Evaporator with image-based control system

Abstract

The present invention relates to a system to control the operating conditions of heat exchanger by acquiring and processing images of a fluid present in a space inside the exchanger.

Description

[0001] EVAPORATOR WITH IMAGE-BASED CONTROL SYSTEM

[0002] DESCRIPTION

[0003] Technical field of the invention

[0004] The present invention relates to the field of the air conditioning systems.

[0005] The present invention, more in detail, relates to a system to control the dynamic state of a fluid in a heat exchanger, in particular of an evaporator, by detecting images of a space inside the exchanger itself.

[0006] Background

[0007] The high efficiency objectives imposed by the species regulations and the most recent heat transfer tube structures highly improved to increase heat transfer performance require a new approach in designing heat exchangers.

[0008] The fact of increasing the overall effectiveness under each operating condition of a heat exchanger, for thermal machines such as chillers or heat pumps, involves several design aspects and requires a deep knowledge of all components of the circuit and of the related weaknesses.

[0009] Three operating conditions have to be carefully monitored in a control logic of a thermal machine during its operation, in particular in evaporators.

[0010] Firstly, the wettability of the tube bundle since, as it is known the main contribution in the heat transfer in evaporators comes from the liquid coolant. The physical reason is attributed to the latent heat of evaporation of the coolant, that is the amount of energy which the liquid phase can "absorb" in the phase exchange. The reflection in the technical application of such feature involves that the geometries of the heat transfer tubes are then suitably devised to increase the evaporation effectiveness. This means that in order to maximize the performances in an evaporator all bundle tubes have to be wetted with the liquid coolant.

[0011] An additional relevant aspect relates to the possible dragging of liquid in the suction flow. Such phenomenon represents one of the main operating limits for a heat machine since it involves a loss of available cooling capacity and, in the most serious cases, significant damages to the compressor mechanics.

[0012] Also the absence of oil accumulations is an important parameter to be monitored to avoid malfunctions and ruptures. In fact, high amounts of oil inside the evaporator can correspond to a lubrification loss and involve serious damages to the compressor mechanics. An oil accumulation can even involve high concentrations inside the exchanger shell and, consequently, the foam formation which favours the liquid dragging in the suction flow. In every case, an oil accumulation reduces considerably the heat transfer performances of the heat transfer tubes since it interferes with boiling phenomena. The oil film which tends to cover the tube bundle, in fact, increases the thermal resistance of the tubes themselves and it modifies indirectly the structures sized suitably to favour the liquid boiling (coolant).

[0013] In order to monitor the above-mentioned operating conditions, the current control logics are based upon algorithms which process the signals mainly coming from sensors of temperature, pressure and / or level of the fluids which work with the heat exchanger.

[0014] However, the known sensor systems have several drawbacks.

[0015] First of all, said sensors succeed in returning only specific information which does not take into consideration the variations associated to the the dynamic state of the working fluids.

[0016] For example, with reference to Figure 1 , the detection of the liquid level in the fluid flow L inside the shell 1 of an exchanger 10 can be influenced by the bubbles which form during the boiling process and by the presence of oil / coolant foam. Moreover, the exchanger 10 frequently, in use, has different levels of liquid along the length of the shell 1 due to the different positions of the suction opening 2 and of the different heat flows, and then of the boiling intensity, in the different regions of the tube bundle 3.

[0017] In particular, in the example illustrated in Figure 1 , three regions are shown having different liquid level inside the same exchanger 10. A first end region A of the space inside the shell 1 , wherein high values of heat flow and, consequently, a low liquid level in the flow L can occur. A second opposite end region C, wherein low values of heat flow and, consequently, a high liquid level in the flow L can occur. A third intermediate region B, wherein high speed values of the flow of the gaseous phase towards the suction opening 2 can occur, wherein the liquid level in the flow L is on the average higher than the liquid level present in said second region C.

[0018] This means that in order to have a reasonably accurate estimation of the profile of fluid level along the shell 1 of the exchanger 10 it is necessary to use several sensors. This involves a cost increase and even a more complex logic for implementing (PLC or other) a control system.

[0019] Additionally, with particular reference to the evaporators of flooded type and to the example shown in Figure 2, their operation generally provides very low overheating values of the gaseous phase of the output fluid which makes difficult to detect the dragging of the liquid component of the fluid flow L in the suction opening 2 by using common sensors. Although it is possible to establish this piece of information by comparing the compressor theoretical delivery temperature value with the actually measured temperature value, such solution not always is applicable due to the lack of information about the operation maps of the compressor. Moreover, the accuracy of methods of this type is low due to the sum of all uncertainties of the considered parameters.

