Electrospray tube sheath flow heat exchange simulation method based on COMSOL

Abstract

The invention belongs to the field of analytical chemistry instruments, and particularly relates to an analog simulation method for the temperature change of an electrospray needle along with sheath flow gas in an ion mobility spectrometry ionization region based on COMSOL Multiphysics, and the method comprises the following steps: constructing a simplified electrospray needle model; according to the obtained electrospray needle model, simulating a laminar flow field and a temperature field of sheath flow gas to simulate a heat dissipation process of the sheath flow gas; and evaluating the influence of the external temperature of the sleeve on the internal sleeve of the electrospray needle model through fluid-solid coupling heat transfer, and performing simulation operation to obtain a simulation result. According to the method, two-dimensional modeling is carried out through software, an actual three-dimensional calculation model of the electrospray needle is highly simplified in an axial symmetry mode, the time cost needed by calculation is saved, and meanwhile the accuracy of the model can be guaranteed. And carrying out compressible flow treatment on sheath flow gas in the spray needle, and carrying out finite element analog simulation of non-isothermal flow through fluid-solid coupling.

Description

Technical Field

[0001] The invention belongs to the field of analytical chemical instruments, and in particular relates to a simulation method for the temperature of an electrospray needle in an ion mobility spectrometer ionization region changing with sheath flow gas based on COMSOL Multiphysics. Background Art

[0002] As an innovative soft ionization technology, electrospray ionization (ESI) has shown wide application potential in the field of chemical analysis. Especially when used in conjunction with ion mobility spectrometry, this technology atomizes liquid samples into fine charged droplets by applying high voltage, and promotes ion formation during the gradual evaporation of the solvent. The advantage of the electrospray ionization source is that it can efficiently ionize various compounds, including polar molecules, and no fragment ions are generated in the process, ensuring the accuracy of the analysis. In addition, this technology also has the characteristics of high sensitivity and suitability for high molecular weight biomacromolecules, so that when combined with analytical techniques such as ion mobility spectrometry, it can significantly improve the analytical ability and efficiency of complex samples, providing strong support for research in fields such as chemistry, materials science and life sciences.

[0003] The migration tube of ion mobility spectrometry requires a relatively high temperature when working, so the temperature of the ionization zone will be much higher than room temperature. In the electrospray ionization source, the heating of the spray needle has a significant impact on the ionization process and analysis results. Heating may cause changes in the physical and chemical properties of the solution, such as accelerated solvent evaporation rate and changes in solution viscosity, which in turn affect droplet formation and charge state. At the same time, changes in the spray needle temperature may also change the surface charge distribution of the solution, affecting the ionization efficiency and the generation of multi-charged ions. These changes may eventually cause ion signal fluctuations, affecting the accuracy and stability of the analysis results. In addition, for heat-sensitive samples, excessively high spray needle temperatures may also cause sample degradation and produce erroneous analysis results. It is also possible that the solute precipitates and clog the spray needle, causing potential damage to the spray needle life and instrument performance. Therefore, in electrospray ionization experiments, the spray needle temperature needs to be precisely controlled to optimize the ionization effect and ensure the reliability of the analysis results.

[0004] Although the existing technologies for measuring the temperature of electrospray needles are diverse, they all have certain limitations. Although thermocouple temperature measurement is accurate, it may interfere with the operation of electrospray and requires frequent calibration; infrared thermal imager temperature measurement is intuitive but is easily affected by many factors, resulting in limited accuracy and high cost; temperature indicator monitoring has a high degree of automation, but it relies on the stability and accuracy of the sensor, and once a fault occurs, it may not be discovered in time; and indirect monitoring by controlling experimental conditions lacks directness and accuracy, and it is difficult to reflect the actual temperature of the spray needle in real time. Traditional temperature measurement technology can usually only provide local or single-point temperature information, and it is difficult to fully reflect the temperature distribution of the spray needle and its surrounding environment.

[0005] Therefore, it is currently necessary to propose a simulation method based on simulation calculation to perform multiple simulations and analyses according to different experimental conditions and parameter settings, so as to find the optimal experimental plan or design parameters. Summary of the invention

[0006] The purpose of the present invention is to provide a simulation method for the temperature of the electrospray needle in the ionization region of ion mobility spectrometry changing with the sheath flow based on COMSOL Multiphysics. This method can not only provide temperature information on the surface of the needle, but also display the temperature distribution inside the needle and the surrounding environment, so as to overcome the defects of the above-mentioned prior art.

