A Metabolic Chamber Aerodynamic Structural Design Method Based on Simulation Technology

Abstract

This invention discloses a method for designing the aerodynamic structure of a metabolic chamber based on simulation technology. The specific steps are as follows: Step 1: Establishment of the metabolic chamber model; Step 2: Mesh generation; Step 3: Initial condition setting; Step 4: Simulation operation steps; Step 5: Generation of simulation curves; Step 6: Analysis of simulation results. This invention focuses on the simulation of airflow organization and concentration field distribution within a closed space. The motion trajectory of the flow field and the gradual development of the concentration field can be clearly presented on the computer screen. Numerical simulation can reproduce the flow scenario and trend in image or numerical form. By using fluid dynamics simulation software to generate the average gas concentration inside the chamber and the concentration change curve at the chamber outlet in the same coordinate system, a suitable aerodynamic structure for the metabolic chamber is found based on the curve with the fastest response time.

Description

Technical Field

[0001] This invention relates to the field of digital simulation technology, specifically to a method for designing the aerodynamic structure of a metabolic chamber based on simulation technology. Background Technology

[0002] A medical metabolic chamber is a device that uses indirect calorimetry to measure human metabolic consumption. It calculates energy expenditure by measuring oxygen consumption and carbon dioxide production within the chamber, using the Weir formula, and can also estimate the proportion of the three macronutrients consumed. Metabolic chambers are typically equipped with beds, toilets, tables, exercise equipment, and pass-through windows for food, allowing subjects to live relatively comfortably inside for 24 hours or even longer, thus enabling long-term monitoring of human energy metabolism.

[0003] Efficient mixing of gases within the metabolic chamber can be achieved by accelerating the flow of gases within the chamber. Currently, commercially available solutions for accelerating airflow in metabolic chambers mainly utilize blowers, ducted air conditioners, or ordinary household air conditioners. Adding an internal circulation system can also achieve this. An internal circulation system typically consists of air supply vents, return air vents, a fan, and ductwork. Through the supply and return air of this system, the gas flow within the chamber is accelerated, ensuring thorough mixing.

[0004] Factors affecting gas mixing efficiency include: (1) type of air supply outlet; (2) basic form of airflow organization (location of supply and return air outlets); (3) internal circulation airflow rate; (4) influence of items inside the chamber (tables, beds, chairs, toilets, etc.); and (5) location of the test subjects. Studying the influence of the above factors on the concentration field inside the chamber ultimately boils down to studying fluid flow.

[0005] In the construction of the metabolic chamber, in order to enable the exhaled gas from the human body to diffuse quickly into the chamber and achieve uniform gas mixing, which facilitates subsequent gas sampling and analysis, it is necessary to study the fluid flow inside the chamber in the aerodynamic structural design of the metabolic chamber. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for designing the aerodynamic structure of a metabolic chamber based on simulation technology. By utilizing fluid dynamics simulation software, the motion trajectory of the flow field and the gradual development of the concentration field can be clearly displayed on a computer screen. Numerical simulation can reproduce the flow scenario and trend in graphical or numerical form, thereby seeking a suitable aerodynamic structure for the metabolic chamber that allows exhaled gases to quickly diffuse within the chamber, achieving uniform gas mixing.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for designing the aerodynamic structure of a metabolic chamber based on simulation technology includes the following steps:

[0009] Step 1: Establishing the Metabolic Chamber Model: Three identical metabolic chamber models are created: Metabolic Chamber A, Metabolic Chamber B, and Metabolic Chamber C. Sampling ports, air inlets, air supply vents, air return vents, and CO2 injection ports are installed on the chambers of Metabolic Chamber A, B, and C. Beds, tables, toilets, sinks, and pass-through windows are placed inside each chamber, simplified as cuboids during modeling. A sampling port is located at the top of the chamber for sampling and detecting CO2 gas within the chamber.

[0010] The air supply and return vents of metabolic chamber A are both located in one of the top corners, with the return vent lower than the air supply vent.

