Methods for determining the crystallization temperature and the volume of a sample of an aqueous salt solution

Abstract

The invention relates to the field of temperature measurement and heat measurement and can be used in the operation of ice detectors. A method for determining the crystallization temperature of a sample of an aqueous salt solution with the aid of a thermoelectric ice detector containing a thermoelectric module, a temperature sensor and a thermoelectric heat flux sensor includes raising the temperature of the sample to a value known to be above the crystallization temperature of the sample, cooling the sample to a temperature below the crystallization temperature, recording a maximum temperature corresponding to a sudden change in the temperature value of the sample accompanied by a sudden change in the heat flux value, and determining the crystallization temperature of the sample using a calibration coefficient. A method for determining the mass (volume) of a sample of an aqueous salt solution includes determining the crystallization temperature of the sample, determining the mass of the crystallized water fraction of the sample, and determining the mass of the sample itself. The technical result is an improvement in the accuracy of measurements of the crystallization temperature and mass (volume) of a sample of an aqueous salt solution that are carried out with unlimited frequency.

Description

[0001] METHODS FOR DETERMINING THE CRYSTALLIZATION TEMPERATURE AND SAMPLE VOLUME OF WATER-SALT SOLUTIONS

[0002] Field of technology

[0003] The proposed invention relates to the field of temperature measurement and heat metering and can be used in the operation of icing sensors for remote detection of icing and determination of environmental conditions similar to conditions for the formation or predisposition to the formation of icing of various surfaces, for example, road surfaces, runways, especially in conditions of using anti-icing agents based on water-salt solutions.

[0004] State of the art

[0005] At present, thermoelectric icing sensors are used to detect icing and determine the conditions for its probable occurrence. Their operation is based on recording the moment of the water-ice and ice-water phase transition. In this case, quantitative characteristics can be determined or estimated - icing temperature and icing intensity (amount of ice). In the road industry, water-salt anti-icing compounds are used. For their effective and economical use, it is necessary to control the temperature and amount of liquid fraction on the road surface.

[0006] What is common is that such icing sensors use a Peltier element (thermoelectric module), which is used to cyclically cool and heat the test sample in a temperature range close to the crystallization temperature.

[0007] The fixation of the phase transition of crystallization or melting of aqueous solutions is based on the physical law of this phenomenon as a first-order phase transition. In this case, a significant amount of heat is released, and the temperature during the phase transition period remains constant - this is, in fact, the phase transition temperature.

[0008] In the publication DIKatz, Frensor: A New Smart Pavement Sensor, Transportation Research Record #1387, pp. 147-150, 1993, ISBN 0309054583 an icing sensor is disclosed, which consists of a Peltier element and a temperature sensor located under the cooled surface of the Peltier element. When cooling a water sample, according to a known physical pattern, a noticeable supercooling of the liquid (water or water-salt solutions) first takes place and only after this does a spontaneous phase transition of crystallization of the water or water-salt solution occur with the release of a significant amount of heat and an increase in the temperature in the sample to a temperature that is interpreted as the phase transition temperature. The method of determination using such a sensor consists in sequentially recording first a sharp change in temperature after supercooling (the first point) and then the maximum temperature (the second point), which is identified as the crystallization temperature.

[0009] However, this method and the device implementing it have disadvantages, primarily the lack of an algorithm for direct quantitative determination of the intensity of crystallization, except for indirect determination by the duration of the crystallization phase.

[0010] A thermoelectric icing sensor is known from RU2534493 (IPC B64D15 / 20, published 27.11.2014), which contains a thermoelectric module made in the form of a Peltier element that functions as a heat pump, and a temperature sensor installed on the external sensitive surface. The Peltier element heats or cools the sensitive surface according to a specified algorithm depending on the ambient temperature and its proximity to the freezing temperature. The temperature sensor monitors the change in temperature. If conditions for ice formation are present on the surface, the temperature of the sensitive surface is stabilized during the water-ice phase transition, and the latent heat of ice formation is released.A known thermoelectric sensor records the specified phase transition temperature, thereby determining the presence of ice formation, and the intensity of ice formation is estimated by the value of the power supply of the heat pump (Peltier element) during this period, since this correlates directly with the released or absorbed heat of the phase transition.