[0007] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a method for simulating heat transfer of electrospray sheath flow based on COMSOL, comprising the following steps:

[0008] Step S1: construct a simplified electrospray needle model;

[0009] Step S2: According to the obtained electrospray needle model, the laminar flow field and temperature field of the sheath gas are simulated to simulate the heat dissipation process of the sheath gas;

[0010] Step S3: Through fluid-solid coupling heat transfer, the influence of the temperature outside the casing on the inner casing of the electrospray needle model is evaluated, and simulation calculations are performed to obtain simulation results.

[0011] The step S1 is specifically:

[0012] Step S1-1: The flow shape of the sheath gas conforms to the laminar flow characteristics, so the laminar flow module is selected for fluid calculation; the heat exchange between the sheath gas and the casing is the heat transfer between the high-speed cold air flow and the high-temperature solid surface, so the solid / fluid heat transfer module is selected; after the two independent physical field calculation modules are selected, the laminar flow module and the solid / fluid heat transfer module are coupled together to perform non-isothermal flow calculation, and the non-isothermal flow that couples the laminar flow module and the solid / fluid heat transfer module is realized by adding independent physical fields of the laminar flow module and the solid / fluid heat transfer module;

[0013] Step S1-2: The geometric model adopts a two-dimensional symmetrical structure, and the innermost layer is set to be a quartz tube. A peek sleeve is provided on the outer layer of the quartz tube. A sheath flow gas domain for sheath gas to pass through is provided between the peek sleeve and the quartz tube, and the gas in the sheath flow gas domain is set to be air;

[0014] Step S1-3: an air domain is set outside the peek tube, and the entire model is extended to 50 mm along the sheath gas flow direction;

[0015] Step S1-4: a 360° rotational symmetry axis is set on the inner boundary of the quartz tube, and a three-dimensional geometric model is formed through the axisymmetry of the two-dimensional geometric model, thereby completing the two-dimensional simplification of the three-dimensional model.

[0016] The outer diameter of the quartz tube is 360 μm;

[0017] The outer diameter of the peek sleeve is 1 / 16 inch and the inner diameter is 750 μm;

[0018] The outer diameter of the air region is 10 mm.

[0019] The step S2 is specifically:

[0020] Step S2-1: In the laminar flow module, the properties of the fluid are set to weakly compressible flow and the material is air;

[0021] Step S2-2: The two axial boundaries of the sheath flow gas are set to be non-slip, one end in the radial direction is set to be the sheath flow gas inlet, and the mass flow is set as the boundary condition, which is converted to a flow rate of 1L / min to increase the convergence of the model; the other end in the radial direction is set to be the sheath flow gas outlet, and the boundary condition is set to the average pressure under the fully developed flow of the sheath flow gas, so that the sheath flow gas in the model does not go through the fluid development process and directly becomes the laminar sheath flow gas, thereby simplifying the model structure;

[0022] Step S2-3: In the solid / fluid heat transfer module: set the inner tube of the quartz tube and the peek sleeve as solid, and set the sheath gas and the air domain outside the peek sleeve as fluid;

[0023] Step S2-4: The heat dissipation process of the sheath flow gas is simulated by simulating the laminar flow field and temperature field of the sheath flow gas through COMSOL.

[0024] In step S2-3, the initial temperature of each area is set as follows:

[0025] The initial temperatures of the quartz tube, sheath flow gas domain, and peek sleeve area were set to 293.15 K. The initial temperature of the air domain outside the peek sleeve was set to 373.15 K, and the axial outermost boundary of the air domain was set to a constant temperature of 373.15 K, which was used as a constant temperature heat source to simulate the external environment of the electrospray needle.

[0026] The step S3 is specifically:

[0027] Step S3-1: setting the coupling relationship between the laminar flow module and the solid / fluid heat transfer module to: non-isothermal flow of weakly compressible flow;

[0028] Step S3-2: Using a free triangle mesh, a mesh is generated for the entire model, and the model is simulated and solved through a steady-state equation to obtain a stable temperature distribution system, that is, a color temperature diagram of the temperature distribution.

