Experimental research of novel aluminium-ammonia heat pipes

Available online at www.sciencedirect.com

ScienceDirect

Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000

ScienceDirect

www.elsevier.com/locate/procedia

Procedia Engineering 205 (2017) 3923–3930

10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China

Experimental research of novel aluminium-ammonia heat pipes Kaimin Yanga,b,c*, Yudong Maoa,b,c, Zhuang Congd, Xiuli Zhanga bb

a a School of Thermal Engineering, Shandong Jianzhu University, Jinan 250101, China Key Laboratory of Renewable Energy Technologies for Buildings, Ministry of Education, Jinan 250101, China cc Shandong Key Laboratory of Renewable Energy Technologies for Buildings, Jinan 250101, China d d Zhongshi Yitong Group, Jinan 250101, China

Abstract The axial heat pipe with Ω-shaped grooves can not only increase the permeability for liquid, but also reduce the flow resistance between the vapor and water greatly. In this paper the thermal characteristics of aluminum-ammonia heat pipes with Ω-shaped grooves were investigated. The conclusion is that the heat pipe has a good ability of dynamic response. With the same operating temperature, the differences between evaporation section and condensation section increase with increasing the input power. The maximum and minimum temperatures of the heat pipes are respectively at the end of the heating section and the beginning of the condensing section. The equivalent thermal conductivity of the heat pipe increases with the increase of the operating temperature, and increases with the increase of input power and liquid filling rate. The total thermal resistance of the heat pipe decreases with the increase of input power, and the heat resistance is the smallest when the angle of heat pipe is 60°. With the increase of the liquid filling rate, the maximum heat transfer capacity of the heat pipe increases, but the amplitude is getting smaller and smaller. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords: Grooved heat pipe; Equivalent heat conductivity; Thermal resistance; Maximum heat transfer capacity

1. Introduction Heat pipe is a reliable and efficient heat transport device, and has been widely used now[1]. Grooved heat pipe provides capillary force by means of micro channels of different shapes in the axial direction of the tube. Compared to the sintered metal core wick structure it has greater porosity, and the channel processing has the advantages of * Corresponding author. Tel.: +086-0531-86361236; fax: +086-0531-86361236. E-mail address: [email protected] 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.032

Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930 Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000

3924 2

simple process, high reliability, it has extremely important significance in space applications and electronic cooling[2]. At present, the research on the grooved heat pipe at home and abroad[3-9] mainly focus on regular groove shape, such as the rectangular, triangular and trapezoidal. Few research on the one with Ω-shaped groove, which are relatively difficult to manufacture, but has better heat transfer performance[10]. Therefore, this paper takes a novel aluminum-ammonia heat pipe as the research project. The axial grooved heat pipe has been designed and processed, and the dynamic response characteristics of the Ω-shaped axial channel are obtained. Also, the heat transfer performance of the heat pipe is studied and the maximum heat transfer capacity of the heat pipe at different operating temperatures is obtained. 2. Heat pipe processing The heat transfer performance of the heat pipe is directly related to the manufacturing process. Therefore, some improvements have been made in the processing and manufacturing process of the experimental object. The experiment object is aluminum-ammonia grooved heat pipe, and the shell material of heat pipe is aluminium alloy 6063. Due to the particularity of the Ω-shape grooved heat pipe’s structure, as shown in Figure. 1, the conventional heat pipe manufacturing process is no longer applicable. The most important part of the heat pipe manufacturing process is cleaning, filling and packaging, it can be seen from Figure. 1 that the cleaning of the Ω-shaped channel is difficult, so it is necessary to improve the existing conventional cleaning method and solve the problem well by introducing ultrasonic technology.

Fig. 1. Cross section parameters of the heat pipe ‫ܦ‬௩ =16mm, ‫ܦ‬௢ =32mm, d=1.2mm, w=0.4mm, δ=0.72mm

In this paper, the ammonia used in the heat pipe is a high-purity NH3 with a purity of 99.9999%, which means the gas-liquid coexistence in the normal state, that is, it is easy to gasification, so it is necessary to avoid the twophase flow effect on the filling process in the measurement. In this paper, by inverting the ammonia tank and cooling the liquid before go into flowmeter and taking some other measures to ensure that the flow measurement of ammonia has been carried out in the form of liquid, and the use of flowmeter and metering pump two flow measuring equipment simultaneously to measure the liquid ammonia can make the final filling accuracy of heat pipe reach to 0.01g. Most of the existing heat pipe experiments cannot achieve the complete package[11-13], the experimental pieces rely on the valves to achieve the seal, and this will have a negative impact to the performance of the heat pipe and experimental work. Aiming at this phenomenon, using small caliber liquid filling pipe to reduce the problem of filling working medium and the package needing to deal with the structure of large dimensions. Sealing of the heat pipe is efficient, and the final shape does not affect the use of heat pipe. 3. Experimental method 3.1. Experimental Facilities The experimental device used in this paper is the same as that used in before work[14], shown in figure 1. The length of the heat pipe tested in this experiment is 1.0m, and the thermocouple is evenly arranged along the axis of



Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930 Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000

3925 3

the heat pipe in the heating section, the insulation section and the condensation section. There are 17 measuring points total along the heat pipe.

