circular cross-section extending in a direction orthogonal to the page. 
     The pair of bilateral blocks  25  is a rigid body of a conductive plate material such as stainless steel plate(s), and, by intervening the blocks between both side portions of the low voltage electrodes  7 , a space of an equal gap amount is formed in the thickness direction of the block(s). 
     Also, (all of) the drawings are expanded in the vertical direction and actual thickness is extremely thin, for example, three mm or less in the case of the low voltage electrode  7 , and three mm or less in the case of the block  25 . 
     Cooling water passages  9  are formed inside the pair of upper and lower low voltage electrodes  7  and combine as a heat sink. Moreover, a cooling water passage  9  is also formed in blocks  25  of one side. The cooling water passages  9  inside the low voltage electrodes  7  are communicated with a cooling water inlet/outlet  12  provided in the base  24  via the blocks  25  in order to circulate cooling water as a coolant. 
     On the other hand, an ozone gas passage  8  is formed in a main surface of the low voltage electrode  7  facing the discharge gap  6  by means of, for example, etching and the like. The ozone gas passage  8  is communicated with an ozone gas outlet  11  provided in the base  24  via an ozone gas passage  8  formed in the blocks  25 . Also, an oxygen gas inlet  10  for supplying oxygen gas to the discharge gaps  6  along a direction orthogonal to the page surface is provided at both side portions of discharge gaps  6 . 
     The dielectric unit(s)  30  disposed in the space surrounded by the upper and low voltage electrodes  7  and the bilateral blocks  25  is a thin sheet shaped rigid body comprising a sandwiched structure of a high voltage electrode  3  sandwiched between a pair of upper and lower glass plates  5 . The high voltage electrode  3  is a conductive thin sheet such as a stainless steel sheet and the like and a portion thereof is led outside as a feed terminal (not shown). 
     The discharge gap forming elastic spacers  26  provided for forming the discharge gap  6  at both sides of the dielectric unit  30  are thin resin wire rods of a circular cross-section having ozone resistance properties and resiliency, and are disposed in the discharge gaps at a predetermined interval. A thickness of each elastic spacer  26  (outside diameter) is set to be 5-6% larger than each gap amount of the discharge gaps  6  in a non-compressed state. 
     With such a setting, the elastic spacer  26  is compressed from above and below by the low voltage electrode  7  and the dielectric unit  30 , and the dielectric unit  30  is resiliently pressed from above and below by an equal pressure by this compression and maintained in a central portion, in the vertical direction, of the above mentioned space. Consequently, the discharge gaps  6  of an equal gap amount are formed at both sides of the dielectric unit  30 . 
     Moreover, in a case where rigid spacers are used instead of the elastic spacers  26 , when the blocks  25  are fastened, of course, the rigid spacers used are of a smaller diameter than the elected discharge gap length (the height of the discharge gap in the laminating direction). Thus, the spacers are not compressed in the laminating direction in the discharge gaps. 
     Next, operation will be explained. 
     When an alternating high voltage is applied between the low voltage electrode  7  and the high voltage electrode  3 , a dielectric barrier discharge is generated in the discharge gap  6  via a dielectric  5 . Oxygen gas is dissociated to single oxygen atoms by this discharge, and, at roughly the same time, a three body collision is induced between these oxygen atoms, other oxygen molecules and a wall and the like and ozone gas is generated. By using this mechanism and continuously supplying oxygen gas to the discharge gaps  6 , the ozone gas generated by the discharge may be continuously derived as ozonized gas from the ozone gas outlet  11 . 
     An ozone generating efficiency derived from this discharge is normally, at most, 20%. That is to say, 80% of the discharge power heats the electrodes and is lost. Also, the generating efficiency of the ozone gas is dependent on the temperature of the electrode (strictly speaking, the temperature of the discharge gas), and the lower the temperature of the electrode the higher the generating efficiency. Hence, the electrodes are directly cooled with cooling water and the like or a rise in gas temperature in the discharge gaps  6  may be suppressed by shortening the gap length of the discharge gap  6 , and the ozone generating efficiency is increased by increasing the electron temperature, ozone decomposition is inhibited and, as a result, an efficient ozonizer capable of deriving highly concentrated ozone gas may be provided. 
     In a conventional ozonizer of such a construction, electrode cooling is one sided cooling of the low voltage electrode  7  side and the high voltage electrode  3  is not cooled. Thus, in a case where the same (amount of) power is supplied, the temperature of the gas in the discharge gaps  6  is about four (4) times that of a both side method for cooling the high and low voltage electrodes. Since the amount of generated ozone which is decomposed is increased by this rise in gas temperature, the discharge power density input to the electrode must be further increased and the ozone gas cannot be efficiently generated. 
     Moreover, when using the elastic spacers  26 , because there are electrons having sufficiently high energy in the discharge gaps  6  due to the discharge, the elastic spacers  26  which are formed of an organic material collide with the high energy electrons (discharge energy) by contact with this discharge and the chemical bond incurs separation damage. When the ozonizer is used in continuous operation, the elastic spacers  26  deteriorate in a short period of time compared to metal spacers and an even flow of gas is made impossible by this deterioration, and there are drawbacks in that efficiency is rapidly reduced and the service life of the apparatus is shortened. 
     Also, even in a case where elastic spacers made of an ozone resistant Teflon (registered trademark) are used, the above mentioned high energy electrons (discharge energy) collide and the chemical bond suffers separation damage. Further, even if a material which is generally “flame retardant material” in air is used, as in the case of highly concentrated ozone or oxygen gas atmosphere “combustible material”, there is a problem in that a sublimation reaction of the elastic spacers is activated by the discharge energy at a portion disposed to directly contact the discharge gap and clean ozone cannot be obtained. 
     On the other hand, in the case where the rigid spacers are used instead of the elastic spacers  26 , they are, naturally, designed to be of a smaller diameter than the elected discharge gap length when being fastened via the blocks  25 . Hence, when the discharge gaps  6  are tiny gaps and a high concentration of ozone is to be generated, a pressure loss of the gap partitioned by the spacers  26  for forming the discharge gaps (pressure loss of the tiny gaps between the dielectric  5  and the spacers  26  for forming the discharge gaps) is much smaller than the pressure loss of the discharge gas passages (pressure loss of the gas passages orthogonal to the page surface of FIG.  25 ). Thus, the even flow of gas is made difficult by the spacers  26  for forming the discharge gaps. Consequently, there are problems in that the ozone generating efficiency is degraded and the ozonizer cannot be made compact. 
     Generally, a fluid cannot be evenly flowed unless the pressure loss of the gap formed by the spacer  26  can be made approximately ten (10) times or more the pressure loss of the discharge passage portion. For example, when the discharge gap  6  is 0.1 mm, a gap between the thickness of the spacer  26  and the discharge gap must be highly precise. It is extremely difficult to manufacture the spacers  26  with this sort of precision and dispose them without contacting the discharge gap. For this reason, a large cost increase is incurred in order to manufacture the spacers  26  with good precision and inexpensive manufacture of the apparatus is impossible. 
     Moreover, in the conventional ozonizer constructed such as above, the electrode module including the pair of upper and lower low voltage electrodes  7 , the bilateral blocks  25  sandwiched between these low voltage electrodes  7 ,  7 , the dielectric units  30  positioned at the inner side of the blocks  25 ,  25  and disposed between the low voltage electrodes  7 ,  7 , and the plurality of elastic spacers  26  for forming the discharge gap(s) provided at both sides of the dielectric unit  30  for forming the discharge gaps  6  is laminated as a plurality via the low voltage electrodes  7  and is secured between the electrode presser plate  22  provided on top and the base  24  provided at the bottom by the plurality of fastening bolts  21  as a fixing means passing through the electrode module at both side portions thereof in the laminating direction. That is, since the structure is such that the dielectric module held between the low voltage electrodes  7  is fastened at both ends thereof, both sides of the electrode module become fulcrums and the low voltage electrodes  7  which are supposed to be straight are deformed to a circular arc shape, and there is a problem in that, particularly in a discharge gap of 0.1 mm in thickness, the gap length cannot be even and highly concentrated ozone cannot be obtained. 
