A calculation method for mass transfer performance of membrane artificial lung

Abstract

The present invention provides a method for calculating the mass transfer performance of a membrane artificial lung, wherein the calculation conditions are: 1) under steady-state and constant temperature conditions, the membrane fibers of the membrane artificial lung are evenly distributed along the length; 2) oxygen and carbon dioxide are ideal gases, and deionized water is in a steady-state laminar flow without axial diffusion; 3) the gas-liquid flow rate is uniform and constant; 4) Henry's law applies to the solubility of oxygen and carbon dioxide in deionized water; the calculation method comprises the following steps: establishing an ordinary differential equation in the oxygen mass transfer process and an ordinary differential equation in the mass transfer process when carbon dioxide is dissolved in deionized water. The present invention calculates the mass transfer performance of oxygen and carbon dioxide on both sides of the membrane artificial lung to explore the influence of the gas-liquid flow rate on the total mass transfer coefficient of oxygen and carbon dioxide and the simulation calculation results of the mass transfer rate of oxygen and carbon dioxide, thereby providing an experimental basis and theoretical basis for subsequent clinical research and application of membrane artificial lungs.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to a method for calculating the mass transfer performance of a membrane artificial lung. Background Art

[0002] Membrane oxygenator is a key device in extracorporeal membrane oxygenation (ECMO). It can provide sufficient gas exchange or perfusion for the heart and lungs, mimicking the lung function of the human body in extracorporeal circulation, and is often used in the treatment of patients with severe cardiopulmonary failure. The key component of the membrane artificial lung is a thin breathable membrane that separates the blood from the gas phase side of the extracorporeal circulation circuit. Oxygen diffuses from the gas phase side into the blood to artificially oxygenate red blood cells, while carbon dioxide diffuses from the blood to the gas phase side for removal.

[0003] The mass transfer process of the membrane artificial lung is similar to that of the human lung, which mainly involves the dissolution of oxygen and the removal of carbon dioxide. The oxygen present in the blood mainly consists of two parts: oxygen dissolved in plasma and oxygen bound to hemoglobin. These two parts of oxygen in the blood are in a dynamic equilibrium state. During the oxygen mass transfer process of the membrane artificial lung, the oxygen in the oxygenator enters the blood through the hollow fiber membrane and dissolves in the plasma. The dissolved oxygen gradually binds to hemoglobin through the cell membrane. As the oxygen binding capacity of hemoglobin reaches its upper limit, the oxygen mass transfer tends to balance. Carbon dioxide in the blood mainly exists in the following two forms: most of it is in the form of HCO3 - It exists in plasma and red blood cells, while a small part is directly dissolved in plasma as HCO3 - Carbon dioxide in the form of HCO3 and dissolved in gas is in a dynamic equilibrium state. - It first diffuses into red blood cells, is converted into dissolved CO2 under the action of carbonic anhydrase and diffuses into plasma, and finally diffuses out of the body through the hollow fiber membrane to achieve the removal of carbon dioxide.

[0004] There are about 300 million alveoli in the human lungs, with a total surface area of ​​about 70m 2 , which is more than 50 times that of commercial membranes. Around the alveoli, there are pulmonary capillaries with a structure similar to that of air ducts. The thickness of the capillary-alveolar interface is about 0.5 μm, which is highly permeable to oxygen and carbon dioxide. For healthy lungs, the O2 pressure gradient is about 40 mmHg and the CO2 pressure gradient is about 6 mmHg. For commercial oxygenators, the single-layer O2 permeation rate is generally required to be 250 cm / min. 3 , CO2 removal 200cm 3 .

[0005] Theoretical analysis of membrane artificial lungs is a hot topic in the field of membrane mass transfer. The exploration of experimental methods can provide a mass transfer effect under actual conditions, while the establishment of appropriate calculation methods can allow researchers to gain an in-depth understanding of the dynamics and gas transfer conditions in local conditions within the membrane artificial lung, thereby allowing researchers to better understand the mass transfer characteristics.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for calculating the mass transfer performance of a membrane artificial lung. By calculating the continuous mass transfer rates of oxygen and carbon dioxide on both sides of a hollow fiber membrane artificial lung, the mass transfer rates of oxygen and carbon dioxide are obtained, and the influencing factors of oxygen and carbon dioxide in the mass transfer process can be more accurately seen, providing an experimental basis and theoretical basis for subsequent clinical research and application of membrane artificial lungs.

