Flow meter for two-phase fluid with extended measurement range

Abstract

The invention relates to a flow meter (1) for liquid / gas cryogenic two-phase fluids, with overspill, comprising a vertical internal tank, the tank being surrounded by an apparatus, a pipe for carrying the fluid of which the flow rate is to be measured opening into the tank, and wherein the tank has one of the following configurations: - one wall of the internal tank is provided with a system of multiple slots for fluid overflow, forming an overflow system, from the tank to the internal space of the apparatus surrounding the tank, wherein the slots have a different width distributed over the height of the tank; or - the internal tank has several consecutive overflow systems, the pipe for carrying the fluid opening into a first overflow, the overflows overflowing consecutively into one another, until overflowing into the internal space of the apparatus surrounding the tank.

Description

Flow meter for two-phase fluids with extended measuring range

[0001] The present invention relates to the field of flow meters for two-phase gas / liquid cryogenic fluids.

[0002] Measuring the flow rate of a two-phase fluid composed of a liquid and a gas is a difficult operation when trying to measure a mass flow rate. Indeed, all sensors measuring a flow rate are hampered when they are placed in the presence of a two-phase liquid whose density changes at any time. This is particularly true for measuring the flow rate of cryogenic fluids such as liquid nitrogen.

[0003] Some flow meters listed in the literature are based on measuring fluid velocity. These include, for example: turbine flow meters: a turbine is installed in the moving fluid and the rotational speed of the turbine gives an image of the fluid velocity. Pitot tube flow meters: two tubes are installed in the moving fluid to be measured. One tube is installed perpendicular to the flow and gives the static pressure, the other is installed parallel to the flow and gives the total dynamic pressure. The difference in dynamic pressure between these two measurements is used to calculate the flow rate.ultrasonic flow meters: some use the Doppler effect (analysis of the frequency reflected by the particles of the fluid which gives an image of the speed of the particle and therefore of the fluid) while others measure a difference in travel time of an ultrasonic wave from upstream to downstream and from downstream to upstream (image of the speed of the fluid).

[0004] In all these cases, when the density of the fluid varies continuously, the transition from volume flow to mass flow is difficult to achieve precisely.

[0005] Other systems use pressure drop measurement to deduce flow rate. These include, for example, calibrated orifice flow meters, which measure pressure drop upstream and downstream of a calibrated orifice placed in the moving fluid. The measurement of these devices is very disturbed when the fluid does not have a constant density and when the gas content in the liquid increases.

[0006] Electromagnetic flow meters, applicable only to fluids with sufficient electrical conductivity, use the principle of electromagnetic induction: An electromagnetic field is applied to the fluid and the electromotive force created (force proportional to the fluid flow rate) is measured. In the case of flow measurement of cryogenic (non-conductive) fluids such as liquid nitrogen, this principle is not applicable.

[0007] Vortex flow meters are based on the phenomenon of vortex generation observed behind a fixed, non-profiled body placed in a moving fluid (Karman effect). Measuring the pressure variations created by these vortices gives the vortex frequency, which is proportional to the fluid velocity when the fluid maintains constant properties. When the fluid density varies, the measurement is distorted.

[0008] Thermal flow meters are based on measuring the temperature increase created by a constant supply of energy. A system with two temperature probes measures the temperature difference between the flow entering and leaving the flow meter. Between these two probes, a resistor provides a known amount of energy. When the heat capacity of the moving fluid is known, the flow rate can be calculated from these measurements. However, this principle is not applicable to two-phase liquids whose thermal behavior (vaporization of the liquid) is completely different from single-phase liquids.

[0009] Only the Coriolis mass flow meter provides an accurate measurement of the mass flow rate of a fluid. The flow meter consists of a U-shaped or omega-shaped or curved tube, through which the fluid circulates. The U-shaped tube is subject to lateral oscillation and measuring the phase shift of the vibrations between the two branches of the U-shaped tube provides an image of the mass flow rate. However, its cost is quite high and when used at very low temperatures (liquid nitrogen at -196°C for example) and with a fluid whose density varies enormously and includes a significant portion in the gas phase, it is necessary to strongly isolate the system (high-performance insulation such as vacuum insulation for example) and despite this, the measurements are distorted when the gas content exceeds a few percent by mass. It should also be noted that the measurement is often made impossible when the fluid velocity is low or zero (in the first half of the measurement range).

[0010] As can be seen, measuring the flow rate of a two-phase liquid and in particular measuring the flow rate of a cryogenic fluid with acceptable accuracy is not easy to achieve with the devices currently available on the market.

[0011] It can nevertheless be noted that systems are currently being marketed.

[0012] For example, we can cite the case of systems based on the principle of measuring the level of a liquid flowing in a channel just before a restriction of the passage section. This system, described in document US- 5,679,905, operates essentially as follows: the two-phase fluid is first separated into a gas phase which is not measured and a liquid phase whose flow rate is measured. This liquid passes into a channel which has a reduction in section at its outlet. The greater the flow rate, the greater the liquid level in the channel and a level measurement in this channel then makes it possible to deduce the instantaneous flow rate. As can be seen, this system does not take into account the gas flow rate which in certain applications is not negligible. On the other hand, this system makes it possible to measure the liquid flow rate with relatively good accuracy without being disturbed by the gas level, which is the desired goal.