[0029] The present invention has the following beneficial effects and advantages:

[0030] 1. The present invention simulates the heat exchange of the sheath gas of the electrospray needle in the ionization zone of the ion mobility spectrometer migration tube in COMSOL finite element software, and obtains heat dissipation results that conform to actual laws. The method is simple and convenient to operate, greatly reduces the experimental time and cost, and has guiding significance for the design of the use conditions of electrospray-related devices.

[0031] 2. The present invention makes the sheath gas present good laminar flow properties in the whole model, and there is an obvious temperature gradient from the inlet to the outlet, with low temperature at the inlet and high temperature at the outlet. And the faster the flow rate, the lower the maximum temperature at the outlet.

[0032] 3. The quartz tube in the present invention has an obvious temperature gradient, and the trend is similar to the temperature distribution of the sheath gas. The higher the sheath gas velocity, the lower the temperature of the quartz tube. The higher the temperature of the external air domain, the higher the temperature of the quartz tube at the same sheath gas velocity.

[0033] 4. The electrospray needle model provided in the present invention can achieve a steady-state result of stable equilibrium. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A two-dimensional geometric model in one embodiment of the present invention;

[0035] Among them, 1 is the quartz tube domain, 2 is the sheath gas domain, 3 is the peek tube domain, 4 is the external air domain, and 5 is the rotational symmetry axis;

[0036] Figure 2 A three-dimensional geometric model that is the axisymmetric version of the two-dimensional geometric model of the present invention;

[0037] Figure 3 is the flow velocity distribution of the sheath gas between the quartz tube and the peek sleeve in the two-dimensional model of the present invention;

[0038] Figure 4 This is a temperature distribution diagram of various parts of the electrospray needle model of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0040] The present invention provides a simulation method for the temperature of an electrospray needle in an ionization region of an ion mobility spectrometer changing with sheath gas flow based on COMSOL Multiphysics:

[0041] Step S1: construct a simplified electrospray needle model;

[0042] The flow shape of the sheath gas conforms to the laminar flow characteristics, so the laminar flow module is selected for fluid calculation; the heat exchange between the sheath gas and the casing is the heat transfer between the high-speed cold airflow and the high-temperature solid surface, so the solid / fluid heat transfer module is selected; after selecting the two independent physical field calculation modules, the laminar flow module and the solid / fluid heat transfer module are coupled together for non-isothermal flow calculation, and the non-isothermal flow that couples the laminar flow module and the solid / fluid heat transfer module is realized by adding independent physical fields of the laminar flow module and the solid / fluid heat transfer module;

[0043] Specifically, Figure 1 As shown in the figure, a two-dimensional geometric model in an embodiment of the present invention is set, and a two-dimensional symmetrical structure is adopted, including the following steps:

[0044] The geometric model adopts a two-dimensional symmetrical structure, wherein the innermost layer is a quartz tube 1, a peek sleeve 3 is provided on the outer layer of the quartz tube, a sheath flow gas domain 2 for sheath flow gas to pass through is provided between the peek sleeve 3 and the quartz tube 1, and the gas in the sheath flow gas domain 2 is set to be air;

[0045] An air region 4 is provided outside the peek sleeve 3, and the entire model is extended to 50 mm along the sheath gas flow direction;

[0046] like Figure 2 As shown, it is a three-dimensional geometric model after the axisymmetry of the two-dimensional geometric model of the present invention. A 360° rotational symmetry axis is set at the inner boundary of the quartz tube 1. The three-dimensional geometric model is formed after the axisymmetry of the two-dimensional geometric model, thereby completing the two-dimensional simplification of the three-dimensional model.

[0047] In this embodiment, the outer diameter of the quartz tube 1 is 360 μm; the outer diameter of the peek sleeve 3 is 1 / 16 inch, and the inner diameter is 750 μm; and the outer diameter of the air space 4 is 10 mm.