[0011] The air supply vent of metabolic chamber B is located near the head of the bed and below the CO2 injection port, while the return air vent is located on the top of the chamber and on the side away from the head of the bed.

[0012] The air supply vent and return vent of the metabolic chamber C are both located on the side wall near the head of the bed, with the air supply vent positioned below the CO2 injection port and the return vent positioned near the top of the chamber.

[0013] Step 2: Mesh Generation: Refine the mesh for the sampling port, air inlet, supply air outlet, return air outlet, and CO2 injection port to ensure the mesh quality meets the calculation requirements;

[0014] Step 3: Setting initial conditions;

[0015] Step 4: Simulation execution steps:

[0016] First, set the CO2 injection port to the wall and run it for 40 seconds to ensure that the gas inside the chamber is mixed evenly.

[0017] After running for 40 seconds, CO2 began to enter through the CO2 injection port at a rate of 1 L / min, and the operation continued for 300 seconds.

[0018] After running for another 300 seconds, the CO2 flow rate was doubled to 2L / min to simulate the human body changing from a resting state to an active state. During the active state, the amount of CO2 emitted by the human body will increase. This process was repeated for 300 seconds.

[0019] Finally, change the CO2 flow rate back to 1 L / min and run for 300 seconds;

[0020] Step 5: Generation of simulation curves: Based on the conditions and algorithm set in Step 3, and under the operation in Step 4, the average gas concentration inside the cabin and the concentration change curve at the cabin outlet are plotted in the same coordinate system according to the operation status.

[0021] Step Six: Analysis of Simulation Results: By comparing the average gas concentration inside the chamber and the concentration change curve at the chamber outlet generated by metabolic chambers A, B, and C in the same coordinate system in Step Five, the one with the fastest response time is the most suitable aerodynamic structure for the metabolic chamber.

[0022] Furthermore, the air supply and return vents of the metabolic chambers A, B, and C are all rectangular structures with dimensions of (600-950)*200mm, and the air supply and return vents are connected to the internal circulation equipment within the chamber for the circulation of gas. The internal circulation equipment is a high-precision air conditioner, and the air inlet and CO2 injection port are both 25mm round holes.

[0023] Furthermore, the initial conditions include the mass fractions of fresh air, wherein the mass fractions of the mixture of O2, CO2, and N2 in the fresh air are 23.1%, 0.046%, and 76.854%, respectively.

[0024] Furthermore, the sampling port is a circular hole with a diameter of 25mm.

[0025] Furthermore, the initial conditions include temperature, which includes the temperature of all gases and the wall surface, and the temperature is kept constant at 300K.

[0026] Furthermore, the gas composition of the supply air vent and the return air vent is the same, and the gas composition of the return air vent is the same as that of the air inlet.

[0027] Furthermore, the specific parameters for the simulation run step in step four are set as follows:

[0028] Step 1: Set the CO2 injection port to a wall, time step: 0.1s, number of time steps: 400, maximum iteration: 40, automatic saving: 50 time steps;

[0029] Step 2: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, where FCO2=1;

[0030] Step 3: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 2L / min, where FCO2=1;

[0031] Step 4: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, where FCO2 = 1.

[0032] Compared with the prior art, the beneficial effects of the present invention are: the airflow organization simulation and concentration field distribution in the enclosed space that the present invention focuses on can clearly present the motion trajectory of the flow field and the gradual development of the concentration field on the computer screen. The numerical simulation can reproduce the flow scenario and trend in the form of images or numerical values. The average gas concentration in the chamber and the concentration change curve at the chamber outlet are generated in the same coordinate system by the fluid dynamics simulation software. Based on the curve response time, a suitable aerodynamic structure of the metabolic chamber can be found.

[0033] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart illustrating the steps of the aerodynamic structural design method for a metabolic chamber based on simulation technology according to the present invention.

[0036] Figure 2 This is a structural model diagram of the metabolic chamber A of the present invention;

[0037] Figure 3 This is a structural model diagram of the metabolic chamber B of the present invention;

[0038] Figure 4 This is a structural model diagram of the metabolic chamber C of the present invention;

[0039] Figure 5 This is a diagram showing the CO2 gas concentration field during the operation of this invention.

