An experimental device and method for studying the heat dissipation loss characteristics of overhead heating pipelines

Abstract

The present invention relates to an experimental device and an experimental method for studying the heat dissipation loss characteristics of overhead heating pipelines, including: an electric heater, a circulating oil pump, a mass flowmeter, a heat preservation test section, a filter, an electric control valve A, an electric control valve B, a main circuit flowmeter, a cooler, a cooling circuit inlet valve, a cooling circuit outlet valve, an oil drain valve, an expansion oil tank, a nitrogen inlet valve, an exhaust valve, an oil injection valve, an exhaust pipe and an expansion pipe. The beneficial effects of the present invention are as follows: By combining the heat dissipation loss characteristics of overhead heating pipelines using different heat dissipation loss test methods, a comprehensive quantitative analysis of the local heat dissipation and total heat dissipation of the heat preservation pipeline is achieved, making up for the current deficiency that the heat dissipation of pipeline supports and piers cannot be directly measured. It is of great significance for finding the weak links in the heat dissipation of heat preservation pipelines, scientifically analyzing the heat dissipation loss characteristics of heat preservation pipelines, and establishing a high-precision heat network heat dissipation loss model.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy, and particularly relates to an experimental device and method for studying the heat dissipation loss characteristics of overhead heating pipelines. Background Art

[0002] In an industrial heat network system, the thermal performance of the heat supply steam insulation pipeline directly determines key characteristic parameters such as the energy efficiency index and the heat supply radius of the heat network system. As the core index for evaluating heat supply of the heat network, the heat dissipation loss of the insulation pipeline directly determines the economic benefits of heat supply. How to effectively analyze and accurately evaluate the heat dissipation loss characteristics of the insulation pipeline is of great significance for the optimal design, efficient and economic operation, and maintenance of the heat network.

[0003] In the National Standard of the People's Republic of China GB / T28638-2012 "Test Method for Heat Dissipation Loss of Heat Insulation Structure of Urban Heating Pipelines and Evaluation Method for Heat Insulation Effect", the test methods for the heat dissipation loss of heating pipelines include the heat flow meter method, the surface temperature method, the temperature difference method, and the heat balance method. Among them, the surface temperature method and the heat flow meter method obtain the local heat dissipation through local measuring points; the temperature difference method calculates the local heat dissipation heat flux density by using the temperatures on each interface of the insulation structure and combining the known thermal conductivity of the insulation material; the heat balance method obtains the total heat dissipation of the entire pipeline section by measuring the enthalpy difference at the head and tail of the pipeline section. The surface temperature method and the heat flow meter method are applicable to areas with uniform heat dissipation heat flux distribution, such as the surface of straight pipelines; the temperature difference method is applicable when the thermal conductivity of the insulation material is known; the heat balance method requires that the heating pipeline is in a steady-state operation condition and there is a significant temperature drop of the medium. It can be seen that these four heat dissipation loss test methods have their own limitations and different application preconditions. For a section of insulation pipeline, if it is necessary to obtain both the total heat dissipation loss and the local heat dissipation loss at the same time, multiple heat dissipation loss test methods must be used comprehensively.

[0004] At present, the test of the pipeline heat insulation performance is mainly limited to the typical simple part composed of a straight pipeline and an insulation material, that is, the heat dissipation loss of the straight pipe insulation. However, in actual overhead heating pipelines, there are also pipe fittings such as elbows, tees, and valves, as well as special structures connected to the pipeline such as pipe supports and concrete piers. The heat dissipation conditions of these parts are significantly different from those of the straight pipe insulation, and in some cases, they play a dominant role in the total heat dissipation loss of the heat network, and in-depth research on them is required.

[0005] CN201410315513.1 proposes a test system for simulating the heat insulation performance of pipelines in a deep water environment. By testing parameters such as the outer surface temperature and heat flux density of the insulation structure, the adiabatic performance of the insulation structure is quantitatively analyzed. However, this system only considers the adiabatic performance of the straight pipe insulation and does not study the heat dissipation loss of special structural parts such as pipe supports in actual projects.

