Mass transfer measuring apparatus

Abstract

The present invention relates to a mass transfer measuring apparatus comprising a heat-insulated chamber (2), to which an air moving device (18) is attached, said air moving device making an air flow move around the inside of the chamber (2) in a manner that can be adjusted for speed, temperature and moisture, said parameters being verifiable through various sensors (3, 4, 5). The apparatus is characterised in that the chamber (2) comprises one or more drying receivers, and a load sensor (6) on each drying receiver, the drying receiver(s) being: - one or more semi-open receivers (7) so that the air flow is not directly incident on respective samples (m) incorporated therein; and / or - one or more open receivers (8, 8') so that the air flow is directly incident on respective samples (m) incorporated therein.

Description

[0001]DESCRIPTIONMass transfer measuring apparatusTECHNICAL SECTORThe field of application of the present invention falls within the industrial sector intended for the manufacture of measuring apparatus, devices and utensils, specifically those intended for measuring the mass transfer of substances (during drying), and more specifically those intended for measuring gas diffusivity and / or the convection mass transfer coefficient at the solid-air or liquid-air interface.The present invention is particularly applicable in industries where precision is required in the prediction of the drying rate and the analysis of mass transfer under different temperature and humidity conditions. Such applications include the food, pharmaceutical and construction materials industries, among others, where this type of analysis is critical.BACKGROUND OF THE INVENTION Drying processes, despite being very common in everyday life, present a great deal of uncertainty when it comes to predicting the time required for the process under given conditions. A fairly common trend in the scientific literature has been to perform experiments from which curves are drawn that relate humidity with time when the process is carried out under fixed conditions. However, when conditions change, the curves representing drying also vary. Therefore, the impossibility of creating an infinite number of curves prevents an accurate prediction of the drying rate under changing conditions. An alternative to the use of empirical drying curves is the use of mass transfer models, which are based on diffusion phenomena and convective mass transfer.Diffusion transfer phenomena use equations where there is a proportionality between the mass transfer rate and the particle concentration gradient between two specific points in a system. The proportionality constant in a diffusion process is the diffusion coefficient defined in Fick's law, also known as diffusivity (^^). Convection transfer phenomena use equations where there is a proportionality between the mass transfer rate and the particle concentration difference between two specific points in a system. In a convection mass transfer process, the proportionality constant is defined as the convection mass transfer coefficient (ℎ). ^). The problem with using these mass transfer models lies in the difficulty of accurately measuring the diffusivity (^^) and the mass transfer coefficient (ℎ^), which may also vary during the process. The invention proposed here focuses on an apparatus capable of measuring both parameters. EXPLANATION OF THE INVENTION The mass transfer measuring apparatus proposed by the invention represents an improvement over what is already known, with the characterising details that make it possible and distinguish it being conveniently included in the final claims that accompany this description. The invention proposes a mass transfer measuring apparatus comprising a thermally insulated chamber to which an air circulating device is coupled. The air circulating device circulates a flow of air inside the chamber in a manner that can be regulated in terms of speed, temperature and humidity.These parameters can be verified by means of various sensors; which are preferably: one or more anemometers, one or more dry-bulb air temperature sensors, and one or more relative air humidity sensors, respectively, these sensors being located inside the chamber. The chamber comprises, inside it, one or more desiccation receivers, and a load sensor (for example, a load cell) in each desiccation receiver. The desiccation receiver(s) absorb heat from the air flow circulating inside the chamber. The desiccation receiver(s) can be semi-open, open, or there can be a combination of both types. In this document, a desiccation receiver is understood to be a component where a sample for measurement is placed, which can be open (for convective mass transfer measurement) or semi-open (for gas diffusivity measurement).The following are the specific features of each type of receiver:- Semi-open receiver: In this document, a semi-open receiver is understood to be a drying receiver shaped such that the air flow does not directly affect a sample incorporated inside the receiver. The semi-open receiver is used to measure the gas diffusivity at the solid-air or liquid-air interface (^^) of the sample incorporated therein, following Fick's law. Diffusivity refers to the capacity of a substance to transfer mass by diffusion (expressed in m² / s). In this document, the term "gas diffusivity" is also used to refer in a simplified manner to "gas diffusivity at the solid-air or liquid-air interface". According to one embodiment, the semi-open receiver has a closed lower part and an open upper part forming an upper opening.Preferably, the semi-open receiver has a constant cross-section. Preferably, the semi-open receiver has a height such that there is a space between its upper opening and a ceiling of the chamber suitable for the air to flow through without significantly altering its velocity. Preferably, assuming that the air flow is constant in its displacement along the chamber, the separation between the upper opening of the semi-open receiver and the ceiling of the chamber is at least about 10 cm. The semi-open receiver may be a tubular container (for example, a cylindrical or prismatic tubular container) arranged vertically, with its lower part closed and its upper part open forming the upper opening. In this document, the term "tube" is used to refer in a simplified manner to a tubular container. According to an exemplary embodiment, the tube has a diameter of between 15 and 30 centimeters.