CN104361147A - Design method of counter flow cooling tower - Google Patents

Abstract

The invention relates to a design method of a counter flow cooling tower. The method comprises the following steps: 1, setting the Lewis number to be 1 and correcting a Lewis relation formula; 2, correcting the performance number N of the cooling tower by a correction coefficient k2; 3, iteratively calculating according to the steps 1 and 2 and a formula described in the specifications to obtain the outlet water temperature of the counter flow cooling tower; 4, iteratively calculating by a formula described in the specifications according to the same line relationship of state points of air entering and exiting from the tower and state points of atmosphere on a psychrometric chart to obtain the moisture content of the air exiting from the tower; 5, iteratively calculating according to a reflux ratio formula to obtain the enthalpy value of the air exiting from the tower; 6, obtaining the corrected outlet water temperature and the corrected state parameters of the air entering and exiting from the tower in the counter flow cooling tower which takes the Lewis number and a filler coefficient into account. According to the design method, the Lewis number and the filler coefficient are fully considered during correction and reflux, the calculation precision is very high, a calculation result is matched with an actual measurement result, and the technical problem that the temperature and humidity of the air entering and exiting from the tower cannot be calculated by taking the enthalpy value as the intermediate quantity is solved.

Description

A kind of method for designing of counterflow cooling tower

Technical field

The present invention relates to a kind of method for designing considering the counterflow cooling tower of Lewis number and the correction of filler coefficients deviation.

Background technology

Cooling tower is an important equipment in air-conditioning system, and the quality of its runnability has a direct impact to the heat exchange of condenser, thus has an impact to the operational efficiency of whole air-conditioning system.

For mechanical-draft cooling tower, there is significant limitation in traditional design method, and result of calculation and the measured result deviation of traditional design method are very large.All using enthalpy as calculating intermediate variable when such as calculating, therefore cannot Exact Solution cooling tower leaving air temp and humidity, be all suppose that tower relative air humidity is 95% ~ 100% usually, this is just artificial causes error.

Owing to going out tower relative air humidity under off-design working condition, impossible guarantee that its relative humidity maintains 95% ~ 100%, such as air quantity is larger, enter tower air mass flow more big city cause the minimizing of air-out relative humidity, and these are all analyze the key that cooling tower air-out affects ambient thermal conditions; Also have to calculate and often commonly use Lewis relation, and this relational expression is derived under equal-enthalpy humidifying condition, might not be suitable for this relational expression to the calculating design of cooling tower; After tower runs a period of time, because filler damages and water distribution inequality, cause filling system off-design value; After departing from, the cooling effect of tower is deteriorated, and cooling power reduces, and when ensure identical heat dissipation capacity, can only add Wind Volume and discharge, thus add the energy consumption of tower.

Summary of the invention

Object of the present invention, overcome the deficiencies in the prior art exactly, there is provided a kind of method for designing considering the counterflow cooling tower of Lewis number and the correction of filler coefficients deviation, thus it is very high to obtain computational accuracy, the energy-conservation counterflow cooling tower that result of calculation and measured result match.

In order to achieve the above object, following technical scheme is adopted:

A method for designing for counterflow cooling tower, comprises the following steps:

Step one, make Lewis number L _ebe 1, revise Lewis relation, namely l in formula _efor Lewis number; σ is the wet exchange coefficient calculated with water capacity, and unit is kg/ (m ²s); α is sensible heat transfer coefficient, and unit is kW/ (m ²dEG C); c _pfor the specific heat at constant pressure of air, unit is kJ/ (kg DEG C);

Step 2, use correction factor k ₂revise the performance mumber N of cooling tower, i.e. N=k ₂a λ ^m, in formula, A and m is packing property related coefficient, and λ is gas-water ratio;

Step 3, according to revise Lewis relation, the performance mumber of the cooling tower of correction, and iterative computation obtains the leaving water temperature of counterflow cooling tower;

Step 4, according to turnover tower air condition point and the same linear relation of atmospheric condition point on psychrometric chart, utilize formula iterative computation obtain counterflow cooling tower go out tower air humidity content, wherein h _aifor entering tower air enthalpy, unit is kJ/kg; h _aafor air enthalpy, unit is kJ/kg; h _aofor going out tower air enthalpy, unit is kJ/kg; d _aifor entering tower air humidity content, unit is kg/kg _{dry air}; d _aafor air water capacity, unit is kg/kg _{dry air}; d _aofor going out tower air humidity content, unit is kg/kg _{dry air};

Step 5, according to reflux ratio formula iterative computation obtain counterflow cooling tower go out tower air enthalpy, wherein r _efor reflux ratio; h _aifor entering tower air enthalpy, unit is kJ/kg; h _aafor air enthalpy, unit is kJ/kg; h _aofor going out tower air enthalpy, unit is kJ/kg;

What what step 6, the leaving water temperature obtained according to step 3, step 4 obtained go out tower air humidity content and step 5 obtained goes out tower air enthalpy, obtains the correction leaving water temperature of the counterflow cooling tower considering Lewis number and filler coefficient and revises turnover tower air status parameter.

