A method for testing the convective heat transfer coefficient of large-diameter corrugated pipes

Abstract

This invention relates to a method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, comprising the following steps: preparing a test specimen and inserting a large-diameter corrugated pipe inside the test specimen; heating the test specimen and blowing air into the pipe at a certain wind speed; measuring the air temperature at the pipe inlet and outlet wall boundaries and the air temperature at the cross-section center; selecting at least three measuring points on the test specimen wall at the pipe outlet to measure the temperature of the test specimen and calculating the average value; calculating the cross-sectional wind speed distribution and average cross-sectional wind speed of the section with fully developed heat transfer based on the wind speed at the pipe inlet; calculating the cross-sectional air temperature distribution and average cross-sectional air temperature at the pipe inlet and outlet; and calculating the heat flux density and the convective heat transfer coefficient. This invention's method for testing the convective heat transfer coefficient can accurately obtain the convective heat transfer coefficient between the air and the inner wall of a pipe, providing a more solid foundation for the thermodynamic coupling analysis of ventilation and heat transfer in large-volume components with small surface areas and rapid internal heating.

Description

Technical Field

[0001] This invention belongs to the field of heat exchange technology, and particularly relates to a method for testing the convective heat transfer coefficient of large-diameter corrugated pipes. Background Technology

[0002] Large-volume concrete structures, due to their small surface area, experience concentrated heat release from cement hydration and rapid internal heating. Therefore, specialized air-cooled or water-cooled temperature control systems are required for cooling during construction. Air-cooled systems typically utilize prestressed corrugated pipes within the concrete as ventilation ducts. When performing a thermodynamic coupling analysis of ventilation and heat exchange in large-volume concrete structures, it is necessary to first determine the convective heat transfer coefficient between the air inside the corrugated pipe and the pipe wall.

[0003] The basic calculation method for the convective heat transfer coefficient is to divide the heat flux density by the temperature difference between the fluid and solid parts. Current methods for testing the convective heat transfer coefficient of corrugated pipes involve uniformly arranging several sensors within the pipe's test section and then averaging the measured data for calculation. However, the actual distribution of air velocity and temperature within a corrugated pipe is not linear, and existing methods cannot obtain the true average values ​​of velocity and temperature. Furthermore, existing research and results on the heat transfer coefficient of corrugated pipes are limited to small-diameter pipes, while prestressed corrugated pipes in large-volume concrete often have larger diameters, making it impossible to directly apply existing results. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for testing the convective heat transfer coefficient of large-diameter corrugated pipes. This method can accurately obtain the convective heat transfer coefficient between the air and the inner wall of the large-diameter corrugated pipe, providing a more solid foundation for the thermo-mechanical coupling analysis of ventilation and heat transfer in large-volume components with small surface coefficients and rapid internal heating rates.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, which includes the following steps:

[0006] S1 prepares the test piece and inserts a large-diameter corrugated pipe inside the test piece;

[0007] S2 heats the test piece and blows air into the large-diameter corrugated pipe at a certain wind speed.

[0008] S3 measures the air temperature at the pipe inlet and outlet wall boundary and the air temperature at the center of the cross section;

[0009] S4 Select at least three temperature measurement points on the wall of the test specimen at the pipe outlet, measure the temperature of the test specimen and calculate the average wall temperature of the specimen.

[0010] S5 calculates the cross-sectional wind speed distribution and average cross-sectional wind speed of the fully developed heat exchange section based on the inlet wind speed of the pipe;

[0011] S6 calculates the average air temperature at the pipe inlet based on the air temperature at the pipe inlet wall boundary and the air temperature at the center of the cross section; and calculates the air temperature distribution and average air temperature at the pipe outlet based on the air temperature at the pipe outlet wall boundary and the air temperature at the center of the cross section.

[0012] S7 calculates the heat flux density based on the average air temperature difference between the pipe outlet and inlet sections and the average wind speed of the fully developed section; and calculates the convective heat transfer coefficient based on the heat flux density.

