A method for constructing a dynamic heat balance model for low-temperature regulation of fruit and vegetable surfaces and applications

Abstract

The application belongs to the field of food preservation, new materials and electronic information technology, and discloses a construction method and application of a dynamic heat balance model for low-temperature regulation of fruit and vegetable surfaces, wherein the model comprises a three-stage coupled heat balance model, which comprises a packaging outer surface heat balance model, a packaging inner surface heat balance model and a fruit and vegetable surface heat balance model. The application constructs a dynamic heat balance model for low-temperature regulation of fruit and vegetable surfaces based on the second law of thermodynamics, establishes a thermodynamic model with the lowest fruit and vegetable surface temperature as the target condition, realizes accurate regulation of the fruit and vegetable surface temperature through a three-stage heat balance system, integrates three mechanisms of radiation refrigeration, dynamic coupling of respiratory heat and optimization of packaging material parameters, and solves the problems of large temperature fluctuation and high energy consumption in traditional preservation technology. The core is to establish a synergistic regulation network of environment-packaging-fruit and vegetable through a layered heat balance equation, and finally realize the target of fruit and vegetable surface temperature being lower than the ambient temperature by more than 10 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the fields of food preservation, new materials and electronic information technology, and particularly relates to a construction method and application of a dynamic heat balance model for low-temperature regulation on the surface of fruits and vegetables. BACKGROUND

[0002] During the logistics transportation and storage of fruits and vegetables, environmental factors such as temperature, humidity and gas composition have a great influence on the preservation effect of fruits and vegetables. Among them, temperature is one of the key factors affecting the preservation of fruits and vegetables. Low-temperature control not only delays the deterioration of fruits and vegetables, but also maintains their color, flavor and nutritional value. Low temperature can effectively slow down the physiological metabolism of fruits and vegetables and prolong their shelf life. Temperature fluctuations and improper control may increase the respiration rate of fruits and vegetables, thereby accelerating their maturation and aging process and shortening the shelf life.

[0003] Fruits and vegetables will undergo respiration during logistics transportation and thus generate respiratory heat, which is an important factor affecting the shelf life of fruits and vegetables. If the heat generated during respiration is not promptly transferred or dissipated, the local temperature will rise, directly leading to the deterioration of fruits and vegetables. At present, there are many studies on environmental temperature control of fruit and vegetable packaging materials, but the attention to respiratory heat management and heat balance regulation is still insufficient. At present, the modeling research on heat transfer mechanism in fruit and vegetable logistics preservation is relatively less, which leads to the fact that in practical application, the fruit and vegetable packaging solution does not fully consider the regulation and management of heat, and the analysis of fruit and vegetable heat transfer mechanism lays a theoretical foundation for the design of fruit and vegetable heat balance regulation and packaging materials.

[0004] The existing fruit and vegetable preservation technology has the following deficiencies:

[0005] 1. Traditional packaging model: only single heat conduction or convection mechanism is considered, and the dynamic coupling effect of respiratory heat and radiation cooling is not integrated, resulting in a temperature prediction error of more than ±5℃.

[0006] 2. Isolated optimization of material parameters: the solar reflectivity and infrared emissivity of packaging materials are usually designed separately, and there is a lack of synergistic regulation theory.

[0007] 3. Lack of adaptability: no dynamic response model is established for the differences in respiration rates of different fruit and vegetable varieties (such as strawberries and leafy vegetables). SUMMARY

[0008] The purpose of the present application is to overcome the deficiencies in the prior art and provide a construction method and application of a dynamic heat balance model for low-temperature regulation on the surface of fruits and vegetables.

[0009] The technical solution adopted by the present application to solve its technical problems is:

[0010] A dynamic heat balance model for low-temperature regulation of fruit and vegetable surfaces, the model comprising a three-level coupled heat balance model, the model comprising a packaging outer surface heat balance model, a packaging inner surface heat balance model and a fruit and vegetable surface heat balance model, specifically as follows:

[0011] First level: packaging outer surface heat balance model

[0012] The packaging outer surface heat balance model can represent the heat exchange between the packaging outer surface and the environment: the packaging outer surface dissipates heat through radiation and convection, absorbs radiant heat from the sun and atmospheric radiation, and at the same time conducts heat inward through the packaging material;

[0013] Second level: packaging inner surface heat balance model

[0014] The packaging inner surface heat balance model can represent the heat transfer between the packaging inner surface and the internal space: the packaging inner surface dissipates heat through radiation, receives heat conducted from the packaging outer surface, and at the same time forms a dynamic balance with the radiant heat of the fruit and vegetable surface;

[0015] Third level: fruit and vegetable surface heat balance model

[0016] The fruit and vegetable surface heat balance model can represent the heat generation and dissipation of the fruit and vegetable itself: the fruit and vegetable generates heat through respiration, at the same time absorbs radiant heat from the packaging inner surface and transmitted solar radiation heat, and finally reaches balance through surface radiation heat dissipation;

[0017] The three-level coupled heat balance model does not operate independently, but is closely related through heat transfer and feedback mechanism; the three-level balance model works simultaneously in actual application, without sequence. For example: when the outer surface is heated by solar radiation (first level), heat is simultaneously transferred through conduction to affect the inner surface (second level), and then change the temperature of the fruit and vegetable surface (third level); a sudden change in fruit and vegetable respiration heat (third level) will be fed back to the inner surface (second level) through radiation, and finally affect the heat dissipation efficiency of the outer surface (first level).

