CN102706397A - Water-flow measuring device with large diameter and low pressure head and measuring method - Google Patents

Abstract

The invention relates to a water-flow measuring device with large diameter and low pressure head of a thermal power station and a measuring method, in particular to a water-flow measuring device with a large diameter and a low pressure head and a measuring method in an online manner. The water-flow measuring device comprises a water tower, circulation water-flow pipelines and a condenser, a bypass pipeline is arranged on the circulation water-flow pipelines in the water-flow measuring device, pressure tapping holes are arranged on portions, which are positioned in front of the bypass pipeline, of a main pipeline, and other pressure tapping holes are arranged on portions, which are positioned between bypass areas, of the main pipeline. Since an existing water-flow measuring device is modified and theoretical deduction is performed by the aid of the method, the problem that a spot circulation water flow device with the large caliber and the low indenter cannot be measured in an online manner is resolved, in addition, necessary operation parameters are provided for optimized operation of a cold-end system of a unit, the water-flow measuring device with the large diameter and the low pressure head and the measuring method have a certain practical significance in terms of energy conservation and emission reduction advocated by National Development and Reform Commission. The device and the method fill gaps home and abroad, and have considerable market application prospect and social benefit.

Description

Big caliber low head measuring water flow device and method

Technical field

The present invention relates to a kind of big caliber low head measuring water flow device and method of fuel-burning power plant, especially big caliber low head discharge on-line measurement device and method.

Background technology

Power station unit circulating water flow is because caliber is big at present, and pressure head is low, can't realize on-line measurement; Adopt the ultrasonic flow meter off-line measurement, measured condition restriction and be difficult to measure, even it is also very low to measure accuracy.Because unit does not have circulating water flow, bring certain difficulty for unit s cold end system optimization operation, be unfavorable for that unit is energy-saving and cost-reducing.

Summary of the invention

In order to solve the technical matters of above-mentioned existence, the invention provides a kind of big caliber low head measuring water flow device and method, purpose is to realize the on-line measurement work of big caliber low head discharge, and accuracy of measurement is higher.

The present invention realizes through following technical scheme:

Big caliber low head measuring water flow device, it comprises water tower, circulating water flow pipeline and condenser are to be provided with bypass duct on the pipeline of the circulating water flow in flow apparatus, are provided with pressure port on the trunk line before bypass duct; Be provided with pressure port on the trunk line in the bypass interval.

Described pressure port is provided with two.

Described pressure port is a calibrating installation.

Big caliber low head water flow measuring method is: G ₁=kG ₂

Described G ₁=kG ₂Derivation following:

Get I, II, III, IV is measured the cross section for two groups, can list following equation according to the Bernoulli equation of the constant total stream of viscous fluid:

(1): I, the II cross section:

$z_I+\frac{p_1}{\mathrm{\ρg}}+\frac{v_1^2}{2g}=z_{\mathrm{II}}+\frac{p_{\mathrm{II}}}{\mathrm{\ρg}}+\frac{v_{\mathrm{II}}^2}{2g}+h_{w1}$

(2): III, the IV cross section:

$z_{\mathrm{III}}+\frac{p_{1\mathrm{II}}}{\mathrm{\ρg}}+\frac{v_{1\mathrm{II}}^2}{2g}=z_{\mathrm{IV}}+\frac{p_{\mathrm{IV}}}{\mathrm{\ρg}}+\frac{v_{\mathrm{IV}}^2}{2g}+h_{w3}$

Wherein: z is the position ability head that fluid has;

is the piezometric tube ability head that fluid has, and ρ is a fluid density;

is the speed ability head that fluid has;

h _wBe the energy loss of fluid,

Be merely the function of Reynolds number for laminar motion λ, promptly

υ is that fluid motion viscosity is only relevant with temperature.