[0013] It should be noted in passing that for this system to function properly, it must be well insulated from heat inputs that could vaporize part of the isolated liquid and thus disrupt the level measurement. This is why vacuum insulation is used in this system.

[0014] It should also be noted that for the system to work, there must be two phases in the flow meter, which prevents it from operating with a sub-cooled liquid (clear liquid without a gas phase).

[0015] It should also be noted that this document uses a V-shaped slot, which has the disadvantage of being difficult to produce with great precision. A 5% variation in the slot width has very serious consequences because it makes the measurement inaccurate in the same proportions.

[0016] We can also cite the case of phase separator flow meters.

[0017] In fact, in the case where the measurement of liquid and gas flow rates is necessary, a system is sometimes used which uses the same principle of phase separation before the flow measurement.

[0018] Thus, commercially available devices have the following arrangement:The two-phase liquid first passes through a phase separator which separates the liquid phase from the gas phase;The gas phase is directed to a volume flow meter (turbine type for example) with temperature compensation;The liquid phase is also directed to a volume flow meter (turbine type for example);These two flow measurements are then converted into mass measurement and added.

[0019] A priori, this device is more expensive than the previous one, we can think that it will be very precise. In practice, we note that the measurement of the liquid flow is affected by errors which fluctuate according to the pressure and temperature conditions of the liquid entering the flow meter. These measurement errors are due to the presence of gas in the liquid phase which passes through the flow meter. Indeed, when the liquid leaves the phase separator to go towards the flow meter, a part of the liquid vaporizes, either because of heat inputs or because of the pressure drop due to a rise of the liquid, or because of a pressure drop due to the pressure loss created by the flow meter itself.

[0020] Finally, to measure the flow rate of a cryogenic liquid, we can also overcome the problems mentioned above by creating pressure and temperature conditions different from the equilibrium pressure (boiling limit). In this area, the most commonly used method is, for example, a flow meter at the outlet of a cryogenic pump (high pressure side). In this case, the liquid is, for example, pumped into a tank where it is at equilibrium and is pressurized by the pump, with almost no increase in temperature. The pipes and the flow meter that follow can then create a pressure drop; this will not result in vaporizing the liquid, provided that the pressure drop is significantly lower than the increase in pressure created by the pump.

[0021] In this case, a classic vortex, turbine or other type flow meter can be used as long as it can withstand low temperatures.

[0022] This technique is, for example, perfectly suited to measuring the flow rate of nitrogen delivery trucks. It is reliable and cost-effective, as the cryogenic pump is required for other reasons.

[0023] On the other hand, when it is necessary to measure the flow of liquid nitrogen at a point where there is no cryogenic pump, then this technique is no longer interesting.

[0024] A solution for simultaneous or alternating measurement of the liquid and gas phases is also known, as described in document FR-3 013 446 in the name of the Applicant, based on the following principle: the fluid arrives in a tank acting as a phase separator; the gas phase is evacuated from the top of the tank via a flow meter operating on a pure gas phase; the liquid phase is evacuated from the bottom of the tank via a flow meter operating on a pure liquid phase; the two phases are then combined at a three-way valve and continue their path; equipped with the two measured flow rates as well as the pressure and temperature of the fluid, the system can calculate the mass flow rate of the fluid passing through the flow meter.

[0025] This system is accurate and works regardless of the two-phase ratio present in the fluid. It works accurately when the fluid is completely gaseous or when it is completely liquid or subcooled, but it also works in all intermediate situations.

[0026] However, this system is penalized by the fact that it is relatively expensive and its installation is relatively complex.

[0027] It must be installed horizontally and its size is quite large (typically 1 meter wide, 1 meter long, 2 meters high).

[0028] The Applicant then endeavored, during previous work, described in document WO 2023 / 011836, to propose a new, simple and reliable solution for measuring the flow rate of cryogenic gas / liquid two-phase fluids, making it possible to solve all or part of the technical problems mentioned above, a solution which was based on the implementation of the following measures (one can refer to the appended document to better visualize this previous solution): 1. A measurement of the flow rate of the non-subcooled liquid phase with a so-called "overflow" system. For this, the two-phase fluid is first naturally separated into a gaseous phase which is not measured and a liquid phase whose flow rate is measured.

[0029] The principle of the spillway is as follows: An obstacle (partition perforated with one or more slots) is installed in the liquid passage, it slows the flow of the liquid. The greater the flow, the more the level upstream of the obstacle will rise. With a calibrated obstacle it is then possible to calculate the flow rate based on the liquid level measured upstream of the obstacle.

[0030] Differential pressure measurement is used to measure the liquid height upstream of the obstacle. Differential pressure sensors available on the market include sensors that can measure low pressure values.

[0031] However, to achieve this pressure level with a cryogenic fluid height, a height of around 300 mm must be obtained. For this reason, it is advantageous to orient the spillway in the vertical direction so that it allows the creation of a high liquid height, and the differential pressure measurement is therefore also quite high.2. A measurement of the flow rate of the subcooled liquid phase with a calibrated orifice (8): when the cryogenic fluid is subcooled, then the flow rate measurement is carried out using a calibrated orifice located upstream or downstream of the spillway.

