CN1587948A - Self circulation pump specific curve test instrument - Google Patents

Abstract

A self-loop desk-top pump characteristic curve is disclosed, comprising feed water tank, inlet valve on inlet pipe and combined pressure and vacuum gauge, with one end of inlet pipe linking to inlet of experimental pump which is linked to motor, pressure gage installed on outlet of experimental pump where links a stabilization water pressure tank whose outlet with water pipe linking to feed water tank, flow regulating valve and flowmeter with manometer on it installed on water pipe. The invention has simplified large structure; phenomenon of rupture working condition is shown clearly by using inlet valve to control the pressure of water flowing into water pipe; using separate self-loop water supply constant water supply system system and only 220V voltage, it is suitable for modern teaching require and has saved special spot for experiment.

Description

Self circulation pump specific curve test instrument

Technical field

The present invention relates to the experimental measurement instrument, relate in particular to a kind of self-circulation table-type pump characteristic curve experiment instrument.

Background technology

Corresponding a certain rated speed n, the actual lift H of pump, shaft power N, the relation between the water flow Q of total efficiency η and pump is called pump curve with curve representation, and it can reflect the serviceability of pump, can be used as the foundation of selecting pump.

The pump characteristic curve experiment is one of important content of courses of mechanical fluid mechanics, yet traditional pump characteristic curve experiment instrument exists certain drawback: one, and equipment is huge, often needs to build special pond and three-phase electrical source of power; Its two, the huge equipment operation maintenance complexity of bringing thus of equipment, operating cost is also higher; Its three, import regulating water level difficulty, fracture operating mode phenomenon is not obvious.

Summary of the invention

The purpose of this invention is to provide a kind of self-circulating pump characteristic test instrument.It has supply tank, is provided with transparent water inlet pipe at supply tank, water inlet pipe is provided with water intaking valve and pressure vacuum meter, the water inlet pipe other end and experimental pump import are joined, experimental pump and motor join, motor and power meter join, tachometer gage is used to measure motor speed, the experimental pump exit is provided with tensimeter, the experimental pump outlet is joined with steady water pressure jar, steady water pressure jar outlet is provided with aqueduct, the aqueduct other end and supply tank join, and aqueduct is provided with flow control valve, the saturating favourable flow counter of literary composition, and the saturating favourable flow counter of literary composition is provided with measuring cell.

Advantage of the present invention:

1) changes the huge practice of structure in the past, its whole experimental system is dwindled being simplified on the experiment table top, and realize independent self-loopa constant pressure water supply system, need not build in the dedicated experiments place;

2) adopt 220V two-phase civil power, power is little, economize on resources, and easy and simple to handle directly perceived, be suitable for modern teaching and want;

3) adopt the water inlet pressure regulation, be implemented in the water inlet pressure control under the constant head, until the cavitation cavitation obviously occurring, fracture operating mode phenomenon is obvious.

Description of drawings

Accompanying drawing is a self-circulating pump characteristic test instrument structural representation.

Embodiment

It has supply tank 1 self-circulation table-type pump characteristic curve experiment instrument, be provided with transparent water inlet pipe 2 at supply tank 1, water inlet pipe 2 is provided with water intaking valve 3 and pressure vacuum meter 12, water inlet pipe 2 other ends and experimental pump 4 imports are joined, experimental pump 4 joins with motor 6, motor 6 joins with power meter 8, tachometer gage 7 is used to measure motor 6 rotating speeds, experimental pump 4 exits are provided with tensimeter 11, experimental pump 4 outlets are joined with steady water pressure jar 5, steady water pressure jar 5 outlets are provided with aqueduct 9, aqueduct 9 other ends and supply tank 1 join, and aqueduct 9 is provided with flow control valve 10, the saturating favourable flow counter 13 of literary composition, the saturating favourable flow counter 13 of literary composition is provided with measuring cell 14.The course of work of the present invention is: the energising starter motor, drive the experimental pump running, and water body is drawn in the water pump in the supply tank, imports in the stabilivolt, again in aqueduct is got back to supply tank behind the pressure-raising.Motor speed has special tachometer gage to record, and power of motor is recorded by power meter, the saturating favourable flow counter of literary composition is set in the aqueduct can records experimental pump water delivery flow.The a plurality of operating modes of conversion record pump curve.

