Passive cold storage box design method based on multi-physics field coupling simulation and passive cold storage box

Abstract

The invention provides a passive cold storage box design method based on multi-physics coupling simulation, which comprises the following steps: step 1, establishing a three-dimensional geometric model of a passive cold storage box in COMSOL Multiphysics, including a box body thermal insulation layer, an internal cavity and an ice plate, and endowing the ice plate with a phase change material attribute module; 2, setting a multi-physical field boundary condition and an initial state, and setting a transient solver; 3, setting a solid heat transfer control equation; and 4, parametric scanning is adopted, a simulated temperature-time curve is obtained through transient solution, and ice plate distribution meeting the cold storage condition is screened. According to the method, the temperature field distribution and the temperature-time change curve in the passive cold storage box can be obtained, so that a better arrangement mode meeting the cold storage requirement is determined, the temperature of the cavity in the cold storage box can be maintained to be less than or equal to 15 DEG C by adopting the mode, and the duration time reaches more than 40 hours.

Description

Technical Field

[0001] This invention belongs to the field of phase change materials technology, specifically relating to a passive cold storage box design method and a passive cold storage box based on multi-physics field coupling simulation. Background Technology

[0002] Passive cold storage boxes are crucial equipment in cold chain transportation, and their cold insulation performance directly affects the safety of temperature-sensitive materials such as biological agents and vaccines. Current mainstream technologies have significant limitations. Firstly, there is the limitation of timeliness: existing cold storage boxes generally rely on a single cold source (such as ice packs or dry ice). Limited by the insufficient latent heat of phase change of the storage materials and heat loss from the box structure, the measured cold insulation time at 10℃ is typically less than 24 hours (CN115218534B indicates that traditional solutions only achieve 29.26 hours), making it difficult to meet the rigid requirements of 72-hour long-term temperature control in cross-border logistics and other scenarios. Secondly, there is the bottleneck of material performance: the phase change temperature of phase change materials (PCMs) is negatively correlated with their latent heat (as CN115218534B reveals that "high latent heat materials are difficult to simultaneously possess low-temperature phase change characteristics"), and they are prone to overcooling, phase separation, and leakage problems. Commercially available PCMs mostly have phase change temperatures concentrated in a narrow temperature range, making it difficult to adapt to the wide range of temperature changes during transportation. Furthermore, current passive cold storage structure designs are still relatively crude, with ice plate layouts relying on empirical rules and failing to consider the cold bridging effect caused by the non-uniform temperature field inside the enclosure (e.g., the heat flux density at the sealed door can be 3.2 times that of the sidewall), exacerbating localized cold leakage. Simultaneously, PCM parameters are decoupled from the structural thermodynamic properties, lacking systematic optimization methods. Therefore, it is urgent to overcome the cold insulation bottleneck through collaborative innovation of materials and structures.

[0003] COMSOL Multiphysics, a multiphysics coupled simulation platform based on advanced numerical methods, demonstrates significant technological advantages in the field of temperature field simulation. Its core capabilities lie in the collaborative solution of multiphysics fields (such as the coupling of fluid dynamics and heat transfer) and high-precision transient analysis, providing scientific tools for the thermodynamic optimization of cold chain equipment. Through transient modeling of latent heat release / absorption in phase change materials, three-dimensional geometric modeling of ice plates, and the definition of material thermophysical parameters (such as thermal conductivity and specific heat capacity) and boundary conditions (such as ambient temperature and heat flux), the software can accurately simulate non-uniform temperature field distributions. Therefore, in the design of passive cold storage boxes, using multiphysics coupled simulation results to drive experimental design can shift the development of passive cold storage boxes from experience-driven to data-driven, effectively shortening the experimental cycle and improving R&D efficiency. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a design method and a passive cold storage box based on multiphysics coupling simulation. The method first uses COMSOL Multiphysics software to simulate the ice plate positions and materials with different phase transition temperatures in existing passive cold storage boxes, obtaining the temperature field distribution and temperature-time curves in the passive cold storage box under different arrangements and ice plate spacings. The optimal arrangement that meets the cold storage requirements is then selected. Next, based on the simulation results, phase change materials with different concentrations of mannitol and sodium formate are synthesized, and the passive cold storage box is assembled. The simulation results are verified by comparing the measured temperature curves with the simulation results, ultimately achieving a material-structure coupling design closed loop.

