CN204330647U - A kind of system for measuring tube bank heat transfer characteristic - Google Patents

Abstract

The utility model discloses a kind of system for measuring tube bank heat transfer characteristic, comprise intake stack, it is air inlet on the left of intake stack, intake stack inside is provided with axial flow blower from left to right successively, air channel gate and venturi section, the first straight length is connected on the right side of venturi section, first straight length inside is provided with pitot tube, pitot tube is connected with microbarograph, removable heat-exchanging tube bundle test section is connected with on the right side of first straight length, the second straight length is connected on the right side of heat-exchanging tube bundle test section, it is exhaust outlet on the right side of second straight length, the left and right sides of heat-exchanging tube bundle test section is equipped with temperature sensor I, temperature sensor I is connected with data acquisition unit I.Native system only needs the test section changing design heat-exchanging tube bundle, and supporting air channel and water side ducts need not be changed, and system has versatility; System measuring point chooses the use needs meeting measurement mechanism, measures accurately; Ensure thermal equilibrium, test findings error is less.

Description

A system for measuring heat transfer characteristics of tube bundles

technical field

The utility model relates to a system for measuring the heat transfer characteristics of tube bundles.

Background technique

In engineering practice, heat exchangers are widely used in power, chemical industry, metallurgy, aerospace, air conditioning, refrigeration, machinery, textile, construction and other industries. Heat exchangers have different forms according to different uses and heat exchange environments. Among them, the heat exchange tube bundle is widely used in the indirect convection heat exchange process of two media. In order to enhance the effect of convective heat transfer, on the basis of traditional heat exchange tubes, reprocessing is carried out, mainly including coating or porous surface and other treated surfaces, rough surfaces, extended surfaces such as fins, spoiler elements, twisted belts or spiral blades Such as swirl components, spiral tubes, etc.

In the indirect heat exchanger of two media, the amount of heat transfer per unit time is proportional to the temperature difference between the hot and cold fluids and the heat transfer area, that is, Q=KAΔt, where K——the heat transfer coefficient is the reflection of the heat transfer An indicator of the strength of the heat transfer effect of the device. The overall heat transfer coefficient K of the tube bundle is related to the heat conduction of the tube bundle and the convective heat transfer coefficient of the two media. Different tube bundles have different overall heat transfer coefficients and convective heat transfer coefficients due to their different external heat transfer surface structures. Therefore, it is very important to guide the design and application of different heat transfer tube bundles in actual engineering by measuring the overall heat transfer coefficient of the experimental section and the convective heat transfer coefficient of the wind side at different wind speeds for different enhanced heat transfer tube bundles.

At present, there is no system that can accurately measure the heat transfer coefficient of different heat exchange tube bundles. The main problems are: according to different design conditions, it is necessary to set up supporting air ducts and water side pipes, and the experimental platform is not universal; the experimental platform is limited by the location of the building, and the measurement is not accurate; there are many factors affecting heat transfer, and the heat balance of the test is difficult. Guaranteed, the experimental results have large errors.

Utility model content

The purpose of this utility model is to overcome the above-mentioned deficiencies in the prior art and provide a system for measuring the heat transfer characteristics of the tube bundle. Replacement, with versatility.

In order to achieve the above object, the utility model adopts the following technical solutions:

A system for measuring the heat transfer characteristics of tube bundles, including an air inlet duct, the left side of which is an air inlet, and the inside of the air inlet duct is sequentially provided with an axial flow fan, an air duct gate, and a Venturi In the middle section, the right side of the Venturi section is connected to the first straight pipe section of a certain length that meets the accuracy of measuring instruments such as pitot tubes. The right side of the straight pipe section is connected with a replaceable heat exchange tube bundle test section (which can be replaced according to different working conditions), and the right side of the heat exchange tube bundle test section is connected with a second straight pipe section of a certain length, and the second straight pipe section The right side is the air outlet, and the left and right sides of the heat exchange tube bundle test section are equipped with temperature sensors I, the temperature sensor I is connected to the data collector I, and the data collector I measures the progress of the heat exchange tube bundle test section hourly. The air temperature of the air outlet and exhaust air outlet. The lower end of the heat exchange tube bundle test section is connected to a water inlet pipe, the upper end of the heat exchange tube bundle test section is connected to a water outlet pipe, and the water inlet pipe is connected to a constant temperature water bath through a rotameter and a centrifugal water pump. The outlet pipe is connected with a constant temperature water bath.