[0006] Due to the complex actual overhead heating pipe network, affected by factors such as dynamic changes in steam parameters, load fluctuations, environmental condition changes after long distances, along - line hydrophobicity, and changes in solar radiation, it is not possible to conduct steady - state experimental research under controlled variable conditions at the heat network site.

[0007] In summary, in order to accurately obtain the heat dissipation of each part including straight pipes, pipe fittings, supports, and piers, find the weak links in the heat dissipation of insulated pipes, scientifically analyze the characteristics of heat dissipation loss of insulated pipes, and establish a high - precision heat network heat dissipation loss model, it is urgent to design an experimental device and method for the heat dissipation loss characteristics of overhead heating pipes to conduct a comprehensive quantitative analysis of the local heat dissipation and total heat dissipation of insulated pipes. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an experimental device and method for studying the heat dissipation loss characteristics of overhead heating pipes.

[0009] This experimental device for studying the heat dissipation loss characteristics of overhead heating pipes includes an electric heater, a circulating oil pump, a heat - insulation test pipeline, a circulating bypass, a main - loop flowmeter, a cooler, and an expansion tank;

[0010] The outlet of the electric heater is connected to the inlet of the circulating oil pump, and the outlet of the circulating oil pump is respectively connected to the heat - insulation test pipeline and the circulating bypass; an electric control valve B is installed on the circulating bypass; a mass flowmeter is installed at the inlet section of the heat - insulation test pipeline, the outlet of the mass flowmeter is connected to the inlet of the heat - insulation test section, the outlet of the heat - insulation test section is connected to a filter and an electric control valve A, and the outlets of the electric control valve A and the electric control valve B are combined into one path and then connected to the inlet of the main - loop flowmeter;

[0011] The outlet of the main - loop flowmeter is connected to the inlet of the high - temperature side of the cooler, and the outlet of the high - temperature side of the cooler is connected to the inlet of the electric heater; the inlet and outlet of the low - temperature side of the cooler are respectively provided with a cooling - loop inlet valve and a cooling - loop outlet valve;

[0012] The expansion tank is connected to the electric heater through an exhaust pipeline and an expansion pipeline, and a nitrogen inlet valve, an exhaust valve, and an oil injection valve are installed on the top of the expansion tank.

[0013] Preferably: stop valves A and B are respectively installed near the inlet and outlet of the heat - insulation test section. The pipeline after stop valve A is divided into two paths, which are respectively connected to two test sections; one path is connected to the indoor test section, and a stop valve C is set near the inlet of the indoor test section, and the other path is connected to the outdoor test section, and a stop valve D is set near the inlet of the outdoor test section;

[0014] The indoor test section and the outdoor test section are mirror images of each other. The test section is provided with a straight pipe section, elbows, and a pipe support pier assembly 30. Thermal resistors are installed at the inlet, middle, and outlet of the test section respectively. Globe valves E and F are installed at the outlets of the indoor test section and the outdoor test section respectively. The outlets of globe valves E and F are combined into one path to connect to the inlet of globe valve B.

[0015] Preferably: The insulated test section is arranged in a U-shaped tube layout.

[0016] Preferably: In the insulated test section, the working pipe is covered with a thermal insulation layer and an outer protective layer. The pipe support pier assembly includes a support and a concrete pier for the support; the upper end of the support penetrates the thermal insulation layer and the outer protective layer and is connected to the working pipe, and the lower end is fixed on the concrete pier.

[0017] Preferably: The working pipe, thermal insulation layer, outer protective layer, elbows, and support pier assembly used in the insulated test section are all of unified specifications.

[0018] Preferably: The size of the working pipe used in the insulated test section is less than or equal to DN150.