[0011] In this sensor, the temperature determination algorithm is similar to the previous example - based on the phase transition temperature stabilizing for a time. The ice formation intensity assessment is approximate. The disadvantage of this is the inaccurate determination, since this is an indirect assessment based on the energy consumption of the Peltier element. Energy consumption significantly depends on the operating conditions (ambient temperature, heat exchange with the environment) and the operability of the Peltier element itself. The closest analogue of the present invention is the method for determining the phase transition temperature and the volume of a liquid sample using a thermoelectric icing sensor according to RU2779247 (B64D15 / 20, 05.09.2022). The known method is implemented using a thermoelectric icing sensor.The thermoelectric module built into such a sensor, made in the form of a Peltier element, provides a cyclic heating-cooling mode of the sensitive external sensitive surface of the cuvette with a sample of water or water-salt solution. The icing sensor can also contain a built-in heat flow sensor for measuring the intensity of icing - the amount of liquid in the sample.

[0012] In the cooling phase provided by the Peltier element, if there is a liquid sample (water or solution) in the cuvette, the fact of crystallization is recorded by a sharp measurement of the temperature measured by the temperature sensor and a sharp jump in the signal of the heat flow measured by the sensor. In this case, the phase transition temperature is determined at the maximum of the temperature jump of this cooling phase. The crystallization temperature is also determined in the heating phase by a characteristic break in the temperature-time curve. The sample volume is determined by the integral of the heat released in the cooling phase after the recorded onset of crystallization until the recorded heat release returns to the value preceding the onset of crystallization. The measured amount of heat is converted into the sample volume by the known value of the latent heat of crystallization of water.

[0013] The known method is well applicable for determining the crystallization temperature and sample volume only in the case of pure water. As applied to water-salt solutions, this method and all analogs in general have significant drawbacks associated with the fact that they do not take into account the physical characteristics of water-salt solutions, due to which the use of such methods leads to significant deviations of the measured values ​​from the true ones.

[0014] Phase transformation in water-salt solutions should be considered in the context of a two-component phase diagram of a water-salt solution, in contrast to pure water. Most practically significant water-salt solutions of salts, such as NaCl, CaCl2, etc., are characterized by a eutectic phase diagram, which has a eutectic composition of the solution with a minimum crystallization temperature. The liquidus line leads to this point. Due to this, the initially supercooled water-salt two-component solution begins spontaneous crystallization with the release of heat due to the crystallization of water with simultaneous saturation of the remaining solution with salt and an increase in temperature (Fig. 1a). Crystallization with an increase in temperature is the first phase, which occurs with a simultaneous shift in the concentration of the solution towards saturation with salt.The temperature cannot exceed the temperature value lying on the liquidus line at the point corresponding to the maximum increase in the sample temperature, due to the released heat of crystallization. Then the phase transition (crystallization of water from the solution) will continue, but with a decrease in temperature (this is the second phase of crystallization). Then the water fraction of the solution will also crystallize into ice, and the concentration of the salt of the remaining solution will further increase in accordance with the course of the liquidus line of the phase diagram.

[0015] Therefore, the maximum Td recorded by the temperature sensor on the temperature-time cooling curve (Fig. 16), taken in the known method and other mentioned methods as the desired crystallization temperature, is not the true crystallization temperature Tf (hereinafter also simply the crystallization temperature Tf) of the original sample. This is the temperature maximum Td, characterizing the shift along the liquidus line of the phase diagram of the water-salt solution (Fig. 1a). In practice, this shift turned out to be significant: as numerous experiments by the authors of the present invention have shown, the measured temperature Td and the true crystallization temperature Tf differ by approximately 1.5 times, and in general for the above-mentioned water-salt solutions this value fits into a fairly narrow range of approximately 1.3 to 1.7, preferably from 1.4 to 1.6, more preferably it is approximately 1.5.