Further, described correction turnover tower air status parameter comprises correction air dry-bulb temperature and correction air relative humidity.

Compared with prior art, beneficial effect of the present invention is:

1) the design's method takes into full account Lewis number, the correction of filler coefficient and backflow, and computational accuracy is very high, and result of calculation and measured result match;

2) the design's method utilizes air to mix rule and solves turnover tower aerial temperature and humidity, solves and is intermediate quantity with enthalpy and cannot solves the difficult problem passing in and out tower humiture;

3) the design solves the problem that filling system departs from, and has saved energy consumption.

Accompanying drawing explanation

Fig. 1 is countercurrent tower evaluation work schematic diagram;

Fig. 2 is the computing method flow chart of steps of countercurrent tower in the design's method;

Fig. 3 is the calculating verification step process flow diagram of countercurrent tower in the design's method.

Embodiment

Describe the present invention in detail below in conjunction with accompanying drawing and specific implementation method, be used for explaining the present invention in exemplary embodiment and description of the present invention, but not as a limitation of the invention.

Fig. 1 is countercurrent tower Computing Principle in the design's method.In Fig. 1, chilled water flow of inlet water is Q, and chilled water water flow is Q-Q _u(Q _ufor the cooling water evaporation water yield), inflow temperature t ₁, leaving water temperature t ₂, enter tower air mass flow G, enter tower air dry-bulb temperature θ ₁, go out tower air dry-bulb temperature θ ₂, air inlet wet-bulb temperature τ ₁, go out tower air ' s wet bulb temperature τ ₂, ψ ₁enter tower relative air humidity, ψ ₂go out tower relative air humidity.In countercurrent tower, the motion of water and air can be considered One-Dimensional flows process, and namely water, gas are evenly distributed on horizontal section, and water flows from the top down, air then under up flow.

Technical scheme of the present invention is realized by following 6 steps:

Step one, Lewis relation derive under the condition of adiabatic humidiflcation, and in cooling tower, the caloic exchange process of water and air is not necessarily suitable for this formula.Definition L _efor Lewis number, Lewis relation is revised.Work as L _ewhen=1, the caloic pass being air adiabatic humidification is:

$L_e=\frac{\mathrm{\α}}{\mathrm{\σ}{c}_p}=1$ (formula 1)

In formula, σ is the wet exchange coefficient calculated with water capacity, units/kg/(m ²s); α is sensible heat transfer coefficient, unit kW/ (m ²dEG C); c _pfor the specific heat at constant pressure of air, unit kJ/ (kg DEG C); L _efor Lewis number.

The performance mumber N of step 2, cooling tower represents the cooling power that cooling tower has under certain packing and tower, and the characteristic of itself and packing, constructive geometry size, cooling water inflow is relevant.In cooling tower actual motion, intrinsic numeric may depart from standard condition value, in order to the departure degree of actual value and standard condition value is described, uses correction factor k ₂represent.K ₂actual is correction to property of cooling tower number, and because the reasons such as cooling tower filler is aging, filling surface fouling, filler weathering disengaging cause cooling tower cooling number to decline, the cooling power of the filler of unit volume declines in other words, therefore needs to revise it.K ₂value be (0,1].Therefore N can be expressed as (wherein, k ₂=1 represents performance mumber under standard condition)

N=k ₂a λ ^m(formula 2)

In formula, A, m are packing property related coefficient, are determined or producer provides by experiment; λ is gas-water ratio.

Step 3, according to revise Lewis relation, the performance mumber of the cooling tower of correction, and iterative computation obtains the leaving water temperature of counterflow cooling tower.

Step 4, according to mixing rule, turnover tower air condition point and atmospheric condition point represent on psychrometric chart and on same straight line, therefore can must obtain:

$\frac{h_{\mathrm{ai}}-h_{\mathrm{aa}}}{d_{\mathrm{ai}}-d_{\mathrm{ao}}}=\frac{h_{\mathrm{ao}}-h_{\mathrm{aa}}}{d_{\mathrm{ao}}-d_{\mathrm{aa}}}$ (formula 3)

H in formula _aifor entering tower air enthalpy, unit kJ/kg; h _aafor air enthalpy, unit kJ/kg; h _aofor going out tower air enthalpy, unit kJ/kg.D _aifor entering tower air humidity content, units/kg/kg _{dry air}; d _aafor air water capacity, units/kg/kg _{dry air}; d _aofor going out tower air humidity content, units/kg/kg _{dry air}.

