Patent Publication Number: US-2010126702-A1

Title: Structure cooling method

Description:
TECHNICAL FIELD 
     The present invention relates to a high-efficiency energy-saving and cooling method using heat of evaporation of water. 
     BACKGROUND ART 
     In recent years, resolution of global warming caused by excessive use of fossil fuel, heat-island phenomenon in urban areas, and the like is an urgent issue. On the other hand, improvement in quality of living environment by natural symbiosis is also in demand. Hitherto, to address the issues, various novel energies and energy-saving systems are proposed. 
     One of effective methods of directly removing heat of a structure, that is, positively taking heat quantity is so-called water sprinkling using heat of evaporation of water. Water sprinkling is customarily performed all over the place, and it is empirically proved that the cooling effect of water sprinkling is high. However, the efficiency is not always high. To be specific, although it seems that an entire target surface of water sprinkling is wet, in reality, the target surface is not sufficiently wet due to a water film caused by cohesion power of water and repulsion between water and the target surface. Consequently, the vaporization area is limited, and it is difficult to remove sufficient vaporization heat. 
     In recent years, various methods are proposed to improve wet area of a target surface and increase the efficiency of heat removal by evaporation heat of water. In general, the methods are roughly divided into a method of covering a target surface with a hydrophilic coating film or photocatalyst and a method of mixing an additive such as surfactant to water.
     Patent Document 1: Japanese Unexamined Patent Publication No. 2004-324043   Patent Document 2: Japanese Unexamined Patent Publication No. 2002-201727   Patent Document 3: Japanese Unexamined Patent Publication No. 6-185131   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention  
     The former method include film coating of coating (spraying) and baking a coating material containing a superhydrophilic pigment such as titanium dioxide having a photocatalyst function, pasting of a hydrophilic film or a hydrophilic laminate film, or a surface process method performed by physical or chemical vapor deposition of titanium dioxide or the like. However, a material cost and a construction cost of the methods are very high. Application of any of the methods to an existing structure by a method of making the surface hydrophilic requires a work of replacing a building material or coating, pasting, mounting, or the like at the site, and the construction is large-scaled, so that the use of the structure accompanying the construction may be regulated. There is also a problem from viewpoints of design such as a change in colors and structures of the existing building. In addition, deposition of organic and inorganic matters on a surface process layer, abrasion and erosion of the surface process layer, and function display disturbance due to deterioration with time are unavoidable, and a heavier economic burden occurs due to repair, re-coating or the like. The spread of the method is therefore limited. 
     The latter method has a problem such that, if water containing an additive flows outside of a system, environmental pollution occurs. It is therefore necessary to provide a water tank and circulate water in the system. Naturally, secondary use of the stored water containing the additive to another application is difficult for the reasons such that it may cause inhibition of growth of plants and the like and an adverse influence on human bodies. When splash of water and the like is also considered, a concern in safety aspect cannot be completely removed. Further, when a large amount of rain temporarily flows in or the additive is decomposed due to light, microorganisms, and other reasons, the additive concentration decreases with time. Consequently, it is necessary to periodically replenish the additive while measuring the additive concentration. On the contrary, when the additive concentration increases due to evaporation of water, water has to be added. In addition, adhesion of the additive to an object to which water is sprayed, contamination, or the like occurs, and therefore the method cannot be used in practice. The inventors of the present invention have also attempted to improve a surface active potency by passing water between strong magnetic fields but, as a result, could obtain only an effect to a degree in an error range of measurement. 
     To solve the above-mentioned problems, the inventors of the present invention have attempted novel technical ideas for many years. As a result of keen study, the inventors have succeeded to improve evaporation heat cooling capability by a method which can be applied to a wide-range of object without changing the physical and chemical natures of a target surface. Microbubbles and nanobubbles are different from normal bubbles and various functions thereof have been found and applied. However, improvement in wetability and surface active potency on a target surface has not been reported. The inventors have examined a method of improving the property of spray water itself as a method of improving wetability without adding a wetability improving agent and without performing chemical treatment for specially improving wetability of a target surface, enlarging evaporation area, and increasing cooling effect without causing large deterioration in evaporation performance due to deposition of fragments. The inventors have paid attention to an air/water mixture and invented a cooling method capable of stably achieving the object by using an air/water mixture containing fine bubbles in a microbubble and nanobubble region, that is, each having a diameter of about 75 μm, desirably, 50 μm or less. Study of microbubbles and nanobubbles has advanced rapidly in recent years, and it is known that an air/water mixture state lasts for a few minutes to a few days. The air/water mixture described in the present invention does not refer to a state where gas is completely dissolved in water and the mixture is uniform but refers to a state where fine bubbles and water coexist relatively stably. Originally, the air/water mixture is used for clarification of water, prevention of disease damage and growth promotion on fish and shellfish, growth promotion of plants, cleaning with bubbles, sludge floating process, decomposition of contaminants, and the like. However, there is no idea of using the air/water mixture in the field of energy saving and prevention of heat island phenomenon by cooling as an object of the present invention. Although the principle mechanism of the present invention is not clear, it is considered as follows. Fine bubbles, that is, microbubbles or nanobubbles have charges, and the inside of a bubble is in a state of high pressure and high energy. The periphery of the fine bubble is charged, and an electric double layer is formed. An influence is given to the surface tension of water, the material of a target surface is attracted by static attraction, so-called affinity between the target surface and the air/water mixture is improved, and interfacial tension per unit length of the air/water mixture and the target surface is reduced. As a result, the contact angle is decreased, and wetability is significantly improved. 