[0013] Furthermore, in the above-described method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, in step S5,

[0014] The cross-sectional wind speed distribution v(r) of the fully developed heat transfer section is calculated using the following formula, which is a function of the distance r from the center of the section:

[0015]

[0016] The average cross-sectional wind speed v of the fully developed heat exchange section is calculated using the following formula. m :

[0017]

[0018] In the formula, R is the bellows radius, v in This refers to the inlet wind speed.

[0019] Furthermore, in the above-described method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, in step S6,

[0020] The average air temperature T at the pipe inlet section is calculated using the following formula. m，in :

[0021]

[0022] The cross-sectional air temperature distribution T(r) at the outlet is calculated using the following formula. out It is a function of the distance r from the center of the cross section:

[0023]

[0024] The average air temperature T at the pipe outlet section is calculated using the following formula. m，out :

[0025]

[0026] In the formula, R is the radius of the bellows, t1 is the air temperature at the wall boundary, and t2 is the air temperature at the center of the measured cross-section.

[0027] Furthermore, in the above-described method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, in step S7,

[0028] The heat flux density q is calculated using the following formula:

[0029]

[0030] Then calculate the convective heat transfer coefficient h according to the following formula:

[0031]

[0032] In the formula, T m，in T m，out These are the average cross-sectional temperatures at the inlet and outlet of the large-diameter corrugated pipe, respectively. T is the average temperature of the airflow. w ρ represents the average wall temperature of the specimen at the outlet of the large-diameter corrugated pipe. a For air at temperature T a Temperature under certain conditions, v m For the cross-sectional average wind speed of the fully developed heat exchange section, A c Let A be the cross-sectional area of ​​the pipe. p For the total heat exchange area, c p The specific heat of air under standard wind pressure.

[0033] Furthermore, in the above-described method for testing the convective heat transfer coefficient of a large-diameter corrugated pipe, in step S4, three temperature measurement points are selected on the wall of the test piece at the pipe outlet. The three temperature measurement points are evenly distributed and close to the wall of the large-diameter corrugated pipe.

[0034] Furthermore, in the above-described method for testing the convective heat transfer coefficient of a large-diameter corrugated pipe, in step S1, the large-diameter corrugated pipe is arranged horizontally at the center of the test piece.

[0035] Furthermore, in the above-described method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, in step S1, the length of the test piece is not less than 20 times the pipe diameter.

[0036] The beneficial technical effects of this invention are as follows:

[0037] 1) The convective heat transfer coefficient testing method of the present invention obtains the cross-sectional wind speed distribution function and temperature distribution function of the fully developed heat transfer section. Based on the velocity distribution function and temperature distribution function, the average velocity and average temperature of the cross-section of the fully developed heat transfer section can be accurately calculated, thereby accurately calculating the convective heat transfer coefficient. This improves the testing accuracy of the convective heat transfer coefficient and provides a more solid foundation for the thermo-mechanical coupling analysis of ventilation and heat transfer in large-volume components (such as concrete structures).

[0038] 2) The convective heat transfer coefficient testing method of the present invention only requires measuring the inlet wind speed when calculating the average wind speed of the cross section, and only requires measuring the center position of the cross section and the pipe wall position when calculating the average air temperature of the cross section. This effectively reduces the number of measuring points, improves the working efficiency of convective heat transfer coefficient testing, and saves costs and time. Attached Figure Description

[0039] Figure 1 This is a flowchart of the convective heat transfer coefficient testing method of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of the test specimen of the present invention.

