2.1 Construction of thermosyphon heat pipe

Thermosyphon is a vessel closed at both ends and attached with a small charging pipe placed at one of the ends. The air in the vessel is evacuated creating a vacuum, then charged with working fluid through the charging pipe. The pipe is usually divided into the following sections:


The materials for the manufacturing of thermosyphon are carefully selected to ensure its effective performance. Other considerations are the type and the quantity of working fluid to be charged into the pipe.

#### 2.2 Operation of thermosyphon heat pipe

The working principles of thermosyphon are similar to that of the wick heat pipe, but differ in the process of the return of the condensed liquid in the condenser due to the absence of wick structure. For proper operation of thermosyphon, the condenser is placed at the top of the evaporator so that the condensed liquid will return to the evaporator by gravity. Figures 4 and 5 show a schematic diagram and a model of a typical thermosyphon (constructed in the University of Birmingham, UK) with heat supplied by coil of wire and heat rejected to the flowing water in the water jacket provided on the condenser section [17]. However, in some operation set ups, the heat can be supplied by hot water surrounding the evaporator of the pipe.

#### 2.2.1 Operation limits of heat pipe

Heat pipe (with or without wick materials) operates within certain limits which are shown in Figure 6. For the heat pipe to operate, the maximum capillary pumping pressure must be greater than the total pressure drop; thus:

$$
\Delta P\_{c,\max} \ge \Delta P\_l + \Delta P\_v + \Delta P\_\mathcal{g} \tag{1}
$$

2.3 Advantages of thermosyphon over wick heat pipe

ii. More compactness

Limitation of heat pipe for heat transport.

3D view of a typical thermosyphon pipe.

Thermosyphon Heat Pipe Technology

DOI: http://dx.doi.org/10.5772/intechopen.85410

Figure 6.

11

Figure 5.

iv. Cost-effectiveness

iii. High durability and reliability

vi. Simplicity in construction

on the overall thermal resistance Rth, given by:

advantages over wick heat pipe, some of which are listed below:

v. Less weight due to the absence of wick materials

2.4 Measurement of the performance of thermosyphon

Apart from the general advantages of heat pipe, thermosyphon has other

i. Relative low-temperature difference between the heat source and heat sink

The performance of thermosyphon under different conditions is evaluated based

Rth <sup>¼</sup> Tae � Tac Qin

(2)

The pressure drop is the sum of the following:

ΔPl = Pressure drop necessary for the liquid to return from the condenser to the evaporator.

ΔPv = Pressure drop necessary for the vapour to rise from the evaporator to the condenser.

ΔPg = Pressure due to gravity whose value depends on the angle of inclination of the pipe.

If condition in Eq. (1) is not met (capillary limit), then the wick materials will dry out and the pipe will not operate. Detailed discussions on the heat pipe limits (shown in Figure 6) are available in heat pipe books, which can be referred.

Figure 4. Dimensions of a typical thermosyphon with water manifold [17].

The materials for the manufacturing of thermosyphon are carefully selected to ensure its effective performance. Other considerations are the type and the quantity

The working principles of thermosyphon are similar to that of the wick heat pipe, but differ in the process of the return of the condensed liquid in the condenser due to the absence of wick structure. For proper operation of thermosyphon, the condenser is placed at the top of the evaporator so that the condensed liquid will return to the evaporator by gravity. Figures 4 and 5 show a schematic diagram and a model of a typical thermosyphon (constructed in the University of Birmingham, UK) with heat supplied by coil of wire and heat rejected to the flowing water in the water jacket provided on the condenser section [17]. However, in some operation set ups, the heat

Heat pipe (with or without wick materials) operates within certain limits which

ΔPl = Pressure drop necessary for the liquid to return from the condenser to the

ΔPv = Pressure drop necessary for the vapour to rise from the evaporator to the

ΔPg = Pressure due to gravity whose value depends on the angle of inclination of

If condition in Eq. (1) is not met (capillary limit), then the wick materials will dry out and the pipe will not operate. Detailed discussions on the heat pipe limits (shown in Figure 6) are available in heat pipe books, which can be referred.

ΔPc,max ≥ ΔPl þ ΔPv þ ΔPg (1)

are shown in Figure 6. For the heat pipe to operate, the maximum capillary pumping pressure must be greater than the total pressure drop; thus:

can be supplied by hot water surrounding the evaporator of the pipe.

The pressure drop is the sum of the following:

Dimensions of a typical thermosyphon with water manifold [17].

of working fluid to be charged into the pipe.

Recent Advances in Heat Pipes

2.2 Operation of thermosyphon heat pipe

2.2.1 Operation limits of heat pipe

evaporator.

condenser.

the pipe.

Figure 4.

10

Figure 5. 3D view of a typical thermosyphon pipe.
