A method for detecting carbon dioxide value of a museum cultural relic display cabinet ventilation rate

Abstract

The application relates to the field of cultural relic collections, and particularly discloses a carbon dioxide numerical detection method for the air exchange rate of a museum cultural relic display cabinet, which comprises the following steps: according to the structural parameters of the cultural relic display cabinet, a three-dimensional physical model of the cultural relic display cabinet is built by using CFD software, and the model is calibrated by using experimental measurement results. The carbon dioxide numerical detection method for the air exchange rate of the museum cultural relic display cabinet is used to carry out digital experiments in a virtual space, and then the air exchange rate of the cultural relic display cabinet is measured, without adding carbon dioxide tracer gas in the real display cabinet, so that the cultural relics are not damaged, the storage environment of the cultural relics is not affected, and the method is safe for the detector and the environment.

Description

Technical Field

[0001] This invention relates to the field of cultural relics collections, and in particular to a method for detecting carbon dioxide levels in the ventilation rate of museum artifact display cases. Background Technology

[0002] The airtightness of a display case is an important indicator for evaluating its quality. A well-sealed display case can isolate pollutants in the outside air to a certain extent, thereby effectively reducing the impact of external environmental pollutants on the internal environment of the display case. At the same time, it has a buffering effect on changes in humidity in the external environment. Therefore, the airtightness of the display case is also the main basis for formulating humidity control measures inside the case. The airtightness of a display case is usually expressed by the air exchange rate of the display case, which is the ratio of the volume of air entering the display case from the outside to the volume of the display case in one day without external power or pressure difference.

[0003] Currently, the main method for determining the ventilation rate of display cases is the carbon dioxide tracer gas experiment. The method is as follows: First, a certain amount of high-concentration carbon dioxide gas is introduced into the display case. As outside air continuously seeps into the display case through its gaps, the high-concentration carbon dioxide gas inside the case also seeps out through the gaps. With the exchange of gases inside and outside the case, the high-concentration carbon dioxide gas inside the case is continuously diluted. Since there is no pressure difference between the inside and outside of the case, the amount of gas entering the display case and the amount of gas seeping out of the display case at the same time are the same, and the concentration of carbon dioxide in the outside air is constant. Therefore, the ventilation rate of the display case can be calculated using the following formula:

[0004] C-C1=(C0-C1)·exp(-R0·t);

[0005]

[0006] In the formula, C is the carbon dioxide concentration inside the display case, C1 is the initial carbon dioxide concentration inside the case, C0 is the carbon dioxide concentration in the air, t is time, R0 is the air exchange rate of the display case, q is the air intake of the display case per unit time, and V is the volume of the display case.

[0007] However, this experimental method can be further improved: First, introducing high-concentration carbon dioxide as a tracer gas into the display case alters the preservation environment of the cultural relics to some extent, which is not conducive to the cleanliness and stability requirements of the preservation environment; Second, it is necessary to purchase carbon dioxide gas sources and corresponding gas detection equipment, and the experiment requires a constant temperature environment, which increases the experimental cost due to the high requirements of the experimental environment; Third, this experiment can only be carried out in a constant environment, and changes in ambient temperature and humidity will cause deviations in the measurement results, so the measured results cannot be directly applied to different and constantly changing environments.

[0008] Therefore, a fast and low-cost detection method is needed.

[0009] In recent years, with the development of computer technology and fluid mechanics, more and more practical engineering problems can be solved using numerical simulation technology. CFD, or Computational Fluid Dynamics, is an emerging interdisciplinary field that integrates fluid mechanics and computer science. It starts with computational methods and uses the rapid computing power of computers to obtain approximate solutions to fluid control equations. The basic characteristics of computational fluid dynamics are numerical simulation and computer experiments. Starting from fundamental physical theorems, it has largely replaced the expensive fluid dynamics experimental equipment, and has had a significant impact on scientific research and engineering technology. CFD software usually refers to commercial CFD programs with good human-computer interaction interfaces. Currently, the more mainstream CFD software includes CFX, Fluent, Phoenics, Star-CD, Comsol, Star-ccm+, Flow-3D, etc. Summary of the Invention

[0010] In view of this, the purpose of this invention is to provide a method for detecting carbon dioxide in the ventilation rate of museum artifact display cases. The method is based on CFD technology to conduct digital experiments in virtual space to measure the ventilation rate. It does not require the addition of tracer gas in the actual display case, does not damage the artifacts, does not affect the preservation environment of the artifacts, and is safe for the testers and the environment.