[0008] In order to achieve the above object, the present invention particularly adopts the following technical solutions:

[0009] The present invention provides a method for calculating the mass transfer performance of a membrane artificial lung, wherein the calculation conditions are:

[0010] 1) Under steady-state and constant temperature conditions, the membrane fibers of the membrane artificial lung are evenly distributed along their length;

[0011] 2) Oxygen and carbon dioxide are ideal gases, and deionized water flows in a steady laminar flow without axial diffusion;

[0012] 3) The gas and liquid flow rate is uniform and constant;

[0013] 4) Henry's law applies to the solubility of oxygen and carbon dioxide in deionized water;

[0014] The calculation method comprises the following steps:

[0015] Under the above calculation conditions, the ordinary differential equation for oxygen mass transfer is established:

[0016]

[0017] Under the above established conditions, carbon dioxide is dissolved in deionized water, and the ordinary differential equation for carbon dioxide mass transfer is established:

[0018]

[0019] In formula (1) and formula (2), v l is the flow rate of deionized water, in m·s -1 ; is the mass concentration of oxygen in the deionized water liquid phase and oxygen gas phase, in mg·L -1 ; is the mass concentration of carbon dioxide in the deionized water liquid phase, is the mass concentration of carbon dioxide diffused into the oxygen gas phase, in mg·L -1 ; K is the total mass transfer coefficient, in m·s -1 ; a is the ratio of the surface area to the volume of the membrane artificial lung, in m 2 ·m -3 ; z is the length of the membrane wire of the membrane artificial lung, in m;

[0020] Among them, in formula (1) and formula (2), the method for solving the total mass transfer coefficient K includes the following steps:

[0021] The mass transfer correlation equation of the gas phase in the mass transfer process is:

[0022]

[0023] D g is the gas phase diffusion coefficient, and the calculation formula is:

[0024]

[0025] In formula (3) and formula (4), k g is the gas phase mass transfer coefficient, in m·s -1 ;d e is the fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D g is the gas phase diffusion coefficient, in m 2 ·s -1 ; T is temperature, unit is K; P is the total pressure of oxygen introduced, unit is Pa; V A 、V B is the molecular mass of the gas phase, in g·mol -1 ;μ A , μ B is the liquid gram-molar volume of the gas phase at normal boiling point, in cm 3 gmol -1 ;

[0026] For the flow of gas phase in the pores of the membrane artificial lung, the mass transfer correlation under non-wetted conditions is:

[0027]

[0028] In formula (5), k m is the pore mass transfer coefficient of the membrane artificial lung, in m·s -1 ;D g is the diffusion coefficient, in m 2 ·s -1; ε is the porosity of the pores on the membrane artificial lung; τ is the curvature factor, which is 1 / ε; δ is the membrane wall thickness of the membrane artificial lung, in m;

[0029] The mass transfer correlation equation of deionized water in the mass transfer process is:

[0030]

[0031] In formula (6), k l is the mass transfer coefficient of deionized water, in m·s -1 ;d e is the membrane fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D l is the diffusion coefficient of the gas phase in deionized water, in m 2 ·s -1 ;

[0032] Calculate the total mass transfer coefficient K, the formula is:

[0033]

[0034] In formula (7), H is Henry's constant;

[0035] Among them, the solution formula for Reynolds number Re in equation (3) and equation (6) is:

[0036]

[0037] Among them, the solution formula of Schmidt number Sc in equation (3) and equation (6) is:

[0038]

[0039] In formula (8) and formula (9), d e is the diameter, in m; u is the fluid velocity, in m·s -1 ; ρ is the fluid density, in kg·m -3 ; μ is the fluid viscosity, unit is Pa·s; D is the diffusion coefficient, unit is m 2 ·s -1 ;

[0040] Substituting the result of formula (7) into formula (1) and formula (2), the mass transfer rates of oxygen and carbon dioxide are obtained respectively, which are the simulation values, representing the mass transfer performance of the membrane artificial lung.

[0041] Regarding the membrane filament length z and the membrane fiber length L, the membrane fiber length L is a constant, while the membrane filament length z can be any value between 0 and L and is a variable.

[0042] Based on the research of "A Mathematical Model to Predict CO2 Removal in HollowFiber Membrane Oxygenators", the present invention establishes a calculation method for the mass transfer performance of membrane artificial lungs. By calculating the mass transfer efficiency of oxygen and carbon dioxide in the membrane artificial lungs, the influence of gas-liquid flow rate on the total mass transfer coefficient of oxygen and carbon dioxide and the simulation calculation results of the mass transfer rate of oxygen and carbon dioxide are explored, providing an experimental basis and theoretical basis for the subsequent clinical research and application of membrane artificial lungs.

[0043] Preferably, the calculation method further includes a method for verifying the mass transfer rates of oxygen and carbon dioxide obtained above, comprising the following steps:

[0044] Oxygen enters the membrane artificial lung, and carbon dioxide is dissolved in deionized water and enters the model artificial lung to transfer mass with oxygen. After the mass transfer is completed, oxygen is expelled, and then carbon dioxide is replenished and re-enters the membrane artificial lung. After stabilization, the deionized water at the inlet and outlet of the membrane artificial lung is collected for calculation to obtain the mass transfer rate of oxygen and carbon dioxide, which is the experimental value.