[0040] Figure 6 This is a diagram showing the CO2 gas velocity field during the operation of this invention.

[0041] Figure 7 The graph shows the changes in average gas concentration inside the chamber and concentration at the chamber outlet during a 900-second cycle of operation of this invention.

[0042] Figure 8 This is an enlarged graph of the first 80 seconds of the 90-cycle period of this invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] like Figure 1 As shown, the present invention provides a method for designing the aerodynamic structure of a metabolic chamber based on simulation technology, which specifically includes the following steps:

[0045] Step 1: Establishment of the metabolic chamber model: Use fluid dynamics simulation software (such as AnsysFluent simulation software) to create three identical metabolic chamber models, namely metabolic chamber A, metabolic chamber B, and metabolic chamber C, with chamber dimensions of 3200*2300*2400mm. The chambers contain a bed, table, toilet, sink, and pass-through window, which are simplified to cuboids during modeling. Sampling ports, air inlets, air supply ports, air return ports, and CO2 injection ports are set on the chambers.

[0046] The air inlet is located on the side of the cabin and is a 25mm round hole for supplying fresh air into the cabin. The CO2 injection port is located at the head of the bed and is also a 25mm round hole for simulating CO2 produced by human respiration. A 25mm diameter sampling port is located on the top of the cabin for sampling and detecting CO2 gas inside the cabin. The air supply and return vents of the cabin are both rectangular structures with dimensions of (600~950)*200mm. Preferably, the air supply and return vents are rectangular structures with dimensions of 600*200mm. The air supply and return vents are connected to the internal circulation equipment of the gas inside the cabin. The internal circulation equipment is a high-precision air conditioner. Preferably, the temperature control accuracy of the high-precision air conditioner is ±0.5℃ and the internal circulation air volume is 19000L / min.

[0047] like Figure 2 As shown, the air supply vent and return vent of metabolic chamber A are both located in one of the top corners, and the return vent is lower than the air supply vent.

[0048] like Figure 3 As shown, the air supply vent of metabolic chamber B is located near the head of the bed and below the CO2 injection port, while the return air vent is located on the top of the chamber and on the side away from the head of the bed.

[0049] like Figure 4 As shown, the air supply vent and return vent of the metabolic chamber C are both located on the side wall near the head of the bed, with the air supply vent positioned below the CO2 injection port and the return vent positioned near the top of the chamber.

[0050] Step 2: Mesh generation: Use fluid dynamics simulation software to generate a mesh for the built model (such as the Meshing software included in Ansys Fluent simulation software). Refine the mesh for each gas inlet and outlet section to ensure that the mesh quality meets the calculation requirements.

[0051] Step 3: Setting initial conditions:

[0052] In the fluid dynamics simulation software, the k-ε standard wall function is selected for the viscous model; the energy equation is set to "on"; the component transport is selected for the calculation model, and the inlet diffusion option is checked.

[0053] The solution method is to choose the SIMPLE algorithm (the SIMPLE algorithm is a semi-implicit method for pressure coupling equations and is a widely used numerical method for solving flow fields in computational fluid dynamics);

[0054] The temperature is 300K (the temperature of all gases and walls is 300K, meaning the temperature remains constant).

[0055] Humidity is: without considering the effect of humidity (no moisture factor was added, so it can be considered as dry gas and environment);

[0056] Gravity is taken into account, and the gravitational acceleration is set to 9.80 m / s². 2 ;

[0057] The time is set to transient;

[0058] The composition of fresh air is simplified to a mixture of O2, CO2 and N2, with mass fractions of 23.1%, 0.046%, and 76.854%, respectively.

[0059] The air inlet is set as a velocity inlet, and the incoming fresh air is the aforementioned fresh air at a velocity of 3.397 m / s. At this time, the air intake into the cabin through the 25 mm round hole is approximately 100 L / min.

[0060] The gas outlet inside the chamber is set as a pressure outlet to prevent backflow.