- Open receiver: In this document, an open receiver is understood to mean a drying receiver shaped such that the air flow directly affects a sample incorporated into the receiver. The open receiver may be a receiver shaped like a container, for example, in the form of a tray, plate or similar; or it may be a bare receiver. In this document, the terms “tray” and “plate” are used to refer in a simplified manner to a “tray-shaped container” and a “plate-shaped container”, respectively. In this document, a bare receiver is understood to mean a drying receiver shaped like an area inside the chamber (for example, at the base of the chamber), which receives the respective sample without a container. The open receiver is used to measure the convection mass transfer coefficient at the solid-air or liquid-air interface (ℎ^) of the sample incorporated therein.Mass transfer coefficient is a parameter that measures the efficiency of the convective mass transfer process over a given surface area (in kg / m² s). In this document, the term “convective mass transfer coefficient” is also used to refer in a simplified manner to the “convective mass transfer coefficient at the solid-air or liquid-air interface”. Optionally, the chamber may house a combination of one or more semi-open receivers and one or more open receivers. This configuration is used to measure both parameters (^^, ℎ^). Preferably, one or more containers that make up the respective desiccation receivers are removable. In the case where there are several receivers of the same type in the chamber: the receivers may be identical, or there may be receivers that differ in shape and / or dimension (for example, there may be receivers with different base areas and / or different heights).According to one embodiment, the chamber simultaneously includes open receivers of different sizes, shapes, and / or heights; and / or semi-open receivers of different sizes, shapes, and / or heights; to measure one or different types of samples. If the apparatus comprises several desiccation receivers, these can be arranged in different ways, giving rise to different specific embodiments. In one embodiment, the desiccation receivers are arranged in rows. In another embodiment, the desiccation receivers are arranged in staggered rows. In yet another embodiment, the desiccation receivers are arranged irregularly.As mentioned above, the apparatus comprises different types of sensors, in particular, anemometer(s), dry-bulb air temperature sensor(s), relative air humidity sensor(s), and charge sensor(s). According to one embodiment, at least the dry-bulb air temperature sensors and the relative air humidity sensors are distributed uniformly inside the chamber. Preferably, one dry-bulb air temperature sensor and one relative air humidity sensor are provided in each drying receiver, each sensor being able to be placed either on the outside or inside of the corresponding drying receiver. The charge sensor(s) are preferably installed in the base of the drying receiver(s), respectively. Each sample incorporated into a drying receiver is a solid or liquid mass to which a gas or liquid, for example, water, benzene, acetone, or any other, is adsorbed.The load sensor in each desiccation receiver records the change in mass of the sample over time. The change in mass of the sample over time is caused by the effect of the air flow generated by the air circulator. As mentioned above, the air circulator circulates air around and above the chamber's receiver(s). If the chamber houses one or more semi-open receivers (e.g., tubular), a gas concentration gradient is generated in each semi-open receiver from the surface of the solid or liquid mass of the sample to the top of the semi-open receiver.The difference in gas concentration between the surface of the solid or liquid mass and the air circulating above the upper opening of the semi-open receiver causes particle movement by diffusion following Fick's law, the application of which allows the calculation of the gas diffusivity at the solid-air or liquid-air interface (^^) of the sample. In the event that the chamber houses one or more open receivers (for example, tray-shaped or naked), the solid or liquid mass of each sample is in contact with the air circulating through the chamber, such that the movement of the particles that come off the sample is carried out by convection, which allows the calculation of the mass transfer coefficient by convection at the solid-air or liquid-air interface (ℎ^) of the sample.According to one embodiment, the air circulating device comprises the following components: - A driving means: The driving means is responsible for driving the air into the chamber. According to one embodiment, the driving means comprises one or more fans. - A temperature regulating means: The temperature regulating means is responsible for regulating the temperature of the air driven by the driving means before it is introduced into the chamber. According to one embodiment, the temperature regulating means comprises one or more resistors that heat the air driven by the driving means. The resistor or resistors can be of variable power, for example, by means of a potentiometer. Additionally or alternatively, the temperature regulating means can comprise one or more heat exchangers that heat or cool the air driven by the driving means.The heat exchanger or exchangers may be cold exchangers or hot exchangers, or there may be a combination of both types. - A humidity regulating means: The humidity regulating means is responsible for regulating the humidity of the air propelled by the driving means before it is introduced into the chamber. Preferably, the humidity regulating means is arranged between the driving means and the temperature regulating means. According to an exemplary embodiment, the humidity regulating means comprises: one or more humidifiers, responsible for increasing the humidity of the air; and / or one or more dehumidifiers, responsible for decreasing the humidity of the air. Preferably, the humidifier or humidifiers comprise a porous bed of fiber or mesh through which a current of water is circulated, allowing the air propelled by the driving means to be humidified before being introduced into the chamber.Preferably, the dehumidifier or dehumidifiers consist of a cold exchanger, with a temperature lower than the dew point, which reduces air humidity through condensation. According to one embodiment, the air circulation device comprises an inlet duct responsible for conducting the air driven by the driving means into the chamber. Preferably, the temperature regulating means is installed in the inlet duct. The inlet duct can have different configurations, giving rise to different embodiments: According to one embodiment, the inlet duct has a constant cross-section. According to another embodiment, the inlet duct has a variable cross-section that progressively increases in the direction of air flow into the chamber. According to another embodiment, the inlet duct has a variable cross-section that progressively decreases.According to an exemplary embodiment, the apparatus of the present invention comprises one or more diffusers, which contribute to the formation of a laminar air flow in the chamber, and the formation of a constant temperature profile along the height and width of the chamber. Preferably, the diffuser or diffusers are of the type that comprises a porous bed. In this document, "porous bed" is understood to be a set of solid particles with spaces between them through which a fluid can pass. The porous bed can be formed of fiber or mesh. Some