[0032] The liquid passes through the calibrated orifice and generates a pressure difference. By calculation, it is then possible to obtain the flow rate of the subcooled cryogenic fluid.

[0033] It should be noted here that this flow measurement system does not work when the fluid is not subcooled. When it is saturated (or at equilibrium), the presence of gas in the liquid distorts the measurement, the variation in measured pressure generates more two-phase flow. The measured pressure difference is not representative of the quantity of cryogenic fluid passing through the calibrated orifice. It is therefore necessary to know at all times the state of the cryogenic fluid, subcooled or not.3. A measurement of the subcooling state of the cryogenic fluid (determination of the state of the cryogenic fluid: subcooled or gas-liquid equilibrium): to know the state of the cryogenic fluid being evaluated, the subcooling state of the cryogenic fluid whose flow rate is to be measured is measured.

[0034] To this end, the liquid level present downstream of the weir is measured. When this level is zero, the cryogenic fluid is not undercooled, while in the opposite case, the cryogenic fluid is undercooled: Case No. 1: If the sensor measuring the liquid height in the device (delta P2, downstream of the weir) indicates a near-zero value, the fluid therefore has a gas phase and a liquid phase. The sensor measuring the pressure difference on the calibrated orifice (Delta P3) will also indicate a non-zero value (gas + liquid). Case No. 2: If the sensor measuring the liquid height in the device (∆P2, downstream of the weir) indicates a non-zero value, the fluid therefore has only a liquid phase. The sensor measuring the pressure difference on the calibrated orifice (∆P3) will indicate a value representative of the flow rate of pure liquid.

[0035] To reliably detect whether the fluid is in case No. 1 or in case No. 2, a pressure difference measurement is carried out in a second volume downstream of the spillway (∆P2) as seen previously. This volume is either filled with gas (case No. 1) or filled with liquid (case No. 2), due to the difference in density between the liquid and gas phases, and thus makes it possible to define whether the fluid is pure liquid or a two-phase fluid.

[0036] And when ∆P3 is negative, this means that the fluid flow is reversed (from downstream to upstream): In this case, this flow is neutralized and not taken into account by the flow meter. The error is thus minimized.4. calculation of an estimate of the two-phase rate: thanks to the system described above in accordance with the prior art, we can, as we have understood, measure the liquid phase whatever the conditions, but we can go further and carry out calculations based on the two measurements (via weir and calibrated orifice) and then estimate the two-phase rate. This rate makes it possible to determine the gas phase and thus refine the measurement of total fluid flow.

[0037] The advantages of this earlier flow meter can be summarized as follows: moderate cost; a measurement offering very good accuracy (typically 2%); a system that cannot give rise to an erroneous measurement when the flow rate is zero or slightly negative and the cryogenic fluid is boiling in the flow meter; ease of installation; it provides reliable measurements when the gas rate in the fluid varies from 0 to 100%, the system even allowing the flow rate to be measured when the liquid is undercooled.

[0038] The present invention seeks to improve the flow meter of the prior art described above, because in fact, if until recently, it had been thought of dedicating a flow meter to a given range of flow rates, for this the idea was to size the diameter of the calibrated orifice and the width of the slots according to the flow rate range.

[0039] But in fact, for slots () sized for a given flow range, if the flow to be measured turns out to be higher than the maximum value of the planned sized range, we will then observe an overflow from the top of the device.

[0040] We can in fact consider several very broad flow rate ranges of interest: From 100kg / h to 500kg / h Up to 1000kg / h Up to 2000kg / h etc…

[0041] According to the present invention, it is then desired to allow the same flow meter to cover several flow ranges, based on the initial structure of the flow meter described in the document cited above WO 2023 / 011836.

[0042] However, if we could initially propose working with a spillway having a much greater height, but the disadvantage would then be that the manufacture of the boiler part would be larger, more restrictive, and therefore more expensive.

[0043] It is then proposed according to the present invention, for a maximum liquid flow rate, and to limit the height of the device within reasonable limits, to implement: not one but several successive spillways, these spillways having slots of different widths, which flow into one another; or a single spillway but with slots whose width varies over the height of the spillway.

[0044] A first embodiment of such a structure is illustrated by the attached [Figure 2], which uses 3 successive spillways, equipped with rectangular slots.

[0045] Spillway 1 (1 er spillway encountered by the fluid flow whose flow rate is to be measured): the slots (small width) are sized for the smallest flow rate range of interest. If the flow rate to be measured is higher than the maximum value of this first range, an overflow will be observed (arrow F1)

[0046] If no overflow occurs, the measurements made on this spillway will be considered valid.

[0047] Spillway 2: the slots (average width) are sized for the flow range of interest which can be described as average. If the flow to be measured is higher than the maximum value of this second range, an overflow (arrow F2) will be observed towards the 3 e spillway.

[0048] If no overflow is observed, the measurements taken on this spillway will be considered valid but less precise than those obtained on spillway No. 1 in the absence of overflow.

[0049] Spillway 3: The slots (width “high”) are sized for the range of interest with the highest flow rate.

[0050] We can consider that in this [Figure 2], the pressure differences can be read as follows: the pressure differences ∆P1A = P1A – P1A', ∆P1B= P1B – P1B', and ∆P1C= P1C- P1C' correspond to the ∆P1 represented and used in the previous mode of the (respectively for the three spillways implemented in this [Figure 2]).