[0061] The supply and return air vents of the internal circulation system have equal areas and are both set as velocity inlets. The air velocity at the return air vent is -2.64 m / s, where the negative value represents exhaust from inside the cabin to the outside. At this time, the gas flow rate through the 600*200 rectangular hole is approximately 19000 L / min. The air velocity at the supply air vent is 2.64 m / s. The gas composition at the supply and return air vents is the same, which is achieved by writing a program.

[0062] The sampling port is a pressure outlet, and the gas composition at the return port is the same as that at the air inlet, which is achieved by writing a UDF program.

[0063] Standard initialization: cabin air is initialized to air.

[0064] Monitor the sampling port and the average CO2 concentration inside the chamber;

[0065] All other surfaces are designed as insulated walls;

[0066] Step 4: Simulation execution steps:

[0067] Step 1: Set the CO2 injection port to a wall, time step: 0.1s, number of time steps: 400, maximum iteration: 40, automatic saving: 50 time steps;

[0068] Step 2: Set the CO2 injection port to open, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, 0.03397m / s (approximately 1L / min), where FCO2 = 1 (concentration is 100%, representing 100% CO2 entering);

[0069] Step 3: Set the CO2 injection port to open, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 2L / min, 0.06794m / s, where FCO2=1;

[0070] Step 4: Set the CO2 injection port to open, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, 0.03397m / s, where FCO2=1;

[0071] First, set the CO2 injection port to the wall and run for 40 seconds to ensure the gas inside the chamber is mixed evenly.

[0072] After running for 40 seconds, CO2 began to enter through the CO2 injection port at a rate of 1 L / min, and the operation continued for 300 seconds.

[0073] After running for another 300 seconds, the CO2 flow rate was doubled to 2L / min to simulate the human body changing from a resting state to an active state. During the active state, the amount of CO2 emitted by the human body will increase. This process was repeated for 300 seconds.

[0074] Finally, change the CO2 flow rate back to 1 L / min and run for 300 seconds;

[0075] The concentration field and velocity field after running for 120 seconds are as follows: Figure 5 and Figure 6 As shown, the motion trajectory of the flow field and the gradual development of the concentration field can be clearly presented on the computer screen. Numerical simulation can reproduce the flow scenario and trend in the form of images or numerical values.

[0076] Step 5: Generation of Simulation Curves: Based on the conditions and algorithm set in Step 3, and under the operation in Step 4, the fluid dynamics simulation software plots the average gas concentration inside the chamber and the concentration change curves at the chamber outlet in the same coordinate system, as shown below. Figure 7 The figure shown is a curve plotted over a 900-second cycle, as follows: Figure 8 The image shows an enlarged curve during the first 80 seconds of a 900-second cycle.

[0077] Step Six: Analysis of Simulation Results: By comparing the average gas concentration changes inside and at the outlet of metabolic chambers A, B, and C generated in Step Five under the same coordinate system, from... Figure 7 As can be seen, at the same time, there are certain errors between the average concentration inside the chamber and the concentration at the outlet for different schemes. Among them, the side-supply and side-return scheme in metabolic chamber C has the smallest error. Figure 7 Magnifying the coordinate axes, such as Figure 8 As shown, by focusing on the changes in the concentration in the chamber during the first 80 seconds, it can be clearly seen that the side-supply and side-return response time in metabolic chamber C is the fastest. Therefore, the aerodynamic structure of metabolic chamber C is more effective than that of metabolic chambers A and B. The response time in the curve is the fastest, making it the most suitable aerodynamic structure for metabolic chambers.

[0078] Therefore, when constructing the metabolic chamber, its aerodynamic structure should be assembled in the same way as that of metabolic chamber C, so as to maximize the mixing response time of the gases inside the constructed metabolic chamber.