examples of porous beds are: a sheet with holes, a foam rubber panel, etc. Preferably, at least one of the diffuser or diffusers is arranged at the entrance to the chamber. According to an exemplary embodiment, at least one of the diffuser or diffusers arranged at the entrance to the chamber comprises a prechamber, which acts as a means of homogenizing the temperature and humidity of the air flow.Preferably, at least one of the diffuser or diffusers is arranged at the chamber outlet. According to one embodiment, the air circulation device forces the air through a sector that modifies the direction of the air before entering the chamber. This reduces the air speed and distributes it better, thereby contributing to the formation of the laminar air flow in the chamber and to the formation of the constant temperature profile along the height and width of the chamber. According to one embodiment, the apparatus comprises a turbulence-generating means, which contributes to the formation of a turbulent air flow in the prechamber. Preferably, the turbulence-generating means comprises: - one or more agitators, consisting of a turbine whose action interferes with the air flow in a direction different from the circulation of said flow; and / or - one or more baffles that force a change in the flow direction.Additionally or alternatively, turbulent air flow can also be achieved in other ways, such as by increasing the air velocity (e.g., by increasing the velocity of the driving medium), by modifying the flow area, and / or by removing diffusers. According to one embodiment, the chamber comprises a hatch, preferably at the top or at the side. When the hatch is opened, the interior of the chamber can be accessed, allowing one or more components inside the chamber to be introduced, manipulated, and / or replaced; for example, it allows the drying receiver(s) to be introduced, it allows the sample(s) to be added to the respective drying receiver(s), it allows the sensors to be manipulated or replaced if necessary, etc.The gas diffusivity at the solid-air or liquid-air interface (^^), the convection mass transfer coefficient at the solid-air or liquid-air interface (ℎ^), and other related parameters such as, for example, the drying rate, can be calculated by a programmable processing means, from the data obtained by the load sensor or sensors of the apparatus of the present invention. The programmable processing means may be external to the present invention or, according to an exemplary embodiment, may form part of it. According to an exemplary embodiment, the apparatus of the present invention comprises a communication means that is responsible for receiving data (for example, operating instructions from the programmable processing means) and / or transmitting data (for example, to send data captured by the weight sensor or sensors to the programmable processing means).According to an exemplary embodiment, the means of communication is of the wireless type. The fundamentals on which the measurement of gas diffusivity at the solid-air or liquid-air interface (^^) and the measurement of the mass transfer coefficient by convection at the solid-air or liquid-air interface (ℎ^) are based are described below. Basis of the measurement of gas diffusivity at the solid-air or liquid-air interface (^. ^). The diffusion process consists of the movement of particles due to differences in concentration in a given area. Since the gas concentration at the surface of a solid or liquid mass is greater than that of the surrounding air, the particles move from the solid or liquid to the air by diffusion. This process follows Fick's Law (according to equation I) where ^^ is the mass concentration of gas, i.e., kg of gas / m3; ^ is the mass transfer area at the surface of the solid or liquid expressed in m2; ^^ is the diffusivity (m 2 / s) of the gas in air, which depends on the nature of the solid or liquid, the temperature and the pressure;^ is the distance in the direction in which the change in gas concentration occurs (concentration gradient). Fick's Law makes it possible to calculate the mass of gas released from the solid or liquid by diffusion in the direction of the decreasing gas concentration gradient (^^̇) in kg of gas / s. The mass fraction of gas in air (ω ^ ) is expressed as the ratio between the mass of gas (m ^ ) and the mass of dry air (m ^^^^ ). This fraction can be calculated from the measurement of the partial pressures of the gas (^^) and the air at a given point (^^^^^) (see equation II). where ^ ^ is the molecular weight of the gas (for water it is ^ ^^^^^ = 18 g / mol), ^ ^^^^ is the molecular weight of air (estimated to be ^^^^^=28.93 g / mol), ^^ is the partial pressure of the gas, and ^^^^^is the partial pressure of air. The partial pressure of air (^^^^^) plus the partial pressure of gas (^^) is the total pressure of the mixture, ^ = ^^ + ^^^^^. In order to express Fick's Law in terms of the mass fraction of gas, equation I is multiplied and divided by the density of air (^^^^^), where L is the length of the drying receiver (e.g., the length of the tube, if applicable). The density of air (^^^^^) depends on the pressure (^) and the temperature (^) and is calculated using equation IV, from the Universal Law of Ideal Gases: ^⋅ ^ = ^^^^^ ⋅ ^ ⋅ ^^ ^ = ^^^^ ^ ⋅ ^ ^ ^ ^ ^^^^ / ^ ^^^^ ^ · ^ = ^ where ^ is the pressure (expressed in Pa), ^^^^^ the molecular weight of air (estimated at ^ = 28.93 g / mol), ^ the temperature (expressed in K), ^ the volume (expressed in m ), ^ the universal constant of ideal gases ^ = 8.314 Pa / m 3 mol . K. The air at the surface of the solid or liquid in the diffusion process is considered saturated, that is, the gas under study is at saturation pressure at a given temperature (^^^). The mass fraction under these conditions is calculated according to equation V. where ^ ^ is the molecular weight of the gas (for water it is ^ ^^^^^ = 18 g / mol), ^ ^^^^is the molecular weight of air (estimated in ^ ^^^^ =28.93 g / mol), ^ ^^ is the saturation pressure of the gas and ^ ^^^^ is the partial pressure of air. The partial pressure of air (^^^^^) plus the saturation pressure of the gas (^^^) is the total pressure of the mixture, ^ = ^^^ + ^^^^^. Equation II for calculating the absolute humidity of the air can be particularized for water as equation VI. Equation VII corresponds to the calculation of the absolute humidity of the air under saturation conditions. ^ ^ ^^^^^^^^^ ^^ = ^^^^^^ = 0.622^ − ^^^^^^^^^^(VII) In the case of water, the saturation pressure in a mass of vapor at a given temperature is the pressure from which the mass of water begins to condense. This is usually collected in tables. In the case of water, the saturation pressure in a mass of air at a given temperature can be calculated with equation VIII, expressed in pascals, and the temperature in degrees Celsius. By recording the mass variation in each of the semi-open receivers over time, this mass variation corresponds to the mass diffusion ^^̇, in kg of gas released per second (kg gas / s) ^ − ^ ^̇ ^ ^ ^ = ^^ − ^^ (X), where:- ^ is the mass of the desiccation receiver plus the sample at the instant - ^^ is the mass of the desiccation receiver plus the sample at the instant ^^Equation XI, which expresses the gas diffusivity at the solid-air or liquid-air interface, is obtained by clearing ^^ in equation IX: Basis of measurement of the mass transfer coefficient by convection at the solid-air or liquid-air interface. Gas particle loss occurs through convective mass transfer phenomena when the air surrounding the particles is in motion. The transfer process is much faster than diffusion because once the particle is released, it is entrained, leaving a higher concentration gradient at the solid-air or liquid-air interface. By analogy with convective heat transfer processes, equation XII is defined. That is, the mass flow rate of gas transferred to the air during the drying process is proportional to the transfer area (A), times the air density (ρ^^^^), and the difference between the mass fraction of gas in the air near the surface of the solid or liquid and the mass fraction of gas in the circulating air ^ω^^ − ω^^. The mass fraction of gas in the circulating air is calculated using equation II (VI for water vapor in air).The mass fraction of gas in the air near the surface of the solid or liquid is assumed to be saturated and is calculated using equation V (VII for air saturated with water vapor). The proportionality constant is called the convection mass transfer coefficient (ℎ). ^ ). The convective mass transfer coefficient (ℎ^) can be calculated from the Sherwood number ^ℎ, defined as the ratio of mass mobilized by convection to diffusion. where:- ^^ is the characteristic length. In the case of an air flow circulating on a horizontal flat surface, ^^ is the length of the surface in the same direction as the air flow circulates. In the case of the air flow circulating perpendicular to a cylindrical surface (as shown in figure 7-A) or prismatic surface, ^^ is considered the width of the cross section, understanding as such, the largest dimension of the cross section in the direction perpendicular to that of the air flow (as shown in figure 7-B, which indicates the characteristic length ^^ of several examples of cross sections).- The Sherwood number (^ℎ) can be calculated based on the Reynolds number (^^) and the Schmidt number (^^).The form of the function depends on the geometry and the circulation regime of the fluid (laminar or turbulent), taking the same correlation equations as those used to calculate the Nusselt number (Nu) in the analysis of the convection heat transfer coefficient, replacing the Prandtl number (^^) by the Schmidt number, and the Nusselt number by the Sherwood number. Below is a table showing the analogies between the processes of heat transfer and mass transfer by convection, in the most relevant aspects. In summary:- To measure the gas diffusivity at the solid-air or liquid-air interface (^^), the following steps are followed: 1. The mass or masses of solid or liquid to be sampled are incorporated into the respective semi-open receivers. 2. The different components of the air circulating device (drive medium, temperature regulating medium, etc.) are configured to generate the desired conditions inside the chamber. 3. ^^ is measured at time t1. 4. ^^ is measured at time t2. 5. ^^̇ is found using equation X: 6. ^^ is found by equation XI: - To measure the convection mass transfer coefficient at the solid-air or liquid-air interface (ℎ^), the following steps are followed: 1. The mass or masses of solid or liquid to be sampled are incorporated into the respective open receivers. 2. The different components of the air circulating device (propelling medium, temperature regulating medium, etc.) are configured to generate the desired conditions inside the chamber. 3. ^^ is measured at time t1. 4. ^^ is measured at time t2. 5. ^^̇ is found using equation X: ^ − ^ ^ ^^ ^ ̇ = ^^ − ^^ (X)6. ℎ^ is found by equation XIV: which is derived from equation XII by solving for ℎ^. Several advantageous aspects of the present invention are set out below: - Thanks to the apparatus of the present invention, values ​​of mass variation with time can be easily and accurately obtained, and from this, values ​​of the convection mass transfer coefficient (ℎ^) and of the gas diffusivity (^^). Obtaining ℎ ^ and ^ ^ It allows to determine the drying speed for any condition of temperature and relative humidity of the drying air. Currently there are models to predict the coefficient of mass transfer by convection (ℎ ^ ), based on the calculation of the Sherwood number, which depends on the Schmidt (^^) and Reynolds (^^) numbers. However, all of them require knowledge of the gas diffusivity (^ ^ ) to calculate the convective mass transfer coefficient (ℎ ^), for which there are no theoretical models but only empirical ones. The apparatus of the present invention allows to verify whether the theoretical mass transfer models for calculating ℎ are fulfilled ^ , and empirical models to calculate ^ ^, which may vary in the process. - The apparatus of the present invention is versatile: The chamber of the apparatus can simultaneously house semi-open receivers for measuring gas diffusivity (^^) and open receivers for measuring the convection mass transfer coefficient (ℎ^), such that both parameters can be evaluated simultaneously. The chamber of the apparatus can also simultaneously include a variety of sizes and shapes of drying receivers for the same measurement test, which may also have different heights. In addition, there may be one or more drying receivers containing a different mass quantity of sample than other drying receiver(s). The apparatus also allows simultaneous tests to be carried out with different types of solids and / or liquids, for example, with one type of sample in each drying receiver.That is, the type of material in some samples may be different from that in others, and so may the particle size of the samples. The device also allows simultaneous testing with different types of gases and / or liquids adsorbed by the solids or liquids in the samples, for example, a different type in each desiccation receiver. The concentration of adsorbed gas and / or liquid may also be different. The arrangement of several desiccation receivers distributed within the chamber means that different temperatures are reached in them, since those closest to the air source are more exposed to the influence of air temperature than those further away. This means that measurements can be made at different temperatures with the same positional configuration of the desiccation receivers.This is very advantageous, since both the gas diffusivity (^^) and the convection mass transfer coefficient (ℎ^) depend on the temperature. In this way, the apparatus of the present invention allows to determine ^^ and ℎ^ at different temperatures simultaneously, parameters that are involved in the theoretical models of mass transfer. The apparatus of the invention can apply air flows in laminar regime or in turbulent