CN107870179A - Method for measuring thermal contact resistance of asphalt concrete - Google Patents

Abstract

The invention discloses a kind of method for measuring bituminous concrete thermal contact resistance, the thermal contact resistance tested using thermal-flow sensor test method(s) between bituminous concrete and heat exchange pipeline, the seamless steel pipe arranged by burying temperature sensor, heat flow transducer and winding type in test specimen, temperature sensor is embedded among test specimen, respectively away from surface 20mm, 40mm, 60mm, 80mm；Heat flow transducer is fixed on the outer wall of seamless steel pipe interlude steel pipe, and steel pipe is away from surface of test piece 80mm；After test material preparation, surrounding is wrapped up using heat-insulating heat-preserving material, causes heat as far as possible only along gravity direction transmission, is used as thermal source using infrared lamp during thermal-arrest, be can control the different in flow rate and heat transferring medium of temperature to flow in pipe；After the temperature difference and the hot-fluid that measure contact interface, according to the definition of thermal contact resistance, you can thermal contact resistance is calculated.Computational methods of the present invention according to thermal contact resistance, can obtain the situation of change of thermal contact resistance under different gradation, different thermal conductivity factor test specimens, different temperatures.

Description

Method for measuring thermal contact resistance of asphalt concrete

technical field

The invention belongs to the technical field of road engineering materials, in particular to a method for measuring contact thermal resistance of asphalt concrete.

Background technique

Asphalt pavement has a strong solar radiation absorption capacity (absorption rate of 0.3-3μm wavelength is 0.86-0.90), and the maximum temperature of the pavement can reach 70°C. Under the coupling effect of temperature and load, the pavement is prone to rutting, wrapping, and moving Such as permanent deformation damage, thus greatly reducing the service life of asphalt pavement. In addition, the temperature of the road surface also has a huge impact on the atmospheric temperature. About 95% of the solar energy absorbed by the road surface is released to the environment in the form of sensible heat and long-wave radiation. The slow heat dissipation process is an important factor that intensifies the urban "heat island effect". Asphalt pavement solar collector (APSC) can collect this part of energy and reduce the temperature of the pavement. By embedding heat exchange pipes inside the asphalt pavement, the heat exchange medium can be used to take away the solar energy absorbed by the asphalt pavement in high temperature seasons. In addition, the absorbed energy can be used for domestic water heating, auxiliary heat source for ground source heat pump systems in cold areas, and snow and ice melting on road surfaces in winter (combined with cross-seasonal energy storage technology) according to different needs.

In recent years, solar heat collecting asphalt pavement has received more and more attention, and its heat collecting performance, influencing factors and optimal design are hot issues of concern. In fact, the optimization of APSC heat collection performance depends on the in-depth understanding of its heat transfer characteristics. Compared with ordinary asphalt pavement, the heat transfer process of APSC is more complicated, especially the contact thermal resistance between concrete and heat exchange pipes, which is the key link affecting the heat collection performance of APSC.

The present invention intends to study a method for measuring the contact thermal resistance of asphalt concrete on the basis of research at home and abroad. The research results can deepen the understanding of the heat transfer characteristics of solar collector asphalt pavement, which is of great significance for the development of corresponding drag reduction measures and the improvement of APSC heat collection performance.

Contents of the invention

The purpose of this invention is to provide a method for measuring the contact thermal resistance of asphalt concrete, based on the real contact state between asphalt concrete and heat exchange pipes, using the self-developed heat flow sensing test method to accurately measure the contact thermal resistance between the two .

The object of the present invention is achieved by the following technical solutions: the method for measuring the thermal contact resistance of asphalt concrete comprises the following steps:

Step 1: Prepare a cuboid-shaped asphalt mixture specimen;

Step 2: Embed 4 temperature sensors, 1 heat flow sensor and 1 seamless steel pipe in the test piece. The 4 temperature sensors are buried in the middle of the test piece, 20mm, 40mm, 60mm, and 80mm away from the upper surface of the test piece; seamless The steel pipe is composed of two U-shaped openings with opposite opening directions. The heat flow sensor is set on the outer wall of the steel pipe in the middle parallel section of the seamless steel pipe, and is adjacent to the temperature sensor set at a distance of 80mm from the upper surface of the test piece. 80mm on the surface;

