CN1804943A - Self-circulation electrical momentum law experimental instrument - Google Patents

Abstract

The invention discloses an auto-cycle electric surveying momentum rule laboratory apparatus. It comprises an auto-cycle water provider, a water pump inside the auto-cycle water provider, wherein the auto-cycle water provider is connected with the low port of the constant voltage water tank by up water pipe and low water pipe; it arranges an unsteady water overflow plate, a water stable plate and a working plate in the constant voltage water tank; it opens a water stable hole on the flank of the water stable plate; it arranges a flow exit pipe jet on the working plate; it divides the overflow area, the water stable area, the constant voltage area and the water returning area in the constant voltage water tank; it fixes the impact plane on the flank of the constant voltage water tank; the impact plane is connected with the relay sensor and the electric measurer.

Description

Self-circulation electrical momentum law experimental instrument

Technical field

The present invention relates to the experimental measurement instrument, relate in particular to a kind of self-circulation electrical momentum law experimental instrument.

Background technology

Momentum law is one of fluid mechanics, hydraulic basic theories, and its equation of momentum is the momentum law mathematic(al) representation in fluid mechanics, hydraulics in the theoretical mechanics.It has reflected the momentum change of fluid motion and the relation between the acting force, its characteristics are to know the flow process of flow range inside, and only need know that its borderline mobility status gets final product, thereby it can be used to the convenient interaction force problem between the fluid and boundary surface in the rapidly avried flow that solves.Therefore, the experiment of momentum law is an indispensable content in the teaching link.

Because the distribution of flow rate of fluid u on flow section generally is difficult to determine, for the purpose of simplifying research, in engineering reality, replace u to calculate total amount of flow with mean velocity in section υ usually, but the momentum and the actual momentum that calculate by υ have difference, and the error that is caused is revised with momentum correction factor β.The momentum correction factor is the ratio of the actual momentum by end face and the momentum that passes through with corresponding mean velocity in section in the unit interval in the representation unit time.

At present, the mode of similar experimental apparatus measurement momentum force both domestic and external all is to adopt the method for mechanical dynamometry.Yet traditional momentum testing equipment exists certain drawback: one, for a constant voltage water level is arranged, a relatively large water system and overflow system must be arranged, and floor area is big; Its two, by manual counterweight or mechanical equilibrium, equilibration time is long, difficult stablizing; Its three, mechanical dynamometry, mechanical-force-transmission is inter-agency to exist friction inevitably, or other external force influences, influences experimental precision, most experimental facilitiess can not be verified momentum law quantitatively, more can't measure the momentum correction factor of jet; Its four, experimental implementation is loaded down with trivial details, time-consuming, and require acting head height (more than 5～10 meters), water requirement is big, energy consumption is high.So domestic have many universities and colleges to have no alternative but cancel this important experiment of momentum law.

Summary of the invention

The purpose of this invention is to provide a kind of self-circulation electrical momentum law experimental instrument.

It has self-circulating water feeder, in self-circulating water feeder, be provided with water pump, self-circulating water feeder is connected with downcomer by upper hose with the constant pressure water tank end opening, constant pressure water tank and water return pipeline join, the self-loopa water recovery apparatus is divided in the outlet of water return pipeline afterbody, the constant pressure water tank sidewall has pressure stable hole, be provided with the varying head overflow plate in the constant pressure water tank, water-stabilizing board and working plate, water-stabilizing board's side direction has steady water hole, set out the stream ozzle on the working plate, overflow plate, water-stabilizing board and working plate will be divided into overflow area in the constant pressure water tank, steady pool, areas of permanent pressure and backwater zone, on the corresponding side constant pressure water tank of outflow tube mouth sidewall, load and impact flat board, impact flat board and connect force transducer successively, electric pilot.Impact flat board and have guide plate, be subjected to dash dull and stereotyped, at guide plate, be subjected to be provided with diversion trench towards between the flat board.

Advantage of the present invention:

1) change the huge practice of structure in the past, its whole experimental system is dwindled simplification, easy and simple to handle directly perceived, and be suitable for the modern teaching requirement, also saved the experimental arrangement place simultaneously;

2) adopted independent self-loopa constant pressure water supply system, recycling experiment water body economizes on resources;

3) initiative utilization force transducer is surveyed momentum force, and is accurately directly perceived;

4) set out stream directional stream-guidance device specially, eliminate the external force influence, data are more accurate reliable.