[0020] With reference now to Figure 3, the operation mode of the flooded evaporators does not make possible a simple recovery of the oil from the shell 1 of the exchanger 10 due to the low speeds of the gaseous phase of the fluid flow L at the exit of the area of the tube bundle 3. In particular, when the liquid coolant evaporates and reaches the suction line, the oil tend to accumulate inside the shell 1 until reaching an equilibrium between the incoming and outcoming flow rates. If oil recovery systems are not implemented, said flow equilibrium is generally reached when the high oil concentrations inside the shell 1 lead to the formation of foam F. The latter fills-in the empty spaces among the tubes of the tube bundle 3 and reaches the suction line, dragged by the coolant in gaseous phase. Such foam F, being a mixture of oil and liquid coolant, involves a dragging of liquid in the flow L of suction with the previously described negative effects.

[0021] In this context, the sensor means used nowadays for monitoring the operating parameters of a heat exchanger are not capable of detecting accurately and timely conditions of (incipient) modification of the fluid motion regimes inside thereof, or monitoring the courses of such variations in specific time ranges, for an effective control of the operating conditions of refrigerating apparatuses and thermal machines in general.

[0022] Summary of the invention

[0023] The technical problem placed and solved by the present invention then is to provide an improved control system of a heat exchanger, in particular an evaporator, allowing to recognize timely and automatically anomalies or malfunctions of said exchanger associated to the dynamic state (for example a motion regime) of a fluid present in a space inside the shell.

[0024] Such problem is solved by a control system according to claim 1 . The invention also relates to a method to control the dynamic state of a fluid inside a heat exchanger according to claim 11 .

[0025] Preferred features of the invention are set forth by the depending claims. In the most general embodiment of the invention, the control system comprises a heat exchanger, at least one image grabbing device and a data processing unit.

[0026] The heat exchanger preferably is an evaporator, still more preferably of flooded type, spray type, falling film type or direct expansion type, and it comprises a shell confining an inner space wherein a plurality of heat transfer tubes extends, arranged like a bundle. The heat exchanger is configured to perform a heat transfer process with a phase change of a fluid from liquid to vapor or from vapor to liquid.

[0027] The above-mentioned image acquisition device is arranged and configured to acquire images of the fluid inside the shell and / or images of the fluid leaving the interior side of the heat transfer tubes.

[0028] The data processing unit is configured to assess said images with respect to the dynamic state of the fluid, in particular with respect to a reference operating condition, and to classify the dynamic state of the fluid. The processing unit then generates output information based on the assessment of the images and / or classification of the dynamic state of the fluid. Said output information, in particular under the form of a piece of (for example digital) data or command, is suitable to control the dynamic state of the fluid in the heat exchanger.

[0029] It will be appreciated that the invention allows to recognize fluid motion schemes / regimes, anomalies and malfunctions in a timely and punctual manner since it is based on the evaluation and / or classification of images. Moreover, advantageously, the data processing system implements an algorithm based on artificial intelligence and it allows to solve many of the previously mentioned problems affecting, in particular, the control of refrigerating unit such as chiller and heat pumps.

[0030] The proposed solution provides a more accurate and timely control to detect motion models / regimes and anomalies related to the evolution of the working fluids inside the circuit, with respect to the control which can be obtained with the known systems wherein the signals received by detection sensors of specific parameters represent information crystallized in a time and space instant, however incomplete and difficult to be processed.

[0031] Moreover, although an operator skilled in the art is capable of recognizing the operating conditions of a heat exchanger by looking at inside thereof for a determined time interval, an instantaneous evaluation and / or classification of the dynamic state of a fluid for a simultaneous control action on the exchanger cannot be achieved through an operator-depending activity. In fact, an immediate intervention is essential to modify the operation conditions of the exchanger with the purpose of avoiding serious damages to the thermal machine if one of the above-described malfunctions occurs.

[0032] Moreover, any change in the operating conditions of the exchanger in turn affects instantaneously and continuously the dynamic state of the fluid itself. This means that the system according to the invention is capable of introducing new control functionalities, in particular for the refrigerating units, which to date cannot be integrated in the known systems.

[0033] Other advantages, features and use modes of the present invention will result evident from the following detailed description of some embodiments, shown by way of example and not for limiting purposes.