[0005] According to a first aspect of the present invention, a passive cold storage box design method based on multiphysics coupling simulation is proposed, comprising the following steps: Step 1: Create a three-dimensional geometric model of the passive cold storage box in COMSOL Multiphysics, including the box insulation layer, internal cavity and ice plate, and assign the phase change material property module to the ice plate; Step 2: Set the multiphysics boundary conditions and initial state, and set up the transient solver; Step 3: Establish the governing equations for heat transfer in solids; Step 4: Using parametric scanning, the simulated temperature-time curve is obtained through transient solution, and the distribution of ice plates that meet the cold storage conditions is selected.

[0006] In some embodiments, the ice plate in step 1 includes a first ice plate, a second ice plate, and a third ice plate arranged sequentially; the phase change temperature range of the first ice plate, the second ice plate, and the third ice plate are independently set to -10~10℃, and the latent heat of phase change is independently set to 170~230J / g. In practical applications, different phase change temperatures and phase change enthalpies can be achieved according to different ratios of raw materials (such as mannitol and sodium formate).

[0007] In some implementations, the multiphysics boundary condition in step 2 is: setting the ambient temperature to 20±5℃ (target cold storage environment); And / or, the initial state in step 2 is: the temperature of the ice plate is set to -20℃ (simulating pre-cooling state), and the air temperature of the internal cavity is set to -20℃ (simulating pre-cooling loading). And / or, the time range of the transient solver in step 2 is set to 0~96h (covering the target cooling duration), and the time step is adaptively adjusted.

[0008] In some implementations, the governing equations in step 3 are the heat conduction equation and the heat convection equation; The heat conduction equation includes the heat transfer control equation for the insulation layer of the enclosure: ; in, The density of the cold storage box is set to 28~32 kg / m³. 3 ; The specific heat capacity of the cold storage box is set to 1800~2100 J / kg·K; The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K); And the heat transfer control equations for the stored material: ; in, The density of the stored items; Specific heat capacity of the stored item; The thermal conductivity of the stored item; The heat convection equations include those for heat convection between the outer wall of the box and the external environment: ; in, The heat transfer coefficient for natural air convection is set to 8~10 W / (m²). 2 ·K); The ambient temperature is set to 293.15±5K. The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K).

[0009] In some implementations, the cold storage conditions in step 4 are: the temperature of the internal cavity ≤ 15°C, and the duration ≥ 40h.

[0010] In some implementations, before obtaining the simulated temperature-time curve through transient solution in step 4, the method further includes: assigning differentiated PCM parameters to each ice plate; The phase change temperature of the first ice plate is set to 2~10℃ and the latent heat is set to 200~230J / g; And / or, the phase change temperature of the second ice plate is set to -2~2℃ and the latent heat is set to 200~230J / g; And / or, the phase change temperature of the third ice plate is set to 2~10℃ and the latent heat is set to 200~230J / g.

[0011] This invention controls the phase change temperature and latent heat of an ice plate by adjusting the proportions of the filling materials inside the ice plate. For example, the first ice plate may contain a 1%~1.3% mannitol aqueous solution and a 1%~3% sodium formate aqueous solution; the second ice plate may contain a 0.8%~1% mannitol aqueous solution and a 3%~5% sodium formate aqueous solution; and the third ice plate may contain a 1%~1.3% mannitol aqueous solution and a 1%~3% sodium formate aqueous solution.

[0012] In some embodiments, the first ice plate, the second ice plate, and the third ice plate also independently contain a water-absorbing resin with a concentration of 0.3% to 2%, wherein the water-absorbing resin is selected from 60 to 100 mesh and / or 100 to 200 mesh high molecular weight water-absorbing resin.

[0013] The first ice plate, as described above, is used to resist heat convection, the second ice plate is used to suppress heat loss through conduction, and the third ice plate is used to delay cold leakage.