Description of drawings

Fig. 1 is the self-circulation electrical momentum law experimental instrument structural representation;

Fig. 2 (a) is the utility model water conservancy diversion slab construction side view;

Fig. 2 (b) is the utility model water conservancy diversion slab construction front elevation;

Fig. 3 (a) is the velocity flow profile front elevation in the utility model trumpet type inlet nipple (l=3d) exit;

Fig. 3 (b) is the midship section velocity flow profile side view in the utility model trumpet type inlet nipple (l=3d) exit.

Embodiment

Self-circulation electrical momentum law experimental instrument has self-circulating water feeder 1, in self-circulating water feeder 1, be provided with water pump, self-circulating water feeder 1 is connected with downcomer by upper hose with constant pressure water tank 3 end openings, constant pressure water tank 3 joins with water return pipeline 19, self-loopa water recovery apparatus 11 is divided in the outlet of water return pipeline 19 afterbodys, constant pressure water tank 3 sidewalls have pressure stable hole 2, be provided with varying head overflow plate 4 in the constant pressure water tank 3, water-stabilizing board 5 and working plate 6, water-stabilizing board's 5 side direction have steady water hole, set out stream ozzle 7 on the working plate 6, overflow plate 4, water-stabilizing board 5 and working plate 6 will be divided into overflow area 15 in the constant pressure water tank, steady pool 16, areas of permanent pressure 17 and backwater zone 18, on outflow tube mouth 7 corresponding side constant pressure water tank 3 sidewalls, load and impact flat board 8, impact dull and stereotyped 8 and connect force transducer 9 successively, electric pilot 10.Described impact dull and stereotyped 8 has guide plate 12, it is dull and stereotyped 14 to be subjected to dash, and is provided with diversion trench 13 at guide plate 12, between being subjected to dash dull and stereotyped 14.

The course of work of the present invention is: start water pump in the self-circulating water feeder, self-circulating water feeder supplies water in constant pressure water tank, treat that water level is constant in the constant pressure water tank, evenly penetrate water column in the outflow tube mouth, impact dull and stereotyped, its impulsive force can be responded to by force transducer, is delivered to electric pilot, is shown by the direct numerical value of electric pilot.

Experimental provision of the present invention, its principle of work is based on the momentum law of constant total stream, and its equation is:

$\stackrel{\→}{F}=\mathrm{\ρQ}({\mathrm{\β}}_2{\stackrel{\→}{\mathrm{\υ}}}_2-{\mathrm{\β}}_1{\stackrel{\→}{\mathrm{\υ}}}_1)$

(1)

If the flow path direction that comes of definition current is the x direction, then the momentum law equation of x direction is:

F _x＝ρQ(β ₂υ _2x-β ₁υ _1x)(2)

Because current after impacting flat board, penetrate along diversion trench (being 90 ° of angles with coming flow path direction), so υ _1x=υ ₁, υ _2x=υ ₂Cos90 °=0, then the momentum law equation of x direction can turn to:

F _x＝ρQ(0-β ₁υ ₁)＝-ρQβ ₁υ ₁(3)

More than in 3 formulas:

---the momentum force vector; The density of ρ---fluid; The flow of Q---fluid;

β ₁, β ₂---be respectively the momentum modifying factor that flows into and flow out the fluid that impacts flat board;

---be respectively to flow into and flow out the average velocity that impacts dull and stereotyped fluid and vow.

This experiment momentum force directly reads through the electric pilot reading after can treating that head is stablized in the constant pressure water tank; If record flow Q, outflow tube mouth caliber in the water return pipeline, read momentum force numerical value under the corresponding state again, can calculate the momentum correction factor that this goes out the flowing water body.

Experiment content

(1) the momentum force F of measurement current _x

Start water pump in the self-circulating water feeder, self-circulating water feeder supplies water in constant pressure water tank, after treating that the interior water level of constant pressure water tank is constant, penetrate the uniform flow in the outflow tube mouth, directly impact dull and stereotyped, its impulsive force can be responded to by force transducer, is delivered to electric pilot, and the electric pilot gauge outfit shows that numerical value is the momentum force F of current _x

(2) set out conductance to device, elimination vertically goes out flow component makes υ _2x=0.The equation of momentum

F _x＝ρQ(β ₂υ _2x-β ₁υ _1x)

In υ _2x, pass to experimental apparatus, owing to do not have guide piece, υ _2xOften not exclusively be zero, this experimental provision adopts the impact flat board of a tape guide plate, diversion trench and the incidence rate vector of jet

Perpendicular, behind the jet impulse flat board,, impact flat board along leaving perpendicular to the x direction of principal axis by the diversion trench on the flat board, therefore reached strict control rate vector With the inlet velocity vector At an angle of 90, make υ in the momentum law _2x=0.

