Patent Application
20100126702
The present invention relates to a high-efficiency energy-saving and cooling method using heat of evaporation of water.
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.
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.
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 (2a) 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 (2a) 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.
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.
Hereinafter, embodiments of the present invention will be described.
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.
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.
γs=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 (
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-316177 | Nov 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/072588 | 11/21/2007 | WO | 00 | 5/20/2009 |
