CN108520095B - Method for forecasting water temperature in base pipe of indirect air-cooling radiator - Google Patents

Method for forecasting water temperature in base pipe of indirect air-cooling radiator Download PDF

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CN108520095B
CN108520095B CN201810187643.XA CN201810187643A CN108520095B CN 108520095 B CN108520095 B CN 108520095B CN 201810187643 A CN201810187643 A CN 201810187643A CN 108520095 B CN108520095 B CN 108520095B
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宋小军
赵顺安
李陆军
杨岑
宋志勇
黄春花
冯晶
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China Institute of Water Resources and Hydropower Research
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Abstract

The invention discloses a method for forecasting the water temperature in a base pipe of an indirect air-cooling radiator, which comprises the following steps: (1) firstly, selecting a base pipe of a radiator to be tested to obtain the following parameters: the height of the base pipe, the inner radius of the base pipe, the outer radius of the base pipe and the heat conductivity coefficient of the wall of the base pipe; obtaining the difference between the water temperature in the base pipe and the temperature of the outer wall of the base pipe according to the heat transfer quantity transferred to the base pipe by the water flow in the base pipe and the heat transfer quantity of the pipe wall of the base pipe; (2) determining the flow velocity of water in the base pipe, the hydraulic diameter of the base pipe and the physical parameters of the water in the base pipe to obtain the heat dissipation coefficient of the water side; (3) and obtaining the water temperature in the base pipe according to the detected temperature of the outer wall of the base pipe. The invention provides a forecasting formula of the water temperature in the tube based on the basic principle of heat transfer science, and forecasts the water temperature in the tube in real time through the detected temperature of the outer wall of the base tube, thereby providing technical support for the anti-freezing scheme of the indirect air cooling tower radiator.