Step 3: using a radiant light source to heat the test piece, and after starting the heating, collect the temperature of each measuring point of the asphalt concrete measured by the temperature sensors set at 20mm, 40mm, and 60mm from the upper surface of the test piece at intervals of 30 minutes, and The temperature T _p and heat flow q _p of the outer wall of the seamless steel pipe measured by the temperature sensor and heat flow sensor set at 80 mm from the upper surface of the test piece, and the asphalt concrete For the temperature of each measuring point, use the least square method to fit and extrapolate the data to obtain the temperature T _a at the interface of asphalt concrete at different times. According to Fourier's law, derive the fitted temperature-time curve to obtain different heat flux q _a at the interface of asphalt concrete at time;

Step 4: Bring T _a , T _p , q _a and q _p into the formula The thermal contact resistance R _C of asphalt concrete can be obtained when heated at different times;

Step 5: When the temperature is heated to the maximum value, that is, when the fluctuation of the temperature value is small, stop the radiation light source to heat the test piece, and pass the heat exchange medium into the seamless steel pipe. After the heat exchange medium is started, every 30 minutes , collect the temperature of each measuring point of asphalt concrete measured by the temperature sensors set at 20mm, 40mm, and 60mm from the upper surface of the test piece, and the temperature of the outer wall of the seamless steel pipe measured by the temperature sensor and heat flow sensor set at 80mm from the upper surface of the test piece. For temperature T _p ' and heat flow q _p ', the collection can be stopped after the temperature of each measuring point is stable. According to the temperature of each measuring point of asphalt concrete measured by the temperature sensor installed at 20mm, 40mm, and 60mm on the upper surface of the specimen, the minimum two The data is fitted and extrapolated by multiplication to obtain the temperature T _a ' at the interface of asphalt concrete at different times. According to Fourier's law, the fitted temperature-time curve is derived to obtain the heat flow at the interface of asphalt concrete at different times density q _a ';

Step 6: Bring T _a ', T _p ', q _a ' and q _p ' into the formula The contact thermal resistance R _C ' of asphalt concrete at different cooling times can be obtained.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention adopts self-developed heat flow sensing test method, and the measuring device mainly includes radiation light source, heat flow sensor, temperature sensor, asphalt concrete rutting specimen, test bench, heat exchange working medium, water pump and assembly accessories, and measuring device It is easy to obtain in the market and economical.

(2) According to the calculation method of contact thermal resistance, the change of contact thermal resistance at different gradations, different thermal conductivity test pieces, and different temperatures can be obtained.

Description of drawings

Fig. 1 is a schematic diagram of the heat flow sensing test method of the present invention.

Fig. 2 is a schematic diagram of embedding heat exchange pipes (seamless steel pipes) according to the present invention.

Fig. 3 is that the present invention adopts AC-5 gradation curve diagram.

Fig. 4 is the gradation curve diagram of AC-10 adopted by the present invention.

Fig. 5 is a gradation curve diagram of AC-20 used in the present invention.

Detailed ways

Based on the definition of thermal contact resistance and Fourier’s law of heat conduction, by embedding heat exchange pipes, temperature sensors, and heat flow sensors inside the rutting specimen, a heat flow sensing test method was designed to measure the thermal contact resistance, and the irradiance intensity, cycle Water temperature, specimen insulation and other test conditions.

In order to ensure the accuracy of the burial depth of the temperature sensor (2, 4, 6cm and 8cm) and the heat flow sensor (8cm) in the present invention, the rut specimen is prepared by layered rolling molding, wherein the wiring of the sensor Lead out through drilling; fix the position of the sensor and heat exchange pipe during rolling to avoid sinking and displacement.

The preparation of the test piece of the present invention is designed according to the following indicators:

(1) Raw materials

Raw materials mainly include coarse aggregate, fine aggregate, mineral powder, SBS modified asphalt, and thermally conductive phase filler graphite (used to improve the thermal conductivity of asphalt mixture). Coarse aggregate and fine aggregate are Zhenjiang Maodi limestone, mineral powder is limestone mineral powder, and graphite is graphite powder produced by Tianjin Dengke Chemical Reagent Co., Ltd. The performance indexes of each raw material are shown in Table 1 to Table 5.

Table 1 Performance indicators of SBS modified asphalt

Table 2 Coarse aggregate performance test results

Table 3 Fine aggregate performance index

Table 4 limestone slag performance test results

Table 5 Main Properties of Graphite

(2) The gradation used in the preparation of the test piece

In order to evaluate the impact of different graded asphalt mixtures on contact thermal resistance, the present invention adopts three kinds of graded grades of AC-5, AC-10 and AC-20 with different maximum nominal particle sizes, and the results are as shown in Figure 3- 5.