[0018] Further, the fruit and vegetable respiration heat is calculated by the following method:

[0019] First, determine the basic respiration rate of the fruit and vegetable at the reference temperature, according to the difference between the actual temperature of the fruit and vegetable and the reference temperature, the volume and weight of the fruit and vegetable, and the temperature sensitivity coefficient of the respiration rate, calculate the dynamic respiration rate at the current temperature.

[0020] The dynamic heat balance model as described above is applied in the design of fruit and vegetable packaging materials at different storage temperatures.

[0021] The dynamic heat balance model as described above is applied in the establishment of a low-temperature area on the surface of fruit and vegetable to achieve the effect of radiation refrigeration.

[0022] Application of the dynamic heat balance model as described above to analyze the following variable conditions in the logistics transportation and / or storage preservation of fruits and vegetables: storage environment difference and / or fruit and vegetable property difference and / or fruit and vegetable weight difference.

[0023] Further, the fruit and vegetable property difference includes variety, maturity.

[0024] The construction method of the surface low-temperature area refrigeration effect using the dynamic heat balance model as described above comprises the following steps:

[0025] The heat transfer mechanism model is analyzed, the spectral reflectivity of the packaging material in the solar wave band 0.4-2.5 μm is greater than or equal to 0.9, and the infrared emissivity in the atmospheric window wave band 8-13 μm is greater than or equal to 0.9, the thermal conductivity coefficient is selected to be less than or equal to 0.04 W / (m·K), the thickness is 200-500 μm, the fruit surface temperature Fruit temperature is taken as the target constraint condition, the low-temperature area is established on the fruit surface, and the fruit surface temperature can be lower than the ambient temperature by 10 DEG C.

[0026] Application of the construction method as described above in the logistics transportation and storage preservation of fruits and vegetables.

[0027] The advantages and positive effects obtained by the present application are:

[0028] 1. The present application proposes to build a heat balance model based on the physiological metabolism change of fruits and vegetables, to establish an environment-packaging-fruit and vegetable coordinated regulation network through layered heat balance equations, and to ultimately realize the target of the fruit and vegetable surface temperature being lower than the ambient temperature by 10 DEG C or more. Figure 2 、 Figure 3 Optimal parameters are selected (the reflectivity of the packaging material in the solar wave band is greater than or equal to 0.9, the emissivity in the atmospheric window wave band (8-13 μm) is greater than or equal to 0.9, the thermal conductivity coefficient is less than or equal to 0.3 W / m·K, and the thickness is determined to be 200-500 μm.), the spectral parameters of the packaging material are regulated through modeling, the fruit and vegetable surface temperature is lower than the ambient temperature through the heat balance model, a low-temperature area is established on the fruit and vegetable surface, the reflectivity and emissivity of the material are regulated, the fruit and vegetable surface temperature is lower than the ambient temperature through the heat balance model, and the radiation refrigeration effect is realized. The development of this modeling technology will provide a new idea and method for fruit and vegetable preservation, and further promote the development of the fruit and vegetable logistics industry.

[0029] 2. This invention constructs a dynamic thermal balance model for low-temperature regulation of fruit and vegetable surfaces based on the second law of thermodynamics. Using the lowest possible surface temperature as the target condition, the thermodynamic model is established. A three-tiered thermal balance system enables precise regulation of fruit and vegetable surface temperature, integrating three mechanisms: radiative cooling, dynamic coupling of respiration and heat, and optimization of packaging material parameters. This solves the problems of large temperature fluctuations and high energy consumption in traditional preservation technologies. Its core is the establishment of a synergistic regulation network between the environment, packaging, and fruits and vegetables through a layered thermal balance equation, ultimately achieving the goal of keeping the fruit and vegetable surface temperature at least 10°C lower than the ambient temperature.

[0030] 3. This invention can precisely control the temperature inside the packaging. By optimizing the thermal conductivity of the packaging material, the design of the air gap layer, and the coating to control heat radiation, it can precisely control the temperature balance inside and outside the packaging, effectively reducing the impact of temperature fluctuations on the quality of fruits and vegetables.