[0019] Preferably: There is an oil drainage branch on the connecting pipeline between the electric heater and the circulating oil pump, and an oil drainage valve is installed on the oil drainage branch.

[0020] Preferably: The resistance coefficient of the electric control valve A is greater than that of the electric control valve B, and the main flow passes through the circulating bypass.

[0021] An experimental method for studying the heat dissipation loss characteristics of overhead heating pipelines includes the following steps:

[0022] Step 1: Adjust the liquid level height in the expansion tank to a predetermined value;

[0023] Step 2: Close the inlet valve, oil filling valve, and oil drainage valve of the cooling circuit, open the outlet valve of the cooling circuit, and keep the electric control valves A and B fully open; open the nitrogen inlet valve and the exhaust valve, and fill with nitrogen to expel air. After the air is completely expelled, close the exhaust valve. When the pressure in the expansion tank reaches the predetermined value, close the nitrogen inlet valve; open globe valves A, B, C, and E, and close globe valves D and F to put the indoor test section into operation;

[0024] Step 3: Set the target temperature and the heating rate, start the circulating oil pump to the maximum speed, and start heating; at this time, the electric control valve B is closed and the electric control valve A is fully open, and the flow rate of the insulated test circuit reaches the maximum;

[0025] Step 4: After the experimental loop reaches the target temperature, open the exhaust valve to release part of the gas and adjust the system pressure to the set value; reduce the rotational speed of the circulating oil pump, adjust the electric control valve B to the maximum opening, and reduce the opening of the electric control valve A to form a temperature drop between the inlet and outlet fluids in the insulation test section.

[0026] Step 5: Calculate the total heat dissipation power: After the system reaches the thermal equilibrium state, collect the experimental data. The total heat dissipation power of the test section obtained by the heat balance method is

[0027] Q t = Mc p (T in - T out ) (1)

[0028] where M is the measured mass flow rate of the heat transfer oil in the test section, c p is the specific heat capacity of the heat transfer oil, T in and T out are the inlet and outlet fluid temperatures of the test section respectively;

[0029] Step 6: Use a heat flow meter to measure the outer surfaces of the straight pipe section and the elbow respectively. After taking the average value of multiple measurements, obtain the average heat dissipation heat flux density q p of the outer surface of the straight pipe section and the average heat dissipation heat flux density q b of the outer surface of the elbow, and then obtain

[0030] Q p = πDL p L p q p (2)

[0031] Q b = q b A b N b (3)

[0032] where D p is the diameter of the outer sheath of the straight pipe section, L p is the total length of the straight pipe section in the test section, A b is the area of the outer sheath of a single elbow, N b is the number of elbows in the test section, Q p and Q b are the heat dissipation powers of the straight pipe section and the elbow respectively;

[0033] Step 7: According to the energy conservation in the test section, obtain

[0034] Q s = Q t - Q p - Q b (4)

[0035] Among them, Q s is the heat dissipation power of the pipe support pier in the test section; for convenient use, the heat dissipation heat flux density of the insulated pipe support pier is quantified,

[0036] Q s = πD p L s q s N s (5)

[0037] Among them, L s is the projected length of the pipe support pier in the axial direction of the pipe, q s is the equivalent heat dissipation heat flux density of the pipe support pier, N s is the number of pipe support piers in the test section; by combining equations (1 to 5), we can obtain

[0038]

[0039] Step 8: Open the stop valve D and the stop valve F, close the stop valve C and the stop valve E, put the outdoor test section into operation, and repeat steps to steps to conduct the experiment on the influence of environmental factors on the heat dissipation loss characteristics of the overhead heating pipeline;

[0040] Step 9: Turn off the heating power supply, open the cooling circuit inlet valve and the cooling circuit outlet valve, put the cooler into operation, close the electric control valve B, increase the rotational speed of the circulating oil pump and the opening degree of the electric control valve A, and the fluid temperature in the circuit decreases.