[0016] The second disadvantage of the closest analogue is that the measured heat value is interpreted as the heat of crystallization of the entire sample and the mass ω is calculated based on it, interpreted as the total mass (or total volume) of the entire sample. However, for a water-salt solution, during crystallization until the temperature of the eutectic solution is reached, the sample will consist of two phases - crystallized ice and enriched salt solution, i.e. not the entire sample will be crystallized. The value ω measured by known methods cannot be interpreted as the total mass M (total volume V) of the sample. The discrepancy is also significant - several times for water-salt solutions, depending on the initial concentration. Disclosure of the invention

[0017] The objective of the invention is to create a reliable method of operating a thermoelectric icing sensor in order to obtain accurate, reliable quantitative characteristics of ice formation in water and water-salt solutions in a wide range of concentrations - crystallization temperature and mass (volume) of the sample.

[0018] The technical result of the proposed invention, which is objectively manifested during its implementation, is an increase in the accuracy of measurements carried out with unlimited frequency.

[0019] The stated problem is solved, and the technical result is achieved due to the following:

[0020] - the Peltier element of the thermoelectric icing sensor ensures a cycle of heating and cooling of the solution sample;

[0021] - first comes the heating phase to a temperature significantly higher than the crystallization temperature and is, for example, +15°C. This allows the sample to melt if it was originally ice;

[0022] - then the sample is cooled at a constant rate in order to achieve the maximum possible temperature, which is obviously significantly lower than the crystallization temperature;

[0023] - the fact of the onset of crystallization is recorded by an icing sensor containing a built-in heat flow sensor, based on a sharp change in temperature from the local minimum - the supercooling temperature Tc and a sharp jump in the heat flow sensor signal;

[0024] - the temperature Td of the maximum jump of the specified signal on the time temperature curve is used for the subsequent determination of the phase transition temperature of the initial solution, namely, the crystallization temperature Tf;

[0025] - the true crystallization temperature Tf is determined by applying a correction factor K to the measured value of the temperature Td, in particular in the range from 1.3 to 1.7, preferably from 1.4 to 1.6, more preferably is approximately 1.5.

[0026] The stated problem is solved, and the technical result is also achieved due to the following:

[0027] - the intensity of ice formation (amount of ice, water) is determined by the above-mentioned measurement result of the heat flow sensor. The measured integral of the released heat of crystallization Q is used to determine the crystallized part of the sample ш by the known specific heat of crystallization of water;

[0028] - based on the value of ш, measured by the temperature Tfin on the liquidus line of the end of the measurement and the true temperature Tf of crystallization, the concentration values ​​of the water-salt solution are calculated at points Xfin and Xf on the liquidus line of the phase diagram, respectively. From here, the total mass M (total volume V) of the sample is calculated using a simple proportion between M and gi, Xfin and Xf, following from the phase diagram of the water-salt solution.

[0029] It should be noted that for the icing sensor, the specified definition of the intensity of ice formation (amount of ice, water) corresponds to, or is equivalent to, the definition of the mass or volume of a water-salt solution.

[0030] Brief description of the drawings

[0031] Fig. 1a shows the phase diagram of a water-salt solution using NaCl as an example and a typical change in temperature (T) and concentration (X) over time during crystallization with supercooling. The following are marked: TfO is the point of the true, sought-after crystallization temperature of the solution of initial concentration XfO; Tc is the supercooling point; Td and Xd are the point on the liquidus line to which the temperature recorded by the temperature sensor will rise; Tfin and Xfin are the final point on the liquidus line, corresponding to the temperature at the end of the measurement cycle.

[0032] Fig. 16 shows a typical time course of temperature with cooling with a crystallization event measured by an icing sensor, and shows points TO - the temperature of the beginning of cooling; Td, Tfin - the temperatures given in the phase diagram in Fig. 1a.