[0031] 4. This invention can extend the shelf life of fruits and vegetables: This model optimizes the heat transfer mechanism, reduces the respiration rate of fruits and vegetables, and reduces the heat generated by respiration, thereby delaying the ripening and freshness deterioration process of fruits and vegetables and significantly extending their shelf life.

[0032] 5. This invention can improve the adaptability of packaging materials: based on the actual storage temperature and the differences in fruit and vegetable varieties and quality, the optimal packaging material with the best spectral characteristics and thermal conductivity can be selected by substituting into the theoretical equation.

[0033] 6. The model of this invention has a wide range of applications. It is not only suitable for the preservation of fruits and vegetables, but can also be extended to the preservation of other agricultural products, cold chain logistics, and warehouse management, demonstrating broad application prospects.

[0034] 7. This invention provides a new method for constructing a heat balance model, which can accurately simulate and analyze the heat transfer and conversion between the external environment and the internal temperature of fruits and vegetables. It has high accuracy and practicality and is an innovation in heat balance models.

[0035] 8. This invention constructs a new equation for the surface low-temperature region based on the radiation cooling effect. Figure 2 The fruit and vegetable surface temperature is lower than the storage environment temperature. As shown in the figure, the solid line is below the dashed line. This can effectively create a low-temperature zone on the surface of fruits and vegetables, improve the thermal management efficiency of packaging, and has significant innovation.

[0036] 9. The present invention solves the following problems:

[0037] (1) Establish a dynamic preservation control mechanism based on mathematical models to avoid excessively high surface temperatures of fruits and vegetables;

[0038] (2) Explore the relationship between the thermal conductivity of the packaging material, the spectral characteristics and the heat balance equation;

[0039] (3) Analyze the efficiency of heat transfer in the logistics environment (such as cold chain transportation).

[0040] 10、The present application optimizes the design of fruit and vegetable packaging materials and improves the respiratory heat management capability; the present application constructs a fruit and vegetable packaging heat balance simulation model to provide guidance for designing fruit and vegetable packaging materials; and the present application provides a mathematical equation basis for establishing a low-temperature area on the surface of fruits and vegetables in the logistics process.

[0041] 11、The present application constructs a dynamic heat balance model for low-temperature regulation of the surface of fruits and vegetables based on the second law of thermodynamics, establishes a thermodynamic model by taking the lowest fruit and vegetable surface temperature as the target condition, optimizes the thermal conductivity of the packaging material, the design of the air gap layer and the control of the thermal radiation of the coating, and can control the temperature balance inside and outside the packaging. This theoretical framework provides a quantitative basis for the development of precise temperature control strategies in the logistics process of agricultural products, and significantly reduces the impact of temperature fluctuations on the quality of fruits and vegetables. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a heat transfer mechanism model analysis and steady-state heat transfer model in the present application; the upward arrow of the two blue arrows is marked on the right side of the arrow, i.e. qcond, and the rest of the upward arrows are marked near the top of the arrow, and the downward arrows are marked near the bottom of the arrow;

[0043] Figure 2 It is a graph of the reflectivity (r) of the packaging material regulating the temperature of the fruit and vegetable surface in the present application;

[0044] Figure 3 It is a graph of the emissivity (ε) of the packaging material regulating the temperature of the fruit and vegetable surface in the present application;

[0045] Figure 4 It is a graph of the emissivity of the packaging material regulating the heat compensation coefficient in the present application;

[0046] Figure 5 It is a graph of the actual application scenario in the fruit and vegetable logistics process in the present application. DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with the embodiments, which are descriptive and not limiting, and cannot limit the protection scope of the present application by the following embodiments.

[0048] The various experimental operations involved in the embodiments are conventional techniques in the art, and the parts not specifically noted herein can be implemented by referring to various commonly used tool books, scientific and technical literature or related instructions, manuals, etc. before the filing date of the present application.

[0049] The dynamic thermal balance model for low-temperature regulation of fruit and vegetable surfaces realizes accurate regulation of the surface temperature of fruits and vegetables through a three-level thermal balance system, integrates three mechanisms of radiation refrigeration, dynamic coupling of respiratory heat, and optimization of packaging material parameters, and solves the problems of large temperature fluctuations and high energy consumption in traditional preservation technology. The core is to establish a coordinated regulation network of environment-packaging-fruit and vegetable through a layered thermal balance equation, ultimately achieve the goal of fruit and vegetable surface temperature being more than 10℃ lower than the ambient temperature, realize innovation breakthrough through multi-physical field coupling (thermal radiation-conduction-physiological metabolism), and establish a three-level physical coupling thermal balance model, which provides a quantifiable and reusable theoretical framework for fruit and vegetable preservation.

