Dynamic heat balance model for fruit and vegetable surface low-temperature regulation and control, construction method and application

Abstract

The invention belongs to the technical field of food preservation, new materials and electronic information, and discloses a dynamic heat balance model for fruit and vegetable surface low-temperature regulation, a construction method and application, the model comprises a three-stage coupling heat balance model, and the model comprises a package outer surface heat balance model, a package inner surface heat balance model and a fruit and vegetable surface heat balance model. A dynamic heat balance model for fruit and vegetable surface low-temperature regulation and control is built based on the second law of thermodynamics, a thermodynamic model is built with the lowest fruit and vegetable surface temperature as the target condition, and precise regulation and control of the fruit and vegetable surface temperature are achieved through a three-stage heat balance system. The three mechanisms of radiation refrigeration, breathing heat dynamic coupling and packaging material parameter optimization are integrated, and the problems of large temperature fluctuation and high energy consumption in a traditional preservation technology are solved. The core of the method is to establish an environment-package-fruit and vegetable coordinated regulation network through a layered heat balance equation, and finally the purpose that the surface temperature of fruits and vegetables is 10 DEG C or above lower than the environment temperature is achieved.

Description

Technical Field

[0001] The present invention belongs to the fields of food preservation, new materials and electronic information technology, and in particular to a dynamic thermal balance model for low-temperature regulation of the surface of fruits and vegetables, a construction method and an application thereof. Background Art

[0002] During the logistics, transportation, and storage of fruits and vegetables, environmental factors such as temperature, humidity, and gas composition have a significant impact on their preservation. Temperature is a key factor influencing fruit and vegetable preservation. Low temperatures not only delay their decay but also preserve their color, flavor, and nutritional value. Low temperatures effectively slow their metabolic activity, extending their shelf life. However, drastic temperature fluctuations and improper temperature control can increase the respiration rate of fruits and vegetables, accelerating their maturation and aging process and shortening their shelf life.

[0003] During the logistics and transportation process, fruits and vegetables will respire and generate respiratory heat, which is a major factor affecting the shelf life of fruits and vegetables. If the heat generated during the respiration process is not transferred or dissipated in time, the increase in local temperature will directly lead to a decline in the quality of fruits and vegetables. Currently, there have been many studies on environmental temperature control of fruit and vegetable packaging materials, but there is still insufficient attention paid to respiratory heat management and thermal balance regulation. At present, there are relatively few modeling studies on heat transfer mechanisms in fruit and vegetable logistics and preservation. As a result, in practical applications, fruit and vegetable packaging solutions fail to fully consider heat regulation and management. The analysis of the heat transfer mechanism of fruits and vegetables lays a theoretical foundation for the thermal balance regulation of fruits and vegetables and the design of packaging materials.

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

[0005] 1. Traditional packaging model: Only considers a single heat conduction or convection mechanism, and does not integrate the dynamic coupling effect of respiratory heat and radiative cooling, resulting in a temperature prediction error of more than ±5°C.

[0006] 2. Isolated optimization of material parameters: The solar reflectivity and infrared emissivity of packaging materials are usually designed separately, lacking a theory of coordinated regulation.

[0007] 3. Insufficient adaptability: A dynamic response model has not been established for the differences in respiratory rates between different fruit and vegetable varieties (such as strawberries and leafy vegetables). Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a dynamic thermal balance model for low-temperature regulation of fruit and vegetable surfaces, a construction method and applications.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] A dynamic thermal balance model for low-temperature regulation of fruit and vegetable surfaces 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. The specific details are as follows:

[0011] Level 1: Package outer surface thermal balance model

[0012] The package outer surface heat balance model can characterize the heat exchange between the package outer surface and the environment: the package outer surface dissipates heat through radiation and convection, absorbing radiation heat from the sun and the atmosphere, while conducting heat inward through the packaging material;

[0013] Level 2: Thermal balance model of the inner surface of the package

[0014] The package inner surface thermal balance model can characterize the heat transfer between the package inner surface and the internal space: the package inner surface dissipates heat through radiation and receives heat conducted from the package outer surface, while forming a dynamic balance with the radiant heat from the fruit and vegetable surface.