[0045] The experimental values ​​were compared with the simulated values.

[0046] The present invention also provides a device adapted to the above-mentioned calculation method, including a membrane artificial lung, wherein an oxygen inlet is provided at the end of the membrane artificial lung, a carbon dioxide inlet is provided at the upper end of the membrane artificial lung, an oxygen outlet is provided at the lower end of the membrane artificial lung, and a carbon dioxide outlet is provided at the end of the membrane artificial lung. The simulation value is obtained by calculating the total mass transfer coefficient of the model artificial lung.

[0047] Preferably, the membrane artificial lung is connected to a verification device, which includes an oxygen cylinder, the oxygen cylinder is connected to the oxygen inlet of the membrane artificial lung, the carbon dioxide inlet of the membrane artificial lung is connected to an oxygen removal device, the oxygen outlet of the model artificial lung is connected to a liquid storage tank storing deionized water, the liquid storage tank is connected to the oxygen removal device, and the oxygen removal device is connected to the carbon dioxide cylinder. The experimental value is obtained by calculating the concentration of deionized water at the carbon dioxide inlet and oxygen outlet of the membrane artificial lung, and compared with the simulation value for verification.

[0048] The device adapted by the method for verifying the mass transfer performance of oxygen and carbon dioxide on both sides of the model artificial lung assembly mainly consists of two mass transfer parts:

[0049] 1) In the gas phase, the oxygen pressure is first adjusted by a steel cylinder, and then passed into the membrane wire of the membrane artificial lung through a gas flow meter. Part of the oxygen will pass through the membrane pores and enter the deionized water part, dissolving in the deionized water, and the rest of the oxygen will be discharged through the other end of the membrane artificial lung;

[0050] 2) For the deionized water part, the deionized water is first stored in a liquid storage tank, and then transported to the top of the oxygen removal device by a peristaltic pump, and flows into the oxygen removal device in the form of a spray, while carbon dioxide is introduced from the bottom of the oxygen removal device. The bottom is designed to be disc-shaped, and there are small holes on the disc, which allows carbon dioxide to evenly pass into the simulated liquid, thereby achieving the effect of discharging oxygen and introducing carbon dioxide. The deionized water that discharges oxygen and introduces carbon dioxide flows out from the bottom of the oxygen removal device, and is sent to the outside of the membrane filaments of the membrane artificial lung through a peristaltic pump and a flowmeter. After the mass transfer is completed, it is discharged from the other end and flows into the liquid storage tank, thereby achieving a circulation effect. Sampling ports are provided at both ends of the membrane artificial lung.

[0051] The mass transfer efficiency of carbon dioxide and oxygen can be calculated by measuring the concentrations of carbon dioxide and oxygen in the deionized water at the inlet and outlet of the membrane artificial lung.

[0052] Compared with the prior art, the present invention has at least the following advantages:

[0053] (1) The present invention establishes a calculation method for the mass transfer performance of oxygen and carbon dioxide on both sides of the membrane artificial lung. Through the calculation method, the local dynamics and gas transmission conditions of the membrane artificial lung can be more clearly understood, the mass transfer characteristics can be better understood, and the influencing factors of the oxygen and carbon dioxide mass transfer rates can be described concisely and accurately.

[0054] (2) The present invention sets up a verification method to compare the simulated value of the mass transfer rate obtained by calculation with the experimental value obtained by verification, thereby ensuring the accuracy of the calculation method and providing an experimental basis and theoretical basis for subsequent clinical research and application of membrane artificial lungs. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0056] Figure 1 A process flow chart of a verification device provided by an embodiment of the present invention;

[0057] Figure 2 Comparison between the simulated and experimental values ​​of oxygen mass transfer coefficient at different gas-liquid flow rates;

[0058] Figure 3 Comparison between the simulated and experimental values ​​of the carbon dioxide mass transfer coefficient at different gas-liquid flow rates.

[0059] in,

[0060] 1-Oxygen cylinder; 2-Oxygen buffer tank; 3-Liquid storage tank; 4-Membrane artificial lung; 5-Oxygen removal device; 6-Carbon dioxide buffer tank; 7-Carbon dioxide cylinder. DETAILED DESCRIPTION

[0061] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0062] Example

[0063] like Figure 1-3 As shown, this embodiment provides a method for calculating the mass transfer performance of a membrane artificial lung. The present invention is to explore the influencing factors of the mass transfer effect of oxygen and carbon dioxide in a membrane artificial lung. It mainly conducts theoretical research on the liquid phase side, gas phase side and membrane phase side of the membrane artificial lung, so as to have a deeper understanding of the dynamics and gas transmission conditions under local conditions in the membrane artificial lung, thereby better understanding the mass transfer characteristics.