The water inlet pipe and the water outlet pipe of the heat exchange tube bundle test section are equipped with a temperature sensor II, and the temperature sensor II is connected to the data collector II, and the data collector II measures the water inlet and outlet of the heat exchange tube bundle test section hourly. The water temperature of the water mouth.

The end of the water inlet pipe is connected with an air release valve, and the air release valve is connected with the test section of the heat exchange tube bundle.

The constant-temperature water bath is an electrically heated constant-temperature water bath whose temperature can be set and the heating time can be recorded. The constant temperature water bath adopts electric heating, and has a built-in heating tube bundle operation timing function, which can accurately calculate the electric heating power for heat balance calculation; the constant temperature water temperature can be adjusted by itself, and the accuracy can reach ±0.5°C.

Constant temperature water bath, water inlet pipe, heat exchange tube bundle test section and water outlet pipe form a water loop, in which the heat exchange tube bundle test section is the flowing water side; air inlet, axial flow fan, Venturi section, first straight pipe section, heat exchange The outer air passage of the tube bundle and the second straight pipe section form an air loop, wherein the outer air passage of the heat exchange tube bundle is the air side.

The beneficial effects of the utility model are: the system only needs to replace the test section of the designed heat exchange tube bundle, and the supporting air duct and water side pipeline do not need to be replaced, and the system has versatility; the selection of system measurement points meets the needs of the use of the measurement device, and the measurement is accurate ; The system guarantees heat balance, and the error of the test result is small.

Description of drawings

Fig. 1 is the structural schematic diagram of the utility model measuring tube bundle heat transfer characteristic system;

Figure 2 is a trend diagram of the overall heat transfer coefficient and the air side convective heat transfer coefficient changing with the wind speed;

In the figure, 1 is the air inlet, 2 is the axial flow fan, 3 is the air duct gate, 4 is the Venturi section, 5 is the pitot tube, 6 is the micromanometer, 7 is the test section of the converter tube bundle, and 8 is the data collector , 9 is a temperature sensor, 10 is an air outlet, 11 is a rotameter, 12 is a centrifugal water pump, 13 is a constant temperature water bath, 14 is the first straight pipe section, and 15 is the second straight pipe section.

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is further described.

As shown in Figure 1, the system for measuring the heat transfer characteristics of tube bundles includes an air inlet duct, the left side of which is an air inlet 1, and the interior of the air inlet duct 1 is sequentially provided with an axial flow fan 2, The air duct gate 3 and the Venturi section 4, the right side of the Venturi section 4 is connected to the first straight pipe section 14 of a certain length that satisfies the accuracy of measuring instruments such as pitot tubes. The micromanometer 6 is connected, the right side of the first straight pipe section 14 is connected with a replaceable heat exchange tube bundle test section 7 (which can be replaced according to different working conditions), and the right side of the heat exchange tube bundle test section 7 is connected with a second straight pipe bundle of a certain length. Pipe section 15, the right side of the second straight pipe section 15 is the air outlet 10, and the left and right sides of the heat exchange tube bundle test section 7 are equipped with temperature sensors 9, the temperature sensors 9 are connected to the data collector 8, and the data collector 8 measures time by time The air temperature of the air inlet 1 and the air outlet 10 of the heat exchange tube bundle test section 7. The lower end of the heat exchange tube bundle test section 7 is connected to the water inlet pipe, and the upper end of the heat exchange tube bundle test section 7 is connected to the water outlet pipe. The water inlet pipe is connected to the electric heating constant temperature water bath 13 that can set the temperature and record the heating time through the rotameter 11 and the centrifugal water pump 12. catch. The water outlet pipe of the heat exchange tube bundle test section 7 is connected to a constant temperature water bath 13 .