[0014] In some embodiments, the passive cold storage box design method further includes: Step 5.1: Assemble the passive cold storage box according to the ice plate distribution described in Step 4, and fill the ice plate with ternary composite phase change material; Step 5.2: Test the measured temperature-time curves of multiple temperature measurement points inside the passive cold storage box at an environment of 20±5℃; Step 5.3: Compare the measured temperature-time curve with the simulated temperature-time curve. If the average deviation is >5%, iteratively adjust the position of the ice plate or the ratio of the ternary composite phase change material. The measured cold preservation time is ≥40h.

[0015] The temperature measurement points mentioned in step 5.2 can be set as needed, for example, including the geometric center points of the six sides of the passive cold storage box and the center of the space formed by the ice plate dividing the cavity of the passive cold storage box.

[0016] In some preferred embodiments, the number of iterations in step 5.3 is ≤5.

[0017] According to a second aspect of the present invention, a passive cold storage box is provided, wherein multiple ice plates are provided inside, and the positions of the ice plates are obtained according to the passive cold storage box design method described in the first aspect of the present invention.

[0018] In some embodiments, the ice plate is filled with a ternary composite phase change material, which is composed of mannitol aqueous solution, sodium formate aqueous solution and water-absorbing resin. The concentration of the mannitol aqueous solution is 0.8% to 1.3%, the concentration of the sodium formate aqueous solution is 1% to 5%, and the concentration of the superabsorbent resin is 0.3% to 2%.

[0019] In some embodiments, the ice plate includes a first ice plate, a second ice plate, and a third ice plate arranged in parallel from top to bottom in a vertical direction. The first ice plate is close to the lower part of the top inner wall of the passive cold storage box, the second ice plate is fixed in the middle of the passive cold storage box at a central height, and the third ice plate is close to the upper part of the bottom inner wall of the passive cold storage box.

[0020] In some embodiments, the ice plate includes a first ice plate, a second ice plate, and a third ice plate arranged parallel from front to back along the depth direction of the box. The first ice plate is in close contact with the inner front wall of the passive cold storage box, the second ice plate is fixed in the middle of the passive cold storage box along the depth direction, and the third ice plate is in close contact with the inner rear wall of the passive cold storage box.

[0021] In some embodiments, the ice plate includes a first ice plate, a second ice plate, and a third ice plate arranged parallel from left to right along the width direction of the box. The first ice plate is close to the left inner wall of the passive cold storage box, the second ice plate is fixed in the middle of the passive cold storage box along the width direction, and the third ice plate is close to the right inner wall of the passive cold storage box.

[0022] The dimensions of the ice plates are determined by the dimensions of the passive cold storage box and can be adjusted as needed. For example, when set vertically, the length of the ice plates can be 70% to 80% of the width of the cold storage box (front view direction). Of course, the three ice plates can be the same size or different sizes, and this invention does not impose any particular limitation on this.

[0023] According to one embodiment of the present invention, at least the following beneficial effects are achieved: 1. This invention employs a multi-physics field coupled ice plate layout design method, integrating temperature field distribution and phase change material modules into a COMSOL model to achieve dynamic matching between ice plate spatial arrangement and thermodynamic properties. Simultaneously, it quantifies the influence of ice plate coordinates (X,Y,Z) and spacing (d) on the temperature field through parametric scanning to locate the optimal layout. Based on the temperature field simulation results, the optimal phase change material is selected. Finally, a closed-loop correction mechanism is established between simulation, manufacturing, and actual measurement: when the average deviation between the measured and simulated temperature curves is >5%, the PCM parameters are adjusted by changing the relative contents of the main cold storage agent mannitol (concentration of 0.5%~1.3%), the phase change temperature regulator sodium formate (concentration of 1%~5%), and the fixative superabsorbent resin (concentration of 0.3%~2%). This simulated target guides material synthesis, and the design of the passive cold storage box is completed through multiple iterations. The designed passive cold storage box has a long-term temperature control of more than 40 hours (the internal temperature of the box is maintained at ≤15℃, and can be maintained for more than 72 hours) and a wide temperature range adaptability. The adjustable range of the phase change temperature of the PCM is extended to -10~10℃. Therefore, this passive cold storage box can cover the entire scenario of vaccine refrigeration (2~8℃), vegetable and fruit refrigeration and fresh food cold chain transportation.

