CN1017931B - Apparent Viscosity Quick Measuring Device and Its Measuring Method - Google Patents

Abstract

The invention can rapidly and directly measure the more exact mechanical quantity-the apparent viscosity function of the non-Newtonian fluid.

The samples were made to flow in an L-tube, giving a continuous change from maximum to 0 shear rate, collected and converted by a micropressure sensor and sent to a microprocessor after A/D conversion, and then calculated according to a self-derived formula giving the shear rate and the corresponding apparent viscosity in pairs. This allows one-time experiments to give a new idea of a range of shear rates and corresponding apparent viscosities. The experimental procedure is automatically carried out and is easy to master by non-professionals.

Can be used in biological, pharmaceutical, chemical, oil, and food sectors.

Description

The invention is applicable to the measurement of apparent viscosity, one of the non-Newtonian rheological properties.

In the following description, the symbols η _a and η _p represent two different concepts of apparent viscosity, γ represents the shear rate, and τ represents the shear stress (or wall shear stress).

The status of existing methods for measuring non-Newtonian rheological properties is: (1) η _a is confused with η _p , but in fact they are not equal. The physical meaning of η _a is the ratio of shear stress and shear rate, but because of the non-Newtonian As far as Newtonian fluid is concerned, the latter two are not proportional, that is, η _a is essentially a function of shear rate η _p is a formal borrowing of the calculation results of Newtonian fluid when measuring non-Newtonian fluid, that is, non-Newtonian fluid Put it into a viscometer suitable for Newtonian fluid to measure it, and calculate it according to the formula of Newtonian fluid. (2) Even if the two are not confused, the measurement method is quite complicated, that is: first measure a series of η _p and then turn to calculate η _a (γ), this method must measure a series of pressure and flow Obtain the corresponding pseudo-apparent viscosity, and then obtain the value of [d(Lgη _p )/d(Lgτ)] on the double-logarithmic curve coordinate graph, and finally obtain the apparent viscosity η _a at different τ, and in It is easy to cause errors when seeking [d(Lgη _p )d(Lgτ)]. Such a method is not convenient to be widely used in biomedical research, especially for clinical medical workers, and is not convenient to be used in the quality control and management sites of industries such as chemical industry and food.

The purpose of the present invention is to seek a kind of measuring method of easy and quick and theoretically stricter apparent viscosity η _a and design a kind of instrument that can implement this method, it can be widely used in biomedical research, chemical industry, food etc. Industrial quality control and management scene.

The overall composition diagram is shown in Figure 1.

The technical key of the present invention is to embody the following theoretical results in a simple way:

According to the constitutive equation, equilibrium equation and capillary geometric conditions of non-Newtonian fluid, it can be derived

η _a = πR ⁴ P/[2L(3Q+P·dQ/dP)] (1)

τ=RP/2L (2)

Here P is the pressure difference across the capillary, _Q1 is the flow rate in the tube, R and L are the tube radius and length, respectively. η _a is the apparent viscosity, τ is the shear stress, and d is the differential sign.

According to formula (1), it can be seen that η _a (τ) can be obtained as long as the change of flow rate with pressure is known. There are different schemes to achieve this. According to the analysis, we have found a rather simple new scheme, which constitutes one of the characteristics of this method:

For the L tube shown in Figure 3, AO is the pressure-driven tube, and OB is the capillary tube. It is not difficult to deduce from formulas (1) and (2)

η _a =K ₁ h/[3(dh/dt)+h(dh/dh)] (3)

τ=K ₂ h (4)

In the formula, d is the differential sign, h is the derivative of h to time, namely dh/dt; dh/dh is d(dh/dt)/dh

K ₁ and K ₂ are constants related to the geometry of the tube and the density of the sample.

In this way, it is only necessary to measure the change of h with time, and the dependence relationship between η _a and τ (or 'τ) can be obtained in a one-time experiment, and the relationship between ht can be obtained through the pressure at point D in the figure The sensor detects the corresponding change in pressure when the liquid level in the AO section falls freely over time. This change of pressure is directly proportional to the change of h, and the collected information is immediately sent to the A/D conversion circuit and microprocessor for further digital processing, and a series of η _a is quickly given in pairs and τ.

The special equipment contained in the present invention consists of three units: the body part, the detection and control part, and the temperature control part (as shown in Figure 1).