Because pipe level, z here _I=z _II, z _III=z _IV,The two sections distance is relatively than short and L simultaneously ₁=L ₃, can think v _I=v _II, v _III=v _IVBy above-mentioned (1), (2) step obtains:

（3）： $\frac{p_I-p_{\mathrm{II}}}{\mathrm{\ρg}}=h_{w1}$

（4）： $\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{\mathrm{\ρg}}=h_{w3}$

Formula (3)/(4) are obtained

（5）： $\frac{p_I-p_{\mathrm{II}}}{p_{\mathrm{III}}-p_{\mathrm{IV}}}=\frac{h_{w1}}{{\mathrm{<figure-callout\; id="3"\; label="h\; w"\; filenames="120508145918.png"\; state="\{\{state\}\}">h</figure-callout>}}_w}=\left(\frac{64}{{\mathrm{Re}}_1}\frac{L_1}{D}\frac{v_1^2}{2g}\right)/\left(\frac{64}{{\mathrm{Re}}_3}\frac{L_3}{D}\frac{v_3^2}{2g}\right)$

$=\frac{v_1^2}{{\mathrm{Re}}_1}\frac{{\mathrm{Re}}_3}{v_3^2}=\frac{v_1}{v_3}$

According to the flow law of conservation:

G ₁=G ₂+G ₃

That is:

$\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{1}{4}\mathrm{\&pi;}{d}^2{v}_2+\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_3$

Obtain:

（6）： $v_1={\left(\frac{d}{D}\right)}^2{v}_2+v_3$

Can get by equation (5), (6):

（7）： $v_1=\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}{\left(\frac{d}{D}\right)}^2{v}_2$

Can get circulating water flow by equation (7):

（8）： $G_1=\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="120508145918.png"\; state="\{\{state\}\}">G</figure-callout>}}_2}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}$

Order:

$\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}=k$

Then formula (8) can be written as:

G ₁＝kG ₂

Described: G ₁With G ₂Be linear relationship, the k related coefficient of two sections differential pressure that is and measures wherein in the actual engineering, if when the cross section differential pressure is very little, can be checked the numerical value of k through thermal equilibrium.

Described total stream Bernoulli equation is derived under certain condition, should satisfy following restrictive condition:

(1) flow constant, promptly $\frac{{\&PartialD;V}_x}{\&PartialD;t}=\frac{{\&PartialD;V}_y}{\&PartialD;t}=\frac{{\&PartialD;V}_x}{\&PartialD;t}=0;$

(2) mass force that acts on the fluid has only gravity, i.e. U=-gz;

(3) fluid is incompressible, ρ=const;

(4) continuous along total stream a fluid stream flow, q _v=const when having a fluid stream branch or interflow as if the longshore current bundle, answers segmentation to list Bernoulli equation with whole fluid gross energy conservations;

(5) flowing on the flow section of row Bernoulli equation must be gradual flowing, can and have the not sudden turn of events to flow before two sections.

Advantage and beneficial effect:

1, the present invention is owing to transform existing flow measurement device, and combines the inventive method to carry out theoretical derivation, and its theoretical derivation is correct, matches with testing laboratory waterpower experimental result;

2, solve on-the-spot circulating water flow and can't carry out the on-line measurement problem;

3, be unit s cold end system optimization operation, necessary running parameters is provided,, have certain practical significance the energy-saving and emission-reduction that National Development and Reform Committee advocates;

4, apparatus of the present invention can be used as product widespread production, considerable benefit.

Because circulating water pipeline is thicker, flow is bigger, does not also have a kind of flow measurement device ability on-line measurement circulating water flow so far.The present invention has then effectively solved the difficult technical matters of on-line measurements such as caliber is big, pressure head is low, and this technology has been filled up domestic and international blank, has better market application and considerable social benefit.

Description of drawings

Fig. 1 is a calculating synoptic diagram of the present invention;

Fig. 2 is a measurement mechanism synoptic diagram of the present invention.

Among the figure: water tower 1, circulating water flow 2, condenser 3, the first calibrating installations 4, the second calibrating installations 5, flow apparatus 6.

