SECURE PIPES SERIES

In this case, the heat pipe is a thermosiphon. When the condenser is located above the evaporator in a gravitational field, gravity can return the liquid.

SECURE PIPES SERIES

Wick structures used in heat pipes include sintered metal powder, screen, and grooved wicks, which have a series of grooves parallel to the pipe axis. In a standard heat pipe, the condensed liquid is returned to the evaporator using a wick structure exerting a capillary action on the liquid phase of the working fluid. The saturated liquid vaporizes and travels to the condenser, where it is cooled and turned back to a saturated liquid. Water heat pipes are sometimes filled by partially filling with water, heating until the water boils and displaces the air, and then sealed while hot.ДЇor the heat pipe to transfer heat, it must contain saturated liquid and its vapor (gas phase). Copper/water heat pipes have a copper envelope, use water as the working fluid and typically operate in the temperature range of 20 to 150В вЊ. The vast majority of heat pipes for room temperature applications use ammonia (213вЂ“373В K), alcohol ( methanol (283вЂ“403В K) or ethanol (273вЂ“403В K)), or water (298вЂ“573В K) as the working fluid. Working fluids are chosen according to the temperatures at which the heat pipe must operate, with examples ranging from liquid helium for extremely low temperature applications (2вЂ“4 K) to mercury (523вЂ“923В K), sodium (873вЂ“1473В K) and even indium (2000вЂ“3000В K) for extremely high temperatures. 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 attainedВ 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 fanДЄ 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.

Secure pipes