[0041] The beneficial effects of the present invention are:

[0042] 1) Through reasonable thermal fluid design, the present invention comprehensively uses two heat dissipation loss measurement methods, namely the heat balance method and the heat flow meter method, to achieve the measurement of the total heat dissipation and local heat dissipation of the insulated pipeline; and by combining the principle of energy conservation, the quantitative analysis of the complex heat dissipation situation of the insulated pipe support pier is realized, making up for the current deficiency that the heat dissipation of the pipe support pier cannot be directly measured, and better solving the problem of measuring the heat dissipation loss of the overhead heating pipeline.

[0043] 2) Through the comparison between the completely mirrored indoor test section and outdoor test section, the present invention provides conditions for exploring the influence of environmental variables on the heat dissipation characteristics of the insulated pipeline. Description of the Drawings

[0044] Figure 1 is a schematic diagram of the experimental device system for studying the heat dissipation loss characteristics of the overhead heating pipeline;

[0045] Figure 2 is a schematic diagram of the structure of the insulation test section;

[0046] Figure 3It is a schematic diagram of the structure of a thermal insulation pipeline support and pier.

[0047] In the figure: electric heater 1, circulating oil pump 2, mass flowmeter 3, thermal insulation test section 4, filter 5, electric control valve A 6, electric control valve B 7, main circuit flowmeter 8, cooler 9, cooling circuit inlet valve 10, cooling circuit outlet valve 11, oil drain valve 12, expansion oil tank 13, nitrogen inlet valve 14, exhaust valve 15, oil injection valve 16, exhaust pipe 17, expansion pipe 18, indoor test section 19, outdoor test section 20, stop valve A 21, stop valve B 22, stop valve C 23, stop valve D 24, stop valve E 25, stop valve F 26, thermal resistor 27, straight pipe section 28, elbow 29, pipeline support and pier assembly 30, working pipe 31, thermal insulation layer 32, outer protection layer 33, support 34, concrete pier 35. Specific implementation manners

[0048] The present invention will be further described below in conjunction with embodiments. The description of the following embodiments is only for helping to understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0049] Embodiment 1

[0050] As an embodiment, as Figures 1 to 3 shown: This experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines includes an electric heater 1, a circulating oil pump 2, a mass flowmeter 3, a thermal insulation test section 4, a filter 5, an electric control valve A 6, an electric control valve B 7, a main circuit flowmeter 8, a cooler 9, a cooling circuit inlet valve 10, a cooling circuit outlet valve 11, an oil drain valve 12, an expansion oil tank 13, a nitrogen inlet valve 14, an exhaust valve 15, an oil injection valve 16, an exhaust pipe 17, and an expansion pipe 18. Among them, as Figure 2 shown, the thermal insulation test section 4 can be divided into two parts, an indoor test section 19 and an outdoor test section 20, and includes a stop valve A 21, a stop valve B 22, a stop valve C 23, a stop valve D 24, a stop valve E 25, a stop valve F 26, a thermal resistor 27, a straight pipe section 28, an elbow 29, and a pipeline support and pier assembly 30. As Figure 3 shown, the structure of the thermal insulation pipeline support and pier includes a working pipe 31, a thermal insulation layer 32, an outer protection layer 33, a support 34, and a concrete pier 35.