[0015] Level 3: Fruit and vegetable surface thermal balance model

[0016] The fruit and vegetable surface heat balance model can characterize the heat generation and loss of the fruit and vegetable itself: the fruit and vegetable generates heat through respiration, while absorbing radiant heat from the inner surface of the packaging and transmitted solar radiation, ultimately achieving a balance through surface radiation heat dissipation.

[0017] The three-level coupled thermal balance model does not operate independently; rather, it is closely linked through heat transfer and feedback mechanisms. In practice, the three-level balance model operates simultaneously, with no order of precedence. For example, when solar radiation heats the outer surface (level 1), heat simultaneously affects the inner surface (level 2) through conduction, thereby changing the surface temperature of fruits and vegetables (level 3). A sudden change in the respiratory heat of fruits and vegetables (level 3) can be fed back to the inner surface (level 2) through radiation, ultimately affecting the heat dissipation efficiency of the outer surface (level 1).

[0018] Furthermore, the respiratory heat calculation of fruits and vegetables is achieved by the following method:

[0019] First, determine the basic respiration rate of fruits and vegetables at the reference temperature. Then, calculate the dynamic respiration rate at the current temperature based on the difference between the actual temperature of fruits and vegetables and the reference temperature, the volume and weight of fruits and vegetables, and the temperature sensitivity coefficient of the respiration rate.

[0020] The application of the dynamic thermal balance model described above in guiding the design of fruit and vegetable packaging materials at different storage temperatures.

[0021] The dynamic heat balance model described above is used to establish a low-temperature area on the surface of fruits and vegetables to achieve a radiative cooling effect.

[0022] The dynamic heat balance model described above is used to analyze the following variable conditions in logistics transportation and / or storage and preservation: storage environment differences and / or fruit and vegetable characteristics differences and / or fruit and vegetable weight differences.

[0023] Furthermore, the differences in fruit and vegetable characteristics include variety and maturity.

[0024] The method for constructing the surface low-temperature region cooling effect using the dynamic heat balance model described above includes the following steps:

[0025] By analyzing the heat transfer mechanism model, the spectral reflectivity of the packaging material in the solar band of 0.4-2.5μm and the infrared emissivity in the atmospheric window band of 8-13μm should be ≥0.9. The thermal conductivity should be ≤0.04W / (m·K) and the thickness should be 200-500μm. The lowest surface temperature of fruits and vegetables was used as the target constraint condition, and a low-temperature area was established on the surface of fruits and vegetables to achieve a surface temperature of fruits and vegetables that was 10℃ lower than the ambient temperature.

[0026] The construction method described above is applied in the logistics, transportation, storage and preservation of fruits and vegetables.

[0027] The advantages and positive effects achieved by the present invention are:

[0028] 1. The present invention proposes to build a thermal balance model based on the physiological metabolic changes of fruits and vegetables, and establish a collaborative control network of environment-packaging-fruits and vegetables through a hierarchical thermal balance equation, ultimately achieving the goal of lowering the surface temperature of fruits and vegetables by more than 10°C below the ambient temperature. Select the optimal parameters ( Figure 2 、 Figure 3 , select packaging materials with excellent spectral characteristics: a reflectivity of ≥0.9 in the sunlight band, an emissivity of ≥0.9 in the atmospheric window band (8-13 μm), a thermal conductivity of ≤0.3 W / m·K, and a thickness of 200-500 μm. Through modeling and manipulation of the packaging material's spectral parameters, a thermal balance model was used to investigate how the surface temperature of fruits and vegetables could be lower than the ambient temperature, creating a low-temperature zone on the surface of fruits and vegetables. By manipulating the material's reflectivity and emissivity, a thermal balance model was used to investigate how the surface temperature of fruits and vegetables could be lower than the ambient temperature, achieving a radiative cooling effect. The development of this modeling technology will provide new ideas and methods for fruit and vegetable preservation, further promoting the development of the fruit and vegetable logistics industry.

