Method for measuring the thermal conductivity of ice

Abstract

The present invention discloses a method for measuring the thermal conductivity of ice, comprising the following steps: S1: constructing a measuring device, the measuring device comprising a transparent tube, the outer wall of the transparent tube being coated with a thermal insulation foam layer, a heater plate and a thermocouple being fixedly mounted on one end of the transparent tube, the thermocouple being located outside the heater plate, and the thermocouple and the heater plate being fixedly sealed to one end of the transparent tube by epoxy resin; the other end of the transparent tube being sealed by a detachable rubber cover, the thermocouple being bonded inside the rubber cover; S2: constructing a thermal conductivity model of ice; S3: preparing ice to be measured in the transparent tube; S4: using the measuring device constructed by S1 to measure the ice prepared in step S3, and a host computer software automatically calculating the thermal conductivity to obtain experimental data. The present invention provides accurate and rapid measurement. This method uses a more accurate theoretical model as its theoretical basis, and the current value and the measured data curve can be viewed on the software interface at any time after the measurement begins. No post-processing of the data is required, and the results can be obtained in real time.

Description

Technical Field

[0001] The invention belongs to the technical field of measuring the thermal conductivity of ice, and in particular relates to a method for measuring the thermal conductivity of ice. Background Art

[0002] In current technology, the steady-state method or quasi-steady-state method is generally used to measure the thermal conductivity of ice.

[0003] The steady-state method involves heating one end of the sample and dissipating heat at the other. When the heating and dissipation powers are equal, steady-state is reached, and the thermal conductivity can be calculated. The quasi-steady-state method involves combining two samples and heating both ends simultaneously without heat dissipation. The thermal conductivity is then calculated when the temperature difference between the center and the ends remains constant.

[0004] The following problems are inevitable when calculating the thermal conductivity of ice using either the steady-state method or the quasi-steady-state method:

[0005] 1. Ice melts easily at room temperature, and the temperature difference between ice and room temperature is large. Heat is transferred in any direction, but not entirely along the axis from one end to the other. Furthermore, it takes time for ice to reach a steady or quasi-steady state. Ice does not have the conditions to remain heated for a long time without melting, which leads to large errors in the measurement process and calculation results.

[0006] 2. The experimental results need to be post-processed, the data processing is huge, and the data processing process will also bring cumulative errors. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies of the existing technology and propose a method for measuring the thermal conductivity of ice. The method improves the measuring device and simultaneously makes ice with the device during the measurement process so that the device and the ice have the same temperature. At the same time, the thermal conductivity model is optimized, which can further improve the measurement accuracy of the thermal conductivity of ice.

[0008] The technical purpose of the present invention is achieved through the following technical solution: a method for measuring the thermal conductivity of ice, which comprises the following steps:

[0009] S1: Build a measuring device, comprising a transparent tube, the outer wall of which is covered with a thermal insulation foam layer, a heater plate and a thermocouple fixedly mounted on one end of the transparent tube, the thermocouple being located outside the heater plate, the thermocouple and the heater plate being fixedly sealed to one end of the transparent tube with epoxy resin; the other end of the transparent tube is sealed with a detachable rubber cover, the thermocouple being bonded inside the rubber cover;

[0010] S2 constructs the heat conduction model of ice as follows:

[0011] In the formula

[0012] λ is the thermal conductivity of ice; ρ is the density of ice; c is the specific heat capacity of ice; P is the heating power of the heater; t is the time from the start of heating; is the temperature difference between the two ends of the ice; S is the internal cross-sectional area of ​​the transparent tube; is the derivative of the temperature difference between the two ends of the ice with respect to time;

[0013] S3 preparing ice to be measured in the transparent tube;

[0014] In step S4, the ice prepared in step S3 is measured using the measuring device constructed in step S1, and the upper computer software automatically calculates the thermal conductivity to obtain experimental data.

[0015] Preferably, in step S3, the heat-insulating foam layer is coated on the transparent tube, and then water is placed in the transparent tube. The ends of the transparent tube are sealed with a rubber cap and then placed in a refrigerator for freezing to obtain ice to be measured.

[0016] Preferably, step S4 is performed under vacuum conditions.

