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. Cut-away view of a 500 μm thick flat heat pipe with a thin planar capillary (aqua coloured) 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. Cross section of a heat pipe for cooling the CPU of a laptop computer. This 120 mm diameter vapor chamber (heat spreader) heat sink design thermal animation was created using high-resolution CFD analysis and shows temperature contoured heat sink surface and fluid flow trajectories predicted using a CFD analysis package.
Structure, design and construction Diagram showing components and mechanism for a heat pipe containing a wick Heat pipes keep ground frozen and inhibit water transfer into the open pit during mining activities at Ekati Diamond Mine This 100 mm by 100 mm by 10 mm high thin flat heat pipe (heat spreader) animation was created using high resolution CFD analysis and shows temperature contoured flow trajectories, predicted using a CFD analysis package. The effective thermal conductivity varies with heat pipe length and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper. The liquid then returns to the hot interface through capillary action, centrifugal force, or gravity and the cycle repeats.ĭue to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquid, releasing the latent heat. Īt the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. Heat-transfer device that employs phase transition A laptop computer heat pipe systemĪ heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.
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