[0050] A dynamic thermal balance model for low-temperature regulation of fruit and vegetable surfaces, the model includes a three-level coupled thermal balance model, which includes a packaging outer surface thermal balance model, a packaging inner surface thermal balance model, and a fruit and vegetable surface thermal balance model, specifically as follows:

[0051] First level: packaging outer surface thermal balance model

[0052] The packaging outer surface thermal balance model can represent the heat exchange between the outer surface of the packaging and the environment: the outer surface of the packaging dissipates heat through radiation and convection, absorbs radiation heat from the sun and atmospheric radiation heat, and at the same time conducts heat inward through the packaging material;

[0053] Second level: packaging inner surface thermal balance model

[0054] The packaging inner surface thermal balance model can represent the heat transfer between the inner surface of the packaging and the internal space: the inner surface of the packaging dissipates heat through radiation, receives heat conducted from the outer surface of the packaging, and at the same time forms a dynamic balance with the radiation heat of the fruit and vegetable surface;

[0055] Third level: fruit and vegetable surface thermal balance model

[0056] The fruit and vegetable surface thermal balance model can represent the heat generation and dissipation of the fruit and vegetable itself: the fruit and vegetable generates heat through respiration, absorbs radiation heat from the inner surface of the packaging and transmitted solar radiation heat, and finally reaches balance through surface radiation heat dissipation;

[0057] The three-stage coupling heat balance model does not work independently, but is closely related through heat transfer and feedback mechanism; the three-stage balance model works simultaneously in practical application, without sequence. For example: when the solar radiation heats the outer surface (first stage), the heat synchronously affects the inner surface (second stage) through conduction, and then changes the surface temperature of fruits and vegetables (third stage); the respiratory heat mutation of fruits and vegetables (third stage) will be fed back to the inner surface (second stage) through radiation, and finally affect the heat dissipation efficiency of the outer surface (first stage).

[0058] The dynamic heat balance model described above realizes the calculation of respiratory heat of fruits and vegetables by the following method:

[0059] First, the basic respiration rate of fruits and vegetables at the reference temperature is determined, and the dynamic respiration rate at the current temperature is calculated according to the difference between the actual temperature and the reference temperature of fruits and vegetables, the volume and weight of fruits and vegetables, and the temperature sensitivity coefficient of respiration rate.

[0060] The dynamic heat balance model of the above-mentioned low-temperature regulation of fruit and vegetable surface is as follows:

[0061] The coupling relationship of the first equation reflects the environmental interaction property, and the thermodynamic equilibrium (T out ) of the outer surface of the package:

[0062] q emi，out +q conv，out =ε out，ir ·q atm +q cond +ε sun ·q sun ;

[0063] Wherein, q emi，out represents the radiation heat flux emitted by the outer surface of the fruit and vegetable package, with the unit of W / m 2 ; q conv，out represents the convective heat transfer flux between the outer surface of the fruit and vegetable package and the environment, with the unit of W / m 2 ; ε out，ir represents the infrared emissivity of the outer surface of the fruit and vegetable package, with the unit of 1; q atm represents the atmospheric radiation heat flux, with the unit of W / m 2 ; q cond represents the conduction heat flux from the inside to the outside of the fruit and vegetable package, with the unit of W / m 2 ; ε sun represents the absorption rate of the fruit and vegetable packaging material to solar radiation, with the unit of 1; q sun represents the solar radiation heat flux, with the unit of W / m 2 ;

[0064] The coupling relationship of the second equation reflects the heat conduction of the fruit and vegetable package, and the thermodynamic equilibrium (T in ) of the inner surface of the package:

[0065] q emi，in+ q cond = ε in，ir · q emi，fruit ;

[0066] wherein q emi，in represents the radiative heat flux emitted from the inner surface of the fruit and vegetable package, with the unit of W / m 2 ; q cond represents the conductive heat flux from the inside of the fruit and vegetable package to the outside, with the unit of W / m 2 ; ε in，ir represents the infrared emissivity of the inner surface of the fruit and vegetable package, with the unit of 1; q emi，fruit represents the radiative heat flux generated by the fruit and vegetable, with the unit of W / m 2 ;

[0067] The coupling relationship of the third-order equation reflects the physiological heat generation of the fruit and vegetable and the thermodynamic equilibrium (T fruit ) of the surface of the fruit and vegetable:

[0068] ρ p ackage，ir · q atm + τ package，sun · q sun + q resp + q emi，in = ρ emi，in · q emi，fruit ;

[0069] wherein ρ ackage，ir represents the reflectivity of the packaging material to the thermal radiation emitted by the fruit and vegetable, with the unit of 1; q atm represents the atmospheric radiative heat flux, with the unit of W / m 2 ; τ package，sun represents the transmittance of the fruit and vegetable packaging material to visible light, with the unit of 1; q sun represents the solar radiative heat flux, with the unit of W / m 2 ; q resp represents the heat generated by the respiration of the fruit and vegetable, with the unit of W / m 2 ; q emi，in represents the radiative heat flux emitted from the inner surface of the fruit and vegetable package, with the unit of W / m 2 ; ρ emi，in represents the reflectivity of the inner surface of the packaging material to the thermal radiation of the fruit and vegetable, with the unit of 1; q emi，fruit represents the radiative heat flux generated by the fruit and vegetable, with the unit of W / m 2 ;