[0041] In the diagram: 1 - Specimen; 2 - Large-diameter corrugated pipe Detailed Implementation

[0042] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0043] like Figure 1 The diagram shows a method for testing the convective heat transfer coefficient of large-diameter corrugated pipes provided by this invention, comprising the following steps:

[0044] S1 prepares the test specimen and inserts a large-diameter corrugated pipe (large-diameter corrugated pipe refers to a pipe with a diameter of not less than 100mm) inside the test specimen, such as Figure 2 As shown; in which, the large-diameter corrugated pipe runs through the center of the test piece along its length, thus ensuring uniform wind speed and temperature distribution; the length of the test piece is not less than 20 times the diameter of the large-diameter corrugated pipe;

[0045] S2 heats the test piece and blows air into the pipe at a certain wind speed (the wind speed is determined according to actual needs);

[0046] S3 measures the air temperature at the pipe inlet and outlet wall boundaries and the air temperature at the center of the cross section; this effectively reduces the number of measuring points and improves work efficiency.

[0047] S4 requires selecting at least three temperature measurement points on the wall of the test specimen at the pipe outlet to measure the specimen temperature and calculate the average wall temperature value, preferably three measurement points. It should be noted that the three temperature measurement points should be evenly distributed and close to the wall of the large-diameter corrugated pipe.

[0048] S5 calculates the cross-sectional wind speed distribution and average cross-sectional wind speed of the fully developed heat exchange section based on the inlet wind speed of the pipe; the cross-sectional wind speed distribution is a function of the distance from the center of the cross-section. The average wind speed across the cross section is In the formula: R is the bellows radius, v in Inlet wind speed;

[0049] S6 calculates the average air temperature at the inlet of the large-diameter corrugated pipe, the air temperature distribution at the outlet, and the average air temperature at the cross-section center based on the air temperature at the wall boundary at the inlet and outlet of the large-diameter corrugated pipe; among which...

[0050] The average air temperature at the inlet cross-section is

[0051] The air temperature distribution at the outlet section is a function of the distance r from the center of the section.

[0052] The average air temperature at the outlet section is

[0053] In the formula, R is the bellows radius, t1 is the air temperature at the wall boundary, and t2 is the air temperature at the center of the measured section.

[0054] S7 is based on the average air temperature difference at the inlet and outlet of the large-diameter corrugated pipe and the average wind speed v at the cross-section of the fully developed heat exchange section. m Calculate the heat flux density q; then, based on the heat flux density q and the average wall temperature T of the specimen at the outlet of the large-diameter corrugated pipe... w and the average airflow temperature T at the inlet and outlet of the large-diameter corrugated pipe a Calculate the convective heat transfer coefficient h:

[0055] Heat flux density is The convective heat transfer coefficient is

[0056] In the formula, T m，in T m，out These are the average cross-sectional temperatures at the inlet and outlet of the large-diameter corrugated pipe, respectively. T is the average temperature of the airflow. w ρ represents the average wall temperature of the specimen at the outlet of the large-diameter corrugated pipe. a For air at temperature T a Temperature under certain conditions, vm A is the average cross-sectional wind speed. c Let A be the cross-sectional area of ​​the pipe. p For the total heat exchange area, c p The specific heat of air under standard wind pressure.

[0057] The following is an illustration through specific examples:

[0058] Step 1: Prepare the test specimen. The specimen is a rectangular concrete block with a large-diameter corrugated pipe arranged along its length and at the middle position. The pipe diameter is d = 100 mm and the specimen length is L = 2 m. A large-diameter corrugated pipe is defined as a pipe with a diameter greater than 100 mm.

[0059] Step 2, heat the test piece and apply wind speed v in =2.54m / s air is blown into the test specimen pipe;

[0060] Step 3: Measure the air temperature at the wall boundary and the center of the cross-section at the pipe inlet and outlet to obtain t. 1，in =25.2℃, t 2，in =24.8℃, t 1，out =43.2℃, t 2，out =31.4℃;

[0061] Step 4: Select three measuring points at the outlet to measure the concrete temperature and calculate the average wall temperature value to obtain T. w =42.6℃;