[0064] The mass transfer resistance of oxygen and carbon dioxide is mainly divided into the mass transfer resistance on the gas phase side, the mass transfer resistance in the membrane pores and the mass transfer resistance on the liquid side. Since the diffusion resistance of oxygen and carbon dioxide in the liquid phase is relatively large, the mass transfer effect is mainly controlled by the liquid phase side.

[0065] The conditions for this calculation method are:

[0066] 1) The calculation method is based on steady-state and constant temperature conditions, and the membrane fibers of the membrane artificial lung are evenly distributed along the length;

[0067] 2) Oxygen and carbon dioxide are ideal gases, and deionized water flows in a steady laminar flow without axial diffusion;

[0068] 3) The gas and liquid flow rate is uniform and constant;

[0069] 4) Henry's law applies to the solubility of oxygen and carbon dioxide in deionized water.

[0070] The calculation method includes the following steps:

[0071] Step 1- Obtain the simulation value:

[0072] (1) Establish the ordinary differential equation for oxygen mass transfer in membrane artificial lung:

[0073]

[0074] Dissolve carbon dioxide in deionized water and establish the ordinary differential equation for carbon dioxide mass transfer in the membrane artificial lung:

[0075]

[0076] In formula (1) and formula (2), v l is the flow rate of deionized water, in m·s -1 ; is the mass concentration of oxygen in the deionized water liquid phase and oxygen gas phase, in mg·L -1 ; is the mass concentration of carbon dioxide in the deionized water liquid phase, is the mass concentration of carbon dioxide diffused into the oxygen gas phase, in mg·L -1 ; K is the total mass transfer coefficient, in m·s -1 ; a is the ratio of the surface area to the volume of the membrane artificial lung, in m 2 ·m -3 ; z is the length of the membrane wire of the membrane artificial lung, in m;

[0077] In this embodiment, since the amount of carbon dioxide in the gas phase is too small and the amount of oxygen is too large relative to the carbon dioxide, carbon dioxide is basically not counted. Therefore, the gas phase side is calculated as all oxygen.

[0078] Wherein, in formula (1), the method for solving the total mass transfer coefficient K includes the following steps:

[0079] Oxygen flows in the tube, the flow state of oxygen is laminar flow, the transfer process of oxygen in the gas phase is the diffusion of oxygen molecules, and the mass transfer correlation of oxygen in oxygen is:

[0080]

[0081] D g is the oxygen diffusion coefficient, and the calculation formula is:

[0082]

[0083] In formula (3) and formula (4), k g is the oxygen mass transfer coefficient, in m·s -1 ;d e is the fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D gis the oxygen diffusion coefficient, in m 2 ·s -1 ; T is temperature, unit is K; P is the total pressure of oxygen introduced, unit is Pa; V A 、V B are the molecular weights of oxygen, in g·mol -1 ;μ A , μ B is the gram-molar volume of liquid oxygen at its normal boiling point, in cm 3 gmol -1 ;

[0084] For the flow of oxygen in the membrane pores, the mass transfer resistance it encounters is mainly related to wetting and non-wetting. The membrane artificial lung in the present invention is made of PMP hollow fiber material, which has a certain hydrophobicity. Therefore, the present invention only considers the mass transfer process of oxygen in the membrane pores under non-wetting conditions. In the actual process, the internal microporous structure of the hollow fiber membrane is relatively complex. In general, its mass transfer correlation formula is:

[0085]

[0086] In formula (5), k m is the pore mass transfer coefficient of the membrane artificial lung, in m·s -1 ;D g is the oxygen diffusion coefficient, in m 2 ·s -1 ; ε is the porosity of the pores on the membrane artificial lung; τ is the curvature factor, which is 1 / ε; δ is the membrane wall thickness of the membrane artificial lung, in m;

[0087] For the flow of deionized water in the shell, it is mainly physical absorption, the flow of deionized water is laminar flow, and the mass transfer correlation of oxygen in deionized water is:

[0088]

[0089] In formula (6), k l is the mass transfer coefficient of deionized water, in m·s -1 ;d e is the fiber diameter, in m; L is the fiber length, in m; D l is the diffusion coefficient of oxygen in deionized water (obtained from the records in Aspen Plus), in m 2 ·s -1 ;

[0090] The mass transfer coefficient k of oxygen in oxygen is calculated according to formulas (3), (4), (5) and (6): g , oxygen mass transfer coefficient k in the membrane pores mand the mass transfer coefficient k of oxygen in deionized water l , calculate the total mass transfer coefficient K, the formula is:

[0091]

[0092] In formula (7), H is Henry's constant;

[0093] Among them, the solution formula for Reynolds number Re in equation (3) and equation (6) is:

[0094]

[0095] Among them, the solution formula of Schmidt number Sc in equation (3) and equation (6) is:

[0096]

[0097] In formula (8) and formula (9), d e is the diameter, in m; u is the fluid velocity, in m·s -1 ; ρ is the fluid density, in kg·m -3 ; μ is the fluid viscosity, unit is Pa·s; D is the diffusion coefficient, unit is m 2 ·s -1 .