Below in conjunction with embodiment the present invention is explained further details, but protection scope of the present invention is not limit by embodiment.

Embodiment

The present invention is a kind of big caliber low head measuring water flow device, and it comprises water tower 1, and circulating water flow pipeline and condenser 3 mainly are to increase by one section bypass duct on the pipeline of the circulating water flow 2 in flow apparatus 6, measure the circulating water flow G of this bypass ₂And increase by two pressure ports on the trunk line before bypass duct as first calibrating installation, measure its differential pressure; Increase by two pressure ports on the trunk line in the bypass interval as second calibrating installation, measure its differential pressure.Differential pressure gauge according to first calibrating installation, second calibrating installation record is calculated coefficient of flow k, finally calculates circulating water flow G ₁

As shown in Figure 2, through water tower 1 cooled recirculated water,, get in the turbine condenser 3 and carry out heat exchange successively through water circulating pump, circulating water flow 2 water inlet pipes, get into water tower 1 cooling through circulating water flow 2 outlet conduits then, so move in circles.

Application process of the present invention is following:

Install branch line additional at the circulating water flow trunk line, adopt certain means measurement branches piping flow.Derive main, subtube discharge relation through Bernoulli equation in theory; Testing laboratory's waterpower experimental verification the correctness of deriving in theory; Reach measurement circulating water flow purpose through the measurement branches pipeline flow, wherein can obtain COEFFICIENT K through on-the-spot heat balance test.

Big caliber low head water flow measuring method of the present invention is through G ₁=kG ₂Obtain.

Derivation of equation process is following:

As shown in Figure 1, get I, II, III, IV is measured the cross section for two groups, can list following equation according to the Bernoulli equation of the constant total stream of viscous fluid:

(1): I, the II cross section:

$z_I+\frac{p_1}{\mathrm{\&rho;g}}+\frac{v_1^2}{2g}=z_{\mathrm{II}}+\frac{p_{\mathrm{II}}}{\mathrm{\&rho;g}}+\frac{v_{\mathrm{II}}^2}{2g}+h_{w1}$

(2): III, the IV cross section:

$z_{\mathrm{III}}+\frac{p_{1\mathrm{II}}}{\mathrm{\&rho;g}}+\frac{v_{1\mathrm{II}}^2}{2g}=z_{\mathrm{IV}}+\frac{p_{\mathrm{IV}}}{\mathrm{\&rho;g}}+\frac{{\mathrm{<figure-callout\; id="2"\; label="v\; IV"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{IV}}^{}}{2g}+{\mathrm{<figure-callout\; id="3"\; label="h\; w"\; filenames="120508145918.png"\; state="\{\{state\}\}">h</figure-callout>}}_w$

Wherein: z is the position ability head that fluid has;

is the piezometric tube ability head that fluid has, and ρ is a fluid density;

is the speed ability head that fluid has;

h _wBe the energy loss of fluid,

Be merely the function of Reynolds number for laminar motion λ, promptly

υ is that fluid motion viscosity is only relevant with temperature.

Because pipe level, z here _I=z _II, z _III=z IV, the relatively short and L of two sections distance simultaneously ₁=L ₃, can think v _I=v _II, v _III=v _IVBy above-mentioned (1), (2) step obtains:

（3）： $\frac{p_I-p_{\mathrm{II}}}{\mathrm{\&rho;g}}=h_{w1}$

（4）： $\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{\mathrm{\&rho;g}}={\mathrm{<figure-callout\; id="3"\; label="h\; w"\; filenames="120508145918.png"\; state="\{\{state\}\}">h</figure-callout>}}_w$

