WO1994023203A1

WO1994023203A1 - Bypass flowmeter for measuring hydraulic characteristics of pumping installations

Info

Publication number: WO1994023203A1
Application number: PCT/GR1994/000006
Authority: WO
Inventors: Athanassios Nassikas
Original assignee: Athanassios Nassikas
Priority date: 1993-04-07
Filing date: 1994-04-06
Publication date: 1994-10-13
Also published as: AU6385194A

Abstract

The present invention concerns a system of measuring the hydraulic characteristics of pumping installations with a BY PASS system and with the main interest in the pumping station of ground water wells. The flow measurement with a BY PASS system is known from the existing technology. The present invention gives us the ability to measure accurately the flow through a multihole pipe, the total manometric, the pumping level, the pressure at the exit of the pump and the efficiency of the pump by the use of only one BY PASS system with three valves. The method and the mechanism of the present invention are highly reliable in the case of using a BY PASS system based on a magnetic flowmeter. The present invention is applicable to the management of a pump station so that information may be obtained about the study of hydraulic characteristics of the region where the pump will be installed, and about the measurement of the efficiency of the pumping installation. This information can help in the direction of taking all the necessary steps to save energy consumed by a pump station and more specificaly by a pump station of deep ground water wells. Such steps to save energy would involve effecting - by the aid of a computer and a frequency converter or a gear box - the pump's rpm, controlling the pump's performance and testing the pump manufacturer's credibility.

Description

BYPASS FLOWMETER FOR MEASURING HYDRAULIC CHARACTERISTICS OF

PUMPING INSTALLATIONS

DESCRIPTION

The existing technique

In the market the BY PASS flowmeters based on the principle of the ratio of the BY PASS flow to the main flow are already available. The flow through the BY PASS is achieved because of the pressure drop at the edges of the BY PASS through an orifice or through a Venturi system. To date in every case of flow measuring a mechanism intervenes in the pipe where the measurement takes place. With the present invention, already operating mechanisms can be used but with the addition of all those elements necessary for the measurement of the total manometric of the pump, the pumping level, the exit pressure, and the efficiency of the pump.ln addition to these a flow measurement mechanism is proposed based on a more accurate BY PASS technique, by introducing a multihole pipe in the pipe of the flow.

Design description

The present invention can be made understood by the aid of the description and of the drawing of fig. 1 and refers to an application example relating to a pumping station of ground water wells. All the elements in the following text relate to figure 1. The pipe 8 bottom closed, with two or more holes 9 is perpendicular to direction of the flow in the pipe 7 of a pumping station of ground water wells which includes the head 5 the multi stage pump 3, the pipe 4 the electrical motor 6 the electrical table 20 and the energy meter 21.The pipe 8 is connected with the pipe 7 and with the magnetic, flow meter 10, according to a proposed application, which indicates the signal of the passing flow on the table, or the embedded control and monitor system 11. The flowmeter 10 is connected with the pipe 22, which is connected with the pipes 23 & 24 and with the valve 14. The valve 14 is connected with the pipe 15 closed at the edge with a small hole 16 (order of 2mm). The pipe 23 is connected with the valve 12, and with the pipe 7 at the point 25. The pipe 24 is connected with the valve 13 which is connected with the pipe 17 which is placed between the pipe 4 and the casing 26 of the bore hole. The edge of the pipe 17 is closed with an edging pipe 18 which has a small hole 19 of the order of 1 to 2 mm. The element 18 is placed above the pump 3 as well as under the hydrostatic water level 1 and the dynamic water level 2 of the bore hole.

Operation

A. When valves 13 and 14 are closed and the valve 11 open, the passing flow through pipe 8 and the flowmeter 10 is such that :

^PTOT9 - ^P25 = ^P9 + P/2 9²-^P25 = P/^{2 V}9² ~Q²~Q² BYPASS (Q) where Pg=P₂₅ the pressure in the pipe 7 at the points 9, V₉ the approximate mean value of velocity, because of the holes 9, of the flow profile at the same crossection, Q the flow of the pumping station and Q_Bγp_Ass _(Q) the flow through the BYPASS when measuring the flow.ln this way by Q_BYp_{ASS Q\} is measured the flow ^Q of the pumping station given that Q~QBYPASS _(Q)

B. When valves 12,13 are closed and 14 open the flow enters holes 9 and exits from hole 16. The following relation is valid:

