Field of the invention

This invention relates to a device for measuring total gas content in a liquid, in particular a liquid used for transfer of energy.

Energy transfer systems such as heat pumps and cooling systems use liquids for transfer of heat for example between a cold side and a hot side of a system. Examples of such liquids include water, brine, glycols and various oils. Such liquids contain a certain amount of gas dissolved therein, for various reasons. Gas may for example enter the system when filling liquid or due to leakage. Gas may also diffuse into the system, in particular when the system comprises tubes or pipes made of plastic. Moreover, some liquids form gases over time.

This poses a problem because gas in a system for liquids may disturb flow and pump pressure. For example, the pressure may decrease locally in a pump so that the gas forms bubbles which may cause cavitation. Gas may also cause corrosion in the system. Gas bubbles may decrease pump efficacy. Gas may also decrease heat transfer efficacy by blocking surface area of heat exchangers.

For this reason, such systems may have valves or other devices for degassing the liquid therein. However, it is often difficult to know when a system needs to be degassed. The rate of collection of gas in the system may vary over time. Hence, there is a need for a device for easily monitoring the amount of total gas in the system. Such a device can for example be used to know when the system needs to be degassed.

Various systems for analysis specific compounds in liquids, such as oxygen or carbon dioxide, are known. However, such devices do not determine the amount of total gas unless a specific analysis device is used for each and every compound that is expected to be in the system. Hence there is a need for a device for easily measuring the amount of total gas in a closed liquid system.

There is also a need for a device for measuring total gas content in body of water, such as the sea, a lake or a river. For example, environmental waste may release large amounts of gas such as hydrogen sulfide.

Summary of invention

In a first aspect of the invention there is provided a device for measuring total gas content in a liquid where said liquid is contained in a closed system, the device comprising means for isolating a portion of the liquid from the system in an analysis container, means for decreasing the pressure in the analysis container, a gas collecting space in fluid connection with the analysis container and arranged above the analysis container such that gas will be collected in the gas colleting space such that an interface between the liquid and the gas may form in the gas collecting space, a first electrical pole being elongated and arranged in the gas collecting space such that it extends through the interface between the liquid and the gas, and a second pole formed by the inner surface of the gas collecting space, means for determining the capacitance between the first pole and the second pole, such that the determined capacitance is related to the volume of gas collected in the gas collecting space.

This provides a simple and reliable means of measuring total gas content. Any type of gas can be detected.

The gas collecting space may be vertically arranged on the analysis container.

The upper part of the analysis container may be funnel shaped. This has the advantage of directing gas bubbles to the gas collecting space. In a second aspect of the invention there is provided a system comprising a liquid the system comprising a device according to the first aspect of the invention. The liquid may be used for the transfer of heat. The system may be a cooling system or a heating system, for example.

In a third aspect of the invention there is provided a method for determining total gas in a liquid in a system using a device according to the first aspect of the invention, the method comprising the steps of a) isolating a portion of the liquid in the analysis container, b) decreasing the pressure in the analysis container c) measuring the capacitance over the first and second poles, d) using the capacitance to determine the volume of gas in the gas collecting space or otherwise relating the capacitance to a volume of gas in the gas collecting space.

Fig. 1 is a schematic drawing of a system, where a device is seen from the side.

Fig. 2 is a schematic top view of a gas collecting space.

Fig. 3 is a schematic top view of a gas collecting space.

Fig. 4 is a schematic drawing of a gas colleting space seen from the side.

Fig. 5 is a schematic drawing of a gas colleting space seen from the side.

Fig. 6 is a flowchart that shows a method.

Fig. 7 is a schematic drawing showing various embodiments of a water analysis device.

Detailed description

"Total gas" may refer to any gas that is dissolved in the liquid such as for example oxygen, nitrogen, carbon dioxide or noble gasses. "Total gas" includes gases that are dissolved in the liquid and also gases that become liquids by forming chemical compounds at a high pressure but become gases at lower pressures. Examples of such gases are carbon dioxide, which to a large extent forms carbonic acid in water at high pressure but become gaseous carbon dioxide at lower pressure. Similar procedures occur with ammonia and hydrogen sulfide.

