Isobar® Heat Pipes - For Electronic Cooling Devices

Electronic Cooling All electronic components, from computer chips to high-end power converters, generate heat, and rejection of this heat is necessary for their optimum and reliable operation. As electronic designs require higher power transfer in more compact enclosures, dissipating the heat load becomes a critical design factor. Many of today's electronic devices require cooling beyond the capability of standard metallic heat sinks. Isobar® Heat Pipe meets this need and is rapidly becoming a mainstream thermal management tool.

Electronics have traditionally been cooled by fan/heat sink combinations. However, new high-tech design electronics require higher power dissipation, with some standard fan/heat sinks no longer meeting thermal required specifications. The alternative for cooling electronics: Isobar® Heat Sink. The Isobar Heat Sink works using natural convection by taking advantage of Isobar® Heat Pipe's ability to transfer and dissipate heat energy efficiently and effectively. It offers low thermal resistance and high power capability, which is very practical given the fact that many electronics are operating today at or over the 100-watt level.

The Isobar Heat Sink consists of three basic parts:

  • Heat input plate, which is fastened to the electronic.
  • Isobar® Heat Pipe, which transfers the heat energy from the heat input plate to the fin stack.
  • Fin stack, a group of fins that dissipate the heat energy into the air

Isobar Heat Sinks from Acrolab offer the following benefits:

  • Ability to transport heat at high rate over considerable distance with extremely small temperature drop
  • Constructional simplicity
  • Exceptional design flexibility
  • Require no external power) remote cooling fins
  • Make efficient use of space
  • Low cost and considerable return on investment

Isobar Operating Principles (Theory)

Isobar Operating Principles Isobar is a closed tube or chamber of different shapes whose inner surfaces are lined with a porous capillary wick. The wick is saturated with the liquid phase of a working fluid and the remaining volume of the chamber contains the vapour phase. Heat applied in Figure 1 at the evaporator by an external source vaporizes the working fluid in that section. The resulting difference in pressure drives vapour from the evaporator to the condenser. At condenser section, vapour condenses releasing the latent heat of vaporization (energy release or storage due to phase change from vapour to liquid or liquid to vapour). Depletion of liquid by evaporation causes the liquid-vapour interface in the evaporator to enter into the wick surface and a capillary pressure is developed there. This capillary pressure pumps the condensed liquid back to the evaporator for re-evaporation. That is, the Isobar can continuously transport the latent heat of vaporization from the evaporator section to the condenser without drying out the wick. This process will continue as long as the flow passage for the working fluid is not blocked and a sufficient capillary pressure is maintained. The heat pipe can therefore transport a large amount of heat at high rate with a small unit size.

Isobar Construction

For operating temperature ranges of 0°C to 280°C, Isobar chambers and wick structures are manufactured from pure copper and charged with purified water as a working fluid. Isobars are typically manufactured as cylinders or flat shapes as shown in Figure 2. Custom shapes with different degrees of curvatures are also available. To optimize cooling efficiency, isobars are also manufactured with different fin array structures .

Wick Structures

The purpose of a wick is to provide:
  • The necessary flow passages for the return of the condensed liquid.
  • Surface pores at the liquid-vapour interface for the development of the required capillary pumping pressure.
  • A heat-flow path between the inner wall of the container and the liquid-vapour interface.

Effective Wick

Generally, an effective wick structure requires small surface pores for large capillary pressure, large internal pores (in the direction normal to the liquid flow) for minimal liquid-flow resistance, and an uninterrupted highly conductive heat-flow path across the wick thickness for a small temperature drop.

Screen Wick

The most common wick structure is the wrapped-screen wick (homogeneous wick) shown in Figure 5. The surface pore size of this wick is inversely proportional to the mesh number, which is defined as number of pores per inch. The flow resistance for liquid flow can be controlled by the wrapping tightness. This allows flexibility in structure. One particular wick type (composite wick structure, made of two materials) is a tunnel wick. The tunnel wick, shown in Figure 5, is a pressure primed, high performance wick. Thread grooves are provided for low heat-flow resistance.

Isobar Cooling Modules
Isobar Cooling Modules

Isobar Cooling Modules

Acrolab has developed high-efficiency Isobar Cooling Modules capable of dissipating up to 130 wattage load. Isobars carry heat to the cooling fins where it is dissipated to surrounding air by forced convection. Cooling Modules offer low thermal resistance and high power capability. Isobars manufactured by Acrolab are; copper, water, and copper wick design that operate in any orientation. Acrolab's experienced staff of dedicated engineers is always ready to assist in developing specialized solutions to solve specific technical or design problems in custom products. Just contact us, and your problem is guaranteed to get the attention it rightfully deserves.

Isobar Cooling Modules

Acrolab has developed high efficiency Isobar Cooling Modules capable of dissipating up to 120 watt load with 12°C temperature drop. Isobars carry heat to the cooling fins where it is dissipated to surrounding air by forced convection. Cooling Modules offer low thermal resistance and high power capability. Isobars manufactured by Acrolab are: copper, water, and copper wick design that operate in any orientation.

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