Example

1. To prepare full-thickness rut plate specimens (300mm×300mm×150mm), three 5cm rut plate molds and two 3cm rut plate molds are required, and holes should be drilled around the molds so that the sensor can pass through the holes (to prevent the rut instrument from being pressed in real time. heat flow sensor and temperature sensor are cut off). The whole test piece is composed of the first test piece, the second test piece, the third test piece and the fourth test piece, and the embedding positions of the first sensor, the second sensor, the third sensor and the fourth sensor are respectively above Surface 2cm, 4cm, 6cm, 8cm.

First prepare the first test piece with a height of 8 cm, and dig 1 cm down to pass the seamless steel pipe (outer diameter 20 mm, inner diameter 16 mm) through the hole to form a steel pipe with three parallel sections and two U-shaped sections in the opposite opening direction It is seamlessly connected, and the distance between the three parallel sections is 100mm. The layout is shown in Figure 2. Embed a heat flow sensor and a fourth temperature sensor on the outer wall of the steel pipe in the middle parallel section of the seamless steel pipe. Both the heat flow sensor and the fourth temperature sensor are located in the middle of the first specimen. In real time, the position of the sensor and the heat exchange pipe needs to be fixed to avoid displacement and sinking), and then stand still for 24 hours; after 24 hours, the second test piece with a height of 2 cm is prepared according to the same method, and the third temperature is set on the second test piece. The sensor is buried in the middle of the test piece, the front of the rutting instrument is compacted 3 times, and the reverse side is compacted 13 times; then a third test piece with a height of 3 cm is prepared, and the second temperature sensor is buried in the middle of the test piece, and the front of the rutting instrument is compacted. 3 times and 13 times on the reverse side; finally prepare the fourth test piece with a height of 2 cm, and bury the first temperature sensor in the middle of the fourth test piece. The preparation of the thick rut plate specimen is completed, and the front view is shown in Figure 1. After standing for 24 hours, the surrounding of the specimen is wrapped with heat-insulating materials.

2. Use 2×275W infrared lamps as the irradiation light source; first simulate the cooling process after the road surface is heated up, that is, heat and wait for the temperature to stabilize, then pass water to cool, and wait for the temperature to reach the maximum value, that is, the temperature fluctuation is small, then stop heating, and send to no Water is passed through the seam steel pipe, and the temperature of the circulating water will increase after repeated cycles. Therefore, tap water can be continuously introduced instead of circulating water, and the room temperature should be kept stable, and the water temperature should be kept within 0.5°C as much as possible. After passing through the water, the test can be ended after the temperature of each measuring point is stable. Take the temperature and heat flux density of each measuring point every 30 minutes; secondly, simulate the process of heating up the road surface and cooling with water at the same time, that is, radiation and water flow at the same time, and end the test after the temperature is stable, and take the temperature of each measuring point every 30 minutes and heat flux density. During the test, the room temperature was controlled at 21±0.5°C, and the temperature of the heat exchange medium (tap water) was 19±0.5°C.

3. The temperature of each measuring point of the asphalt concrete is measured by the temperature sensor, and the temperature T _a of the asphalt concrete interface (at the 7cm of the test piece) is obtained by fitting and extrapolating the temperature of the test piece 9cm, 11cm, and 13cm by the least square method, according to Fourier's law, _by deriving the fitted temperature-time curve _, the heat flux q _a at the asphalt concrete interface (at 7 cm of the specimen) can be obtained; Heat flow sensor measurement; bring the obtained data into the formula The thermal contact resistance R _C can be obtained.

According to the analysis of the above test results, it can be seen that:

① It is feasible to measure the contact thermal resistance between asphalt concrete and heat exchange pipes by using the self-developed heat flow sensing test method. This method can obtain the distribution of temperature and heat flux density in concrete, and it is tried to calculate the contact thermal resistance in the quasi-steady state heat transfer process.

②This method adopts three gradations of AC-5, AC-10 and AC-20 to test asphalt concrete. The contact thermal resistance of AC-5 is smaller than that of AC-10 and AC-20, so AC-5 should be preferred Grading and other fine gradings with smaller nominal particle sizes are used to pave the buried pipe layer of the solar heat collecting asphalt pavement.