P₉ + p/2 V_g ² = P_at + p/2 V₁₆ ² + ΣΔP_f

where P_at is the atmospheric pressure and ΣΔP_f any kind of losses. The quantities p/2 V₉ ², ΣΔP_f are of small order of magnitude compared with the quantities P₉,P_at, p/2 V₁₆ ². Thus it is valid : P₉ - P_at = p/2 V₁₆ ² ~ Q² _{BYPASS (P)}. On calibration P₉-P_at is measured through the same BYPASS already measuring the flow. According to the above mentioned it is valid : ^P9 ^{" P}at - ^K1 ^Q BYPASS (P)

where QBYPASS ₍P₎ '^{s tne} *'^ow passing through the BYPASS when measuring the relative pressure P=P₉-P_at> and K., a coefficient derived from the comparison of the measurements made with this invention with the direct measurements of the pressure with a manometer of high precision. In this way we can measure the pressure P= P_g -P_at by measuring the BYPASS flow. The hole 16 is so small, of the order of 2 mm, that the dynamic head V₁₆ ²/2g is of a much larger order compared with V_g ²/2g and (1/pg) ΣΔP_f. The fluid during the pressure measurement P=P₉-P_at can either be discharged to the atmosphere or be returned to the head 5 and dropped into the well through the clearance of the pipes 4 and 26.

C. When valve 12,14 are closed and 13 open the flow enters the holes

9 and moves through the elements 10,24,13,17,18,19 below the pumping level 2. Thus it is valid:

P_a + p/2 V ² + γh₉ = P_1B - γh₁ 1₉9 + p/2 V '19² + ΣΔP f∑

where y is the specific gravity of water, and the levels are measured with reference to the dynamic pumping level 2. If the hole 19 is small enough (order of 1 mm) then the quantities ∑ΔP_β*, p/2 V₉ ² are very small compared with the rest of the quantities, and because P₁₉ = γh₁₉ + P^ it is finally valid:

2 _

^P9 ⁺ Y^h9 ^{* P}at = P/2 - *2 ^Q BYPASS (H)

where Q_Bγ_PAss ₍H₎ ^{the flow} measured by the BYPASS when measuring the Pg + γh₉ -P_at. Q_Bγ_PAss ₍H₎' ^{clue t0} ^e continuity law, is proportional to V₁₉ and Kg is a coefficient derived by measuring the quantity P₉+γh_g-P_at through a precise measurement of the pressure P₉-P_at and a precise measurement of the water level. The quantity P₉+γh_g-P_at is equal to ΔP-ΣΔP_f∑A where ΣΔP_fΣA is the pressure drop, due to friction, in the pipes 4 and 7 as well as at the head 5 while the quantity ΔP is the pressure difference produced by the pump 3. ΔP expressed in meters is the total manometric pump head H. Thus it is valid:

H - (1/γ) ΣΔP_f∑A = (K2/γ) Q² _BYPASS (H)

and H = (KJJ/Y) Q² _{BYPASS (H)} + (1/γ) ∑ΔP^

The quantity (1/γ) ∑ΔP^ can be estimated on the basis of the characteristics of the pipe 4, the head 5 and the pipe 7 and is proportional to the square of the pump flow. The necessary information for the calculation of this quantity is cited in the reference books:

1. H.Shames 1962. Mechanics of Fluids. McGraw - Hill Inc. NY.

2. K.B.Akritidis 1979. Pumps Gartaganis Publ. Thessaloniki, Greece.

The quantity (Kg/γ) Q² _Bγ_PAss (H) ^{can be} concidered as a total height, and in this case it takes into account the total pumping station loss including the

As indicated above :

1. In case A with the BYPASS flowmeter 10, the flow Q of the pumping station is measured.

2. In case B with the same flowmeter the relative pressure P₉-P_at is measured.

3. In case C with the same flowmeter the total manometric pump head is measured. Thus, using the value N of power measured by 21 , the quantities of flow and the total manometric head it is valid:

ⁿτoτ = n_k x n_p = (Q.H) / (ON)

where n_τoτ the total efficiency of the pump station, Q the flow, H the total manometric head, N the consumed power, n_k the efficiency of the electric motor, n the pump efficiency and C a coefficient for the units used. According to case C it is valid: γh₉ - Q _{BYPASS (H)} - (P₉-P_at)

and according to case B

hg = (K2/Y) Q BYPASS (H) ^" (^Kl/Y) °* BYPASS (P)

Thus with the same flowmeter we can measure 1. the pump flow Q 2. the pump exit pressure P₉-P_at

3. the total manometric H

4. the total efficiency of the istallation n_τoτ

5. the pump efficiency n_p when the electric motor efficiency n_k is known

6. the dynamic water level h₉ The case of measuring by a magnetic flowmeter is of particular importance because of its precision and of its being uninfluenced by measurements even in the case in which there are particles in the flow.