[0024] 2. This design, through a simulated pre-screening scheme, reduces the number of physical experiment rounds from >20 to ≤5, compressing the R&D cycle to 2.5 months, demonstrating advantages in both high R&D efficiency and cost optimization. Furthermore, the designed passive cold storage box utilizes water-based PCM, replacing dry ice and liquid nitrogen, which are prohibited by air transport regulations, thus meeting cross-border cold chain security requirements. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of the ice plate arrangement in Embodiment 1 of the present invention; Figure 2 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the ice plate arrangement in Embodiment 2 of the present invention; Figure 4 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the ice plate arrangement in Embodiment 3 of the present invention; Figure 6 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 3 of the present invention; Figure 7 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 4 of the present invention; Figure 8 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 5 of the present invention; Figure 9 This is a simulation diagram of the temperature field distribution in the cold storage box in Embodiment 6 of the present invention; Figure 10 The graphs show the temperature change over time in the cold storage box in Embodiments 1-6 of the present invention. Figure 11 The graphs show the temperature change over time in the cold storage box in Embodiments 1 and 7 of the present invention. Figure 12 This is a simulation diagram of the temperature field distribution in the cold storage box in Comparative Example 1 of the present invention; Figure 13 The graph shows the temperature change over time in the cold storage box in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] This invention provides a high-efficiency passive cold storage box. By optimizing the arrangement and spacing of the ice plates and designing differentiated phase change temperatures, it can maintain the internal temperature below 15°C for 40-72 hours or more when the ambient temperature is ≤25°C. This passive cold storage box is suitable for long-term storage of temperature-sensitive items such as vaccines (2-8°C), refrigerated fruits and vegetables, and fresh food cold chain transportation, significantly extending the shelf life of pharmaceutical active ingredients, cold chain food, and the stability of industrial products.

[0028] This invention utilizes COMSOL Multiphysics software to dynamically simulate the influence of different ice plate positions and materials with different phase change temperatures on the temperature field of a cold storage box. Based on the numerical simulation results, the temperature field distribution and temperature-time curves are analyzed to select the optimal method that meets the cold storage requirements. Then, based on the simulation results, phase change materials are synthesized (materials with a phase change temperature of 2~10℃ and a latent heat of 200~230J / g include: 1%~1.3% mannitol aqueous solution, 1%~3% sodium formate aqueous solution, and 0.3% superabsorbent resin; materials with a phase change temperature of -2~2℃ and a latent heat of 200~230J / g include: 0.8%~1% mannitol aqueous solution, 3%~5% sodium formate aqueous solution, and 0.3% superabsorbent resin), and a passive cold storage box is assembled. The simulation results are verified by comparing the measured temperature curves with the simulation results, ultimately achieving a material-structure coupling design closed loop.

[0029] The model building steps are as follows: (1) Selection of physical field: Solid heat transfer physical field is selected for this experiment; (2) Establish the geometric model: the geometry of the cold storage box and the ice plate, wherein the dimensions of the cold storage box are 500*350*255mm, and the dimensions of the ice plate are determined according to the dimensions of the cold storage box; (3) Set boundary conditions: heat transfer in solids and phase change heat transfer in phase change materials; The governing equation for solid-state heat transfer in the cold storage tank is: ; in, The density of the cold storage box is set to 28~32 kg / m³. 3 ; The specific heat capacity of the cold storage box is set to 1800~2100 J / kg·K; The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K).

[0030] The governing equation for heat transfer in solid food is: ; in, Set the density of the food to 900~1010 kg / m³ 3 ; The specific heat capacity of the food was set to 3900~4000 kJ / kg·K; The thermal conductivity of the food is set to 0.40~0.50 W / (m·K).