[0033] Fig. 2 shows an example of the method implementation at an initial ambient temperature Ta equal to 0°C. The concentration of the NaCl salt XO in the sample and the sample crystallization temperature TfO are 7.88% and -5°C, respectively. The sample volume is 30 μl. The change in temperature Ti and the heat flux qi measured with a time step i are shown. The characteristic moments are marked: i = 0 - the beginning of the experiment from the ambient temperature T = Ta; i = nl - stabilization of the initial temperature Tn0 = T0, the beginning of the cooling phase; i = n2 - the ultimate supercooling of the water sample to Tnl = Tc; i = n3 - the point of local maximum temperature Tn2 = Td; i = n3 - the end of the crystallization measurement Tn3 = Tfin. Implementation of the invention

[0034] The proposed methods for measuring ice formation characteristics - crystallization temperature and mass (volume) of the sample - are implemented using a thermoelectric icing sensor as follows (Fig. 1a, b).

[0035] At the beginning of the measurement cycle, the temperature of the sample is adjusted by means of a Peltier element from the initial ambient temperature Ta to a fixed value TO, for example, +15°C, and stabilized for a short holding time. This temperature is significantly higher than the crystallization temperature of the water-salt solution, which is usually below 0°C. The holding time allows the sample to melt if it was initially in the form of ice, for example, at low ambient temperatures. A specialist will understand how to select the required holding time depending on the initial conditions and the type of water-salt solution.

[0036] The sample is then cooled at a constant rate toward the lower temperature limit provided by the Peltier element, which is obviously significantly lower than the crystallization temperature. If there is no sample in the cuvette, this temperature will be reached without phase transition events, and then the measurement ends.

[0037] If there is a sample in the cuvette, the fact of the beginning of crystallization is recorded by two measuring signals - a sharp change in temperature from the supercooled state Tc, measured by the temperature sensor, and a sharp jump in the signal measured by the heat flow sensor from the released heat of crystallization. In this case, the temperature after the beginning of crystallization, which is determined at the point of maximum Td of the said signal jump, is then used to calculate the crystallization temperature Tf of the initial solution.

[0038] To convert the measured value of temperature Td into the desired crystallization temperature Tf, a calibration coefficient K is used, which is preferably in the range from 1.3 to 1.7, preferably from 1.4 to 1.6, more preferably is approximately 1.5: t > T d (1)

[0039] Т T ~ ~K

[0040] The calibration coefficient K is specified, for example, during preliminary calibration of the icing sensor. At the end of crystallization, which is monitored by the drop in the signal of the heat flow sensor to the value that was immediately before the start of crystallization, the measurement ends, and the final temperature Tfin is recorded.

[0041] The intensity of ice formation, and accordingly the amount of sample, is determined in two steps.

[0042] 1. Based on the measurement results of the heat flow sensor, the mass m of the crystallized water fraction of the water-salt solution is determined. The integral of the heat flow is calculated for the period of ice crystallization from the moment of supercooling with temperature Tc to the end of the measurement cycle at temperature Tfin. In this case, an adjustment is made for the initial heat flow at temperature TO.

[0043] Calculation formula: where ш is the mass of the crystallized aqueous fraction of the sample water; QK is the specific heat of crystallization of water; At is the time step of measuring the heat flow value; qo is the heat flow at the beginning of the cooling phase of the measurement cycle; qi is the heat flow at the i-th measurement step from the beginning of crystallization (i=l is the beginning of crystallization), n is the last step of measuring water crystallization.

[0044] 2. Using the previously established values ​​of Tf and Tfin, respectively, and the known values ​​of the concentration X, Xfin of the aqueous salt solution at these temperatures on the liquidus line, for example, the phase diagram of an aqueous solution of NaCl, the total mass of the sample M is found according to the proportion following from the phase diagram of the aqueous salt solution (Fig. 1):

[0045] The established concentration X of the water-salt solution according to reference data allows one to determine the physical density of the solution and calculate the sample volume V based on the calculated mass M.