There is hot reflux in step 5, cooling tower actual motion, namely enter in the air of cooling tower the soft air being mixed into this tower of a part and discharging; Reflux ratio can represent

$r_e=\frac{h_{\mathrm{ai}}-h_{\mathrm{aa}}}{h_{\mathrm{ao}}-h_{\mathrm{aa}}}$ (formula 4)

R in formula _efor reflux ratio, unit %; h _aifor entering tower air enthalpy, unit kJ/kg; h _aafor air enthalpy, unit kJ/kg; h _aofor going out tower air enthalpy, unit kJ/kg.

What what step 6, the leaving water temperature obtained according to step 3, step 4 obtained go out tower air humidity content and step 5 obtained goes out tower air enthalpy, obtains the correction leaving water temperature of the counterflow cooling tower considering Lewis number and filler coefficient and revises turnover tower air status parameter.Described correction turnover tower air status parameter comprises correction air dry-bulb temperature and correction air relative humidity.

Countercurrent tower method for designing and checking:

As shown in Figure 2, atmospheric parameter, Lewis number L is inputted _e, correction factor k ₂, packing property related coefficient A and m, reflux ratio and inflow temperature, suppose initial to enter tower air enthalpy, dry-bulb temperature and inflow temperature, add that an increment is as beginning calculated value using initial value, increment can just can be born, by formula 1, formula 2 He carry out iteration and go out leaving water temperature, go out out tower air humidity content by formula 3 iteration, go out out tower air enthalpy by formula 4 iteration, finally solve air dry-bulb temperature and the relative air humidity of leaving water temperature and turnover tower.

The result:

As shown in Figure 3, obtain atmospheric parameter, reflux ratio by carrying out field performance test to counterflow cooling tower, inflow temperature calculates theoretical leaving water temperature in bringing into and designing program, and contrasts with actual measurement leaving water temperature.As seen from the figure, the leaving water temperature of theory calculate is no more than 2% with the relative error of actual measurement leaving water temperature, and this illustrates that the design's method can reflect cooling tower caloic process exactly, also verifies method for designing reliability.

Above the technical scheme that the embodiment of the present invention provides is described in detail, apply specific case herein to set forth the principle of the embodiment of the present invention and embodiment, the explanation of above embodiment is only applicable to the principle helping to understand the embodiment of the present invention; Meanwhile, for one of ordinary skill in the art, according to the embodiment of the present invention, embodiment and range of application all will change, and in sum, this description should not be construed as limitation of the present invention.

Claims (2)

1. a method for designing for counterflow cooling tower, is characterized in that, comprises the following steps:

Step one, make Lewis number L _ebe 1, revise Lewis relation, namely l in formula _efor Lewis number; σ is the wet exchange coefficient calculated with water capacity, and unit is kg/ (m ²s); α is sensible heat transfer coefficient, and unit is kW/ (m ²dEG C); c _pfor the specific heat at constant pressure of air, unit is kJ/ (kg DEG C);

Step 2, use correction factor k ₂revise the performance mumber N of cooling tower, i.e. N=k ₂a λ ^m, in formula, A and m is packing property related coefficient, and λ is gas-water ratio;

Step 3, according to revise Lewis relation, the performance mumber of the cooling tower of correction, and iterative computation obtains the leaving water temperature of counterflow cooling tower;

Step 4, according to turnover tower air condition point and the same linear relation of atmospheric condition point on psychrometric chart, utilize formula iterative computation obtain counterflow cooling tower go out tower air humidity content, wherein h _aifor entering tower air enthalpy, unit is kJ/kg; h _aafor air enthalpy, unit is kJ/kg; h _aofor going out tower air enthalpy, unit is kJ/kg; d _aifor entering tower air humidity content, unit is kg/kg _{dry air}; d _aafor air water capacity, unit is kg/kg _{dry air}; d _aofor going out tower air humidity content, unit is kg/kg _{dry air};

Step 5, according to reflux ratio formula iterative computation obtain counterflow cooling tower go out tower air enthalpy, wherein r _efor reflux ratio; h _aifor entering tower air enthalpy, unit is kJ/kg; h _aafor air enthalpy, unit is kJ/kg; h _aofor going out tower air enthalpy, unit is kJ/kg;

What what step 6, the leaving water temperature obtained according to step 3, step 4 obtained go out tower air humidity content and step 5 obtained goes out tower air enthalpy, obtains the correction leaving water temperature of the counterflow cooling tower considering Lewis number and filler coefficient and revises turnover tower air status parameter.

2. the method for designing of counterflow cooling tower according to claim 1, is characterized in that: described correction turnover tower air status parameter comprises correction air dry-bulb temperature and correction air relative humidity.