     Further, a conventional ozone passage  8  is manufactured without being gas sealed. Thus, 100% of the oxygen gas raw material cannot be supplied to each electrode module sandwiched by the laminated low voltage electrodes  7 . That is, a “short pass phenomena” occurs in which oxygen gas escapes directly to the ozone gas outlet without passing through the discharge passage of the electrode module. When this “short pass phenomena” takes place, the ozone generating efficiency of the electrode module is reduced and highly concentrated ozone cannot be generated; further, since the concentration of the ozone generated by the discharge gap  6  is diluted by a short pass fluid flow of the raw material oxygen gas, there is a problem in that highly concentrated ozone gas cannot be further derived. 
     SUMMARY OF THE INVENTION 
     The present invention was made to overcome all of the above mentioned problems. 
     A first object of the present invention is to provide an ozonizer in which an electrode module construction has high reliability without damaging ozone generating characteristics and, nevertheless, the life of the electrode module may be increased. 
     A second object of the present invention is to provide an ozonizer in which lamination of an extremely thin sheet-shaped electrode module may be performed by means of a simple operation and further compact modularization may be realized. 
     A third object of the present invention is to provide an ozonizer in which a construction of both a high voltage electrode  3  and a low voltage electrode  7  is capable of being cooled well. 
     A fourth object of the present invention is to provide an ozonizer in which a purity of generated ozone gas is high, that is, clean ozone gas may be generated. 
     According to one aspect of the present invention there is provided an ozonizer including a flat plate-shaped low voltage electrode, a flat plate-shaped high voltage electrode facing a main surface of the low voltage electrode. The ozonizer also includes a flat plate-shaped dielectric and a spacer for forming a discharge gap of a thin thickness in a laminating direction provided between the low voltage electrode and the high voltage electrode, a high voltage electrode cooling unit for forming a cooling water passage insulated from the high voltage electrode inside the high voltage electrode. An alternating voltage is applied between the low voltage electrode and the high voltage electrode and a discharge is produced in the discharge gap injected with oxygen gas to produce ozone gas. 
     Thus, the cooling efficiency of the discharge gaps is improved and the temperature of the discharge gaps may be satisfactorily reduced. Accordingly, power density may be increased without decreasing ozone generating efficiency, and size reduction and cost reduction may be provided for an apparatus in which it is possible to reduce the number of electrode modules. Further, since the high voltage electrodes are cooled via the high voltage electrode cooling unit, standard service water may be used as cooling water without using ion exchanged water and the like of small electric conductivity. Thus, an electric conductivity monitoring device or ion exchanged water circulating equipment and the like is unnecessary and, by reducing the number of apparatus components, it is possible provide for cost reductions or reduce maintenance costs. 
     According to another aspect of the present invention there is provided an ozonizer including a flat plate-shaped low voltage electrode, a flat plate-shaped high voltage electrode facing a main surface of the low voltage electrode. The ozonizer also includes a flat plate-shaped dielectric and a spacer for forming a discharge gap of a thin thickness in a laminating direction provided between the low voltage electrode and the high voltage electrode. The ozonizer also includes a high voltage electrode cooling unit for forming a cooling water passage insulated from the high voltage electrode inside the high voltage electrode, a manifold block provided adjacent to the low voltage electrode and formed with a cooling water passage connected with the cooling water passage provided in the low voltage electrode, or formed with an ozone gas passage connected with the ozone gas passage provided in the low voltage electrode, both main surfaces of the low voltage electrode facing the discharge gap are covered in an inorganic dielectric film. A main surface of the dielectric facing the high voltage electrode is coated with a conductive film having conductive properties, and the conductive film contacts the high voltage electrode. 
     Thus, it is possible to form discharge gaps for generating clean ozone in which metallic contamination does not develop and the cooling efficiency of the discharge gaps may be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a typical explanatory drawing for explaining the ozonizer of the present invention; 
         FIG. 2  is a typical detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 1 of the present invention; 
         FIG. 3  is a top view of a low voltage electrode of an ozonizer of an Embodiment 2 of the present invention; 
         FIG. 4  is cross sectional perspective view taken along the line IV—IV in  FIG. 3 ; 
         FIG. 5  is cross sectional perspective view taken along the line V—V in  FIG. 3 ; 
         FIG. 6  is an explanatory drawing of a high voltage electrode cooling unit  2  of an ozonizer of Embodiment 3 of the present invention; 
         FIG. 7  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 5 of the present invention; 
         FIG. 8  is a top view of a low voltage electrode of an ozonizer of an Embodiment 6 of the present invention; 
         FIG. 9  is cross sectional perspective view taken along the line IX—IX in  FIG. 8 ; 
         FIG. 10  is cross sectional perspective view taken along the line X—X in  FIG. 8 ; 
         FIG. 11  is a top view of a low voltage electrode of an ozonizer of an Embodiment 7 of the present invention; 
         FIG. 12  is cross sectional perspective view taken along the line XII—XII in  FIG. 11 ; 
         FIG. 13  is cross sectional perspective view taken along the line XIII—XIII in  FIG. 11 ; 
         FIG. 14  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 8 of the present invention; 
         FIG. 15  is a side elevation of a high voltage electrode and a dielectric of an ozonizer of an Embodiment 9 of the present invention; 
         FIGS. 16A and 16B  are drawings of a dielectric, as viewed from the top and as viewed from the side, respectively, of ozonizer of an Embodiment 10 of the present invention; 
         FIG. 17  is a side elevation of a high voltage electrode and a dielectric of an ozonizer of an Embodiment 11 of the present invention; 
         FIG. 18  is a cross sectional drawing of a manifold block of an ozonizer of an Embodiment 14 of the present invention; 
         FIG. 19  is a top view of a low voltage electrode of an ozonizer of an Embodiment 15 of the present invention; 
         FIG. 20  is cross sectional perspective view taken along the line XX—XX in  FIG. 19 ; 
         FIG. 21  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 16 of the present invention; 
         FIG. 22  is a drawing of a dielectric of an ozonizer of an Embodiment 18 of the present invention as viewed from the top; 
         FIG. 23  is a top view of a low voltage electrode of an ozonizer of an Embodiment 19 of the present invention. 
         FIG. 24  is cross sectional perspective view taken along the line XIV—XIV in FIG.  23 . 
         FIG. 25  is a cross sectional drawing of a conventional ozonizer; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be explained below with reference to the drawings. 
       FIG. 1  is a typical explanatory drawing for explaining a flat plate laminated ozone generating apparatus. The flat plate laminated ozone generating apparatus comprises an ozonizer  100  as an essential construction for generating ozone, an ozone transformer  200  for supplying power to the ozonizer  100  and a high frequency inverter  300 . 
     The high frequency inverter  300  changes to a required frequency power input from a power source input  404  and outputs it to an inverter output cable  403 . The ozone transformer  200  increases this power to a predetermined voltage and supplies it as power necessary for generating ozone to the ozonizer  100 . The high frequency inverter  300  further has the function of regulating current/voltage and controls a supplied power injection rate. 
     High voltage supplied from the ozone transformer  200  is supplied to high voltage electrodes  3  of the ozonizer from a high voltage cable  401  through a high voltage bushing  120 . On the other hand, low voltage is supplied to a low voltage electrode  7  from a low voltage cable  402  via a base  24 . 
     The ozonizer  100  includes a plurality of electrode modules  102  comprising high voltage electrodes  3  and a low voltage electrode  7 . A predetermined number of electrode modules  102  are laminated on the base  24  in a direction of an arrow Z in the drawing to construct an ozonizer electrode  101 . The ozonizer electrode  101  is covered by a generator cover  110 . An ozonizer oxygen gas inlet  130  for supplying oxygen gas including trace amounts of nitrogen and carbon dioxide is provided at the generator cover  110 . The supplied oxygen gas impregnates the generator cover  110  and is entrapped in later-described discharge gaps. Meanwhile, an ozone gas outlet  11  for expelling ozone gas formed by the after-described discharge gaps to outside from the ozonizer  100  and a cooling water inlet/outlet  12  for bringing in and putting out cooling water for cooling the electrode modules  102  are provided in the base  24 . 