[0011] To achieve the above objectives, the present invention provides a method for detecting carbon dioxide levels in the ventilation rate of museum artifact display cases, comprising the following steps:

[0012] (1) Based on the structural parameters of the cultural relic display case, construct a three-dimensional physical model of the cultural relic display case;

[0013] (2) Conduct experimental tests on the environment of the cultural relic display case in step (1). Temperature and humidity sensors are placed on the outside and inside of the display case to continuously monitor the environment inside and outside the case and obtain the measured temperature and humidity results inside and outside the display case.

[0014] (3) The measured results of the ambient temperature outside the cabinet obtained in step (2) are compiled using programming software. After compilation, the results are imported into CFD software as the temperature boundary conditions of the model for calculation. At the same time, the measured results of the ambient humidity outside the cabinet obtained in step (2) are compiled using programming software. After compilation, the results are imported into CFD software as the humidity boundary conditions at the connection between the inside and outside of the cabinet for calculation. A three-dimensional model of the material exchange and energy exchange between the display case and the external environment is obtained, and the results of the temperature change inside the cabinet over time are output.

[0015] (4) After calibrating the calculated temperature of the cabinet obtained in step (3) based on the measured temperature of the cabinet obtained in step (2), output a three-dimensional model of the material and energy exchange between the temperature-calibrated display cabinet and the external environment.

[0016] (5) In the CFD software, based on the corrected three-dimensional model obtained in step (4), input the initial carbon dioxide concentration and water vapor concentration inside the cabinet as the initial conditions of the model, input the water vapor concentration outside the cabinet and the carbon dioxide concentration in the environment outside the cabinet as the boundary conditions of the model, and output the result of the change of carbon dioxide concentration inside the cabinet over time.

[0017] (6) Using data analysis software, plot the results of the change in carbon dioxide concentration in the cabinet over time obtained in step (5), and fit it using an exponential decay equation. When R 2 When the value is ≥0.99, the calculated parameter R0 is the air exchange rate of the display case.

[0018] Preferably, in step (1), the artifact display case includes a base for placing artifacts and an isolation cover covering the artifacts. The isolation cover is a rectangular transparent glass frame structure with an opening at the bottom. There is a gap between the isolation cover and the base, which is the part that connects the display case to the outside world. The three-dimensional physical model is provided with an interface corresponding to the gap.

[0019] Preferably, in step (2), the continuous monitoring is carried out for 24 hours and a set of data is uploaded and saved every 15 minutes.

[0020] Preferably, in step (3), the experimental measurement curves of temperature and humidity outside the display case are compiled into a user-defined function (UDF) by programming software and used as the temperature and humidity boundary conditions of the model for calculation. As a further improvement of the technical solution of the present invention, in step (4), the model is calibrated by setting the average deviation and the maximum deviation threshold between the temperature value calculated by the model and the experimentally measured temperature value.

[0021] Preferably, in step (4), when the average deviation and the maximum deviation between the temperature value calculated by the three-dimensional model and the measured value are both less than the measurement error of the experimental instrument, the result is judged to be consistent.

[0022] Preferably, in step (4), the adjustable parameter of the three-dimensional model is the value of the natural convection heat transfer coefficient between the display case and the external environment.

[0023] Preferably, in step (5), a component transport model is introduced, and the gas in the fluid area inside the display case is set as a mixture of carbon dioxide, water vapor and dry air. The mass fraction of carbon dioxide in the display case is set to 0.025 in the initial state, the mass fraction of water vapor is set according to the measured humidity value, and the mass fraction of carbon dioxide in the air outside the display case is set to 0.00048 as the boundary condition of the outlet.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] I. This invention can quantitatively and in detail describe the air exchange process inside and outside the display case under actual environmental temperature and humidity changes. The three-dimensional model calibrated by experimental results has high prediction accuracy.

[0026] Second, this invention is based on CFD to conduct digital experiments in virtual space and then measure the ventilation rate. There is no need to add tracer gas in the real display case, so it does not damage the cultural relics, does not affect the cleanliness and stability of the cultural relics preservation environment, and is harmless to the testers and the environment.

[0027] Third, this invention is fast and low-cost, requiring no purchase of tracer gas source or gas analysis and detection equipment, and has no requirements for the detection environment;

[0028] Fourth, once the numerical model of this invention is established and calibrated, the air exchange rate of the display case under various environmental conditions (temperature and humidity) can be measured by numerical simulation. Under any ambient temperature and humidity, without changing the environmental conditions for the preservation of cultural relics, the air exchange rate of the museum display case can be calculated in a fast and low-cost manner.