     Means for Solving the Problems  
     To achieve the above object, in a method for cooling a structure by using heat of evaporation of water according to a first aspect of the present invention, an air/water mixture ( 5 ,  31 ) including 300 pieces/mL or more of micro air bubbles each having a diameter of 75 μm or less on generation is sprayed on a target surface of a structure. 
     In a second aspect of the present invention, the method for cooling a structure according to the first aspect is characterized in that a water-retention/water-spread layer having a continuous capillary structure including a surface opening and an average hole diameter of 75 μm to 3 mm, and having a thickness of 10 mm or less is made to exist on the target surface, and the air/water mixture ( 5 ,  31 ) is intermittently supplied. 
     Further, in a third aspect of the present invention, the method for cooling a structure according to the second aspect is characterized in that the target surface on which the water-retention/water-spread layer having the capillary structure is made to exist is a surface structure with projections and depressions having a level difference of 1 mm to 300 mm. 
     In a fourth aspect of the present invention, the method for cooling a structure according to any one of the first to third aspects is characterized in that a unit ( 29 ) for generating the air/water mixture ( 5 ,  31 ) is mounted in some midpoint of a part extending from a water supply source ( 2   a ) to a water spray port ( 5 ,  30 ,  49 ) provided near the target surface. 
     In a fifth aspect of the present invention, the method for cooling a structure according to any one of the first to third aspects is characterized in that a unit ( 29 ) for generating the air/water mixture ( 5 ,  31 ) is mounted in a water spray port ( 5 ,  30 ,  49 ) part provided near the target surface, in a part extending from a water supply source ( 2   a ) to the water spray port ( 5 ,  30 ,  49 ). 
     In a sixth aspect of the present invention, the method for cooling a structure according to any one of the first to third aspects is characterized in that a water tank ( 14 ) is provided and the air/water mixture ( 5 ,  31 ) generated in a part of the water tank ( 14 ) is used. 
     In the present invention, the target surface refers to a roof surface, a wall face, a road surface, a ground surface, a slope, a retaining wall, or other faces. 
     The air/water mixture is not a mixture obtained by completely dissolving gas into water but a mixture in which fine bubbles are dispersed in water. To stabilize the air/water mixture, that is, to stabilize the property of the air/water mixture, the size of the dispersed bubble exerts a large influence. In the case of practically using the present invention, for example, in a period during which the air/water mixture is sprayed from an air/water mixture generating unit via nozzles or slits onto a target surface causing the target surface to be wet, and until the air/water mixture completely evaporates, the air/water mixture has to exist stably. Although the period varies depending on the structure itself, the temperature condition on the surface of the structure, ambient temperature, humidity, wind velocity, and the like, about five minutes to a few hours is necessary as the period. To realize this, it was found that the diameter of the bubble in the air/water mixture needs to be about 75 μm or less, preferably, 50 μm or less. When the diameter of the fine bubble exceeds 75 μm, reduction and compression of the bubbles does not easily occur and the bubbles float up in the water. It is therefore difficult to obtain a stable air/water mixture. The property of the air/water mixture largely varies depending on the concentration of fine bubbles (pieces/mL). According to the study of the inventors of the present invention, it was found that an effect is displayed when the number of bubbles is 300 pieces/mL with respect to the bubble concentration of the air/water mixture used in the present invention. However, higher concentration of fine bubbles is desirable. Further, in consideration of energy saving, the cooling effect, and power cost, at least 1,000 pieces/mL or larger is desirable. Since the fine bubbles are charged, even when the concentration of the bubbles becomes higher, the fine bubbles repel each other. Therefore, the bubbles do not combine with each other to become a large bubble that float up and go out of the system. 
     A method of carrying the air/water mixture to the target surface include spraying from above of the target surface, downward flow from an upstream side to a downstream side, in the case where the target surface is a layer-like material having a capillary structure, transfer of water supplied from a lower layer part or the center of the layer to the surface via a capillary, or the like. 
     Spraying means that the air/water mixture is supplied promptly and in a wide range to the entire target surface. The air/water mixture needs to be evaporated within time in which the air/water mixture stably exists. In view of the time in which the air/water mixture stably exists, it was found that a method of spraying the air/water mixture from nozzle or slit structures from the top face is the most effective. 
     If permitted from the viewpoint of design and cost, it is effective to use a capillary structure layer in the target surface to correct spray unevenness and cut waste in spray. In this case, it is necessary to complete transfer and evaporation by the capillary phenomenon in a thickness direction and a plane direction within the time in which the effect of the air/water mixture can be maintained. As a result of the study of the inventors, it was found that the present method can be realized by using fabric, nonwoven fabric, an interconnected-cell sheet, a porous thin layer, a composite material obtained by binding organic/inorganic granular members or fiber material by a binder, or the like. Since the upper limit of the fine bubble diameter is 75 μm, the capillary continuation is disturbed by the bubbles unless the average hole diameter is 75 μm or larger, and it becomes difficult to transfer the air/water mixture. When the average hole diameter is 3 mm or larger, it is difficult to perform vertical transfer of about 10 mm. To enlarge the evaporation area, preferably, the target surface having the capillary structure layer further includes projections and depressions having a level difference. The projections and depressions preferably have a level difference of at least about 1 mm to enlarge the evaporation area. If the level difference of projections and depressions is too large, passage of air is disturbed, so that the limit is about 300 mm. The projections and depressions are provided by methods such as press working the target surface from the top face with a mold when the target surface itself is processed or when the capillary structure layer is applied, utilizing projections and depressions created when the capillary structure layer is formed by spraying, and applying a capillary structure sheet having projections and depressions in the thickness direction. The method can be effective not only to a roof surface but also to a wall surface, a slope, a retaining wall surface, and the like. 