With reference to Fig. 1, the system 1 can be for example a part of a heating system or a cooling system, such as a part of a heat exchanger or other device for transfer of heat. Examples of systems include heat pumps or other systems for extracting heat or cold from for example drilled energy wells, bodies of water, waste heat in industry or wastewater, district heating systems and district cooling systems and large-scale freezers such as freezers in supermarkets. System 1 contains a liquid which may be for example water, brine, glycol, alcohol or mixtures these, oil, or aqueous solutions of organic or non-organic salts. System 1 is closed such that liquid or gas cannot leave the system unless a valve or similar is opened. System 1 may comprise a number of different pipes or tanks, and may also comprise tanks or valves for controlling the flow of liquid. Typically, the liquid in system 1 is circulating, for example with the aid of one or more pumps.

Device 2 is connected to the system 1 with conduits 3. Device 2 comprises means for isolating a part of the liquid in the system 1 from the rest of the system 1. The means for isolating a part of the liquid may be an analysis container 4 which is connected to system 1 but which can be disconnected from system 1, for example with the aid of valves 5a, 5b. The volume of the analysis container 4 is preferably known. The analysis container 4 is connected to means for decreasing the pressure in the analysis container 4 such as a pump 6. The means for decreasing the pressure in the analysis container may alternatively be means for increasing the volume of the analysis container 4. For example, a side wall of the analysis container 4 may be flexible such that it can alter between an inward bulging state and an outward bulging state. In yet a different embodiment the analysis container 4 is a cylinder with a piston that can move to alter the pressure inside.

Hence a sample of the liquid in system 1 can be isolated from the rest of the system 1 using the valves 5a, 5b. The sample is then subjected to low pressure with the aid of pump 6. A suitable final pressure in the analysis container 4 may be 0.5-0.6 bar ATA. Valve 5b may be a one-way valve. With reference to Figs 1 to 5, the top of the analysis container 4 is in fluid connection with a gas collecting space 8 arranged above the analysis container 4. The gas collecting space 8 may be elongated and have a main axis that is non-horizontal, preferably vertical (as seen in the figures). The gas collecting space 8 may preferably have the same width (z) along its main axis (Fig. 4). The gas collecting space 8 preferably has the shape of a cylinder. The gas collection space 8 may extend non-horizontally, preferably vertically, from the analysis container 4 as seen in Figs 1 and 4.

Any fluid connection between the analysis container 4 and the gas collecting space 8 should preferably be arranged so that bubbles are not trapped, but that all gas bubbles are collected in the gas collecting space 8. The upper part 13 of the analysis container 4 may be funnel shaped as seen in Fig. 1 in order to avoid trapping of gas bubbles in the upper part of the analysis container 4 but to funnel gas to the gas collecting space 8.

Decreasing the pressure in the analysis container 4 will make gas in the liquid collect in the gas collecting space 8. A horizontal interface 12 between the liquid and the gas will form in the gas collecting space 8.

The analysis container 4 may have any suitable volume for example from 0.1 to 10 liters but other volumes are possible depending on the gas measured and other conditions. The volume of the gas collecting space 8 is selected depending on which gases can be expected to be present in system 1, which depends on the liquid in the system 1 and other factors. A suitable volume of the gas collecting space 8 may be at least 5 % of the volume of the analysis container 4. When the liquid is water-based and the system 1 is expected to contain carbon dioxide, the volume of gas collecting space 8 may have to be much larger, such as several times the volume of the analysis container 4. The same considerations may have to be made when other gases that can be present in large amounts in the liquid in question. A gas collecting space 8 with a large volume will result in a device 2 with a lower sensitivity but a larger detection range, whereas a smaller volume of the gas collecting space 8 will result in higher sensitivity but smaller detection range. The gas collecting space 8 forms a capacitor where a first electrical pole 9 is an elongated member arranged in the gas collecting space 8 such that it extends through the interface 12 between the liquid and the gas, and a second pole 10 on the inner surface of the gas collecting space 8. The first pole 9 is preferably elongated such as for example a rod or a wire. The capacitance between the first pole 9 and second poles 10 is used to determine the amount of gas in the gas collecting space 8. There is an open space between the first pole 9 and the second pole 10 which is filled by liquid or gas. The first pole 9 may be arranged in the middle of the gas collecting space 8. The first pole 9 may be parallel to the main axis of the gas collecting space 8. The first pole 9 may have a length such that it does not extend below the gas collecting space 8 as seen in the figures.

The fist pole 9 is preferably made from a conducting material which is insulated. The first pole 9 may be a metal wire or a metal rod, such as a copper wire. The second pole 10 is preferably made of a conducting metal such as stainless steel.

As mentioned above, the gas collecting space 8 may have a non-horizontally elongated shape. The gas collecting space 8 may have an even width. This has the advantage of providing a linear relationship between the capacitance and the gas volume as described below.

