CN1595473A - Self-circulating Reynolds experiment instrument with automatic color killing - Google Patents

Abstract

The invention discloses a self-circulating Reynolds tester with an automatic decolorizing display liquid. It has a self-circulating water supply device and a water pump inside the self-circulating water supply device. The water pump is controlled by a thyristor stepless speed regulator. The constant pressure water tank is connected with the experimental pipeline in sequence. There is a self-circulating water return device below. The constant pressure water tank is connected to the self-circulating water supply through the upper water pipe and the lower water pipe. The constant pressure water tank is equipped with an overflow plate and a water stabilizing plate. The flow plate and water stabilizing plate divide the constant pressure water tank into overflow area, constant pressure area and water stabilizing area. The diversion tube, the invention adopts an independent self-circulating constant pressure water supply system, which is easy and intuitive to operate, and uses an automatic decolorization display liquid to replace the traditional display liquid, which solves the problem that the traditional Renault tester equipment is easily stained by the display liquid and the water body cannot be reused defect.

Description

Self-circulating Reynolds tester with automatic decolorization

technical field

The invention relates to an experimental measuring instrument, in particular to a self-circulating Reynolds experimental instrument with automatic decolorization of display liquid.

Background technique

The two flow states of the fluid have different motion characteristics. In laminar flow, there is no mixing of particles between the flow layers, and the particles move in an orderly and straight line; on the contrary, in turbulent flow, the particles are mixed between the flow layers, which is a disordered random motion. Whether the specific flow is turbulent or non-turbulent (laminar flow), the Re number can be used as a criterion to distinguish. Reynolds experiment clearly demonstrates the existence of laminar flow and turbulent flow. Reynolds tester is an experimental instrument specially used for Reynolds experiments.

Renault's teaching experiment is one of the important teaching contents of fluid mechanics. However, the traditional Renault tester has certain disadvantages: first, in order to have a constant pressure water level, a relatively large water supply system and overflow system must be installed, which occupies a large area; It is difficult to achieve stability for a while; third, the tracer reagents seriously stain the water body and experimental pipelines. First, the water cannot be reused, and the water consumption is too large;

Contents of the invention

The object of the invention is to provide a self-circulating Reynolds tester with an automatic decolorizing display liquid.

It has a self-circulating water supply device and a water pump inside the self-circulating water supply device. The water pump is controlled by a thyristor stepless speed regulator. The constant pressure water tank is connected with the experimental pipeline in sequence. There is a self-circulating water return device below. The constant pressure water tank is connected to the self-circulating water supply through the upper water pipe and the lower water pipe. The constant pressure water tank is equipped with an overflow plate and a water stabilizing plate. The flow plate and water stabilizing plate divide the constant pressure water tank into overflow area, constant pressure area and water stabilizing area. The guide tube, the needle at the end of the guide tube is aimed at the center of the entrance of the experimental pipeline, and the display liquid with automatic decolorization is housed in the said display liquid container, and its composition is phenolphthalein: sodium hydroxide = 1: 2 ~ 3 ratio, hydrogen The concentration of sodium oxide is 1/1000～1/2000.

Advantages of the present invention:

1) Instead of the previous practice of bulky structure, the entire experimental system is reduced and simplified, the operation is simple and intuitive, and it is suitable for modern teaching requirements, and it also saves the experimental layout space;

2) A new type of automatic decolorizing tracer reagent is used to replace the traditional tracer reagent, which solves the defects that the traditional Renault experimental equipment is easily stained by the tracer reagent and the water body cannot be reused;

3) An independent self-circulating constant pressure water supply system is adopted to reuse the experimental water body and save resources.

Description of drawings

The accompanying drawing is a schematic diagram of the structure of the self-circulating Reynolds experimental instrument with an automatic decolorizing display liquid.