[0079] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0080] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for designing the aerodynamic structure of a metabolic cabin based on simulation technology, characterized in that, Includes the following steps: Step 1: Establishing the Metabolic Chamber Model: Three identical metabolic chamber models are created: Metabolic Chamber A, Metabolic Chamber B, and Metabolic Chamber C. Sampling ports, air inlets, air supply vents, air return vents, and CO2 injection ports are installed on the chambers of Metabolic Chamber A, B, and C. Beds, tables, toilets, sinks, and pass-through windows are placed inside each chamber, simplified as cuboids during modeling. A sampling port is located at the top of the chamber for sampling and detecting CO2 gas within the chamber. The air supply and return vents of metabolic chamber A are both located in one of the top corners, with the return vent lower than the air supply vent. The air supply vent of metabolic chamber B is located near the head of the bed and below the CO2 injection port, while the return air vent is located on the top of the chamber and on the side away from the head of the bed. The air supply vent and return vent of the metabolic chamber C are both located on the side wall near the head of the bed, with the air supply vent positioned below the CO2 injection port and the return vent positioned near the top of the chamber. Step 2: Mesh Generation: Refine the mesh for the sampling port, air inlet, supply air outlet, return air outlet, and CO2 injection port to ensure the mesh quality meets the calculation requirements; Step 3: Setting initial conditions; Step 4: Simulation execution steps: First, set the CO2 injection port to the wall and run it for 40 seconds to ensure that the gas inside the chamber is mixed evenly. After running for 40 seconds, CO2 began to enter through the CO2 injection port at a rate of 1 L / min, and the operation continued for 300 seconds. After running for another 300 seconds, the CO2 flow rate was doubled to 2L / min to simulate the human body changing from a resting state to an active state. During the active state, the amount of CO2 emitted by the human body will increase. This process was repeated for 300 seconds. Finally, change the CO2 flow rate back to 1 L / min and run for 300 seconds; Step 5: Generation of simulation curves: Based on the conditions and algorithm set in Step 3, and under the operation in Step 4, the average gas concentration inside the cabin and the concentration change curve at the cabin outlet are plotted in the same coordinate system according to the operation status. Step Six: Analysis of Simulation Results: By comparing the average gas concentration inside the chamber and the concentration change curve at the chamber outlet generated by metabolic chambers A, B, and C in the same coordinate system in Step Five, the one with the fastest response time is the most suitable aerodynamic structure for the metabolic chamber.

2. The method for metabolic cabin aerodynamic structure design based on simulation technology according to claim 1, characterized in that: The air supply and return vents of metabolic chambers A, B, and C are all (600~950). The structure is a 200mm rectangular shape, and the air supply and return vents are connected to the internal circulation equipment in the cabin for the circulation of air inside the cabin. The internal circulation equipment is a high-precision air conditioner, and the air inlet and CO2 injection port are both 25mm round holes.

3. The method for metabolic cabin aerodynamic structure design based on simulation technology according to claim 1, characterized in that: The initial conditions include the mass fractions of fresh air, wherein the mass fractions of the mixture of O2, CO2 and N2 in the fresh air are 23.1%, 0.046%, and 76.854%, respectively.

4. The method for metabolic cabin aerodynamic structure design based on simulation technology according to claim 1, characterized in that: The sampling port is a circular hole with a diameter of 25 mm.

5. The method for metabolic cabin aerodynamic structure design based on simulation technology according to claim 1, characterized in that: The initial conditions include temperature, which includes the temperature of all gases and the wall surface, and the temperature is kept constant at 300K.

6. The method for metabolic cabin aerodynamic structure design based on simulation technology according to claim 1, characterized in that: The gas composition of the supply air vent and the return air vent is the same, and the gas composition of the return air vent is the same as that of the air inlet.

7. The aerodynamic structural design method for a metabolic chamber based on simulation technology according to claim 1, characterized in that: The specific parameters for the simulation run step in step four are set as follows: Step 1: Set the CO2 injection port to a wall, time step: 0.1s, number of time steps: 400, maximum iteration: 40, automatic saving: 50 time steps; Step 2: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, where FCO2=1; Step 3: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 2L / min, where FCO2=1; Step 4: Set the CO2 injection port to CO2 injection port, time step: 0.1s, number of time steps: 3000, maximum iteration: 40, automatic saving: 50 time steps, 1L / min, where FCO2=1; Where FCO2=1 means that 100% CO2 enters.

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