[0051] The working medium of this experimental device is heat-conducting oil. The electric heater 1 is the heat source of this experimental device, which can control the temperature of the heat-conducting oil in the experimental loop and conduct experiments at different working temperatures. The outlet of the electric heater 1 is connected to the inlet of the circulating oil pump 2. The outlet pipeline of the circulating oil pump 2 is divided into a heat preservation test pipeline and a circulating bypass. An electric control valve B7 is installed on the circulating bypass, and a mass flowmeter 3 is installed at the inlet section of the heat preservation test pipeline. The outlet of the mass flowmeter 3 is connected to the inlet of the heat preservation test section 4. The outlet of the heat preservation test section 4 is equipped with a filter 5 and an electric control valve A6. The outlets of the electric control valve A6 and the electric control valve B7 are merged into one path and then connected to the inlet of the main loop flowmeter 8. The outlet of the main loop flowmeter 8 is connected to the high-temperature side inlet of the cooler 9. The high-temperature side outlet of the cooler 9 is connected to the inlet of the electric heater 1. The inlet and outlet of the low-temperature side of the cooler 9 are respectively provided with a cooling loop inlet valve 10 and a cooling loop outlet valve 11. The expansion oil tank 13 and the electric heater 1 are interconnected through an exhaust pipeline 17 and an expansion pipeline 18. A nitrogen inlet valve 14, an exhaust valve 15 and an oil injection valve 16 are installed on the top of the expansion oil tank 13. There is an oil drainage branch on the connecting pipeline between the electric heater 1 and the circulating oil pump 2, and an oil drainage valve 12 is installed on the oil drainage branch.

[0052] A stop valve A21 and a stop valve B22 are respectively installed near the inlet and outlet of the heat preservation test section 4. The pipeline after the stop valve A21 is divided into two paths and respectively connected to the indoor test section 19 and the outdoor test section 20, and a stop valve C23 and a stop valve D24 are respectively set near the inlets of the indoor test section 19 and the outdoor test section 20. The indoor test section 19 and the outdoor test section 20 are mirror images of each other. Straight pipe sections 28, elbows 29 and pipeline support pier assemblies 30 are provided on the test sections, and resistance thermometers 27 are respectively installed at the inlets, middles and outlets of the test sections to measure the temperature change of the heat-conducting oil. Stop valves E25 and stop valves F26 are respectively installed at the outlets of the indoor test section 19 and the outdoor test section 20. The outlets of the stop valves E25 and stop valves F26 are merged into one path and connected to the inlet of the stop valve B22. The working pipes 31 of the heat preservation test section 4 are the same, and the working pipes 31 are covered with the same heat preservation layer 32 and outer protection layer 33, and the elbows and pipeline support pier assemblies 30 used are the same.

[0053] The heat-conducting oil heated by the electric heater 1 is driven by the circulating oil pump 2 to flow to the heat preservation test pipeline and the circulating bypass. The flow rates of the heat preservation test pipeline and the circulating bypass are controlled by the electric control valves A6 and B7. In the heat preservation test section 4, the heat balance method needs to be used to measure the heat dissipation loss. The use condition of the heat balance method is that there is a significant temperature drop of the medium in the heat preservation pipeline, which requires a small mass flow rate in the heat preservation test section and a large pipeline heat dissipation area. Therefore, the heat preservation test section 4 adopts a U-shaped pipe arrangement to increase the heat dissipation area. The resistance coefficient of the electric control valve A6 is greater than that of the electric control valve B7, so that the main flow passes through the circulating bypass, and the electric control valve B7 needs to ensure that the main loop flow rate is above the safety value to avoid the risk of overheating of the electric heater 1.

[0054] The electric heater 1 is equipped with a thermocouple for over-temperature control, and thermocouples and pressure sensors are arranged on the main loop of the experimental device; a heat flux meter is used in the heat preservation test section 4 to measure the heat dissipation heat flux on the outer surfaces of the straight pipe section 28 and the elbow 29.

[0055] The working pipe 31 used in the heat preservation test section 4 has a size not larger than DN150. When the flow area of the working pipe is large, in order to ensure a small mass flow rate, the flow velocity in the working pipe is very low, resulting in an overly slow circulation speed of the heat-conducting oil in the experimental device and making it difficult to reach the thermal equilibrium state.

[0056] The indoor test section 19 and the outdoor test section 20 are arranged as mirror images of each other to study the influence of changes in outdoor environmental factors on the heat dissipation performance of the heat-insulated pipeline under the condition that other conditions are the same.

[0057] By switching the stop valves C23, D24, E25, and F26, the indoor test section 19 and the outdoor test section 20 can operate independently respectively.