Typical quantities :

1. Q 0 to 3000 m³/h

2. H 1 to 20 at (10 to 200 m)

3. h₉ 0 to 70m

4. Hole 16 order of 2mm 5. Hole 19 order of 1mm

The whole system can operate automatically when valves 12,13,14 operate at time intervals guided by a computer program.in such a way that i turn one is open when the other two closed. The corresponding results are recorded and processed by a computer fed with the hydraulic characteristics already described. The neccecity for the measurements

The measurement of the quantities described above is necessary - both for hydrological reasons (level measurements) and to save energy in the case of pumping water from ground water wells. It is known that the variation of the pumping manometric head shifts the operation point from the normal operation point and this results in a drop in the efficiency. We can understant this by measuring only the flow. Thus by means of 3 to 4 speed gear Box or by means of a frequency converter it is possible, depending on the case to increase or to decrease the rpm and thereby to achieve an optimum efficiency of the pumping operation. In addition it is possible to have high clearance or damaged -eg. due to sand- blades and that results in a drop in the efficiency. This information, obtained from the measurment of the efficiency with the present method, can lead to the repair of the blades, to the repair of the rolling bearings, to the adjustement of the clearance, or to the change the pump type. So with the present method it is possible to check the credibility of the pump manufacturers.

The change in the rpm can have as a result the optimum function of the pump and this can be achieved either through a gear box or a frequency converter as was mentioned earlier, or through an assisting pump of controlled rpm -through a gear box or a frequency converter- connected serially with the main pump.ln the case of an assisting pump the main pump has sufficient manometric to bring the water up to the ground level at the pressure of the order of 1 to 2 at, while the assisting pump has a manometer which covers the operational requirements of the whole system.

What is mentioned above, in the drawing and in the description, is a typical application of the present invention and changes in the mentioned magnitudes fall within the claims of the invention. Characteristically it is mentioned that the holes of the pipe 8 of the BY-PASS can be of a diameter analogous to the distance from the center of the pipe 7. Also, these holes can be replaced by a triangle shaped opening on pipe 8. In a conventional measurement of the pump efficiency we would require a, magnetic flowmeter and one or two -single or differential- manometers while with the present method we require only a bypass magnetic flowmeter.

Claims

1. Method of measuring the hydraulic characteristics of pumping installations using only one BY-PASS flowmeter comprising: the flow measurement by a BY-PASS flowmeter with the routes, necessary for the other measurements of the present method, closed by valves, the pressure measurement of the fluid downstream the pump pipe by the • same flowmeter with the routes, necessary for the other measurements of the present method, closed by valves, and with the said flowmeter connected with a pipe ending in a narrow passage so that the measured pressure may be proportional to the square of the flow through the mentioned flowmeter. the measurement of the total pump station manometric head with the routes, necessary for the other measurements of the present method closed by valves and with the said flow meter connected with a pipe -which goes under the pumping level- ending in a narrow passage so that the measured total manometric head may be proportional to the square of the flow through the mentioned flowmeter. - the measurement of the water dynamic level by subtracting the above mentioned measured pressure from the total manometric head, the measurement of the pump installation efficiency with the said method of measuring the flow and the total manometric head and by the aid of an electric power meter.

2. Method as in claim 1 through which the measurements processed by a computer affect, as a feed back, a frequency converter so as to change the rpm of an assisting pump connected serially with the main pump a fact which results in the approximation to the optimum operation point of the whole system.

3. Method as in claim 1 through which the measurements processed by a computer affect as a feed back a gear box so as to change the rpm of an assisting pump connected serially with the main pump a fact which results in the approximation to optimum operation point of the whole system.

4. Mechanism of measurement of the hydraulic characteristics of a pump installation based on only one BY-PASS flow meter comprising:

- a BYPASS flow meter measuring the flow, with the routes for the other measurements of the present mechanism closed by valves, the said flowmeter working as a pressure meter with the routes for the other measurements of the present mechanism closed by valves connected with a pipe ending in a narrow passage so that the measured pressure may be proportional to the square of the flow through the flowmeter. the said flowmeter working as a pump total head meter with the routes for the other measurements of the present mechanism closed by valves, connected with a pipe -which goes under the pumping level- ending in a narrow passage so that the measured total manometric head may be proportional to the square of the flow through the flowmeter a mechanism of measuring the water level working by the aid of the above mentioned meters, which measures the water level as the difference of the indications of the above mentioned meters, a mechanism of measuring the pump total efficiency working by the aid of the above mentioned meters and by the aid of an electric power meter

5. The mechanism of claim 4 when the used flowmeter is such that: 1) upstream it is connected with a pipe closed at one edge with two or more open holes perpendicular to the measured flow.inserted in and connected with the pipe, in which the flow is to be measured. 2) downstream it is connected with the pipe, in which the flow is to be measured at a point of the cross-section defined by the plane of the above mentioned holes which when more than one, result in a precise measurement of the flow as they tend to measure the mean value of velocity of the flow profile.

The mechanism of the claims 4 and 5 where the used BY PASS flowmeter is magnetic.