     In the flat plate laminated ozone generating apparatus constructed such as above, the present invention particularly relates to the ozonizer  100  which is an essential portion of the ozone generating apparatus, and specifically, to a construction of a an ozonizer electrode  101  and an electrode module  102  of the ozonizer  100 . 
     Embodiment 1 
       FIG. 2  is a typical detailed cross sectional drawing of an ozonizer electrode of an ozonizer of Embodiment 1 of the present invention. In  FIG. 2 , an ozonizer electrode  101  comprises a flat plate-shaped low voltage electrode  7 , a flat plate-shaped high voltage electrode  3  facing a main surface of the low voltage electrode  7 , a flat plate-shaped dielectric  5  and a spacer (not shown) for forming a discharge gap  6  of a thin thickness in a laminating direction provided between the low voltage electrode  7  and the high voltage electrode  3 . 
     The ozonizer electrode  101  further comprises a high voltage electrode cooling unit  2  for forming a cooling water passage insulated from the high voltage electrode  3  inside the high voltage electrode  3 . 
     In the ozonizer electrode  101 , an alternating voltage is applied between the low voltage electrode  7  and the first high voltage electrode  3  ( 3 - 1 ) and the low voltage electrode  7  and the second high voltage electrode  3  ( 3 - 2 ), respectively, and a discharge is produced in the first discharge gap  6  ( 6 - 1 ) and the second discharge gap  6  ( 6 - 2 ) injected with oxygen gas to produce ozone gas. 
     Power is supplied to a feed terminal  4  of the high voltage electrode  3  from an ozone transformer  200  (shown in  FIG. 2 ) via a high voltage bushing  120 . The high voltage electrode  3  is made of a metal such as stainless steel, aluminum and the like. A main surface of the dielectric  5  is adhered to the high voltage electrode  3 . The dielectric  5  is made of a material such as ceramic, glass, silicon and the like. A discharge gap  6  is formed between the dielectric  5  and low voltage electrode  7  by means of a later-described spacer. In the present embodiment, the discharge gap  6  is formed in a disk shape and oxygen gas impregnated in the generator cover  110  of  FIG. 1  is injected from an entire periphery of the discharge gap  6  toward a central direction. 
     Oxygen gas flowing in the discharge gap  6  is converted to ozone by applying an alternating voltage between the low voltage electrode  7  and the high voltage electrode  3 . The ozone gas converted to ozonified oxygen by the discharge gap  6  is led to the ozone gas outlet  11  from a central portion of the low voltage electrode  7  via an ozone gas passage  8  provided in the low voltage electrode  7 . 
     The low voltage electrode  7  is a thin sheet-shaped conductive rigid body comprising two (2) conductive plates, such as stainless steel plates and the like, joined so as to form the ozone gas passage  8  there-between. A cooling water passage  9  for increasing an ozone generating efficiency is provided in the low voltage electrode  7  in addition to the ozone gas passage(s)  8 . A gas temperature in the discharge gap  6  is lowered by flowing cooling water in the cooling water passage  9 . 
     On the other hand, the high voltage electrode cooling unit  2  is provided inside each high voltage electrode  3  for cooling the high voltage electrode  3 . The high voltage electrode cooling unit  2  comprises a flow tube  2   b  made of a high thermal conducting/high electric insulating material for circulating cooling water therein inserted in a through hole bored through the high voltage electrode  3 , and a thermal conducting adhesive  2   a  of high thermal conductivity filled between the flow tube  2   b  and the through hole for fixing the flow tube  2   b  in the through hole. 
     The ozone gas passage  8  formed in the low voltage electrode  7  is connected to the ozone gas outlet  11  provided in the base  24  via an ozone gas passage  8  formed in a manifold block  23 . On the other hand, the cooling water passages  9  formed in the low voltage electrode  7  and low voltage electrode  7  are connected to the cooling water inlet/outlet  12  provided in the base  24  via a cooling water passage  9  formed in the manifold block  23 . 
     Although not specifically shown in the drawings, a gasket material, such as an O-ring and the like, is sandwiched between low voltage electrode  7  and manifold block  23  or base  24  for water-tightness of the cooling water. Moreover, a gasket material, such as an O-ring and the like, is also sandwiched for air-tightness of the ozone gas. 
     An electrode module(s)  102  comprising the low voltage electrode  7 , high voltage electrode  3 , dielectric  5 , spacer and high voltage electrode cooling unit  2  is fastened and fixed between an electrode presser plate  22  and the base  24  by fastening bolts  21  passing through each structural element. The discharge gaps  6  are maintained at a predetermined thickness in the laminating direction by means of the manifold block  23 . 
     Moreover, in the present embodiment, the dielectric  5 , necessary for silent (dielectric barrier) discharge, is provided between the low voltage electrode  7  and high voltage electrode  3  and the spacer is disposed between this dielectric  5  and the low voltage electrode  7  to provide the discharge gap  6 . However, the spacer may also be disposed between the high voltage electrode  3  and the dielectric  5  to provide the discharge gap  6 . 
     Next, operation will be explained, when an alternating voltage is applied between the low voltage electrode  7  and the high voltage electrode  3  a silent (dielectric barrier) discharge is produced by the discharge gap  6 . When oxygen gas is passed in the discharge gap  6 , the oxygen is converted and ozone is produced. The oxygen gas impregnating the generator cover  110  passes through the discharge gap  6  formed between the low voltage electrode  7  and dielectric  5  and in this course is converted to ozone. In the present embodiment, the high voltage electrode  3 , dielectric  5  and discharge gap  6  formed there-between are each formed in a an approximate disk shape. The oxygen gas flows from an entire periphery of the dielectric  5  toward a center and becomes ozonified oxygen gas in the discharge gaps  6 . 
     In order to efficiently create ozone it is necessary that the discharge gap  6 , which is a space of particularly thin thickness, be precisely maintained. The electrode module laminated body is fastened between the electrode presser plate  22  and the base  24  by means of the plurality of fastening bolts  21  disposed in the blocks  23  and passing through both side portions thereof in the laminating direction so as to obtain a predetermined gap precision. The discharge gap(s)  6  is formed by means of discharge gap spacers (not shown) disposed at a surface of the low voltage electrode  7 . That is to say, a thickness of the discharge gap  6  (height in the laminating direction) is set by a height of these discharge gap spacers. The precision of the discharge gaps  6  is maintained by uniformly processing the height of the discharge gap spacers and by fastening each electrode with the fastening bolts  21 . 
     As an additional means for efficiently creating ozone, a method for lowering a temperature inside the discharge gaps  6  may be given. A method is conceived wherein the high voltage electrode  3  and low voltage electrode  7  are provided as electrodes and both these electrodes are cooled with water or gas and the like. Although, between water and gas, a cooling effect is greater with water, in a case where water is used it is necessary to decrease an electric conductivity (use ion exchanged water etc.) of the cooling water because a high voltage is applied at the high voltage electrode  3 . On the other hand, although there is an advantage in that this is not necessary in a case where gas is used, there are disadvantages in that the construction becomes complicated and there is a lot of noise or a heat capacity of the coolant is small. 
     In the present embodiment, the discharge gaps  6  are formed adjacent to the low voltage electrode  7  and the discharge gaps  6  are cooled by providing cooling water passages  9  in the low voltage electrode  7 . Also, the high voltage electrode cooling unit  2  is provided inside the high voltage electrode  3  for cooling the high voltage electrode  3 , and heat generated by the high voltage electrode  3  is cooled by cooling water flowing inside the cooling unit  2 . Accordingly, it is possible to maintain a low gas temperature of the discharge gaps  6  by concurrently cooling the low voltage electrode  7  and high voltage electrode  3 . 