[0098] Substitute the result of equation (7) into equation (1) and solve it using Matlab software Ode45 to find the concentration of oxygen on the liquid phase side of deionized water, that is, the outlet concentration of oxygen.

[0099] Wherein, in formula (2), the method for solving the total mass transfer coefficient K includes the following steps:

[0100] Carbon dioxide is dissolved in deionized water and flows in the shell side. The flow state is laminar flow. Its mass transfer correlation in oxygen is:

[0101]

[0102] D g is the carbon dioxide diffusion coefficient, and the calculation formula is:

[0103]

[0104] In formula (3) and formula (4), k g is the carbon dioxide mass transfer coefficient, in m·s -1 ;d e is the fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D g is the carbon dioxide diffusion coefficient, in m 2 ·s -1; T is temperature, unit is K; P is the total pressure of oxygen introduced, unit is Pa; V A 、V B is the molecular mass of oxygen and carbon dioxide, in g·mol -1 ;μ A , μ B is the liquid gram-mole volume of oxygen and carbon dioxide at normal boiling point, in cm3·gmol -1 ;

[0105] For the flow of carbon dioxide in the membrane pores, the mass transfer resistance it encounters is mainly related to wetting and non-wetting. The membrane artificial lung in the present invention is made of PMP hollow fiber material, which has a certain hydrophobicity. Therefore, the present invention only considers the mass transfer process of oxygen in the membrane pores under non-wetting conditions. Since the internal microporous structure of the hollow fiber membrane is relatively complex in the actual process, its mass transfer correlation formula is generally:

[0106]

[0107] In formula (5), k m is the pore mass transfer coefficient of the membrane artificial lung, in m·s -1 ;D g is the carbon dioxide diffusion coefficient, in m2·s -1 ; ε is the porosity of the pores on the membrane artificial lung; τ is the curvature factor, which is 1 / ε; δ is the membrane wall thickness of the membrane artificial lung, in m;

[0108] For the flow of deionized water in the shell, it is mainly physical absorption, the flow of deionized water is laminar flow, and the mass transfer correlation of carbon dioxide in deionized water is:

[0109]

[0110] In formula (6), k l is the mass transfer coefficient of deionized water, in m·s -1 ;d e is the fiber diameter, in m; L is the fiber length, in m; D l is the diffusion coefficient of carbon dioxide in deionized water (obtained from the records in Aspen Plus), in m 2 ·s -1 ;

[0111] The mass transfer coefficient k of carbon dioxide in oxygen calculated according to equations (3), (4), (5) and (6) is: g , mass transfer coefficient k of carbon dioxide in the membrane pores m and the mass transfer coefficient k of carbon dioxide in deionized water l , calculate the total mass transfer coefficient K, the formula is:

[0112]

[0113] In formula (7), H is Henry's constant;

[0114] Among them, the solution formula for Reynolds number Re in equation (3) and equation (6) is:

[0115]

[0116] Among them, the solution formula of Schmidt number Sc in equation (3) and equation (6) is:

[0117]

[0118] In formula (8) and formula (9), d e is the diameter, in m; u is the fluid velocity, in m·s -1 ; ρ is the fluid density, in kg·m -3 ; μ is the fluid viscosity, unit is Pa·s; D is the diffusion coefficient, unit is m 2 ·s -1 .

[0119] In this embodiment, when equations (8) and (9) are substituted into equation (3), the fluid is oxygen, and when equations (8) and (9) are substituted into equation (6), the fluid is deionized water.

[0120] Substitute the result of equation (7) into equation (2) and solve it using Matlab software Ode45 to obtain the mass concentration of carbon dioxide in the deionized water liquid phase, that is, the outlet concentration of carbon dioxide.

[0121] The calculated outlet concentrations of oxygen and carbon dioxide are calculated to obtain the mass transfer rates of oxygen and carbon dioxide, which are the simulation values.