Fig. 2. Schematic of experimental set up 1-heat pipe, 2-thermocouples, 3-electrical heaters, 4-DC electrical source, 5-watercooling jacket, 6thermostatic waterbath, 7-data acquisition system, 8-computer, 9-insulating layer

3.2. Experimental Data Processing The temperature of each measure point in evaporation section, adiabatic section and condensation section, respectively, is average of that measuring at the last one minute in steady stage: 60

ti =  tn / 60

（1）

n =1

The temperature of evaporation section, adiabatic section and condensation section, respectively is average of point temperature which locate in each section: Ne

tw,e =  ti / N e n =1

Na

tw,a =  ti / N a n =1

Nc

tw,c =  ti / N c

（2）

n =1

Taking the average of temperature at each measure point in adiabatic section as the temperature of working medium, that is the working temperature of heat pipes:

t work ≅ t v,a = t w,a

（3）

The axial temperature difference is temperature difference between evaporation section and condensation section:

Δtaxi = tw,e − tw,c Using Equivalent Thermal Conductivity to evaluate the performance of heat pipe[14].

（4）

Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930 Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000

3926 4

4. Results and discussion 4.1. Head load response characteristics The response time to the heat load during the start and shutdown stage is an important parameter that reflects the performance of the heat pipe. In this paper, the transient response of the heat pipe in the process of starting and closing down is studied. Figure 3 shows how the temperature changes with different input powers, when the heat pipe works at different cold source temperatures. Figure 3 shows the heat source temperatures were set at 5℃ and 25℃ respectively. Shut down the heat pipe after heating for 10min immediately, then keep the experimental system running for another 10min. During that the temperature of the evaporation section, insulation section and the condensation section changes, which shown in Figure 3. From the analysis of the data, it can be seen: with different cold source temperature, the heat pipe’s starting and closing down characteristics are basically the same. The sharp rising of the heat pipe temperature mainly occurs in the first 4 minutes, during which the temperature and pressure of the ammonia in the heat pipe are rapidly increased, and then the temperature promotion become slow after reaching a certain value, finally reaches to the saturated temperature and saturated pressure. After closing the heat source, the heat pipe temperature can basically reach to the same as that of the cold source within 3-6mins. The temperature change is similar to the startup process, it has quickly reduced at the beginning and then slow-changing until it is stable. At the same cold source temperature, with the increase of input power, both the start and shut down of the heat pipe are faster, but it takes longer to reach steady state, meanwhile the corresponding temperature on the whole surface is higher, which also reflects the heat pipe can quickly respond to heating load changing. With the same heating load, when the cold source temperature is higher, both the starting and closing down of the heat pipe take longer time. 45

o

30

o

35

60w 60w 60w 100w 100w 100w

55

Temperature( C)

40

Temperature( C)

60

60W 60W 60 W 100W 100W 100W

25 20 15

50 45 40 35 30

10

25

5 0

200

400

600

800

1000

1200

0

200

400

T (s)

(a) Tc=5℃

600

800

1000

1200

1400

T (s)

(b) Tc=25℃ Fig. 3. The profile of temperature of heat pipe

4.2. Temperature distribution Figure 4(a) shows the axial temperature distribution at different operating temperatures (0℃, 4℃, 8℃, 12℃, 16 ℃ , 20 ℃ ) when the heat pipe is placed vertically, and Figure 4(b)-(d) for the fixed heat pipe operating temperatures, different input powers. From Figure 4(b)-(d), the temperature difference between the hot and cold section of the heat pipe increases with the increase of heating power. The maximum temperature of the evaporation section appears near the 3rd point of the measuring point. The steam in the heat pipe is heated and moved along the cavity of the tube to the condensing section. During the process, the fluid has continually been heated and the temperature is rising. Meanwhile, the temperature rise increases with the increase of input power. With higher input power, the larger heat flux density has been set to the local surface near to the 3rd point, so the liquid ammonia vaporizes here greater than other locations.



Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930 Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000

3927 5

With the input power increases, the temperature difference between evaporation section and condensing section may increase sharply, that means the maximum heat transport capacity of heat pipe. The temperature in the insulation section is consistent, which is related to the working characteristics of the heat pipe, but also to the experimental process with good insulation effect. The lowest temperature of the heat pipe appears at the measuring point 12, which is the intersection of the condensing section and the adiabatic section. That may be because the position is the place where cooling oil go into the system, and the cooling effect is good. 26 24

o

20

4C o 12 C o 20 C

20

16

Temperature( C)

14

o

o

Temperature( C)

18

20W 40W 60W 80W 100W 120W

25

o

0C o 8C o 16 C

22

12 10 8 6 4

15 10 5

2 0

0 -2 -4

-5

0

2

4

6

8

10

12

14

16

18

0

2

4

6

8

28 24 22 20

34

16

18

20W 40W 60W 80W 100W 120W

32 30 28 26

Temperature( C)

18

o

o

14

36

20W 40W 60W 80W 100W

26

Temperature( C)

12

（b）Tw=12℃

（a）

16 14 12 10 8

24 22 20 18 16 14 12 10

6

8

4 2

10

Temperature measure points in the axial direction

Temperature measuring point in the axial direction

6

0

2

4

6

8

10

12

14

16

Temperature measure points in the axial direction

18

4

0

2

4

6

8

10

12

14

16

18

Temperature measure points in the axial direction

（c）Tw=16℃

（d）Tw=20℃ Fig. 4. The axial temperature distribution of heat pipe

4.3. equivalent thermal conductivity Figure 5(a)-(c) shows the variation trend of the equivalent thermal conductivity of the heat pipe at different operating temperatures when the liquid filling rate ranges from 0.8 to 1.4, respectively, Figure 5(d) is a comparison of the equivalent thermal conductivity of a heat pipe with different liquid filling rates at the same operating temperature. It can be seen from Figure 5, the equivalent thermal conductivity of the heat pipe varies with the input power changing at different operating temperatures. At the same operating temperature, the equivalent thermal conductivity increases with the increase of input power. At the same input power, the equivalent thermal conductivity increases with the increase of operating temperature. At the same operating temperature, the equivalent thermal conductivity increases basically with the increase of liquid filling rate. In Figure 5(d), the fluctuation of the curve with a liquid filling rate of 1.0 is due to the uncertainty of the experimental data, but still in a reasonable range.

6 3928

28000

28000

27000

27500 27000 26500

26000 25000 24000 23000 o

Tw=20 C o Tw=10 C o Tw=0 C

22000 21000 20000 19000

20

40

60

80

100

Equivalent thermal conductivity(W/mK)

Equivalent thermal conductivity(W/mK)

Kaimin Yang,Yang et al./etProcedia Engineering 00 (2017) 000–000 Kaimin al. / Procedia Engineering 205 (2017) 3923–3930

26000 25500 25000 24500 24000 23500 23000 22500

o

Tw=20 C o Tw=10 C o Tw=0 C

22000 21500 21000 20500 20000 20

40

60

(a) FR=0.8

120

31000

30000 29000 28000 27000 26000 o

25000

Tw=20 C o Tw=10 C o Tw=0 C

24000 23000 22000 21000 20000 20

40

60

80

100

Input power(W)

(c) FR=1.4

120

140

Equivalent thermal conductivity(W/mK)

Equivalent thermal conductivity(W/mK)

100

(b) FR=1.0

31000

19000

80

Input power(W)

Input power(W)

30500 30000 29500 29000 28500 28000 27500 27000 26500 26000

FR=1.4 FR=1.4 FR=0.8

25500 25000 24500 24000 23500 23000

20

40

60

80

100

120

140

Input power(W)

(d) Twork=20℃

Fig. 5. The profile of equivalent thermal conductivity against input power

4.4. Total thermal resistance Figure 6 shows the thermal resistance varies with the input power changing when the liquid filling rate is 1.4. In the range of input power and cold source temperature given in this test, the thermal resistance of the heat pipe is small and fluctuates in the range of 0.11-0.17(K/W). The thermal resistance of the heat pipe decreases gradually with the increase of input power, of which the changing amplitude is also decreasing, and finally tends to remain unchanged, that is the same as mentioned in literature 13. It can be seen from the figure 6, the minimum thermal resistance appears when the inclination angles was set to 60° that means the inclination angle has a certain influence on the heat transfer of the heat pipe. 4.5. Maximum heat transfer capacity Figure 7 shows the maximum heat transfer capacity of the heat pipe varies with the operating temperature changing. It can be seen from the figure, the best operating temperature of the heat pipe is 20℃, and the maximum heat transfer capacity of the heat pipes with the liquid filling rate of 0.8, 1.0 and 1.4 is 67W, 80W and 82.4W respectively. The maximum heat transfer capacity of the heat pipe increases with the increase of the liquid filling rate, but after the liquid filling rate is more than 1.0, the increase of the liquid filling rate has no obvious effect on the heat transfer capacity.