[0031] The outer wall of the cold storage box undergoes thermal convection with the external environment, as shown in the following equation: ; in, The heat transfer coefficient for natural air convection is set to 8~12 W / (m²). 2 ·K); The ambient temperature is set to 298.15K. The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K); The governing equations for phase change heat transfer in cold storage materials are as follows: ; in, , The specific isobaric heat capacity of the cold storage material before and after phase change is set to 2000~2200 J / kg·K and 4000~4400 J / kg·K, respectively. , The thermal conductivity of the cold storage material before and after the phase change is set to 0.34~0.38 W / (m·K) and 0.73~0.77 W / (m·K), respectively. The heat absorbed by solid cold storage materials; The heat absorbed by the liquid cooling material; ρ is the density of the phase change material; u is the velocity vector (m / s); (4) Mesh generation: The mesh is set to the standard cell size (24909 triangular cells); (5) Select solver: Select a linear solver to solve the partial differential equations, and set the relative and absolute tolerances to 0.01 and 0.001, respectively; (6) Output the calculation results.

[0032] The instantaneous temperature change in the cold storage box was simulated and calculated using the thermal conductivity and phase change modules of COMSOL Multiphysics, and the cooling rate and temperature distribution were obtained.

[0033] Example 1 This embodiment discloses a design method for a passive cold storage box. In this embodiment, three layers of ice plates are arranged parallel to each other along the vertical direction (height direction) inside the cold storage box. The dimensions of the three ice plates are all 368 mm * 240 mm * 17 mm. Figure 1 As shown. Figure 1The first ice plate is fixed to the lower part of the inner wall of the top of the box, the second ice plate is fixed in the middle of the box, and the third ice plate is fixed to the upper part of the inner wall of the bottom of the box. The three ice plates are parallel to each other and parallel to the bottom surface of the box, roughly dividing the internal space of the box into two areas in the vertical direction: an upper cavity and a lower cavity. The food in the box is simulated by a cylinder.

[0034] Three ice plates were set to different phase transition temperatures. The first and third ice plates had a phase transition temperature of 5℃ and a phase transition enthalpy of 200 J / g, while the second ice plate had a phase transition temperature of 0℃ and a phase transition enthalpy of 200 J / g. The temperature field changes were observed by setting different phase transition temperatures. A three-dimensional heat transfer model of the cold storage box and ice plates was established using COMSOL Multiphysics software, with a time range of 0–96 h and a step size of 0.1 h. The initial temperature of the ice plates and the initial temperature of the air inside the box were set to -20℃, and the temperature field changes were simulated and analyzed. Figure 2 and Figure 10 The second ice plate, having the lowest phase change temperature, was the first to melt and absorb heat. Subsequently, the first and third ice plates continued to absorb heat after reaching their phase change temperatures. It can be seen that the overall temperature remained below 15℃ for more than 72 hours.

[0035] Example 2 like Figure 3 As shown in this embodiment, three layers of ice plates are arranged parallel to each other along the width of the cold storage box. The dimensions of the three ice plates are all 236mm*170mm*30mm. Figure 3 The first ice plate is fixed to the inside of the left side wall of the box, the second ice plate is fixed to the middle of the box's width, and the third ice plate is fixed to the inside of the right side wall. The three ice plates are parallel to each other and parallel to the side walls of the box, dividing the interior space into two areas in the width direction: a left cavity and a right cavity. The food inside the box is represented by a cylinder.

[0036] Three ice plates were set to different phase transition temperatures. The first and third ice plates had a phase transition temperature of 5℃ and a phase transition enthalpy of 200 J / g, while the second ice plate had a phase transition temperature of 0℃ and a phase transition enthalpy of 200 J / g. The temperature field changes were observed by setting different phase transition temperatures. A three-dimensional heat transfer model of the cold storage box and ice plates was established using COMSOL Multiphysics software, with a time range of 0–96 h and a step size of 0.1 h. The initial temperature of the ice plates and the initial temperature of the air inside the box were set to -20℃. The temperature field changes were simulated and analyzed. Figure 4 and Figure 10 As shown, the cooling rates of the two cavities are not significantly different, allowing items to be stored at below 15°C for 60 hours.