[0048] Step S2: According to the obtained electrospray needle model, the laminar flow field and temperature field of the sheath gas are simulated by software to simulate the heat dissipation process of the sheath gas;

[0049] Specifically, step S2-1: in the laminar flow module, the properties of the fluid are set to weakly compressible flow, and the material is air;

[0050] Step S2-2: The two axial boundaries of the sheath flow gas are set to be non-slip, one end in the radial direction is set to be the sheath flow gas inlet, and the mass flow setting is used as the boundary condition, which is converted to a flow rate of 1L / min to increase the convergence of the model; the other end in the radial direction is set to be the sheath flow gas outlet, and the boundary condition is the "average pressure" under the "fully developed flow", so that the sheath flow gas in the model does not go through the fluid development process and directly becomes the laminar sheath flow gas, simplifying the model structure;

[0051] Step S2-3: in the solid / fluid heat transfer module: the inner tube of the quartz tube 1 and the peek sleeve 3 are set as solids, and the sheath gas and the air domain 4 outside the peek sleeve 3 are set as fluids;

[0052] In setting the initial temperature of each area, the initial temperatures of the quartz tube 1, sheath flow air domain 2 and peek sleeve 3 are set to: 293.15K; the initial temperature of the air domain 4 outside the peek sleeve 3 is set to 373.15K, and the axial outermost boundary of the air domain 4 is set to a constant temperature of 373.15K, which is used as a constant temperature heat source to simulate the external environment of the electrospray needle.

[0053] Step S2-4: The heat dissipation process of the sheath flow gas is simulated by simulating the laminar flow field and temperature field of the sheath flow gas through COMSOL.

[0054] Step S3: Through fluid-solid coupling heat transfer, the influence of the temperature outside the sleeve on the internal quartz tube is evaluated, and simulation calculation is performed to obtain simulation results.

[0055] Specifically, step S3-1: setting the coupling relationship between the laminar flow module and the solid / fluid heat transfer module to: non-isothermal flow of weakly compressible flow;

[0056] Step S3-2: Use a free triangle mesh to generate a mesh for the entire model, and simulate and solve the model through the steady-state equation to obtain a stable temperature distribution system, that is, a color temperature diagram of the temperature distribution, such as Figure 4 shown.

[0057] Embodiment 1:

[0058] In this embodiment, the temperature of the electrospray needle in the ionization region of the simulated ion mobility spectrometer changes with the sheath gas flow as shown in the figure Figure 3 , Figure 4 As shown; including the following steps:

[0059] (1) Establishment of physical field model:

[0060] Enter the initial page of the software, select "Model Wizard" for new creation, select 2D axisymmetry for spatial dimension, select fluid flow and heat transfer physics field for physical field, and select steady state for study.

[0061] (2) Model establishment:

[0062] The overall size of the model is set to 50 mm×5 mm with the two-dimensional symmetry axis as the center. According to the size of the peek sleeve 3 and the quartz tube 1, the parts of the two-dimensional model are divided and then formed into a joint body.

[0063] (3) Setting of material parameters:

[0064] Click on the completed two-dimensional geometric model, and set the physical property parameters of the quartz tube 1, sheath flow gas domain 2, peek sleeve 3, and air respectively.

[0065] (4) Setting of initial values, domain and boundary conditions:

[0066] Set the fluid, fluid-solid heat transfer boundary conditions, inlet and outlet, wall conditions, etc. The inlet in the flow field is set to mass flow, the outlet boundary is set to fully developed flow, and the fluid flow rate is 1L / min. The temperature conditions in fluid-solid heat transfer are set by the user, the external air domain is set to 373.15K, and the quartz tube, sheath gas, peek sleeve, etc. are all 293.15K.

[0067] (5) Grid division:

[0068] Free triangular mesh is used to generate mesh for the entire model.

[0069] (6) Calculation and solution:

[0070] In this study, the solver adopted steady-state calculation, and the laminar flow field and heat transfer physical fields were checked at the same time in a single calculation, and the non-isothermal flow with coupled flow field and heat transfer was checked at the same time.

[0071] The above described operation construction embodiment can obtain Figure 4 From the temperature distribution, it can be seen that the temperature of the quartz tube in the center is the lowest, and the temperature gradually decreases along the direction of the sheath flow, while the sheath flow itself has an obvious temperature rise phenomenon.

[0072] In summary, the present invention uses software to perform two-dimensional modeling, and in an axisymmetric manner, highly simplifies the actual three-dimensional calculation model of the electrospray needle, saving the time cost required for calculation while ensuring the accuracy of the model. The sheath flow in the needle is treated as a compressible flow, and a finite element simulation of non-isothermal flow is performed through fluid-solid coupling.