③ This method uses graphite to improve the thermal conductivity of asphalt concrete, which can accelerate the transfer of heat to the inside of the specimen and reduce the contact thermal resistance between the concrete and the heat exchange pipe. Therefore, when the road performance and mechanical properties of concrete meet the requirements, asphalt mixture with better thermal conductivity should be used.

④ This method uses different radiation conditions to study the influence of asphalt concrete surface temperature on the thermal contact resistance. It is found that the change trends of the thermal contact resistance of the three gradations are similar. The thermal contact resistance increases with the increase of temperature and tends to be stable at the temperature After that, the contact thermal resistance of the AC-5 grading specimen is still the smallest.

Claims (9)

1. the method for measuring bituminous concrete thermal contact resistance, it is characterised in that comprise the following steps：

Step 1：Prepare the bitumen mixture specimen of rectangular shape；

Step 2：4 temperature sensors, 1 heat flow transducer and 1 seamless steel pipe, 4 TEMPs are buried in test specimen Device is embedded among test specimen, respectively away from test specimen upper surface 20mm, 40mm, 60mm, 80mm；Seamless steel pipe is by opening direction opposite 2 U-shaped compositions, heat flow transducer are arranged on the intermediate parallel section outer wall of steel pipe of seamless steel pipe, and with away from test specimen upper surface 80mm The temperature sensor for locating to set is close to seamless steel pipe is arranged on away from the 80mm of test specimen upper surface；

Step 3：The test specimen is heated using radiating light source, after beginning to warm up, at interval of 30 minutes, gathered away from test specimen Each measuring point temperature of bituminous concrete that the temperature sensor measurement set at upper surface 20mm, 40mm, 60mm obtains, and away from test specimen The temperature T for the seamless steel pipe outer wall that the temperature sensor and heat flow transducer measurement set at the 80mm of upper surface obtains_pAnd hot-fluid q_p, according to the obtained each measuring point temperature of bituminous concrete of temperature sensor measurement set at test specimen upper surface 20mm, 40mm, 60mm Degree, extrapolation is fitted to the data with least square method and obtains the temperature T of bituminous concrete interface at different moments_a, according to Fu In leaf law, the temperature-time curve derivation to fitting, try to achieve the heat flow density of bituminous concrete interface at different moments q_a；

Step 4：By T_a、T_p、q_aAnd q_pBring formula intoIt can obtain pitch when heating at different moments The thermal contact resistance R of concrete_C；

Step 5：Treat that temperature is heated to maximum, stop radiating light source and the test specimen is heated, and be passed through and change into seamless steel pipe Thermal medium, start after being passed through heat transferring medium, at interval of 30 minutes, gather away from setting at test specimen upper surface 20mm, 40mm, 60mm Each measuring point temperature of bituminous concrete that temperature sensor measurement obtains, and away from the temperature sensor set at the 80mm of test specimen upper surface The temperature T of the seamless steel pipe outer wall obtained with heat flow transducer measurement_p' and hot-fluid q_p', it can stop after each measuring point temperature stabilization Only gather, respectively surveyed according to the bituminous concrete that the temperature sensor measurement set at test specimen upper surface 20mm, 40mm, 60mm obtains The data are fitted extrapolation with least square method and obtain the temperature T of bituminous concrete interface at different moments by point temperature_a', according to According to Fourier law, the temperature-time curve derivation to fitting, the hot-fluid for trying to achieve bituminous concrete interface at different moments is close Spend q_a'；

Step 6：By T_a'、T_p'、q_a' and q_p' bring formula intoIt can obtain pitch when cooling down at different moments The thermal contact resistance R of concrete_C'。

2. the method as described in claim 1, it is characterised in that described bituminous concrete uses AC-5, AC-10 or AC-20 Grading.

3. the method as described in claim 1, it is characterised in that the specification of rut test piece is 300mm × 300mm × 150mm.

4. the method as described in claim 1, it is characterised in that the spacing between three parallel-segments of seamless steel pipe is 100mm.

5. the method as described in claim 1, it is characterised in that the external diameter 20mm of seamless steel pipe, internal diameter 16mm.

6. the method as described in claim 1, it is characterised in that bituminous concrete composition include coarse aggregate, fine aggregate, miberal powder, SBS modified pitch and heat conduction phase filling graphite.

7. the method as described in claim 1, it is characterised in that heat transferring medium uses running water.

8. the method as described in claim 1, it is characterised in that radiating light source uses infrared lamp.

9. the method as described in claim 1, it is characterised in that test specimen surrounding is wrapped up using heat-insulating heat-preserving material.