[0029] 2. This invention constructs a dynamic heat balance model for low-temperature surface control of fruits and vegetables based on the second law of thermodynamics. This model uses the lowest surface temperature as the target condition. This model achieves precise surface temperature control through a three-level heat balance system. This system integrates three mechanisms: radiative cooling, dynamic coupling of respiratory heat, and optimization of packaging material parameters. This approach addresses the large temperature fluctuations and high energy consumption associated with traditional preservation technologies. The core of this approach is the establishment of a coordinated control network between the environment, packaging, and fruits and vegetables, using a layered heat balance equation. Ultimately, this model achieves a surface temperature at least 10°C below the ambient temperature.

[0030] 3. The present invention can accurately control the temperature inside the package. That is, by optimizing the thermal conductivity of the packaging material, the design of the air gap layer, and the control of heat radiation by the coating, it can accurately control the temperature balance inside and outside the package, effectively reducing the impact of temperature fluctuations on the quality of fruits and vegetables.

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

[0032] 5. The present invention can improve the adaptability of packaging materials: according to the actual storage temperature and the differences in fruit and vegetable varieties and quality, the packaging material with the optimal spectral characteristics and thermal conductivity can be selected by entering the theoretical equation.

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

[0034] 7. The present invention provides a new method for constructing a thermal 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 the thermal balance model.

[0035] 8. This invention constructs a new surface low temperature region equation based on the radiation cooling effect ( Figure 2 The surface temperature of fruits and vegetables (Fruit temperature) is lower than the storage environment temperature (Environment temperature). As shown in the figure, the solid line part is below the dotted line part. This can effectively create a low-temperature area on the surface of fruits and vegetables, improve the thermal management efficiency of packaging, and is significantly innovative.

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

[0037] (1) Establish a dynamic fresh-keeping 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, spectral characteristics and thermal balance equation of packaging materials;

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

[0040] 10. The present invention optimizes the design of fruit and vegetable packaging materials and improves respiratory heat management capabilities. The present invention constructs a thermal balance simulation model for fruit and vegetable packaging to provide guidance for the design of fruit and vegetable packaging materials. The present invention provides a mathematical equation basis for establishing low-temperature areas on the surface of fruits and vegetables during logistics.

[0041] 11. Based on the second law of thermodynamics, the present invention constructs a dynamic thermal balance model for low-temperature regulation of the surface of fruits and vegetables. By establishing a thermodynamic model with the lowest surface temperature of fruits and vegetables as the target condition, optimizing the thermal conductivity of the packaging material, the design of the air gap layer, and the control of thermal radiation by the coating, the temperature balance inside and outside the package can be controlled. This theoretical framework provides a quantitative basis for the development of precise temperature control strategies in the logistics process of agricultural products, significantly reducing the impact of temperature fluctuations on the quality of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the heat transfer mechanism mode analysis and steady-state heat transfer model diagram in the present invention; the description of the upward arrow between the two blue arrows is marked on the right side of the arrow. , the description text of the other upward arrows is marked near the top of the arrow, and the description text of the downward arrows is marked near the bottom of the arrow;

[0043] Figure 2 is the reflectivity of the packaging material in the present invention ( ) Chart for regulating the surface temperature of fruits and vegetables;

[0044] Figure 3 is the emissivity of the packaging material in the present invention ( ) Control diagram for surface temperature of fruits and vegetables;

[0045] Figure 4 This is a graph showing the regulation of the emissivity of the packaging material with respect to the thermal compensation coefficient in the present invention;

[0046] Figure 5 A diagram is constructed for the actual application scenario in the fruit and vegetable logistics process of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the following examples. The following examples are descriptive rather than restrictive, and the scope of protection of the present invention cannot be limited by the following examples.

[0048] The various experimental operations involved in the specific embodiments are all routine techniques in the field. For parts not specifically annotated in this document, ordinary technicians in this field can refer to various commonly used reference books, scientific literature or related instructions, manuals, etc. before the filing date of this invention to implement them.

