Method for measuring the aperture of a sand core filter funnel

Abstract

The present application relates to the technical field of solid-liquid separation in laboratory testing, and particularly relates to a sand core filter funnel aperture measuring method, a measuring device of a filter plate hole of a sand core filter funnel is connected, a titration tube is used to drop a layer of pure water film with a preset thickness on the filter plate of the sand core filter funnel; a gas pressure device is started to stably and slowly pressurize the filter bottle, the filter plate surface is observed from above, when the first bubble appears, the pressure value of the digital pressure device at this time is recorded, the pressure average value of n times of tests is calculated; when the bubbles uniformly appear on the filter plate surface, the pressure value of the digital pressure device at this time is recorded, the pressure average value of n times of tests is calculated, the maximum aperture and the average aperture of the filter plate are calculated; the uncertainty of the sand core filter funnel aperture measuring method is evaluated, the accuracy of the measurement is calculated and judged, the maximum aperture and the average aperture of the filter plate hole of the filter funnel can be measured, the accuracy of the measurement is judged, and the accuracy and reliability of the sand core filter funnel aperture measuring method are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laboratory detection solid-liquid separation, and particularly relates to a sand core filter funnel pore size measurement method. BACKGROUND

[0002] The sand core filter funnel is a commonly used filter equipment in the laboratory, mainly composed of a filter plate, a filter membrane and a sand core, and is a tool for separating and filtering precipitates and microorganisms of different particle sizes to achieve the purpose of clarifying liquid. In recent years, the sand core filter funnel is widely used in laboratory research and production in the fields of chemistry, biology, medicine and the like due to its high filtering precision, fast filtering speed and simple operation. In many biological, chemical and highway tests, the pore size of the sand core filter funnel needs to be measured, because the size of the funnel diameter and the capacity diameter affects the filtering speed, and the capacity size determines the amount of liquid that can be processed at a time. However, according to different use scenarios, the general pore size specification of the sand core filter funnel is 0.6 ~ 30 The pore size is small and the structure is special, and the minimum measurement size of the standard gauge block circulating in the industry is 0.5 mm, so it cannot be directly measured, but relies on the introduction of the manufacturer. However, some tests need to know the size of the maximum pore size and the average pore size, otherwise it will cause the test data to be inaccurate due to the inaccurate nominal pore size of the manufacturer, and other major influences. Therefore, there is an urgent need for a method for accurately measuring the pore size of the filter plate of the sand core filter funnel. SUMMARY

[0003] The present application provides a sand core filter funnel pore size measurement method, which is intended to solve the defects of the prior art.

[0004] The present application adopts the following technical solutions:

[0005] A sand core filter funnel pore size measurement method, comprising the following steps:

[0006] S1: install the sand core filter funnel on the matched suction filter bottle to be in a sealed state, the side wall of the suction filter bottle is sealed connected with the air pressure device through a pipeline, and a digital pressure device for displaying the pressure value is also connected on the sealed pipeline; an electron microscope for real-time observation of the filter plate in the sand core filter funnel is installed on the top of the sand core filter funnel, and the electron microscope and the digital pressure device are connected with a computer;

[0007] S2: the test environment temperature is set to 20℃±1℃, the relative humidity is 50%, and a layer of pure water film with a predetermined thickness is dropped on the filter plate of the sand core filter funnel by using a burette;

[0008] S3: Start the air pressure device to steadily and slowly pressurize the filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears. Calculate the average pressure of n tests as ΔP1.

[0009] S4: Continuously apply pressure. When bubbles appear uniformly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time. Calculate the average pressure of n tests as ΔP2.

[0010] S5: Calculate the maximum and average pore diameter of the sand core filter funnel plate;

[0011] S6: Uncertainty assessment of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced by the resolution of the digital pressure gauge, and the standard uncertainty u3 introduced by the maximum permissible error of the digital pressure gauge; then, calculate and judge the accuracy of the maximum aperture and average aperture measurement respectively.

[0012] In some embodiments, in S2, before dripping a thin film of pure water of a predetermined thickness onto the filter plate of the sand core filter funnel using a burette, an airtightness check is performed on the experimental equipment: the vent valve leading to the suction flask is closed, the air pressure device is started to introduce a certain amount of gas, and when the digital pressure counter value is displayed as 1.5 kPa ~ 2.5 Pa, the precision control valve is closed, and the change in the value of the digital pressure device is observed. If the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, then the airtightness meets the requirements.

[0013] In some embodiments, in S2, a thin film of pure water is dripped onto the filter plate of the sand core filter funnel using a burette, and the thickness of the film is 1cm to 2cm.