[0062] Step 5: Calculate the cross-sectional wind speed distribution and average cross-sectional wind speed of the fully developed heat exchange section based on the inlet wind speed, and obtain the cross-sectional wind speed distribution as follows: The average wind speed across the cross section is

[0063] Step 6: Calculate the cross-sectional air temperature distribution and average cross-sectional air temperature at the pipe inlet and outlet. The average cross-sectional air temperature at the inlet is obtained as follows: The air temperature distribution at the outlet section is as follows The average air temperature of the cross section is

[0064] Step 7: Calculate the heat flux density and the convective heat transfer coefficient to obtain the heat flux density as follows: The convective heat transfer coefficient is

[0065] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art based on the technical solutions and inventive concepts disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for testing the convective heat transfer coefficient of large-diameter corrugated pipes, comprising the following steps: S1 prepares the test piece and inserts a large-diameter corrugated pipe inside the test piece; S2 heats the test piece and blows air into the large-diameter corrugated pipe at a certain wind speed. S3 measures the air temperature at the pipe inlet and outlet wall boundary and the air temperature at the center of the cross section; S4 Select at least three temperature measurement points on the wall of the test specimen at the pipe outlet, measure the temperature of the test specimen and calculate the average wall temperature of the specimen. S5 calculates the cross-sectional wind speed distribution and average cross-sectional wind speed of the fully developed heat exchange section based on the inlet wind speed of the pipe; S6 calculates the average air temperature at the pipe inlet based on the air temperature at the pipe inlet wall boundary and the air temperature at the center of the cross section; and calculates the air temperature distribution and average air temperature at the pipe outlet based on the air temperature at the pipe outlet wall boundary and the air temperature at the center of the cross section. S7 calculates the heat flux density based on the average air temperature difference between the pipe outlet and inlet sections and the average wind speed in the fully developed section; and calculates the convective heat transfer coefficient based on the heat flux density. In step S5, the cross-sectional wind speed distribution v(r) of the fully developed heat exchange section is calculated according to the following formula, which is a function of the distance r from the center of the cross-section: The average cross-sectional wind speed v of the fully developed heat exchange section is calculated using the following formula. m : In the formula, R is the bellows radius, v in Inlet wind speed; In step S6, the average air temperature T at the pipe inlet section is calculated according to the following formula. m，in : The cross-sectional air temperature distribution T(r) at the outlet is calculated using the following formula. out It is a function of the distance r from the center of the cross section: The average air temperature T at the pipe outlet section is calculated using the following formula. m，out : In the formula, R is the bellows radius, t1 is the air temperature at the wall boundary, and t2 is the air temperature at the center of the measured section. In step S7, the heat flux density q is calculated according to the following formula: Then calculate the convective heat transfer coefficient h according to the following formula: In the formula, T m ，i n T m ，o u t These are the average cross-sectional temperatures at the inlet and outlet of the large-diameter corrugated pipe, respectively. T is the average temperature of the airflow. w ρ represents the average wall temperature of the specimen at the outlet of the large-diameter corrugated pipe. a For air at temperature T a Density under the condition, v m For the cross-sectional average wind speed of the fully developed heat exchange section, A c Let A be the cross-sectional area of ​​the pipe. p For the total heat exchange area, c p Specific heat of air under standard wind pressure.

2. The method for testing the convective heat transfer coefficient of large-diameter corrugated pipes as described in claim 1, characterized in that: In step S4, three temperature measurement points are selected on the wall of the test piece at the pipe outlet. The three temperature measurement points are evenly distributed and close to the wall of the large-diameter corrugated pipe.

3. The method for testing the convective heat transfer coefficient of large-diameter corrugated pipes as described in claim 1, characterized in that: In step S1, the large-diameter corrugated pipe is arranged horizontally at the center of the test piece.

4. The method for testing the convective heat transfer coefficient of large-diameter corrugated pipes as described in claim 1, characterized in that: In step S1, the length of the test piece is not less than 20 times the diameter of the pipe.

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