[0051] In a two-phase situation, the measurement of the liquid phase is made in the spillway: For spillway 1, the measurement should ideally be made between P1A and P1A'. This measurement will be converted into the height of liquid in spillway 1. A mathematical formula, classic in this field of overflows:

[0052] explained in the following, will then convert this level into liquid flow rate through the slot. When the level measurement is too close to an upper limit, this spillway will be considered overflowing and this measurement will not be taken into account. For spillway 2, the measurement should ideally be made between P1B and P1B'. Similarly, this measurement will give us the liquid level as well as the liquid flow rate through the slot of spillway 2. When the level measurement is too close to an upper limit, this spillway will be considered overflowing and this measurement will not be taken into account. For spillway 3, the measurement should ideally be made between P1C- P1C'. Similarly, this measurement will give us the liquid level as well as the liquid flow rate through the slot of spillway 3. When the level measurement is too close to an upper limit, this spillway will be considered overflowing.In this case, the flow rate will be higher than the measuring capacity of the device and all measurements will be neutralized.

[0053] The symbols of the mathematical formulas cited below must be understood as follows: Q is the flow rate in m 3 .s -1 µ is the spillway flow coefficientLs is the width of the spillway, in mmh is the liquid height, in mmg is the acceleration of gravity in ms -2

[0054] To simplify the system, the measurement can be made between P1A and P1C' for spillway 1, between P1B and P1C' for spillway 2 and between P1C and P1C' for spillway 3.

[0055] A single calibrated orifice (diameter) can be used to measure the entire fluid in two-phase (the liquid phase represents more than 95% of the total flow, so it is essential that the measurement in the weir is accurate) and in pure liquid. The constraint is linked to the fact of using an accurate sensor to measure the differential pressure.

[0056] According to another example of an embodiment of the invention illustrated in the appendix, a single spillway is used, provided with rectangular slots of different widths distributed over the height of the spillway: Slots of “low” thickness on the 1 er third (h1) in the lower part of the spillway Slots of “medium” thickness on the 2 ème third (h2-h1) of the spillwayAnd slots of “high” thickness on the 3 ème third (h3-h2) in the upper part of the spillway

[0057] As will then be clear to those skilled in the art, for the measurement of small flow rates the liquid passes through the portion of slots at the bottom of the tank, for the measurement of medium flow rates the liquid passes through the small and medium slots of the spillway, while for the measurement of large flow rates the liquid passes through all the slots available on the spillway.

[0058] As an example here, we can adopt a slot width of 1mm at the bottom of the spillway, 2mm in the middle and 4mm at the top of the spillway. We can also adopt a greater width difference from one spillway to another, such as 0.2mm for the bottom, 1mm for the middle and 5mm for the top. Depending on the needs, the difference can also be smaller, for example 1mm at the bottom, 1.5mm in the middle and 2mm at the top. Finally, we can also adopt variable width differences between the slots, such as 0.5mm at the bottom, 1mm in the middle and 3mm at the top.

[0059] According to another example of an embodiment of the invention, illustrated in the appended context, a single spillway is implemented, provided with triangular-shaped slots of different widths distributed over the height: slots of “low” thickness in the lower part of the spillway and progressively slots of increasingly greater thickness up to the upper part of the reservoir.

[0060] For example, the slot could have a width of 0mm at the bottom and 5mm at the top. Generally speaking, this slot will advantageously have a width varying from 0 to 2mm at the bottom and 1 to 10mm at the top.

[0061] In order to better assist in understanding the different embodiments of reservoirs and spillways in accordance with the present invention illustrated here, the following will be found in the appendix: In view a): a partial schematic view facing the slots of the widths implemented in the 3 successive spillways of [Figure 2]. In view b): a partial schematic view facing the slots of the single spillway of the, with its slot width decreasing from the top to the bottom of the spillway. In view c): a partial schematic view facing the slots of the single spillway of the.

[0062] Let us explain in the following an example of flow calculation for the example of the implementation mode of the (single spillway, slots of decreasing width from the top to the bottom of the spillway).

[0063] As seen above, the flow rate can be expressed by the following classic formula:

[0064] Where Q is the flow rate in m 3 / s

[0065] µ is the spillway discharge coefficient

[0066] Ls is the width of the overhanging threshold, in mm

[0067] h is the liquid height, in mm

[0068] g is the acceleration of gravity in ms -2

[0069] If the calculated height is less than h1, the flow in the spillway must be calculated with the “low” slot width (1st third), therefore by applying the formula with the low slot width of the 1st third.

[0070] If the calculated height h is less than h1 (a liquid height h corresponds to a flow rate, as we have understood): We calculate the flow rate which flows through the lower slot for the slot width of the 1st third and the height h. The total flow rate is equal to this flow rate.

[0071] If the calculated height h is between h1 and h2: We calculate the flow rate flowing through the low slot for the slot width of the 1st third and the height h1, and We calculate the flow rate flowing through the middle slot for the slot width of the 2nd third and the height h2-h1,

[0072] The total flow rate is then the sum of these 2 flow rates.