[0037] Example 3 like Figure 5 As shown, in this embodiment, three layers of ice plates of the same size are arranged parallel to each other along the depth direction inside the cold storage box. The dimensions of each layer of ice plate are 400mm*140mm*23mm. Specifically... Figure 5 The first ice plate is fixed to the inner front side (front), the second ice plate is fixed to the middle of the box's depth (middle), and the third ice plate is fixed to the inner rear side (rear). The three ice plates are parallel to each other and parallel to the box's side walls, dividing the interior space into two areas in the depth direction: a front cavity and a rear cavity. A cylinder is used to simulate the food inside the box.

[0038] Three ice plates were set to different phase transition temperatures. The first and third ice plates had a phase transition temperature of 5℃ and a phase transition enthalpy of 200 J / g, while the second ice plate had a phase transition temperature of 0℃ and a phase transition enthalpy of 200 J / g. The temperature field changes were observed by setting different phase transition temperatures. A three-dimensional heat transfer model of the cold storage box and ice plates was established using COMSOL Multiphysics software, with a time range of 0–96 h and a step size of 0.1 h. The initial temperature of the ice plates and the initial temperature of the air inside the box were set to -20℃. The temperature field changes were simulated and analyzed. Figure 6 and Figure 10 As shown, the cooling rates of the two cavities are not significantly different, allowing items to be stored at below 15°C for 40 hours.

[0039] Example 4 In this embodiment, the arrangement and dimensions of the ice plates inside the cold storage box are the same as in Embodiment 1. The three ice plates are set to different phase transition temperatures: the first ice plate has a phase transition temperature of 5°C and a phase transition enthalpy of 200 J / g; the second ice plate has a phase transition temperature of 0°C and a phase transition enthalpy of 200 J / g; and the third ice plate has a phase transition temperature of 8°C and a phase transition enthalpy of 200 J / g. These different phase transition temperatures are used to observe changes in the temperature field.

[0040] A three-dimensional heat transfer model of the cold storage box and ice plate was established using COMSOL Multiphysics software, with a time range of 0-96 hours and a step size of 0.1 hours. The initial temperature of the ice plate and the initial temperature of the air inside the box were set to -20℃. Figure 7 and Figure 10 The middle ice plate, having the lowest phase change temperature, is the first to undergo phase change, absorbing a large amount of heat. The upper and lower ice plates undergo phase change successively to maintain a lower temperature environment. The system eventually reaches a dynamic equilibrium state, forming a significant "cold top, warm bottom" reverse vertical temperature gradient.

[0041] Example 5 In this embodiment, the arrangement and dimensions of the ice plates inside the cold storage box are the same as in Embodiment 1. The three ice plates are set to different phase transition temperatures: the first ice plate has a phase transition temperature of 8°C and a phase transition enthalpy of 200 J / g; the second ice plate has a phase transition temperature of 0°C and a phase transition enthalpy of 200 J / g; and the third ice plate has a phase transition temperature of 5°C and a phase transition enthalpy of 200 J / g. These different phase transition temperatures are used to observe changes in the temperature field.

[0042] A three-dimensional heat transfer model of the cold storage box and ice plate was established using COMSOL Multiphysics software, with a time range of 0-96 hours and a step size of 0.1 hours. The initial temperature of the ice plate was set to -20℃, and the initial temperature of the air inside the box was set to 25℃. Figure 8 and Figure 10 As shown, the cooling rates of the upper and lower cavities are not significantly different, creating a unique temperature field distribution with lower temperatures on both sides and higher temperatures in the middle, which can preserve items at temperatures below 15°C for 50 hours.

[0043] Example 6 In this embodiment, the arrangement and dimensions of the ice plates inside the cold storage box are the same as in Embodiment 1. The three ice plates are set to different phase transition temperatures: the first ice plate has a phase transition temperature of 8°C and a phase transition enthalpy of 200 J / g; the second ice plate has a phase transition temperature of 0°C and a phase transition enthalpy of 200 J / g; and the third ice plate has a phase transition temperature of 8°C and a phase transition enthalpy of 200 J / g. These different phase transition temperatures are used to observe changes in the temperature field.