[0049] This dynamic thermal balance model for low-temperature surface temperature regulation of fruits and vegetables achieves precise control of surface temperature through a three-level thermal balance system. It integrates three mechanisms: radiative cooling, dynamic coupling of respiratory heat, and optimization of packaging material parameters. This addresses the large temperature fluctuations and high energy consumption issues inherent in traditional preservation technologies. Its core approach is to establish a collaborative control network between the environment, packaging, and fruits and vegetables through a layered thermal balance equation, ultimately achieving the goal of maintaining surface temperatures at least 10°C below ambient. This innovative breakthrough is achieved through multi-physics coupling (thermal radiation, conduction, and physiological metabolism), establishing a three-level physically coupled thermal balance model. This 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 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. The specific details are as follows:

[0051] Level 1: Package outer surface thermal balance model

[0052] The package outer surface heat balance model can characterize the heat exchange between the package outer surface and the environment: the package outer surface dissipates heat through radiation and convection, absorbing radiation heat from the sun and the atmosphere, while conducting heat inward through the packaging material;

[0053] Level 2: Thermal balance model of the inner surface of the package

[0054] The package inner surface thermal balance model can characterize the heat transfer between the package inner surface and the internal space: the package inner surface dissipates heat through radiation and receives heat conducted from the package outer surface, while forming a dynamic balance with the radiant heat from the fruit and vegetable surface.

[0055] Level 3: Fruit and vegetable surface thermal balance model

[0056] The fruit and vegetable surface heat balance model can characterize the heat generation and loss of the fruit and vegetable itself: the fruit and vegetable generates heat through respiration, while absorbing radiant heat from the inner surface of the packaging and transmitted solar radiation, ultimately achieving a balance through surface radiation heat dissipation.

[0057] The three-level coupled thermal balance model does not operate independently; rather, it is closely linked through heat transfer and feedback mechanisms. In practice, the three-level balance model operates simultaneously, with no order of precedence. For example, when solar radiation heats the outer surface (level 1), heat simultaneously affects the inner surface (level 2) through conduction, thereby changing the surface temperature of fruits and vegetables (level 3). A sudden change in the respiratory heat of fruits and vegetables (level 3) can be fed back to the inner surface (level 2) through radiation, ultimately affecting the heat dissipation efficiency of the outer surface (level 1).

[0058] The above dynamic heat balance model can calculate the respiratory heat of fruits and vegetables through the following method:

[0059] First, determine the basic respiration rate of fruits and vegetables at the reference temperature. Then, calculate the dynamic respiration rate at the current temperature based on the difference between the actual temperature of fruits and vegetables and the reference temperature, the volume and weight of fruits and vegetables, and the temperature sensitivity coefficient of the respiration rate.

[0060] The dynamic thermal balance model for low-temperature control of the surface of fruits and vegetables is as follows:

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

[0062] ;

[0063] in, Indicates the radiant heat flux emitted from the outer surface of the fruit and vegetable packaging, in W / m²; Indicates the convective heat flux between the outer surface of the fruit and vegetable packaging and the environment, in W / m²; Represents the infrared emissivity of the outer surface of fruit and vegetable packaging, with a unit of 1; It represents the atmospheric radiation heat flux in W / m²; Indicates the conductive heat flux from the inside to the outside of the fruit and vegetable packaging, in W / m²; Indicates the absorption rate of fruit and vegetable packaging materials to solar radiation, with a unit of 1; Represents the solar radiation heat flux in W / m²;

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

[0065] ;

[0066] in, Indicates the radiant heat flux emitted from the inner surface of the fruit and vegetable packaging, in W / m²; Indicates the conductive heat flux from the inside to the outside of the fruit and vegetable packaging, in W / m²; Represents the infrared emissivity of the inner surface of fruit and vegetable packaging, with a unit of 1; Indicates the radiant heat flux generated by fruits and vegetables, in W / m²;