[0073] If the calculated height h is between h2 and h3: We calculate the flow rate flowing through the low slot for the slot width of the 1st third (bottom) and the height h1, We calculate the flow rate flowing through the medium slot for the slot width of the 2nd third (intermediate) and the height h2-h1, We calculate the flow rate flowing through the wide slot for the slot width of the 3rd third (top) and the height h3-h2,

[0074] The total flow rate is then the sum of these 3 flow rates.

[0075] The heights h1, h2 and h3, the low, medium and high slot widths can be adapted to “tier” measuring ranges as desired.

[0076] Let us explain in the following an example of flow rate calculation for the example of the implementation mode of [Figure 2].

[0077] It will be recalled that in this [Figure 2], the pressure differences ∆P1A = P1A – P1A', ∆P1B= P1B – P1B', and ∆P1C= P1C- P1C' can be compared to the ∆P1 represented and used in the previous mode of the (for the three spillways implemented in this [Figure 2]), therefore for each of these three spillways to a pressure difference between the bottom of the tank considered and the atmosphere surrounding the tank within the interior space within the device.

[0078] A data acquisition and processing system is capable of carrying out the following evaluations: a. a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between P1A' and P1C' (i.e. two points located in the space surrounding the tank within the interior space, making it possible to deduce the height of liquid downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank); b. based on this state information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the supply pipe of the fluid whose flow rate is to be measured at the equipment, either when the fluid is 100% gaseous or 100% liquid (sub-cooled), or when we are in the presence of a two-phase fluid,by applying the following approach: when the pressure difference ∆P1A = P1A – P1A' characterizing the first spillway encountered by the fluid is between a given minimum level and a given maximum level (maximum corresponding to an overflow level (for example, this maximum level could be a value between 50mm and 500mm), we then have a flow rate that can be described as "low" or "low" flow rate: the pressure differential between P1A and P1A' makes it possible to deduce the height of liquid in tank No. 1 and subsequently the flow rate of fluid passing through the slots of tank No. 1,this using the coefficients related to the width of the slots of tank No. 1. when the pressure difference ∆P1A = P1A – P1A' is greater than the given maximum level (causing an overflow of tank No. 1) and the pressure difference ∆P1B = P1B – P1B' is between a given minimum level and a given maximum level (there is then no overflow of tank No. 2) (for example, this maximum level could be a value between 50mm and 500mm), we then have a flow rate that can be described as an "average" flow rate: the pressure differential between P1B and P1B' allows us to deduce the height of liquid in tank No. 2 and subsequently the flow rate of fluid passing through the slots of tank No. 2, this using the coefficients related to the width of the slots of tank No. 2. when the pressure difference ∆P1B = P1B – P1B' is greater at a given maximum level (sign of an overflow of tank No. 2) (for example,this maximum level could be a value between 50mm and 500mm) and that the pressure difference ∆P1C= P1C – P1C' is between a minimum and a maximum (sign that no overflow of tank 3 is observed, flow rate that can then be described as "medium high"): the pressure differential between P1C and P1C' makes it possible to deduce the height of liquid in tank No3 and subsequently the flow rate of fluid passing through the slots of tank No3, this using the coefficients linked to the width of the slots of tank No3.,

[0079] Let us now consider the case of the method implementing a single spillway with a slot width decreasing from the top to the bottom of this spillway.

[0080] As described above, a single spillway is used here, equipped with rectangular slots of different widths distributed over the height of the spillway: Slots of “low” thickness on the 1 erthird (h1) in the lower part of the spillway Slots of “medium” thickness on the 2 ème intermediate third (h2-h1) of the spillwayAnd slots of “high” thickness on the 3 ème third (h3-h2) in the upper part of the spillway

[0081] A data acquisition and processing system is then capable of carrying out the following evaluations: a. a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between P1A' and P1C' (i.e. two points located in the space surrounding the tank within the interior space, making it possible to deduce the height of liquid downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank); b.based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the supply pipe of the fluid whose flow rate is to be measured to the equipment, when the fluid is 100% gaseous or 100% liquid (undercooled), or when we are in the presence of a two-phase fluid by applying the following approach: when the pressure difference between P1C and P1C' on the one hand, and between P1B and P1B' on the other hand are zero and the pressure difference between P1A and P1A' is not zero (we are then dealing here with what can be described as a "small" flow rate): the pressure differential ∆P1A = P1A – P1A' makes it possible to deduce the height of liquid in the first lower third of the spillway, and subsequently the flow rate of fluid passing through the slots of this first lower third, this using the coefficients to the width of the slots in this first lower third of the tank.when the pressure difference between P1C and P1C' is zero, but the pressure difference between P1B and P1B' is not (we are then dealing here with what can be described as an "average" flow rate: the pressure differential between P1B and P1B' makes it possible to deduce the height of liquid in the lower two thirds of the spillway (h2) and subsequently the flow rate of fluid passing through the slots of the lower reservoir, this by using the coefficients linked to the width of the slots of the lower reservoir (1st third), and we add to this flow rate the flow rate of fluid passing through the slots of the intermediate reservoir, this by using the coefficients linked to the width of the slots of this intermediate reservoir (h2-h1).when the pressure difference between P1C and P1C' is not zero (here we can speak of "large" flow rate), this pressure difference between P1C and P1C' makes it possible to deduce the height of liquid in tanks No1, No2 and No3 and subsequently the flow rate of fluid passing through the slots of tank No1 (low), this using the coefficients linked to the width of the slots of this low tank, flow rate to which we add the flow rate of fluid passing through the slots of tank No2 (intermediate), this using the coefficients linked to the width of the slots of this intermediate tank, and to which we finally add the flow rate of fluid passing through the slots of tank No3 (high third), this using the coefficients linked to the width of the slots of this tank No3.