Description

Method for forecasting water temperature in base pipe of indirect air-cooling radiator
Technical Field
The invention relates to the field of antifreezing of an air cooling radiator of an indirect air cooling tower in a thermal power plant, in particular to the technical field of water temperature monitoring in a base pipe of the indirect air cooling radiator.
Background
The indirect air cooling system refers to an indirect air cooling system (a heler type indirect air cooling system) of a hybrid condenser, an indirect air cooling system (a hamlet type indirect air cooling system) with a surface condenser, and the like. The system mainly comprises a surface condenser, an air cooling radiator, a circulating water pump, a nitrogen charging protection system, a circulating water supplementing system, a radiator cleaning system and the like, and an air cooling tower. The system is basically similar to a conventional wet cooling system, and is different from the conventional wet cooling system in that an air cooling tower is used for replacing a wet cooling tower, a closed circulating cooling water system is used for replacing an open circulating cooling water system, and the circulating water adopts desalted water.
Because the closed circulating cooling water system is adopted to replace the open circulating cooling water system, the indirect air cooling system has good water-saving performance, and therefore, the indirect air cooling system is widely applied to thermal power plants in the three north areas rich in coal and water.
In the northwest of China, the indirect air cooling radiator of the core equipment is easy to freeze and damage in winter, and the safe and economic operation of a power plant is seriously influenced, so that the anti-freezing of the indirect air cooling system is very important. Aiming at the anti-freezing problem of the radiator of the indirect air cooling tower, related researchers and power plant operators in China carry out related research and provide specific anti-freezing measures. However, the problem to be taken into consideration is that because the indirect air cooling tower is not uniform in water distribution, the maximum temperature difference between the triangles of different cooling towers in the same sector can reach 16 ℃, and the maximum temperature difference between different cooling base pipes of the same cooling column can reach 12 ℃, the water temperature in each base pipe of the radiator needs to be monitored, and the early warning and the freezing are timely carried out. At present, the commonly adopted method is to install an on-line monitoring system for the wall temperature of a base pipe on the outer wall of an indirect air-cooling radiator, and the monitoring mode has the advantages that the wall temperature of the base pipe at different positions can be displayed in real time, and areas which are possibly frozen are early warned; the defect is that the temperature of the pipe wall is different from the temperature of water in the pipe, the difference changes along with the change of the operating condition, and the water temperature in the pipe cannot be directly obtained through the real-time measured temperature of the pipe wall. This error can have some effect on the specific application of anti-freeze measures.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a method for forecasting the water temperature in a base pipe of an indirect air cooling radiator based on the actual temperature of the pipe wall by analyzing the influence factor of the difference value of the water temperature in the pipe and the pipe wall temperature based on the basic principle of heat transfer science aiming at the defects of the prior art.
The technical scheme is as follows: the invention relates to a method for forecasting the water temperature in a base pipe of an indirect air-cooling radiator, which comprises the following steps:
(1) according to a base pipe of the radiator to be tested, the following parameters are obtained: height l of base pipe, inner radius r of base pipe1Outer radius of base pipe r2And base pipe wall thermal conductivity λw(ii) a According to water flow transmission in the base pipeGiving the heat transfer capacity of the base pipe and the pipe wall heat transfer capacity of the base pipe, and obtaining the difference value between the water temperature in the base pipe and the temperature of the outer wall of the base pipe:
Figure BDA0001590764290000021
in the formula, Tf1The water temperature in the base pipe, TwinIs the temperature of the inner wall of the base tube, phi is the heat transfer capacity, TwouIs the outer wall temperature of the base tube, Kf1Water side heat dissipation coefficient;
(2) obtaining the flow velocity v of water in the base pipef1Hydraulic diameter d of base pipeeAnd the physical property parameter of the water in the base pipe to obtain the heat radiation coefficient K of the water sidef1：
Figure BDA0001590764290000022
In the formula, muf1Viscosity coefficient, p, corresponding to water temperaturef1Density of water, C, corresponding to water temperaturepIs the specific heat at constant pressure of water, alphaf1Is the thermal conductivity of water;
(3) obtaining the water temperature in the base pipe according to the detected temperature of the outer wall of the base pipe:
Figure BDA0001590764290000023
the invention further preferably adopts the technical scheme that the water side heat dissipation coefficient K in the step (2)f1The acquisition method comprises the following steps:
a. reynolds number Re according to the flow of water in the base pipef1And the prandtl number Pr corresponding to the water temperaturef1Obtaining Nuusch number Nu of water in the base pipe under the forced convection heat transfer:
Figure BDA0001590764290000031
wherein n is a constant, n is 0.4 when the fluid is heated, and n is 0.3 when the fluid is cooled;
b. obtaining the flowing Reynolds number Re of water in the base pipef1：
Figure BDA0001590764290000032
c. Obtaining the Prandtl number Pr corresponding to the water temperaturef1：
Figure BDA0001590764290000033
d. According to the water side heat dissipation coefficient Kf1And nuschett number Nu
Figure BDA0001590764290000034
Obtaining water side heat radiation coefficient Kf1：
Figure BDA0001590764290000035
Further, in the step (1), the difference between the temperature of the water in the base pipe and the temperature of the outer wall of the base pipe is obtained by the following steps:
a. obtaining the heat transfer phi transferred by the water flow in the base pipe to the base pipe1：
φ1＝AKf1(Tf1-Twin)＝2πr1lKf1(T f1-Twin)；
b. Obtaining the heat transfer phi of the tube wall of the base tube2：
Figure BDA0001590764290000036
c. Law of conservation of energy phi1＝φ2And obtaining the difference value between the water temperature in the base pipe and the temperature of the outer wall of the base pipe:
Figure BDA0001590764290000041
in the formula, the heat transfer phi is equal toφ1＝φ2。
Has the advantages that: the invention provides a forecasting formula of the water temperature in the tube based on the basic principle of heat transfer science, obtains the water temperature in the tube in real time through the detected temperature of the outer wall of the base tube, and provides technical support for the anti-freezing scheme of the indirect air cooling tower radiator.
Drawings
FIG. 1 is a schematic structural view of a base pipe according to the present invention.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the embodiments.
Example (b): a method for forecasting the water temperature in a base pipe of an indirect air cooling radiator comprises the following steps:
(1) according to a base pipe of the radiator to be tested, the following parameters are obtained: height l of base pipe, inner radius r of base pipe1Outer radius of base pipe r2And base pipe wall thermal conductivity λw(ii) a According to the heat transfer quantity transferred to the base pipe by the water flow in the base pipe and the heat transfer quantity of the pipe wall 1 of the base pipe, the difference value between the water temperature in the base pipe and the temperature of the outer wall of the base pipe is obtained, and the specific method comprises the following steps:
a. obtaining the heat transfer phi transferred by the water flow in the base pipe to the base pipe1：
φ1＝AKf1(Tf1-Twin)＝2πr1lKf1(Tf1-Twin)，
In the formula Tf1The water temperature in the base pipe, TwinIs the temperature of the inner wall of the base tube, Kf1Water side heat dissipation coefficient;
b. obtaining the heat transfer phi of the tube wall 1 of the base tube2：
Figure BDA0001590764290000042
In the formula, TwouThe temperature of the outer wall of the base tube;
c. law of conservation of energy phi1＝φ2Obtaining the water temperature in the base pipe and the outer wall temperature of the base pipeThe difference between:
Figure BDA0001590764290000051
wherein the heat transfer phi is equal to phi1＝φ2In the improved mode, when the size and the material of the base pipe are fixed, the difference value between the water temperature in the base pipe and the temperature of the outer wall of the base pipe is only related to the heat transfer quantity and the heat dissipation coefficient of the water side.
(2) Obtaining the flow velocity v of water in the base pipef1Hydraulic diameter d of base pipeeAnd obtaining the water side heat dissipation coefficient K according to the physical parameters of water in the base pipef1According to the physical property parameter table of water,. mu.f1、ρf1、CpAnd alphaf1Can be fitted as a function of water temperature, returning to the equation:
Figure BDA0001590764290000052
when the wall temperature is measured, all the unknown parameters in the formula can be functions of the water temperature, and the water temperature can be obtained through iterative calculation.
The specific method comprises the following steps:
a. for the forced convection heat transfer in the pipe, when the Pr number of the fluid is more than 0.6, acquiring the Nutscher number Nu of the water in the base pipe under the forced convection heat transfer:
Figure BDA0001590764290000053
in the formula, Ref1Is Reynolds number of flow, Prf1N is a constant which is the prandtl number corresponding to the water temperature, and is 0.4 when the fluid is heated and 0.3 when the fluid is cooled;
b. obtaining the flowing Reynolds number Re of water in the base pipef1：
Figure BDA0001590764290000054
In the formula, muf1Viscosity coefficient, p, corresponding to water temperaturef1Water corresponding to water temperatureDensity of (v)f1Is the flow velocity of water in the base pipe, deIs the hydraulic diameter of the base pipe;
c. obtaining the Prandtl number Pr corresponding to the water temperaturef1：
Figure BDA0001590764290000061
In the formula, CpIs the specific heat at constant pressure of water, alphaf1Is the thermal conductivity of water;
d. according to the water side heat dissipation coefficient Kf1And nuschett number Nu
Figure BDA0001590764290000062
Obtaining the heat dissipation coefficient K of the water outlet sidef1：
Figure BDA0001590764290000063
From the formula, the heat dissipation coefficient of the water side is related to the physical parameters of water besides the flow velocity in the pipe and the diameter of the base pipe, and the values of the physical parameters of water are shown in table 1.
(3) Finally obtaining the water temperature in the base pipe according to the detected temperature of the outer wall of the base pipe:
Figure BDA0001590764290000064
TABLE 1 physical Property parameter Table of Water
Figure BDA0001590764290000065
Figure BDA0001590764290000071
Figure BDA0001590764290000081
Figure BDA0001590764290000091
As noted above, while the present invention has been shown and described with reference to certain preferred embodiments, it is not to be construed as limited thereto. Various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (2)