[0067] The coupling relationship of the three-level equation reflects the physiological heat production of fruits and vegetables, the surface thermodynamic balance of fruits and vegetables (T fruit ):

[0068] ;

[0069] in, Indicates the reflectivity of the packaging material to the heat radiation emitted by fruits and vegetables, with a unit of 1; It represents the atmospheric radiation heat flux in W / m²; Represents the transmittance of fruit and vegetable packaging materials to visible light, with a unit of 1; Represents the solar radiation heat flux in W / m²; Indicates the heat generated by the respiration of fruits and vegetables, in W / m²; Indicates the radiant heat flux emitted from the inner surface of the fruit and vegetable packaging, in W / m²; Indicates the reflectivity of the inner surface of the packaging material to the heat radiation of fruits and vegetables, with the unit being 1; Indicates the radiant heat flux generated by fruits and vegetables, in W / m²;

[0070] The calculation formulas for the above-mentioned radiation heat fluxes are as follows (the radiation heat flux describes the thermal balance between the outer and inner surfaces of the package, corresponds to the coupling relationship of the first-order equation, reflects the environmental interaction properties, and further quantifies the heat dissipation capacity of the barrier):

[0071]

[0072] 、 and They represent the outer surface temperature of the fruit and vegetable packaging, the inner surface temperature of the fruit and vegetable packaging, and the temperature of the fruit and vegetable, respectively, and the unit is K; 、 Respectively represent the infrared emissivity of the outer surface and inner surface of the fruit and vegetable packaging, with the unit being 1; Stefan-Boltzmann constant Expressed as ;

[0073] in, The calculation formula is as follows (the dynamic respiratory heat model describes the surface heat balance of fruits and vegetables, corresponds to the coupling relationship of the third-order equation, and provides a physiological heat source):

[0074]

[0075] Represents the ambient temperature, in K; 、 They represent the integral of the angle between the solar radiation direction and the surface normal direction, and the integral of the wavelength of sunlight, respectively, and both have a unit of 1; It represents the integral of the angle between the solar radiation direction and the surface normal direction, with a unit of 1; Represents the blackbody emissivity, with a unit of 1; Indicates the wavelength of the sun, in nm; Indicates atmospheric transmittance, unit is 1;

[0076] in, The calculation formula is as follows:

[0077]

[0078] It represents the angle between the incident solar radiation direction and the surface normal direction, and the unit is K; Indicates the actual spectral distribution of sunlight on the Earth's surface, in W / m 2 ; Indicates the wavelength of the sun, in nm; It represents the integral of the wavelength of sunlight, with a unit of 1;

[0079] in, The calculation formula is as follows:

[0080]

[0081] S represents the area of the refrigeration material, in m 2 ; Indicates the mass of fruits and vegetables in kg; The heat coefficient of respiration under baseline conditions is expressed as CO2 release in J / mg.

[0082] Indicates the respiration rate at a specific temperature of 0-40°C, expressed as the amount of CO2 released per unit time, in mg / (kg*h) (i.e. the mass of carbon dioxide produced per unit mass of fruit and vegetables per unit time); The calculation formula is: ; Indicates the baseline respiration rate, expressed as the amount of CO2 released per unit time, in mg / (kg*h) (i.e., the mass of carbon dioxide produced per unit mass of fruit and vegetables per unit time); It indicates the multiple of the respiration rate increase when the temperature rises by 10 K, with the unit being 1; Represents the temperature of fruits and vegetables, in K;

[0083] in, 、 The calculation formula is as follows (the characteristics of the packaging material describe the heat transfer between packages and determine the heat transfer efficiency. It corresponds to the coupling relationship of the second-order equation):

[0084]

[0085] 、 and They represent the outer surface temperature of the fruit and vegetable packaging, the inner surface temperature of the fruit and vegetable packaging, and the temperature of the fruit and vegetable, respectively, and the unit is K; Represents the convective heat transfer coefficient of the outer surface of the fruit and vegetable packaging, with the unit of W / (m²·K); Indicates the thermal conductivity of fruit and vegetable packaging materials, with a unit of 1; Represents the thickness of the fruit and vegetable packaging material, in m;