     The downward flow means supply of the air/water mixture by water stream from an upstream side to a downstream side generated by gravity. However, for example, in a surface with projections and depressions such as a wavy roof tile or a wavy metal roof, the water stream is concentrated in depressions, so that the entire target surface cannot be made wet. Even if the target surface is flat, it takes time for water on the upstream side to reach the downstream side. In addition, as the temperature of the target surface becomes higher due to sun light, radiation heat of a peripheral structure, heat accumulation of the target, and the like, the stability of the air/water mixture decreases. As a result, the air/water mixture cannot exist stably on the downstream side, and the effect cannot be expected. (For example, in the case where the air/water mixture flows downward thinly on the entire target surface having a gradient of 3° at 60° C., bubbles in the air/water mixture cannot be visibly recognized in a part over 5 m). Therefore, to make the downstream side and projections entirely wet, large amount of water supply is necessary. The water is wasted and transfer energy is also wasted. Therefore, in the case where the target surface is perpendicular or has a large gradient, the downward flow is used. 
     Also in the case where the capillary structure sheet is thick and the air/water mixture is supplied from the lower layer part or the layer center part by the capillary phenomenon, it is difficult to transfer the air/water mixture to the surface of the capillary structure and evaporate the mixture within the time in which the air/water mixture exists stably. Therefore, it is preferred that the thickness of the capillary structure sheet does not exceed 10 mm. 
     The air/water mixture generating method includes, roughly, a Venturi tube method, a pore method, a pressure dissolution and cavitation method, an ultrasonic method, a gas-liquid mixing/shearing method, an ultrahigh-speed turning method, or the like. Any of the methods can be used for the present invention. Among the methods, in the Venturi tube method and the pore method, it is practically difficult at present to make fine bubbles disperse and economically obtain a stable air/water mixture. On the other hand, the pressure dissolution and cavitation method and the ultrasonic method are methods of forming bubbles from a gas substance dissolved in water and can realize fine bubble dispersion. However, in both of the methods, bubbles of only the dissolved gas amount can be formed. In the case of the ultrasonic method, fine bubbles once generated are crushed by pulse impact. Consequently, it is difficult to generate an air/water mixture sufficient to improve wetability under present conditions. The pressure dissolution and cavitation method has a drawback such that pressurization energy is necessary to increase the dissolution amount. Also by the gas-liquid mixing/shearing method, fine bubble dispersion can be realized. Further, by setting a so-called gas-liquid double-layer fluid of a so-called ultrahigh-speed turning type to an ultrahigh-speed turning flow, fine bubble dispersion can be realized. Using any of the methods, a generated air/water mixture which is suspended in opaque white color contains a larger number of fine bubbles. There is an air/water mixture generator capable of obtaining thousands of pieces of fine bubbles per mL each having an average diameter of 10 to 15 μm, and it is preferable to use such a generator. 
     The air/water mixture generating unit can be mounted in any place in a part extending from a water supply source to a water spray port. Specifically, it can be roughly divided into (1) the case where the unit is mounted in a path extending from the water supply source to the water spray port, (2) the case where the unit is mounted in the water spray port, and (3) the case where, if a water tank is provided, the unit is provided in the water tank. The cases have different characteristics, and are properly selected based on the scale of the target surface, the structure, the kind of the water supply source, the distance between the water tank and the water spray port in the case of mounting the water tank, general economic efficiency, and the like. 
     By mounting the air/water mixture generating unit in the path extending from the water supply source to the water spray port, transfer time of the air/water mixture to the water spray port can be shortened. In the case of directly using tap water, ground water, industrial water, or the like as the water supply source, it is preferable to provide the air/water mixture generating unit in a part closest to the water spray port. 
     Effects of the Invention 
     According to the simple facility of the present invention, additional cooling is hardly required. Even in the case where additional cooling is necessary, a small additional cooling load is required. Thus, large energy saving is realized. As compared with normal water sprinkling, a clearer effect is displayed. The method can be called an innovative method which can be applied to cooling of a target surface in a wide range irrespective of the fact that the target surface is newly provided or already provided. Further, the method can be also widely applied to various materials of the target surface and is not easily influenced by dust and an adhered substance. The technique can be used also in the case where the target surface wears like the road surface. A high effect can be displayed for energy saving, reduction in the heat island phenomenon, and the like. 
     In the present invention, deterioration in a building material does not directly cause deterioration in evaporation performance, so that deterioration in performance with time does not easily occur. The economic burden is also reduced, and the effect of spreading the present invention can be expected. 