[0034] Brief description of figures

[0035] The figures of the enclosed drawings will be referred to, wherein:

[0036] ■ Figures 1 , 2 and 3, show, each one, a lateral schematic view of an embodiment of a heat exchanger, in particular of an evaporator, wherein examples of critical operating conditions are highlighted with the purpose of controlling the operation of the exchanger itself and underlying the technical problem placed by the present invention;

[0037] Figure 4 shows a vertical section of a schematic view of a control system of the dynamic state of a fluid in a heat exchanger according to a preferred embodiment of the invention;

[0038] ■ Figure 5 shows a schematic view of a cross section of the system of Figure 4;

[0039] ■ Figure 6 shows schematically the field of view on the tube bundle of one image grabbing device of the exchanger of Figure 4;

[0040] ■ Figure 7 shows a schematic view of a lateral section of a structural detail of the system of the invention, according to two different sizes.

[0041] Detailed description of preferred embodiments

[0042] The present invention will be described hereinafter by making reference to the above-mentioned Figures.

[0043] In general terms, the present invention relates to a control system of the dynamic state of a fluid in a heat exchanger.

[0044] In the context of the present invention, the expression “dynamic state of a fluid” relates to phenomena of dynamic variation in the state of a fluid linked to the operating conditions of the heat exchanger. In particular, the dynamic state of a fluid relates to a fluid dynamic condition and, in particular, to phenomena of dragging of liquid phase in the gaseous phase, of variation in the liquid phase level, of accumulation of substances in the fluid, more generally to a variation in a motion regime, which occur in the inner space of the exchanger.

[0045] A control of the dynamic state of the fluid in a heat exchanger then is meant to describe the control under the fluid dynamic profile of parameters such as for example (distribution of) speed, amount, (operating or service) fluid flow rates, but even mixtures of the fluid with substances and / or exclusively of accumulations of substances in the exchanger, related to a specific state of the fluid (or mixtures thereof or additional substances) during the use of the exchanger rather than a control limited to a state change of the fluid (or of mixtures thereof or additional substances) itself.

[0046] In particular, the dynamic state of the fluid is characterized by the amount of liquid fluid in the vapor and / or by the level of the liquid fluid with respect to the bundle height of the heat transfer tubes and / or by the accumulation of at least one foreign substance, in particular oil, in the fluid.

[0047] Moreover, it is specified that the control system of the present invention comprises a heat exchanger configured to perform a heat transfer process with a main mode of phase change of the fluid, or from liquid to vapor or from vapor to liquid. Different phase changes of the fluid, for example from solid to liquid and vice versa - even if potentially achievable during the use of said heat exchanger - are associated to phenomena and parameters the control thereof lies outside the objectives of the present invention.

[0048] With reference to Figure 4, a vertical section of a preferred embodiment of the control system 100 of the present invention is illustrated schematically.

[0049] Said system 100, as said, comprises a heat exchanger 10 having a shell 1 confining an inner space S and a plurality of heat transfer tubes 3 extending in the inner space S of the shell 1 and being arranged as a bundle.

[0050] The heat exchanger 10 is configured to perform a heat transfer process with a phase change of a fluid L from liquid to vapor or from vapor to liquid. Preferably, the heat exchanger 10 is a component of a refrigerating unit and acts as a flooded evaporator or a spray evaporator or a falling film evaporator. For said types, the heat exchanger 10 is configured to generate vapor by evaporating the fluid L being in the inner space S of the shell 1 and being in contact with the outer surface of at least a portion of the tubes 3 of heat exchange.

[0051] According to an alternative embodiment of the invention, the heat exchanger acts as a (direct) dry expansion evaporator and it is configured to generate vapor by evaporating the fluid L which flows inside the heat transfer tubes 3.

[0052] The heat exchanger 10 can act even as a condenser configured to generate liquid by condensing a vapor being in the inner space S of the shell 1 and being in contact with the outer surface of at least a portion of the heat transfer tubes 3.

[0053] Operating modes and possible structural configurations of the above-mentioned types of heat exchanger are within the knowledge of a person skilled in the art and will not further detailed hereinafter.

[0054] The control system 100 of the invention further comprises one image grabbing device arranged and configured to acquire images of the fluid L inside the shell 1 or images of the fluid L leaving the interior side of the heat transfer tubes 3.

[0055] In a preferred embodiment, such image grabbing device is illustrated in Figure 4 and Figure 5, designated as a whole with reference 4 and it is coupled to the shell 1 of the exchanger 10.

[0056] Preferably, said device comprises a chamber 4 positioned at an opening 1a obtained on the shell 1. Such opening 1a is configured to allow to observe the the space S inside the shell 1 of the exchanger 10, while guaranteeing structural continuity to the shell 1 .

