**3. Characteristics of the developed passive devices**

The heat pipes and thermosyphon were produced by copper tubes ASTM B-75 Alloy 122 with an outer diameter of 9.45 mm, an inner diameter of 7.75 mm, and a length of 200 mm. The rod was obtained from a full copper bar ASTM B-75 Alloy 122 with the same dimensions of the developed heat pipes and thermosyphon. All the devices had an evaporator of 80 mm


**Table 1.** Main features of the heat transfer passive devices.

**Figure 9.** Welding the capillary end.

**Figure 8.** Filling station with the heat pipe.

360 Bringing Thermoelectricity into Reality

**Figure 10.** Phosphor bronze screen mesh #100. (a) General view (b) micro-scale image.

in length, an adiabatic region of 20 mm in length, and a condenser of 100 mm in length. The working fluid used is distilled water with filling ratios related to the evaporator volume based on the best performance of each capillary structure. **Table 1** shows the main characteristics of the heat transfer passive devices analyzed in this research.

The sintered heat pipe was produced by the sintering process with a copper powder and a temporary mandrel. The average diameter of the copper powder particle is 10.9 μm. The porous structure manufactured has a thickness of 1.5 mm (**Figure 12a**). The microscale image of the capillary structure of sintered copper powder is presented in **Figure 12b**. More informa-

Heat Pipe and Thermosyphon for Thermal Management of Thermoelectric Cooling

http://dx.doi.org/10.5772/intechopen.76289

363

To achieve successful results, the experimental tests must reproduce the operation conditions as close as possible to the application for thermal management of thermoelectric cooling. Then, to evaluate the thermal performance of the analyzed passive heat transfer devices, an

The essential experimental apparatus for the experimental tests, shown in **Figure 13**, is composed of a data logger (*Agilent*™ 34970A with 20 channels), a power supply unit (*Keysight* ™ U8002A), a laptop (*Dell*™), an uninterruptible power supply (*NHS*™), a universal support,

For the evaluation of the temperature of the different heat transfer passive devices, K-type thermocouples *Omega Engineering*™ are used. They should be fixed on the outer surface of devices by a thermosensitive adhesive strip *Kapton*™. They should be distributed in the length of the heat pipes and thermosyphon. Thus, there are three thermocouples in the evaporator (*Tevap*,1, *Tevap*,2, and *Tevap*,3), one thermocouple in the adiabatic section (*Tadiab*) e four thermocouples in the condenser (*Tcond*,1, *Tcond*,2, *Tcond*,3, and *Tcond*,4) in passive devices (heat pipes and thermosyphon), as shown in **Figure 14**. For the rod, two thermocouples were fixed in the evaporator

experimental apparatus and some experimental procedures were used.

tion about this sintered heat pipe can be found in [26].

**4. Experimental tests**

**4.1. Experimental apparatus**

**Figure 13.** Experimental apparatus.

and a fan (*Ultrar*™).

The mesh heat pipe used one layer of phosphor bronze screen mesh #100 (**Figure 10a**) as capillary structure. A microscale image of screen mesh #100 is shown in **Figure 10b**. The image was obtained by backscattered electron detector (BSD) for scanning electron microscope (SEM). More information about this mesh heat pipe can be found in [23].

The grooved heat pipe shown schematically in **Figure 11a** had 32 microgrooves made by the wire electrical discharge machining (wire-EDM). **Figure 11b** presents the axial microgrooves details with an average diameter of 220 μm by a micro-scale image. The image was obtained by backscattered electron detector (BSD) for scanning electron microscope (SEM). More details about this heat pipe can be found in [24, 28].

**Figure 11.** Microgrooves made by wire-EDM. (a) Scheme of microgroove profile and (b) microscale image.

**Figure 12.** Structure sintered copper powder. (a) General view and (b) microscale image.

The sintered heat pipe was produced by the sintering process with a copper powder and a temporary mandrel. The average diameter of the copper powder particle is 10.9 μm. The porous structure manufactured has a thickness of 1.5 mm (**Figure 12a**). The microscale image of the capillary structure of sintered copper powder is presented in **Figure 12b**. More information about this sintered heat pipe can be found in [26].
