What is a heat pipe?
A heat pipe is an extreme efficient heat conductor. A typical heat pipe consists of a vessel in which its inner walls are lined with a wick structure. The heat pipe vessel is first vacuumed, then charged with a working fluid, and hermetically sealed. When the heat pipe is heated at one end (evaporator), the working fluid evaporates from liquid to vapor, where the phase change occurs. The vapor then travels through the hollow core of the heat pipe from evaporator to the other end (condenser) at near sonic speed, where the lower temperature at the condenser induces the vapor to condense back to liquid, and release heat, which is being removed by a heat sink or other means. The liquid then travels back to the evaporator of the heat pipe via the wick by capillary force. The energy required to change phase from liquid to gas is called the latent heat of evaporation. For example, the latent heat of evaporation for water is 539 cal/g. The specific heat of water is 1 cal/g°C. Therefore, the working fluid in a heat pipe can transport a very large amount of heat and makes heat pipes 100 to 1000 times better than a solid copper rod. Figure 1 is a schematic of a heat pipe.
When to consider a heat pipe?
There are three thermal conditions that may lead to the use of heat pipe:
- Heat pipe to act as a primary heat conductive Thermal Path – When a heat source and heat sink need to be placed apart, a heat pipe can be a very effective thermal path for heat transportation from the heat source to the heat sink.
- Heat pipe to aid heat conducting of a solid – Heat pipe can add the efficiency and transport capacity of a thermal shunt.
- Heat pipe to aid heat spreading across the plane – Heat pipe can be used to increase the heat spreading across a large heat sink base, thereby effectively increasing the heat sink base thermal conductivity. The effect of this is the decrease of the temperature gradient across the heat sink base (increase in efficiency), thereby lowering the heat source temperature. Refer to our Slim Cold Plate