[0044] A three-dimensional heat transfer model of the cold storage box and ice plate was established using COMSOL Multiphysics software, with a time range of 0-96 hours and a step size of 0.1 hours. The initial temperature of the ice plate was set to -20℃, and the initial temperature of the air inside the box was set to 25℃. Figure 9 and Figure 10 Initially, the temperature in the middle is lower. Subsequently, the upper and lower ice plates undergo a phase change, absorbing heat and causing the temperature on both sides to drop, forming a unique temperature field distribution with a higher temperature in the middle and a lower temperature on both sides. This allows items to be stored at temperatures below 15°C for 60 hours.

[0045] Example 7 In this embodiment, the ice plates are placed in the most effective way—the placement method in Embodiment 1. From Figure 10It can be seen that Example 1 has the best cold preservation effect. Therefore, this example selects a phase change temperature similar to that in Example 1 for actual measurement, and the ice plate size is consistent with that in Example 1. Three ice plates were adjusted to different phase change temperatures: the first ice plate had a phase change temperature of 4℃ and a phase change enthalpy of 230 J / g (mannitol aqueous solution concentration of 1%~1.2%, sodium formate aqueous solution concentration of 2.5%~3%); the second ice plate had a phase change temperature of -2℃ and a phase change enthalpy of 210 J / g (mannitol aqueous solution concentration of 0.8%~1%, sodium formate aqueous solution concentration of 4%~4.5%); and the third ice plate had a phase change temperature of 4℃ and a phase change enthalpy of 230 J / g (mannitol aqueous solution concentration of 1%~1.2%, sodium formate aqueous solution concentration of 2.5%~3%). The cold storage box was placed in a real environment at room temperature of 25℃, and the average temperature of the center points of the six side walls and the center points of the two cavities was monitored in real time. Figure 11 As shown, the data is not much different from the simulation data in Example 1, and the data can be stored at below 15°C for more than 60 hours.

[0046] Comparative Example 1 In this comparative example, three layers of ice plates are arranged parallel to each other along the vertical direction (height direction) inside the cold storage box, and the size of the ice plates is consistent with that of Example 1. In this example, compared to Example 1, the spacing between the ice plates is adjusted from 102mm to 51mm, and the three layers of ice plates are parallel to each other and parallel to the bottom surface of the box. A cylinder is used to simulate the food inside the box.

[0047] Three ice plates were set to different phase transition temperatures. The first and third ice plates had a phase transition temperature of 5℃ and a phase transition enthalpy of 200 J / g, while the second ice plate had a phase transition temperature of 0℃ and a phase transition enthalpy of 200 J / g. The changes in the temperature field were observed by setting different phase transition temperatures. A three-dimensional heat transfer model of the cold storage box and ice plates was established using COMSOL Multiphysics software. The initial temperature of the ice plates and the initial temperature of the air inside the box were set to -20℃, and the changes in the temperature field were simulated and analyzed. Figure 12 and Figure 13 It can be seen that the temperature rises slowly in the central area of ​​the cold storage box. After 50 hours, the temperature rises at a faster rate, which contrasts with the slow temperature rise in Example 1. Comparative Example 1 can maintain 15°C for 57 hours.

[0048] As can be seen from the above embodiments, the different ice plate placement positions and phase change temperatures set by the present invention can maintain the internal temperature below 15°C for more than 40 hours when the ambient temperature is ≤25°C. Moreover, the actual test results show that the difference from the simulation results is less than 5%. Therefore, this passive cold storage box can cover scenarios such as vaccine refrigeration, fruit and vegetable refrigeration, and fresh food cold chain transportation.

[0049] The above descriptions are merely several preferred embodiments of the present invention, but the present invention is not limited to the specific implementation methods described above. The specific implementation methods described above are illustrative and not restrictive. Researchers in the art, under the guidance of the present invention and in accordance with the spirit and principles of the present invention, can make improvements and modifications, all of which fall within the protection scope of the present invention.