[0070] wherein the calculation formula of each radiative heat flux is as follows (the radiative heat flux indicates the thermal equilibrium of the outer surface of the package and the inner surface of the package, corresponds to the coupling relationship of the first-order equation, reflects the environmental interaction attribute, and further quantifies the heat dissipation capacity of the interlayer):

[0071]

[0072] T out , T in and T fruit represent the temperature of the outer surface of the fruit and vegetable packaging, the inner surface of the fruit and vegetable packaging, and the fruit and vegetable, respectively, in K; ε out，ir , ε in，ir represent the infrared emissivity of the outer surface and the inner surface of the fruit and vegetable packaging, respectively, in 1; the Stefan-Boltzmann constant σ is expressed as σ = 5.67 x 10 -8 W / (m 2 ·K 4 );

[0073] wherein the calculation formula of q atm is as follows (a dynamic respiration heat model explains the surface heat balance of the fruit and vegetable, corresponds to the coupling relationship of the three-level equation, and provides a physiological heat source):

[0074]

[0075] T amb represents the ambient temperature, in K; dθ and dλ represent the angle integral of the solar radiation direction and the outer normal direction and the integral of the solar wavelength, respectively, both in 1; θ represents the angle integral of the solar radiation direction and the outer normal direction, in 1; I BB represents the blackbody emissivity, in 1; λ represents the solar wavelength, in nm; τ atm represents the atmospheric transmittance, in 1;

[0076] wherein the calculation formula of q sun is as follows:

[0077]

[0078] θ sun represents the angle between the incident solar radiation direction and the outer normal direction, in K; I AM1.5G represents the actual spectral distribution of sunlight on the earth's surface, in W / m 2 ; λ represents the solar wavelength, in nm; dλ represents the integral of the solar wavelength, in 1;

[0079] wherein the calculation formula of q resp is as follows:

[0080]

[0081] S represents the area of the refrigeration material, in m 2 ; M fruitMass of fruits and vegetables, unit: kg; H heat Coefficient of heat released by respiration under the reference condition, expressed by CO2 release, unit: J / mg;

[0082] R resp Respiration rate at a specific temperature of 0-40℃, expressed by CO2 release per unit time, unit: mg / (kg*h) (i.e. mass of CO2 produced per unit mass of fruits and vegetables per unit time); R resp The calculation formula is as follows: R0Respiration rate under the reference condition, expressed by CO2 release per unit time, unit: mg / (kg*h) (i.e. mass of CO2 produced per unit mass of fruits and vegetables per unit time); Q 10 Temperature increase of 10K, unit: 1; T fruit Temperature of fruits and vegetables, unit: K;

[0083] Wherein, q cond , q conv，out The calculation formula is as follows (the characteristics of the packaging material indicate heat transfer between packages, which determines the heat transfer efficiency. The coupling relationship corresponds to the second-order equation):

[0084]

[0085] q conv，out = h out ·(T fruit -T in )

[0086] T out , T in and T fruit represent the temperature of the outer surface of the fruits and vegetables packaging, the temperature of the inner surface of the fruits and vegetables packaging, and the temperature of the fruits and vegetables, respectively, unit: K; h out represent the convective heat transfer coefficient of the outer surface of the fruits and vegetables packaging, unit: W / (m 2 ·K); k package indicates the thermal conductivity of the fruits and vegetables packaging material, unit: 1; t package represents the thickness of the fruits and vegetables packaging material, unit: m;

[0087] The construction method of the surface low-temperature area refrigeration effect of the dynamic heat balance model as described above comprises the following steps:

[0088] The heat transfer mechanism model is analyzed, the spectral reflectivity of the packaging material in the solar wave band (0.4-2.5 μm) is greater than or equal to 0.9, and the infrared emissivity in the atmospheric window wave band (8-13 μm) is greater than or equal to 0.9, the thermal conductivity of the selected packaging material is less than or equal to 0.03 W / (m·K), the thickness is 200-500 μm, and the fruit surface temperature Fruit temperature is the lowest as the target constraint condition, and a low-temperature area is established on the fruit surface, so that the fruit surface temperature can be lower than the ambient temperature by 10 DEG C.

[0089] Related discussion on heat transfer mechanism:

[0090] - Convective heat transfer: convective heat transfer between the gas inside and outside the package, and the heat transfer efficiency is adjusted through the air gap layer design.