Detailed ways

The self-circulating Reynolds experimental instrument with automatic decolorization has a self-circulating water supply device 1, and a water pump is installed in the self-circulating water supply device. The water pump is controlled by a thyristor stepless speed regulator 3, and the constant pressure water tank 4 is connected with the experimental pipeline 8 in turn. , the tail of the experimental pipeline 8 is provided with a flow regulating valve 9, and the outlet of the experimental pipeline is provided with a self-circulating water return device 2, and the constant pressure water tank 4 is connected with the self-circulating water supply device 1 through an upper water pipe and a lower water pipe, and an overflow is provided in the constant pressure water tank 4 Plate 7, water stabilizing plate 6, water stabilizing plate 6 has water stabilizing holes laterally, overflow plate 7 and water stabilizing plate 6 divide the constant pressure water tank into overflow area 10, constant pressure area 11 and water stabilizing area 12 , the upper part of the constant pressure water tank 4 is provided with a display liquid container 5 that can be automatically decolorized, and the display liquid container 5 is provided with a diversion tube with a diversion needle 13, and the needle at the end of the diversion tube is aligned with the center of the entrance of the experimental pipeline 8. Said display liquid container 5 is equipped with display liquid with automatic decolorization, and its composition is phenolphthalein: sodium hydroxide=1: 2～3 proportioning, and the concentration of sodium hydroxide is 1/1000～1/2000.

The working process of the present invention is: under the constant pressure water head, the flow regulating valve regulates the flow rate in the test pipeline, and the display liquid (colored water) flows into the test pipeline at the same time, and the streamline formed by the display liquid in the observation test pipeline can be distinguished. There are two flow states of laminar flow and turbulent flow in the water body in the pipeline.

Experiment of the present invention, circular tube Reynolds number, its computing formula is:

$\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&upsi;d</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;dv</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; KQ</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;dv</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula:

Re--Reynolds number;

υ--fluid flow rate;

v--fluid viscosity;

d--diameter of round pipe;

                                                                                                                            

The flow rate Q in the experimental pipeline, the inner diameter d of the experimental pipeline and the temperature t of the experimental water body are measured in the experiment. The fluid viscosity v is obtained by looking up the water temperature t table. Using the above two formulas, the Reynolds number of the water body in the experimental pipeline can be calculated.

The main component of the automatic decolorizing display liquid of the present invention is a mixed solution of phenolphthalein and sodium hydroxide. The characteristic of the phenolphthalein solution is that it is colorless under weakened and acidic conditions, and the solution appears red when the alkalinity of the solution reaches a certain value. Reagent working process in the present invention is: phenolphthalein and sodium hydroxide are measured respectively by phenolphthalein: sodium hydroxide=1: 2～3 ratio, phenolphthalein is fully dissolved with dehydrated alcohol, and sodium hydroxide is dissolved with distilled water, and concentration is 1/ 1000～1/2000, then mix the two reagents, stir evenly, the reagent will turn red, this is the automatic decolorizing display solution. The display liquid is placed in the display liquid container, enters the pipeline through the needle of the diversion tube, and moves forward together with the experimental water body to display the flow state in the pipeline. The water body in the water supply device is in a neutral state, showing that the alkalinity of the liquid is reduced, and the solution is colorless, which automatically disappears. After working for a long time, the water body in the experiment is alkalized, and the water body appears red. Add an appropriate amount of dilute hydrochloric acid to the water body to neutralize. Water can be decolorized. The display liquid has no pollution to the water body, the pipe wall and the surrounding environment.

Experimental content

(1) Observe two flow states.

Start the water pump to supply water to fill the water tank to the overflow state. After stabilization, open the regulating valve slightly, and inject the colored water into the experimental pipeline to make the colored water flow in a straight line. Observe the laminar flow state of the water flow in the pipe through the movement of the colored water particles, then gradually open the large regulating valve, and observe the hydraulic characteristics of the change from laminar flow to turbulent flow through the change of the straight line of the colored water. By gradually closing the regulating valve, the hydraulic characteristics of changing from turbulent flow to laminar flow can be observed.