     With respect to construction, it is sufficient to add a supply water source, a water supply pipe, an air/water mixture generating unit, water spray nozzles and slits and, as necessary, a water tank, a water lifting pump, and the like to a structure. In addition, to further increase the efficiency, it is effective to make a capillary structure layer exist on a target surface. 
     By using the present invention, a material and construction cost for manufacturing, carrying, mounting, and replacing the material itself of the target surface is unnecessary. One of the effects large in the viewpoint of popularization is that regulation/change in the material cost, construction time, and design is also unnecessary or kept at the minimum. Since maintenance such as cleaning, re-coating, re-mounting, and injection of an agent after mounting is hardly necessary, there is also an effect in practice. Also in the case of providing the capillary structure layer in order to further improve the efficiency, the maintenance is hardly necessary. 
     In the present invention, an additive is not required at all, so that maintenance such as injection of an agent is hardly required. There is an effect that water suitable for the environment, plants, and human bodies can be assured. Therefore, the water can be used for other applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a pressure-vessel-type air/water mixture generating apparatus. 
         FIG. 2  is a schematic view of an open-type air/water mixture generating apparatus. 
         FIG. 3  is a schematic view of a water-tank-type air/water mixture generating apparatus. 
         FIG. 4  is a schematic view of a partition-wall-water-tank-type air/water mixture generating apparatus. 
         FIG. 5  is a schematic view of a partition-cylinder-water-tank-type air/water mixture generating apparatus. 
         FIG. 6  is a general perspective view of a structure to which the present invention is applied. 
         FIG. 7  is a schematic view of a wet state of water and a solid when a water droplet is dropped on a surface of the solid. 
         FIG. 8  is a diagram showing contours of marks of droplets fallen and dried on a glass plate. 
         FIG. 9  is a diagram showing contours of marks of droplets fallen and dried on a coated steel plate. 
         FIG. 10  is a schematic diagram of a laboratory building in an evaporative cooling test. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  Unit body 
           2  Water supply pipe 
           2   a  Water supply source 
           3  Intake pipe 
           3   a  Intake port 
           4  Air/water mixture generating unit 
           5  Air/water mixture 
           6  Water spray pipe 
           6   a  Water spray pipe water pickup part 
           7  Water spray port 
           8  Target surface temperature control unit 
           9  Electromagnetic valve 
           10  Water pump 
           11  Vent pipe 
           12  Water level indicator 
           12   a  Water level sensor 
           12   b  Water level sensor 
           13  Water pump 
           14  Water tank 
           15  Clarification circulation pipe 
           15   a  Clarification circulation pipe water pickup part 
           16  Air pump 
           17  Air filter 
           18  Circulation pipe 
           18   a  Circulation pipe water pickup part 
           19  Circulation pump 
           20  Partition wall 
           21  Partition cylinder 
           22  Object 
           23  Water 
           24  Structure 
           24   a  Roof 
           25  Water tank 
           26  Water lifting pipe 
           27  Sand filter 
           28  Water lifting pump 
           29  Air/water mixture generating unit 
           30  Water spray port 
           31  Air/water mixture 
           32  Gutter 
           33  Water collecting pipe 
           34  First stream cutting mechanism 
           35  Grit tank 
           36  Large-dust filter 
           37  Water utilization valve 
           38   a  Water spray control valve 
           38   b  Circulation control valve 
           39  Overflow pipe 
           40  Water faucet 
           41  Freeze damage preventing valve 
           42  Clarification circulation pipe 
           43  Water spray pipe 
           44  Target surface temperature control unit 
           45  Wall 
           46  Ceiling 
           47  Roof 
           48  Floor 
           49  Water spray port 
           50   a  to  50   e  Contours of fallen and dried droplets of surfactant mixed water 
           51   a  to  51   e  Contours of fallen and dried air/water mixture 
           52   a  to  52   e  Contours of fallen and dried tap water 
           53   a  to  53   e  Contours of fallen and dried droplets of surfactant mixed water 
           54   a  to  54   e  Contours of fallen and dried air/water mixture 
           55   a  to  55   e  Contours of fallen and dried tap water 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention will be described.  FIG. 1  is a schematic view of a pressure-vessel-type air/water mixture generating apparatus as an example of an air/water mixture generating unit mounted in a path extending from a water supply source to a water spray port. Water pressure-fed by a water pump  10  from a water supply source  2   a  passes through a water supply pipe  2  and is sent to a air/water mixture generating unit  4 . On the other hand, air is sent from an intake port  3   a  to the air/water mixture generating unit  4  via an air filter  17  and an intake pipe  3  by an air pump  16 . The water and air are mixed in the air/water mixture generating unit  4  to generate an air/water mixture  5 . The generated air/water mixture  5  is sent from a water spray pipe water pickup part  6   a  positioned above the air/water mixture generating unit  4  via a water spray pipe  6  to a water spray port  7  typified by, for example, a nozzle or a slit. In this case, water pressure in the air/water mixture generating unit  4  is set to be sufficiently higher than water pressure in the water spray pipe water pickup part  6   a , that is, in a unit body  1 . In the case where a pressure difference necessary to generate the air/water mixture  5  can be obtained, the method of the present invention can be applied. To increase a microscopic bubble amount, by sending pressurized air using the air filter  17  for the intake pipe  3 , an air/water ratio can be increased and a feeding amount of the air/water mixture  5  can be increased. The water pump  10  can be on/off controlled according to the lower or upper limit of temperature set for a target surface by a target surface temperature control unit  8  made by a temperature sensor and a control switch mounted on the target surface. Specifically, when the temperature of the target surface rises to the upper-limit set temperature, the water pump  10  operates. When the temperature of the target surface drops to the lower-limit set temperature, the water pump  10  stops. 
