FIELD OF THE INVENTION

The present invention relates to a method and apparatus providing cooling of seawater surfaces comprising a bubble curtain creating a transport of colder seawater from below a seawater surface from a pre-calculated depth, wherein the colder seawater from the pre-calculated depth used for the cooling is a mix of different temperature layers of seawater, wherein the mix of seawater layers has an avarage temperature close to or equal to a target temperature of the seawater surface.

BACKGROUND OF THE INVENTION

The ocean of the earth is an essential part of the weather system governing the climate we experience as humans as well as for animals. The climate change we may experience in the future will probably result in increased sea water temperatures.

An increase in seawater temperature may be beneficial for example for industrial fish farming in some northern sea water areas. However, there are also examples of problems related to marine wildlife due to increasing seawater temperatures. For example, a higher seawater surface temperature may provide thermal stress and for example coral bleaching and/or infectious diseases in coral reefs are known consequences. Other problems may be related to respective types of fish which may be able to live in higher water temperaturs.

Another emerging interest of using bubble curtains is related to carbon dioxid reduction in oceans. For example, the article "ARTIFICIAL UPWELLING - A REFINED NARRATIVE" by Jurchott, M., Oschlies, A., & Koeve,

W. (2023). Geophysical Research Letters, 50, e2022GL101870 disclose:

The current story about artificial upwelling (AU) is that it brings nutrient-rich deep water to the ocean's surface, which speeds up the biological carbon pump (BCP). The response of the solubility pump and the CO2 emission scenario is considered in our improved story. Using global ocean-atmosphere model experiments, we show that the effectiveness of a hypothetical maximum AU deployment in all ocean areas where AU is predicted to lower surface pCO2, the draw down of CO2 from the atmosphere during the years 2020-2100, strongly depends on the CO2 emission scenario and ranges from 1.01 Pg C/year (3.70 Pg CO2/year) under RCP 8.5 to 0.32 Pg C/year (1.17 Pg CO2/year) under RCP 2.6 Under the highest emission scenario (RCP 8.5), the solubility pump works just as well as the BCP. However, when CO2 emissions are low, the solubility pump responds by releasing CO2.

However, the effectiviness of the biological carbon pump depends on the seawater surface temperature providing the most benefiscial temperature for the biological activity.

Seawater surface temperatures may also influence weather systems. For example, tropical storms may increase its energy when the storm passes over warmer seawater surface areas. The most extreme case is a tropical storm turning into a tropical cyclone. Research into tropical cyclone development mechanisms has revealed that if the seawater surface temperature is above 26.5°C a tropical storm may develop into a tropical cyclone since the storm may gain more energy from the warmer sea surface water. If the seawater surface temperature is below 26.5°C a tropical storm passing the seawater surface area cannot turn into a tropical cyclone (source). The tropical storm will lose part of its energy when passing seawater surfaces below this temperature limit (source).

Therefore, there is an interest in developing techniques and systems that may be able to cool respective areas of seawater surfaces to be at a temperature below for example 26,5°C, or at temperatures minimizing thermal stress for marine life, etc.

A known technical solution enabling manipulation of seawater surface conditions is denoted bubble curtains. A pipe with an adapted plurality of holes is submerged to a depth in the seawater below a thermocline in the seawater

(an abrupt temperature gradient in a body of water) and compressed air is then applied to the submerged pipe. Compressed air will then flow out of the adapted holes in the pipe and then bubbles will move upwards towards the seawater surface. The ascending bubbles will incorporate or entrain surrounding water generating a vertical flow of deeper water flowing upwards to the seawater surface. If the deeper water is colder than the seawater surface temperature a cooling of the sea water surfaces may be possible. A surface current of cider water will be generated. The size of the area manipulated by a bubble curtain is a function of the length of the pipe and any natural water currents in the seawater surface area being mixed with water currents generated by the ascending bubbles.