[0091] - Conduction heat transfer: optimization of the thermal conductivity of the material itself, and selection of a composite material with low thermal conductivity.

[0092] - Radiative heat transfer: in the process of radiative heat transfer, the radiative properties of the fruit and the surface of the packaging material are mainly determined by their emissivity and reflectivity.

[0093] The related heat transfer mechanism model analysis and steady-state heat transfer model are shown in Figure 1 The present application is based on the theory of multi-physical field coupling to construct a steady-state heat transfer model for analyzing the heat transfer characteristics of the fruit and vegetable packaging system. As shown in Figure 1 The model uses a layered structure to describe the thermal boundary conditions, and can be divided into four layers according to the heat transfer path: the environment layer (Environment), the composite packaging layer (Fruit Package), the air gap layer (Air Gap), and the fruit surface layer (Fruit Surface). Each layer realizes energy transport through different heat transfer mechanisms. At the interface between the environment layer and the packaging layer, thermal radiation and convective heat transfer constitute the main heat transfer path; the heat conduction within the packaging constitutes the main heat transfer path; and the heat radiation and convective heat transfer at the surface of the packaging and the fruit constitute the main heat transfer path. The research results can provide a theoretical basis for optimizing the thermal physical parameters and structure design of fruit and vegetable packaging materials.

[0094] Example 1

[0095] The modeling experiment parameter setting is specifically that the initial temperature of the fruit surface is set to 0 DEG C, the experimental simulation time interval is 10 ms, the thickness of the packaging material is set to 10 mm, and the emissivity of the material is set to 1. For packaging materials with different visible light reflectivity, the reflectivity of the fruit and vegetable packaging material is selected as 0.6, 0.7, 0.8, 0.9, 1.0, and the heat transfer mechanism inside and outside the fruit and vegetable packaging is simulated. The experimental data is loaded in the form of a file, and the dynamic relationship between the ambient temperature and the fruit temperature is recorded. The ambient temperature is controlled at 0-40 DEG C, and the fruit temperature change curve is used to analyze the influence of the spectral characteristics of the packaging material on the preservation effect.

[0096] The use effect of the model, the experimental simulation results are as shown in Figure 2 The curves of different solar radiation intensities show the trend of dynamic adjustment of fruit and vegetable temperature, and the gray dotted line represents the ambient temperature reference curve as a comparison reference. The simulation results show that when the reflectivity of the packaging material is high, the fruit and vegetable surface temperature is more likely to approach the ambient temperature. When the reflectivity of the packaging material is 1.0, the fruit and vegetable surface temperature is always 10°C lower than the ambient temperature. It is analyzed that the packaging material realizes fruit and vegetable surface cooling through radiation refrigeration effect. When the reflectivity of the packaging material is 0.9, when the ambient temperature is less than 9°C, the fruit and vegetable surface temperature is higher than the ambient temperature, and the respiratory heat generated by the fruit and vegetable is higher than the radiation heat emitted by the outer surface of the packaging material; when the ambient temperature is greater than 9°C, the fruit and vegetable surface temperature is less than the ambient temperature, and the respiratory heat generated by the fruit and vegetable is lower than the radiation heat emitted by the outer surface of the packaging material; when the ambient temperature is 9°C, the respiratory heat generated by the fruit and vegetable is equal to the radiation heat emitted by the outer surface of the packaging material, so there is no temperature difference. By adjusting the reflectivity and thermal conductivity of the material, suitable packaging materials can be designed for different environmental conditions. Lower radiation intensity is suitable for cold chain preservation, and under higher radiation intensity, insulation effect can be achieved by increasing the reflectivity of the material. The method provides a fruit and vegetable temperature optimization scheme based on solar radiation intensity regulation, which is suitable for various logistics scenes. According to the optimal storage temperature of different fruits and vegetables, packaging materials with corresponding spectral characteristics can be selected.

[0097] Example 2

[0098] The modeling experimental parameters are set as follows: the initial temperature of the fruit and vegetable surface is set to 0°C, the experimental simulation time interval is 10 m / s, the thickness of the packaging material is set to 10 mm, and the solar waveband reflectivity is 1. For packaging materials with different near-infrared radiation rates, the emissivity of the fruit and vegetable packaging material is selected as 0.6, 0.7, 0.8, 0.9, and 1.0, and the heat transfer mechanism inside and outside the fruit and vegetable packaging is simulated and displayed. The experimental data are loaded in the form of a file, which records the dynamic relationship between the ambient temperature and the fruit and vegetable temperature. The ambient temperature is controlled at 0-40°C, and the fruit and vegetable temperature change curve is used to analyze the influence of the spectral characteristics of the packaging material on its preservation effect. The experimental data are loaded in the form of a file, which records the dynamic change relationship between the ambient temperature and the fruit and vegetable temperature. The ambient temperature ranges from zero Celsius, and the output result is the fruit and vegetable temperature change curve under different radiation rate materials, which is used to analyze the regulation ability of the material to heat transfer.