[0046] Examples of implementation of the invention

[0047] An experimental icing sensor was manufactured according to the description of the Russian patent RU209777 (G08B 19 / 02, 23.03.2022), consisting of a thermoelectric module (Peltier element), while the icing sensor is equipped with a thermoelectric heat flow sensor connected by its lower part to the Peltier element. The opposite upper part of the heat flow sensor forms an external surface sensitive to ice formation and is equipped with a temperature sensor.

[0048] Measurements were carried out at three ambient temperatures Ta: 0°C, -15°C and -30°C using aqueous-salt solutions of NaCl with three specified crystallization temperatures TfO: -2°C, -5°C and -8°C, as well as samples of pure water with TfO=0°C.

[0049] The specified samples of water-salt solutions with a given crystallization temperature were prepared according to the known relationship between the crystallization temperature and the concentration of a given salt (3.34%, 7.88% and 11.75%, respectively).

[0050] At each temperature Ta for a solution with a given crystallization temperature TfO, measurements were carried out with different values ​​of sample volume V0, set precisely in the range of 10-50 µl: 10, 30 and 50 µl.

[0051] For example, at an ambient temperature of Ta=0°C, a precisely measured drop of a water-salt solution with a given crystallization temperature of TfO=-5°C (salt concentration of 7.88%) and a volume of V0=30 µl was placed in the measuring cuvette of the icing sensor.

[0052] In this case, the mass of the sample is also known from the known dependence of the density of the water-salt solution (in this case, NaCl) on the salt concentration.

[0053] An explanation of a specific example of a measurement cycle is given in Fig. 2.

[0054] By controlling the thermoelectric cooler (Peltier element), the temperature of the water sample in the cuvette, measured by the temperature sensor, changes from the ambient Ta=0°C to the temperature T0=+15°C. This is the preliminary phase of heating and stabilization of the initial temperature TO. In this case, the Peltier element works as a heater (from Ta=0°C to T0=+15°C). In this case, the readings of the temperature sensor Ti and the heat flux sensor qi are recorded at equal intervals of time At=0.14 s, where Ti, qi are the readings of the temperature and heat flux, respectively, in the i-th time interval (i=0...N, where 0 is the beginning of the measurements, N is the end of the measurements).

[0055] Thus, an array of data Ti and qi for i=0...N is accumulated.

[0056] After the temperature stabilizes at the value T0 = +15°C, a gradual uniform decrease in temperature is set by controlling the thermoelectric cooler. The readings qnO of the heat flux sensor before the temperature decrease are stored separately, as is the corresponding time interval number i = n0. When the limiting temperature Tc of supercooling of the liquid is reached, which is not known in advance and is noticeably lower than 0°C, spontaneous crystallization of the sample in the cuvette begins. This moment is recorded by a sharp change in temperature towards its increase (Fig. 2, solid curve). The temperature value Tp1 is stored, as is the number i = nl. This is the supercooling temperature Tp1 = Tc.

[0057] The heat flow sensor readings also show a change (a sharp increase) in the signal associated with the release of crystallization heat (Fig. 2, dotted curve). In this case, the value qnl of the heat flow before this change is stored in the time interval i=nl.

[0058] The temperature increases and reaches a local maximum, which is stored as Tn2 (i=n2). The temperature Tn2 is the temperature on the liquidus line of the phase diagram Td. It is lower than the crystallization temperature TfO of the initial solution, but is related to it by a ratio through the calibration coefficient K. The calibration coefficient K is determined in advance during the calibration of the icing sensor. In this specific example, in particular, the value K=1.5 is used, but as numerous experiments by the authors of the present invention have shown, the calibration coefficient K for the above-mentioned water-salt solutions lies in the range of approximately 1.3 to 1.7, preferably - from 1.4 to 1.6, more preferably - is approximately 1.5.