[0122] Step 2 - Obtain experimental values:

[0123] The experimental values ​​are obtained using the following verification device:

[0124] like Figure 1As shown, the verification device includes a membrane artificial lung 4. In the present embodiment, the material of the membrane artificial lung 4 is selected as PMP hollow fiber membrane artificial lung. Of course, in a specific implementation manner, the material can be selected according to actual needs to prepare the membrane artificial lung. The left and right ends of the membrane artificial lung 4 are provided with an oxygen inlet and a carbon dioxide outlet, and the upper and lower ends are provided with a carbon dioxide inlet and an oxygen outlet. The oxygen inlet is connected to an oxygen buffer tank 2, and the oxygen buffer tank 2 is connected to an oxygen cylinder 1. The carbon dioxide inlet of the membrane artificial lung 4 is connected to an oxygen removal device 5, and the oxygen removal device 5 is connected to a carbon dioxide buffer tank 6, and the carbon dioxide buffer tank 6 is connected to a carbon dioxide cylinder 7. The oxygen outlet of the membrane artificial lung 4 is connected to a liquid storage tank 3, and the liquid storage tank 3 is connected to the oxygen removal device 5.

[0125] The oxygen removal device 5 is provided with fillers inside, and the bottom is disc-shaped with uniform small holes on the bottom. The deionized water after mass transfer will flow into the oxygen removal device 5 from the top of the oxygen removal device 5 in a spraying manner, and the oxygen obtained by mass transfer in the deionized water after mass transfer is discharged through the fillers, and then carbon dioxide is introduced into the deionized water from the holes set at the bottom to ensure that the deionized water remains fresh.

[0126] Of course, in this embodiment, carbon dioxide is mixed with deionized water before entering the membrane artificial lung 4. In the membrane artificial lung 4, the oxygen in the tube side and the carbon dioxide mixed in the deionized water in the shell side are mass transferred. Therefore, the carbon dioxide inlet is actually the deionized water inlet, and the oxygen outlet is actually the deionized water outlet.

[0127] The method for using the verification device comprises the following steps:

[0128] (1) Deionized water is delivered to the liquid storage tank 3 via a peristaltic pump, and the constant temperature water tank is turned on to control the temperature at 37°C. The temperature of the oxygen removal device 5 is controlled at 37°C in advance. When the temperature of the liquid storage tank 3 is constant at about 37°C, the deionized water is delivered to the top of the oxygen removal device 5 via a peristaltic pump and flows into the oxygen removal device 5 in the form of a spray.

[0129] (2) Open the carbon dioxide cylinder 7, adjust it through the gas flow meter, and deliver it to the bottom of the oxygen removal device 5, and evenly introduce it into the deionized water. A ventilation duct is provided on the top, and the excess gas is discharged into the ventilation system through the ventilation duct;

[0130] (3) After the deionized water passes through the oxygen removal device 5 to discharge oxygen and introduce carbon dioxide, it flows out from the bottom of the oxygen removal device 5, is transported by a peristaltic pump and regulated by a deionized water flowmeter, is transported to the inlet of the membrane artificial lung 4, and then flows into the liquid storage tank 3 from the outlet of the membrane artificial lung 4;

[0131] (4) After the deionized water circulation system is stable, open the oxygen cylinder 1, adjust the appropriate pressure and flow, and deliver it to the inlet of the membrane artificial lung 4. After the excess oxygen comes out from the outlet of the membrane artificial lung 4, it is introduced into the ventilation system;

[0132] (5) Adjust the required parameters, and after they are stable for 30 minutes, quickly take out deionized water from the inlet and outlet of the membrane artificial lung 4 to test the concentrations of oxygen and carbon dioxide.

[0133] Test content:

[0134] The gas phase pressure was maintained at 0.2 MPa, the temperature was 37 °C, the gas-liquid ratio was 5:1, and the deionized water flow rate was tested at 50 mL min -1 -300mL·min -1 The inlet and outlet concentrations of oxygen and carbon dioxide in deionized water under experimental conditions;

[0135] Test content method:

[0136] The concentration of oxygen in deionized water is determined by an oxygen meter. The oxygen electrode is calibrated according to the instructions, the dissolved oxygen electrode is cleaned with distilled water, and then inserted into the solution to be measured.

[0137] The concentration of carbon dioxide in deionized water is determined by titration as follows:

[0138] (1) Weigh solid sodium hydroxide and dissolve it in 30g of distilled water. Let it stand in a plastic bottle for four or five days. Take 1mL of the clear solution and place it in a 1000mL volumetric flask. Dilute it to the mark with distilled water and shake it well to make a 0.02mol·L -1 Sodium hydroxide solution, the exact concentration needs to be calibrated;

[0139] (2) Weigh 0.5 g of phenolphthalein and dissolve it in 50 mL of 95% alcohol. After the solution is complete, add 50 mL of distilled water and add 0.02 mol·L -1 Sodium hydroxide solution turns slightly red, prepare 0.5% phenolphthalein, and transfer into a 100 mL volumetric flask;

