SCIENCE CHINA Technological Sciences, Volume 61 , Issue 11 : 1732-1744(2018) https://doi.org/10.1007/s11431-018-9252-9

## Thermal design of a novel heat sink cooled by natural convection with phase transition in the series loop

• AcceptedApr 9, 2018
• PublishedJun 14, 2018
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### Abstract

In this paper, a novel heat sink, cooled by natural convection, with phase transition in the circulation loop was designed, and the heat sink was applied on averaging temperature and cooling the electronic equipment. The working fluid in the heat sink was driven by the capillary pump. Numerical simulations were performed, to study the heat transfer performance of two systems with various heating power, filling ratios and refrigerants. The influences of above elements on temperature uniformity of two systems were also studied and the thermal performances of two systems were compared. The volume of fluid (VOF) model was utilized to simulate fluid motion in ANSYS FLUENT. The simulation results indicate that the temperature differences of the system comprising two substrates (system 1) are very small under suitable filling ratio conditions, and the thermal performance of system 1 is preferable to the system comprising one substrate (system 2) at the same volume. Besides, the simulation results also show that the system using R245fa possesses excellent temperature uniformity for the same filling ratio and heating power. Finally, the experiments were investigated and the experimental results proved the correctness of the theoretical model.

### Funded by

the National Natural Science Foundation of China(GrantNo.51225602)

### Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant No. 51225602).

### References

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• Figure 1

(Color online) Structure of cooling system 1 (unit: mm). (a) Horizontal direction; (b) vertical orientation.

• Figure 2

Sectional view of flow passages and fins (unit: mm).

• Figure 3

The cross-section views of the capillary pump (unit: mm). (a) Radial view; (b) axial view.

• Figure 4

(Color online) The circulation flow of working fluid in the looped flow passages of system 1.

• Figure 5

(Color online) Structure of cooling system 2 (unit: mm). (a) Horizontal direction; (b) vertical orientation.

• Figure 6

(Color online) The circulation flow of working fluid in the looped flow passages of system 2.

• Figure 7

(Color online) The input power of system.

• Figure 8

(Color online) The experimental device.

• Figure 9

The thermocouple locations.

• Figure 10

(Color online) Contours of temperature of substrate. (a) Evaporation substrate; (b) condensation substrate.

• Figure 11

(Color online) Contours of phase volume fraction and velocity vector. (a) System 1; (b) system 2.

• Figure 12

(Color online) Maximum temperature difference of (a) evaporation substrate and (b) condensation substrate vs heating power.

• Figure 13

(Color online) Average temperature difference of two substrates vs heating power.

• Figure 14

(Color online) Maximum temperature difference of the substrate vs filling ratios for R245fa, R1233zd and R134a.

• Figure 15

(Color online) Maximum temperature of system 2 vs filling ratios for R245fa, R1233zd and R134a.

• Figure 16

(Color online) Maximum temperature difference of the substrate vs heating power.

• Figure 17

(Color online) Maximum temperature of system 1 and system 2 vs heating power (filling ratio 50%).

• Figure 18

(Color online) Maximum temperature difference of the substrate in system 1 and system 2 vs heating power (filling ratio 50%).

• Table 1   Table 1Structure parameters of system 1
 Parameters Value (mm) Length of substrate 700 Width of substrate 370 Thickness of substrate 2 Spacing between two substrates 85 Length of right channel 610 Length of left channel 670 Height of channel 8 Width of channel 2 Spacing between flow passages 17 Length of right fin 580 Length of left fin 640 Height of fin 40 Thickness of fin 0.5 Internal spacing of fin 10 External spacing of fin 12 Diameter of capillary pump 40 Length of capillary wick 210 Diameter of capillary wick 30 Diameter of liquid passage 12 Height of vapor passage 3
• Table 2   Table 2The heating power
 Total power (W) Q1 (W) Q2 (W) Q3 (W) Q4 (W) 500 150 135 110 105 400 120 108 88 84 300 90 81 66 63 200 60 54 44 42 100 30 27 22 21
• Table 3   Table 3The convective heat transfer coefficients
 Qin(W) System 1 System 2 hlf,in hlf,out hrf,in hrf,out hs hf,in hf,out hs 100 0.97 1.91 1.08 2.06 2.65 1.33 2.37 2.82 200 1.38 2.42 1.52 2.57 2.93 1.82 2.89 3.11 300 1.69 2.76 1.86 2.92 3.14 2.14 3.20 3.30 400 1.98 3.04 2.15 3.20 3.30 2.42 3.46 3.46 500 2.11 3.17 2.29 3.36 3.38 2.61 3.63 3.56
• Table 4   Table 4Grid independent check
 Mesh size(cells) System 1 System 2 1656589 919863 581983 1143527 751847 445805 ΔTs,rs (K) 3.43 3.94 3.55 7.63 8.10 8.42 ΔTs,ls (K) 1.66 2.06 1.8 ΔTs,ds (K) 0.45 0.55 0.51 – Tmax (K) 362.69 363.14 362.96 375.40 375.06 374.75
• Table 5   Table 5Maximum temperature difference of substrate and maximum temperature in system 1
 R134a R1233zd R245fa 10% 30% 60% 10% 30% 60% 10% 30% 60% ΔTs,rs (K) 6.44 6.13 5.82 5.02 4.20 4.07 4.88 3.23 3.03 ΔTs,ls (K) 4.19 3.79 3.53 3.02 2.17 2.08 2.93 1.70 1.59 ΔTs,ds (K) 2.07 1.71 1.59 1.53 1.12 1.06 1.27 0.47 0.44 Tmax (K) 359.46 358.92 358.48 358.23 357.72 357.43 358.22 356.55 356.37
• Table 6   Table 6Comparison between experimental and simulation data of system 1 for heat load 400 W
 Filling ratio (%) $T¯e,ls$(K) $T¯s,ls$(K) $T¯e,rs$(K) $T¯s,rs$(K) $ΔTe,ls$(K) $ΔTs,ls$(K) $ΔTe,rs$(K) $ΔTs,rs$(K) $ΔTe,ds$(K) $ΔTs,ds$(K) 40 327.50 330.75 331.06 330.97 3.97 1.71 7.53 3.22 3.56 0.22 50 327.71 330.76 330.18 330.98 3.26 1.72 5.50 3.18 2.47 0.22 60 327.59 330.80 330.17 331.00 3.20 1.59 5.10 3.03 2.58 0.20

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