     Furthermore, the high voltage electrode cooling unit  2  provided inside the high voltage electrode  3  comprises the flow tube  2   b  of high thermal conductivity and high electrical insulating properties and electrical insulation is maintained. In accordance with such a construction, it is not necessary to lower the electric conductivity of the cooling water flowing in the high voltage electrode cooling unit  2  and standard service water may be used. Thus, there is also an advantage in that the cooling water may be common with that for cooling the low voltage electrode  7 . 
     Accordingly, in the present embodiment, the cooling efficiency of the discharge gaps  6  is improved and the temperature of the discharge gaps  6  may be satisfactorily reduced. Thus, power density may be increased without decreasing ozone generating efficiency, and size reduction and cost reduction may be provided for in an apparatus in which it is possible to reduce the number of electrode modules. Further, since the high voltage electrodes  3  are cooled via the high voltage electrode cooling unit  2 , standard service water may be used as cooling water without using ion exchanged water and the like of a small electric conductivity. Thus, an electric conductivity monitoring device or ion exchanged water circulating equipment and the like is unnecessary and, by reducing the number of apparatus components, it is possible to provide for cost reductions or reduce maintenance costs. 
     Embodiment 2 
       FIG. 3  is a top view of a low voltage electrode  7  of an ozonizer of Embodiment 2 of the present invention.  FIG. 4  is cross sectional perspective view taken along the line A—A in FIG.  3 .  FIG. 5  is cross sectional perspective view taken along the line B—B in FIG.  3 . As shown in  FIGS. 4 and 5 , the low voltage electrode  7  is constructed from two (2) metal electrodes, an upper low voltage electrode  7   a  and a lower low voltage electrode  7   b . Grooves of several mm in depth are formed by etching or machining in advance a main surface of the two electrodes  7   a ,  7   b . Then, the two electrodes  7   a ,  7   b  are adhered such that these grooves line up to produce the low voltage electrode  7 . The lined up grooves form an ozone gas passage  8  and cooling water passage(s)  9  inside the low voltage electrode  7 . 
     Furthermore, an ozone gas passage  8  and cooling water passage  9  extending in the laminating direction are formed in an ozone gas/cooling water deriving portion  900  at one end portion (left side in  FIG. 3 ) of the low voltage electrode  7 . Here, the cooling water passage  9  is divided into a cooling water inlet  9   a  and a cooling water outlet  9   b . The cooling water passage(s)  9  connected to the cooling water inlet  9   a  and cooling water outlet  9   b  is formed over an approximate entirety inside the low voltage electrode  7 , as shown by the dotted line in FIG.  3 . That is, they are formed as a plurality of concentric disk shapes from a center to a peripheral portion in an approximately disk-shaped low voltage electrode discharge portion  700 . Moreover, adjacent concentric disk-shaped cooling water passages  9  are partitioned by ribs of a thin width. On the other hand, the ozone gas passage  8  formed inside the low voltage electrode  7  extends from the passage extending in the laminating direction at the end portion to the central portion and is connected to an opening formed in both main surfaces at the central portion. 
     The ozone gas passage  8  extending in the laminating direction and provided at the end portion of the low voltage electrode  7  and the cooling water passages  9  are connected with the ozone gas passage and cooling water passage formed in the manifold block  23  and finally connected to the ozone gas outlet  11  and cooling water outlet/inlet  12  provided in the base  24 . 
     A plurality of round convex portions for forming the discharge gaps  6  are formed by similar etching or machining over entire main surfaces which are at opposite sides of the surfaces where grooves are formed for forming the ozone gas passage  8  and cooling water passages  9  of the two electrodes  7   a ,  7   b , respectfully. The above ozone gas passage  8  is communicated with the opening formed in the surface for forming the discharge gaps  6 . 
     Generated ozone gas is led from the central portion of the low voltage electrode  7  through the ozone gas passage  8  provided in the low voltage electrode  7  to the ozone gas passage  8  extending in the laminating direction in the ozone gas/cooling water deriving portion  900  of one end portion of the low voltage electrode  7 . On the other hand, cooling water flowing throughout the whole interior of the low voltage electrode  7  enters the low voltage electrode  7  from a cooling water inlet opening  9   a  of the ozone gas/cooling water deriving portion  900  and cools the entire surface(s) of the low voltage electrode discharge portion  700  and comes out the cooling water outlet opening  9   b  of the ozone gas/cooling water deriving portion  900 . 
     The collection of ozone gas outlets and collective structure of inlets/outlets of cooling water in the ozone gas/cooling water deriving portion  900  at the end portion of the low voltage electrode  7  is connected to the ozone gas outlet  11  and cooling water inlet/outlet  12 , respectfully, provided in the base  24  in cooperation with the manifold blocks  23  provided adjacent to the low voltage electrode  7 . Thus, in the present embodiment, collective coupling and piping members are eliminated by forming passages in the low voltage electrode  7  and manifold block  23  and a compact and simplified ozonizer is realized by reducing the space for these coupling and piping members. 
     Accordingly, in the present embodiment, an airtight circulating space is constructed by adhering together at least two (2) metal plates with convexoconcave processing within several mm by etching or machining the low voltage electrode  7 , and because the ozone gas passage  8  and the cooling water passages  9  are formed so as to be separated in an airtight manner, it is possible to decrease the thickness of the low voltage electrode  7  and reduce the size of the apparatus. Furthermore, since piping for deriving cooling water and ozone is unnecessary, assembly and disassembly may be simply performed and a low cost ozonizer may be provided. 
     Moreover, in the present embodiment, although the low voltage electrode  7  is made by joining together two (2) electrodes  7   a ,  7   b , three (3) or more electrodes may also be joined to form an ozone gas passage  8  and cooling water passages  9  at an inside portion thereof. 
     Also, in the present embodiment, although the discharge gap  6  is provided between the low voltage electrode  7  and dielectric  5  and the ozone gas passage  8  is formed inside the low voltage electrode  7 , a discharge gap may be provided between the high voltage electrode  3  and dielectric  5  and an ozone gas passage may be formed inside the high voltage electrode  3 . 
     Embodiment 3 
       FIG. 6  is an explanatory drawing of a high voltage electrode cooling unit  2  of an ozonizer of Embodiment 3 of the present invention. The high voltage electrode  3  comprises a square plate-shape and convex portions having diameters of the same length as one square side are formed on both upper and lower main surfaces thereof. In the high voltage electrode  3 , five (5) parallel through holes are bored inside a surface parallel with the main surface. Flow tubes  2   b  made of a high thermal conducting/high electric insulating material, such as glass or ceramic, are inserted in the through holes. Moreover, a thermal conducting adhesive  2   a  of high thermal conductivity is filled between the flow tubes  2   b  and the through holes and the flow tubes  2   b  are fixed in the through holes. 
     Cooling water manifolds  2   d  are provided so as to connect end portions of each flow tube  2   b . The cooling water manifolds  2   d  comprise approximately long, thin shapes extending along two (2) sides facing the high voltage electrode  3 . Manifolds are formed inside the cooling water manifolds  2   d  along a center axis. One end of the manifold(s) is closed. A cooling water inlet  2   e  is provided at an end portion of one of the cooling water manifolds  2   d . A cooling water outlet  2   f  is provided at an end portion of the other cooling water manifold  2   d . The manifolds formed inside the cooling water manifolds  2   d  are communicated with each flow tube  2   b.    
     Next, operation will be explained. Generated heat from a discharge is produced from both surfaces of the high voltage electrode  3 . This heat propagates to an inner portion of the high voltage electrode  3 , which is made of a material having good thermal conduction, and is absorbed by cooling water flowing in cooling water passages  2   c  inside the flow tubes  2   b . Thus, a temperature of the high voltage electrode  3  is maintained low. Both ends of the flow tubes  2   b  are collected together by means of the cooling water manifolds  2   d  and cooling water comes in and goes out through these manifolds. 
     Cooling water entering from the cooling water inlet  2   e  provided in cooling water manifold  2   d , is diverted by the cooling water manifold, absorbs heat in each of the flow tubes  2   b  and exits from the cooling water outlet  2   f . Since a high voltage electric potential is electrically insulated by the flow tube  2   b , there is no (electrical) leakage from the cooling water and it is not necessary to use a high electric resistance water (i.e., ion exchanged water). The same service water for cooling the low voltage electrode  7  may be used. In accordance with such a construction, by directly cooling the high voltage electrode  3 , the construction is simple and energy efficient cooling may be performed, and a high performance ozonizer may be provided. 