An example of cooling a seawater surface area providing tropical cyclone mitigation is disclosed in the publication US 20090272817 which disclose a method and apparatus for reducing the intensity of tropical cyclones. A method may include positioning a fleet of submersibles in an area of ocean through which at least a portion of a tropical cyclone's central core will pass within a predetermined amount of time. The submersibles are maneuvered to a depth greater than a depth of a thermocline in this area of the ocean. The submersibles maintain their station and depth for a finite amount of time, during which they may release a gas to form bubble plumes which rise toward the ocean's surface. The bubble plumes entrain and upwell cold sub-thermocline water toward the surface of the ocean, i.e., colder water from deep calm water below. The cooled ocean surface reduces the intensity of the tropical cyclone whose portion of central core passes through the cooled area. An apparatus to generate a bubble plume may include a gas source, a gas manifold to releasably collect gas from the gas source, and a cover having perforations of a predetermined shape, size, and spacing to produce a predetermined rate of upwelling of seawater. The apparatus may further include a duct to receive at least a portion of the generated bubble plume and channel the cold upwelled seawater toward the surface of the ocean.

Another example is disclosed in US 3683627 disclosing an improved means and method for upwelling or raising sub-surface water to the surface of a body of water for manifold purposes. By dissolving air in the water and providing excess air, the water rises in a vertical current and is accelerated as the pressure on the water at various levels decreases toward the surface, causing the water to give off the dissolved air in a multitude of tiny bubbles which further accelerates the flow of water to the surface. A Scientific investigation of the properties of a bubble curtain is disclosed in the article "Current Produced by an Air Curtain in Deep Water". The Dock and Harbor

Authority, Vol. 42, pp 15-22" by Bulson P.S. from 1961.

Bubble curtains are not only used for sea surface control of temperatures but also providing for example a water surface current moving floating objects away, or lifting relatively warmer water from below the seawater surface which may stop formation of ice in wintertime.

Cooling of a seawater surface is dependent on several factors. For example, mitigating a tropical cyclone development or mitigating thermal stress in coral reefs may require cooling of larger seawater surfaces. The assumption that bringing colder water from deeper seawater layers can cool a larger surface layer may be difficult due to an observation by the invetor of the present invention that cold water has higher density and weight and hence the colder water will probably sink again and cannot stay long enough to provide an effective cooling of a larger seawater surface area. Other factors as known in prior art influencing the effectivity of the cooling may for example be the salinity of respective water volumes that are mixed in the seawater surface layer and hence there is a difference in density (weight) between the respective seawater volumes that are mixed. This influences the end temperature of the mixed water which may make it difficult to reach a desired temperature of the mixed seawater volume, for example at a target surface temperature of 26,5°C, which is known to be a threshold value when for example a tropical storm may gain more energy from the sea surface and turn into a tropical cyclone.

Therefore, there is a need of an improved method and system cooling a seawater surface area to a target temperature with a bubble curtain technique.

OBJECT OF THE INVENTION

It is an object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a control of a seawater surface temperature by upwelling mixed water from below the seawater surface having an average temperature close to a target temperature of the seawater surface temperature. SUMMARY OF THE INVENTION

Thus, the above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a bubble curtain uplifting water from below a seawater surface wherein a depth in the water from wherein bubbles are created by the bubble curtain installation is given by a defined target temperature of the surface water.

The invention is particularly, but not exclusively, advantageous for obtaining a system comprising a bubble curtain configurable to manipulate a temperature of a seawater surface to be in an order of magnitude of a defined target temperature, wherein a pipe of the bubble curtain is positioned at an adjustable depth below the seawater surface, wherein an average temperature of respective seawater layers of a sea water column between a respective one of the adjustable positions of the pipe and the sea water surface equals in magnitude the defined target temperature and is upwelled and mixed by bubbles released through holes arranged in respective walls of the pipe, wherein the bubbles are ascending and entraining water from the respective seawater layers of the sea water column.