regime, for example, because the air circulating device is designed for this purpose. In the case of semi-open receiver / s, it is convenient to have an air flow in laminar regime, transverse to its upper opening, in order to achieve a measurement in a uniform regime, but measurements can also be made having an air flow in turbulent regime. The versatility of the present invention contrasts with the lack of versatility of other apparatus of the prior art.Such prior art devices require specific adjustments for each type of measurement, which limits their versatility. Unlike them, and based on the above, the present invention allows simultaneous measurements of ^. ^ and ℎ ^under a single apparatus, reducing complexity and increasing precision, allowing it to be adapted to a wide variety of real-time applications. Examples of applications of the apparatus of the invention include, but are not limited to, obtaining water diffusivity in the drying of different types of biomass, such as wood, straw, food, leaves, or even in soil, as well as the volatilization of hydrocarbons or other substances in contaminated soil. The apparatus of the invention can also be applied to obtaining water diffusivity in the drying of hides, ceramics, and stone materials. In this document, the word "comprises" and its variants are to be interpreted as open-ended expressions that are not intended to exclude the possibility of other technical characteristics or components additional to those explicitly mentioned.Furthermore, the word "comprises" includes the case "consists of", being interpreted as a closed-type expression that is limited solely to the technical characteristics or components explicitly mentioned. For those skilled in the art, other objects, advantages and characteristics of the invention will be derived partly from the description and partly from the practice of the invention. In addition, the present invention covers all possible combinations of embodiments indicated herein. DESCRIPTION OF THE DRAWINGS To complement the description being made and in order to aid in a better understanding of the characteristics of the invention, a set of figures is attached to this specification, as an integral part thereof, in which the following is represented for illustrative and non-limiting purposes: Figure 1 schematically shows a perspective view of an example of the mass transfer measuring apparatus object of the invention.Specifically, a device is shown with a chamber that houses several semi-open, tube-shaped drying receivers inside, for measuring gas diffusivity at the solid-air or liquid-air interface; and an open drying receiver, for measuring the convection mass transfer coefficient, more specifically, a bare receiver made up of an area at the base of the chamber configured to receive a sample without a container. Figure 2-A shows an enlarged view of one of the tubes in Figure 1. Figure 2-B schematically shows a section of the tube shown in Figure 2-A, which includes a solid mass sample inside, and the profile that defines the gas concentration gradient generated from the surface of said mass to the upper opening of the tube is represented. Figures 3-A and 3-B schematically show respective elevation views of an example of a semi-open tube-shaped receiver (Fig.3-A), and an example of an open, tray-shaped receiver (Fig. 3-B). A sample mass incorporated into each receiver is represented. A laminar flow of air over each receiver is represented by arrows. Figure 4 schematically shows a perspective view of another example of the mass transfer measuring apparatus object of the invention. In this example, all the drying receivers are semi-open, tube-shaped receivers. Arrows are included that represent changes in direction of the air flow as it passes through the apparatus. Figure 5 schematically shows a perspective view of another example of the apparatus of the invention, in this case an example with an arrangement of the temperature regulating means and diffusers to achieve a permanently horizontal flow of air. This example includes several semi-open, cylindrical tube-shaped receivers, and several open, tray-shaped receivers.Figures 6-A and 6-B show schematic plan views of two possible preferred options for distributing the drying receptors within the chamber of the apparatus; specifically, with a distribution in the form of in-line rows (Figure 6-A) and with a distribution in the form of staggered rows (Figure 6-B). Figures 7-A and 7-B are included to explanatory support for the concept of “characteristic length” (^^). Figure 7-A shows a perspective view of an air flow (represented by arrows) circulating perpendicularly to a cylindrical surface. Figure 7-B shows several plan views of several examples, in which the air flow circulates perpendicularly to several pieces with different cross sections, respectively, and in which the characteristic length (^) is indicated. ^) corresponding. PREFERRED EMBODIMENT OF THE INVENTION In view of the aforementioned figures, and in accordance with the adopted numbering, there can be seen in them two non-limiting embodiment examples of the mass transfer measuring apparatus of the invention, which comprises what is indicated and described in detail below. Thus, looking at figures 1, 4 and 5, the apparatus of the invention comprises the following components: - A thermally insulated chamber (2). - An air circulating device (18) coupled to the chamber (2), to circulate air through the interior of the chamber (2) in a regulated manner, in terms of speed, temperature and humidity. - Sensors (3, 4, 5) to verify the speed, temperature and humidity of the air. - One or more drying receivers inside the chamber (2), in which the respective samples (m) to be studied are deposited. - A load sensor (6) in each drying receiver.The drying receiver or receivers may be of the semi-open type (7), of the open type (8, 8'), or there may be a combination of receivers of both types, as explained in more detail below: - Figure 4 shows a configuration with several drying receivers, all of them semi-open receivers (7). A semi-open receiver is understood to be a drying receiver shaped so that the air flow does not directly affect the sample (m) incorporated in the receiver. The semi-open receivers are used to measure the gas diffusivity at the solid-air or liquid-air interface (^^) of the respective samples (m) incorporated therein, following Fick's law. - According to another configuration not shown in the figures, the drying receiver or receivers of the chamber (2) are all open receivers (8, 8').An open receiver is understood to be a drying receiver shaped such that the air flow directly affects a sample (m) incorporated in the receiver. Open receivers are used to measure the convection mass transfer coefficient at the solid-air or liquid-air interface (ℎ^) of the respective samples (m) incorporated therein. Figures 1 and 5 show a configuration with a combination of one or more semi-open receivers (7) and one or more open receivers (8, 8'). This configuration is used to measure the gas diffusivity