     Accordingly, in the present embodiment, the construction is such that the high voltage electrode cooling unit  2  is provided inside the high voltage electrode  3  and electrically insulated by the flow tube  2   b  of high thermal conductivity and excellent electrical insulating properties, and further, thermal conduction is improved by filling the thermal conducting adhesive  2   a  of high thermal conductivity in the space between the high voltage electrode  3  and the flow tube  2   b  to suppress thermal resistance. Thus, ion exchanged water and the like of a small electric conductivity is unnecessary and standard service water may be used as cooling water. Thus, an electric conductivity monitoring device or ion exchanged water circulating equipment and the like is unnecessary and, by reducing the number of apparatus components, it is possible provide for cost reductions and reduce maintenance costs. 
     Also, a plurality of flow tubes  2   b  are provided lined up and parallel with the main surface of the high voltage electrode  3 . Thus, the flat plate-shaped high voltage electrode  3  may be efficiently cooled. 
     Embodiment 4 
     The present embodiment relates to a method of joining metal plates. As a common method for joining the two (2) metal sheets  1   a ,  1   b , a brazing method using a brazing filler as a bonding agent may be given. Incidentally, because ozone circulates in the ozone gas passage  8 , the ozone gas causes an oxidation reaction with the brazing filler and this produces adverse phenomena for the ozonizer such as ozone gas decomposition, the creation of oxides and the like. Here, in the present invention, this common brazing method is not employed. 
     That is to say, this common brazing method is not used in joining the two electrodes  7   a ,  7   b  of Embodiment 2. In the present embodiment, a heating/pressure type joining method is used for joining the two metal plates. In this method, two metal plates are pressed together in the laminating direction with a large pressure while heating and the metal (plates) are fused at their contact surfaces to be joined together. The metal is melted at the particular melting point of the metal. Thus, it is possible to join the metal by means of a predetermined heat and predetermined pressure which are determined by the joining material. Another bonding agent is also not used at all, to say nothing of brazing filler. Thus, it is possible to generate clean ozone without producing an oxide reactant due to ozone. 
     Accordingly, in the present invention, since the joining method used for adhering two or more metal plates joins by means of heat and pressure only, without using a bonding agent, ozone caused corrosion of the bonding agent does not occur and it is possible to realize an ozonizer having a long life and high reliability. 
     Embodiment 5 
       FIG. 7  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 5 of the present invention. In the present invention, an entire discharge surface of the low voltage electrode  7  facing the discharge gap  6  is covered with a dielectric film  13  of an inorganic material. This dielectric film  13  faces the discharge gap  6 . A thickness of the dielectric film  13  is sufficient to block metal ions. 
     In an ozonizer constructed such as above, both surfaces of the discharge gap  6  for producing a silent discharge are enclosed with the inorganic material, and clean ozone without metallic contamination may be generated by passing oxygen gas through this gap. 
     Embodiment 6 
       FIG. 8  is a top view of a low voltage electrode  7  of an ozonizer of an Embodiment 6 of the present invention.  FIG. 9  is cross sectional perspective view taken along the line IX—IX in FIG.  8 .  FIG. 10  is cross sectional perspective view taken along the line X—X in FIG.  8 . In the present embodiment, an entire discharge surface of the low voltage electrode  7  facing the discharge gap  6  is covered with a ceramic dielectric film  13   a . The ceramic dielectric film  13   a  faces the discharge gap  6 . A plurality of small, disk-shaped, ceramic dielectric discharge gap spacers  13   a   1  for forming the discharge gap  6  are disposed on the ceramic dielectric film  13   a.    
     In an ozonizer constructed such as above, oxygen gas flows into the discharge gap  6  from an outer periphery of the low voltage electrode  7  and ozone is formed by means of a silent discharge while the oxygen gas passes between the ceramic dielectric discharge gap spacers  13   a   1 , and the ozone passes through an inner portion of the low voltage electrode  7  and flows out to the outside by means of an ozone gas passage  8  formed in a central portion of the low voltage electrode  7 . At this time, because the spacers are also an inorganic material, in addition to both surfaces enclosing the discharge gap  6  with the inorganic material, a further clean ozone without metallic contamination may be generated. 
     Moreover, the ceramic dielectric film  13   a  is formed by a thermal spraying technique and a thickness thereof is controlled to several â. m in thickness. Further, according to this thermal spraying technique it is also possible to concurrently form the ceramic dielectric discharge gap spacers  13   a   1 . 
     Embodiment 7 
       FIG. 11  is a top view of a low voltage electrode  7  of an ozonizer of an Embodiment 7 of the present invention.  FIG. 12  is cross sectional perspective view taken along the line XII—XII in FIG.  11 .  FIG. 13  is cross sectional perspective view taken along the line XIII—XIII in FIG.  11 . In the present embodiment, an entire discharge surface of the low voltage electrode  7  facing the discharge gap  6  is covered with a glass dielectric film  13   b . The glass dielectric film  13   b  faces the discharge gap  6 . A plurality of small, disk-shaped, glass dielectric discharge gap spacers  13   b   1  for forming the discharge gap  6  are disposed on the glass dielectric film  13   b.    
     In an ozonizer constructed such as above, oxygen gas flows into the discharge gap  6  from an outer periphery of the low voltage electrode  7  and ozone is formed by means of a silent discharge while the oxygen gas passes between the glass dielectric discharge gap spacers  13   b   1 , and the ozone passes through an inner portion of the low voltage electrode  7  and flows out to the outside by means of an ozone gas passage formed in a central portion of the low voltage electrode  7 . At this time, because the spacers are also an inorganic material, in addition to both surfaces enclosing the discharge gap  6  with the inorganic material, a further clean ozone without metallic contamination may be generated. 
     Moreover, in making the glass dielectric film  13   b , first, a glass plate of a quartz material is subjected to a shot blasting treatment using a mask and the convex glass dielectric discharge gap spacers  13   b   1  are formed. Then, the glass dielectric film  13   b  is adhered to the low voltage electrode  7  by means of an adhesive  13   b   2 . 
     Embodiment 8 
       FIG. 14  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of an Embodiment 8 of the present invention. In the present embodiment, a main surface of the dielectric  5  at the high voltage electrode  3  side is covered all over with a conductive film  14 . 
     In a case where the conductive film  14  is not provided, when a surface of the high voltage electrode  3  and a surface of the dielectric  5  are pressed together by mechanical pressure only without using an adhesive or the like, the surface of the high voltage electrode  3  and surface of the dielectric  5  cannot be closely contacted. A gap develops in one portion of a contact surface(s) and an improper discharge (local discharge) occurs in this gap. This improper discharge is a problem in that it damages the dielectric  5 , degrades the ozone generating efficiency and interferes with the generation of clean ozone. 
     In the present embodiment, by applying the conductive film  14  on the surface of the dielectric  5 , even if, for example, the contact surfaces cannot be completely closely joined and a gap develops in one portion of the contact surfaces, since the conductive film  14  of the dielectric  5  and high voltage electrode  3  have the same electric potential, it is possible to prevent an improper discharge, and it is possible to prevent the occurrence of metallic contamination. 
     Embodiment 9 
       FIG. 15  is a side elevation of a high voltage electrode  3  and a dielectric  5  of an ozonizer of an Embodiment 9 of the present invention. In the present embodiment, the high voltage electrode  3  and dielectric  5  are joined together so that there are no gaps there-between by means of a conductive adhesive. In this sort of construction as well, it is possible to increase adhesion between the high voltage electrode  3  and dielectric  5 , an improper discharge may be prevented and it is possible to prevent the occurrence of metallic contamination. Furthermore, positioning adjustments and the like are unnecessary and assembly is facilitated. 