(2) Determine the critical Reynolds number and reproduce the whole process of the Reynolds experiment in that year.

a. Determine the lower critical Reynolds number

Open the regulating valve to make the flow in the pipe completely turbulent, and then gradually close the flow regulating valve. During the adjustment process, only the small flow regulating valve is allowed to be closed, and the large flow regulating valve is not allowed to be opened. After stabilizing for a period of time, observe its shape until the color water flow is just in line, which means that the turbulent flow has just changed to laminar flow. At this time, the lower critical Reynolds value can be measured between 2000 and 2300. However, Reynolds obtained the lower critical Reynolds number of the garden pipe flow as 2320 in the experiment, because the lower critical Reynolds number is not absolutely irrelevant to the interference. Reynolds conducted the experiment in an environment where the interference of the environment was minimal, and the water body in the water tank was long before the experiment. Under the stable condition of time, it is obtained after repeated careful measurements. However, due to the influence of environmental interference factors in a large number of experiments by later generations, it is difficult to repeatedly obtain the exact value of Reynolds' experiment, which is usually between 2000 and 2300. Therefore, starting from engineering practicality, the critical Reynolds number of garden tubes introduced in textbooks is generally 2000. If the measured Reynolds number is too small, the valve should be opened to turbulent flow and then re-measured.

b. Determination of upper critical Reynolds number

Turn on the water pump, after the water tank overflows, open the regulating valve slightly to make laminar flow appear in the pipe, gradually open the regulating valve to a large extent, pay attention, only open the large regulating valve, and do not close the small valve, when the colored water flow just disperses, it means that the laminar flow has just improved For turbulent flow, there is an upper critical Reynolds value. According to the experimental measurement, the measured value of the upper critical Reynolds number is in the range of 3000-5000, which is closely related to the speed of operation, the degree of turbulence of the water tank, and external interference. Relevant scholars have done a lot of experiments, some got 12,000, some got 20,000, and some even got 40,000. In actual water flow, interference always exists, so the upper critical Reynolds number is an indeterminate value, which has no practical significance.

Outcome analysis

(1) The flow state criterion adopts dimensionless parameters instead of critical flow velocity.

In Reynolds' experiments before 1883, he found that there were two flow states in the circular tube flow—laminar flow and turbulent flow, and there was a critical flow velocity υ _c ′ for converting laminar flow into turbulent flow, υ _c ′ and the viscosity of the fluid v, the diameter d of the garden pipe is related, that is

υ _c '=f(v,d) (3)

Therefore, in a broad sense, υ _c ′ cannot be used as a criterion for flow state transition.

In order to distinguish the flow state, Reynolds did a lot of experiments on liquids with different pipe diameters and different viscosities, and obtained a dimensionless parameter (υd/v) as the criterion of the flow state of the pipe flow. He not only profoundly revealed the law of fluid state transformation, but also set a model for future generations to use dimensionless methods to conduct experimental research. The same dimensionless number as the Reynolds number can be obtained by using the Rayleigh method of dimensionless analysis.

It can be considered that the functional relationship of formula (3) can be expressed by the product of exponents. Right now

${\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

where K is a dimensionless coefficient.

The dimension relation of formula (4) is

$<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; LT</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}^{{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

From the principle of dimensional harmony, we get

L: 2α ₁ +α ₂ =1

T: α ₁ = -1

Simultaneous solution: α ₁ =1, α ₂ =-1.

Substituting the above results into formula (4), we get

${\mathrm{\&upsi;}}^{\&prime;}=K\frac{v}{d}$ or $K=\frac{{\mathrm{\&upsi;}}^{\&prime;}d}{v}----\left(6\right)$

The Reynolds experiment has completed the determination of the K value and the verification of whether it is a constant. As a result, K=2320 was obtained. Thus, the dimensionless number υd/v becomes suitable for any pipe diameter. Criterion for flow state transitions of any Newtonian fluid. Due to Reynolds' contribution, υd/v is named Reynolds number.