Temperature sensors are installed on the water inlet and outlet pipes of the heat exchange tube bundle test section 7, and the temperature sensors are connected to the data collector, and the data collector measures the water temperature of the water inlet and water outlet of the heat exchange tube bundle test section hourly.

A vent valve is connected to the end of the water inlet pipe, and the vent valve is connected to the test section 7 of the heat exchange tube bundle. The constant temperature water bath 13, the water inlet pipe, the heat exchange tube bundle test section 7 and the water outlet pipe form a water loop, wherein the heat exchange tube bundle test section 7 is the flowing water side; the air inlet 1, the axial flow fan 2, the Venturi section 4, the The straight pipe section 14, the outer air duct of the heat exchange tube bundle, and the second straight pipe section 15 form an air loop, wherein the outer air duct of the heat exchange tube bundle is the air side.

The replaceable heat exchange tube bundle test section is flanged to the air duct. Using the "nine square grid" method, the average wind speed of the steady flow cross-section is obtained by measuring with a pitot tube and a micromanometer. Set the temperature sensor, and use the data collector to measure the air temperature at the inlet and outlet of the test section hourly.

The "nine-square grid" method is to divide the cross-section of the rectangular air duct with steady flow before and after the measured tube bundle into sixteen equal parts, and measure nine fixed points at the fixed points of the horizontal and vertical quarters respectively. The wind speed on the cross-section of the rectangular air duct is uneven, and the measurement error of a single point is relatively large. In order to reduce the measurement error, the "nine-square grid" method is used for measurement to obtain the average wind speed of the cross-section.

The self-made electric heating constant temperature water bath that can set the temperature and record the heating time is connected to the heat exchange tube bundle and supplies water to the heat exchange tube bundle through a centrifugal water pump and a rotameter. Water and outlet water temperature sensors are used to measure the inlet and outlet water temperatures of the test section hourly with a data collector.

The constant temperature water bath adopts electric heating, and has a built-in heating tube bundle operation timing function, which can accurately calculate the electric heating power for heat balance calculation; the constant temperature water temperature can be adjusted by itself, and the accuracy can reach ±0.5°C.

Example 1:

Direct measurement of cooling water flow, inlet water temperature, outlet water temperature, air inlet temperature, outlet temperature, and wind speed of rectangular air ducts including 8 rows and 8 rows of parallel rectangular elliptical finned tube bundles.

The basic dimensions of the rectangular elliptical fin tube bundle are shown in Table 1.

In the actual measurement, the measurement is carried out according to the following steps:

(1) The constant temperature water bath is filled with water and heated to the set temperature;

(2) Turn on the water pump and run it at a low speed until the air in the test tube bundle is emptied and water overflows from the vent valve, and run the water pump at a high speed until the working condition is stable (the temperature measurement of the inlet and outlet pipe sections on the water side is the same);

(3) Turn on the fan, fully open the gate, run at the maximum wind speed for half an hour, wait for the working condition to stabilize, and read the time period when the heating device of the constant temperature water bath is frequently turned on, which is used to check the heat absorption and heating capacity of the water side Heat balance; the heating amount is the heating amount of the constant temperature water bath; the heat absorption is calculated by the formula, that is, cm(t ₁ -t ₂ )=4.187×water mass flow×(inlet water temperature-outlet water temperature);

(4) Read the inlet and outlet temperatures of the water side and the air side of the data acquisition instrument, and adopt the "nine square grid" method to obtain the average wind speed of the cross section by measuring with a pitot tube and a micromanometer;

(5) Adjust the opening of the gate, and after the working condition is stable (30min), repeat the step (4) to obtain the inlet and outlet temperatures of the water side and the air side at different wind speeds, and the average wind speed of the cross section;

(6) Process the experimental data, remove test bad points (heat balance error exceeds 10%), and calculate the heat transfer coefficient of the heat exchange tube bundle.