Respective aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be disclosed and elucidated with reference to the embodiments described herein.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates an example of embodiment of the present invention.

Figure 2 illustrates further details of the example of embodiment illustrated in Figure 1.

Figure 3 illustrates further details of the example of embodiment illustrated in Figure 1.

Figure 4 illustrates another example of embodiment of the present invention. DETAILED DESCRIPTION OF AN EMBODIMENT

Although the present invention is disclosed in connection with specific examples of embodiments, it should not be construed as being in any way limited to the presented examples. The accompanying claim set defines the scope of protection of the present invention. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Further, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention.

Furthermore, combining individual features mentioned in different claims may possibly be advantageously, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Figure 1 illustrates an example of how a bubble curtain 10 is functioning. A pipe 10a with a perforated surface (holes in the pipe walls) is lowered down to a certain depth in the seawater. The pipe 10a should not rest on a seabed surface such that it is common to attach for example floats that are anchored to the seabed (not illustrated). Compressed air (not illustrated) is supplied in one end of the pipe 10a which is then released through the respective holes in the pipe wall of the pipe 10a. The bubbles are lighter than the water (due to the air inside the bubbles) and the bubbles will be ascending accelerated towards the seawater surface. The ascending of the bubbles is illustrated by the arrow 12 in Figure 1.

The ascending bubbles will entrain surrounding water 11a, lib upwards on both sides of the bubble curtain 10 from the pipe 10a to the seawater surface 18. A natural seawater surface water current 17 is illustrated moving towards the bubble curtain 10. When the ascending bubbles 12 interfere with the natural seawater surface water current 17 parts of the bubbles 12 are moving away from the bubble curtain 10 on both sides 13a, 13b of the bubble curtain 10. When the respective water currents 17, 14a, 14b meet like this the water of the meeting water currents will be mixed in a turbulent manner as illustrated by the reference numeral 15a, 15b and 16, for example. Figure 2 illustrates a cross sectionional view of a water volume wherein a pipe 10a is located at a specified depth below the seawater surface 18. Between the pipe 10a and the seawater surface 18 there is a vertical cross sectional view of a vertical water column 19 from which the bubbles 12 entrain water. The entrained water from the ascending water bubbles 12 is mixed in the upper surface volume below the seawater surface 18 with a natural water current 17 moving towards a first side of the bubble curtain 10. Due to the natural water current 17 mixed water as discussed with reference to Figure 1 moves to a second side of the bubble curtain 10 opposite the first side of the bubble curtain 10. The line 21 illustrate the extent of the affected seawater surface area from the bubble curtain on the first side and second side of the bubble curtain 10. The length of the line 21 illustrates how far the upwelled seawater from below the seawater surface can reach due to the induced surface current away from the bubble curtain 10.

When a certain depth is selected for the pipe 10a of the bubble curtain 10, the temperature of the mixed water is dependent on the selected depth, i.e., the temperature of the ascending water bubles entraining water from the surrounding water the ascending bubbles passes. Therfore, if respective temperatures of respective layers of water between the depth position of the pipe 10a and the seawater surface 18 is known it is possible to calculate a possible temperature of the mixed water in the surface of the water, which may be a target temperature, for example a target temperature of 26,5°C when tropical cyclone mitigation is the object of the deployment of the bubble curtain 10.

By varying the depth location of the pipe 10a different target temperatures may be possible to achieve, and since a target temperature according to the present invention of the cooling water is the target temperature of the sea water surface a more efficient surface water cooling is achieved since the cooling water remains longer on the sea water surface because the cooling water has approximately the same weight (density) as the surface water layer that is cooled, and the cooling water wil not sink downwards as known with other prior art cooling techniques, for example collecting colder water from below a thermocline.