[0029] Of course, other advantages, objectives and features of the present invention will be apparent in part from the following description, and in part from the understanding of those skilled in the art through study and practice of the invention. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute a limitation thereof.

[0031] Figure 1 This is a flowchart of a method for detecting carbon dioxide values ​​in the ventilation rate of a museum artifact display case according to the present invention.

[0032] Figure 2 This is a schematic diagram of the three-dimensional physical model of the display case established in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram comparing the temperature of CFD simulation results and measured results in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram illustrating the numerical results of the change of carbon dioxide concentration in the display case over time in an embodiment of the present invention.

[0035] Figure 5 This is a schematic diagram of the experimental measurement results of the change of carbon dioxide concentration in the display case over time in an embodiment of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Please see Figure 1 This invention provides a numerical detection method for ventilation rate, specifically a numerical detection method for carbon dioxide in the ventilation rate of museum artifact display cases based on CFD and existing carbon dioxide tracer gas experimental detection methods, which mainly includes the following 6 steps.

[0038] (1) Use CFD software (specifically Fluent software) to build a three-dimensional physical model of the museum artifact display case.

[0039] In this step, the artifact display case may include a base for placing the artifact and an isolation cover covering the artifact. The isolation cover is a rectangular transparent glass frame structure with an opening at the bottom. There is a gap between the isolation cover and the base, which is the part of the display case that connects to the outside world (also called the connection point). The three-dimensional physical model is provided with an interface corresponding to the gap.

[0040] This step can be broken down as follows: Using the actual measured dimensions of the artifact display case and the material information of each component, create a three-dimensional physical model of the artifact display case in CFD software; based on the actual situation, establish an interface connecting the artifact display case to the external gas; in the CFD software, by setting the thickness L1(m) of the shell of each boundary layer of the above model, represent the thickness L1(m) of the glass solid wall; by setting the wall thickness L... N (m), representing the thickness L of the solid wall of each component. N (m).

[0041] (2) Wireless temperature and humidity sensors are installed on the outside and inside of the artifact display case to continuously monitor the environment inside and outside the case for 24 hours to obtain the measured temperature and humidity results inside and outside the display case.

[0042] (3) Use programming software (specifically Visual C++ software) to compile the measured results of the external ambient temperature obtained in step (2), and import them into the CFD software as the temperature boundary conditions of the model for calculation; at the same time, use programming software to compile the measured results of the external ambient humidity obtained in step (2), and import them into the CFD software as the humidity boundary conditions at the connection between the inside and outside of the cabinet for calculation, so as to obtain a three-dimensional model of the material exchange and energy exchange between the cultural relic display case and the external environment, and output the results of the temperature change inside the cabinet over time.

[0043] (4) Use the temperature change data inside the cabinet obtained in step (2) to calibrate the temperature calculation results of the three-dimensional model obtained in step (3); if the two results match, the three-dimensional model is considered to be accurate and can be used for the next numerical experiment; if the two results do not match, adjust the adjustable parameters of the three-dimensional model until the two results match.

[0044] In this step, when the average deviation and the maximum deviation between the temperature value calculated by the three-dimensional model in step (3) and the measured value are both less than the measurement error of the instrument (which can be the temperature and humidity sensor used in this embodiment) (specifically, it can be regarded as 0.3℃), it is determined that the result is consistent; otherwise, it is determined that the result is inconsistent.

[0045] In this step, the adjustable parameter of the 3D model is the value of the natural convection heat transfer coefficient h between the display case and the external environment.

[0046] (5) In the CFD software, using the corrected three-dimensional model obtained in step (4), set the initial mass fraction of carbon dioxide tracer gas in the display case to characterize the initial concentration of carbon dioxide in the display case, set the initial mass fraction of water vapor in the display case to characterize the initial ambient humidity in the display case, set the mass fraction of carbon dioxide in the air in the part of the display case connected to the outside to characterize the concentration of carbon dioxide in the outside air, and set the mass fraction of water vapor in the outside air to characterize the ambient humidity in the outside air.

[0047] As can be seen, in calibrating the model, this embodiment selected the measured temperature results for model calibration, and fully considered the heat transfer process (heat conduction and natural convection) and mass transfer process between the display case and the external environment (the humidity change of the external environment was used as the boundary condition of the model for calculation, and the initial humidity inside the display case was used as the initial condition of the model for calculation).