[0086] The method for constructing the surface low-temperature region cooling effect using the dynamic heat balance model described above includes the following steps:

[0087] The heat transfer mechanism model was analyzed and the packaging material was optimized to have a spectral reflectivity of ≥0.9 in the sunlight band (0.4-2.5μm) and an infrared emissivity of ≥0.9 in the atmospheric window band (8-13μm). A thermal conductivity of ≤0.03 W / (m·K) and a thickness of 200-500μm were selected. The lowest surface temperature of fruits and vegetables was used as the target constraint, and a low-temperature zone was established on the surface of fruits and vegetables to ensure that the surface temperature of fruits and vegetables was 10°C lower than the ambient temperature.

[0088] Discussion on heat transfer mechanism:

[0089] - Convective heat transfer: Convective heat transfer between the gas inside and outside the package, with the heat transfer efficiency adjusted by the air gap design.

[0090] - Conduction heat transfer: Optimize the thermal conductivity of the material itself and choose composite materials with lower thermal conductivity.

[0091] - Radiative heat transfer: In the process of radiative heat transfer, the radiation characteristics of the surface of fruits, vegetables and packaging materials are mainly determined by their emissivity and reflectivity.

[0092] The analysis of relevant heat transfer mechanism patterns and steady-state heat transfer models can be found in Figure 1 The present invention constructs a steady-state heat transfer model based on multi-physics field coupling theory to analyze the heat transfer characteristics of the fruit and vegetable packaging system. Figure 1As shown, the model uses a hierarchical structure to describe thermal boundary conditions. Based on the heat transfer paths, it can be divided into four layers: the environment layer, the composite packaging layer (fruit package), the air gap layer (air gap), and the fruit and vegetable surface layer (fruit surface). Energy transfer between these layers is achieved through differentiated heat transfer mechanisms. At the interface between the environment layer and the packaging layer, thermal radiation and convection are the primary heat transfer paths; within the package, thermal conduction is the primary heat transfer path; and between the package and the fruit and vegetable surface, thermal radiation and convection are the primary heat transfer paths. The research results provide a theoretical basis for optimizing the thermal physical properties and structural design of fruit and vegetable packaging materials.

[0093] Example 1

[0094] The modeling experimental parameters were set as follows: the initial surface temperature of the fruit and vegetable was set to 0°C, the simulation interval was 10ms, the packaging material thickness was set to 10 mm, and the material emissivity was set to 1. Reflectances of 0.6, 0.7, 0.8, 0.9, and 1.0 were selected for packaging materials with varying visible light reflectivity to simulate the heat transfer mechanism inside and outside the fruit and vegetable packaging. The experimental data was loaded into a file, recording the dynamic relationship between ambient temperature and the temperature of the fruit and vegetable. The ambient temperature was controlled between 0 and 40°C, and the temperature curves of the fruit and vegetable were used to analyze the impact of the spectral characteristics of the packaging material on its preservation effectiveness.

[0095] The use effect of the model and the experimental simulation results are as follows: Figure 2 The curves for different solar radiation intensities show the dynamic temperature regulation of fruits and vegetables. The gray dashed line represents the ambient temperature baseline curve for comparison. Simulation results show that when the packaging material has a higher reflectivity, the surface temperature of fruits and vegetables is closer to the ambient temperature. When the packaging material reflectivity is 1.0, the surface temperature of fruits and vegetables is always 10°C lower than the ambient temperature, indicating that the packaging material cools the surface of fruits and vegetables through the radiative cooling effect. When the packaging material reflectivity is 0.9, when the ambient temperature is less than 9°C, the surface temperature of fruits and vegetables is higher than the ambient temperature, and the respiratory heat generated by the fruits and vegetables is higher than the radiant heat emitted by the outer surface of the packaging material. When the ambient temperature is greater than 9°C, the surface temperature of fruits and vegetables is lower than the ambient temperature, and the respiratory heat generated by fruits and vegetables is lower than the radiant heat emitted by the outer surface of the packaging material. When the ambient temperature is 9°C, the respiratory heat generated by fruits and vegetables is equal to the radiant heat emitted by the outer surface of the packaging material, resulting in no temperature difference. By adjusting the material reflectivity and thermal conductivity, it is possible to design appropriate packaging materials for different environmental conditions. Lower radiation intensities are suitable for cold chain preservation, while higher radiation intensities can be achieved by increasing the reflectivity of the material to achieve thermal insulation. This method provides a temperature optimization solution for fruits and vegetables based on solar radiation intensity regulation, applicable to various logistics scenarios. Packaging materials with corresponding spectral characteristics can be selected based on the optimal storage temperature of different fruits and vegetables.