[0099] The experimental simulation results are as shown in Figure 3As shown in FIG. 6, when the solar waveband reflectivity of the packaging material reaches 1.0, the surface temperature of the fruits and vegetables is always lower than the ambient temperature by more than 5°C. By analyzing the reflectivity of the packaging material, it can be found that when the reflectivity is equal to 1.0, the material can completely reflect the energy of the visible light part, thereby avoiding the temperature rise caused by absorbing visible light energy. In addition, the packaging material can also emit a part of the energy to the external environment in the form of infrared radiation, so as to achieve the cooling effect. Under the same temperature conditions, the cooling amplitude is in a positive relationship with the emissivity of the packaging material, that is, the higher the emissivity, the more significant the cooling effect. By adjusting the near-infrared radiation rate, the material thickness, and the time interval, the thermal equilibrium optimization design can be realized for different logistics environments. High-radiation-rate materials are suitable for cold-chain transportation and can reduce heat accumulation; low-radiation-rate materials are suitable for heat preservation transportation and help maintain the appropriate temperature of fruits and vegetables. The method provides a precise and efficient solution for the design of fruit and vegetable preservation packaging and is suitable for various transportation, storage, and sales scenarios.

[0100] Example 3

[0101] The modeling experiment parameters are set as follows: the initial temperature of the fruit and vegetable surface is set to 0°C, the experiment time interval is 1 ms, and the packaging material thickness is 10 mm. For packaging materials with different near-infrared radiation rates, the emissivity of the fruit and vegetable packaging material is selected as 0, 0.6, and 1, and the thermal compensation capacity (expressed in terms of unit area of thermal compensation power) of the fruits and vegetables under different radiation rate materials is simulated. The dynamic relationship between the ambient temperature and the thermal compensation capacity is recorded by Matlab. The ambient temperature starts from 0°C, and the thermal compensation capacity curve is used to evaluate the influence of different radiation rates on thermal energy management.

[0102] The experimental results are shown in FIG. 7. Figure 4 As the emissivity of the packaging material increases, the thermal compensation capacity of the fruits and vegetables significantly increases, which indicates that the stronger the theoretical refrigeration power of the material, the greater the possibility of establishing a low-temperature region on the surface of the fruits and vegetables. This theoretical modeling provides an important theoretical basis for optimizing the thermal management performance of the packaging material and helps to further improve the preservation effect of fruits and vegetables and the management efficiency of cold-chain logistics.

[0103] Example 4 - Actual application scenario construction

[0104] The thermal equilibrium model has a wide range of applications in many actual scenarios, especially in the logistics transportation and storage processes of perishable agricultural products. Taking fruit and vegetable packaging as an example, as shown in FIG. 8, Figure 5As shown, the model can effectively simulate and analyze the heat transfer and conversion between the external environment (such as air temperature, sunlight radiation, etc.) and the internal temperature of fruits and vegetables. In this process, the model can evaluate the relationship between the heat generated by the respiration of fruits and vegetables (Tfruit) and the external environment temperature (Tamb), the internal temperature of the package (Tin), and the external temperature of the package (Tout). The model can also design appropriate packaging materials according to different qualities and respiratory heat of fruits and vegetables, optimize heat management strategies, and maintain fruits and vegetables in the best preservation state during transportation and storage, thereby reducing the loss of fruits and vegetables. This application is not only suitable for fruits and vegetables, but can also be extended to the preservation of other perishable foods, cold chain logistics, and warehouse management, etc. fields, to improve the overall food safety and quality.

[0105] Although the embodiments of the present application are disclosed for illustrative purposes, those skilled in the art can understand that various alternatives, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, therefore, the scope of the present application is not limited to the disclosed content of the embodiments.