1. The body part consists of:

a. Horizontal capillary (OB) (as shown in Figure 3 and Figure 1), the material is glass, the configuration of the outlet end is shown in Figure 1, and its curved part is used to store samples and facilitate repeated experiments. Capillary (OB) ) geometric parameters to ensure that the kinetic energy correction rate and the influence of the end effect are as small as possible. can be ignored, while ensuring that the laminar flow condition is met. The configuration of the outlet port is also designed to facilitate automatic control of liquid flow.

b. The vertical pipe (AO) (as shown in Figure 3) is a pressure-driven pipe with two inner diameters of 2mm and 3mm. The length is 300mm to ensure a sufficiently large upper limit of shear stress. The inner diameter is uniform along the length direction, and what the prototype of the present invention uses is a finished burette.

c. Tee joint (O), used to connect the horizontal capillary (OB), vertical tube (OA) and the pressure sensor (3).

d. Body box, composed of horizontal capillary (OB), vertical tube (OA), small U-shaped tube CB and three-way joint. An L tube is placed in a box, and hot air is passed through the box to form an air bath (17) , to adjust the temperature.

2. Detection and control part

2.1 The detection part consists of:

a. Pressure sensor (3):

In order to ensure sufficient accuracy of the measurement results, this device puts forward higher requirements on the sensor, and the resolution of the sensor used is 1mmH ₂ O, which is about 0.5% of the maximum liquid level height h. The sensor linearity is better. The prototype of the present invention adopts BVP type micro-pressure sensor (manufactured by Bengbu Semiconductor Device Factory)

b. Amplifier (10):

It is an ordinary differential amplifier circuit, which is used to properly amplify the signal from the pressure sensor to meet the requirements of the A/D converter for the input amplitude.

c. A/D conversion circuit (as shown in Figure 4)

The circuit is a 12-bit A/D conversion circuit, which is composed of ADC1210 chip, clock pulse circuit, regulated power supply, analog signal input circuit, data output and interface circuit of single board computer.

ADC1210 is the core part of the A/D conversion chip, which completes the A/D conversion work. Its resolution is 12 bits, and the conversion accuracy is 0.25%. Its conversion logic diagram is shown in Figure 5. The ADC1210 converts the analog quantity to a digital quantity approximately bit by bit, that is, at a certain moment, a quantity is output from the D/A internally and compared with an unknown analog quantity input, and the control logic can realize control similar to binary search. It first makes the highest bit D _12-1 = 1, after D/A conversion, an analog voltage V ₂ of half the entire range is obtained and compared with the input voltage, if V _X > V _S , this bit is reserved. If V _X < V _S , clear this bit to "0", then make the next bit D _12-2 = 1 and compare it with V _X after D/A conversion with the previous result.... Repeat this process until D ₀ 1 is compared with V _X to decide whether to keep this bit (D ₀ ) by V _X > V _S or V _X < V _S. In this way, after 12 comparisons, the state of the 12-bit register is the converted data. The end signal changes from high level to low level.

The clock pulse circuit uses a 555 integrated circuit. Its wiring diagram is shown in accompanying drawing 4. It produces a 65KH ₂ square wave, and its waveform is shown as CP in accompanying drawing 5. The clock source is the synchronous signal of A/D conversion. When the A/D chip is started, ADC1210 converts one bit per clock cycle, so the clock frequency determines the speed of A/D conversion. It can be changed by adjusting the resistance and capacitance. Frequency, and at the same time, it can be seen that the waveform is regular on the oscilloscope.

The stabilized power supply adopts two-stage stabilized voltage. First, the voltage is changed to 25V by a transformer. After rectification and filtering, the voltage becomes +5V after the three-terminal stabilized integrated block 7812 and 7805, which is used for ADC1210 to compare the voltage.

Analog signal input circuit, there is one analog input in this system, so there is no multi-way switch, and the analog value changes slowly, so the signal from the amplifier is directly input into one channel, and the sample holder in the auxiliary circuit is omitted.

The interface circuit between the data output and the single-board computer adopts the PIO port as the interface. Since PIO is a programmable device with I/O ports, it does not require other external logic to connect with external devices. After the conversion, the IN command can be used to make the A/D chip read data. We directly use the two PIO ports that have been configured on the single-board computer, among which the 8 bits of PIO port B are used as the low 8-bit data transmission port output by the A/D chip, and the PA ₄ -PA ₇ terminals of the 8-bit terminals of PIO port A are used as The high four-bit data transmission port output by the A/D chip.

d. Microprocessor (8):

Z80 single-board computer or other microprocessors can be used to process, calculate, and output the data sent by the A/D converter to complete the temperature control of the present invention, the automatic control of experimental operations, zero adjustment, and input results.

2.2 Control part: (as shown in Figures 4 and 5)

The sample driving and automatic control part of the present invention is composed of an electromagnetic pump, a self-made electromagnetic valve, a liquid level detector and several relays, and is controlled by a microcomputer program.

The computer gives a start signal, the solenoid valve 2 is pulled in, the electric pump works, and the liquid level in the vertical pipe rises. When it rises to the liquid level detection position, the liquid level controller outputs a level, which is input by PIO and applies for an interruption to the CPU. After the execution of the interrupt service program, give the pump a signal to stop working, and at the same time, the solenoid valve 1 is closed to keep the liquid level stable for a period of time, the solenoid valves 1 and 2 are released, the liquid level drops naturally, and then the A/D conversion is started to start sampling.