     Embodiment 10 
       FIGS. 16A and 16B  are drawings of a dielectric  5 , as viewed from the top and as viewed from the side, of ozonizer of an Embodiment 10 of the present invention. The present embodiment includes a metallic contamination suppressing construction at an edge portion of the conductive film  14 . When a high voltage electric potential is applied to the conductive film  14 , an abnormal corona discharge occurs at an edge portion thereof. This abnormal corona discharge causes metallic contamination. In the present embodiment, an insulating film  16  is coated all around a portion formed by a step of an outer circumferential portion of the conductive film  14 . Hence, it is possible to prevent the abnormal corona discharge from occurring at the edge portion and it is possible to prevent the occurrence of metallic contamination. 
     Other constructions are similar to Embodiment 8. 
     Embodiment 11 
       FIG. 17  is a side elevation of a high voltage electrode  3  and a dielectric  5  of an ozonizer of an Embodiment 11 of the present invention. In the present embodiment, an insulating film  16  is coated all around a portion formed by a step of an outer circumferential portion of the conductive adhesive  15 . Thus, it is possible to prevent the abnormal corona discharge from occurring at the edge portion of the conductive adhesive  15  and it is possible to prevent the occurrence of metallic contamination. 
     Other constructions are similar to Embodiment 9. 
     Embodiment 12 
     In the present embodiment, an outside diameter of the high voltage electrode  3  is smaller than an outside diameter of the dielectric  5  and smaller than an outside diameter of the conductive film  14  provided on a surface of the dielectric  5 . Other constructions are similar to Embodiment 8. 
     By making the outside diameter of the high voltage electrode  3  smaller than the outside diameter of the dielectric  5  and the conductive film  14 , the abnormal corona discharge is done away with and metallic contamination may be prevented. In a case where the outside diameter of the conductive film  14  is smaller than the high voltage electrode  3 , a discharge occurs between the high voltage electrode  3  and dielectric  5  and causes metallic contamination. 
     Embodiment 13 
     The present embodiment will be described with reference to FIG.  2 . In  FIG. 2 , An ozonizer electrode  101  comprises a flat plate-shaped low voltage electrode  7 , a flat plate-shaped high voltage electrode  3  facing a main surface of the low voltage electrode  7 , a flat plate-shaped dielectric  5  and a spacer (not shown) for forming a discharge gap  6  of a thin thickness in a laminating direction provided between the low voltage electrode  7  and the high voltage electrode  3 . 
     The ozonizer electrode  101  further comprises a high voltage electrode cooling unit  2  for forming a cooling water passage insulated from the high voltage electrode  3  inside the high voltage electrode  3 . 
     In the ozonizer electrode  101 , an alternating voltage is applied between the low voltage electrode  7  and the high voltage electrode  3  and a discharge is produced in the discharge gap  6  injected with oxygen gas to produce ozone gas. 
     The ozonizer electrode  101  also comprises a manifold block  23  provided adjacent to the low voltage electrode  7  and formed with a cooling water passage  9  connected with the cooling water passage  9  provided in the low voltage electrode  7 , and formed with an ozone gas passage  8  connected with the ozone gas passage  8  provided in the low voltage electrode  7 . 
     Ozone gas, having been converted to ozonified oxygen by the discharge gap(s)  6 , passes through the ozone gas passage  8  in the low voltage electrode  7  from a central portion of the low voltage electrode  7  and is led to an end portion of the low voltage electrode  7 . A cooling water passage  9  is provided in the low voltage electrode  7 , in addition to the ozone gas passage  8 , in order to in increase an ozone generating efficiency. A cooling water inlet/outlet for taking cooling water in and out is provided in the end portion of the low voltage electrode  7  extending in a laminating direction, similar to the ozone gas passage. Manifold blocks  23  are inserted between two (2) vertically adjacent low voltage electrodes  7  and the ozone gas passages  8  and cooling water passages  9  of the respective low voltage electrode  7  are communicated by these manifold blocks  23 . Accordingly, in such a construction, the ozone gas outlet and cooling water inlet/outlet may be gathered in one place and an apparatus may be provided which is small in size, light weight, of high quality and has a reduced number of components. 
     Embodiment 14 
       FIG. 18  is a cross sectional drawing of a manifold block  23  of an ozonizer of an Embodiment 14 of the present invention. The manifold block  23  is divided into two (2) members in a laminating direction, that is, an upper manifold block  23   a  and a lower manifold block  23   b . An ozone gas passage  8  and cooling water passage  9  are formed in both so as to pass therethrough in a laminating direction. The ozone gas passage(s)  8  and cooling water passage(s)  9  are connected to the ozone gas passages  8  and cooling water passages  9  provided in the high voltage electrode  7 . 
     Cylindrical portions which extend toward the top-side of the drawing and provided so as to enclose the ozone gas passage  8  and cooling water passage  9  are formed on the lower manifold block  23   b . On the other hand, the upper manifold block  23   a  includes concave portions into which these cylindrical portions are inserted. The ozone gas passage  8  and cooling water passage  9  are formed in a central portion of these concave portions. The cylindrical portions and concave portions are engaged having a gap which allows for sliding in the laminating direction, so as to have a cylinder and piston relationship. O-rings  23   c  for maintaining air-tightness are disposed between the cylindrical portions and concave portions. Also, a disc spring  23   d  is disposed between the upper manifold block  23   a  and lower manifold block  23   b  so as to have elasticity in the laminating direction. The manifold blocks  23  of the present invention, being of such a construction, include passages extending in the laminating direction connected to the ozone gas passages  8  and cooling water passages  9  provided in the low voltage electrode  7  and may expand and contract in the laminating direction of the electrodes. 
     As mentioned in Embodiment 1 for instance, the precision of the discharge gap  6  must be increased in order to improve ozone generating efficiency. Hence, the precision of the discharge gaps  6  is improved by increasing the height precision of the discharge gap forming spacers and fastening the electrode as a whole to the base  24  by means of the presser plate  22  and the fastening bolts  21 . Nevertheless, the low voltage electrode  7  is provided adjacent to the manifold block  23  and an adverse influence acts on the electrode fastening when there is a strong joining strength with the manifold block  23  and there is a concern that the precision of the discharge gaps  6  will not be maintained. 
     Namely, in Embodiment 2 and with reference to  FIG. 2 , starting with the high voltage electrode  3  and low voltage electrode  7  many members are laminated and fastened to the base  24  by means of the fastening bolts  21 . In this laminate, the discharge gaps  6  are formed by discharge gap forming spacers. Meanwhile, since many members are laminated in the laminate, errors in each of the members accumulate and a certain error develops in the longitudinal direction. The low voltage electrode  7  is, for example, rigid bodies made of stainless steel and the like. Thus, no matter how precisely the block sandwiched between both low voltage electrodes  7  is manufactured, the low voltage electrode  7  is distorted by the error in the longitudinal direction of the laminate. The occurrence of this distortion makes it impossible to precisely form the discharge gaps  6 . In comparison, the manifold block  23  of the present embodiment is of construction having elasticity in the laminating direction of the electrodes. Thus, an error in the longitudinal direction of the laminate may be absorbed and it is possible to precisely form the discharge gaps  6 . 
     Accordingly, in the present embodiment, because there is provided the manifold block  23  formed with the cooling water passage  9  or ozone gas passage  8  connected to the cooling water passages  9  or ozone gas passages  8  provided in each electrode, respectfully, the space provided for piping for cooling water and for piping for deriving ozone gas may be reduced, and it is possible decrease the size of the apparatus, reduce the weight and reduce the number of components and it is possible to provide for increased quality of the apparatus. 
     Also, the manifold block  23  of the present embodiment is of a construction having elasticity in the laminating direction of the electrodes. Thus, it is possible to eliminate the adverse influence on the gap length of the discharge gap caused by the fastening of the manifold block  23  and the precision of the discharge gaps may be improved. 