Claims

1. A method for constructing a dynamic thermal equilibrium model for low-temperature regulation of fruit and vegetable surfaces, characterized in that: The model includes a three-level coupled thermal equilibrium model, which comprises a thermal equilibrium model for the outer surface of the packaging, a thermal equilibrium model for the inner surface of the packaging, and a thermal equilibrium model for the surface of fruits and vegetables, as detailed below: Level 1: Thermal equilibrium model of the outer surface of packaging The thermal balance model of the outer surface of packaging can characterize the heat exchange between the outer surface of packaging and the environment: the outer surface of packaging absorbs radiative heat from the sun and atmospheric radiation through radiative and convective heat dissipation, while conducting heat inward through the packaging material; Level 2: Thermal equilibrium model of the inner surface of the packaging The thermal balance model of the inner surface of the packaging can characterize the heat transfer between the inner surface of the packaging and the internal space: the inner surface of the packaging dissipates heat through radiation and receives heat conducted in from the outer surface of the packaging, while forming a dynamic balance with the radiative heat of the fruit and vegetable surface. Level 3: Fruit and Vegetable Surface Thermal Balance Model The surface heat balance model of fruits and vegetables can characterize the heat generation and dissipation of fruits and vegetables: fruits and vegetables generate heat through respiration, and at the same time absorb radiant heat from the inner surface of the packaging and radiant solar heat transmitted in, and finally achieve balance through surface radiative heat dissipation. The three-level coupled thermal equilibrium model does not operate independently, but is closely linked through heat transfer and feedback mechanisms; the three-level equilibrium models work simultaneously in practical applications without any order of operation. The coupling relationship of the first-order equations reflects the environmental interaction properties; the thermal equilibrium model of the outer surface of the packaging: ； in, This represents the radiant heat flux emitted from the outer surface of fruit and vegetable packaging, expressed in W / m². This represents the convective heat flux between the outer surface of fruit and vegetable packaging and the environment, expressed in W / m². Infrared emissivity of the outer surface of fruit and vegetable packaging, expressed in units of 1; This represents atmospheric radiative heat flux, with units of W / m². This represents the heat flux conducted from the inside to the outside of fruit and vegetable packaging, expressed in W / m². This indicates the absorption rate of solar radiation by fruit and vegetable packaging materials, expressed in units of 1. This represents solar radiative heat flux, expressed in W / m². The coupling relationship of the second-order equations reflects the heat conduction in fruit and vegetable packaging, and the heat balance model of the inner surface of the packaging: ； in, This indicates the radiant heat flux emitted from the inner surface of fruit and vegetable packaging, expressed in W / m². This represents the heat flux conducted from the inside to the outside of fruit and vegetable packaging, expressed in W / m². Infrared emissivity of the inner surface of fruit and vegetable packaging, expressed in units of 1; This represents the radiant heat flux generated by fruits and vegetables, expressed in W / m². The coupling relationship of the third-order equations reflects the physiological heat production of fruits and vegetables, and the thermodynamic equilibrium of the fruit and vegetable surface: ； in, The reflectivity of the packaging material to the heat radiation emitted by fruits and vegetables is expressed in units of 1. This represents atmospheric radiative heat flux, with units of W / m². The unit represents the transmittance of visible light to fruit and vegetable packaging materials, expressed in units of 1. This represents solar radiative heat flux, expressed in W / m². This represents the heat generated by the respiration of fruits and vegetables, expressed in W / m². This indicates the radiant heat flux emitted from the inner surface of fruit and vegetable packaging, expressed in W / m². The reflectivity of the inner surface of the packaging material to the heat radiation from fruits and vegetables is expressed in units of 1. This represents the radiative heat flux generated by fruits and vegetables, expressed in W / m².

2. The method for constructing a dynamic thermal equilibrium model according to claim 1, characterized in that: The respiratory heat of fruits and vegetables can be calculated using the following method: First, determine the baseline respiration rate of fruits and vegetables at the reference temperature. Then, based on the difference between the actual temperature of the fruits and vegetables and the reference temperature, the volume and weight of the fruits and vegetables, and the temperature sensitivity coefficient of the respiration rate, calculate the dynamic respiration rate at the current temperature.

3. The application of the method for constructing the dynamic thermal balance model as described in claim 1 or 2 in guiding the design of fruit and vegetable packaging materials at different storage temperatures.

4. The method for constructing the dynamic thermal balance model as described in claim 1 or 2 is applied to establish a low-temperature region on the surface of fruits and vegetables to achieve radiative cooling effect.

5. The application of the method for constructing the dynamic thermal balance model as described in claim 1 or 2 in analyzing the following variables in logistics transportation and / or storage and preservation: differences in storage environment and / or differences in fruit and vegetable characteristics and / or differences in fruit and vegetable weight.

6. The application according to claim 5, characterized in that: The differences in fruit and vegetable characteristics include variety and maturity.

7. A method for constructing the surface low-temperature region cooling effect using the dynamic thermal equilibrium model construction method as described in claim 1 or 2, characterized in that: Includes the following steps: The heat transfer mechanism model was analyzed. The packaging material had a spectral reflectance ≥0.9 in the solar band (0.4-2.5μm) and an infrared emissivity ≥0.9 in the atmospheric window band (8-13μm). A thermal conductivity ≤0.04W / (m·K) and a thickness of 200-500μm were selected. The goal was to minimize the fruit and vegetable surface temperature. A low-temperature region was established on the fruit and vegetable surface to achieve a surface temperature 10℃ lower than the ambient temperature.

8. The application of the method for constructing the surface low-temperature zone cooling effect as described in claim 7 in the logistics transportation and storage preservation of fruits and vegetables.

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