[0014] In some embodiments, in S3, the pneumatic device is activated to steadily and slowly pressurize the filtration flask. The surface of the filter plate is observed from above, and the pressure value P1 of the digital pressure device is recorded when the first bubble appears. The average pressure of n tests is calculated as ΔP1, which is then converted into the average maximum pore size. max First, the effect of ambient temperature on the aperture result is tested: if the ratio of the calculated aperture to the aperture under the same working conditions is less than the preset value under the test ambient temperature, then the test ambient temperature meets the test requirements.

[0015] In some embodiments, the influence of ambient temperature is detected while the influence of liquid column difference is also detected:

[0016] According to the liquid pressure formula (1):

[0017] p=ρgh (1)

[0018] In the formula: p is the pressure, and the unit is Pa;

[0019] ρ is the density of the liquid, with units of kg / m³. 3 ;

[0020] g is the acceleration due to gravity, and its unit is N / kg.

[0021] h represents the liquid column difference, in meters (m).

[0022] Calculate the effect of the preset liquid column difference on the orifice measurement results: If the ratio of the calculated orifice diameter to the orifice diameter under the same working conditions is less than the preset value, then the test liquid column difference meets the test requirements.

[0023] In some embodiments, in S5, the maximum pore size and average pore size of the filter plate are calculated using formula (2):

[0024] (2)

[0025] In the formula: ΔP is the additional pressure, in Pa;

[0026] d is the pore size of the bubble, in meters (m).

[0027] γ is the surface tension of the liquid, with units of N / m;

[0028] When ΔP is ΔP1, the bubble pore size is the maximum pore size d. max The unit is meters (m).

[0029] When ΔP is ΔP2, the bubble pore size is the average pore size. The unit is meters (m).

[0030] In some embodiments, in S6, the accuracy of the measurement of the maximum pore size of the sand core filter funnel is determined:

[0031] The standard uncertainty u1 introduced by the repeatability of sand core filter funnel pore size measurement:

[0032] The maximum pore size of the sand core filter funnel was measured, i.e., the pressure value when the first air bubble appeared was read. Ten measurements were taken in total, and the average pressure was calculated. The average pressure was calculated according to formula (3):

[0033] (3)

[0034] In the formula: u1 is the standard uncertainty introduced by the repeatability of the sand core filter funnel aperture measurement, and the unit is Pa;

[0035] n represents the total number of measurements;

[0036] p i The pressure value is from the i-th measurement, in Pa.

[0037] This is the average of n pressure values, expressed in Pa.

[0038] Standard uncertainty u2 introduced by the resolution of the preset-level digital pressure gauge:

[0039] The standard uncertainty introduced by the resolution of the preset grade digital pressure gauge is evaluated using Type B. The resolution of the preset grade digital pressure gauge is selected as P3Pa, which follows a uniform distribution. The pressure is then calculated according to formula (4):

[0040] (4)

[0041] In the formula, u2 is the standard uncertainty introduced by the resolution of the digital pressure gauge, and the unit is Pa;

[0042] P3 represents the resolution of the digital pressure gauge, measured in Pa.

[0043] The standard uncertainty u3 introduced by the maximum permissible error of the preset grade digital pressure gauge:

[0044] The standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge is evaluated using Type B. The error of the preset grade digital pressure gauge is ±P4 Pa. Taking the half-width as P4 Pa, the pressure is calculated according to formula (5):

[0045] (5)

[0046] In the formula, u3 is the standard uncertainty introduced by the maximum permissible error of the preset level digital pressure gauge, and the unit is Pa;

[0047] P4 represents the error of the digital pressure gauge, in Pa.

[0048] Calculate the combined standard uncertainty according to formula (6). :

[0049] (6)

[0050] According to formula (2), the conversion is as follows: ,length The maximum pore size uncertainty of the sand core filter funnel is expressed in μm.

[0051] The maximum pore size expansion uncertainty u of the sand core filter funnel is calculated according to formula (7):

[0052] u (7)

[0053] In the formula, u is the maximum pore size expansion uncertainty of the sand core filter funnel, in μm;

[0054] K is the sensitivity coefficient;

[0055] The maximum pore size uncertainty of the sand core filter funnel is expressed in μm.

[0056] When the ratio of u to the maximum pore size of the sand core filter funnel is less than 1%, the method for measuring the maximum pore size is accurate; otherwise, it is inaccurate.