[0017] Preferably, the transparent tube is an acrylic tube.

[0018] Preferably, in step S2, the first 50 sets of data collected after the start of measurement are discarded, i.e. To reduce the impact of electromagnetic interference on measurement data.

[0019] Preferably, in step S2, P=0.95P0, where P0 is the rated heating power of the heating plate.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention measures accurately and quickly. This method uses a more accurate theoretical model as its theoretical basis, and the current value and the measured data curve can be seen in the software interface at any time after the measurement begins. There is no need to process the data later, and the results can be obtained in real time.

[0022] 2. When making ice, put the insulating foam layer and the transparent tube into the refrigerator to freeze. In this way, after making ice, the insulating foam layer, ice and transparent tube have the same temperature, which has a better insulation effect on the ice and further improves the measurement progress.

[0023] 3. The present invention performs measurements in a vacuum environment, isolating heat conduction between the environment and the ice. The vacuum environment causes the heat flow in the ice to be concentrated in axial conduction, extending the ice working time and further improving the accuracy of the measurement data. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention.

[0025] Figure 2 Schematic diagram of the measurement system of the present invention.

[0026] Figure 3 Schematic diagram of Fourier's law of heat conduction.

[0027] In the above drawings: transparent tube 1, thermal insulation foam layer 2, heating plate 3, first thermocouple 4, rubber cover 5, second thermocouple 6. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] Reference Image Figure 2 As a preferred embodiment of the present invention, this embodiment provides a method for measuring the thermal conductivity of ice, which includes the following steps:

[0031] S1 builds the measuring device, such as Figure 1 As shown, the measuring device includes a transparent tube 1, which is made of acrylic or organic glass. The outer wall of the transparent tube 1 is covered with a thermal insulation foam layer 2. A heating plate 3 and a first thermocouple 4 are fixedly mounted on one end of the transparent tube 1. The first thermocouple 4 is located outside the heating plate 3. The first thermocouple 4 and the heating plate 3 are fixedly sealed to one end of the transparent tube 1 by epoxy resin. The other end of the transparent tube 1 is sealed by a detachable rubber cover 5. A second thermocouple 6 is bonded inside the rubber cover 5.

[0032] S2 constructs the heat conduction model of ice as follows:

[0033] In the formula

[0034] λ is the thermal conductivity of ice; ρ is the density of ice; c is the specific heat capacity of ice; P is the heating power of the heater; t is the time from the start of heating; is the temperature difference between the two ends of the ice; S is the internal cross-sectional area of ​​the transparent tube; is the derivative of the temperature difference between the two ends of the ice with respect to time;

[0035] S3 preparing ice to be measured in the transparent tube;

[0036] In step S4, the ice prepared in step S3 is measured using the measuring device constructed in step S1, and the upper computer software automatically calculates the thermal conductivity to obtain experimental data.

[0037] When constructing the heat conduction model of the present invention, a one-dimensional heat transfer model is constructed based on Fourier's heat conduction law. Figure 3 ,

[0038] Attachment Figure 3 It can be expressed as:

[0039]

[0040] In this set of equations, the first equation is the one-dimensional heat conduction equation, the second and third equations are boundary conditions, and the fourth equation is the initial condition.

[0041] Where T refers to T(x, t), which means that temperature is a function of coordinate x and time t; It is a coefficient introduced for the sake of simplicity. ρ refers to the density of ice, c refers to the specific heat capacity of ice, λ refers to the thermal conductivity of ice, and q c is the heat flux density, P is the heating power of the heating plate, S is the cross-sectional area of ​​the ice, and t0 is the temperature of the ice column at t = 0. t Indicates the first-order derivative of T(x, t) with respect to time, T xx = represents the second derivative of the coordinates. The second formula means that at x = 0, the first derivative of T(x, t) with respect to the coordinates is 0, that is, x = 0 is adiabatic, and heat neither flows in nor out here. The third formula means that at x = L, the first derivative of T(x, t) with respect to the coordinates is equal to That is Fourier's experimental law: the amount of heat q flowing through a unit area per unit time is c Proportional to the temperature drop, the proportionality coefficient is the thermal conductivity: The solution to this system of equations is:

[0042] Where B n The coefficients of the series terms of the solution, considering the exponential terms of n = 1, 2, ignoring the high-order coefficient terms,

[0043] (When n=3, if Then the exponential term e -5 ≈0.7%, which can be ignored), then

[0044]

[0045] Substitute x=0 and x=L:

[0046]

[0047]

[0048] Subtracting the following equation from the above equation yields:

[0049]

[0050] Transpose the terms and take the logarithm to get:

[0051]

[0052] Then take the derivative with respect to time t: (in the formula )

[0053]

[0054] The expression for the final thermal conductivity obtained by deformation is:

[0055]

[0056] Where a = λ / ρc, where λ, ρ, and c are the thermal conductivity, density, and specific heat of ice, respectively; P is the heating power applied to the heater; x is the distance from a point in the ice to the non-heated surface; and t is the time elapsed since the start of heating. is the time derivative of the temperature difference between the two ends of the icicle, It is the temperature difference between the two ends of the ice, that is, the temperature of the non-heated end minus the temperature of the heated end.

[0057] In some embodiments, in step S3, an insulating foam layer is wrapped around a transparent tube, and then water is filled in the transparent tube. The ends of the transparent tubes are sealed with rubber caps and then placed in a refrigerator to freeze to obtain ice to be measured. After the ice is made, the insulating foam layer has the same temperature as the ice and the transparent tube, which has a better insulation effect on the ice and further improves the measurement progress.

[0058] In other embodiments, step S4 is performed under vacuum conditions to isolate heat conduction between the environment and the ice. The vacuum environment causes the heat flow in the ice to be concentrated in axial conduction, thereby extending the ice working time and further improving the accuracy of the measurement data.

[0059] In other preferred embodiments, in step S2, the first 50 sets of data collected after the start of measurement are discarded, i.e. To reduce the impact of electromagnetic interference on measurement data.

[0060] In other preferred embodiments, in step S2, P = 0.95P0, where P0 is the rated heating power of the heating plate. Heat propagates not only axially but also radially in the produced ice. It is assumed that 95% of the heat propagates axially, while 5% propagates radially and does not reach the other end.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for measuring the thermal conductivity of ice, characterized in that: It includes the following steps: S1: Build a measuring device, comprising a transparent tube, the outer wall of which is covered with a thermal insulation foam layer, a heater plate and a thermocouple fixedly mounted on one end of the transparent tube, the thermocouple being located outside the heater plate, the thermocouple and the heater plate being fixedly sealed to one end of the transparent tube with epoxy resin; the other end of the transparent tube is sealed with a detachable rubber cover, the thermocouple being bonded inside the rubber cover; S2 constructs the heat conduction model of ice as follows: In the formula λ is the thermal conductivity of ice; ρ is the density of ice; c is the specific heat capacity of ice; P is the heating power of the heater; t is the time from the start of heating; is the temperature difference between the two ends of the ice; S is the internal cross-sectional area of ​​the transparent tube; is the derivative of the temperature difference between the two ends of the ice with respect to time; S3 preparing ice to be measured in the transparent tube; In step S4, the ice prepared in step S3 is measured using the measuring device constructed in step S1, and the upper computer software automatically calculates the thermal conductivity to obtain experimental data.

2. The method for measuring the thermal conductivity of ice according to claim 1, wherein: In step S3, a heat-insulating foam layer is coated on the transparent tube, and then water is placed in the transparent tube. The ends of the transparent tube are sealed with a rubber cap and then placed in a refrigerator for freezing to obtain ice to be measured.

3. The method for measuring the thermal conductivity of ice according to claim 1, wherein: S4 is carried out under vacuum conditions.

4. The method for measuring the thermal conductivity of ice according to claim 1, wherein: The transparent tube is an acrylic tube.

5. The method for measuring the thermal conductivity of ice according to claim 1, wherein: In step S2, the first 50 sets of data collected after the measurement starts are discarded, i.e. To reduce the impact of electromagnetic interference on measurement data.

6. The method for measuring the thermal conductivity of ice according to claim 1, wherein: In step S2, P=0.95P0 is taken, where P0 is the rated heating power of the heating plate.

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