[0048] (6) The results of the change of carbon dioxide mass fraction in the tracer gas inside the display case over time were exported using CFD software. The carbon dioxide mass fraction was plotted against time t in the analysis software, and the result was fitted using an exponential decay equation. When the coefficient of determination R... 2 When the value is ≥0.99, the calculated parameter R0 is the air exchange rate of the display case.

[0049] The following specific embodiment illustrates the carbon dioxide numerical detection method for the ventilation rate of museum artifact display cases provided by the present invention.

[0050] This embodiment uses a desktop display case for cultural relics, with a length, width, and height of 1.2m, 0.6m, and 0.355m respectively. The bottom is framed by a metal border, with a wooden board in the center. A 2mm gap connects the interior of the case to the external environment; this gap is the connection point between the display case and the outside world. Except for the bottom, the other five sides of the display case are made of transparent acrylic glass with a thickness of 0.012m. Based on the above dimensions and materials, a three-dimensional digital model of the display case was created, as shown below. Figure 2 As shown.

[0051] Wireless temperature and humidity monitoring terminals (composed of temperature and humidity sensors) are installed on the outside of the five glass covers of the artifact display case, in the gaps between the glass covers (both are considered the exterior of the display case), and inside the display case. These terminals record the changes in temperature and humidity inside and outside the display case over 24 hours. The temperature and humidity data are collected and saved every 15 minutes. When measuring the temperature and humidity outside the glass covers, the temperature and humidity sensors can be placed on the outer surface of the glass covers; when measuring the temperature and humidity in the gaps between the glass covers, the temperature and humidity sensors can be placed outside the glass covers and close to the gaps.

[0052] Temperature data collected from the five glass enclosures were compiled using a User Defined Function (UDF) and imported into the CFD software as temperature boundary conditions for the glass enclosures. Temperature and humidity data collected from the gaps in the display case were also compiled using a UDF and imported into the CFD software as temperature boundary conditions for the pressure-outlet and water vapor concentration boundary conditions for the mixed gas. The model calculations used the standard k-ε turbulence model for transient solutions, with the total pressure at the pressure-outlet set to 0.

[0053] The model outputs the temperature results at the location of the temperature and humidity sensor inside the cabinet. The model calculates the temperature change over time and compares it with the measured values ​​inside the cabinet. Figure 3 As shown, the average deviation is 0.12℃ and the maximum deviation is 0.29℃, both of which are less than the sensor's measurement error of 0.3℃. Therefore, it is believed that the model has good accuracy in describing the material and energy exchange between the display case and the external environment, taking into full account the constantly changing temperature and humidity of the environment where the display case is located.

[0054] In the above display case model, a component transport model (Species Transport) is introduced, and the gas in the fluid zone inside the display case is set as a mixture of carbon dioxide (CO2), water vapor (H2O), and dry air. The initial mass fraction of carbon dioxide inside the case is set to 0.025, and the mass fraction of water vapor is set to 0.012 (the actual measured mass fraction of water vapor). The mass fraction of carbon dioxide in the outside air is set to 0.00048 as the boundary condition for the outlet, while the remaining parameters of the model remain unchanged; the mass fraction here represents the concentration of the relevant gas. Other parameters of the display case model (including material density, thermal conductivity, etc.) are kept constant during the calculation.

[0055] The model outputs and saves the change in carbon dioxide mass fraction within the display case over time every 15 minutes. An exponential decay fit is applied to the carbon dioxide relationship output by the model over time to obtain the ventilation rate of the display case. The results are as follows: Figure 4 As shown.

[0056] To further verify the accuracy of the numerical detection method, the traditional carbon dioxide tracer gas method was used to measure the air exchange rate of the display case (the measurement formula can be found in the background section), and the results are as follows. Figure 5 As shown.

[0057] The results of the numerical detection method and the traditional detection method for calculating the air exchange rate of the display case are similar, as shown in Table 1 below. This indicates that the results of the numerical detection method have high accuracy, which means that the numerical detection method for detecting the air exchange rate of museum artifact display cases can, to some extent, replace the traditional carbon dioxide tracer gas method.

[0058] Table 1 Comparison of numerical detection results and experimental measurement results for the calculated ventilation rate of the artifact display case.