     Embodiment 15 
       FIG. 19  is a top view of a low voltage electrode  7  of an ozonizer of an Embodiment 15 of the present invention.  FIG. 20  is cross sectional perspective view taken along the line I—I in FIG.  19 . The present embodiment relates to disposition of discharge gap spacers  7   c . Grooves of several mm in depth are formed by etching or machining in advance one main surface of two electrodes  7   a ,  7   b . These grooves are lined up to form an ozone gas passage  8  and cooling water passage(s)  9 . Ribs  7   d  for separating passages are provided between adjacent grooves. The discharge gap spacers  7   c  of the present embodiment are disposed at a position opposite the ribs  7   d . That is to say, the discharge gap spacer(s)  7   c  is disposed on a surface of the low voltage electrode  7  facing the discharge gap  6  at a position which passes through the rib  7   d  in the laminating direction. 
     Cooling water passages  9  are formed around an entire surface inside the low voltage electrode  7 . A thickness of the ribs  7   d  for separating the passages is made as thin as possible in order to increase a surface area of the cooling water passages  9  even a little. On the other hand, a diameter of the discharge gap spacers  7   c  for forming the discharge gaps  6  is preferably as small as possible to increase the discharge gaps  6 . The low voltage electrode  7  is, as a whole, a thin rigid body made of stainless steel and the like and in a case where pressure increases in the laminating direction, although the portions having the ribs  7   d  are strong against deformation, the locations without the ribs  7   d  are weak. That is, they are recessed. Since the discharge gap spacers  7   c  of the present embodiment are disposed at a position opposite the ribs  7   d , there is accordingly almost no deformation of the low voltage electrode  7 . Consequently, deformation of the discharge gaps  6  may be suppressed and it is possible to form highly precise discharge gaps  6 . 
     Accordingly, in the present embodiment, the discharge gap spacers  7   c  are disposed at positions opposite the ribs  7   d  forming the cooling water passages  9  of the low voltage electrode  7 . Thus, the low voltage electrode  7  is not deformed and the adverse influence on the discharge gaps  6  due to fastening the electrodes may be eliminated and the ozone generating efficiency increased. 
     Embodiment 16 
       FIG. 21  is a detailed cross sectional drawing of an ozonizer electrode of an ozonizer of Embodiment 16 of the present invention. The present embodiment includes the construction of Embodiment 5 in which the inorganic dielectric film  13  is coated on the low voltage electrode  7 , the construction of Embodiment 8 wherein one surface of the dielectric  5  is coated with the conductive film  14  and the construction of Embodiment 13 in which the low voltage electrode(s)  7  is sandwiched by the manifold block(s)  23 . 
     Hence, it is possible to form discharge gaps  6  for generating clean ozone in which metallic contamination does not develop and the cooling efficiency of the discharge gaps  6  may be improved. 
     Embodiment 17 
     The present embodiment will be explained using  FIGS. 1 and 2 . In an ozonizer electrode  101  of the present embodiment, a total of four (4) electrode modules  102  comprising, as shown in  FIG. 2 , a flat plate-shaped low voltage electrode  7 , a flat plate-shaped high voltage electrode  3  facing a main surface of the low voltage electrode  7 , a flat plate-shaped dielectric  5  and a spacer (not shown) for forming a discharge gap  6  of a thin thickness in a laminating direction provided between the low voltage electrode  7  and the high voltage electrode  3  and a high voltage electrode cooling unit  2  for forming a cooling water passage insulated from the high voltage electrode  3  inside the high voltage electrode  3 , are laminated as shown in  FIG. 1 , i.e., N−1, N−2, N−3, N−4. 
     Accordingly, since, in the present embodiment, a plurality of electrode modules are laminated, it is possible to increase the capacity of the apparatus while yet making it compact. 
     Moreover, although a total of four (4) electrode modules are laminated in the present embodiment, the number of modules is not limited to four (4) and similar effects may be obtained by laminating another number. 
     Embodiment 18 
       FIG. 22  is a drawing of a dielectric  5  of an ozonizer of an Embodiment 18 of the present invention as viewed from the top. A discharge is caused between the low voltage electrode  7  and high voltage electrode  3  via the dielectric  5  and ozone is generated. On the other hand, an ozone gas passage  8  extending from a central portion to an end portion of the low voltage electrode  7  is formed inside the low voltage electrode  7 . Although cooling water circulates in and cools another portion of the low voltage electrode  7 , cooling water does not circulate in the portion of the ozone gas passage  8  which is not satisfactorily cooled. Thus, a temperature increases in this ozone gas passage  8  portion. Ozone generated in this portion is decomposed by the temperature increase. 
     In the present embodiment, a special conductive film  14   a  is used which can partition a region where a discharge is not caused and a region where a discharge is caused. The special conductive film  14   a  is provided on an entire surface of the dielectric  5  except a portion facing the ozone gas passage  8 . That is, in the present embodiment, by applying the conductive film everywhere except above the ozone gas passage  8 , it is possible to make a construction wherein a (temperature) increase of the ozone gas is suppressed and ozone gas decomposition is not caused. 
     Accordingly, in the present embodiment, the conductive film  14   a  is provided at the portion other than the location facing the ozone gas passage  8  formed in the low voltage electrode  7 . Hence, there is no conductive film over the ozone gas passage  8  of the low voltage electrode  7  and because generated heat from a discharge does not occur on the ozone gas passage  8 , generated ozone gas does not decompose and the apparatus may be made to have good efficiency. 
     Embodiment 19 
       FIG. 23  is a top view of a low voltage electrode  7  of an ozonizer of an Embodiment 19 of the present invention.  FIG. 24  is cross sectional perspective view taken along the line XIV—XIV in FIG.  23 . The present embodiment relates to disposing discharge gap forming spacers for forming discharge gaps  6 . A discharge is caused between the low voltage electrode  7  and high voltage electrode  3  via the dielectric  5  and ozone is generated. On the other hand, an ozone gas passage  8  extending from a central portion to an end portion of the low voltage electrode  7  is formed inside the low voltage electrode  7 . Although cooling water circulates in and cools another portion of the low voltage electrode  7 , cooling water does not circulate in the portion of the ozone gas passage  8  which is not satisfactorily cooled. Thus, a temperature increases in this ozone gas passage  8  portion. Ozone generated in this portion is decomposed by this temperature increase. 
     In the present embodiment, ceramic dielectric anti-discharge spaces  13   a   2  are provided covering an entire portion facing the ozone gas passage  8  so that a discharge will not be performed at the portion facing the ozone gas passage  8 . Ceramic dielectric discharge gap forming spacers  13   a   1 , similar to those in Embodiment 6, are provided in other portions which perform discharge. In the present embodiment, the ceramic dielectric anti-discharge spacers  13   a   2  are provided covering an entire portion facing the ozone gas passage  8  so that a discharge will not occur on the ozone gas passage  8 , and by making this a non-discharge region, a construction is made such that a (temperature) increase of the ozone gas is suppressed and ozone gas decomposition is not caused. 
     That is to say, in the present embodiment, the spacer comprises the ceramic dielectric discharge gap forming spacers  13   a   1  provided at the portion other than the location facing the ozone gas passage  8  formed in the low voltage electrode  7  for forming discharge gaps  6  and the ceramic dielectric anti-discharge spacers  13   a   2  provided at the position facing the ozone gas passage  8  formed in the low voltage electrode  7  for eliminating a predetermined space of the discharge gaps  6 . Thus, generated heat from a discharge does not occur on the ozone gas passage  8 , the generated ozone gas does not decompose and the apparatus may be made to have good efficiency. 