1. A method for forecasting water temperature in a base pipe of an indirect air cooling radiator is characterized by comprising the following steps:
(1) according to a base pipe of the radiator to be tested, the following parameters are obtained: height l of base pipe, inner radius r of base pipe1Outer radius of base pipe r2And base pipe wall thermal conductivity λw(ii) a According to the heat transfer quantity transferred to the base pipe by the water flow in the base pipe and the pipe wall heat transfer quantity of the base pipe, the difference value between the water temperature in the base pipe and the outer wall temperature of the base pipe is obtained:
a. obtaining the heat transfer phi transferred by the water flow in the base pipe to the base pipe1：
φ1＝AKf1(Tf1-Twin)＝2π r1lKf1(Tf1-Twin)；
b. Obtaining the heat transfer phi of the tube wall of the base tube2：
Figure FDA0003004834310000011
c. Law of conservation of energy phi1＝φ2And obtaining the difference value between the water temperature in the base pipe and the temperature of the outer wall of the base pipe:
Figure FDA0003004834310000012
in the formula, Tf1Is in the base pipeWater temperature, TwinPhi is the temperature of the inner wall of the base tube, phi is the heat transfer quantity transferred to the air by the base tube wall, and phi is equal to phi1＝φ2，TwouIs the outer wall temperature of the base tube, Kf1The water side heat dissipation coefficient is shown, and A is the area of the inner wall surface of the base tube;
(2) obtaining the flow velocity v of water in the base pipef1Hydraulic diameter d of base pipeeAnd the physical property parameter of the water in the base pipe to obtain the heat radiation coefficient K of the water sidef1：
Figure FDA0003004834310000013
In the formula, muf1Viscosity coefficient, p, corresponding to water temperaturef1Density of water, C, corresponding to water temperaturepIs the specific heat at constant pressure of water, alphaf1Is the thermal conductivity of water;
(3) obtaining the water temperature in the base pipe according to the detected temperature of the outer wall of the base pipe:
Figure FDA0003004834310000021
2. the method for forecasting the water temperature in the base pipe of the indirect air-cooling radiator as claimed in claim 1, wherein the water side heat dissipation coefficient K in the step (2)f1The acquisition method comprises the following steps:
a. reynolds number Re according to the flow of water in the base pipef1And the prandtl number Pr corresponding to the water temperaturef1Obtaining Nuusch number Nu of water in the base pipe under the forced convection heat transfer:
Figure FDA0003004834310000022
wherein n is a constant, n is 0.4 when the fluid is heated, and n is 0.3 when the fluid is cooled;
b. obtaining the flowing Reynolds number Re of water in the base pipef1：
Figure FDA0003004834310000023
c. Obtaining the Prandtl number Pr corresponding to the water temperaturef1：
Figure FDA0003004834310000024
d. According to the water side heat dissipation coefficient Kf1And nuschett number Nu
Figure FDA0003004834310000025
Obtaining water side heat radiation coefficient Kf1：
Figure FDA0003004834310000031
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