[0140] (3) Weigh 2 g of potassium hydrogen phthalate that has been dried to constant weight, add 500 mL of distilled water, and prepare 0.02 mol·L -1 Potassium hydrogen phthalate, transfer into a 500mL volumetric flask;

[0141] (4) Use a pipette to draw 0.02 mol·L -1Place 20 mL of potassium hydrogen phthalate in a conical flask, add 3 drops of the prepared phenolphthalein solution, and titrate with the sodium hydroxide solution to be calibrated until it turns light red and does not fade within one minute. Record the volume of sodium hydroxide consumed V0. The calculation formula for sodium hydroxide solution is:

[0142]

[0143] Where W is the concentration of sodium hydroxide, in mol·L -1 ; V0 is the volume of sodium hydroxide consumed, in mL.

[0144] (5) Take 10 mL of sample, add 6 drops of phenolphthalein solution, and titrate with sodium hydroxide solution until the solution turns light red. Record the consumed volume as V.

[0145] The formula for calculating carbon dioxide concentration is:

[0146]

[0147] In the formula, is the carbon dioxide concentration, in mg·L -1 ; V is the volume of sodium hydroxide solution consumed, in mL; V 样 is the sampling volume in mL.

[0148] The formula for calculating the mass transfer rate of oxygen and carbon dioxide is:

[0149]

[0150] Where N is the mass transfer rate, in mL min -1 ·m -2 ; C is the concentration of oxygen or carbon dioxide, mg·L -1 ;υ 液 is the flow rate of deionized water, in mL·min -1 ; ρ is density, unit is g·L -1 ; A is the membrane area of ​​the membrane artificial lung, in m 2 ;

[0151] When calculating the mass transfer rate of oxygen, C1 is the oxygen concentration of deionized water at the carbon dioxide inlet of the membrane artificial lung, and C2 is the oxygen concentration of deionized water at the oxygen outlet of the membrane artificial lung;

[0152] When calculating the mass transfer rate of carbon dioxide, C1 is the carbon dioxide concentration of deionized water at the oxygen outlet of the membrane artificial lung, and C2 is the carbon dioxide concentration of deionized water at the carbon dioxide inlet of the membrane artificial lung, and the experimental values ​​N of the mass transfer rates of oxygen and carbon dioxide are obtained respectively.

[0153] Step 3 - Compare the experimental values ​​with the simulated values:

[0154] like Figure 2 and Figure 3 As shown, Figure 2 Comparison between the simulated and experimental values ​​of the oxygen mass transfer coefficient at different gas-liquid flow rates. Figure 3 This is a comparison between the simulated value and the experimental value of the carbon dioxide mass transfer coefficient under different gas-liquid flow rates. According to the comparison of the oxygen mass transfer coefficient, it can be seen that the error of the oxygen mass transfer rate of deionized water is basically within 20%. The provided calculation method can better describe the mass transfer process of oxygen in the simulated liquid. According to the comparison of the carbon dioxide mass transfer coefficient, it can be seen that the error of the carbon dioxide mass transfer rate of deionized water is within 30%. The main reason is that the influence of carbonate ions and bicarbonate ions is not analyzed during the simulation calculation process, so this leads to a certain error between the simulated value and the experimental value, but it can basically describe the mass transfer process of carbon dioxide in the simulated liquid.

[0155] The present invention establishes a calculation method for the mass transfer performance of oxygen and carbon dioxide on both sides of the membrane artificial lung to explore the influence of the gas-liquid flow rate on the total mass transfer coefficient of oxygen and carbon dioxide and the simulated calculation results of the mass transfer rates of oxygen and carbon dioxide, and compares them with the experimental values ​​to verify the feasibility and accuracy of the calculation method, ensure that the calculation method can accurately reflect the mass transfer performance of oxygen and carbon dioxide of the membrane artificial lung, and provide an experimental basis and theoretical basis for subsequent clinical research and application of membrane artificial lungs.