[0057] In some embodiments, in S6, the accuracy of the measurement of the average pore size of the sand core filter funnel is determined:

[0058] Standard uncertainty introduced by the repeatability of average pore size measurement of sand core filter funnel :

[0059] The average pore size of the sand core filter funnel was measured, i.e., the pressure value was read when bubbles appeared uniformly on the surface of the filter plate. Ten measurements were taken in total, and the average pressure was calculated according to formula (8):

[0060] (8)

[0061] In the formula: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa;

[0062] n represents the total number of measurements;

[0063] The pressure value is from the i-th measurement, in Pa.

[0064] This is the average of n pressure values, expressed in Pa.

[0065] Standard uncertainty introduced by the resolution of the preset level digital pressure gauge :

[0066] The standard uncertainty introduced by the resolution of the preset-grade digital pressure gauge is evaluated using Type B criteria. The resolution of the preset-grade digital pressure gauge is selected as [value missing]. Pa, following a uniform distribution, the pressure is calculated according to formula (9):

[0067] (9)

[0068] In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa;

[0069] This refers to the resolution of a digital pressure gauge, measured in Pa.

[0070] Standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge :

[0071] The standard uncertainty introduced by the maximum permissible error of the preset-grade digital pressure gauge is evaluated using Type B. The error of the preset-grade digital pressure gauge is ± 4 Pa, take half width as If the pressure is 4 Pa, then the pressure is calculated according to formula (10):

[0072] (10)

[0073] In the formula, The standard uncertainty introduced for the maximum permissible error of the preset-grade digital pressure gauge, in Pa;

[0074] This refers to the error of the digital pressure gauge, expressed in Pa.

[0075] Calculate the combined standard uncertainty according to formula (11) :

[0076] (11)

[0077] According to formula (2), the conversion is as follows: , The average pore size uncertainty of the sand core filter funnel is expressed in μm.

[0078] The uncertainty of the average pore size expansion of the sand core filter funnel is calculated according to formula (12). :

[0079] (12)

[0080] In the formula, The mean pore size expansion uncertainty of the sand core filter funnel is expressed in μm.

[0081] k is the sensitivity coefficient;

[0082] The average pore size uncertainty of the sand core filter funnel is expressed in μm.

[0083] when If the ratio of the average pore size to the average pore size of the sand core filter funnel is less than 1%, then the method for measuring the average pore size is accurate; otherwise, it is inaccurate. Beneficial effects

[0084] This invention discloses a method for measuring the pore size of a sand core filter funnel. Compared with the prior art, this invention has the following advantages:

[0085] The measurement method of this invention is based on the principle of liquid surface tension. A thin film of pure water of a predetermined thickness is dripped onto the filter plate of a sand core filter funnel using a burette. Then, a pressure device is activated to steadily and slowly pressurize the filtration flask. The surface of the filter plate is observed under a microscope, and the pressure value P1 of the digital pressure device when the first bubble appears and the pressure value P2 when bubbles uniformly appear on the filter plate surface are recorded. According to the maximum bubble pressure method, when the force generated on the end face of the pore is slightly greater than the surface tension of the liquid in the pore of the sand core funnel, the bubble escapes from the pore. This additional pressure is related to the surface tension of the liquid. The surface tension is directly proportional to the radius of curvature of the bubble and inversely proportional to the radius of curvature of the bubble. When the additional pressure is at its maximum, the radius of curvature R and the aperture radius r of the sand core funnel are equal. The maximum aperture and average aperture of the sand core funnel can be calculated according to the Laplace formula. Then, the accuracy of the maximum aperture and average aperture measurement is calculated and judged by comprehensively calculating the standard uncertainty u1 introduced from the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced from the resolution of the digital pressure gauge, and the standard uncertainty u3 introduced from the maximum permissible error of the digital pressure gauge. This ensures the accuracy of the sand core funnel aperture measurement method. Attached Figure Description

[0086] 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, which constitute a part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention.

[0087] Figure 1 A flowchart of the method for measuring the pore size of a sand core filter funnel provided in an embodiment of the present invention;

[0088] Figures 2-11 The pressure image provided in this embodiment of the invention when the first bubble appears was measured ten times.

[0089] Figures 11-21 The pressure image provided in this embodiment of the invention shows the pressure when bubbles appear uniformly on the surface of the filter plate. The measurement was repeated ten times. Detailed Implementation

[0090] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0091] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0092] like Figure 1 - Figure 21 As shown, the technical solution of the present invention is as follows:

[0093] A method for measuring the pore size of a sand core filter funnel includes the following steps:

[0094] S1: Install the sand core filter funnel on the matching vacuum flask to make it in a sealed state. The side wall of the vacuum flask is sealed to the air pressure device through a pipeline. A digital pressure device for displaying the pressure value is also connected to the sealed pipeline. An electron microscope for real-time observation of the filter plate inside the sand core filter funnel is installed on the top of the sand core filter funnel. The electron microscope and the digital pressure device are both connected to a computer.