[0082] The present invention then relates to a flow meter for cryogenic liquid / gas two-phase fluids, comprising: A pipe for supplying the fluid whose flow rate is to be measured, in the flow meter, pipe provided with a calibrated orifice; A vertical internal tank, tank surrounded by a device, tank into which said supply pipe opens, and where the tank has one of the following configurations: i. According to a first embodiment, a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the device surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: Small width slots located in a low flow rate range on a lower part of the tank, for example on the 1 erthird in the lower part of the tank; Slots of average width located in an average range of flow rates on an intermediate part of the tank, for example on the 2 ème third of the tank; andWide slots located in a high flow range on the upper part of the tank, for example on the 3 ème third in the upper part of the tank.

[0083] or else: j. according to a 2nd mode, the internal reservoir comprises several successive overflow systems, the fluid supply pipe opening into a first overflow, the overflows successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow in the series.Pressure sensors for measuring the following pressure differences: A pressure difference (∆P3) between the upstream and downstream of said calibrated orifice A pressure difference(s) ∆P1 (∆P1A, ∆P1B, etc.) between the bottom of each spillway and the atmosphere surrounding each spillway within the interior space within the device, for measuring the liquid level in each spillway; A pressure difference ∆P2 (P1A'-P1C', etc.) existing between two points located in the space surrounding the tank within said interior space, for deducing the liquid height downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank. a data acquisition and processing system, capable of carrying out the following evaluations: a.a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data ∆P2; b. based on this state information, the determination of said flow rate using either the pressure differential ∆P3 when the fluid is 100% gaseous or 100% liquid (sub-cooled), or the pressure differential ∆P1 which makes it possible to deduce the height of liquid in the spillway(s) and subsequently the flow rate of fluid passing through the slots.

[0084] According to one of the embodiments of the invention, the flow meter is characterized in that a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the device surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: Small width slots located in a low flow rate range on a lower part of the tank, for example on the 1 er third in the lower part of the tank; Slots of average width located in an average range of flow rates on an intermediate part of the tank, for example on the 2 ème third of the tank; andWide slots located in a high flow range on the upper part of the tank, for example on the 3 ème third in the upper part of the tank.

[0085] and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (∆P2 (P1A'-P1C', ….)), allowing the height of liquid downstream of the tank to be deduced, and giving the level of liquid invasion downstream of the tank; based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of said calibrated orifice present on the fluid supply pipe, when the fluid is 100% gaseous or 100% liquid (undercooled), or if a two-phase fluid is present by applying the following approach:1.when the pressure difference ∆P1C = P1C - P1C' on the one hand, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device, and when the pressure difference ∆P1B= P1B - P1B' on the other hand, pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, are zero, but the pressure difference ∆P1A= P1A - P1A', pressure difference existing between the bottom of the lower part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not zero, the pressure differential ∆P1A= P1A - P1A' makes it possible to deduce the height of liquid in the lower part of the tank, for example on the 1. erthird in the lower part of the tank, and subsequently the flow rate of fluid passing through the slots of this first lower third, this using the coefficients related to the width of the slots of this first lower third of the tank;2.when the pressure difference ∆P1C = P1C - P1C', the pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is zero, but the pressure difference ∆P1B= P1B - P1B', the pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not, the pressure differential ∆P1B= P1B - P1B' makes it possible to deduce the height of liquid in the lower two-thirds of the spillway (h2) and subsequently the flow rate of fluid passing through the slots of the lower tank, this by using the coefficients linked to the width of the slots of this lower tank, and we add to this flow rate the flow rate of fluid passing through the slots of the intermediate tank, this by using the coefficients linked to the width of the slots of this intermediate tank (h2-h1).3.when the pressure difference ∆P1C = P1C - P1C', the pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is not zero, this pressure difference ∆P1C = P1C - P1C' makes it possible to deduce the height of liquid in the entire internal tank and subsequently the flow rate of fluid passing through the slots of the lower tank, this using the coefficients linked to the width of the slots of this lower tank, flow rate to which is added the flow rate of fluid passing through the slots of the intermediate tank, this using the coefficients linked to the width of the slots of this intermediate tank (h2-h1), and to which is finally added the flow rate of fluid passing through the slots of the upper tank, this using the coefficients linked to the width of the slots of this upper tank.