[0057] Embodiments of the invention providing two or more openings coupled with respective image grabbing devices are not excluded.

[0058] Moreover, the tube bundle 3 of the heat exchanger 10 can have arrangements and shapes different from the illustrated ones, but it has to be necessarily arranged in the inner space S so that an observation region \ / of said inner space S remains defined, which is without heat transfer tubes 3 and it is placed between the same bundle and the suction 2 of the exchanger 10.

[0059] Said opening 1a is preferably obtained on the shell 1 in a position so as to face said observation region V, as illustrated by way of example in Figure 6.

[0060] By further referring to Figure 7, said opening 1a preferably comprises a window 1 b made of glassy material carried by a supporting element 11 coupled, or implemented in one piece, with the wall of the shell 1. In the illustrated example, the supporting element 11 is a hollow projection of the shell 1 and the window 1 b is positioned inside the cavity H of said projection to occupy entirely an end of the supporting element 11 distal with respect to the inner space S of the shell 1.

[0061] Preferably, the used glass is wholly transparent, non-deformable and nonopaque.

[0062] The window 1 b made of glass is configured and sized based upon the type of fluid used in the circuit to be resistant to the pressure and the (present or forming) chemical agents inside the exchanger 10. The common applications require a design pressure of at least 10 bar between the shell 1 and the external environment.

[0063] For example, the window 1 b can be made of glass that meets the DIN 7080 standard.

[0064] The opening 1a is advantageously configured to maximize the ratio between the surface of the window 1 b and the extension E of the cavity H of the supporting element 11. In particular, an increase in the extension E of said cavity corresponds to obtaining a viewing angle (designated in Figure 7 with the segments w) of the image grabbing device 4 on the inner space S reduced with respect to the viewing angle (designated in Figure 4 and Figure 7 with the segments w’) obtainable with an extension E’ of said lower cavity H and the surface of the window 1 b being equal (tunnel effect).

[0065] On the contrary, the fact of increasing the surface of the window 1 b made of glass can guarantee a wider viewing angle, but it generally requires a higher thickness s of the glass in order to meet the required pressure resistance requirements.

[0066] In a preferred embodiment, the image grabbing device 4 is a chamber without filters for wavelengths in the infrared (NoIR), so as to favour the observation in an environment (the inner space S of the shell) typically characterized by low light conditions. Moreover, advantageously, it is possible to use infrared LEDs to illuminate the desired regions and to reduce the energy consumption and the consequent heat losses. Preferably, the image grabbing device 4 is characterized by a minimum resolution which depends upon the sizes of the shell 1 and upon the viewing angle of the opening 1a with the purpose of being able to detect one or more of the parameters which characterize the dynamic state of the observed fluid, for example the liquid phase dragged in suction, in particular the liquid droplets.

[0067] As mentioned above, the motion regime of a two-phase flow in fact is a dynamic state of the fluid and it has its own “geometry”. Such geometry, for its nature, can be detected strictly only and exclusively on a visual level, for example with reference to different sizes and shapes of the above-mentioned liquid droplets in the flow. The traditional instruments can detect the conditions under which with a certain probability it is possible that the fluid is in a specific motion regime, but they do not detect it directly. This means that if determined motion regimes are reproduced by varying the operating conditions (for example, pressure, temperature, and so on) in the exchanger it is possible to correlate these variables to the motion regime itself and to use them to process estimates. Such estimates, however, have inevitably a certain degree of uncertainty due to a correlation on empiric base which the detection of the system of the invention, advantageously, allows to overcome.

[0068] Still with reference to Figure 6, if for example the length Z of a heat transfer tube 3 placed in the centre of the bundle and observable from the opening 1a is equal to 200 mm and covers 80% of the width of the acquired image, the minimum resolution of the chamber 4 should be of at least 2500 pixel to allow to detect fluid drops having sizes at least equal to 0.1 mm.

[0069] Said images are evaluated with respect to a dynamic state of the reference fluid by a processing unit. Such unit classifies the detected dynamic state and generates output information based on the above-mentioned evaluation and / or classification.

[0070] Such output information is suitable to control the dynamic state of the fluid in the heat exchanger 10.

[0071] According to an embodiment variant, the inner space S of the shell 1 can be divided into two or more portions, with respect to its own extension, by (not illustrated) separating means such as for example one baffle. In this case, the data processing unit is configured to assess separately the state of the fluid in each portion, to classify separately the dynamic state of the fluid in each portion and to generate output information for each section separately.

