Standard heat pipes also known as Constant Conductance Heat Pipes (CCHPs) in Spacecraft Thermal Control. As shown in Figure 1, heat is transferred by the evaporation and condensation of a working fluid:
- Heat transfer to the evaporator vaporizes liquid within the wick.
- Vapor pressure drives fluid to the condenser
- Heat transfer from the condenser condenses vapor at the wick.
- Liquid returns to the evaporator by capillary forces generated in the wick
Figure 2 shows two examples of copper water heat pipes used to cool discrete components. The heat pipes can be bent as necessary between the heat source and sink. The typical bend radius is greater than 3 times the O.D. of the heat pipe; see Figure 3.
Figure 1. Standard Heat Pipe.
Figure 2. Heat pipes can be bent into tight curves.
Figure 3 Copper-Water Heat Pipes Used for Electronics Chip Cooling.
The benefits of a standard heat pipe include:
- High Thermal Conductivity (10,000 to 100,000 W/m K)
- Low Cost
- Shock/Vibration tolerant
There are several limitations for standard heat pipes:
Most heat pipes are not structural components
- Heat is transported from discrete sources (HiK plates or Vapor Chambers can be used to remove heat over large areas)
- Heat flows in both directions (Diode heat pipes only allow the transfer of heat from the evaporator to the condenser)
- Power is only limited by the source and sink conditions Variable Conductance Heat Pipes and Pressure Controlled Heat Pipes can be used when a variable thermal link is required.
ACT’s heat pipe calculator can be used to estimate the performance of standard copper-water heat pipes.