Heat pipes

Heat pipes are often used for cooling system. Heat pipe is defined as a vapor-liquid phase-change device that transfers heat from a hot reservoir to a cold reservoir using capillary forces generated by a wick or porous material and a working fluid (The CRC Handbook of Thermal Engineering). How does heat pipe work?

Heat pipe has three basic components, those are container, working fluid, and capillary structure. When heat pipe receives heat, temperature will increase including working fluid. If working fluid has already saturated, it will change its phase to be vapor. This vapor will through capillary structure and transfer heat to the wall of heat pipe. Then after release heat, working fluid becomes liquid and goes to the heat source again. This phenomenon is repeated again.

Heat pipes has many advantages, such as high heat transfer capacity, precise isothermal control, functional independence of evaporator and condenser, quick thermal response, remote applications, high reliability, small size and light weight. Because of its advantages, heat pipe is often used in cooling system such as electronic cooling system.

Besides electronic cooling system, heat pipe also is used for water heater using solar energy. Because it has very high transfer capacity, heat radiation from sun is received and used to heat water. This hot water is used for residential needs.

The simplest heat pipes that can be made is using pipe (copper) and water as working fluid. To adjust with the requirement, the pressure inside heat pipes should be decreased using vacuum pump. So, boiling temperature of water will be decreased and can be used for below 100 Celsius degree. Other working fluid can be used for low temperature are acetone, ammonia, methanol.

For high temperature, heat should use another working fluid. Based on operating temperature, heat pipes usually use cesium, potassium, sodium, Lithium. Cesium is used in range 300 to 600 Celsius. Potassium is used in range 400 to 1000 Celsius. Sodium is used in range 500 to 1200 Celsius. And Lithium is used in range 900 to 1700 Celsius.