[0072] The output information of the processing unit is preferably a piece of data of digital type, suitable to be used as input for a central control unit, operatively associated to the system 100, for example a PLC unit.

[0073] According to a preferred embodiment, said output information can include, alternatively or in combination to the digital piece of data, a signal suitable to actuate at least one control means, for example to operate a valve.

[0074] The evaluation of the images and / or the classification of the dynamic state of the fluid is performed preferably based on artificial intelligence algorithms implemented in the data processing unit.

[0075] The image grabbing device 4 and the processing unit can be arranged in an integrated way as one single body and coupled to the shell 1 of the exchanger 10, with minimum advantages of overall dimension compactness.

[0076] Embodiments can provide the arrangement of the above-mentioned LED lighting source for the image grabbing device 4 in the same one single body which includes the processing unit.

[0077] A case can be provided to contain and protect the image grabbing device 4 and the data processing unit and to allow an easy installation on the heat exchanger 10.

[0078] The present invention has been sofar described with reference to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, as defined by the protective scope of the herebelow reported claims.

Claims

CLAIMS1. A system (100) to control the dynamic state of a fluid (L) in a heat exchanger (10), the system comprising■ a heat exchanger (10) comprising- a shell (1 ) confining an inner space (S),- a plurality of heat transfer tubes (3) extending in the inner space (S) of the shell (1 ) and being arranged as a bundle, the heat exchanger (10) being configured to perform a heat transfer process with a phase change of a fluid from liquid to vapor or from vapor to liquid,■ at least one image grabbing device (4) arranged and configured to acquire images of the fluid (L) inside the shell (1 ) or images of the fluid (L) leaving the interior side of the heat transfer tubes (3),■ a data processing unit configured to assess said images with respect to the dynamic state of the fluid, to classify the dynamic state of the fluid and to generate output information based on the assessment of the images and / or classification of the dynamic state of the fluid, said output information being suitable to control the dynamic state of the fluid in the heat exchanger (10).

2. The system according to claim 1 , wherein the heat exchanger (10) is a flooded evaporator or a spray evaporator or a falling film evaporator and it is configured to generate vapor by evaporating the fluid (L) being in the inner space (S) of the shell (1) and being in contact with the outer surface of at least a portion of the heat transfer tubes (3).

3. The system according to claim 2, wherein the dynamic state of the fluid is characterized by the amount of liquid fluid in the vapor and / or the level of theliquid fluid relative to the bundle of the heat transfer tubes (3) and / or the accumulation of at least one foreign substance, particularly oil, in the fluid.

4. The system according to claim 1 , wherein the heat exchanger (10) is a condenser being configured to generate liquid by condensing a vapor being in the inner space (S) of the shell (1 ) and being in contact with the outer surface of at least a portion of the heat transfer tubes (3).

5. The system according to one or more of the preceding claims, wherein the inner space (S) of the shell (1 ) is subdivided into at least two sections by at least one baffle and the data processing unit is configured to assess the state of the fluid (L) in each section separately, to classify the dynamic state of the fluid in each section separately and to generate output information for each section separately.

6. The system according to claim 1 , wherein the heat exchanger (10) is a dry expansion evaporator being configured to generate vapor by evaporating a fluid flowing on the interior side of the heat transfer tubes (3).

7. The system according to one or more of the preceding claims, wherein the data processing unit uses an algorithm based on artificial intelligence.

8. The system according to one or more of the preceding claims, wherein the output information of the data processing unit is a digital type of information.

9. The system according to one or more of the preceding claims, wherein the output information of the data processing unit is a signal suitable to operate at least one control means, particularly to operate a valve.

10. The system according to one or more of the preceding claims, wherein at least the image grabbing device (4) and the data processing unit are coupled with the shell (1 ).

11. A method to control the dynamic state of a fluid (L) in a heat exchanger (10), the method comprising the steps of: a) operating the heat exchanger (10) comprising■ a shell (1 ) confining an inner space (S),■ a plurality of heat transfer tubes (3) extending in the inner space (S) of the shell (1), wherein the heat exchanger (10) generates vapor by evaporating a fluid (L) being in the inner space (S) of the shell (1 ) and being in contact with the outer surface of at least a portion of the heat transfer tubes (3), b) acquiring images of the fluid (L) in said inner space (S) by at least one image grabbing device (4), c) applying a data processing unit to assess such images with respect to the dynamic state of the fluid, to classify the dynamic state of the fluid and to generate output information based on the assessment of the images and / or classification of the dynamic state of the fluid, d) using said output information to control the dynamic state of the fluid (L) in the heat exchanger (10).

Images