Formula (3)/(4) are obtained

（5）： $\frac{p_I-p_{\mathrm{II}}}{p_{\mathrm{III}}-p_{\mathrm{IV}}}=\frac{h_{w1}}{{\mathrm{<figure-callout\; id="3"\; label="h\; w"\; filenames="120508145918.png"\; state="\{\{state\}\}">h</figure-callout>}}_w}=\left(\frac{64}{{\mathrm{Re}}_1}\frac{L_1}{D}\frac{v_1^2}{2g}\right)/\left(\frac{64}{{\mathrm{Re}}_3}\frac{L_3}{\mathrm{<figure-callout\; id="3"\; label="D\; v"\; filenames="120508145918.png"\; state="\{\{state\}\}">D</figure-callout>}}\frac{v_{}^{}}{}\frac{{}_3^2}{2g}\right)$

$=\frac{v_1^2}{{\mathrm{Re}}_1}\frac{{\mathrm{Re}}_3}{{\mathrm{<figure-callout\; id="3"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_3^2}=\frac{v_1}{{\mathrm{<figure-callout\; id="3"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_3}$

According to the flow law of conservation

G ₁=G ₂+G ₃

Promptly

$\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{1}{4}\mathrm{\&pi;}{d}^2{\mathrm{<figure-callout\; id="2"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_2+\frac{1}{4}\mathrm{\&pi;}{D}^2{\mathrm{<figure-callout\; id="3"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_3$

Obtain

（6）： $v_1={\left(\frac{d}{D}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_2+{\mathrm{<figure-callout\; id="3"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_3$

Can get by equation (5), (6):

（7）： $v_1=\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}{\left(\frac{d}{D}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="v"\; filenames="120508145918.png"\; state="\{\{state\}\}">v</figure-callout>}}_2$

Can get circulating water flow by equation (7):

（8）： $G_1=\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="120508145918.png"\; state="\{\{state\}\}">G</figure-callout>}}_2}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}$

Order

$\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}=k$

Then formula (8) can be written as:

G ₁＝kG ₂

Following formula G ₁With G ₂Be linear relationship, the related coefficient of two sections differential pressure of k and measurement wherein in the actual engineering, if when the cross section differential pressure is very little, can be checked the numerical value of k through thermal equilibrium.

Total stream Bernoulli equation is derived under certain condition, should satisfy following restrictive condition:

(1) flow constant, promptly $\frac{{\&PartialD;V}_x}{\&PartialD;t}=\frac{{\&PartialD;V}_y}{\&PartialD;t}=\frac{{\&PartialD;V}_x}{\&PartialD;t}=0;$

(2) mass force that acts on the fluid has only gravity, i.e. U=-gz;

(3) fluid is incompressible, ρ=const;

(4) continuous along total stream a fluid stream flow, q _v=const when having a fluid stream branch or interflow as if the longshore current bundle, answers segmentation to list Bernoulli equation with whole fluid gross energy conservations;

(5) flowing on the flow section of row Bernoulli equation must be gradual flowing, can and have the not sudden turn of events to flow before two sections.

Claims (7)

1. big caliber low head measuring water flow device; It comprises water tower (1); Circulating water flow pipeline and condenser (3) is characterized in that: be provided with bypass duct on the pipeline of the circulating water flow (2) in flow apparatus (6), be provided with pressure port on the trunk line before bypass duct; Be provided with pressure port on the trunk line in the bypass interval.

2. big caliber low head measuring water flow device according to claim 1, it is characterized in that: described pressure port is provided with two.

3. big caliber low head measuring water flow device according to claim 1, it is characterized in that: described pressure port is a calibrating installation.

4. big caliber low head water flow measuring method is characterized in that: G ₁=kG ₂

5. big caliber low head water flow measuring method according to claim 4 is characterized in that: described G ₁=kG ₂Derivation following:

Get I, II, III, IV is measured the cross section for two groups, can list following equation according to the Bernoulli equation of the constant total stream of viscous fluid:

(1): I, the II cross section:

$z_I+\frac{p_1}{\mathrm{\&rho;g}}+\frac{v_1^2}{2g}=z_{\mathrm{II}}+\frac{p_{\mathrm{II}}}{\mathrm{\&rho;g}}+\frac{v_{\mathrm{II}}^2}{2g}+h_{w1}$