Fig. 2 shows the section of the gas collection space 8 seen along the line a-a in Fig. 1. The gas collecting space 8 may have any profile such as square or oval, but is preferably circular as in Fig. 2. The interior area A of the cross-section a-a of the gas collecting space 8 may be known.

Fig. 3 shows a different example of how the section a-a of the gas collection interface can be arranged. Here the section a-a is shaped like a square and the first pole 9 is not arranged in the middle of the gas collecting space 8. Arranging the first pole 9 closer to one wall of the second pole 10 will decrease the capacitance compared to placing the first pole 9 in the middle like in Fig. 2. A non- limiting example of how the capacitance between the first pole 9 and the second pole 10 will now be described. However, the skilled person understands that different approaches may be employed to use the capacitance between the first pole 9 and the second pole 10 to determine the amount of gas in the gas collecting space.

The capacitance C for a cylindrical capacitor as shown in Fig. 5, which is essentially the same arrangement as in Fig. 2, can be determined as where

E= the relative dielectric constant for the material

E _o = the dielectric constant for air

I = length of the capacitor

D= inner diameter of the capacitor d=diameter of the first pole

In general, the dielectric constant is much lower for gases than for liquids and the dielectric constant for air can be used in most cases.

The capacitance of the capacitor of Fig. 5 can be determined as

Which can be rewritten as

C = a + b (E — l)x (3) Where and

2n E ₀ b ~ D

In — r

For liquids epsilon >1 such that (3) can be rewritten as

C = a + kx (4)

Where k = b (e — 1)

Hence, there will be a linear relationship between the amount of gas in the gas collection space 8 and the capacitance. This relationship can be used to determine x (x being the height of the liquid along the first pole 9 in the gas collecting space 8) and then y (y=l-x) in Fig 5. By measuring the capacitance between the first 9 and second poles 10 with the use of a capacitance meter 11, the height y of the gas pillar in the gas collecting space 8 can be determined. The height y of the gas pillar will be representative of the gas content in the liquid. The diameter D or the area A of the section of the gas collecting space 8 is preferably known. Since the volume of the analysis container 4 is preferably known, the total gas content in the liquid in the system 1 can be determined.

The above calculation is suitable for a cylindrical gas collecting space 8. However, any suitable method may be used to relate the capacitance to the volume of gas. For example, manual /or brute force type calibrations may be used. For example, a threshold capacitance may be used such that a signal is provided when the capacitance is above the threshold capacitance. Such a signal is indicative that the total gas concentration in the liquid is over a threshold.

The gas collecting space 8 may have any suitable shape. For example, the gas collecting space 8 may be cone shaped, where the cone may be pointing upwards. This may have the advantage of providing more sensitive gas detection. In some embodiments, the gas collecting space 8 may be the upper part of the analysis container 4.

With reference to Fig. 6 a method may comprise the steps of 100 isolating a portion of the liquid from the system 1 in the analysis container 4, for example by closing valves 5a and 5b. In step 101 the pressure in the analysis container 4 is decreased. This will cause gas to form in the gas collection space 8. In step 102 the capacitance is measured. In step 103 the capacitance is converted to data representing gas content of the liquid.

The upper end of the gas collecting space may have a degassing valve 14 for releasing the collected gas after measurement. A new sample may then be analyzed.

The capacitance signal detected by the capacitance meter 11 may be treated or processed in any suitable manner. The device 2 may have suitable control circuitry powered by an energy source such as electric power provided from an outlet or a battery. The capacitance signal may for example be digitalized, for example using a A/D converter. However, an analogue signal may be used. The capacitance signal may be converted to a value or data representing gas content, for example using the linear relationship described above. Any suitable combination of hardware and software may be used to treat or process the capacitance signal. The device may for example comprise a memory, a processor and a bus. Any suitable programming language can be used. The device 2 may have an output means for providing data to a user, such as a display for providing information to a user or a communications interface, such as a network interface for providing data to a second device. The device may be arranged to provide a signal corresponding to the total gas content. A capacitance threshold may be used to trigger an alarm, indicating too much gas in the system 1. Water analysis device

With reference to Fig. 7, there is also provided a water analysis device 50 for measuring total gas in a body of water which works in essentially the same manner as the device described above. The water analysis device is arranged to be submerged in a body of water such as the sea, a lake or a river. The device provides a simple and reliable device for measuring total gas content in a body of water.

