CN102162727A - Method for calculating pipe diameters of parallel running balance pipes of open cooling tower - Google Patents

Abstract

The invention relates to a method for calculating pipe diameters of parallel running balance pipes of an open cooling tower. The method is characterized in that: according to the following equation, the pipe diameters of the balance pipes are calculated by a Newton iteration method. In the invention, the pipe diameters, in accordance with the project situation, of the balance pipes can be calculated according to actual engineering situation; therefore, the application of the actual engineering can be guided directly; and the current design situation that the pipe diameters of the balance pipes are mainly estimated is changed.

Description

A kind of computing method of open type cooling tower parallel running balance pipe caliber

Technical field

The invention belongs to the Heating,Ventilating and Air Conditioning (HVAC) technical field, particularly the computing method of open type cooling tower parallel running balance pipe caliber.

Background technology

Cooling tower is established balance pipe when parallel running and bottom among actual moving process, rising pipe is not established electric butterfly valve, and when having only the operation of part cooling tower, a cooling tower moisturizing occurs and the phenomenon of an other cooling tower spilling water, i.e. spill and leakage phenomenon through regular meeting.At present, about the closely-related balance pipe caliber of phenomenon problem therewith, also provide the computing formula of this caliber without any teaching material or standard, all recommendation in actual engineering according to design manual, adopt the method for " identical " to estimate with cooling tower water inlet pipe and water outlet pipe caliber, and various problems have appearred in this evaluation method in actual engineering, can not satisfy the request for utilization of actual engineering.And the research that problem is relevant therewith is also rarely found.

Summary of the invention

The objective of the invention is to propose a kind of computing method of open type cooling tower parallel running balance pipe caliber.

The objective of the invention is to be achieved through the following technical solutions.

In the accompanying drawing, MV is an electric butterfly valve, when a certain unit is out of service, plays the shutoff effect; BV is a Hand-operated butterfly valve, opens at ordinary times, plays the shutoff effect during maintenance; CWP is a cooling-water pump, WCC water-cooled unit.

The present invention supposes that at first cooling tower 1 and its water inlet electric butterfly valve MV close cooling tower 2 operations.Because cooling tower 2 tops have water to enter, and cooling tower 1 and cooling tower 2 water outlets simultaneously, cause the water level of two cooling towers to change, produce difference in height, thereby impel water to flow into cooling tower 1 through balance pipe c from cooling tower 2, when reaching mobile equilibrium, the height of water level difference is Δ h, i.e. state shown in the accompanying drawing.And wanting to guarantee that the spill and leakage phenomenon does not take place cooling tower 1, Δ h must be less than the difference in height of overflow pipe gap place water level with the water level of beginning during moisturizing.And this difference in height Δ h also is unique power of flow among the balance pipe c.

Want the caliber of calculated equilibrium pipe c, know the flow that balance pipe c need bear earlier.And when current reached mobile equilibrium, pipeline a must equate with flow between the balance pipe c.But because the throughput ratio of accurate Calculation pipeline a is difficult, the present invention roughly estimates the flow of the pipeline a that flows through earlier from the relation of pipeline a and pipeline b flow.Be to calculate the basis then with the Bernoulli equation, by setting up the computation model of cooling tower, analyze the hydraulic performance of cooling tower, calculate the discharge of the pipeline a that flows through, progressively derive the flow that balance pipe bears and the pressure differential at two ends thereof again, the equation of equilibrium establishment pipe PIPE DIAMETER CALCULATION.Concrete computation process is as follows:

One, the analysis of pipeline a and pipeline b flow

According to Hydrodynamics Theory, suppose that in operational process water is ideal fluid, and be permanent flowing.

Then according to Bernoulli equation, the energy equation between 1-1 section and 3 sections is:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="Pa"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Pa</figure-callout>}}_1}{\mathrm{\&rho;g}}+{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">h</figure-callout>}}_1=\frac{P_3}{\mathrm{\&rho;g}}+\frac{{V_a}^2}{2g}+(\frac{{\mathrm{\&lambda;l}}_a}{d_a}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_a)\&times;\frac{{V_a}^2}{2g}---\left(1\right)$

Energy equation between 2-2 section and 3 sections is:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="Pa"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Pa</figure-callout>}}_2}{\mathrm{\&rho;g}}+{\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">h</figure-callout>}}_2+\frac{{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_2^{\&prime;2}}{2g}=\frac{P_3}{\mathrm{\&rho;g}}+\frac{{\mathrm{<figure-callout\; id="2"\; label="V\; b"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_b^{}}{2g}+(\frac{{\mathrm{\&lambda;l}}_b}{d_b}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_b)\&times;\frac{{\mathrm{<figure-callout\; id="2"\; label="V\; b"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_b^{}}{2g}---\left(2\right)$

