Heat pipes are heat transfer elements that rely on phase change of the working fluid within them to transfer heat, featuring the following basic characteristics.

Excellent thermal conductivity

The heat pipe primarily relies on the phase change of the working fluid between vapor and liquid states for heat transfer, resulting in a very low thermal resistance and high thermal conductivity. Compared to metals like silver, copper, and aluminum, a heat pipe of the same weight can transfer several orders of magnitude more heat. Of course, high thermal conductivity is relative, as there is always a temperature difference, and it is impossible to violate any thermodynamic laws. The heat transfer capability of the heat pipe is limited by various factors, and there are certain thermal transfer limitations. The axial thermal conductivity of the heat pipe is strong, while the radial conductivity does not see significant improvement (except for radial heat pipes).

2. Excellent isothermal properties

The steam inside the heat pipe is in a saturated state, with the pressure of the saturated steam depending on the saturation temperature. The pressure drop produced when the saturated steam flows from the evaporation section to the condensation section is very small. According to the equations in thermodynamics, the temperature drop is also very small, thus the heat pipe exhibits excellent isothermal properties.

3. Variable Heat Flux Density

Heat pipes can independently alter the heating area of the evaporation section or the cooling section, meaning they can input heat with a smaller heating area while outputting heat with a larger cooling area, or vice versa, with a larger heat transfer area inputting heat and a smaller cooling area outputting heat. This allows for the modification of heat flux density and addresses thermal transfer challenges that are difficult to solve with other methods.

4. Heat flow direction's酌 reversibility

A horizontally placed heat pipe with a core, due to its internal circulation driven by capillary force, can act as an evaporation section at either end upon heating and as a condensation section at the opposite end for dissipating heat. This feature is applicable for temperature equalization in spacecraft and artificial satellites in space, as well as for heat exchangers and other devices that release heat first and then absorb it.

5. Hot Diode and Thermal Switch Performance

Thermosiphons can be made into thermal diodes or thermal switches. A thermal diode allows heat to flow in only one direction, not the opposite. A thermal switch, on the other hand, begins to operate when the heat source temperature exceeds a certain threshold, and ceases to transfer heat when the temperature falls below that level.

6. Constant Temperature Feature (Controllable Heat Pipe)

The heat resistance of various components in a standard heat pipe generally does not change with the amount of heating. Therefore, when the heating amount varies, the temperature of the heat pipe's reservoir section also changes accordingly. However, people have developed another type of heat pipe—the variable thermal conductivity pipe—which reduces the heat resistance in the condensation section as the heating amount increases and increases it as the heating amount decreases. This allows the steam temperature to change very little even when the heating amount fluctuates dramatically, achieving temperature control. This is the isothermal characteristic of the heat pipe.

7. Environmental Adaptability

Thermal pipes can be shaped to accommodate the conditions of the heat and cold sources, and can be used as motor shafts, gas turbine blades, drill bits, and more. They can also be designed in a separate configuration for long-distance or situations where hot fluids cannot mix, facilitating heat exchange. Thermal pipes are suitable for use both on the ground (in the gravitational field) and in space (in zero gravity fields).