at the solid-air or liquid-air interface (^^) and the convection mass transfer coefficient at the solid-air or liquid-air interface (ℎ^) of the respective samples (m), both parameters being able to be measured simultaneously. Preferably, the semi-open receiver or receivers (7) have their lower part closed (70), and their upper part open forming an upper opening (71).More preferably, the semi-open receiver or receivers are tube-shaped containers (7), which are arranged vertically with their lower part closed (70) over the respective load sensor (6), and which are open at their top, forming the upper opening (71). An enlarged view of a tube-shaped container (7) can be seen in Figure 2-A, according to the indicated characteristics. The tube (7) can be, for example, a cylindrical tube (as shown in Figure 2-A) or prismatic. Preferably, the tube (7) has a constant cross section to avoid variations in the air flow lines.Furthermore, the tube (7) may have different possible configurations in terms of its height, respecting the following condition: The tube (7) has a height such that there is a space between its upper opening (71) and a ceiling of the chamber (2) suitable for the air to flow without its speed being significantly altered (in this way, the complete development of the air flow regime is allowed). Preferably, said space is at least 10 cm. Preferably, the open receiver or receivers are: - One or more containers in the form of a tray (8), plate or similar, which are located on the respective load sensors (6); and / or - One or more bare receivers (8'). A bare receiver is understood to be a drying receiver made up of an area inside the chamber (2) (for example, at the base of the chamber) that receives the respective sample (m) without a container. A load sensor (6) is arranged in each bare receiver (8').Figure 1 shows a configuration with several cylindrical tubes (7) and a bare receiver (8'). Figure 4 shows a configuration with several semi-open receivers, all of them cylindrical tubes (7). Figure 5 shows a configuration with several cylindrical tubes (7) and several trays (8). As indicated, a semi-open receiver (7) is used to measure the gas diffusivity at the solid-air or liquid-air interface (^^) of a sample (m) incorporated in the receiver. This is because the semi-open receiver (7) prevents contact of the air flow circulating through the chamber (2) with the solid or liquid mass of the sample (m). In this way, the movement of the suspended particles inside the semi-open receiver (7) only occurs by diffusion.The existence of air flow transverse to the upper opening (71) of the semi-open receiver (7) guarantees a constant gradient inside the receiver, from the surface of the solid or liquid mass of the sample (m), where the air is considered saturated, to the upper opening (71) of the semi-open receiver (7), where the particle concentration is considered unsaturated. This allows the application of Fick's law for the calculation of gas diffusivity at the solid-air or liquid-air interface (^^). Figure 3-A shows the arrangement of an air flow and the particles of a sample (m) incorporated in a tube (7). The sample (m) occupies a space of a lower height than the tube (7), so it is protected from the direct action of the air flow circulating above the upper opening (71) of the tube (7).The laminar flow of air above the upper opening (71) of the tube (7) ensures that the concentration gradient of particles (p) other than air (water or any other gas), represented in figure 2-B, remains linear in the height of the tube (7), from the surface of the solid or liquid mass of the sample (m) to the upper opening (71). As indicated above, an open receiver (8, 8') is used to measure the mass transfer coefficient by convection at the solid-air or liquid-air interface (ℎ^). This is because, in an open receiver (8, 8'), the solid or liquid mass of the sample (m) is in direct contact with the air flow circulating through the chamber (2), and, consequently, the movement of the particles that come off the sample (m) is mainly carried out by convection. Figure 3-B shows the arrangement of an air flow and the particles of a sample (m) incorporated in a tray (8).In this case, the sample (m) occupies a space of equal height to the tray (8), so that the upper surface of the sample (m) is directly exposed to the direct action of the air flow circulating above the tray (8). The chamber (2) may simultaneously include semi-open receivers (for example, tubes (7)) of different sizes, shapes and heights, allowing measurements to be made with one or different types of samples (m). Additionally or alternatively, the chamber (2) may simultaneously include open receivers (for example, trays (8)) of different sizes, shapes and heights, allowing measurements to be made with one or different types of samples (m). The arrangement of the drying receivers may have different possible distributions.According to one embodiment, the drying receivers (e.g. tubes (7) according to the examples shown in Figures 6-A and 6-B) have a homogeneously distributed arrangement, for example, in the form of straight rows (Fig. 6-A) or in the form of staggered rows (Fig. 6-B). According to another embodiment, the drying receivers are distributed without any regularity in their arrangement. As shown in Figures 1 and 4, according to a preferred embodiment, the air circulating device (18) comprises the following components: - A driving means (9), responsible for driving the air into the chamber (2). The driving means (9) comprises a fan. - A humidity regulating means (10), responsible for regulating the humidity of the air driven by the driving means (9) before it is introduced into the chamber (2).The humidity regulating means (10) comprises a humidifier, responsible for increasing the humidity of the air; and / or a dehumidifier, responsible for decreasing the humidity of the air. Preferably, the humidifier comprises a porous bed of fiber or mesh through which a current of water is circulated, increasing the humidity of the air. Preferably, the dehumidifier is formed by a cold exchanger with a temperature lower than the dew point, which decreases the humidity of the air by condensation. Preferably, this cold exchanger is installed together with the humidifier after the driving means (9) and before a temperature regulating means (11) described below. - A temperature regulating means (11), which regulates the temperature of the air driven by the driving means (9), preferably after it has passed through the humidity regulating means (10). The temperature regulating means (11) comprises a resistance and / or a heat exchanger.The resistance may be of variable power, for example, by means of a potentiometer. The heat exchanger may be a cold exchanger or a hot exchanger. According to a preferred embodiment shown in Figure 5: - the driving means (9) comprises several fans; - the temperature regulating means (11) comprises several resistances and / or heat exchangers (cold and / or hot); - the humidity regulating means (10) comprises several