       FIG. 2  is a schematic view of an open-type air/water mixture generating apparatus as another example. Pressurized water pressure-fed from the water supply source  2   a  passes through the water supply pipe  2  via an electromagnetic valve  9  and is sent to the inside of the unit body  1 . The fluid level of the air/water mixture  5  in the unit body  1  is mechanically or electrically sensed by a water level indicator  12  and is controlled by opening/closing the electromagnetic valve  9  in accordance with the setting of the lower or upper limit of the water level. Specifically, when the water level decreases to a water level sensor  12   a , the electromagnetic valve  9  is opened to supply water. When the water level rises to a water level sensor  12   b , the electromagnetic valve  9  is closed. A circulation pipe water pickup part  18   a  is provided in a lower part of the unit body  1 , and the water in the unit body  1  is sent to the air/water mixture generating unit  4  via a circulation pipe  18  by a circulation pump  19 . On the other hand, air is sent from the intake port  3   a  to the air/water mixture generating unit  4  via the air filter  17  and the intake pipe  3 . The water and air are mixed in the air/water mixture generating unit  4  to generate the air/water mixture  5 . The generated air/water mixture  5  is sent from a water spray pipe water pickup part  6   a  positioned above the air/water mixture generating unit  4  via the water spray pipe  6  to the water spray port  7  by a water pump  13 . The flow rate of the pressurized water has to be higher than that of the water pump  13  so that the air/water mixture  5  in the unit body  1  does not run out. If the flow rate of the pressurized water is insufficient, it is sufficient to provide the water supply source  2   a  with another pump to apply pressure. A vent pipe  11  is provided in an upper part of the unit body  1  so that the pressure in the unit body  1  becomes normal pressure. The water pump  13  and the circulation pump  19  are on-off controlled by the target surface temperature control unit  8  made by a temperature sensor and a control switch mounted on the target surface in accordance with the upper or lower limit of the set temperature of the target surface. Specifically, when the temperature of the target surface rises to the upper-limit set temperature, the water pump  13  and the circulation pump  19  operate. When the temperature of the target surface drops to the lower-limit set temperature, the water pump  13  and the circulation pump  19  stop. Although at least two pumps of the water pump  13  and the circulation pump  19  are necessary in the present method, a pump with required minimum output can be used. There is also an advantage that the unit body  1  may not have a pressure-proof specification. 
     The air/water mixture can be also generated by water spray ports. In this case, since the air/water mixture generating mechanism has to be provided for each of the plurality of water spray ports, the cost becomes high. On the other hand, there are advantages such as (1) time to evaporation of the air/water mixture on the target surface of the structure from the air/water mixture generation becomes shorter, and it becomes easier to maintain wet effect of the air-water mixture, and (2) a pump for transferring the generated air/water mixture becomes unnecessary and the cost can be lowered. The most economical method in relation with the area of the target surface, the structure, and the like is selected. It is desirable to generate an air/water mixture at or near each of water spray ports in the case where transfer distance of the air/water mixture is long, for example, on a road surface, in a commercial facility such as a large-scaled factory, a retaining wall, a slope, or the like. 
     The water tank is a tank for storing tap water, ground water, rain water, or the like. The whole water tank can be set as an air/water mixture generating unit. However, in the case where the water tank is large, to always stably maintain a gas phase ratio of the air/water mixture in the whole tank, the air/water mixture generating unit has to be always operated, and this is unpreferable since the power consumption becomes excessive. Consequently, it is preferable to mount the air/water mixture generating unit in a part of the water tank, position an opening of a pipe to the water spray port just above the unit, and immediately send the air/water mixture to the water spray port. More preferably, a flat, curved, or cylindrical partition wall is provided in a part of the water tank, and the air-water mixture generating unit is provided in a lower part of the partition wall, and an end of the pipe to the water spray port is positioned just above the unit. By making the air/water mixture generated in a part of the water tank circulate in the tank at the time of stop of water spray or the like to increase gas solubility in the whole tank, the air/water mixture at the time of water spray can be generated more promptly and efficiently. 
       FIG. 3  is a schematic view of a water-tank-type air/water mixture generating apparatus as an example of the air/water mixture generating unit provided in the water tank. Water taken from a clarification circulation pipe water pickup part  15   a  passes through a clarification circulation pipe  15  and is sent to the air/water mixture generating unit  4  via the circulation pump  19 . The water is mixed with air supplied from the intake port  3   a  via the air filter  17  and the intake pipe  3  in the air/water mixture generating unit  4  to generate the air/water mixture  5 . The generated air/water mixture  5  is sent from the water spray pipe water pickup part  6   a  positioned just above the air/water mixture generating unit  4  via the water spray pipe  6  to the water spray port  7  by the water pump  13 . The water pump  13  and the circulation pump  19  are on/off controlled according to the lower or upper limit of temperature set for a target surface by the target surface temperature control unit  8  made by a temperature sensor and a control switch mounted on the target surface. Specifically, when the temperature of the target surface rises to the upper-limit set temperature, the water pump  13  and the circulation pump  19  operate. When the temperature of the target surface drops to the lower-limit set temperature, the water pump  13  and the circulation pump  19  stop. On the other hand, the circulation pump  19  is timer-controlled separately via a power source line. The clarification circulation pipe  15  has the action of circulating the water in the water