     According to one aspect of the present invention there is provided an ozonizer comprising: 
     a flat plate-shaped low voltage electrode; 
     a flat plate-shaped high voltage electrode facing a main surface of the low voltage electrode; 
     a flat plate-shaped dielectric and a spacer for forming a discharge gap of a thin thickness in a laminating direction provided between the low voltage electrode and the high voltage electrode; 
     a high voltage electrode cooling unit for forming a cooling water passage insulated from the high voltage electrode inside the high voltage electrode; 
     an alternating voltage is applied between the low voltage electrode and the high voltage electrode and a discharge is produced in the discharge gap injected with oxygen gas to produce ozone gas. Thus, the cooling efficiency of the discharge gaps is improved and the temperature of the discharge gaps may be satisfactorily reduced. Accordingly, power density may be increased without decreasing ozone generating efficiency, and size reduction and cost reduction may be provided for an apparatus in which it is possible to reduce the number of electrode modules. Further, since the high voltage electrodes are cooled via the high voltage electrode cooling unit, standard service water may be used as cooling water without using ion exchanged water and the like of small electric conductivity. Thus, an electric conductivity monitoring device or ion exchanged water circulating equipment and the like is unnecessary and, by reducing the number of apparatus components, it is possible provide for cost reductions or reduce maintenance costs. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the high voltage electrode cooling unit comprises a high thermal conducting/high electric insulating flow tube inserted in a through hole bored through the high voltage electrode; and a thermal conducting adhesive of high thermal conductivity filled between the flow tube and the through hole for fixing the flow tube in the through hole. Hence, ion exchanged water and the like of a small electric conductivity is unnecessary and standard service water may be used as cooling water. Thus, an electric conductivity monitoring device or ion exchanged water circulating equipment and the like is unnecessary and, by reducing the number of apparatus components, it is possible provide for cost reductions and reduce maintenance costs. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     a plurality of the flow tubes are disposed side by side parallel to a main surface of the high voltage electrode. Thus, the flat plate-shaped high voltage electrode may be efficiently cooled. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     an ozone gas passage and a cooling water passage are formed inside the low voltage electrode by adhering together two or more metal flat plates formed with grooves on main surfaces thereof so that the grooves line up. Hence, it is possible to decrease the thickness of the low voltage electrode and reduce the size of the apparatus. Furthermore, since piping for deriving cooling water and ozone is unnecessary, assembly and disassembly may be simply performed and a low cost ozonizer may be provided. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the flat metal plates are adhered together by heat and pressure only. Thus, ozone caused corrosion of the bonding agent does not occur and it is possible to realize an ozonizer having a long life and high reliability. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     both main surfaces of the low voltage electrode facing the discharge gap are covered in an inorganic dielectric film. Hence, the discharge gap constructed so as to be completely sandwiched with the inorganic material, and metallic contamination caused by metal sputtering in a discharge may be suppressed and it is possible to provide an ozonizer which generates clean ozone gas. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the dielectric film is made of a ceramic material. Hence, the ceramic dielectric film may be formed by a thermal spraying technique and a thickness thereof controlled to several â. m in thickness. Further, in accordance with to this thermal spraying technique, it is also possible to concurrently form the ceramic dielectric discharge gap spacers. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the dielectric film is made of a glass material. Thus, the dielectric film may be easily formed by adhering a glass plate of a quartz material to the low voltage electrode by means of an adhesive. Also, the convex glass dielectric discharge gap spacers may be easily formed by means of a shot blasting treatment using a mask prior to adhering the glass plate to the low voltage electrode. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     a main surface of the dielectric facing the high voltage electrode is coated with a conductive film having conductive properties, and the conductive film contacts the high voltage electrode.// Hence, by applying the conductive film on the surface of the dielectric and contacting this conductive film covered surface and the high voltage electrode, even if, a gap occurs between the conductive film and the high voltage electrode, the conductive film and high voltage electrode have the same electric potential and a local discharge may be prevented, and it is possible to prevent the occurrence of metallic contamination. Furthermore, since the high voltage electrode and conductive film may be joined by simple pressure welding, assembly and disassembly may be facilitated and there is also an advantageous effect in that components may be recycled. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the dielectric and the high voltage electrode are adhered by means of a conductive adhesive. Thus, gaps between the dielectric and high voltage electrode may be eliminated a local discharge may be prevented and it is possible to prevent the occurrence of metallic contamination. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     a peripheral edge portion of the conductive film is coated with an inorganic insulating film. Hence, it is possible to suppress the abnormal corona discharge from occurring at the peripheral edge portion of the conductive film and the occurrence of metallic contamination may be prevented. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     a peripheral edge portion of the conductive adhesive is coated with an inorganic insulating film. Thus, it is possible to suppress the abnormal corona discharge from occurring at the peripheral edge portion of the conductive adhesive and the occurrence of metallic contamination may be prevented. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     an outside diameter of the high voltage electrode is smaller than that of the dielectric. Thus, it is possible to eliminate the abnormal corona discharge and prevent the occurrence of metallic contamination. Also, it is possible to suppress damage to the dielectric and an ozonizer having high reliability and a long-life dielectric may be provided. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     an outside diameter of the high voltage electrode is smaller than that of the conductive film covering the dielectric. Thus, it is possible to further eliminate the abnormal corona discharge and prevent the occurrence of metallic contamination. Also, it is possible to further suppress damage to the dielectric and an ozonizer having high reliability and a long-life dielectric may be provided. 
     According to another aspect of the present invention there is provided an ozonizer comprising, 
     a manifold block provided adjacent to the low voltage electrode and formed with a cooling water passage connected with the cooling water passage provided in the low voltage electrode, or formed with an ozone gas passage connected with the ozone gas passage provided in the low voltage electrode. Hence, the space provided for piping for cooling water and for piping for deriving ozone gas may be reduced, and it is possible decrease the size of the apparatus, reduce the weight and reduce the number of components and it is possible to provide for increased quality of the apparatus. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the manifold block has an elastic structure with an elastic function in a laminating direction of the low voltage electrode and the high voltage electrode. Thus, it is possible to eliminate the adverse influence on the gap length of the discharge gap due to fastening the manifold block and the precision of the discharge gaps may be improved. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the spacer is disposed at a position facing a rib forming the cooling water passage of the low voltage electrode. Hence, deformation of the low voltage electrode may be eliminated and, consequently, deformation of the discharge gaps may be suppressed and it is possible to form highly precise discharge gaps. 
     According to still another aspect of the present invention there is provided an ozonizer comprising: 
     a flat plate-shaped low voltage electrode; 
     a flat plate-shaped high voltage electrode facing a main surface of the low voltage electrode; 
     a flat plate-shaped dielectric and a spacer for forming a discharge gap of a thin thickness in a laminating direction provided between the low voltage electrode and the high voltage electrode; 
     a high voltage electrode cooling unit for forming a cooling water passage insulated from the high voltage electrode inside the high voltage electrode; 
     a manifold block provided adjacent to the low voltage electrode and formed with a cooling water passage connected with the cooling water passage provided in the low voltage electrode, or formed with an ozone gas passage connected with the ozone gas passage provided in the low voltage electrode; and 
     both main surfaces of the low voltage electrode facing the discharge gap are covered in an inorganic dielectric film; and 
     a main surface of the dielectric facing the high voltage electrode is coated with a conductive film having conductive properties, and the conductive film contacts the high voltage electrode. Thus, it is possible to form discharge gaps for generating clean ozone in which metallic contamination does not develop and the cooling efficiency of the discharge gaps may be improved. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     an plurality of electrode modules comprising the low voltage electrode, the high voltage electrode, the dielectric, the spacer, the electrode cooling sheet and the high voltage electrode cooling unit are laminated. Thus, it is possible to change the capacity of the apparatus in accordance with the number of electrode modules which are laminated and the capacity may be easily increased; on the other hand, the apparatus may be made compact even if the capacity is increased. 
     According to another aspect of the present invention there is provided an ozonizer wherein, 
     the conductive film is provided at a portion other than a position facing the ozone gas passage formed in the low voltage electrode. Thus, there is no conductive film over the ozone gas passage of the low voltage electrode and because generated heat from a discharge does not occur on the ozone gas passage, generated ozone gas does not decompose and the apparatus may be made to have good efficiency. 
     According to still yet another aspect of the present invention there is provided an ozonizer wherein, 
     the spacer comprises a discharge gap forming spacer provided at a portion other than a position facing the ozone gas passage formed in the low voltage electrode for forming the discharge gap and an anti-discharge spacer provided at a position facing the ozone gas passage formed in the low voltage electrode for eliminating a predetermined space of the discharge gap. Thus, generated heat from a discharge does not occur on the ozone gas passage, the generated ozone gas does not decompose and the apparatus may be made to have good efficiency.