[0095] S2: The test environment temperature is set to 20℃±1℃ and the relative humidity is 50%. A thin film of pure water of a predetermined thickness is dripped onto the filter plate of the sand core filter funnel using a burette.

[0096] S3: Start the air pressure device to steadily and slowly pressurize the filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears. Calculate the average pressure of n tests as ΔP1.

[0097] S4: Continuously apply pressure. When bubbles appear uniformly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time. Calculate the average pressure of n tests as ΔP2.

[0098] S5: Calculate the maximum and average pore diameter of the sand core filter funnel plate;

[0099] S6: Uncertainty assessment of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced by the resolution of the digital pressure gauge, and the standard uncertainty u3 introduced by the maximum permissible error of the digital pressure gauge; then, calculate and judge the accuracy of the maximum aperture and average aperture measurement respectively.

[0100] The preferred embodiments disclosed in this invention, such as... Figures 1-21 As shown:

[0101] This invention discloses a method for measuring the pore size of a sand core filter funnel, comprising the following steps:

[0102] S1: The sand core filter funnel is installed on a matching vacuum flask to form a seal. The side wall of the vacuum flask is sealed to the air pressure device through a pipeline. A digital pressure device for displaying pressure values ​​is also connected to the sealed pipeline. An electron microscope for real-time observation of the filter plate inside the sand core filter funnel is installed on the top of the sand core filter funnel. The electron microscope and the digital pressure device are both controlled and connected by a computer.

[0103] The digital pressure device used in this experiment is a 0.05 grade digital pressure gauge with a range of (0~40) Pa; the pneumatic device can be a manual pressure pump with micro-pressure adjustment function or an electric fully automatic pressure calibrator. This experiment uses a fully automatic pressure calibrator.

[0104] S2: The ambient temperature for this test is set at (20±1)℃, and the relative humidity is 50%;

[0105] First, perform an airtightness check on the experimental equipment: close the vent valve to the filtration flask, start the pressure device to introduce a certain amount of gas, and when the digital pressure counter value is displayed as 1.5 kPa to 2.5 Pa, close the precision control valve and observe the change in the value of the digital pressure device. If the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, the airtightness meets the requirements; otherwise, it does not meet the requirements and the system needs to be reconnected until it is qualified.

[0106] A thin film of pure water is dripped from the top of the sand core filter funnel onto the filter plate using a burette. The thickness of the water film is set to 1cm to 2cm, and 1cm is selected in this embodiment.

[0107] S3: Start the fully automatic pressure calibrator and slowly and steadily pressurize the filtration flask. Observe the surface of the filter plate through a microscope. When the first bubble appears, record the pressure value P1 of the digital pressure gauge. Calculate the average pressure of n tests as ΔP1, and convert it to the average value of the maximum pore size. max .

[0108] This method, based on the maximum bubble pressure method, involves designing and fabricating a dedicated measuring device to measure the pore size (including maximum and average pore size) of the sand core filter funnel plate. The outer surface of the sand core filter funnel is moistened with water and then sealed on a matching suction flask. With the flask sealed, pure water with known surface tension is dripped into the sand core filter funnel to form a thin film. The suction flask is then slowly pressurized using a fully automatic pressure calibrator. At this point, a pressure is applied to the liquid surface within the funnel pores, creating a pressure difference (Δ). p = p 大气 - p系统 When the force generated on the end face of the pore is slightly greater than the surface tension of the liquid in the pore of the sand core funnel, the bubble escapes from the pore. This additional pressure is directly proportional to the surface tension and inversely proportional to the radius of curvature of the bubble, as shown in the following formula: Laplace's formula (2) :

[0109] (2)

[0110] In the formula: ΔP is the additional pressure, in Pa;

[0111] d is the curvature diameter of the bubble, in meters (m).