tank  14  to facilitate diffusion of the air/water mixture  5  which is not sent to the water spray pipe  6  into the water tank  14 . With this action, the gas solubility in the water tank  14  promptly reaches a saturation state. By making the gas solubility in the water tank  14  saturated in this manner, the air/water mixture  5  of higher concentration can be obtained in the air/water mixture generating unit  4 . Further, when a dissolved oxygen amount in the water tank  14  increases, environment is created in which aerobic microbes in the water tank  14  easily develop and activate, and decomposition of organic matters such as fallen leaves and bird dropping temporarily mixed is promoted. Therefore, it is also preferable from the viewpoint of maintenance of water quality. The fluid level of the air/water mixture  5  in the water tank  14  is mechanically or electrically sensed by the water level indicator  12 . By opening/closing the electromagnetic valve  9  in accordance with the setting of the lower or upper limit of the level to temporarily supply tap water, the water in the water tank  14  does not run out. Specifically, when the water level decreases to the water level sensor  12   a , the electromagnetic valve  9  is opened to supply tap water. When the water level rises to the water level sensor  12   b , the electromagnetic valve  9  is closed. 
       FIG. 4  is a schematic view of a partition-wall-water-tank-type air/water mixture generating apparatus as an example for using an air/water mixture in the water tank more efficiently. In a part of the water tank  14 , an air/water mixture generation area having a partition wall  20  is provided. The partition wall  20  may be impermeable or permeable. In the case of the permeable partition wall  20 , permeability resistance to a degree that the generated air/water mixture  5  is not diffused is sufficient. Water is supplied to the air/water mixture generating unit  4  via the clarification circulation pipe water pickup part  15   a , the clarification circulation pipe  15 , and the circulation pump  19 . The water is mixed with air supplied from the intake port  3   a  via the air filter  17  and the intake pipe  3  in the air/water mixture generating unit  4  to generate the air/water mixture  5 . The generated air/water mixture  5  is then transferred from the water spray pipe water pickup part  6   a  positioned just above the air/water mixture generating unit  4  via the water spray pipe  6  and the water pump  13  to the water spray port  7 . The water pump  13  and the circulation pump  19  are on/off controlled by the target surface temperature control unit  8 . Specifically, when the temperature of the target surface rises to the upper-limit set temperature, the water pump  13  and the circulation pump  19  operate. When the temperature of the target surface drops to the lower-limit set temperature, the water pump  13  and the circulation pump  19  stop. On the other hand, more preferably, the circulation pump  19  is timer-controlled separately via a power source line, and the gas solubility in the water tank  14  is saturated. The fluid level of the air/water mixture  5  in the water tank  14  is mechanically or electrically sensed by the water level indicator  12 . By opening/closing the electromagnetic valve  9  in accordance with the setting of the lower or upper limit of the level to temporarily supply tap water, the water in the water tank  14  does not run out. Specifically, when the water level decreases to the water level sensor  12   a , the electromagnetic valve  9  is opened to supply tap water. When the water level rises to the water level sensor  12   b , the electromagnetic valve  9  is closed. 
       FIG. 5  shows an example of providing a partition cylinder  21  having a cylindrical shape with only the bottom hermetically closed in order to use the air/water mixture more efficiently. Water is supplied to the air/water mixture generating unit  4  provided in a lower part in the partition cylinder  21  via the clarification circulation pipe water pickup part  15   a , the clarification circulation pipe  15 , and the circulation pump  19 . The water is mixed with air supplied from the intake port  3   a  via the air filter  17  and the intake pipe  3  in the air/water mixture generating unit  4  to generate the air/water mixture  5 . The generated air/water mixture  5  is then transferred from the water spray pipe water pickup part  6   a  positioned just above the air/water mixture generating unit  4  via the water spray pipe  6  and the water pump  13  to the water spray port  7 . The water pump  13  and the circulation pump  19  are on/off controlled by the target surface temperature control unit  8 . Specifically, when the temperature of the target surface rises to the upper-limit set temperature, the water pump  13  and the circulation pump  19  operate. When the temperature of the target surface drops to the lower-limit set temperature, the water pump  13  and the circulation pump  19  stop. On the other hand, more preferably, the circulation pump  19  is timer-controlled separately via a power source line, and the gas solubility in the water tank  14  is saturated. In this case as well, the partition cylinder  21  may be impermeable or permeable. Permeability resistance to a degree that the generated air/water mixture  5  is not diffused is sufficient. Further, by mechanically or electrically sensing the fluid level of the air/water mixture  5  in the water tank  14  by the water level indicator  12  and opening/closing the electromagnetic valve  9  in accordance with the setting of the lower or upper limit of the level to temporarily supply tap water, the water in the water tank  14  does not run out. Specifically, when the water level decreases to the water level sensor  12   a , the electromagnetic valve  9  is opened to supply tap water. When the water level rises to the water level sensor  12   b , the electromagnetic valve  9  is closed. 
     As a water supply source, tap water, ground water, industrial water, intermediate water, water for storage, rain water, and other storage waters can be used. In the case of using tap water, although it depends on roof temperature, roof gradient, humidity, wind speed, water spray amount, and droplet diameter, it is desired to provide a water tank and circulate water in consideration of collection, reuse, and the like of water which cannot be evaporated. In the case of using rain water as a water supply source, a water tank is necessary. In any of the cases, water from a roof or the like is collected in the water tank. In the case where water flows more than the capacity of the water tank, excessive water is discharged to a gutter or the like via an overflow pipe. 
