![]() The operating temperature and the maximum heat transport capacity of a heat pipe-limited by its capillary or other structure used to return the fluid to the hot area (centrifugal force, gravity, etc.)-are therefore inescapably and closely related. This can be counterintuitive, in the sense that if a heat pipe system is aided by a fan, then the heat pipe operation may break down, resulting in a reduced effectiveness of the thermal management system-potentially severely reduced. In addition, for a given heat input, it is necessary that a minimum temperature of the working fluid be attained while at the other end, any additional increase (deviation) in the heat transfer coefficient from the initial design will tend to inhibit the heat pipe action. Thermal conduction is still possible through the walls of the heat pipe, but at a greatly reduced rate of thermal transfer. Above the operating temperature, all the liquid has turned to gas, and the environmental temperature is too high for any of the gas to condense. Below the operating temperature, the liquid is too cold and cannot vaporize into a gas. The stated/recommended operating temperature of a given heat pipe system is critically important. The working fluid mass is chosen so that the heat pipe contains both vapor and liquid over the operating temperature range. The heat pipe is partially filled with a working fluid and then sealed. Typically, a vacuum pump is used to remove the air from the empty heat pipe. Thin flat heat pipe (heat spreader) with remote heat sink and fanĪ typical heat pipe consists of a sealed pipe or tube made of a material that is compatible with the working fluid such as copper for water heat pipes, or aluminium for ammonia heat pipes.
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