[0086] According to another embodiment of the invention, the flow meter is characterized in that the internal reservoir comprises several successive overflow systems, the fluid supply pipe opening into a first overflow, the overflows successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow in the series, and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled,from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (∆P2 (P1A'-P1C', ….)), allowing the height of liquid downstream of the tank to be deduced, and giving the level of liquid invasion downstream of the tank;b) based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the fluid supply pipe for which the flow rate is to be measured to the equipment, when the fluid is 100% gaseous or 100% liquid (subcooled), or when a two-phase fluid is present by applying the following approach:1) when the pressure difference ∆P1A = P1A - P1A',pressure difference existing between the bottom of said 1st spillway encountered by the fluid and the atmosphere surrounding the reservoir within the interior space within the device is between a given minimum level and a given maximum level, given maximum level corresponding to an overflow level, this pressure differential ∆P1A= P1A - P1A' makes it possible to deduce the height of liquid in this 1st spillway encountered by the fluid and thus the flow rate of fluid passing through the slots of this 1st spillway encountered by the fluid, this by using the coefficients related to the width of the slots of this first spillway.2) when said pressure difference ∆P1A= P1A - P1A' is greater than said given maximum level, causing an overflow of this 1st spillway encountered by the fluid, and that the pressure difference ∆P1B= P1B - P1B', pressure difference existing between the bottom of the 2nd spillway,spillway following the 1st spillway in the series and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, the pressure differential ∆P1B= P1B - P1B' makes it possible to deduce the height of liquid in spillway No. 2 into which said 1st spillway discharges, and subsequently the flow rate of fluid passing through the slots of this spillway No. 2, this by using the coefficients linked to the width of the slots of this spillway No. 2.3) when said pressure difference ∆P1B= P1B - P1B' is greater than a given maximum level, and the pressure difference ∆P1C= P1C - P1C', pressure difference existing between the bottom of the last spillway in the series, and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a maximum level given,this pressure differential ∆P1C= P1C - P1C' makes it possible to deduce the height of liquid in said last spillway (spillway No. 3) into which said spillway No. 2 discharges, and subsequently the flow rate of fluid passing through the slots of this last spillway, this by using the coefficients linked to the width of the slots of tank No. 3.4) when the pressure difference ∆P1C= P1C - P1C' is greater than a given maximum level, the flow meter is then considered to be overcapacity, namely that the flow rate passing through the device is greater than the measuring capacity of the equipment, and all measurements are then considered to be neutralized.,

[0087] We therefore refer to flow rate calculations using the “coefficients associated with the slot width considered…” (therefore of the portion of wall considered for each embodiment considered), in particular using the classic formula in this field of overflows and recalled above in the present description.

[0088] Or :

[0089] Q is the flow rate in m 3 / s

[0090] µ is the spillway discharge coefficient

[0091] Ls is the width of the overhanging threshold, in mm

[0092] h is the liquid height, in mm

[0093] g is the acceleration of gravity in ms -2

[0094] And therefore the coefficients associated with the slots considered in each calculation, each portion of wall, according to one or other of the said modes are the coefficients linked to the width of the slots considered i.e. Ls and μ, Ls being the slot width.

[0095] And we could illustrate by numerous publications, coming from very diverse sources, the fact that this formula is well known to those skilled in the art of hydraulics, and the fact that the coefficient μ (or m according to the publications) is either approximated to a value of 0.4 or determined experimentally.

[0096] In particular, we can refer to the handbooks of the Suez company:

[0097] https: / / www.suezwaterhandbook.fr / formules-et-outils / formulaire / hydraulique / deversoirs

[0098] Or to the Cassiopeia documentation:

[0099] https: / cassiopee.g-eau.fr / assets / docs / fr / calculators / structures / seuil_denoye.html

[0100] The person skilled in the art is therefore familiar with these formulas, and with the fact that they involve coefficients associated with the slot width considered, namely the flow coefficient and the slot width, and he knows how to measure or determine them.