     Wetability can be theoretically described by interfacial tension and surface tension of an object and water.  FIG. 7  is a schematic view of a wet state of water and a solid when a water droplet is dropped on the surface of the solid. The wet state of an object  22  and water  23  when a small amount of the water  23  is dropped on the object  22  as shown in  FIG. 7  is expressed by the following Young&#39;s equation. 
       γ s=γs w+γw·cos θ   (1) 
     Here, γs denotes surface tension (N/m) per unit length of the object  22 , γw denotes surface tension (N/m) per unit length of the water  23 , γsw denotes interfacial tension (N/m) per unit length of the water  23 /object  22 , and θ denotes contact angle (°). The shape of the water  23  is determined by balance of the surface tension and the interfacial tension. It means that the smaller the angle of θ is, the water  23  spreads thinly and widely on the surface of the object  22 , and wetability is excellent. Therefore, by decreasing γsw and γw, wetability improves. For example, in the case of performing hydrophilic process on the surface of the object  22 , γw decreases and wetability improves. On the other hand, in the case of adding surfactant to the water  23 , γsw and γw decreases and wetability improves. In the case of dropping air/water mixture in place of the water  23 , it is considered that fine air bubbles are taken, affinity between the water  23  and air improves, and γw decreases. However, as described below in an example ( FIGS. 8 and 9 ), since affinity of an air/water mixture “b” is more excellent than that of tap water “c” when dropped on a glass plate ( FIG. 8 ) and a coated zinc steel plate ( FIG. 9 ), it is considered that γsw also decreases. Further, a viscosity reduction effect of the air/water mixture is also added and, as a result, a large wet effect is shown. 
       FIG. 6  is a general perspective view of a structure to which the present invention is applied. A structure  24  is equipped with a water tank  25 . To a roof  24   a  of the structure  24 , a target surface temperature control unit  44  capable of performing on/off control at two set temperatures of upper and lower limits is attached. When the temperature of the roof  24   a  rises to the upper-limit set temperature, a water spray control valve  38   a  is opened, a water lifting pump  28  operates to spread air/water mixture  31  on the surface of the roof  24   a , and cooling by heat of evaporation on the surface of the roof  24   a  is promoted. When the temperature decrease to the lower-limit set temperature, the water spray control valve  38   a  is closed, and the water lifting pump  28  is stopped. The water spray control valve  38  may be timer-controlled. In some midpoints of a water lifting pipe  26 , a sand filer  27  and an air/water mixture generating unit  29  are provided. The air/water mixture  31  generated by the air/water mixture generating unit  29  is sent to the roof  24   a  of the structure  24  and is spread to a wide range in short time by one or more water spray ports  30  typified by nozzles, slits, or the like to form a water film of the air/water mixture  31  on the surface of the roof  24   a  of the structure  24 . A part of the spread air/water mixture  31  evaporates to remove heat of evaporation from the roof  24   a  of the structure  24 . On the other hand, the water which is not evaporated is collected by a gutter  32  and is collected again in the water tank  25  via a first stream cutting mechanism  34 , a grit tank  35 , and a large-dust filter  36  mounted in some midpoints in a water collecting pipe  33 . At the time of cooling of the present invention, tap water, ground water, intermediate water, and the like can be used. As a large amount of water is necessary, it is most preferable to use rain water stored and clarified in consideration of water charge, water lifting load, and the like. In this embodiment, a function of storing rain water when it rains is also provided. In the case where water of an amount exceeding the capacity of the water tank flows in the water tank due to a large amount of rain or the like, the rain water of the excess amount is discharged to the outside of the system via an overflow pipe  39 . When the water in the water tank  25  becomes insufficient due to water shortage or the like, by opening a water faucet  40 , tap water, industrial water, or the like can be temporarily used. The quality of water stored in the water tank  25  can be maintained by periodically circulating the water by opening a circulation control valve  38   b  by timer control. By opening a water utilization valve  37 , the stored water can be also effectively used as intermediate water for miscellaneous use. In winter time, since there is the possibility of damage of a pipe caused by freezing, it is preferable to open a freeze damage preventing valve  41 . By spraying the air/water mixture  31  not only to the roof  24   a  but also to the wall surfaces and the periphery of the structure  24 , a larger energy saving effect can be expected. 
     Hereinafter, the present invention will be concretely described by an example. It should be noted that the present invention is not limited thereto. 
     Table 1 shows the contact angles between substrates (a glass substrate and a coated zinc steel plate) of materials and various droplets (surfactant contained water, air/water mixture, and tap water) when the droplets of 5 μL are dropped on the substrates (measured by a contact angle meter “trade name: CA-S microscopic 2 type contact angle meter” manufactured by Kyowa Interface Science Co., Ltd.). Numerical values in Table 1 express average values measured with the number of repetitions of 5, and numerical values in parenthesis indicate the difference between the maximum and minimum values. As the glass substrate, a general-purpose standard product (composition shown in Table 2) made of soda lime glass having a thickness of 1 mm and a size of 100 mm×100 mm was used. As the coated zinc steel plate, a plate of 10 cm×10 cm obtained by cutting a flat part of a metal folded-plate roof “trade name: Yodo Roof 88 (registered trademark) (thickness 0.5 mm, blue)” manufactured by Yodogawa Steel Works, Ltd. was used. The surfactant contained water was obtained by mixing and agitating kitchen detergent made by Kao Corporation “trade name: Family Fresh (registered trademark)” into tap water at a ratio of 0.1 mg/L. The air/water mixture was generated by making air/tap water having a volume ratio of air/tap water of 1/10 pass through the microbubble generator “trade name: BT-50” manufactured by Bubbletank Company. In Table 1, in any of the substrates, the contact angle of the air/water mixture is significantly smaller than that of the tap water and is almost equal to that of the surfactant contained water. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Glass 
                 Coated zinc 
               
