CN106840976B

CN106840976B - Rheometer-based improved interface sliding parameter measurement device and method

Info

Publication number: CN106840976B
Application number: CN201710140077.2A
Authority: CN
Inventors: 刘莹; 宋智翔; 郭飞; 刘向锋; 王玉明
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2017-03-10
Filing date: 2017-03-10
Publication date: 2023-08-29
Anticipated expiration: 2037-03-10
Also published as: CN106840976A

Abstract

The invention provides an improved interface sliding parameter measuring device based on a rheometer, which is characterized in that a sample clamp is arranged on the basis of a lower sample table and a conical plate rotor of the rheometer, an upper clamp plate axially presses the sample clamp and is connected with the lower sample table of the rheometer through an inner hexagonal screw; the invention overcomes the defect that the material of the lower sample table cannot be replaced in the original rheometer, the lower sample can be replaced by any plane material, meanwhile, the accurate measurement of moment under different rotating speeds by the rheometer is utilized, the functional range of the rheometer is expanded, and a convenient measurement method is provided for the measurement of the interface sliding parameters between different materials and liquid.

Description

Rheometer-based improved interface sliding parameter measurement device and method

Technical Field

The invention belongs to the technical field of interface sliding parameter measuring devices, and particularly relates to an improved interface sliding parameter measuring device and method based on a rheometer.

Background

With the widespread use of aqueous lubrication, the solid-liquid interface slip-free hypothesis commonly employed in traditional lubrication simulation calculations is challenging to apply. The more accurate experimental result proves that the surface of the material with poor wettability is easy to generate interface relative sliding, thereby influencing the working performance. The sliding length and the ultimate shear stress are main indexes for measuring the sliding difficulty of a solid-liquid interface. The measurement experiment of solid-liquid surface sliding parameters mostly needs to design precise measurement instruments, and many devices are only suitable for measuring solid-liquid interface sliding parameters under microscopic dimensions, so that in the application of interface sliding, the stage of theoretical modeling simulation by assuming surface parameters is still performed at present, which prevents the interface sliding effect from being directly applied to performance analysis of engineering application.

The existing solid-liquid interface slip parameter testing method mainly comprises a direct measurement method and an indirect measurement method, wherein more optical decolorization fluorescence recovery technology (TIR-FRAP), microparticle development technology (mu-PIV) and near-field laser velocimetry (NFLV) are applied in the direct measurement method to directly observe a flow field close to a solid surface, so that slip parameters between solid and liquid are obtained; in the indirect measurement method, a surface force meter (SFA), an Atomic Force Microscope (AFM) or a micro-channel technology (Capilliry) is adopted, and the slip parameter between solid and liquid is indirectly obtained by comparing the dynamic pressure resistance (or the pressure drop after liquid flows through a micro-channel) when cylinders or microspheres are close with a theoretical calculation value after no slip assumption. In the main method, only specific microscopic solid-liquid interface sliding parameters can be generally measured, a plurality of devices have specific requirements on the shape of the surface to be measured, and most of the devices need to use complicated optical processing procedures or large-scale measuring equipment and cannot meet the measurement requirements on a large number of solid-liquid surfaces in actual engineering.

Due to the defects in the prior art, a measuring device capable of simply testing the interface sliding parameters between the solid-liquid interfaces is not available at present.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide an improved interface sliding parameter measuring device and method based on a rheometer, which can solve the problem of complex solid-liquid interface sliding parameter measurement and conveniently finish the measurement of interface sliding parameters between different solid surfaces and different liquids.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

on the basis of a lower sample table 1 and a conical plate rotor 3 of a rheometer, an annular sample clamp 5 is connected to the lower sample table 1 of the rheometer through a positioning screw 6, the sample clamp 5 is coaxial with the conical plate rotor 3, a cylindrical sample 4 is fixed to the lower sample table 1 of the rheometer through the sample clamp 5 and is positioned at the center of the sample clamp 5, and meanwhile, a clamp upper pressing plate 7 axially presses the sample clamp 5 and is connected with the lower sample table 1 of the rheometer through an inner hexagon screw 8.

The sample clamp 5 is axially positioned by contacting the step surface with the upper surface of the lower sample table 1, is radially positioned by a cylindrical surface, and the cylindrical sample 4 is axially positioned by contacting the step surface with the upper surface of the sample clamp 5 and is radially positioned by cylindrical surface clamping.

The fixture upper pressing plate 7 is connected with the rheometer lower sample table 1 through three inner hexagon screws 8, and the parallelism between the cylindrical sample 4 and the conical plate rotor 3 is adjusted through adjusting the three inner hexagon screws 8.

The invention also provides a measuring method by using the improved interface sliding parameter measuring device based on the rheometer, which comprises the following steps of firstly calculating the sliding length of a solid-liquid interface:

wherein delta is the slip length, R is the radius of the cone-plate rotor 3, and theta ₀ Is the cone angle of the cone plate, omega is the rotating speed of the cone plate rotor 3, M is the measured moment, and mu is the viscosity of the measured liquid;

the value or range of the ultimate shear stress is obtained by the change of the slip length delta with the shear rate.

Compared with the prior art, the invention has the beneficial effects that:

(1) The defect that the lower sample table material cannot be replaced in the original rheometer is overcome, the lower sample can be replaced by any planar material, meanwhile, the precise measurement of the moment of the rheometer at different rotation speeds is utilized, the functional range of the rheometer is expanded, and therefore the interface sliding parameter between any planar material and liquid can be measured conveniently;

(2) The upper clamp plate of the clamp is utilized to simultaneously realize axial limiting and parallelism adjustment of the lower sample.