Claims

A flow meter for cryogenic liquid / gas two-phase fluids, comprising:A supply pipe (2) for the fluid whose flow rate is to be measured, in the flow meter, pipe provided with a calibrated orifice (8);A vertical internal tank, tank surrounded by a device, tank into which said supply pipe opens, and where the tank has one of the following configurations:i) According to a first embodiment, a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the device surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank:Slots of small width located in a low flow rate range on a lower part of the tank, for example on the 1 erthird in the lower part of the tank; Slots of average width located in an average range of flow rates on an intermediate part of the tank, for example on the 2 ème third of the tank; andWide slots located in a high flow range on the upper part of the tank, for example on the 3 èmethird in the upper part of the tank. or: j) according to a 2nd mode, the internal tank comprises several successive overflow systems, the fluid supply pipe opening inside a first overflow, the overflows successively discharging into one another, until discharging into the space inside the device surrounding the tank, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow in the series.Pressure sensors for measuring the following pressure differences: A pressure difference (∆P3) between the upstream and downstream of said calibrated orifice A pressure difference(s) ∆P1 (∆P1A, ∆P1B, etc.) between the bottom of each spillway and the atmosphere surrounding each spillway within the interior space within the device, for measuring the liquid level in each spillway; A pressure difference ∆P2 (P1A'-P1C', etc.) existing between two points located in the space surrounding the tank within said interior space, for deducing the liquid height downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the liquid flooding level downstream of the tank.a data acquisition and processing system, capable of carrying out the following evaluations: a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data ∆P2; b) based on this state information, the determination of said flow rate using either the pressure differential ∆P3 when the fluid is 100% gaseous or 100% liquid (sub-cooled), or the pressure differential ∆P1 which makes it possible to deduce the height of liquid in the spillway(s) and subsequently the flow rate of fluid passing through the slots. A flow meter according to claim 1, characterized in that a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the apparatus surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: Small width slots located in a low flow range on a lower part of the tank, for example on the 1 er third in the lower part of the tank; Slots of average width located in an average range of flow rates on an intermediate part of the tank, for example on the 2 ème third of the tank; andWide slots located in a high flow range on the upper part of the tank, for example on the 3 èmethird in the upper part of the tank.and in that the flow rate of the fluid entering the flow meter is calculated in the following way, the data acquisition and processing system being capable of carrying out the following evaluations:a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (∆P2 (P1A'-P1C', ….)), making it possible to deduce the height of liquid downstream of the tank, and giving the level of liquid invasion downstream of the tank;b) based on this state information, the determination of said flow rate using either the pressure differential measured on both sides of said calibrated orifice present on the fluid supply pipe, when the fluid is 100% gaseous or 100% liquid (sub-cooled),or if we are in the presence of a two-phase fluid by applying the following approach: 1) when the pressure difference ∆P1C = P1C - P1C' on the one hand, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device, and when the pressure difference ∆P1B= P1B - P1B' on the other hand, pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, are zero, but the pressure difference ∆P1A= P1A - P1A', pressure difference existing between the bottom of the lower part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not zero, the pressure differential ∆P1A= P1A - P1A' allows us to deduce the height of liquid in the lower part of the tank, for example on the 1, erthird in the lower part of the tank, and subsequently the fluid flow rate passing through the slots of this first lower third, this using the coefficients related to the width of the slots of this first lower third of the tank;2) when the pressure difference ∆P1C = P1C - P1C', pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is zero, but the pressure difference ∆P1B= P1B - P1B', pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not, the pressure differential ∆P1B= P1B - P1B' makes it possible to deduce the height of liquid in the lower two thirds of the spillway (h2) and subsequently the fluid flow rate passing through the slots of the lower tank, this using the coefficients related to the width from the slots of this low tank,and to this flow rate is added the flow rate of fluid passing through the slots of the intermediate tank, this using the coefficients linked to the width of the slots of this intermediate tank (h2-h1).3) when the pressure difference ∆P1C = P1C - P1C', pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is not zero, this pressure difference ∆P1C = P1C - P1C' makes it possible to deduce the height of liquid in the entire internal tank and subsequently the flow rate of fluid passing through the slots of the lower tank, this using the coefficients linked to the width of the slots of this lower tank, flow rate to which is added the flow rate of fluid passing through the slots of the intermediate tank, this using the coefficients linked to the width of the slots of this intermediate tank (h2-h1),and to which we finally add the flow rate of fluid passing through the slots of the upper reservoir, this using the coefficients linked to the width of the slots of this upper reservoir., A flow meter according to claim 1, characterized in that the internal reservoir comprises several successive overflow systems, the fluid supply pipe opening into a first overflow, the overflows successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow in the series, and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled,from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (∆P2 (P1A'-P1C', ….)), allowing the height of liquid downstream of the tank to be deduced, and giving the level of liquid invasion downstream of the tank;b) based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the fluid supply pipe for which the flow rate is to be measured to the equipment, when the fluid is 100% gaseous or 100% liquid (subcooled), or when a two-phase fluid is present by applying the following approach:1) when the pressure difference ∆P1A = P1A - P1A',pressure difference existing between the bottom of said 1st spillway encountered by the fluid and the atmosphere surrounding the reservoir within the interior space within the device is between a given minimum level and a given maximum level, given maximum level corresponding to an overflow level, this pressure differential ∆P1A= P1A - P1A' makes it possible to deduce the height of liquid in this 1st spillway encountered by the fluid and thus the flow rate of fluid passing through the slots of this 1st spillway encountered by the fluid, this by using the coefficients related to the width of the slots of this first spillway.2) when said pressure difference ∆P1A= P1A - P1A' is greater than said given maximum level, causing an overflow of this 1st spillway encountered by the fluid, and that the pressure difference ∆P1B= P1B - P1B', pressure difference existing between the bottom of the 2nd spillway,spillway following the 1st spillway in the series and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, the pressure differential ∆P1B= P1B - P1B' makes it possible to deduce the height of liquid in spillway No. 2 into which said 1st spillway discharges, and subsequently the flow rate of fluid passing through the slots of this spillway No. 2, this by using the coefficients linked to the width of the slots of this spillway No. 2.3) when said pressure difference ∆P1B= P1B - P1B' is greater than a given maximum level, and the pressure difference ∆P1C= P1C - P1C', pressure difference existing between the bottom of the last spillway in the series, and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a maximum level given,this pressure differential ∆P1C= P1C - P1C' makes it possible to deduce the height of liquid in said last spillway (spillway No. 3) into which said spillway No. 2 discharges, and subsequently the flow rate of fluid passing through the slots of this last spillway, this by using the coefficients linked to the width of the slots of tank No. 3.4) when the pressure difference ∆P1C= P1C - P1C' is greater than a given maximum level, the flow meter is then considered to be overcapacity, namely that the flow rate passing through the device is greater than the measuring capacity of the equipment, and all measurements are then considered to be neutralized.,

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