In the formula: Pa ₁, Pa ₂--water surface atmospheric pressure (Pa) ρ--density (kg/m of water ³)

G--acceleration of gravity (m/s ²) P ₃--3 section part pressure (Pa) V _a--the flow velocity (m/s) of pipeline a

λ--on-way resistance coefficient (nondimensional number) l _a--the length (m) of pipeline a

d _a--diameter (m) the ∑ ξ of pipeline a _a--coefficient of shock resistance and (nondimensional number) of pipeline a

V _b--flow velocity (m/s) V ' of pipeline b ₂--cooling tower 2 water-collecting trays surface water velocity (m/s)

l _b--length (m) d of pipeline b _b--the diameter (m) of pipeline b

∑ ξ _b--coefficient of shock resistance and (nondimensional number) of pipeline b

After various cooling tower samples are calculated, know that into water is when flowing to the water-collecting tray upper surface through packing layer, flow velocity is generally less than 0.01m/s, so will contain V ' in formula (2) ₂That omit.

Since the swabbing action of the blower fan of cooling tower of operation, Pa ₂Can be less than Pa ₁, in order to simplify calculating, ignore this factor here.

(2)-(1) can be obtained:

$\mathrm{\&Delta;h}=(1+\frac{{\mathrm{\&lambda;l}}_b}{d_b}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_b)\&times;\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; b"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_b}^2}{2g}-(1+\frac{{\mathrm{\&lambda;l}}_a}{d_a}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_a)\&times;\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; a"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_a}^2}{2g}---\left(3\right)$

Δ h=h ₂-h ₁, the difference in height of the water level when its maximal value is overflow pipe water inlet place water level and beginning moisturizing.Consult sample and know that its value is probably between 0.2m-0.4m.

In this pipe-connecting mode as shown in Figure 1, l _a=l _bd _a=d _b∑ ξ _a=∑ ξ _bThereby:

$\mathrm{\&Delta;h}=(1+\frac{{\mathrm{\&lambda;l}}_b}{d_b}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_b)\&times;(\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; b"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_b}^2}{2g}-\frac{{V_a}^2}{2g})---\left(4\right)$

Can judge V by formula (4) _b〉=V _aThis shows that always greater than the flow of the pipeline a that flows through, its difference is different along with concrete situation for the flow of the pipeline b that flows through.But if pipe-connecting mode is different from Fig. 1, then because resistance coefficient unequal, the phenomenon of above-mentioned analysis may appear being different from.

Two, the PIPE DIAMETER CALCULATION of balance pipe c

By top calculating as can be known, flow through the flow of balance pipe c always less than half of water inlet pipe total flow.Suppose that the water inlet pipe total flow is Q,, can think that then the balance pipe caliber that calculates is the caliber of comparison safety if getting Q/2 is the flow that balance pipe need be born.(can certainly estimate the flow of pipeline a earlier, and be that the flow that balance pipe need be born comes calculated equilibrium pipe caliber with this flow.) below promptly with the flow of Q/2 as the balance pipe of flowing through, the caliber of balance pipe is discussed.

Utilize Bernoulli equation equally:

Energy equation is arranged between 1-1 section and 2-2 section:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="Pa"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Pa</figure-callout>}}_2}{\mathrm{\&rho;g}}+{\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">h</figure-callout>}}_2+\frac{{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_2^{\&prime;2}}{2g}=(\frac{{\mathrm{\&lambda;l}}_c}{d_c}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c)\&times;\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_c}^2}{2g}+\frac{{\mathrm{<figure-callout\; id="1"\; label="Pa"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Pa</figure-callout>}}_1}{\mathrm{\&rho;g}}+h_1---\left(5\right)$

In the formula: l _c--balance pipe length (m) d _c--balance pipe diameter (m) V _c--water velocity in the balance pipe (m/s)

∑ ξ _c--coefficient of shock resistance and (nondimensional number) of balance pipe c

Ignore Pa equally ₁With Pa ₂The influence of difference, and will contain V ' ₂That ignore, then can release by (5) formula:

$\mathrm{\&Delta;h}=(\frac{{\mathrm{\&lambda;l}}_c}{d_c}+\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c)\&times;\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">V</figure-callout>}}_c}^2}{2g}---\left(6\right)$

Know by flow rate calculation formula Q=A * V again:

$Q_c=\frac{\mathrm{\&pi;}}{4}\&times;{{\mathrm{<figure-callout\; id="2"\; label="d\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">d</figure-callout>}}_c}^2\&times;V_c---\left(7\right)$

Q in the formula _cFlow for the balance pipe c that flows through.