Drawings

FIG. 1 is a semi-sectional view of the structure of the test device of the present invention.

Figure 2 is a semi-sectional view of the original structure of the rheometer used in the present invention.

FIG. 3 is an isometric view of the test device of the present invention.

FIG. 4 is a shear rate-shear stress curve result in an embodiment of the present invention.

FIG. 5 is a shear rate-slip length result in an embodiment of the invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples.

As shown in fig. 1, a rheometer-based interface parameter measuring device is characterized in that on the basis of an original rheometer, a lower sample table 1 and a conical plate rotor 3, a sample clamp 5 is connected to the lower sample table 1 of the rheometer through a positioning screw 6, a cylindrical sample 4 is fixed to the lower sample table 1 of the rheometer through the sample clamp 5, the sample clamp 5 is annular and coaxial with the conical plate rotor 3, the cylindrical sample 4 is positioned at the center of the sample clamp 5, and meanwhile, a clamp upper pressing plate 7 axially presses the sample clamp 5 and is connected with the lower sample table 1 of the rheometer through an inner hexagon screw 8.

The sample fixture 5 is axially positioned by contacting the step surface with the upper surface of the lower sample table 1, radially positioned by the cylindrical surface, axially positioned by contacting the step surface with the upper surface of the sample fixture 5, and axially and radially positioned by clamping the cylindrical surface. During testing, cylindrical sample 4 will have an upward tendency to move due to the upward attraction of conical plate rotor 3 to cylindrical sample 4, which is limited by clamp upper platen 7. In addition, the parallelism between the cylindrical sample 4 and the conical plate rotor 3 can be adjusted by adjusting three inner hexagon screws 8 on the upper clamp plate 7, so that the uniformity of the liquid film 2 and the accuracy of the result are ensured.

The working principle of the invention is as follows:

the materials used for the samples under the rheometer are replaced by using the sample clamp 5 and the clamp upper pressing plate 7, the parallelism between the cylindrical sample 4 to be tested and the conical plate rotor 3 is guaranteed by utilizing the adjustment of three inner hexagon screws 8, the torque in the rotation process is accurately measured by utilizing the rheometer at different rotation speeds, and the slip parameters of the solid-liquid interface, namely the slip length and the limit shear stress, are measured by utilizing the ratio of the torques of different samples at the same shear rate.

After the solid-liquid interface slides, the friction moment measured by the rheometer is lower than that of the surface without sliding. And obtaining the ultimate shear stress of the solid-liquid interface through the critical rotation speed corresponding to the inflection point of the friction moment with the moment lower than the non-slip theoretical value.

Through integral calculation, a corresponding slip length calculation formula can be obtained from the moment value and the rotating speed:

wherein delta is the slip length, R is the radius of the cone plate rotor, and theta ₀ Is the cone angle of the cone plate, Ω is the rotational speed of the rotor, M is the measured torque, μ is the viscosity of the liquid being measured. From the measured change in slip length with shear rate, the magnitude or range of ultimate shear stress can be obtained.

Examples

In the embodiment, an Austria An Dongpa MCR302 rotary rheometer is adopted as a measurement system basis for measurement, a cone plate rotor is a CP50-0.3 rotor, and the model of graphite material is FH82Z5.

The shear rate-moment curve between deionized water and PTFE material and graphite material measured by the measuring device and the shear rate-moment curve between deionized water and lower sample table measured based on the original rheometer are shown in figure 4.

The sliding length-shear rate curve obtained by the above formula is shown in fig. 5 by taking the curve measured by the original sample table as a reference, the sliding length of the measured PTFE material is 45 mu m, the sliding length of the impregnated graphite material is 5 mu m, and the ultimate shear stress of the two materials is less than 1Pa.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations are possible. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The improved interface sliding parameter measuring device based on the rheometer is characterized in that on the basis of a lower sample table (1) and a conical plate rotor (3) of the rheometer, an annular sample clamp (5) is connected to the lower sample table (1) of the rheometer through a positioning screw (6), the sample clamp (5) is coaxial with the conical plate rotor (3), a cylindrical sample (4) is fixed to the lower sample table (1) of the rheometer through the sample clamp (5) and is positioned at the center of the sample clamp (5), meanwhile, a clamp upper pressing plate (7) axially presses the sample clamp (5) and is connected with the lower sample table (1) of the rheometer through an inner hexagon screw (8), and test liquid is clamped between the conical plate rotor (3) and the cylindrical sample (4) during measurement; the sample clamp (5) is axially positioned by contacting the step surface with the upper surface of the lower sample table (1), radially positioned by a cylindrical surface, axially positioned by contacting the step surface with the upper surface of the sample clamp (5), and radially positioned by cylindrical surface clamping; the clamp upper pressing plate (7) is connected with the rheometer lower sample table (1) through three inner hexagon screws (8), and the parallelism between the cylindrical sample (4) and the conical plate rotor (3) is adjusted by adjusting the three inner hexagon screws (8).

2. The method for measuring the interface sliding parameter based on rheometer improvement according to claim 1, wherein the sliding length of the solid-liquid interface is calculated:

wherein delta is the slip length, R is the radius of the conical plate rotor (3), and theta ₀ Is the cone angle of the cone plate, omega is the rotating speed of the cone plate rotor (3), M is the measured moment, and mu is the viscosity of the measured liquid;