[0073] The above description is only an embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for simulating heat transfer of electrospray tube sheath flow based on COMSOL, characterized in that: The following steps are involved: Step S1: construct a simplified electrospray needle model; Step S2: According to the obtained electrospray needle model, the laminar flow field and temperature field of the sheath gas are simulated to simulate the heat dissipation process of the sheath gas; Step S3: Through fluid-solid coupling heat transfer, the influence of the temperature outside the casing on the inner casing of the electrospray needle model is evaluated, and simulation calculations are performed to obtain simulation results.

2. The method for simulating heat transfer of electrospray tube sheath flow based on COMSOL according to claim 1, characterized in that: The step S1 is specifically: Step S1-1: The flow shape of the sheath gas conforms to the laminar flow characteristics, so the laminar flow module is selected for fluid calculation; the heat exchange between the sheath gas and the casing is the heat transfer between the high-speed cold air flow and the high-temperature solid surface, so the solid / fluid heat transfer module is selected; After selecting the two independent physical field calculation modules, the laminar flow module and the solid / fluid heat transfer module are coupled together for non-isothermal flow calculation. By adding the independent physical fields of the laminar flow module and the solid / fluid heat transfer module, the non-isothermal flow of the laminar flow module and the solid / fluid heat transfer module can be realized; Step S1-2: The geometric model adopts a two-dimensional symmetrical structure, wherein the innermost layer is a quartz tube (1), a peek sleeve (3) is provided on the outer layer of the quartz tube, a sheath flow gas domain (2) for sheath flow gas to pass through is provided between the peek sleeve (3) and the quartz tube (1), and the gas in the sheath flow gas domain (2) is set to be air; Step S1-3: an air region (4) is provided outside the peek sleeve (3), and the entire model is extended to 50 mm along the sheath gas flow direction; Step S1-4: a 360° rotational symmetry axis is set on the inner boundary of the quartz tube (1), and a three-dimensional geometric model is formed through the axisymmetry of the two-dimensional geometric model, thereby completing the two-dimensional simplification of the three-dimensional model.

3. The method for simulating heat transfer of electrospray tube sheath flow based on COMSOL according to claim 2, characterized in that: The outer diameter of the quartz tube (1) is 360 μm; The outer diameter of the peek sleeve (3) is 1 / 16 inch and the inner diameter is 750 μm; The outer diameter of the air space (4) is 10 mm.

4. The method for simulating heat transfer of electrospray tube sheath flow based on COMSOL according to claim 1, characterized in that: The step S2 is specifically: Step S2-1: In the laminar flow module, the properties of the fluid are set to weakly compressible flow and the material is air; Step S2-2: The two axial boundaries of the sheath flow gas are set to be non-slip, one end in the radial direction is set to be the sheath flow gas inlet, and the mass flow is set as the boundary condition, which is converted to a flow rate of 1L / min to increase the convergence of the model; the other end in the radial direction is set to be the sheath flow gas outlet, and the boundary condition is set to the average pressure under the fully developed flow of the sheath flow gas, so that the sheath flow gas in the model does not go through the fluid development process and directly becomes the laminar sheath flow gas, thereby simplifying the model structure; Step S2-3: In the solid / fluid heat transfer module: the inner tube of the quartz tube (1) and the peek sleeve (3) are set as solids, and the sheath gas and the air domain (4) outside the peek sleeve (3) are set as fluids; Step S2-4: The heat dissipation process of the sheath flow gas is simulated by simulating the laminar flow field and temperature field of the sheath flow gas through COMSOL.

5. The method for simulating heat transfer of electrospray tube sheath flow based on COMSOL according to claim 4, characterized in that: In step S2-3, the initial temperature of each area is set as follows: The initial temperatures of the quartz tube (1), sheath flow air domain (2) and peek sleeve (3) were set to 293.15 K. The initial temperature of the air domain (4) outside the peek sleeve (3) was set to 373.15 K, and the axial outermost boundary of the air domain (4) was set to a constant temperature of 373.15 K, which was used as a constant temperature heat source to simulate the external environment of the electrospray needle.

6. The method for simulating heat transfer of electrospray tube sheath flow based on COMSOL according to claim 1, characterized in that: The step S3 is specifically: Step S3-1: setting the coupling relationship between the laminar flow module and the solid / fluid heat transfer module to: non-isothermal flow of weakly compressible flow; Step S3-2: Using a free triangle mesh, a mesh is generated for the entire model, and the model is simulated and solved through a steady-state equation to obtain a stable temperature distribution system, that is, a color temperature diagram of the temperature distribution.

Images