Have by (7) formula:

$V_c=\frac{{4Q}_c}{{{\mathrm{\&pi;d}}_c}^2}---\left(8\right)$

(8) formula substitution (6) formula and arrangement are had:

${d_c}^5-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}\&times;d_c-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;l_c\&times;\mathrm{\&lambda;}}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}=0---\left(9\right)$

Formula (9) is the formula of calculated equilibrium pipe caliber.

Again (9) formula is write as the form of function:

$f\left(d\right)=d^5-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}\&times;d-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;l_c\&times;\mathrm{\&lambda;}}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}$

In the formula:

D--balance pipe caliber, g--acceleration of gravity (m/s ²), λ--on-way resistance coefficient (nondimensional number)

l _c--balance pipe length (m), ∑ ξ _c--coefficient of shock resistance and (nondimensional number) of balance pipe c,

Q _c--be the flow of the balance pipe c that flows through

Δ h=h ₂-h ₁For cooling tower 2 and the height of water level of cooling tower 1 when reaching mobile equilibrium poor.

Then by Newton iteration method calculated equilibrium pipe caliber.

The beneficial effect of patent of the present invention is:

After utilizing computing formula of the present invention, any one actual engineering all can be according to the concrete condition of its project, and the input calculating parameter calculates the balance pipe caliber that meets the project situation with the method for Theoretical Calculation.The present invention can directly instruct the application of actual engineering, has changed at present to estimate the design present situation of balance pipe caliber.

Description of drawings

Accompanying drawing is a synoptic diagram of the present invention, and MV is an electric butterfly valve, and BV is a Hand-operated butterfly valve, and CWP is a cooling-water pump, and WCC water-cooled unit, CT-1 are cooling tower 1, and CT-2 is a cooling tower 2, and a is a pipeline, and c is a balance pipe.

Embodiment

The present invention will be described further by following examples.

Embodiment.

It is 250m that certain actual engineering is selected two flows for use ³The cooling tower of/h, designing the water pipe caliber is 200mm.Each parameter value is as follows: λ=0.037, ξ _Elbow=1, ξ _Import=0.9, ξ _Elbow=0.9, ξ _{Butterfly valve}=0.5, ∑ ξ then _c=3.3 balance pipe calculated flow rates are got 125m ³/ h.Δ h gets 0.2m respectively, 0.3m, and 0.4m carries out analog computation.Result such as table one.

Table one

Δh	dc
		0.2m	223.3mm
0.3m	203.2mm
		0.4m	189.5mm

By the result of calculation of table one as can be known, under the certain situation of flow, Δ h is very important to the influence of balance pipe caliber.And consult from sample, the Δ h value of different cooling towers is also incomplete same, and this just tells us the designer, when selecting balance pipe for use, can not simply choose the caliber of the caliber identical, and will carry out detailed calculating at concrete equipment as balance pipe with rising pipe.

$f\left(d\right)=d^5-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}\&times;d-\frac{{{8\mathrm{<figure-callout\; id="2"\; label="Q\; c"\; filenames="HSB00000444308400011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c}^2\&times;l_c\&times;\mathrm{\&lambda;}}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}$

Claims (1)

1. the computing method of an open type cooling tower parallel running balance pipe caliber is characterized in that according to following equation, again by Newton iteration method calculated equilibrium pipe caliber:

$f\left(d\right)=d^5-\frac{{{8Q}_c}^2\&times;\mathrm{\&Sigma;}{\mathrm{\&xi;}}_c}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}\&times;d-\frac{{{8Q}_c}^2\&times;l_c\&times;\mathrm{\&lambda;}}{g\&times;{\mathrm{\&pi;}}^2\&times;\mathrm{\&Delta;h}}$

In the formula:

D--balance pipe caliber, g--acceleration of gravity (m/s ²), λ--on-way resistance coefficient (nondimensional number),

l _c--balance pipe length (m), ∑ ξ _c--coefficient of shock resistance and (nondimensional number) of balance pipe c,

Q _c--be the flow of the balance pipe c that flows through,

Δ h=h ₂-h ₁For cooling tower 2 and the height of water level of cooling tower 1 when reaching mobile equilibrium poor.

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