Experiment of the present invention, pump curve can be represented with following three funtcional relationships

H＝f ₁(Q)；N＝f ₂(Q)；η＝f ₃(Q)

These funtcional relationships all can be recorded by experiment, and its assay method is as follows:

1) flow Q (10 ^-6m ³/ s)

Measure, and determine the Q value with Venturi meter 12, electric pilot 16 according to following formula

Q＝A(Δh) ^B?????????????????????(1)

In the formula: A, B---the coefficient that draws through demarcation in advance provides with instrument;

The piezometric head of Δ h---Venturi meter is poor, is read by pressure reduction electric pilot 16

(cm of unit water column);

Q---flow (10 ^-6m ³/ s)

2) actual lift H (m water column)

The actual lift of pump means that total head is poor between exit of pump section and the admission section, is recording pump import and export pressure, after flow velocity and the pressure gauge epi-position difference, tries to achieve as calculated.Because the interior each point flow velocity of this device is less, kinetic head can be ignored and not remember, so have:

H＝102(h _d-h _s)????????????????(2)

In the formula: H---lift (m water column);

h _d---exit of pump pressure (MPa);

h _s---water pump import pressure (MPa), vacuum values is represented with "-".

3) shaft power (power input of pump) N (W)

N=P ₀η (3)

P ₀＝K·P????????????????????(4)

In the formula: K---power meter gauge outfit value converts the conversion coefficient of real power wattage to;

P---power meter reading value (W);

η ---motor efficiency;

A, b, c, d---electric efficiency fitting formula coefficient, demarcating in advance provides.

4) total efficiency η

$\mathrm{\η}=\frac{\mathrm{\ρgHQ}}{N}\×100\%--\left(6\right)$

In the formula: ρ---the unit weight 1000kg/m of water ³

G---acceleration of gravity (g=9.8m/s ²).

5) experimental result is by the conversion of rated speed

If pump experiment rotation speed n and rated speed n _SpDifference, and rotating speed satisfies | (n-n _Sp)/n _Sp* 100%|＜20% then should be with experimental result by following various the conversion;

$Q_0=Q\left(\frac{n_{\mathrm{sp}}}{n}\right)--\left(7\right)$

$H_0=H{\left(\frac{n_{\mathrm{sp}}}{n}\right)}^2--\left(8\right)$

$N_0=N{\left(\frac{n_{\mathrm{sp}}}{n}\right)}^3--\left(9\right)$

η ₀＝η?????????????????????????????(10)

Each parameter of subscripting in the formula " 0 " all refers to the value under the rated speed.

Analysis of experiments and discussion

1) for this test unit, the actual lift (total (pumping) head) of pump is the import and export pressure difference.

Actual lift H is meant the energy that unit weight liquid is increased from the pump inlet to the pump discharge, just weight is the energy total increment that the liquid of 1 N (newton) is obtained after by pump, and stipulates that its unit represents with meter water column.The H computing formula is:

$H=\frac{P_d-P_s}{\mathrm{\&rho;g}}+\frac{{\mathrm{\&upsi;}}_d^2-{\mathrm{\&upsi;}}_{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="A20041006716900081.png"\; state="\{\{state\}\}">s</figure-callout>}}^2}{2g}+(Z_d-Z_s)$

In the formula: P _d, P _s---the relative pressure of pump discharge and import liquid;

V _d, V _s---the flow velocity of pump discharge and inflow point's liquid; Because of its numerical value less, at this dress

Can ignore in putting and not remember;

Z _d, Z _s---detect the elevation of the optional reference field of pressure gauge system of import and exit pressure.By international standard, the pressure gauge tabular value is a pressure unit with " Pa " (handkerchief), the h in the formula (2) _d, h _sRepresent this experiment value of reading (MPa) respectively, be converted into meter water column when being unit, promptly have with pressure gauge:

1MPa＝102mH ₂O

Because this experiment epi-position difference is zero, and v _d=v _sSo, (2) formula, that is:

H＝102(h _d-h _s)??(mH ₂O)

Stipulate according to experimental standard, the import and export section of calculating pump lift should refer to pump discharge flange and pump intake flange place, stipulate again simultaneously, the position of actual pressure tap should be on (D is pump inlet, outlet diameter) beyond the pump flange 2D smooth-going section, thus by (2) formula calculate the H value should add that measuring point is to the loss of flood peak H between the pump flange _fBut if H _j＜0.002H (B class precision) or H _fDuring＜0.005H (C class precision), then can revise.To this experimental system, the flow process sum 1 that measuring point is imported and exported flange to pump is about 40cm, is example as if the operating point with H=13m, and v is arranged ²/ 2g=0.063m gets resistance coefficient λ=0.02, then by formula

$H_f=\mathrm{\&lambda;}\frac{1}{d}\frac{{\mathrm{\&upsi;}}^2}{2g}$

Can get H _f=0.025m＜0.002H gets final product so this experimental system H calculates by (2) formula.

2) reach 7～8mH when pump entrance place vacuum tightness ₂During the O left and right sides, pump performance obviously worsens, and reason is analyzed in examination.

In this case, minimum pressure in the pump impeller near or reached the water saturation steam pressure, promptly water pump begins to occur the gasification cavitation, when the steam void space that cavitation causes big and when hindering overcurrent, promptly can influence the external characteristics of pump and " fracture operating mode " occur, performance is worsened rapidly.From this experiment h _sThe measuring point situation of=-7.8m sees that the equal deviation characteristic curve of its trial value is more, and the work efficiency of pump obviously descends, show under this operating mode, " fracture operating mode " appearred in test pump, and cavitation phenomenon is very serious, can be observed cavitation phenomenon in the transparent suction hose of this instrument.

3) know that by experiment the water flow of pump is big more, the vacuum tightness of pump inlet place is also big more.

Reason has two.The one, kinetic head has increased, and pressure energy reduces; The 2nd, because kinetic head increases, water pump suction pipe inflow point also increases to the loss of flood peak between the water pump inflow point thereupon, and pressure energy promptly reduces thereupon.Thereby the water flow of pump is big more, and then the vacuum tightness of pump inlet place is also big more.

Can 4) this experimental pump installation elevation be higher than suction well water surface 8m? why?

If the vertical height Z of water pump suction pipe _sReach 7～8m, so its actual suction journey h _sFor:

$H_s=Z_s+H_w+\frac{{\mathrm{\&upsi;}}^2}{2g}$

H in the following formula _wBe the loss of flood peak of suction hose, υ ²/ 2g is the kinetic head of suction hose.Obviously, h _sGreater than 7～8m water column.And see this water pump h according to test findings _sWhen reaching 7～8m, cavitation phenomenon takes place obviously, water pump moves under abnomal condition, and this state is operation down, and not only efficient is very low, and noise and vibration is all very big, and long playing result certainly will will cause the cavitation erosion at position such as impeller.Therefore the installation elevation of this test pump, at most can only 6m about.

Claims (1)

1, a kind of self-circulation table-type pump characteristic curve experiment instrument, it is characterized in that it has supply tank (1), be provided with transparent water inlet pipe (2) at supply tank (1), water inlet pipe (2) is provided with water intaking valve (3) and pressure vacuum meter (12), water inlet pipe (2) other end and experimental pump (4) import are joined, experimental pump (4) joins with motor (6), motor (6) joins with power meter (8), tachometer gage (7) is used to measure motor (6) rotating speed, experimental pump (4) exit is provided with tensimeter (11), experimental pump (4) outlet is joined with steady water pressure jar (5), steady water pressure jar (5) outlet is provided with aqueduct (9), aqueduct (9) other end and supply tank (1) join, aqueduct (9) is provided with flow control valve (10), the saturating favourable flow counter (13) of literary composition, the saturating favourable flow counter (13) of literary composition is provided with measuring cell (14).

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