humidifiers and / or dehumidifiers; - at least one component of the temperature regulating means (11) and one component of the humidity regulating means (10) are arranged together. For example, several resistances and several humidifiers are installed together. Preferably, the air circulating device (18) comprises an inlet duct (14), which is responsible for conducting the air driven by the driving means (9) towards the interior of the chamber (2).The inlet duct (14) may have a variable cross section which, for example, increases progressively in the direction of passage of the air towards the chamber (2), as can be seen in the examples of Figures 1 and 4. Alternatively, the inlet duct (14) may have a constant cross section, as shown in the example of Figure 5. According to a preferred embodiment shown in Figures 1 and 4, the temperature regulating means (11) is installed in the inlet duct (14). As sensors for verifying the speed, temperature and humidity of the air circulating through the chamber (2), one or more anemometers (5), one or more dry bulb air temperature sensors (3), and one or more relative air humidity sensors (4) are preferably incorporated inside the latter.Preferably, the apparatus further comprises one or more diffusers (12) which contribute to the formation of a laminar flow of air in the chamber (2) and the formation of a constant temperature profile along the height and width of the chamber (2). As can be seen in the embodiment of Figure 3-A, said air flow is transverse to the upper opening (71) of the tube (7). Preferably, the diffuser or diffusers (12) comprise a porous bed formed, for example, by fiber or mesh. More preferably, the porous bed of each diffuser (12) is formed as a porous barrier perpendicular to the direction of the air, such that an increase in pressure is generated prior to passing through the holes that give access to the chamber (2), such that the uniform pressure of the air prior to the holes causes the flow to be distributed equally throughout the section.As shown in Figures 1, 4 and 5, according to a preferred embodiment, at least one diffuser (12) is arranged at the entrance to the chamber (2), preferably after the temperature regulating means (11). According to an exemplary embodiment, at least one diffuser (12) arranged at the entrance to the chamber (2) comprises a pre-chamber that acts as a means of homogenizing the temperature and humidity of the air flow. In this case, the air driven by the driving means (9) is introduced into the pre-chamber of the diffuser (12), where it is homogenized in temperature and humidity due to the movement of the air itself. The air circulates towards the porous bed of the diffuser (12). The porous bed represents a barrier that decreases the speed of the air. In this way, an overpressure is produced in the pre-chamber that causes the air to circulate through the porous bed to the chamber (2), achieving a laminar diffusion of the air. This causes the air to circulate uniformly throughout the cross section of the chamber (2).According to one embodiment, the porous bed is defined as a sheet with abundant perforations in the form of small holes. According to another alternative embodiment, the porous bed has a greater thickness, which contributes to the possibility of not including a prechamber for air homogenization. According to the embodiment shown in Figure 1, a diffuser (12) is arranged at the entrance to the chamber (2), formed by a thick porous bed, and does not include a prechamber. According to the embodiments shown in Figures 4 and 5, each of the diffusers (12) arranged at the entrance to the chamber (one diffuser in the case of Figure 4, and two diffusers in the case of Figure 5) comprise a porous bed in the form of a sheet after a prechamber. In the case of Figure 5, the duct (14) itself acts as a prechamber for the first of the diffusers (12).Preferably, especially when the temperature regulating means (11) is incorporated in an inlet duct (14) of small section, the air driven by the driving means (9) does not enter the chamber (2) directly, but is made to pass through a sector that modifies the direction of the air, as shown in the arrow diagram (F) of Figure 4 and, subsequently, the air is made to pass through the porous bed of the diffuser (12) arranged at the inlet of the chamber (2). According to the embodiment of Figure 4, this sector that modifies the direction of the air forms the prechamber defined above.In another embodiment, as shown in Figure 5, a permanently horizontal flow of air (2) is achieved by adjusting the size of the cross section of the inlet duct (14) to the size of the cross section of the chamber (2), and placing diffusers (12) to achieve the uniformization of the air parameters indicated above (speed, temperature and humidity). As shown in Figures 1, 4 and 5, according to a preferred embodiment, the device has one of the air diffusers (12) arranged at the outlet of the air circulation of the chamber (2) in order to hinder the passage of said air and generate an overpressure in the chamber (2) that improves the uniformization of temperatures in its cross sections.Alternatively or additionally, the apparatus also comprises a turbine (not shown in the figures) to achieve a turbulent air flow, although this effect can also be achieved by increasing the air speed, modifying the circulation section, and / or adding baffles in the air inlet section. For its part, to regulate the air speed, preferably, the impeller (9) has a frequency converter, which allows its working power to be regulated in order to vary its speed. The aforementioned diffusers (12) allow the air to be stopped and homogenized in the cross section of the chamber (2). One way to achieve a turbulent air flow is by increasing the speed of the impeller (9) and removing the diffusers (12).Preferably, the semi-open receiver or receivers (7) and the open receiver or receivers formed by containers (for example, tray-shaped (8)) are removable, to facilitate the placement of the samples (m). Preferably, the chamber (2) comprises at least one door (13) at the top or at a side, which, when opened, gives access to the interior of the chamber (2). This allows the introduction, manipulation and / or replacement of one or more components of the interior of the chamber (2); for example: it allows the introduction of drying receivers, it allows samples (m) to be incorporated into the respective drying receivers, it allows sensors (3, 4, 5, 6) to be manipulated or replaced if necessary; etc.Having sufficiently described the nature of the present invention, as well as the manner of putting it into practice, it is not considered necessary to explain it further so that any expert in the field may understand its scope and the advantages derived from it, stating that, within its essence, it may be put into practice in other embodiments that differ in detail from the one indicated as an example, and to which it will also achieve the protection sought provided that its fundamental principle is not altered, changed or modified.