However, it may occure situations wherein the bubbles from the pipe 10a starts to be formed in a distance from the position of the pipe 10a. This can for example be observed with a submerged video camera and the position of the pipr 10a can be lowered further compensating for the distance from the pipe to the position wherin bubbles are generated entraining water.

Figure 2 illustrates a possibility to arrange a temperature sensor 20 that may be floating and for example anchored to the seabed (not illustrated). The temperature sensor may be configured with a wireless transmitter that can send temperature measurements to a control center or to a ship configured with a compressor feeding compressed air to the submerged pipe 10a. A possibility can then be to increase for example the volume of air flowing through the pipe 10a thereby increasing the bubble curtain effect if the temperature is above a defined target temperature of the seawater surface, or the depth location of the pipe 10a is adjusted.

It is within the scope of the present invention that several temperature sensors 20 may be deployed in the seawater area of interest and for example an average temperature of the respective measured temperatures may be used when assessing if a target temperature is achieved. Other techniques providing a same measurement(s) is also within the scope of the present invention.

Figure 3 illustrates an example of a ship 22 configured to deploy a pipe 10a. For example, floats 10b, 10c or trawl doors may be arranged on respective ends of the pipe 10a to keep the pipe 10a fixed to a certain depth in the water. It is also within the scope of the present invention that a buoyancy of the respective floats can be adjusted, for example by filling a chamber of the float with water of blowing filled water in the chamber out with compressed air. Trawl doors can also be used to control the position in the water of the pipe 10a.

The ship 22 is further arranged with a compressor feeding compressed air through a pipe 22b connected in a center position of the pipe 10a.

It also within the scope of the present invention that a bubble curtain 10 according to the present invention can be located stationary on a selected position, or for example the boat 22 can move a bubble curtain 10 across a seawater surface. The bubble curtain can be positioned in the seawater with for example the same technique used for trawls as known from the fishing industry. The compressor arranged for example onboard a ship 22 can be of any conventional compressor type delivering the necessary flux of air with for example a required overpressure (depending on the actual installation depth). Some of the largest commercial compressors have capacities of approximately 6-7 000 Nm3/min of air (N denotes normal air) with working pressure of 16-20 bar and power consumption of some 35 MW. Connecting compressors in parallel will multiply the output capacity to even higher flux rates.

As discussed above, just upwelling cold water may not be enough to achieve a desired temperature of a larger seawater surface. The problem of difference of density of colder water and warmer water that is mixed can be solved according to an aspect of the present invention. With reference to Figure 2, the water column 19 between the pipe 10a and the seawater surface 18 comprises layers of seawater having different temperatures. Therefore, dependent on which depth the pipe 10a is placed in the seawater a mix of upwelled water will be mixed to a temperature from respective water layers of the water column 19 that is a function of the depth the pipe 10a of a bubble curtain 10 is located relative to the water column 19. This is an observation that is different from prior art wherein the depth of a corresponding pip 10a of a bubble curtain is located below a thermocline in the water.

Therefore, increasing the efficiency when cooling a larger seawater area can be achieved by lowering a pipe 10a of a bubble curtain 10 to a depth below the seawater surface 18 defining a seawater column 19 which the bubbles 12 entrain water from respective seawater layers having a combined average temperature equal to a defined target temperature, or a temperature just below or just above the target temperature. An aspect of the present invention is that if too cold water is collected by the bubble curtain 10 the efficiency of the cooling will be less efficient since the colder water rest a shorter time on the sea water surface before sinking due to the higher weight of the cooling water. Therefore, determining the depth of the location wherein the pipe 10a is to be located is of importance for the efficiency of the operation.

With reference to Figure 2, if a temperature sensor 20 measures a temperature above a target temperature it is possible to lower the pipe 10a to a depth providing a more efficient average temperature of the upwelled water. If the temperature sensor measures a temperature below a target temperature the pipe 10a may be lifted upwards.

Therefore, changing a vertical position of a pipe 10a relative to a seawater surface can be used to achieve an efficient temperature control of a larger seawater surface.