3. Temperature control part (18) (as shown in accompanying drawing 1 and accompanying drawing 6):

Stepless adjustable temperature control controlled by thyristor, the accuracy is ±0.5°C for the selected temperature. It is detected by the temperature sensor (14) (thermistor), and then the temperature control loop sends an instruction to the heater (hair dryer) (16) to heat or stop heating to realize the circuit diagram of the temperature control loop as shown in Figure 6 (15) .

The self-designed computer software part of the present invention includes start-up, sample position, sampling, filtering, sensor zero correction, calculation, surface tension correction, display and printing subroutines.

The concrete steps that realize the method for the present invention are:

1. Preparation

Put the L-shaped tube (2) into the main body box (1), inject the sample from port B, and temporarily store the sample in CB to connect the pressure sensor (3), solenoid valves (4), (5) and liquid level sensor (6) Each channel or circuit, the sensor is pre-adjusted and balanced.

2. Sample location

(1) Start the microprocessor 8, make it issue a command to close the solenoid valve a (4), open the solenoid valve b (5) and start the pump (7), and the sample slowly rises from CB to A through the capillary.

(2) When the liquid level reaches A, the liquid level sensor (6) is turned on, and the B port of the microcomputer is given a low level, and the microcomputer 8 notifies the pump to stop working.

(3) Use software delay to keep the liquid level for a short time and let the system settle down.

3. Sampling

(1) The microcomputer (8) notifies the valves (4) and (5) to open, so that the C and B of the L pipe communicate with the atmosphere, and the liquid level height h of the AO section decreases freely. The purpose of setting the C port is just to make the C place be atmospheric pressure, so as to ensure that the liquid level can drop freely.

(2) The pressure sensor continuously converts the pressure signal into a voltage change with time, and this change value is proportional to the height h.

(3) After the voltage value is amplified by a differential amplifier (10), it is sent to a 12-bit A/D converter (11) and converted into a 12-bit digital number.

(4) The microcomputer fetches numbers from the A/D converter at intervals of several T milliseconds, and every sixteen such numbers are shifted to the right by four bits and then added to form a sixteen-bit binary number. It is the average of sixteen densely sampled values, which will be used as the h value for further calculations.

4. Operation

The operation formula is: formula (3) and (4).

Considering the effect of surface tension, formula (3) can be further modified as:

η _a ＝Kdt/[dh/(h-σε)+d ² h/(3·dh)]

In the formula, σ is the coefficient of surface tension, ε is a constant related to the density of the sample and the geometric size of the L tube, and ^d2 is the symbol of the second order differential.

d still means differential.

5. Display and print

As h decreases, the apparent viscosity values at different shear rates from large to small are continuously given, and they are displayed and printed in pairs.

The number of sampling points and time interval can be set in advance, and the software program will automatically make corresponding corrections to the numerical changes caused by different settings.

If necessary, after the first experiment is completed, the instrument will automatically start the second experiment.

The present invention adopts the balance adjustment of the pressure sensor, which can directly use the signal of the pressure sensor to be amplified and sent to 12-bit A/D conversion, and the program will convert the collected data into a value corresponding to the voltage, which will be displayed immediately by the display (13) Come out, can save the voltmeter and accurate, convenient.

Adopt the L-shaped tube sampling of the present invention and the pressure sensor that is matched with it, A/D conversion circuit and microprocessor can provide a series of corresponding apparent viscosity values (tens of tens) in a certain shear rate range in one-off experiment points), greatly shorten the cycle of experiment and data collation, and make the whole experiment automatically and automatically repeatable, easy to operate, and can quickly and directly make a direct and fast calculation of the more clearly defined mechanical quantity - the apparent viscosity function of non-Newtonian fluids. Measurement.

Using an L-shaped tube, during the continuous decline of the sample liquid level in the vertical part from the highest point to 0, the continuous change process from the corresponding maximum shear rate to 0 shear rate is given, that is, the continuous change process of the independent variable , use the micro-pressure sensor to collect and convert this change process, and send it to the microprocessor for processing after A/D conversion.

According to the self-derived formula, the shear rate and the corresponding apparent viscosity function are given in pairs after computer operation. This is the difference with domestic and foreign machines.

It is easy to operate, fast, relatively simple in structure and much lower in cost compared with foreign high-end machines.

It can be used in biology, medicine, chemical industry, oil, food and other departments.