7 3929

Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000 Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930



90

Total resistance(K/W)

o

0 o 30 o 60 o 90

0.155 0.150 0.145 0.140 0.135 0.130 0.125 0.120 0.115

20

40

60

80

100

Input power(W)

Fig. 6 The profile of total resistance against input power

o

0.160

Aximum heat transport capability( C)

0.165

FR=0.8 FR=1.0 FR=1.4

85 80 75 70 65 60 10

15

20

25

30

o

Working temperature( C)

Fig. 7 The profile of maximum heat transport capability against input power

5. Conclusion In this paper, taking the Ω-shaped axial grooved heat pipe as the research object, its heat transfer performance under different operating temperature and different input power is studied experimentally. The axial temperature distribution, equivalent heat transfer coefficient, equivalent thermal resistance and maximum heat transfer capacity of the heat pipe are obtained. Through analysis, the following conclusions are obtained: heat pipe has a good dynamic response characteristics, with different input power and cold source temperature, it can be quickly started or closed down. At the same operating temperature, the temperature difference between evaporation section and condensation section increases with increasing the input power. The maximum and minimum temperatures of the heat pipes are respectively appear at the end of the evaporation section and the first point of the condensing section respectively. The equivalent thermal conductivity of the heat pipe increases with the increase of the operating temperature, and increases with the increase of input power and liquid filling rate. The total thermal resistance of the heat pipe decreases with the increase of input power, and the heat resistance is the smallest when the inclination angle of heat pipe is 60°. With the increase of the liquid filling rate, the maximum heat transfer capacity of the heat pipe increases, but the increase amplitude is getting smaller and smaller. Acknowledgement This paper is supported by Research Fund for the Doctoral Program of Shandong Jianzhu University (0000601337), and Natural Science Foundation of Shandong Province of China (ZR2016EEB15). References [1] Ji Shaobin, Li Shengsheng. Application and development of heat pipes. ShanXi Architecture, 2005, 31(13):140-141. [2] Zhuang Jun, Zhang Hong. Heat Pipe Technology and Engineering Application. Beijing: Chemical Industry Press, 2000. [3] Yan Y. H., Ochterbeck J. M.. Analysis of supercritical startup behavior for cryogenic heat pipe. Journal of Thermophysics and Heat Transfer, 1999, 13(1): 140-145. [4] Thamas S. K., Lykins R. C., et al. Fully developed laminar flow in trapezoidal grooves with shear stress at the liquid-vapor interface. Int. Journal of Heat and Mass Transfer, 2001, 44(18): 3397-3412. [5] Jiao A. J., Riegler R., Ma H. B., et al. Thin film evaporation effect on heat transport capability in a grooved heat pipe. Microfluidics and Nanofluidics, 2005, 1(3): 227-233. [6] Suman B., De S. S., Dasgupta S.. Transient modeling of micro-grooved heat pipe. Int. Journal of Heat and Mass Transfer, 2005, 48(8): 16331646. [7] ZHU Wangfa, CHEN Yongping, et al. Flowing and Heat Transfer Characteristics of Heat Pipe with Axially Swallow-tailed Microgrooves. Journal of Astronautics, 2009, 30(6): 2380-2386. [8] R. Hopkings, A. Faghri, D.. Khrustalev. Flat miniature heat pipes with micro capillary grooves. J. Heat Transfer, 1999.

3930 8

Kaimin Yang et al. / Procedia Engineering 205 (2017) 3923–3930 Kaimin Yang, et al./ Procedia Engineering 00 (2017) 000–000

[9] Fan Chunli, Qu Wei, et al. The Influence of Gravitation on the Heat Transfer Performance of Micro-grooved Flat-plate Heat Pipes. Journal of Engineering for Thermal Energy And Power, 2004, 19 (1): 33-37. [10] Zhang Chengbin, Shi Mingheng, et al. Flow and heat transfer characteristics of heat pipe with axial “Ω”-shaped grooves. Journal of Chemical Industry and Engineering, 2008, 3: 544-550. [11] A. Alizadehdakhel, M. Rahimi, A. A. Alsairafi. CFD modeling of flow and heat transfer in a thermosyphon．International Communications in Heat and Mass Transfer, 2010, 37: 312–318. [12] A. P. Annamalai, V. Ramalingam, Experimantal investigation and computational fluid dynamics analysis of air cooled condenser heat pipe. THERMAL SCIENCE, 2011, 15(3): 759-772. [13] Qu Yan, Luan Tao. The experiment research of heat pipes with axial grooves in the gravitational field. Shandong University, 2005. [14] Yang Kaimin, et al. Mechanism Analysis and Experimental Study of Heat Transfer in Axial Grooved Heat Pipes. Shandong University, 2013.