An important factor is also the speed of an induced surface water current on the seawater surface. The speed is directly related to how much air is pushed through a pipe 10a of a bubble curtain 10 and the induced surface speed should be in the same order as a natural water current speed at the location of the bubble curtain 10 in order to maintain a continuous mixing of the natural surface current and the bubble-induced surface flow.

The pipe diameter of a pipe can be found from practical engineering diagrams based on the working pressure, permissible pressure drop, air flux, and pipe length etc.

The diameter of the holes in the surface of the pipe 10a can be calculated from common knowledge of distributed flow systems. For example, according to the practices with manifolds the total area of the holes should be less than the cross- sectional area of the pipe 10a of the bubble curtain 10.

Here follows some examples, wherein a target temperature of 26.5°C is to be achieved in areas of the Gulf of Mexico. A typical depth of the location of a pipe 10a below the seawater surface in these areas is estimated from known temperature date to be 150 meters.

The depth of 150 meters is decided on knowledge of a temperature profile of respective layers of a water column 19 between a possible position of a pipe 10a and the seawater surface. By adjusting the depth position of the pipe 10a different average temperatures of the water column 19 can be calculated.

It is also within the scope of the present invention to use more than one pipe 10a in a bubble curtain 10, for example in a parallel configuration. Table la. Bubble-induced surface water current speed when 30 000 Nm3/min of air is led down to 150 m.

Table 1 b. Bubble-induced surface water current speed when 10 000 Nm3/min of air is led down to 150 m.

Table 1 c. Bubble-induced surface current speed when 5 000 Nm3/min of air is led down to 150 m.

Respective calculations show that a 'harsh' environment with a natural surface current of 1.5 m/s requires a two pipe solution each with five compressors delivering 30 000 Nm3/min over maximum 1 km length. At the other end of the scale: a single 5 km pipe will be able to homogenize the upper 150 m below 26.5 in a current of up to 35 cm/s. A complicating factor in some applications of an example of embodiment of the present invention is for example the fact that when trying to stop a development of a tropical cyclone it is necessary to identify a trajectory the center of the tropical cyclone will follow over the seawater surface. Further, the depth of the water needs to be deep enough to enable establishment of a seawater column 19 having an average temperature of the respective seawater layers that is close to the target temperature of 26,5°C. The examples above disclose that a depth of 150m can achieve this average temperature in the Gulf of Mexico. This necessary depth need not always be available dependent on the trajectory of a specific tropical storm that is approaching. Respective meteorologic authorities have the capability to estimate a trajectory of a tropical storm, but the trajectory can change. Therefore, deployment of a bubble curtain system or systems according to the present invention needs to be somewhat dynamical. Therefore, a small fleet of ships 22 illustrated in Figure 3 may be stand by at certain areas of a possible trajectory of a tropical storm, and when the trajectory is more certain one or more of the respective ships 22 may deploy a bubble curtain 10 at a calculated depth of the location for the identified deployment(s).

A further possible problem can be that the depth at the location is not deep enough to satisfy the necessary average temperature of a seawater column 19 as disclosed in Figure 2. According to an aspect of the present invention a pipe 10a of a bubble curtain 10 may be arranged with cooling as disclosed in Figure 4. The pipe 10a comprises in this example of an inner tube lOd surrounded by an outer tube lOf defining a space 10g in between the outer and inner tubing lOf and lOd. The inner tubing lOd receives compressed air from an external compressor as discussed in connection with Figure 3. The compressed air flow out of openings lOe arranged as a pipe through the space 10g between the inner and outer tubing lOd, lOf. There are several such openings but only one is illustrated as an example in Figure 4. The space in between respective pipes lOe and the inner and outer tubing lOd, lOf can be connected to a cooling machine that circulates a cooling agent in this space. A cooling machine as known in prior art can be operated and located at a same location as a compressor, for example onboard a ship 22.

