5. Experimental set-up and procedure

For the condenser, they were all fixed with a steel cooling jacket of the same size, with a length of 150 mm and a diameter of 105 mm. The detailed design parameters

Parameters Nomenclature Value External diameter of evaporator (mm) Dhp,o 22 Internal diameter of evaporator (mm) Dhp,in 19.6 T1: internal diameter of vapour channel in three-way fitting (mm) Dtw,in 14 Operating pressure in heat pipe (Pa) Php 1.3 <sup>10</sup>–<sup>4</sup> Evaporator length (mm) Lhp,ev 550 Liquid filling volume (ml) Vfl 85 Transportation line's outer diameter (mm) Dll,o/Dvl,o 22 Transportation line's inner diameter (mm) Dll,in/Dvl,in 19.6 Lengths of vapour/liquid /line (mm) Lvl,T1/Lll,T1 595/445

Mesh screen wire diameter (layer I) (mm) Dowi,ms 7.175 <sup>10</sup>–<sup>2</sup> Mesh screen layer thickness (layer I) (mm) <sup>d</sup>owi,ms 3.75 <sup>10</sup>–<sup>1</sup> Mesh number (layer I) (/m) Nowi,ms 6299 Mesh screen wire diameter (layer II) (mm) Diwi,ms 12.23 <sup>10</sup>–<sup>2</sup> Mesh screen layer thickness (layer II) (mm) <sup>d</sup>iwi,ms 3.75 <sup>10</sup>–<sup>1</sup> Mesh number (layer II) (/m) Niwi,ms 2362 Mesh screen conductivity (W/m °C) kms 394

Lvl,T2/Lll,T2 595/1145

are illustrated in Table 1.

Recent Advances in Heat Pipes

Figure 3.

Table 1.

56

Design parameters of the proposed GALHP.

Fabrication schematics of the proposed GALHP.

#### 5.1 Experimental set-up and instrumentation

Figure 4 shows the test rig of the proposed GALHP. In the rig, an electrical heating tap with the percentage controller, which acts as the heat source, was evenly attached to the external surfaces of the evaporators. The condenser is covered by a steel cooling jacket that allows cooling water to pass through, removing heat from the condenser. A magnetic regeneration water pump was installed in the cooling water loop to power the cooling water cross. A clamp-supported retort stand was used to adjust the inclination angle of the piping installation. The foamy polyurethane was attached to the pipes to provide a satisfactory insulation. During operation, in order to keep a relatively constant condensation temperature, the water tap would remain open to enable adequate amount of cold water to be fed into the loop. When the water tank was fully charged, the drainage valve would be turned open to allow the extra amount of water to be discharged.

A list of the piping elements and test instruments are provided in Table 2. A number of T-type thermocouples were attached to the external surface of heat pipe walls, and installed in the inlet/outlet and inside of cooling jacket and water tank: there were totally four thermocouples (No. 1–4) equidistantly attached along each heat pipe evaporator wall from top to bottom, which were used to measure the temperature distribution along the evaporator wall and their corresponding average temperature at the evaporation sections; another four thermocouples were respectively placed in the mid of heat pipe condenser wall (No. 7), the inlet/outlet

Figure 4. On-site testing rig.


#### Table 2.

List of piping connectors and experimental instruments.


Q (W)

59

14.4

43.2 129.6 100.8 60 30 90

 15 20 10

2

3

> Table 4.

Comparison

 of testing and simulation

 results of the three heat pipes under different modes.

39.95

 35.99

 40.96

 38.65

 0.9413

 6.26

 8.89 10.81

 0.10

 0.08

 0.11

 0.09

 0.9556

 13.71

 10.65 11.76

 360

 380

 90

 10

1

31.31

40.04

42.11

41.14

46.72

48.90

56.53

56.92

 55.99

 48.65

 0.8827

 8.14

 9.98 7.94

 0.14

 0.17

 0.15

 0.18

 0.9855

 13.76

 12.36 9.42

 320

 370

 49.43

 45.65

 0.9825

 1.30

 5.65 5.97

 0.16

 0.20

 0.13

 0.15

 0.9995

 11.88

 6.19 11.47

 1210

 960

 40.99

 43.28

 36.41

 34.12

 0.8346

 6.61

 8.05 7.34

8.00

6.80

 0.11

 0.10

 0.08

 0.09

 0.27

 0.21

 0.32

 0.32

 0.9533

 18.18

 10.63

8.26

10.26

9.46

 410

Study of a Novel Liquid-Vapour Separator-Incorporated Gravitational Loop Heat Pipe

 280

 780

 840

 u (°)

Tcf (°C)

mcf (l/m)

Teva (exp)

Teva (sim)

CR ()

E (%)

U (%)

R (exp)

R (sim)

CR ()

E (%)

U (%)

 Start-up (s)

DOI: http://dx.doi.org/10.5772/intechopen.86048

(°C/W)

(°C)

Table 3. List of operational modes (parameters) for simulation of the three heat pipes.


#### Table 4. Comparison of testing and simulation results of the three heat pipes under different modes.

Study of a Novel Liquid-Vapour Separator-Incorporated Gravitational Loop Heat Pipe DOI: http://dx.doi.org/10.5772/intechopen.86048

No. Name Model no. Description

7 Black nitrile rubber pipe insulation RS: 486-053 ∅ 22 25 mm

Inclination angle (°)

> 60 30

List of operational modes (parameters) for simulation of the three heat pipes.