Claims

1. A design method for a passive cold storage box based on multiphysics coupling simulation, characterized in that, Includes the following steps: Step 1: Create a three-dimensional geometric model of the passive cold storage box in COMSOL Multiphysics, including the box insulation layer, internal cavity and ice plate, and assign the phase change material property module to the ice plate; Step 2: Set the multiphysics boundary conditions and initial state, and set up the transient solver; Step 3: Set the control equations for solid heat transfer; Step 4: Using parametric scanning, the simulated temperature-time curve is obtained through transient solution, and the distribution of ice plates that meet the cold storage conditions is selected.

2. The passive cold storage box design method according to claim 1, characterized in that, The ice plate mentioned in step 1 includes a first ice plate, a second ice plate, and a third ice plate arranged in sequence; the phase change temperature of the first ice plate, the second ice plate, and the third ice plate are independently set to -10~10℃ and the latent heat of phase change is independently set to 170~230J / g.

3. The passive cold storage box design method according to claim 1, characterized in that, The multiphysics boundary condition mentioned in step 2 is: the ambient temperature is set to 20±5℃; And / or, the initial state in step 2 is: the temperature of the ice plate is set to -20℃, and the air temperature of the internal cavity is set to -20℃; And / or, the time range of the transient solver in step 2 is set to 0~96h, and the time step is adaptively adjusted.

4. The passive cold storage box design method according to claim 1, characterized in that, The governing equations mentioned in step 3 are the heat conduction equation and the heat convection equation; The heat conduction equation includes the heat transfer control equation for the insulation layer of the enclosure: ; in, The density of the cold storage box is set to 28~32 kg / m³. 3 ; The specific heat capacity of the cold storage box is set to 1800~2100 J / kg·K; The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K); And the heat transfer control equations for the stored materials: ; in, The density of the stored items; Specific heat capacity of the stored item; The thermal conductivity of the stored item; The heat convection equations include those for heat convection between the outer wall of the box and the external environment: ； in, The heat transfer coefficient for natural air convection is set to 8~10 W / (m²). 2 ·K); The ambient temperature is set to 293.15±5K. The thermal conductivity of the cold storage box is set to 0.028~0.034 W / (m·K).

5. The passive cold storage box design method according to claim 1, characterized in that, The cold storage conditions described in step 4 are: the temperature of the internal cavity ≤ 15℃, and the duration ≥ 40h.

6. The passive cold storage box design method according to claim 2, characterized in that, Before obtaining the simulated temperature-time curve through transient solution in step 4, the method further includes: assigning differentiated PCM parameters to each ice plate; The phase change temperature of the first ice plate is set to 2~10℃ and the latent heat is set to 200~230J / g; And / or, the phase change temperature of the second ice plate is set to -2~2℃ and the latent heat is set to 200~230J / g; And / or, the phase change temperature of the third ice plate is set to 2~10℃ and the latent heat is set to 200~230J / g.

7. The passive cold storage box design method according to any one of claims 1-6, characterized in that, Also includes: Step 5.1: Assemble the passive cold storage box according to the ice plate distribution described in Step 4, and fill the ice plate with ternary composite phase change material; Step 5.2: Test the measured temperature-time curves of multiple temperature measurement points inside the passive cold storage box at an environment of 20±5℃; Step 5.3: Compare the measured temperature-time curve with the simulated temperature-time curve. If the average deviation is >5%, iteratively adjust the position of the ice plate or the ratio of the ternary composite phase change material. The measured cold preservation time is ≥40h.

8. The passive cold storage tank design method according to claim 7, characterized in that, The number of iterations described in step 5.3 is ≤ 5.

9. A passive cold storage box, characterized in that, The interior is equipped with multiple ice plates, the positions of which are determined by the passive cold storage box design method according to any one of claims 1-8.

10. The passive cold storage box according to claim 9, characterized in that, The ice plate is filled with a ternary composite phase change material, which is composed of mannitol aqueous solution, sodium formate aqueous solution and water-absorbing resin. The concentration of the mannitol aqueous solution is 0.8% to 1.3%, the concentration of the sodium formate aqueous solution is 1% to 5%, and the concentration of the superabsorbent resin is 0.3% to 2%.

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