[0096] Example 2

[0097] The modeling experimental parameters were set as follows: an initial surface temperature of 0°C for the fruits and vegetables, a simulation time interval of 10 m / s, a packaging material thickness of 10 mm, and a solar reflectivity of 1. For packaging materials with different near-infrared emissivities, emissivities of 0.6, 0.7, 0.8, 0.9, and 1.0 were selected to simulate the heat transfer mechanism inside and outside the fruit and vegetable packaging. The experimental data was loaded as a file, recording the dynamic relationship between ambient temperature and the temperature of the fruits and vegetables. The ambient temperature was controlled between 0 and 40°C. The temperature curves of the fruits and vegetables were used to analyze the impact of the spectral characteristics of the packaging materials on their preservation effectiveness. The experimental data was loaded as a file, recording the dynamic relationship between ambient temperature and the temperature of the fruits and vegetables. The ambient temperature range started at 0°C, and the output was the temperature curves of the fruits and vegetables under different emissivity materials, which were used to analyze the material's ability to regulate heat transfer.

[0098] The experimental simulation results are as follows Figure 3 As shown, when the packaging material's reflectivity in the solar band reaches 1.0, the surface temperature of fruits and vegetables remains at least 5°C below the ambient temperature. Analysis of the packaging material's reflectivity reveals that when its reflectivity equals 1.0, the material completely reflects the energy of visible light, thereby preventing the temperature rise caused by absorbing visible light energy. Furthermore, the packaging material can also emit some energy to the external environment through infrared radiation, thereby achieving a cooling effect. Under the same temperature conditions, the degree of cooling is directly proportional to the packaging material's emissivity: the higher the emissivity, the greater the cooling effect. By adjusting the near-infrared emissivity, material thickness, and time interval, thermal balance optimization can be achieved for different logistics environments. High-emissivity materials are suitable for cold chain transportation, reducing heat accumulation; low-emissivity materials are suitable for thermal insulation transportation, helping to maintain the desired temperature of fruits and vegetables. This method provides a precise and efficient solution for the design of fresh-keeping packaging for fruits and vegetables, applicable to a variety of transportation, storage, and sales scenarios.

[0099] Example 3

[0100] The modeling experimental parameters were set as follows: an initial surface temperature of 0°C for the fruits and vegetables, a 1 ms experimental interval, and a packaging material thickness of 10 mm. For packaging materials with varying near-infrared emissivity, emissivities of 0, 0.6, and 1 were selected to simulate the thermal compensation capacity (expressed as thermal compensation power per unit area) of fruits and vegetables under these different emissivity conditions. Matlab was used to record the dynamic relationship between ambient temperature and thermal compensation capacity. The ambient temperature started at 0°C, and the thermal compensation capacity curve was used to evaluate the impact of varying emissivity on thermal energy management.

[0101] The experimental results are as follows Figure 4As shown, as the emissivity of the packaging material increases, the thermal compensation capacity of fruits and vegetables significantly increases. This indicates that the greater the theoretical cooling power of the material, the greater the possibility of establishing a low-temperature area on the surface of fruits and vegetables. This theoretical modeling provides an important theoretical basis for optimizing the thermal management performance of packaging materials, helping to further improve the preservation of fruits and vegetables and the management efficiency of cold chain logistics.