[0059] Crystallization of the water sample in the cuvette continues for some time with a duration that depends on the amount of the sample. In this case, a gradual decrease in the measured temperature Ti and the value of the heat flow qi is observed.

[0060] The heat flow sensor determines the moment (i=n3) when the heat flow value becomes equal to or less than the heat flow value at point i=n 1 , i.e. qn3 < qnl.

[0061] The number of this time interval i=n3 and the corresponding temperature TпЗ are remembered. This is the end of the measurement cycle, and TпЗ is the temperature of the end of the measurement cycle Tfin.

[0062] In the entire time interval i=nl ... пЗ, all values ​​of the heat flow sensor readings qi=qnl ... qn3 are stored.

[0063] After the end of the measurement cycle (i=n3), mathematical processing of the measured and stored data arrays is carried out, namely, the following actions are performed.

[0064] 1. Determination of crystallization temperature. The measured value Td (point Tp2) is extracted and using the calibration coefficient of proportionality K=1.5, the desired value of the sample crystallization temperature Tf is calculated:

[0065] 2. Calculation of the heat of crystallization of the sample, its mass and volume.

[0066] Based on the array of heat flow values ​​in the interval qi=qn1 to qi=qn3 (i=n 1 to i==n3), the total amount of crystallization heat Q is found over the time interval At as

[0067] Using the known value of the latent heat of crystallization of water QK = 333 J / G, the mass m of the crystallized portion of water from the total mass of the sample M is found. Namely:

[0068] Q (6) m = —

[0069] Qk

[0070] 3. Determination of the total mass of the sample M.

[0071] Using the known phase diagram of a salt solution (in this case, a NaCl solution), find the salt concentrations corresponding to the values ​​of the established temperatures Tf and Tfin on the phase diagram - Xf for Tf and Xfin for Tfin.

[0072] The dependence of the concentration X on the liquidus line on the temperature T of the NaCl salt solution from 0°C (X = 0%) up to the eutectic solution line is well described by a simple polynomial:

[0073] X = -0.0003 x T 2 - 0.0173 x T (1)

[0074] Using this polynomial, we find Xf and Xfin.

[0075] Next, using proportion (3), which follows from the phase diagram (Fig. 1a), the mass M of the sample is calculated as

[0076] The dependences of the density p of a water-salt solution on the concentration of salt X are known.

[0077] For example, for NaCl this dependence has a simple polynomial form: p = 1 + 0.7558 x X (9) Using this dependence, the sample volume V is found: v = M (U)

[0078] R

[0079] The measured and calculated results of the experiment with a 10 µl solution sample at Ta=0°C are presented in Table 1. The measurement results for three values ​​of ambient temperature for samples of other concentrations (crystallization temperatures) and volumes are also presented in Table 1.

[0080] Table 1. Measurement results a) Ambient temperature Ta=0°C b) Ambient temperature Ta=-15°C c) Ambient temperature Ta=-30°C

[0081] Designations in table 1:

[0082] VO, TfO - specified volume and crystallization temperature of the water-salt solution sample, respectively;

[0083] Ta, Tc, Td, Tfin - the ambient temperature, supercooling temperature, maximum temperature during crystallization, and end of measurement temperature measured by the temperature sensor, respectively;

[0084] Tf - measured crystallization temperature;

[0085] Xf, Xfin - calculated values ​​of solution concentrations at temperatures Tf and Tfin, respectively; p - density of salt solution with concentration Xf;

[0086] Q is the crystallization heat measured by the sensor; ш, v are the mass and volume of crystallized ice, respectively;

[0087] M, V - respectively, the mass and volume of the sample; dT, dV - the measurement accuracy of the temperature and volume of the sample, respectively, relative to the specified values ​​TfO and V0.