[0059] Numerical experimental results 3.44 0.99205 Experimental measurement results 3.19 0.99489

[0060] It should be noted that the embodiments described above are only a part of the embodiments of the present invention, and not all of them; the various embodiments described above can be combined in various ways as needed; the terms and wording used in the specification of the present invention are merely illustrative and do not imply any limitation on the claims of the present invention.

[0061] Those skilled in the art will understand that various changes can be made to the details of the above embodiments without departing from the basic principles of the disclosed embodiments; therefore, the scope of the invention is defined only by the claims, and in the claims, unless otherwise stated, all terms should be understood in the broadest reasonable sense.

[0062] Any obvious modifications made to this invention without departing from its essential content will constitute an infringement of the patent rights of this invention and will incur corresponding legal liability.

Claims

1. A method for numerically detecting carbon dioxide in the ventilation rate of museum artifact display cases, characterized in that, Includes the following steps: (1) Based on the actual structural parameters of the cultural relic display case, construct a three-dimensional physical model of the cultural relic display case; (2) Conduct experimental tests on the environment of the cultural relic display case in step (1). Temperature and humidity sensors are placed on the outside and inside of the display case to continuously monitor the environment inside and outside the case and obtain the measured temperature and humidity results inside and outside the display case. (3) The measured results of the ambient temperature outside the cabinet obtained in step (2) are compiled using programming software. After compilation, the results are imported into the CFD software as the temperature boundary conditions of the model for calculation. At the same time, the measured results of the ambient humidity outside the cabinet obtained in step (2) are compiled using programming software. After compilation, the results are imported into the CFD software as the humidity boundary conditions at the connection between the inside and outside of the cabinet for calculation. A three-dimensional model of the material exchange and energy exchange between the display case and the external environment is obtained, and the results of the temperature change inside the cabinet over time are output. (4) After calibrating the calculated temperature of the cabinet obtained in step (3) based on the measured temperature of the cabinet obtained in step (2), output a three-dimensional model of the material and energy exchange between the temperature-calibrated display cabinet and the external environment. (5) In the CFD software, based on the corrected three-dimensional model obtained in step (4), input the initial carbon dioxide concentration and water vapor concentration inside the cabinet as the initial conditions of the model, input the water vapor concentration outside the cabinet and the carbon dioxide concentration in the environment outside the cabinet as the boundary conditions of the model, and output the result of the change of carbon dioxide concentration inside the cabinet over time. (6) Using data analysis software, plot the results of the change in carbon dioxide concentration in the cabinet over time obtained in step (5), and fit them using the exponential decay equation. When R 2 When the value is ≥0.99, the calculated air exchange rate of the corresponding display case is the air exchange rate of that display case; R 2 The determination coefficient; In step (4), when the average deviation and the maximum deviation between the temperature value calculated by the three-dimensional model and the measured value are both less than the measurement error of the instrument, the result is judged to be consistent. In step (4), the adjustable parameter of the three-dimensional model is the value of the natural convection heat transfer coefficient between the display case and the external environment; In step (5), a component transport model is introduced, and the gas in the fluid area inside the display case is set as a mixture of carbon dioxide, water vapor and dry air. The mass fraction of carbon dioxide in the display case is set to 0.025 in the initial state, the mass fraction of water vapor is set according to the measured humidity value, and the mass fraction of carbon dioxide in the air outside the display case is set to 0.00048 as the boundary condition of the outlet.

2. The method for detecting carbon dioxide levels in the ventilation rate of museum artifact display cases according to claim 1, characterized in that: In step (1), the artifact display case includes a base for placing artifacts and an isolation cover covering the artifacts. The isolation cover is a rectangular transparent glass frame structure with an opening at the bottom. There is a gap between the isolation cover and the base, which is the part that connects the display case to the outside world. The three-dimensional physical model is provided with an interface corresponding to the gap.

3. The method for detecting carbon dioxide levels in the ventilation rate of museum artifact display cases according to claim 1, characterized in that: The CFD software is Fluent.

4. The method for detecting carbon dioxide levels in the ventilation rate of a museum artifact display case according to claim 1, characterized in that: In step (2), the temperature and humidity sensor is a wireless sensor structure.

5. A method for detecting carbon dioxide levels in the ventilation rate of a museum artifact display case according to claim 1, characterized in that: In step (2), the continuous monitoring is carried out for 24 hours.

6. The method for detecting carbon dioxide levels in the ventilation rate of a museum artifact display case according to claim 1, characterized in that: In step (3), the programming software is Visual C++ software.

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