(2): III, the IV cross section:

$z_{\mathrm{III}}+\frac{p_{1\mathrm{II}}}{\mathrm{\&rho;g}}+\frac{v_{1\mathrm{II}}^2}{2g}=z_{\mathrm{IV}}+\frac{p_{\mathrm{IV}}}{\mathrm{\&rho;g}}+\frac{v_{\mathrm{IV}}^2}{2g}+h_{w3}$

Wherein: z is the position ability head that fluid has;

is the piezometric tube ability head that fluid has, and ρ is a fluid density;

is the speed ability head that fluid has;

h _wBe the energy loss of fluid,

Be merely the function of Reynolds number for laminar motion λ, promptly

υ is that fluid motion viscosity is only relevant with temperature.

Because pipe level, z here _I=z _II, z _III=z _IV, the two sections distance is relatively than short and L simultaneously ₁=L ₃, can think v _I=v _II, v _III=v _IVBy above-mentioned (1), (2) step obtains:

（3）： $\frac{p_I-p_{\mathrm{II}}}{\mathrm{\&rho;g}}=h_{w1}$

（4）： $\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{\mathrm{\&rho;g}}=h_{w3}$

Formula (3)/(4) are obtained

（5）： $\frac{p_I-p_{\mathrm{II}}}{p_{\mathrm{III}}-p_{\mathrm{IV}}}=\frac{h_{w1}}{h_{w3}}=\left(\frac{64}{{\mathrm{Re}}_1}\frac{L_1}{D}\frac{v_1^2}{2g}\right)/\left(\frac{64}{{\mathrm{Re}}_3}\frac{L_3}{D}\frac{v_3^2}{2g}\right)$

$=\frac{v_1^2}{{\mathrm{Re}}_1}\frac{{\mathrm{Re}}_3}{v_3^2}=\frac{v_1}{v_3}$

According to the flow law of conservation:

G ₁＝G ₂+G ₃

That is:

$\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{1}{4}\mathrm{\&pi;}{d}^2{v}_2+\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_3$

Obtain:

（6）： $v_1={\left(\frac{d}{D}\right)}^2{v}_2+v_3$

Can get by equation (5), (6):

（7）： $v_1=\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}{\left(\frac{d}{D}\right)}^2{v}_2$

Can get circulating water flow by equation (7):

（8）： $G_1=\frac{1}{4}\mathrm{\&pi;}{D}^2{v}_1=\frac{G_2}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}$

Order:

$\frac{1}{1-\frac{p_{\mathrm{III}}-p_{\mathrm{IV}}}{p_I-p_{\mathrm{II}}}}=k$

Then formula (8) can be written as:

G ₁＝kG ₂

6. according to claim 4 and 5 described big caliber low head water flow measuring methods, it is characterized in that: described: G ₁With G ₂Be linear relationship, the k related coefficient of two sections differential pressure that is and measures wherein in the actual engineering, if when the cross section differential pressure is very little, can be checked the numerical value of k through thermal equilibrium.

7. according to claim 4 and 5 described big caliber low head water flow measuring methods, it is characterized in that: described total stream Bernoulli equation is derived under certain condition, should satisfy following restrictive condition:

(1) flow constant, promptly $\frac{{\&PartialD;V}_x}{\&PartialD;t}=\frac{{\&PartialD;V}_y}{\&PartialD;t}=\frac{{\&PartialD;V}_x}{\&PartialD;t}=0;$

(2) mass force that acts on the fluid has only gravity, i.e. U=-gz;

(3) fluid is incompressible, ρ=const;

(4) continuous along total stream a fluid stream flow, q _v=const when having a fluid stream branch or interflow as if the longshore current bundle, answers segmentation to list Bernoulli equation with whole fluid gross energy conservations;

(5) flowing on the flow section of row Bernoulli equation must be gradual flowing, can and have the not sudden turn of events to flow before two sections.

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