[0088] Comparison of the initial values ​​of the crystallization temperatures TfO of the samples and the specified volume V0 of the sample with the results of measurements of Tf and V, respectively, show good convergence of the values ​​in a wide range of temperature measurement conditions. The accuracy of measuring the crystallization temperature of the sample solution in the entire range is no worse than 0.5°C, and the measurement of the sample volume is no worse than 15%. This fully complies with the requirements for such icing sensors - road situation sensors according to industry standards (see, for example, Standard DIN EN 15518 Winter maintenance equipment. Road weather information systems, 2011).

[0089] At the same time, the values ​​of Td and V, which are measured by the known method - the closest analogue, differ significantly from the sought characteristics of the sample due to the previously given explanations. Only on pure water samples does the closest analogue give similar measurement results. In the case of water-salt solutions, there are significant discrepancies: the measured temperature is approximately 1.5 times lower than the crystallization temperature of the sample; the measured volume, being, in fact, only a part of the crystallized sample, differs noticeably from the specified volume, sometimes several times, depending on the initial concentration of the solution.

[0090] Thus, the proposed method of measurement using a thermoelectric icing sensor solves all the problems of such sensors in relation to measurements of water-salt solutions in a wide range:

[0091] - ensures reliable determination of crystallization temperature;

[0092] - provides highly accurate quantitative determination of sample size based on heat flow sensor readings and processing of results using the proposed method.

[0093] As stated above, for an icing sensor, measuring the mass M or volume V of a sample is equivalent to determining the intensity of ice formation (the amount of ice, water).

[0094] The method of measuring using a thermoelectric icing sensor according to the proposed invention can find wide application in industry, namely, in the field of thermometry and heat metry of thermoelectric icing sensors, especially for monitoring the condition of road surfaces under conditions of using anti-icing agents based on water-salt solutions.

Claims

CLAUSES OF THE INVENTION 1. A method for determining the crystallization temperature of a sample of a water-salt solution using a thermoelectric icing sensor containing a thermoelectric module, a temperature sensor, and a heat flow sensor, which includes: increasing the temperature of the sample to a value that is known to be higher than the crystallization temperature of the sample, cooling the sample to a supercooling temperature Tc below the crystallization temperature Tf, recording the maximum temperature Td corresponding to a jump in the value of the sample temperature with a jump in the value of the heat flow during crystallization of the sample, and determining the crystallization temperature Tf of the sample using a calibration coefficient K according to the formula: Tf = Td / K.

2. A method for determining the crystallization temperature according to item 1, in which cooling of the sample to a temperature below the crystallization temperature is carried out at a constant rate.

3. The method for determining the crystallization temperature according to claim 1, in which the value of the calibration coefficient K lies in the range from 1.3 to 1.7, preferably from 1.4 to 1.6, more preferably is approximately 1.

5.

4. A method for determining the mass of a sample of a water-salt solution using a thermoelectric icing sensor containing a thermoelectric module, a temperature sensor and a heat flow sensor, including: increasing the temperature of the sample to a value that is deliberately higher than the crystallization temperature of the sample, cooling the sample to a supercooling temperature Tc below the crystallization temperature, recording the maximum temperature Td corresponding to a jump in the value of the sample temperature with a jump in the value of the heat flow during crystallization of the sample, determination of the crystallization temperature Tf of the sample using the calibration coefficient K according to the formula: Tf = Td / K, determination of the mass m of the crystallized aqueous fraction of the sample based on changes in the heat flow from the moment the supercooling temperature Tc of the sample is reached until the end of the measurement cycle at temperature Tfin, and determination of the mass M of the sample according to the formula (Xfin -X) / X = w / (M - w), where X, Xfin are the values ​​of the salt concentration in the sample at temperatures Tf and Tfin, respectively.

5. A method for determining the crystallization temperature according to clause 4, in which cooling of the sample to a temperature below the crystallization temperature is carried out at a constant rate.

6. The method for determining the crystallization temperature according to claim 4, in which the value of the calibration coefficient K lies in the range from 1.3 to 1.7, preferably from 1.4 to 1.6, more preferably is approximately 1.5.

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