**2. Heat pipe (HP)**

The heat pipe is a very efficient passive device used to transfer heat. Heat pipes let height transfer rates over large space, with minimum temperature differences, simple structure, and easy control, and no required to pump [6]. Heat pipes consist of locked channels that are partially filled by a suitable working fluid. Heat pipes classify as a traditional heat pipe (HP), Thermosyphon heat pipe, and a pulsating/ oscillating heat pipe (OHP) [7].

#### **2.1 Conventional heat pipe (HP)**

A heat pipe is a tube containing a wick structure filled partially with fluid at the saturated state is lined on the inner surface. It is divided into three sections,

**313**

**Figure 2.**

*Conventional heat pipe [7].*

*Heat Pipes Heat Exchanger for HVAC Applications DOI: http://dx.doi.org/10.5772/intechopen.95530*

shows the operation of a conventional heat pipe (HP).

approaches to transfer heat like a finned heat sink.

with a comparatively small temperature differential.

core and the wick [8].

conductance.

**2.2 Thermosyphon heat pipe**

liquid film by gravity force [10].

closed two-phase heat pipe (thermosyphon) [9].

as shown in **Figure 2**. An evaporator portion, where the heat is added and the liquid phase changes to vapor phase, a condenser region at the other end, where the heat is dissipated, and the condensation process occurs, and an adiabatic (insulated) zone in between, where no heat in or out in this section of the heat pipe and the two phases of working fluid (liquid and vapor) flow in contrary directions through the

In the conventional heat pipe (HP), the condensed (liquid phase) goes back to the evaporator region by the capillary effect of the wick in the HP [7]. **Figure 3**

1.Heat pipes have some advantages features compared to other conventional

2.In steady-state operation, a heat pipe can have an extremely high thermal

3.A heat pipe can transfer a high amount of heat over a relatively long distance

4.Heat pipe with liquid metalworking fluids can have a higher thermal conductance in comparison to the best solid metallic conductors, silver or copper.

Thermosyphon is a simple two-phase closed heat pipe but an effective heat transfer device. It is a wickless heat pipe with a small amount of liquid reservoir at the bottom. The best description of Thermosyphon is by dividing it into three sections, as shown in **Figure 4**. Heat input through the evaporator section will convert the liquid into vapor. The vapor rises and moves across the adiabatic region to the condenser section. The vapor condenses and gives up its latent heat in the condenser section. The liquid was then forced to back to the evaporator section as a

Thermosyphon is a wickless heat pipe, therefore gravity is the major driving force for condensate to return to the evaporator section, so the capillary limit is generally of no concern in the operation of the Thermosyphon. **Figure 4** shows the *Heat Pipes Heat Exchanger for HVAC Applications DOI: http://dx.doi.org/10.5772/intechopen.95530*

*Heat Transfer - Design, Experimentation and Applications*

conditioning system.

**Figure 1.**

3.The operating costs are reduced [5].

*Air conditioning system with precool and reheat coils [4].*

quality of fresh air, and at the same time help save energy.

heat pipe, Thermosyphon, and OHP are systematically summarized.

2.Reduction in energy requirements and amounts of coolants used for the air

The purpose of a heat pipe heat exchanger for heat recovery in hot and cold climates is widely known. The heat pipe exchanger offers a low air pressure drop, related to possible by loop configurations, and heat recovery applications can be extended to milder climates and still pay for themselves. A new possibility is 'cooling' recovery in the summertime, which is now economical enough to be considered. The application of heat pipe as a heat exchanger to recover wasted heat is participated to enhance the dehumidification capacity of a conventional cooling coil is one of the most attractive applications. The used heat pipe heat exchanger in HVAC systems as a dehumidifier device can decrease 10% the air relative humidity that leads to resulting in a remarkable enhancement of the quality of fresh air and a decrease in power demand. The heat pipe is a promising technology to enhance the

The objectives of this chapter are to view heat pipe technology, the mechanism of heat and mass transfer, and assess the performance of heat-pipe heat recovery units for the HVAC system. This chapter presents the updated development status of the heat pipe used as a heat exchanger used in the HVAC system to recover the wasted heat. In this chapter, the experimental and theoretical investigations of the

The heat pipe is a very efficient passive device used to transfer heat. Heat pipes let height transfer rates over large space, with minimum temperature differences, simple structure, and easy control, and no required to pump [6]. Heat pipes consist of locked channels that are partially filled by a suitable working fluid. Heat pipes classify as a traditional heat pipe (HP), Thermosyphon heat pipe, and a pulsating/

A heat pipe is a tube containing a wick structure filled partially with fluid at the saturated state is lined on the inner surface. It is divided into three sections,

**312**

**2. Heat pipe (HP)**

oscillating heat pipe (OHP) [7].

**2.1 Conventional heat pipe (HP)**

as shown in **Figure 2**. An evaporator portion, where the heat is added and the liquid phase changes to vapor phase, a condenser region at the other end, where the heat is dissipated, and the condensation process occurs, and an adiabatic (insulated) zone in between, where no heat in or out in this section of the heat pipe and the two phases of working fluid (liquid and vapor) flow in contrary directions through the core and the wick [8].

In the conventional heat pipe (HP), the condensed (liquid phase) goes back to the evaporator region by the capillary effect of the wick in the HP [7]. **Figure 3** shows the operation of a conventional heat pipe (HP).


#### **2.2 Thermosyphon heat pipe**

Thermosyphon is a simple two-phase closed heat pipe but an effective heat transfer device. It is a wickless heat pipe with a small amount of liquid reservoir at the bottom. The best description of Thermosyphon is by dividing it into three sections, as shown in **Figure 4**. Heat input through the evaporator section will convert the liquid into vapor. The vapor rises and moves across the adiabatic region to the condenser section. The vapor condenses and gives up its latent heat in the condenser section. The liquid was then forced to back to the evaporator section as a liquid film by gravity force [10].

Thermosyphon is a wickless heat pipe, therefore gravity is the major driving force for condensate to return to the evaporator section, so the capillary limit is generally of no concern in the operation of the Thermosyphon. **Figure 4** shows the closed two-phase heat pipe (thermosyphon) [9].

**Figure 2.** *Conventional heat pipe [7].*

#### **Figure 3.**

*Schematic operation of a conventional heat pipe [9].*

#### **Figure 4.** *Schematic operation of a thermosyphon heat pipe [9].*