The equation of momentum can be reduced to:

F _x＝ρQ(β ₂υ _2x-β ₁υ _1x)＝ρQ(0-β ₁υ _1x)

(3) the momentum correction factor β of mensuration current.

This experimental provision through above-mentioned experiment content (1), records the momentum force F of these current _x, record the caliber d of flow Q in the corresponding state lower water-back pipeline and outflow tube mouth simultaneously, can calculate flow velocity υ thus _1x, utilization equation of momentum F _x=ρ Q (β ₂υ _2x-β ₁υ _1x) can calculate the momentum correction factor β that this goes out the flowing water body.

(4) checking υ _2x≠ 0 couple of F _xInfluence.

With certain experiment is example, and this experimental provision through above-mentioned experiment content (1), records the momentum force F of these current _xValue is 51.5 grams (i.e. 0.505 newton), change dull and stereotyped, make water impact arrive flat board after, present and reflux and angle α＞90 that have of x direction ° (are υ _2x≠ 0) hydraulic phenomenon.Adjust the position, make the retroeflection angle unanimity of reflective water flow.Record 135 ° of reflection angle alpha ≈, force transducer records momentum force F _x' be worth be 76.0 the gram (i.e. 0.746 newton).Show υ _2xIf non-vanishing, very big to the momentum force influence.Because υ _2xNon-vanishing, then the equation of momentum becomes

F _x＝ρQ(β ₂υ _2x-β ₁υ _1x)

＝-ρQ[β ₁υ _1x+β ₂υ ₂cos(180°-α)]

F in other words _x' with υ ₂And α increases progressively.

Achievement is analyzed

(1) measures the precision of this experimental provision.

According to the equation of momentum $\stackrel{\→}{F}=\mathrm{\ρQ}({\mathrm{\β}}_2{\stackrel{\→}{\mathrm{\υ}}}_2-{\mathrm{\β}}_1{\stackrel{\→}{\mathrm{\υ}}}_1),$ The momentum law equation of x direction can be reduced to:

F _x＝ρQ(0-β ₁υ ₁)＝-ρQβ ₁υ ₁

So recording momentum modifying factor β precision is subjected to F _x, Q, υ ₁The precision influence of three factors, momentum force F _xPrecision is relevant with the precision of force transducer, Q, υ ₁Precision is relevant with flow of water constant.At above-mentioned three factors, in this experimental provision, corresponding mechanism there is specialized designs.For measuring F _xThe force transducer of value, the present domestic technique of this kind equipment are ripe, in this device, selecting sensibility reciprocal for use is the weight force transducer of 0.5 gram, and through certain experiment test, the actual measurement impulsive force is 51.5 grams (i.e. 0.505 newton), and be stabilized in 51.5 grams (i.e. 0.505 newton), so its deviation ratio: $\mathrm{\&epsiv;}=\&PlusMinus;\frac{0.5}{51.5\&times;2}\&times;100\%=\&PlusMinus;0.485\%<\&PlusMinus;0.5\%.$ Aspect constant current, this device has been done the measure of multiple tracks constant voltage on constant pressure water tank: at first offer pressure stable hole at the constant pressure water tank sidewall, be communicated with atmosphere; Secondly be provided with the varying head overflow plate in constant pressure water tank, guaranteeing has constant water level in the water tank, and the unnecessary water yield is flowed back in the supply tank by water return pipeline through the overflow plate overflow; The 3rd, at constant pressure water tank the water-stabilizing board is set also.Through experiment test, certain flow is measured for four times through volumetric method, and each Measuring Time records flow and is respectively 251.3ml/s, 251.9ml/s, 251.7ml/s, 251.4ml/s all more than 20 seconds, and average discharge is 251.6ml/s, so its maximum deviation rate: $\mathrm{\&epsiv;}=\&PlusMinus;\frac{(251.9-251.3)}{251.6\&times;2}\&times;100\%=\&PlusMinus;0.119\%<\&PlusMinus;0.5\%.$ So the precision of this experimental provision can reach more than 1%.Therefore, the present invention makes the momentum teaching experimental realize for the first time having measured momentum force F accurately with the method for electrical measurement _x, even momentum modifying factor β value.

(2) impact the effect that guide plate and diversion trench are set on the flat board.