According to the heat balance of the system, the overall heat transfer coefficient of the test pipe section and the convective heat transfer coefficient of the air side can be calculated.

Heat balance: Q＝Q ₁ ＝Q ₂ ＝Q ₃ ,

Water side heat exchange: Q ₁ =c ₁ m(t' ₁ -t″ ₁ ),

Air side heat transfer: Q ₂ =c ₂ m'(t' ₂ -t″ ₂ ),

Electric heating capacity: Q ₃ =PT (used to check the heat balance, more than 10% of the bad points in the test should be eliminated), where c ₁ represents the specific heat capacity of the water side, c ₂ represents the specific heat capacity of the air side; m represents the mass of the water side Flow rate, m' represents the mass flow rate of the air side; t′ ₁ represents the water temperature of the water inlet on the water side, t″ ₁ represents the water temperature of the water outlet on the water side; t′ ₂ represents the air temperature of the air inlet on the air side, and t″ ₂ represents the air temperature The air temperature of the exhaust outlet on the side; P is the power of the heating tube of the constant temperature water bath, and T is the heating time.

1) Overall heat transfer coefficient

According to the overall heat transfer: Q=KAΔt,

The overall heat transfer coefficient is obtained as:

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; A\&Delta;t</span>}}$

Among them, the area A is the total area of the experimental pipe section:

A=A1+A2=total area of fins+total area of bare tubes.

The logarithmic average temperature difference Δt should be corrected according to the cross flow to the countercurrent logarithmic average temperature difference to obtain:

Countercurrent logarithmic mean temperature difference: Where Δt _max is the maximum temperature difference between the inlet and outlet of the two fluids, Δt _min is the minimum temperature difference between the inlet and outlet of the two fluids,

According to the dimensionless parameters: $P=\frac{t_2^{\&prime;\&prime;}-t_2^{\&prime;}}{t_1^{\&prime;}-t_2^{\&prime;}},R=\frac{t_1^{\&prime;}-t_1^{\&prime;\&prime;}}{t_2^{\&prime;\&prime;}-t_2^{\&prime;}},$

And check the temperature difference correction coefficient map of "a cross flow, when one fluid is mixed and the other fluid is not mixed" to get the corrected ψ value, and get the logarithmic average temperature difference of the cross flow:

Δt=ψ·Δt _m .

2) Air side convective heat transfer coefficient

First, the calculation of the water side flow state satisfies the applicable conditions of the Seider-Tate correlation, and the Nusselt number Nu _f can be calculated. The physical meaning indicates the dimensionless temperature gradient of the fluid near the wall, which indicates the strength of the convective heat transfer of the fluid. and according to Where d is the pipe diameter, h _f is the convective heat transfer coefficient of the fluid side, and λ is the thermal conductivity coefficient, and the convective heat transfer coefficient of the water side can be calculated

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; N</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 1.86</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; P</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 0.14</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>$

Where h ₁ is the convective heat transfer coefficient on the water side, λ is the thermal conductivity, Nu ₁ is the Nusselt number on the water side, d is the tube diameter, Re ₁ is the Reynolds number on the water side of the heat exchange tube, and Pr ₁ is the Prandtl number , d is pipe diameter, and L is pipe length, and η ₁ is the dynamic viscosity coefficient under the fluid temperature, and η _w is the dynamic viscosity coefficient under the wall surface temperature;

The material of the rectangular elliptical finned tube is steel pipe, and its thermal conductivity λ=45W/(m﹐K), according to

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>$

where K is the overall heat transfer coefficient, h ₁ is the convective heat transfer coefficient on the water side, δ is the wall thickness of the heat exchange tube bundle, λ is the thermal conductivity, h ₂ is the convective heat transfer coefficient on the air side, and the convective heat transfer coefficient on the air side can be obtained Heat transfer coefficient:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}}<span\; class="notranslate">\; .</span>$

According to the above method, the main calculation results obtained in this embodiment are shown in Table 2.