[0156] Finally, it is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the principles and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for calculating the mass transfer performance of a membrane artificial lung, characterized in that: The calculation conditions are: 1) Under steady-state and constant temperature conditions, the membrane fibers of the membrane artificial lung are evenly distributed along their length; 2) Oxygen and carbon dioxide are ideal gases, and deionized water flows in a steady laminar flow without axial diffusion; 3) The gas and liquid flow rate is uniform and constant; 4) Henry's law applies to the solubility of oxygen and carbon dioxide in deionized water; The calculation method comprises the following steps: Under the above conditions, the ordinary differential equation for oxygen mass transfer is established: （1） Under the above conditions, carbon dioxide is dissolved in deionized water, and the ordinary differential equation for carbon dioxide mass transfer is established: （2） In formula (1) and formula (2), is the flow rate of deionized water, in m·s -1 ; , is the mass concentration of oxygen in the deionized water liquid phase and oxygen gas phase, in mg·L -1 , is the mass concentration of carbon dioxide in the deionized water liquid phase, is the mass concentration of carbon dioxide diffused into the oxygen gas phase, in mg·L -1 ; K is the total mass transfer coefficient, in m·s -1 ; a is the ratio of the surface area to the volume of the membrane artificial lung, in m 2 ·m -3 ; z is the length of the membrane wire of the membrane artificial lung, in m; Among them, in formula (1) and formula (2), the method for solving the total mass transfer coefficient K includes the following steps: The mass transfer correlation equation of the gas phase in the oxygen mass transfer process is: （3） D g is the gas phase diffusion coefficient, and the calculation formula is: （4） In formula (3) and formula (4), Sh g is the gas phase Sherwood number, k g is the gas phase mass transfer coefficient, in m·s -1 ;d e is the fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D g is the gas phase diffusion coefficient, in m 2 ·s -1 ; T is temperature, unit is K; P is the total pressure of oxygen introduced, unit is Pa; V A 、V B is the molecular mass of the gas phase, in g·mol -1 ; , is the liquid gram-molar volume of the gas phase at normal boiling point, in cm 3 gmol -1 ; For the flow of gas phase in the pores of the membrane artificial lung, the mass transfer correlation under non-wetted conditions is: （5） In formula (5), k m is the pore mass transfer coefficient of the membrane artificial lung, in m·s -1 ;D g is the gas phase diffusion coefficient, in m 2 ·s -1 ; ε is the porosity of the pores on the membrane artificial lung; is the curvature factor, ;δ is the membrane wall thickness of the membrane artificial lung, in m; The mass transfer correlation equation of the gas phase in the deionized water mass transfer process is: （6） In formula (6), Sh l is the liquid phase Sherwood number, k l is the mass transfer coefficient of deionized water, in m·s -1 ;d e is the membrane fiber diameter of the membrane artificial lung, in m; L is the membrane fiber length of the membrane artificial lung, in m; D l is the diffusion coefficient of the gas phase in deionized water, in m 2 ·s -1 ; Calculate the total mass transfer coefficient K, the formula is: （7） In formula (7), H is Henry's constant; Among them, the solution formula for Reynolds number Re in equation (3) and equation (6) is: （8） Among them, the solution formula for Schmidt number Sc in equation (3) and equation (6) is: （9） In formula (8) and formula (9), d e is the diameter, in m; u is the fluid velocity, in m·s -1 ; ρ is the fluid density, in kg·m -3 ; μ is the fluid viscosity, unit is Pa·s; D is the diffusion coefficient, unit is m 2 ·s -1 ; Substituting the result of equation (7) into equation (1) and equation (2), the mass transfer rates of oxygen and carbon dioxide are obtained respectively, which are the simulation values ​​and characterize the mass transfer performance of the membrane artificial lung.

2. The calculation method according to claim 1, characterized in that: Also included is a method for verifying the mass transfer rates of oxygen and carbon dioxide obtained above, comprising the following steps: Oxygen enters the membrane artificial lung, and carbon dioxide is dissolved in deionized water and enters the model artificial lung to transfer mass with oxygen. After the mass transfer is completed, deionized water is used to drive out oxygen, and then carbon dioxide is replenished and re-enters the membrane artificial lung. After the mass transfer is stable, the deionized water at the inlet and outlet of the membrane artificial lung is collected for calculation to obtain the mass transfer rate of oxygen and carbon dioxide, which is the experimental value. The experimental values ​​were compared with the simulated values.

3. The device adapted by the calculation method described in claim 2, characterized in that: The invention comprises a membrane artificial lung, wherein an oxygen inlet is provided at the end of the membrane artificial lung, a carbon dioxide inlet is provided at the upper end of the membrane artificial lung, an oxygen outlet is provided at the lower end of the membrane artificial lung, and a carbon dioxide outlet is provided at the end of the membrane artificial lung. The simulation value is obtained by calculating the total mass transfer coefficient of the membrane artificial lung.

4. The device according to claim 3, characterized in that The membrane artificial lung is connected to a verification device, which includes an oxygen cylinder, which is connected to the oxygen inlet of the membrane artificial lung, and the carbon dioxide inlet of the membrane artificial lung is connected to an oxygen removal device, and the oxygen outlet of the model artificial lung is connected to a liquid storage tank storing deionized water, which is connected to the liquid storage tank and the oxygen removal device, and the oxygen removal device is connected to the carbon dioxide cylinder. The experimental value is obtained by calculating the concentration of deionized water at the carbon dioxide inlet and the oxygen outlet of the membrane artificial lung, and compared with the simulation value for verification.

Images