[0058] During the experiment, the expansion tank 13 is filled with nitrogen to prevent the oxidation of the heat-conducting oil at high temperatures.

[0059] Example Two

[0060] Based on the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines proposed in Example One, this example provides an experimental method for studying the heat dissipation loss characteristics of overhead heating pipelines, including the following steps:

[0061] Step 1: Adjust the liquid level height in the expansion tank 13 to reach a predetermined value;

[0062] Step 2: Close the cooling circuit inlet valve 10, the oil injection valve 16, and the oil drain valve 12, open the cooling circuit outlet valve 11, and keep the electric control valves A6 and B7 fully open; open the nitrogen inlet valve 14 and the exhaust valve 15, and fill with nitrogen to remove air. After a few minutes, close the exhaust valve 15, and close the nitrogen inlet valve 14 when the pressure in the expansion tank 13 reaches the predetermined value; open the stop valves A21, B22, C23, and E25, and close the stop valves D24 and F26 to put the indoor test section 19 into operation;

[0063] Step 3: Set the target temperature and the heating rate, start the circulation oil pump 2 at the highest speed, and start heating; at this time, close the electric control valve B7 and keep the electric control valve A6 fully open to make the flow rate in the heat preservation test circuit the largest;

[0064] Step 4: After the experimental loop reaches the target temperature, the system pressure increases due to the volume change of the heat transfer oil. Open the exhaust valve 15 to release some gas and adjust the system pressure to the set value; reduce the rotational speed of the circulating oil pump 2, adjust the electric control valve B7 to the maximum opening, and reduce the opening of the electric control valve A6 to cause a significant temperature drop between the inlet and outlet fluids in the insulation test section 4;

[0065] Step 5: Calculate the total heat dissipation power: After the system reaches the thermal equilibrium state, collect the experimental data. According to the heat balance method, the total heat dissipation power of the test section is

[0066] Q t = Mc p (T in - T out ) (1)

[0067] where M is the measured mass flow rate of the heat transfer oil in the test section, c p is the specific heat capacity of the heat transfer oil, T in and T out are the inlet and outlet fluid temperatures of the test section respectively;

[0068] Step 6: Use a heat flow meter to measure the outer surfaces of the straight pipe section 28 and the elbow 29 respectively. After taking the average value of multiple measurements, obtain the average heat dissipation heat flux density q p of the outer surface of the straight pipe section and the average heat dissipation heat flux density q b of the outer surface of the elbow respectively. Then, it can be obtained that

[0069] Q p = πDL p L p q p (2)

[0070] Q b = q b A b N b (3)

[0071] where D p is the outer diameter of the outer sheath of the straight pipe section, L p is the total length of the straight pipe section in the test section, A b is the outer sheath area of a single elbow, N b is the number of elbows in the test section, Q p and Q b are the heat dissipation powers of the straight pipe section and the elbow respectively;

[0072] Step 7: Since the structure of the insulation pipe support pier assembly 30 is relatively complex and the heat dissipation heat flux is uneven, it is difficult to measure its heat dissipation using a heat flow meter. Therefore, according to the energy conservation in the test section, it is obtained that

[0073] Q s = Qt -Q p -Q b (4)

[0074] Among them, Q s is the heat dissipation power of the pipe support pier assembly 30 in the test section; for convenient use, the heat dissipation heat flux density of the thermal insulation pipe support pier assembly 30 is quantified,

[0075] Q s = πD p L s q s N s (5)

[0076] Among them, L s is the projected length of the pipe support pier assembly 30 in the axial direction of the pipe, q s is the equivalent heat dissipation heat flux density of the pipe support pier assembly 30, N s is the number of pipe support pier assemblies 30 in the test section; by combining equations (1 - 5), we can obtain

[0077]

[0078] Step 8: Open the stop valve D24 and the stop valve F26, close the stop valve C23 and the stop valve E25, put the outdoor test section 20 into operation, and repeat steps 3 to 7 to conduct an experiment on the influence of environmental factors on the heat dissipation loss characteristics of the overhead heating pipeline;

[0079] Step 9: Turn off the heating power supply, open the cooling circuit inlet valve 10 and the cooling circuit outlet valve 11, put the cooler 9 into operation, close the electric control valve B7, increase the rotation speed of the circulation oil pump 2 and the opening degree of the electric control valve A6, and gradually cool down the fluid in the circuit.