It is also within the scope of the present inventio to replace the cooling agent with a heated fluid at a selected temperature. This may depend on underwater currents transporting cold water upwards in a water column, or due to the use of an example of embodiment of the present invention. For example, keeping a surface area free from ice, or establishing a temperature in the seawater surface that is benefiscial for a specific biological activity.

Another solution to the problem of too little cold water at a specific location is to arrange a pipe from another location on a seabed wherein the water at this location is below for example a thermocline at the specific location. A pump may then be adding colder water to the location of the bubble curtain. By monitoring the resulting surface temperature, the volume of colder water supplied to the location missing colder water may be increased or reduced just by controlling the pump.

Monitoring surface temperatures with a temperature sensor as discussed in connection with Figure 2 makes it possible to regulate the cooling such that a target temperature of for example 26.5 °C is achieved even though the water is not deep enough at a specific location for a system according to the present invention is located to function as a tropical cyclone mitigation system.

According to an example of embodiment of the present invention, a system comprising a bubble curtain 10 is configurable to manipulate a temperature of a seawater surface 18 to be in an order of magnitude of a defined target temperature of the seawater surface 18, wherein a pipe 10a of the bubble curtain 10 is positioned at an adjustable depth below the seawater surface 18, wherein an average temperature of respective seawater layers of a sea water column 19 located between a respective one of the adjustable positions of the pipe 10a and the sea water surface 18 equals in order of magnitude the defined target temperature and is upwelled and mixed by bubbles released through holes arranged in respective walls of the pipe 10a, wherein the bubbles are ascending and entraining water from the respective seawater layers of the sea water column 19.

According to the example of embodiment of the present invention disclosed above, a temperature profile of a water column 19 is established by measuring respective temperatures of seawater layers of the sea water column 19 and iterating different combinations of temperatures of the respective sweater layers as a function of respective depth positions of the pipe 10a until an average temperature of the column 19 is in the order of magnitude of the defined target temperature.

According to the example of embodiment of the present invention disclosed above, the bubble curtain 10 comprises at least two pipes 10a arranged in parallel in a distance from each other.

According to the example of embodiment of the present invention disclosed above, the pipe 10a comprises a plurality of holes in respective walls of the pipe 10a, wherein the number of holes is limited to form a total summed hole area opening-surface being less than a cross sectional area of the pipe 10a.

According to the example of embodiment of the present invention disclosed above, the pipe 10a is arranged with means for controlling a position of a submerged pipe 10a to be located above a seabed surface with a defined distance from the seabed surface, or below a sea water surface.

According to the example of embodiment of the present invention disclosed above, the means for controlling the position is at least a float arranged with an adjustable bouncy enabling a shift of position of the pipe (10a) upwards or downwards relative to a seawater surface (18), or the means are trawl doors.

According to the example of embodiment of the present invention disclosed above, the pipe 10a comprises an inner tubing lOd surrounded by an outer tubing lOf, wherein the inner tubing lOd receives compressed air from an external located compressor while a space 10g in between the first and second tubing lOd, lOf receives a cooling agent from a cooling machine.

According to the example of embodiment of the present invention disclosed above, a ship 22 is configured to deploy a bubble curtain (10) at a position defined by a meteorological institution.

According to the example of embodiment of the present invention disclosed above, at least one temperature sensor is configured to be deployed in an induced water surface current from the bubble curtain 10. According to the example of embodiment of the present invention disclosed above, a measured temperature from the at least one temperature sensor is used to modify a pressure of a compressor feeding compressed air to the pipe 10a, or the location wherein the pipe 10a is located is adjusted upwards or downwards relative to the sea surface 18.

According to the example of embodiment of the present invention disclosed above, extra colder water is supplied to the location of the system (10) by pumping water from another nearby location comprising colder water.

According to the example of embodiment of the present invention disclosed above, wherein the target temperature is 26,5°C.