[0112] γ is the surface tension of the liquid, with units of N / m;

[0113] If the aperture of the sand core funnel is very small, the formed bubbles are basically spherical. When the bubbles begin to form, the surface is almost flat, and the radius of curvature is at its maximum. As the bubbles form, the radius of curvature gradually decreases until a hemisphere is formed. At this time, the radius of curvature R and the aperture radius r of the sand core funnel filter plate are equal, and the radius of curvature reaches its minimum value. According to formula (2), the additional pressure reaches its maximum value at this time. The additional pressure is the pressure value displayed by the digital pressure gauge. As the bubbles grow further, R increases, and the additional pressure decreases until the bubbles escape. That is, the additional pressure is at its maximum when R=r. The aperture 2r of the sand core funnel filter plate can be calculated.

[0114] Calculate the average pressure of n tests as ΔP1, and convert it to the average value of the maximum orifice diameter. max First, conduct an environmental temperature impact test:

[0115] Since the experiment was conducted at an ambient temperature of (20±1)℃, the relationship between temperature and the surface tension of pure water was: at 19℃, =0.07290 N / m; at 20℃, =0.07275 N / m; at 21℃, =0.07259 N / m;

[0116] The maximum tension difference Δγ = 0.07290 N / m - 0.07259 N / m = 0.00031 N / m. At this point, the additional pressure is P1, which equals 3.10 Pa. Using the Laplace formula, this translates to approximately 0.4 Pa for the orifice diameter. The value is 0.426% of the aperture under the same working conditions, which is less than the preset limit of 1%. Therefore, the influence of ambient temperature is negligible, and the environment meets the test requirements.

[0117] This embodiment underwent three tests, and the additional pressure value P1 is shown in Table 1:

[0118] Table 1

[0119]

[0120] Calculate the average additional pressure ΔP1: ΔP1 = (3.13 + 3.10 + 3.07) / 3 = 3.1 (kPa) = 3100 Pa.

[0121] According to formula (2), where =0.073 N / m, which is the surface tension of pure water. max =94

[0122] The influence of ambient temperature was detected, and the influence of liquid column difference was also detected.

[0123] According to the liquid pressure formula (1):

[0124] P=ρgh (1)

[0125] In the formula: P is the pressure, and the unit is Pa;

[0126] ρ is the density of the liquid, with units of kg / m³. 3 ;

[0127] g is the acceleration due to gravity, and its unit is N / kg.

[0128] h represents the liquid column difference, in meters (m).

[0129] In this experiment, the column height difference h in the sand core funnel was taken as 0.01 m, g as 9.8 N / kg, and ρ as 1 kg / m³. 3 The calculated value of P is 0.1 Pa, which translates to approximately 0.003 Pa in pore size. The difference in liquid column diameter is 0.003% of the orifice diameter under the same working conditions, which is less than the preset limit of 1%, i.e., 0.003% < 1%. Therefore, the influence of the liquid column difference meets the test requirements.

[0130] S4: Continuously apply pressure. When bubbles appear uniformly on the surface of the filter plate, record the pressure value P2 of the digital pressure gauge at this time. Calculate the average pressure of n tests as ΔP2; convert it to the average uniform pore size. 平均 .

[0131] This embodiment underwent three tests, and the additional pressure value P2 is shown in Table 1:

[0132] S5: Calculate the average additional pressure ΔP2, ΔP2 = (4.00 + 4.10 + 4.18) / 3 = 4.09 (Pa).

[0133] According to formula (2), where =0.073 N / m, which is the surface tension of pure water. 平均 =71

[0134] S6: Uncertainty assessment of the method for measuring the aperture of a sand core funnel:

[0135] First, calculate the standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced by the resolution of the digital pressure gauge, and the standard uncertainty u3 introduced by the maximum permissible error of the digital pressure gauge; then, calculate and judge the accuracy of the maximum aperture and average aperture measurements respectively.

[0136] The standard uncertainty u1 introduced by the repeatability of sand core filter funnel pore size measurement:

[0137] The maximum pore size of the sand core filter funnel was measured, specifically the maximum pressure value read when the first air bubble appeared under the microscope. Ten measurements were taken in total, as shown in Table 2. Figures 2-11 Point A in the diagram represents the pressure value corresponding to the appearance of the first bubble on the digital pressure gauge.

[0138] Table 2

[0139]

[0140] Calculate the average pressure using formula (3):

[0141] (3)

[0142] In the formula: u1 is the standard uncertainty introduced by the repeatability of the sand core filter funnel aperture measurement, and the unit is Pa;

[0143] n represents the total number of measurements;

[0144] p i The pressure value is from the i-th measurement, in Pa.

[0145] This is the average of n pressure values, expressed in Pa.

[0146] Calculations show that u1 = 63 Pa.