Claims

CLAIMS 1. Aparato medidor de transferencia de masa caracterizado por que comprende una cámara (2) thermally insulated, to which an air circulating device (18) is coupled that makes c ircular un flujo de aire por la cámara (2) de manera regulable en cuanto a velocidad, temperatura y humedad, siendo dichos parámetros verificables por diversos sensores (3, 4, 5), con la particularidad de que la cámara (2) comprende, en su interior, uno o varios receptores de desecación, y un sensor de carga (6) en cada receptor de desecación, siendo el receptor o receptores de desecación: - uno o varios receptores semiabiertos (7), que sirven para medir la difusividad de gas en la interfase sólido-aire o líquido-aire de respectivas muestras (m) incorporadas en ellos de modo que el flujo de aire no incide directamente sobre dichas muestras (m); o - uno o varios receptores abiertos (8, 8’), que sirven para medir el coeficiente de transferencia de masa por convección en la interfase sólido-aire o líquido-aire de respectivas muestras (m) incorporadas en ellos de modo que el flujo de aire incide directamente sobre dichas muestras (m); o - una combinación de uno o varios de dichos receptores semiabiertos (7), y uno o varios de said open receivers (8, 8').

2. Aparato según la reivindicación 1, caracterizado por que el receptor o receptores semiabiertos (7) have a constant cross section.

3. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que el receptor o receptores semiabiertos (7) son uno o varios recipientes con forma de tubo, que van dispuestos verticalmente con su parte inferior cerrada (70), y su parte superior abierta forming an upper opening (71).

4. Aparato según la reivindicación 3, caracterizado por que el recipiente o recipientes con forma de tubo tienen una altura tal que existe un espacio entre la abertura superior (71) y un techo of the chamber (2) suitable for the air to flow without its speed being altered.

5. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que el receptor or open receivers are: - uno o varios receptores conformados, cada uno, por un recipiente; y / o - uno o varios receptores desnudos (8’) conformados, cada uno, por una zona en el interior de la cámara (2) que recibe la respectiva muestra (m) sin recipiente.

6. Aparato según la reivindicación 5, caracterizado por que el receptor o receptores abiertos conformados por un recipiente o recipientes tienen forma de bandeja (8), plato o similar.

7. Aparato según cualquiera de las reivindicaciones 3 a 6, caracterizado por que uno o más containers are removable.

8. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que la cámara (2) simultaneously includes: - receptores abiertos (8, 8’) de diferentes tamaños, formas y / o alturas; y / o - receptores semiabiertos (7) de diferentes tamaños, formas y / o alturas; para efectuar mediciones de uno o diferentes tipos de muestras (m).

9. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que los receptores de desecación están distribuidos en forma de hileras en línea, o en forma de hileras staggered.

10. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que el dispositivo circulador de aire (18) comprende: - un medio impulsor (9), encargado de impulsar el aire hacia el interior de la cámara (2); - un medio regulador de temperatura (11), encargado de regular la temperatura del aire impulsado por el medio impulsor (9) antes de que se introduzca en el interior de la cámara (2); and - un medio regulador de humedad (10), encargado de regular la humedad del aire impulsado por el medio impulsor (9) antes de que se introduzca en el interior de la cámara (2).

11. Aparato según la reivindicación 10, caracterizado por que el medio impulsor (9) comprendeone or more fans.

12. Aparato según cualquiera de las reivindicaciones 10 u 11, caracterizado por que el air circulating device (18) comprises an inlet duct (14) responsible for c onducir el aire impulsado por el medio impulsor (9) hacia el interior de la cámara (2).

13. Aparato según la reivindicación 12, caracterizado por que el conducto de entrada (14) It has a constant cross section, or one that progressively increases in the direction of air flow towards the chamber (2), or one that progressively decreases in the direction of air flow towards the chamber (2) 14. Aparato según cualquiera de las reivindicaciones 12 o 13, caracterizado por que el medio temperature regulator (11) comprises: - una o varias resistencias que calientan el aire impulsado por el medio impulsor (9); y / o - uno o varios intercambiadores de calor que calientan o enfrían el aire impulsado por el driving means (9); the temperature regulating means (11) being installed in the inlet duct (14).

15. Aparato según cualquiera de las reivindicaciones 10 a 14, caracterizado por que el medio regulador de humedad (10) se dispone entre el medio impulsor (9) y el medio regulador de temperatura (11).

16. Aparato según cualquiera de las reivindicaciones 10 a 15, caracterizado por que el medio regulador de humedad (10) comprende: - uno o varios humectadores, encargados de aumentar la humedad el aire; y / o - uno o varios deshumidificadores, encargados de disminuir la humedad del aire.

17. Aparato según la reivindicación 16, caracterizado por que el humectador o humectadores comprenden un lecho poroso de fibra o malla por el cual se hace circular una corriente de water that increases the humidity of the air driven by the driving medium (9).

18. Aparato según cualquiera de las reivindicaciones 16 o 17, caracterizado por que el deshumidificador o deshumidificadores se conforman por un intercambiador frío, con lower temperature than dew point, which reduces air humidity by condensation.

19. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que los sensores para verificar la velocidad, temperatura y humedad del aire que circula por la cámara (2), son: uno o varios anemómetros (5), uno o varios sensores de temperatura (3) del aire en bulbo seco, y uno o varios sensores de humedad (4) relativa del aire, respectively, these sensors being located inside the chamber (2).

20. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que comprende uno o varios difusores (12) que contribuyen con la conformación de un flujo laminar de aire en la cámara (2), y la conformación de un perfil de temperatura constante a along the height and width of the chamber (2).

21. Aparato según la reivindicación 20, caracterizado por que el difusor o difusores (12) comprenden un lecho poroso formado por fibra o malla.

22. Aparato según cualquiera de las reivindicaciones 20 o 21, caracterizado por que, al menos One of the diffuser or diffusers (12) is arranged at the entrance to the chamber (2).

23. Aparato según la reivindicación 22, caracterizado por que, al menos uno del difusor o diffusers (12) arranged at the entrance of the chamber (2) comprise a pre-chamber, which acts as a means of homogenizing the air flow.

24. Aparato según la reivindicación 23, caracterizado por que comprende un medio generador of turbulence, which contributes to the formation of a turbulent flow of air in the prechamber (2).

25. Aparato según la reivindicación 24, caracterizado por que el medio generador de turbulencia includes: - uno o varios agitadores, conformados por una turbina cuya acción interfiere en el flujo de air in a direction different from the circulation of said flow; and / or - uno o varios bafles que obligan a cambiar la dirección de flujo.

26. Aparato según cualquiera de las reivindicaciones 20 a 25, caracterizado por que al menos One of the diffuser or diffusers (12) is arranged at the exit of the chamber (2).

27. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que el air circulating device (18) drives the air through a sector that modifies the direction of the air before entering the chamber (2).

28. Aparato según cualquiera de las reivindicaciones anteriores, caracterizado por que la cámara (2) comprende una compuerta (13), que, cuando se abre, da acceso al interior de la cámara (2).

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