[0102] Implementation Case 4 – Construction of Actual Application Scenario

[0103] Thermal balance models are widely used in many practical scenarios, especially in the logistics, transportation and storage of perishable agricultural products. Take fruit and vegetable packaging as an example. Figure 5 As shown, this model can effectively simulate and analyze the heat transfer and conversion between the external environment (such as air temperature and solar radiation) and the internal temperature of fruits and vegetables. During this process, the model can evaluate the relationship between the heat generated by the respiration of fruits and vegetables (Tfruit), the external ambient temperature (Tamb), the internal temperature of the packaging (Tin), and the external temperature of the packaging (Tout). The model can also design appropriate packaging materials based on the quality and respiration heat of fruits and vegetables, optimizing thermal management strategies to maintain optimal freshness during transportation and storage, thereby reducing fruit and vegetable losses. This application is not only applicable to fruits and vegetables, but can also be extended to other perishable food preservation, cold chain logistics, and warehouse management, improving overall food safety and quality.

[0104] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A dynamic thermal balance model for low-temperature control of fruit and vegetable surfaces, characterized by: 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, as follows: Level 1: Package outer surface thermal balance model The package outer surface heat balance model can characterize the heat exchange between the package outer surface and the environment: the package outer surface dissipates heat through radiation and convection, absorbing radiation heat from the sun and the atmosphere, while conducting heat inward through the packaging material; Level 2: Package inner surface thermal balance model The package inner surface thermal balance model can characterize the heat transfer between the package inner surface and the internal space: the package inner surface dissipates heat through radiation and receives heat conducted from the package outer surface, while forming a dynamic balance with the radiant heat from the fruit and vegetable surface. Level 3: Fruit and vegetable surface thermal balance model The fruit and vegetable surface heat balance model can characterize the heat generation and loss of the fruit and vegetable itself: the fruit and vegetable generates heat through respiration, while absorbing radiant heat from the inner surface of the packaging and transmitted solar radiation, ultimately achieving a balance through surface radiation heat dissipation. The three-level coupled thermal balance model does not operate independently, but is closely linked through heat transfer and feedback mechanisms; The three-level balance model works simultaneously in actual application without any order.

2. The dynamic thermal equilibrium model according to claim 1, characterized in that: The respiratory heat calculation of fruits and vegetables is achieved through the following method: First, determine the basic respiration rate of fruits and vegetables at the reference temperature. Then, calculate the dynamic respiration rate at the current temperature based on the difference between the actual temperature of fruits and vegetables and the reference temperature, the volume and weight of fruits and vegetables, and the temperature sensitivity coefficient of the respiration rate.

3. Application of the dynamic thermal equilibrium model as claimed in claim 1 or 2 in guiding the design of packaging materials for fruits and vegetables at different storage temperatures.

4. Application of the dynamic thermal equilibrium model according to claim 1 or 2 in establishing a low-temperature area on the surface of fruits and vegetables to achieve a radiative cooling effect.

5. Application of the dynamic heat balance model according to claim 1 or 2 in analyzing the following variable conditions in logistics transportation and / or storage and preservation: storage environment differences and / or fruit and vegetable characteristics differences and / or fruit and vegetable weight differences.

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

7. A method for constructing a surface low-temperature region cooling effect using the dynamic heat balance model according to claim 1 or 2, characterized in that: The steps include: By analyzing the heat transfer mechanism model, the spectral reflectivity of the packaging material in the solar band of 0.4-2.5μm and the infrared emissivity in the atmospheric window band of 8-13μm should be ≥0.

9. The thermal conductivity should be ≤0.04W / (m·K) and the thickness should be 200-500μm. The lowest surface temperature of fruits and vegetables was used as the target constraint condition, and a low-temperature area was established on the surface of fruits and vegetables to achieve a surface temperature of fruits and vegetables that was 10℃ lower than the ambient temperature.

8. Application of the construction method according to claim 7 in the logistics, transportation, storage and preservation of fruits and vegetables.

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