With the improvement of dimensional analysis theory, using dimensional analysis to obtain dimensionless parameters and study the relationship between multiple physical quantities has become one of the important means of experimental research today.

(2) The difference between laminar flow and turbulent flow in terms of kinematics and dynamics is as follows: Kinematic properties Dynamic properties Laminar flow 1. The particles flow in layers regularly. 2. The cross-sectional flow velocity is distributed according to a parabola. 3. The movement element has no pulsation phenomenon. 1. There is no mass transfer between stream layers. 2. No momentum exchange between flow layers. 3. The energy loss per unit mass is proportional to the first power of the flow velocity. turbulence 1. Particles mix with each other for random motion. 2. The cross-sectional flow velocity is distributed according to the exponential law. 3. Irregular pulsation occurs in the movement elements. 1. There is mass transfer between stream layers. 2. Momentum exchange exists between flow layers. 3. The energy loss per unit mass is proportional to the (1.75-2) power of the flow velocity.

(3) The physical meaning of Reynolds number.

其中体积W为特征长度The Reynolds number can be regarded as the ratio of the fluid inertial force to the viscous force. To understand this point, we can analyze it from the dimensions of inertial force and viscous force.

where the volume W is the characteristic length

The cube of L, namely [W]=[L] ³ ; acceleration The dimension of is expressed by the ratio of the characteristic velocity to the dimension of time, that is $\left[\frac{\mathrm{d\&upsi;}}{\mathrm{dt}}\right]=\frac{\left[\mathrm{\&upsi;}\right]}{\left[t\right]}$ So the dimension of the inertial force is

$<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; d\&upsi;</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; ]</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\frac{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ]</span>}$

Viscous force $T=\mathrm{\&mu;\&omega;}\frac{\mathrm{du}}{\mathrm{dn}},$ The dimension of the area ω is the square of the characteristic length L, that is, [ω]=[L] ² , the velocity gradient The dimension of can be expressed by the ratio of the dimension of the characteristic flow velocity and the characteristic length L, that is $\left[\frac{\mathrm{du}}{\mathrm{dn}}\right]=\frac{\left[\mathrm{\&upsi;}\right]}{\left[L\right]}$ So the dimension of the viscous force is

$<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; ]</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; ]</span>$

The ratio of the inertial and viscous forces is

$<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; ]</span>}$

The dimension of the above formula is the same as that of the Reynolds number. The characteristic length L in the formula is expressed by the diameter d in the pipe flow, and the hydraulic radius R in the open channel.

From the above analysis, it can be seen that the Reynolds number can represent the ratio of inertial force to viscous force.

Claims (1)

1, a kind of self-loopa reynolds test instrument that shows liquid with automatic colour killing, it is characterized in that it has self-circulating water feeder (1), in self-circulating water feeder, be provided with water pump, water pump is controlled by controllable silicon stepless speed adjusting gear (3), constant pressure water tank (4) joins with experimental channel (8) successively, experimental channel (8) afterbody is provided with flow control valve (9), self-loopa water recovery apparatus (2) is divided in the experimental channel outlet, constant pressure water tank (4) is connected with downcomer by upper hose with self-circulating water feeder (1), be provided with overflow plate (7) in the constant pressure water tank (4), water-stabilizing board (6), water-stabilizing board (6) side direction has steady water hole, overflow plate (7) and water-stabilizing board (6) will be divided into overflow area (10) in the constant pressure water tank, areas of permanent pressure (11) and steady pool (12), constant pressure water tank (4) top is provided with dress colour killing demonstration liquid container (5) automatically, demonstration liquid container (5) is divided into the mozzle that has water conservancy diversion syringe needle (13), mozzle end syringe needle is aimed at experimental channel (8) inlet center, be equipped with in the said demonstration liquid container (5) and be with automatic colour killing to show liquid, its composition is a phenolphthalein: NaOH=1: 2～3 proportionings, concentration sodium hydroxide are 1/1000～1/2000.

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