[0147] Standard uncertainty u2 introduced by the resolution of the preset-level digital pressure gauge:

[0148] In this embodiment, a 0.05-grade digital pressure gauge is selected. The standard uncertainty introduced by the resolution is evaluated using Type B. The resolution P3 of the 0.05-grade digital pressure gauge is 0.001 Pa, which follows a uniform distribution. According to JJF 1059 "Evaluation and Expression of Measurement Uncertainty", the pressure is calculated according to formula (4):

[0149] (4)

[0150] In the formula, u2 is the standard uncertainty introduced by the resolution of the digital pressure gauge, and the unit is Pa;

[0151] P3 represents the resolution of the digital pressure gauge, measured in Pa.

[0152] Calculations show that u2 = 0.6 Pa.

[0153] The standard uncertainty u3 introduced by the maximum permissible error of the preset grade digital pressure gauge:

[0154] In this embodiment, a 0.05-grade digital pressure gauge is selected. The standard uncertainty introduced by the maximum permissible error is evaluated using Type B. The error of the 0.05-grade digital pressure gauge is ±P4 Pa, and the MPE is ±20 Pa. Taking the half-width as P4 Pa, the calculation is performed according to formula (5):

[0155] (5)

[0156] In the formula, u3 is the standard uncertainty introduced by the maximum permissible error of the preset level digital pressure gauge, and the unit is Pa;

[0157] P4 represents the error of the digital pressure gauge, in Pa.

[0158] In this embodiment, the 0.05-grade digital pressure gauge has an MPE±20Pa value. Taking the half-width as 20Pa, the calculated value is u3=12Pa.

[0159] Calculate the combined standard uncertainty according to formula (6). :

[0160] (6)

[0161] but =64 Pa.

[0162] According to formula (2), the conversion is as follows: ,length The maximum pore size uncertainty of the sand core filter funnel is expressed in μm; the calculated maximum pore size uncertainty of the sand core filter funnel is 2 μm.

[0163] The maximum pore size expansion uncertainty u of the sand core filter funnel is calculated according to formula (7):

[0164] u (7)

[0165] In the formula, u is the maximum pore size expansion uncertainty of the sand core filter funnel, in μm;

[0166] K is the sensitivity coefficient;

[0167] The maximum pore size uncertainty of the sand core filter funnel is expressed in μm.

[0168] According to JJF1059.1 "Determination and Expression of Measurement Uncertainty", taking k=2, the uncertainty of the maximum aperture calibration result is:

[0169] u =2×2=4(μm)

[0170] u / d 最大 =0.043, meaning that when the ratio of the uncertainty of the maximum pore size calibration result to the maximum pore size of the sand core filter funnel is less than the preset value of 1, the measurement method of the maximum pore size is accurate.

[0171] Accuracy assessment of the average pore size measurement of a sand core filter funnel:

[0172] Standard uncertainty introduced by the repeatability of average pore size measurement of sand core filter funnel :

[0173] The average pore size of the sand core filter funnel was measured, specifically the pressure value read when air bubbles appeared uniformly on the filter plate surface. Ten measurements were taken in total, as shown in Table 3. Figures 12-21 :

[0174] Table 3

[0175]

[0176] Calculate the average pressure using formula (8):

[0177] (8)

[0178] In the formula: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa;

[0179] n represents the total number of measurements;

[0180] The pressure value is from the i-th measurement, in Pa.

[0181] This is the average of n pressure values, expressed in Pa.

[0182] Calculations show that Pa.

[0183] Standard uncertainty introduced by the resolution of the preset level digital pressure gauge :

[0184] In this embodiment, a 0.05-grade digital pressure gauge is selected. The standard uncertainty introduced by the resolution of the digital pressure gauge is evaluated using Type B. The resolution of the 0.05-grade digital pressure gauge is selected as [value missing]. Pa, following a uniform distribution, the pressure is calculated according to formula (9):

[0185] (9)

[0186] In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa;

[0187] This refers to the resolution of a digital pressure gauge, measured in Pa.

[0188] A 0.05-grade digital pressure gauge has a resolution of 1 Pa. Calculations show that... =0.6 Pa.

[0189] Standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge :

[0190] In this embodiment, a 0.05-grade digital pressure gauge is selected. The standard uncertainty introduced by the maximum permissible error of the digital pressure gauge is evaluated using Type B. The preset error of the digital pressure gauge is ± 4 Pa, take half width as If the pressure is 4 Pa, then the pressure is calculated according to formula (10):

[0191] (10)

[0192] In the formula, The standard uncertainty introduced for the maximum permissible error of the preset-grade digital pressure gauge, in Pa;

[0193] This refers to the error of the digital pressure gauge, expressed in Pa.