The present invention will be further described below in conjunction with accompanying drawing:

Accompanying drawing 1 is a schematic diagram of the composition of the rapid apparent viscosity measuring device of the present invention, wherein (1) is the measuring body, (2) is the sample, (3) is the pressure sensor, (4) is the solenoid valve a, and (5) is the electromagnetic Valve b, (6) is a liquid level sensor, (7) is a pump, (8) is a microprocessor, (9) is a liquid level control circuit, (10) is an amplifier, (11) is an A/D converter, (12) is the detection and control unit, (13) is the display, (14) is the temperature sensor, (15) is the temperature control circuit, (16) is the heater, (17) is the air bath, (18) is the temperature control Unit, AO is a vertical tube, OB is a horizontal capillary.

Accompanying drawing 2 is the definition schematic diagram of apparent viscosity, and wherein η _a is apparent viscosity, and τ is shear stress, and τ is shear rate.

Accompanying drawing 3 is the L-shaped tube in the quick measuring device of apparent viscosity of the present invention, and wherein AO is pressure-driven tube, OB is capillary, h is height, and L is the length of OB tube.

Accompanying drawing 4 is the schematic diagram of the control circuit of the present invention.

Accompanying drawing 5 is the liquid level control circuit diagram of the present invention.

Accompanying drawing 6 is the schematic diagram of the temperature control circuit of the present invention.

Example:

Utilize the apparent viscosity rapid measuring device of the present invention, several typical samples of sufficient quantity have been measured, and the measurement method results are all approved and verified by the legal measurement unit (Sichuan Provincial Institute of Metrology), and the specific numbers are shown in the table.

Sample Temperature Shear Stress Apparent Viscosity (es) Apparent Viscosity (cp)

(°C) (dyn/cm ² ) measured value standard value measured value standard value

Water 20 1.01±0.02 1.01 1.01±0.02 1.01

37 0.68±0.02 0.68 0.68±0.01 0.68

2# standard oil 20 2.04±0.02 2.071

4# standard oil 20 1.07±0.03 4.153

30% glycerin aqueous solution 37 1.17 1.60±0.03 1.68±0.03 1.68

37 0.15 1.77±0.03 1.85±0.03 1.85

40% glycerin aqueous solution 22 1.86 2.51±0.03 2.67±0.03 2.67

22 0.26 3.10±0.03 3.26±0.03 3.26

Bile 37 4.04 0.83±0.03 0.86±0.04 0.86

37 0.07 0.89±0.03 0.92±0.04 0.92

99.5% ethanol 30 0.05 1.73±0.03 1.36±0.04 1.36

2.87 1.39±0.03 1.12±0.04 1.14

20 0.039 2.29±0.03 1.31±0.03 1.83

20 2.907 1.96±0.03 1.60±0.03 1.61

Rabbit blood 37 4.16 3.04±0.05 3.10±0.05 3.17

1.30 3.30±0.05 3.45±0.05 3.56

＊If there is no existing data for the standard value, it will be included in the "Low Shear 30" machine measured value.

Claims (2)

1, a kind of fast survey device of apparent viscosity, comprise body part, by pressure transducer, amplifier, the A/D change-over circuit, the test section that microprocessor constitutes, by electromagnetic pump, the self-control solenoid valve, liquid level detector, relay, and the control section and the temperature control part branch that constituted by system controlled by computer, it is characterized in that body part is 300mm by length, internal diameter is one of 2mm and 3mm, the internal diameter VERTICAL TUBE and the length of uniformity along its length is 200mm, internal diameter is that the horizontal kapillary of 0.6-1mm passes through two L shaped pipes of export mixes in the three-way connection, another outlet of three-way connection links to each other with pressure transducer, the level other end capillaceous links to each other with little U-shaped pipe, and places the box that can regulate temperature.The A of L type pipe links to each other with liquid level sensor, and B links to each other with two electric solenoid valves respectively with C.

2, a kind of method of utilizing the described device fast measuring of claim 1 apparent viscosity, its step comprises: sample injects and instrument gives the calculating of accent, sample set, sampling, apparent viscosity, the demonstration and the printing of apparent viscosity, it is characterized in that:

(1) to inject little U-shaped pipe from the C mouth temporary for sample;

By microprocessor and liquid level control module, make sample slowly rise to straight tube near the A end from the little U-shaped pipe horizontal kapillary of flowing through, can not overflow;

(2) by the liquid stream control unit, make the interior height of specimen h of VERTICAL TUBE drop to the lowest order of sample continuously, and provide change procedure from corresponding maximum shear rate to 0 shearing rate, pressure transducer detects kapillary pressure at two ends difference variable signal in time with this process;

(3) by microprocessor the sensor signal after the A/D conversion is processed, by following operational formula of deriving voluntarily

η _a＝K ₁dt/[dh/（h-σε）+1/3·（d ²h/dh）]

τ＝K ₂h

Automatically computing, and a series of shearing stress of printout and corresponding apparent viscosity value.

Images