               
                   
                 substrate plate (°) 
                 steel plate (°) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Surfactant contained water 
                 15.0 (1.5) 
                 45.3 (2.3) 
               
               
                   
                 Air/Water mixture 
                 14.8 (1.0) 
                 46.2 (1.8) 
               
               
                   
                 Tap water 
                 23.8 (1.3) 
                 81.6 (2.5) 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 SiO 2   
                 Na 2 O 
                 CaO 
                 MgO 
                 Al 2 O 3   
                 K 2 O 
                 SO 3   
                 Fe 2 O 3   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Compo- 
                 71.9 
                 13.3 
                 7.8 
                 4.0 
                 1.7 
                 1.0 
                 0.2 
                 0.1 
               
               
                 sition (%) 
               
               
                   
               
            
           
         
       
     
       FIG. 8  is a diagram showing contours of marks of droplets of surfactant contained water ( 50   a ,  50   b ,  50   c ,  50   d , and  50   e ), the air/water mixture ( 51   a ,  51   b ,  51   c ,  51   d , and  51   e ), and the tap water ( 52   a ,  52   b ,  52   c ,  52   d , and  52   e ) of 2 μL fallen on the glass plate with the number of repetitions of 5 and dried at room temperature of 28° C. and relative humidity of 70% in a no-wind state. The air/water mixture and the surfactant contained water were generated in a manner similar to the example 1. It is understood that the droplet contact face of each of the air/water mixture and the surfactant contained water is wider than that of the tap water, and the surface is uniformly wet.  FIG. 9  is a diagram showing contours of marks of droplets of surfactant contained water ( 53   a ,  53   b ,  53   c ,  53   d , and  53   e ), the air/water mixture ( 54   a ,  54   b ,  54   c ,  54   d , and  54   e ), the tap water ( 55   a ,  55   b ,  55   c ,  55   d , and  55   e ) of 24 adjusted in a manner similar to the example 1 and fallen on the glass plate with the number of repetitions of 5 and dried at room temperature of 28° C. and relative humidity of 70% in a no-wind state. It is understood that the droplet contact face of each of the air/water mixture and the surfactant contained water is wet wider than that of the tap water. Therefore, it is understood that the air/water mixture has higher wetability for any of organic and inorganic substrates. 
       FIG. 10  is a schematic diagram of a laboratory building in an evaporative cooling test. Table 3 shows highest temperatures in the room (measured in a center part in the room at a level of 1100 mm from the floor surface) when various kinds of water (adjusted in a manner similar to the example 1) were spread (at 1 L/m 2  per hour from 9:00 to 16:00 at the outside highest temperature of 37° C.) using water spray ports  49  (spray nozzles “trade name: Mini Spray 5796” manufactured by Kakudai MFG Co., Ltd.) typified by nozzles, slits, or the like in six places at the top of a roof of a laboratory building (a wooden one-story house including a plywood wall  45  having a thickness of 10 mm, a plywood ceiling  46  having a thickness of 2 mm, a cement tiled roof  47  having an average thickness of 30 mm, and a floor  48  made of concrete having a thickness of 50 mm, and the proportion of a single-layer glass window part and a single-layer glass door part in the wall surfaces is 12.5%) shown in  FIG. 10 . The most excellent cooling effect by evaporation could be confirmed in the case of the air/water mixture. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Highest temperature in 
               
               
                   
                 the room (° C.) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Surfactant contained water 
                 28.4 
               
               
                   
                 Air/Water mixture 
                 28.1 
               
               
                   
                 Tap water 
                 30.2 
               
               
                   
                 Not spreaded 
                 32.9 
               
               
                   
                   
               
            
           
         
       
     
     INDUSTRIAL APPLICABILITY 
     As described above, the present invention relates to a method of positively removing a heat amount from a structure by using heat of evaporation of water and can be used, particularly, in the case of cooling an inside of a building of a general household, a company, or the like from outside, the case of cooling the road surface as a countermeasure against the heat island phenomenon, and the like.