Table 2 Summary of experimental data in the test section

serial number average wind speed overall heat transfer coefficient Air side convective heat transfer coefficient m/s W/ ⁽ m2．K) W/ ⁽ m2．K) 1 11.24 25.41 29.09 2 10.67 24.25 27.63 3 9.68 23.37 26.43 4 9.06 23.23 26.23 5 8.69 22.86 25.75 6 8.39 22.22 25 7 7.63 21.86 24.55 8 7.21 21.65 24.27 9 6.19 18.88 20.82 10 5.41 17.85 19.59

According to the graph drawn from the data in Table 2, the overall heat transfer coefficient and the air side convective heat transfer coefficient change trend graph with wind speed in Figure 2, which intuitively reflects the change of heat transfer performance of the heat exchanger with wind speed Condition. As shown in Figure 2, the overall heat transfer coefficient and the convective heat transfer coefficient on the air side show the same change law at different wind speeds, and the overall trend is that the heat transfer effect increases with the increase of the wind speed, which is consistent with the increase of the wind side turbulence and the increase of the air side convective heat transfer coefficient. It is related to the enhancement of convective heat transfer, which also shows that increasing the turbulence on the low temperature side can enhance the heat transfer effect.

Although the specific implementation of the utility model has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the utility model. Those skilled in the art should understand that on the basis of the technical solution of the utility model, those skilled in the art do not need to Various modifications or deformations that can be made with creative efforts are still within the protection scope of the present utility model.

Claims (9)

1. one kind for measure tube bank heat transfer characteristic system, it is characterized in that, comprise intake stack, it is air inlet on the left of described intake stack, described intake stack inside is provided with axial flow blower, air channel gate and venturi section from left to right successively, the first straight length is connected on the right side of described venturi section, described first straight length inside is provided with pitot tube, pitot tube is connected with microbarograph, removable heat-exchanging tube bundle test section is connected with on the right side of described first straight length, being connected to the second straight length on the right side of described heat-exchanging tube bundle test section, is exhaust outlet on the right side of described second straight length.

2. the system measuring tube bank heat transfer characteristic as claimed in claim 1, it is characterized in that, the left and right sides of described heat-exchanging tube bundle test section is equipped with temperature sensor I.

3. the as claimed in claim 2 system measuring tube bank heat transfer characteristic, it is characterized in that, described temperature sensor I is connected with data acquisition unit I, data acquisition unit I by time mensuration heat-exchanging tube bundle test section air inlet and the wind-warm syndrome of exhaust outlet.

4. the system measuring tube bank heat transfer characteristic as claimed in claim 1, is characterized in that, the lower end of described heat-exchanging tube bundle test section connects water inlet pipe, and the upper end of described heat-exchanging tube bundle test section connects rising pipe.

5. the system measuring tube bank heat transfer characteristic as claimed in claim 4, it is characterized in that, described water inlet pipe is connected with water bath with thermostatic control by spinner-type flowmeter and centrifugal water pump, and described rising pipe is connected with water bath with thermostatic control.

6. the system measuring tube bank heat transfer characteristic as claimed in claim 4, is characterized in that, the water inlet pipe of described heat-exchanging tube bundle test section and rising pipe are equipped with temperature sensor II.

7. the as claimed in claim 6 system measuring tube bank heat transfer characteristic, it is characterized in that, described temperature sensor II is connected with data acquisition unit II, data acquisition unit II by time the water inlet of mensuration heat-exchanging tube bundle test section and water delivering orifice water temperature.

8. the system measuring tube bank heat transfer characteristic as claimed in claim 4, it is characterized in that, described water inlet pipe end is connected with air release, and air release is connected with heat-exchanging tube bundle test section.

9. the system measuring tube bank heat transfer characteristic as claimed in claim 5, is characterized in that, described water bath with thermostatic control is can set temperature and the electrical heating water bath with thermostatic control of record heat time.