[0194] A 0.05-class digital pressure gauge has an MPE ±20 Pa value. Taking half-width as 20 Pa, then... =12 Pa.

[0195] Calculate the combined standard uncertainty according to formula (11) :

[0196] (11)

[0197] but =58 Pa.

[0198] According to formula (2), the conversion is as follows: , The value represents the uncertainty of the average pore size of the sand core filter funnel, in μm; when converted, the uncertainty of the average pore size of the sand core filter funnel is 2 μm.

[0199] The uncertainty of the average pore size expansion of the sand core filter funnel is calculated according to formula (12). :

[0200] (12)

[0201] In the formula, The mean pore size expansion uncertainty of the sand core filter funnel is expressed in μm.

[0202] K is a coefficient;

[0203] The average pore size uncertainty of the sand core filter funnel is expressed in μm.

[0204] According to JJF1059.1 "Determination and Expression of Measurement Uncertainty", taking k=2, the average pore size uncertainty of the sand core filter funnel is:

[0205] =2×2=4(μm)

[0206] / d 平均 =0.056, meaning that when the ratio of the maximum aperture calibration result uncertainty to the average aperture of the sand core filter funnel is less than the preset value of 1, the average aperture measurement method is accurate.

[0207] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A method for measuring the pore size of a sand core filter funnel, characterized in that: Includes the following steps: S1: Install the sand core filter funnel on the matching vacuum flask to make it in a sealed state. The side wall of the vacuum flask is connected to the air pressure device through a sealed pipeline. A digital pressure device for displaying the pressure value is also connected to the sealed pipeline. An electron microscope for real-time observation of the filter plate inside the sand core filter funnel is installed on the top of the sand core filter funnel. The electron microscope and the digital pressure device are both connected to a computer. S2: The test environment temperature is set to 20℃±1℃ and the relative humidity is 50%. A thin film of pure water of a predetermined thickness is dripped onto the filter plate of the sand core filter funnel using a burette. S3: Start the air pressure device to steadily and slowly pressurize the filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears. Calculate the average pressure of n tests as ΔP1. S4: Continuously apply pressure. When bubbles appear uniformly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time. Calculate the average pressure of n tests as ΔP2. S5: Calculate the maximum and average pore diameter of the sand core filter funnel plate; The maximum and average pore diameters of the filter plate are calculated using formula (2): (2) In the formula: ΔP is the additional pressure, in Pa; d is the pore size of the bubble, in meters (m). γ is the surface tension of the liquid, with units of N / m; When ΔP is ΔP1, the bubble pore size is the maximum pore size d. max The unit is meters (m). When ΔP is ΔP2, the bubble pore size is the average pore size. The unit is meters (m). S6: Uncertainty assessment of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced by the resolution of the digital pressure gauge, and the standard uncertainty u3 introduced by the maximum permissible error of the digital pressure gauge; then, comprehensively calculate and judge the accuracy of the maximum aperture and average aperture measurement respectively. Accuracy assessment of the measurement of the maximum pore size of a sand core filter funnel: The standard uncertainty u1 introduced by the repeatability of sand core filter funnel pore size measurement: The maximum pore size of the sand core filter funnel was measured, i.e., the pressure value when the first air bubble appeared was read. Ten measurements were taken in total, and the average pressure was calculated. The average pressure was calculated according to formula (3): (3) In the formula: u 1 The standard uncertainty introduced for the repeatability of sand core filter funnel aperture measurement, in Pa; n represents the total number of measurements; p i The pressure value is from the i-th measurement, in Pa. This is the average of n pressure values, expressed in Pa. Standard uncertainty introduced by the resolution of the preset level digital pressure gauge u 2 : The standard uncertainty introduced by the resolution of the preset-grade digital pressure gauge is evaluated using Type B criteria, and the resolution of the preset-grade digital pressure gauge is selected as [value missing]. If Pa follows a uniform distribution, then the pressure is calculated according to formula (4): （4） In the formula, u2 is the standard uncertainty introduced by the resolution of the digital pressure gauge, and the unit is Pa; This refers to the resolution of a digital pressure gauge, measured in Pa. Standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge u 3 : The standard uncertainty introduced by the maximum permissible error of the preset-grade digital pressure gauge is evaluated using Type B. The error of the preset-grade digital pressure gauge is ± Pa, take half width as Pa, then the pressure is calculated according to formula (5): (5) In the formula, u3 is the standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge, and the unit is Pa; This refers to the error of the digital pressure gauge, expressed in Pa. Calculate the combined standard uncertainty according to formula (6). : (6) According to formula (2), the conversion is as follows: , The maximum pore diameter d of the sand core filter funnel max The uncertainty is expressed in μm. The maximum pore size expansion uncertainty u of the sand core filter funnel is calculated according to formula (7): （7） In the formula, u The maximum pore size expansion uncertainty of the sand core filter funnel is expressed in μm. k Sensitivity coefficient; The maximum pore size uncertainty of the sand core filter funnel is expressed in μm. when u If the ratio of the maximum pore size to the maximum pore size of the sand core filter funnel is less than 1%, then the method for measuring the maximum pore size is accurate; otherwise, it is inaccurate. Accuracy assessment of the average pore size measurement of a sand core filter funnel: Standard uncertainty introduced by the repeatability of average pore size measurement of sand core filter funnel : The average pore size of the sand core filter funnel was measured, i.e., the pressure value was read when bubbles appeared uniformly on the surface of the filter plate. Ten measurements were taken in total, and the average pressure was calculated according to formula (8): (8) In the formula: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa; n represents the total number of measurements; The pressure value is from the i-th measurement, in Pa. This is the average of n pressure values, expressed in Pa. Standard uncertainty introduced by the resolution of the preset level digital pressure gauge : The standard uncertainty introduced by the resolution of the preset-grade digital pressure gauge is evaluated using Type B criteria, and the resolution of the preset-grade digital pressure gauge is selected as [value missing]. Pa, following a uniform distribution, the pressure is calculated according to formula (9): (9) In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; This refers to the resolution of a digital pressure gauge, measured in Pa. Standard uncertainty introduced by the maximum permissible error of the preset grade digital pressure gauge : The standard uncertainty introduced by the maximum permissible error of the preset-grade digital pressure gauge is evaluated using Type B. The preset level digital pressure gauge error is ± Pa, take half width as Pa is calculated according to formula (10): (10) In the formula, The standard uncertainty introduced for the maximum permissible error of the preset-grade digital pressure gauge, in Pa; This refers to the error of the digital pressure gauge, expressed in Pa. Calculate the combined standard uncertainty according to formula (11) : (11) According to formula (2), the conversion is as follows: , The average pore size uncertainty of the sand core filter funnel is expressed in μm. The uncertainty of the average pore size expansion of the sand core filter funnel is calculated according to formula (12). : （12） In the formula, The mean pore size expansion uncertainty of the sand core filter funnel is expressed in μm. k Sensitivity coefficient; The average pore size uncertainty of the sand core filter funnel is expressed in μm. when If the ratio of the average pore size to the average pore size of the sand core filter funnel is less than 1%, then the method for measuring the average pore size is accurate; otherwise, it is inaccurate.

2. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: Before dripping a thin film of pure water of a predetermined thickness onto the filter plate of the sand core filter funnel using a burette in S2, the airtightness of the experimental equipment is checked: close the vent valve to the suction flask, start the air pressure device to introduce a certain amount of gas, and when the digital pressure counter value is displayed as 1.5kPa~2.5kPa, close the precision control valve and observe the change in the value of the digital pressure device. If the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, then the airtightness meets the requirements.

3. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In S2, pure water is dripped onto the filter plate of the sand core filter funnel using a burette, and the thickness of the thin water film is 1cm to 2cm.

4. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In step S3, the pressure device is activated to slowly and steadily pressurize the filtration flask. The surface of the filter plate is observed from above. When the first bubble appears, the pressure value P1 of the digital pressure device is recorded. The average pressure of n tests is calculated as ΔP1, which is then converted to the average value of the maximum pore size. max First, the effect of ambient temperature on the aperture result is tested: if the calculated aperture ratio is less than the preset value under the same working conditions at the test ambient temperature, then the ambient temperature meets the test requirements.

5. The method for measuring the pore size of a sand core filter funnel according to claim 4, characterized in that: The influence of ambient temperature was detected, and the influence of liquid column difference was also detected. According to the liquid pressure formula (1): p=ρgh (1) In the formula: p is the pressure, and the unit is Pa; ρ is the density of the liquid, with units of kg / m³. 3 ; g is the acceleration due to gravity, and its unit is N / kg. h represents the liquid column difference, in meters (m). Calculate the effect of the preset liquid column difference on the orifice measurement results: If the ratio of the calculated orifice diameter to the orifice diameter under the same working conditions is less than the preset value, then the test liquid column difference meets the test requirements.

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