On the momentum experimental facilities in the past, impacting flat board is exactly a simple flat board, current after impacting flat board, along dull and stereotyped, perpendicular to coming flow path direction, to around go out to flow.This impact mode, the water impact flat board, seem flat board and only be subjected to an external force effect, actually this is not so, current are after impacting flat board, form a water layer that is overlying on planar surface, because elastic reaction, water layer has an initial velocity opposite with former water (flow) direction, but influenced by the water viscous force, still be attached to planar surface, to flat board form one with hydraulic impact direction opposing pulling force, therefore, the momentum force that measures by force transducer, be making a concerted effort of two power in fact, and this is often much smaller than real momentum force with joint efforts.For example, we have done once experiment, and when the momentum force of water was 46.5 grams (i.e. 0.456 newton), by this kind flat board, the power that force transducer is sensed had only 41.0 grams (i.e. 0.402 newton).This also is that many in the past momentum experimental facilitiess can't accurately be measured one of reason of momentum force, and momentum modifying factor value just more has no way of measuring.Be different from impact flat board in the past, in this momentum invention experimental provision, impact dull and stereotyped special invention and be provided with guide plate and diversion trench, current are after impacting flat board, perpendicular to coming flow path direction, along the diversion trench between flat board and guide plate form full-section pipe-flow to around go out to flow.Current after the impact are to the pulling force of flat board, by guide plate these current are produced a counterforce counteraction, thereby make this external force of pulling force become an internal force that impacts on the flat board, not influence power sensor determination, the numerical value that force transducer measures, promptly real momentum force numerical value.This also is an important content of this experimental provision of invention.

(3) plan is drilled in the momentum modifying factor theoretical value analysis of vertical water outflowing jet.

Learn by experimental data and conduit entrance segment boundary layer theory of development, the velocity flow profile in trumpet type inlet nipple (l=3d) exit, as shown in Figure 3:

Have according to the definition of momentum modifying factor:

${\mathrm{\&beta;}}_0=\frac{{\&Integral;}_A{u}^2\mathrm{dA}}{{\mathrm{\&upsi;}}^{2}A}$

(4)

Wherein: υ=Q/A;

$u_{\max }=\sqrt{2g{H}_0}$ (H ₀Be the ozzle acting head).Be integration (4) formula, make J=Δ r/RJ that value is calculated as follows:

Q＝Q ₁+Q ₂＝μπR ²u _max(5)

And

(6)

$Q_2={\&Integral;}_{A_2}{u}_{2}d{A}_2={\&Integral;}_{r1}^R\frac{u_1}{\mathrm{\&Delta;r}}(R-r)2\mathrm{\&pi;rdr}$

(7)

Simultaneous (5), (6), (7) formula and abbreviation can get

Solve:

(8)

Again because of:

${\mathrm{\&beta;}}_0=\frac{{\&Integral;}_{A_1}{u_1}^{2}d{A}_1+{\&Integral;}_{A_2}{u_2}^{2}d{A}_2}{{\mathrm{\&upsi;}}^{2}A}$

${\&Integral;}_{A_2}{u_2}^{2}d{A}_2={\&Integral;}_{R-\mathrm{\&Delta;r}}^R{\left[\frac{u_1}{\mathrm{\&Delta;r}}(R-r)\right]}^{2}2\mathrm{\&pi;rdr}$

So:

According to the Pitot tube experimental result, main flow area has =0.993～0.996.

According to aperture ozzle experimental result, the trumpet type inlet nipple there is μ=0.93～0.95.Can get at last:

J＝0.04673～0.06543

β ₀＝1.031～1.047

Therefore, empirical value β ₀The=1.02～1.05th, believable.

Claims (2)

1, a kind of self-circulation electrical momentum law experimental instrument, it is characterized in that it has self-circulating water feeder (1), in self-circulating water feeder (1), be provided with water pump, self-circulating water feeder (1) is connected with downcomer by upper hose with constant pressure water tank (3) end opening, constant pressure water tank (3) joins with water return pipeline (19), self-loopa water recovery apparatus (11) is divided in the outlet of water return pipeline (19) afterbody, constant pressure water tank (3) sidewall has pressure stable hole (2), be provided with varying head overflow plate (4) in the constant pressure water tank (3), water-stabilizing board (5) and working plate (6), water-stabilizing board (5) side direction has steady water hole, set out stream ozzle (7) on the working plate (6), overflow plate (4), water-stabilizing board (5) and working plate (6) will be divided into overflow area (15) in the constant pressure water tank, steady pool (16), areas of permanent pressure (17) and backwater zone (18), on the corresponding side constant pressure water tank of outflow tube mouth (7) (3) sidewall, load and impact dull and stereotyped (8), impact dull and stereotyped (8) and connect force transducer (9) successively, electric pilot (10).

2, a kind of self-circulation electrical momentum law experimental instrument according to claim 1, it is characterized in that, described impact dull and stereotyped (8) has guide plate (12), is subjected to dash dull and stereotyped (14), at guide plate (12), be subjected to dash between dull and stereotyped (14) and be provided with diversion trench (13).

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