The water analysis device 50 has means for isolating a sample from the body of water such as analysis container 4 and a valve for letting in water into the analysis container. The degassing valve 14 may be opened to allow a sample of water to enter the analysis container 4 by allowing gas to escape from the analysis container. The device 50 may have a pump for exchanging the water in the analysis container 4.

Fig. 7 shows an embodiment where a water analysis device 50abc is used for measuring total gas content in a body of water. The water analysis device 50 may be comprised in a housing 51 where the gas collecting space 8 is attached on top of the housing 51. The gas collecting space 8 may alternatively be comprised inside the housing 51. Water analysis device 50a is buoyant and is anchored with an anchor 56 that rests on the seabed 57. Water analysis device 50b is heavier than water and is suspended from a buoy 58 that floats on the water surface 59.

The water analysis device 50 may have suitable attachment means for suspending or anchoring the device in a body of water, such as a noose or a shackle for attaching an anchor 56 or a buoy 58 via wire or rope 60.

The water analysis device 50 has an upper end 52 and a lower end 53 and the device 50 is preferably arranged to be arranged to maintain a level orientation in the water. For example, the water analysis device 50 may have a flotation device 54 in the top end, or a weight 55 in the bottom end, or both. The water analysis device 50 is preferably balanced such that filling the gas collecting space 8 with gas does not change the orientation of the device 50 in a manner that affects the readout. Looking at the suspended water analysis device 50b it may for example be suitable to place the gas collecting space 8 as close to the suspension wire 60 as possible or order to maintain the device 50 level when the gas colleting space 8 is filled with gas.

The device 50 may provide a signal corresponding to a gas amount via a cable to a wireless communication device which may be arranged on buoy 58.

Device 50c is an embodiment where the water analysis device 50c is aboard a remotely operated vehicle or underwater drone 61. Such a vehicle 61 may provide a data storage data facility with a port for extracting stored data after a mission.

The water analysis device 50 is preferably watertight so that it can be submerged to a suitable depth in the body of water. The water analysis device 50 may be arranged to withstand at least 0.3 bars of pressure which is the pressure at a depth of 3 meters. The water analysis device may alternatively be arranged to withstand a pressure of at least 9.78 bar which is the pressure at a depth of 100 m. Hence the housing 50 may be arranged to protect various parts of the water analysis device 50 such as control circuitry, battery, the analysis container 4 and the gas collecting space 8.

By placing the device 50 in a body of water, for example at a suitable depth, the total gas at the depth may be measured in a convenient manner.

A method for determining total gas in sample from a body of water using a water analysis device the method may comprise the steps placing the device in the body of water, such that the upper end is directed upwards towards the surface and the lower end is directed towards the bed of the body of water, isolating a sample of water from the body of water in the analysis container, decreasing the pressure in the analysis container, measuring the capacitance over the first and second poles, and using the capacitance to determine the volume of gas in the gas collecting space. The device evacuation pump may then be used to empty the gas collecting space 8 and the analysis container 4, so that a new sample may be analysed.

CLAUSES

The invention may also be claimed as set out in the following clauses.

1. Device for measuring total gas content in a body of water, the device having an upper end and a lower end, the device comprising means for isolating a sample from the body of water comprising an analysis container, means for decreasing the pressure in the analysis container, a gas collecting space in fluid connection with the analysis container and arranged above the analysis container such that gas will be collected in the gas colleting space such that an interface between the water and the gas will form in the gas collecting space, a first electrical pole being elongated and arranged in the gas collecting space such that it extends through the interface between the liquid and the gas, a second pole formed by the inner surface of the gas collecting space, means for determining the capacitance between the first pole and the second pole, such that the determined capacitance is related to the volume of gas collected in the gas collecting space, the device further comprising control circuitry and an energy source.

2. The device according to claim 1 where the device is watertight such that the device can withstand at least 0.3 bars of water pressure.

3. The device according to any one of claims 1 to 2 where the device is arranged to maintain a level orientation in the water. The device according to any one of claims 1 to 3 where the device has attachment means for suspending or anchoring the device in a body of water. The device according to any one of claims 1 to 4 where the upper part of the analysis container is funnel shaped. A method for determining total gas in sample from a body of water using a device according to any one of claims 1 to 5, the method comprising the steps of a) placing the device in the body of water, such that the upper end is directed upwards towards the surface and the lower end is directed towards the bed of the body of water, b) isolating a sample of water from the body of water in the analysis container, c) decreasing the pressure in the analysis container, d) measuring the capacitance over the first and second poles, e) using the capacitance to determine the volume of gas in the gas collecting space.