Claims

1. A method for using an experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines, characterized in that, Including: an electric heater (1), a circulating oil pump (2), a heat preservation test pipeline, a circulating bypass, a main circuit flowmeter (8), a cooler (9) and an expansion tank (13); The outlet of the electric heater (1) is connected to the inlet of the circulating oil pump (2), and the outlet of the circulating oil pump (2) is respectively connected to the heat preservation test pipeline and the circulating bypass; an electric control valve B (7) is installed on the circulating bypass; a mass flowmeter (3) is installed at the inlet section of the heat preservation test pipeline, the outlet of the mass flowmeter (3) is connected to the inlet of the heat preservation test section (4), the outlet of the heat preservation test section (4) is connected to a filter (5) and an electric control valve A (6), and the outlets of the electric control valve A (6) and the electric control valve B (7) are combined into one path and then connected to the inlet of the main circuit flowmeter (8); The outlet of the main circuit flowmeter (8) is connected to the high-temperature side inlet of the cooler (9), and the high-temperature side outlet of the cooler (9) is connected to the inlet of the electric heater (1); a cooling circuit inlet valve (10) and a cooling circuit outlet valve (11) are respectively arranged at the inlet and outlet of the low-temperature side of the cooler (9); The expansion tank (13) is connected to the electric heater (1) through an exhaust pipeline (17) and an expansion pipeline (18), and a nitrogen inlet valve (14), an exhaust valve (15) and an oil filling valve (16) are installed at the top of the expansion tank (13); The method includes the following steps: Step 1: Adjust the liquid level height in the expansion tank (13) to a predetermined value; Step 2: Close the cooling circuit inlet valve (10), the oil filling valve (16) and the oil drain valve (12), open the cooling circuit outlet valve (11), and keep the electric control valve A (6) and the electric control valve B (7) fully open; open the nitrogen inlet valve (14) and the exhaust valve (15), fill in nitrogen to remove air, close the exhaust valve (15) after the air is completely removed, and close the nitrogen inlet valve (14) when the pressure in the expansion tank (13) reaches the predetermined value; open the stop valve A (21), the stop valve B (22), the stop valve C (23) and the stop valve E (25), close the stop valve D (24) and the stop valve F (26), and put the indoor test section (19) into operation; Step 3: Set the target temperature and the heating rate, start the circulating oil pump (2) to the maximum speed, and start heating; at this time, the electric control valve B (7) is closed, the electric control valve A (6) is fully open, and the flow rate of the heat preservation test circuit reaches the maximum; Step 4: After the experimental circuit reaches the target temperature, open the exhaust valve (15) to release part of the gas to adjust the system pressure to the set value; reduce the speed of the circulating oil pump (2), adjust the electric control valve B (7) to the maximum opening, and reduce the opening of the electric control valve A (6) to form a temperature drop of the inlet and outlet fluids in the heat preservation test section (4); Step 5: Calculate the total heat dissipation power: After the system reaches the thermal equilibrium state, collect the experimental data, and obtain the total heat dissipation power of the test section by the heat balance method as Q t = Mc p (T in - T out )(1) where M is the measured mass flow rate of the heat transfer oil in the test section, c p is the specific heat capacity of the heat transfer oil, and T in and T out are the inlet and outlet fluid temperatures of the test section, respectively; Step 6: Measure the outer surfaces of the straight pipe section (28) and the elbow (29) respectively with a heat flow meter, and obtain the average heat dissipation heat flux density q of the outer surface of the straight pipe section and the average heat dissipation heat flux density q of the outer surface of the elbow respectively after taking the average of multiple measurements, and then obtain p and b then Q p = πD p L p q p (2) Q b = q b A b N b (3) Among them, D p is the outer sheath diameter of the straight pipe section, L p is the total length of the straight pipe section within the test section, A b is the outer sheath area of a single elbow, N b is the number of elbows in the test section, Q p and Q b are the heat dissipation powers of the straight pipe section and the elbow respectively; Step 7: Obtain according to the energy conservation in the test section Q s = Q t -Q p -Q b (4) Among them, Q s is the heat dissipation power of the pipe support pier in the test section; the heat flux density of the heat dissipation of the insulated pipe support pier is quantified to obtain Q s = πD p L s q s N s (5) Among them, L s is the projected length of the pipeline support pier in the pipeline axial direction, q s is the equivalent heat flux density of the pipe support pier, N s is the number of pipe support piers in the test section; the combined formula (1 to 5) is obtained Step 8: Open the stop valve D (24) and the stop valve F (26), close the stop valve C (23) and the stop valve E (25), put the outdoor test section (20) into operation, and repeat Steps 3 to 7 to conduct the experiment on the influence of environmental factors on the heat dissipation loss characteristics of the overhead heating pipeline; Step 9: Turn off the heating power supply, open the cooling circuit inlet valve (10) and the cooling circuit outlet valve (11), put the cooler (9) into operation, close the electric control valve B (7), increase the rotation speed of the circulation oil pump (2) and the opening degree of the electric control valve A (6), and the fluid temperature in the circuit decreases.

2. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 1, characterized in that: Stop valves A (21) and B (22) are respectively installed near the inlet and outlet of the insulation test section (4). The pipeline after the stop valve A (21) is divided into two paths, which are respectively connected to two test sections; one path is connected to the indoor test section (19), and a stop valve C (23) is set near the inlet of the indoor test section (19), and the other path is connected to the outdoor test section (20), and a stop valve D (24) is set near the inlet of the outdoor test section (20); The indoor test section (19) and the outdoor test section (20) are mirror images of each other. Straight pipe sections (28), elbows (29) and pipe support pier assemblies (30) are provided on the test sections, and thermal resistors (27) are respectively installed at the inlet, middle and outlet of the test sections. Stop valves E (25) and F (26) are respectively installed at the outlets of the indoor test section (19) and the outdoor test section (20). The outlets of the stop valves E (25) and F (26) are combined into one path and connected to the inlet of the stop valve B (22).

3. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 2, characterized in that: The insulation test section (4) is arranged in a U-shaped tube layout.

4. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 2, characterized in that: In the insulation test section (4), the working pipe (31) is covered with a thermal insulation layer (32) and an outer protection layer (33). The pipe support pier assembly (30) includes a support (34) and a concrete pier (35) of the support (34); the upper end of the support (34) penetrates through the thermal insulation layer (32) and the outer protection layer (33) and is connected to the working pipe (31), and the lower end is fixed on the concrete pier (35).

5. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 4, characterized in that: The working pipe (31), thermal insulation layer (32), outer protection layer (33), elbow (29) and support pier assembly (30) used in the insulation test section (4) are all of unified specifications.

6. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 5, characterized in that: The size of the working pipe (31) used in the insulation test section (4) is less than or equal to DN150.

7. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 1, characterized in that: There is an oil drain branch on the connecting pipeline between the electric heater (1) and the circulation oil pump (2), and an oil drain valve (12) is installed on the oil drain branch.

8. The method of using the experimental device for studying the heat dissipation loss characteristics of overhead heating pipelines according to claim 1, characterized in that: The resistance coefficient of the electric control valve A (6) is greater than that of the electric control valve B (7), and the main flow passes through the circulation bypass.

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