Standard 100.8 90 10 0.5 1 0.2 1 14.4 90 10 0.5 1 0.2

2 100.8 90 10 0.5 1 0.2

3 100.8 90 10 0.5 1 0.2

4 100.8 90 10 0.5 1 0.2

5 Magnetically coupled regenerative

6 Heating tapes with percentage

9 1/2" LCD Water fluid flow sensor meter digital display rate turbine

10 Data logger and data recording

List of piping connectors and experimental instruments.

Applied heat load (W)

> 43.2 100.8 129.6

pump

controller

Recent Advances in Heat Pipes

flow meter

equipment

Table 2.

Test mode

Table 3.

58

1 PVC-U ball valve RS: 282-5148 Compression fitting size: 20mm

Omega: HTWC102-004

8 T-type thermocouple RS: 621–2164 Min/max temperature sensed: 0.1°C,

Totton: HPR6/8 Max capacity: 5.5 l/min

Max head: 7.4 m

Length: 1220 mm

200–350°C

range: 0–80°C

Cooling-fluid temperature (°C)

> 15 0.5 20 0.5

TD500 series 3 10 channels DataTaker; 0.16% 5-s interval recording

14.4–288 w; 240 V; 0.5 W

k = 0.035 W/m °C at 0°C 0.037 W/m °C at 20°C 0.040 W/m °C at 40°C Min/max temperature sensed

Probe diameter: 0.3 mm

Flow rate range: 1.5–25.0 l/m, fitting for 1/200, BSP: 0.1 l/m, water temperature

> Flow rates of cooling fluid (l/min)

> > 2 0.2 3 0.2

2 PVC-U hose connector RS: 212-3638 1/2in BSPT MX20 mm 3 George fischer 90° PVC-U elbow RS: 279-0575 25 25 mm, L. 33 mm 4 Armorvin HNA hose RS: 339-9921 Clear 5 m 20 mm ID (No. 5/6) of cooling jacket and the mid of water tank (No. 8) to measure their related average temperature; there were still four more thermal couples applied to measure the temperatures at the vapour (No. 9, 11) and liquid (No. 10, 12) transportation lines; all these thermocouples were further connected to a data logger to record the temperature signals at each testing interval. A control box is provided to adjust the power output of the heating belt, which is considered a thermal load.

#### 5.2 Experimental process

A series of laboratory steady-state tests were carried out and the results of the tests were used to evaluate the thermal performance of the proposed GALHP. The testing conditions are displayed in Table 3. During all the sets of tests, the surrounding air temperature and speed were maintained at 20 2°C and 0.01 m/s, respectively. Under initial test conditions, one parameter is changed and the other parameter remains fixed, enabling the development of a correlation between the heat pipe's heat output and associated operating parameters. Once the steady-state conditions have been achieved, the test period is successive 10 h period. The measurement data will be recorded at 5-s interval and logged into the computer system using the DT500 data logger to enable the follow-up analyses to be undertaken.

### 6. Computer model validation using the experimental results

Table 4 provides the comparison between the testing and the simulation results under all selected testing conditions. The mean correlation coefficient (CR) was found no less than 0.8346 and the root mean square percentage deviation (E) was below 18.18%. This indicated that the developed simulation model could predict the thermal performance at a reasonable accuracy. The differences resolved above may be caused by theoretical and/or inaccurate measurements. From the theoretical side, some simplified assumptions and empirical equations were involved; from the experimental side, a few of the uncertainties addressed above may be the potential reasons for the deviation. Based on these considerations, the errors may be attributed to the theoretical inaccuracies and it would be better for the simulation model to be refined to further improve its accuracy in making predictions based on the experimental results.

Author details

and Xinru Wang<sup>4</sup>

\*, Chuangbin Weng<sup>2</sup>

1 School of Engineering, University of Hull, UK

\*Address all correspondence to: xudong.zhao@hull.ac.uk

provided the original work is properly cited.

Technology, Guangzhou, China

, Xingxing Zhang<sup>3</sup>

2 School of Civil and Transportation Engineering, Guangdong University of

Study of a Novel Liquid-Vapour Separator-Incorporated Gravitational Loop Heat Pipe

DOI: http://dx.doi.org/10.5772/intechopen.86048

3 Department of Energy, Forest and Built Environments, Dalarna University,

4 Department of Architecture and Built Environment, University of Nottingham,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

, Zhangyuan Wang<sup>2</sup>

Xudong Zhao<sup>1</sup>

Falun, Sweden

Ningbo, China

61

#### 7. Conclusion

This chapter reported the study of a novel liquid-vapour separator-incorporated gravity-assisted loop heat pipe (GALHP), which was designed, constructed, and tested. A parallel comparison between simulation and experimental results was made.

Under the specified operational conditions, the start-up timing of the proposed GALHP was 410 s. The overall thermal resistance was 0.11°C/W, indicating that it has small heat transfer resistance owing to its unique structure that led to the even liquid film distribution and thus reduced flow resistance. The actual effective thermal conductivity was 29,968 W/°C m, indicating that it achieved significant improvement in terms of heat transfer. All of these data provide evidence that the proposed GALHP is a super-performance heat transfer device that can be widely used in gravity-assisted heat transfer operations to achieve significant thermal management in a variety of practical applications.

Study of a Novel Liquid-Vapour Separator-Incorporated Gravitational Loop Heat Pipe DOI: http://dx.doi.org/10.5772/intechopen.86048
