Phase Change Cooling

A Two-Phase Heat Transfer Technology

Phase change cooling involves changing the state of a thermally conductive medium from a liquid to a gas, and back, creating a heat exchanger. The heat pipe is an example of a cooling module used in dissipating heat for many types of electronic products.

It utilizes phase change heat transfer inside enveloped structures, where the working fluid evaporates in heated zone, and vapor moves to the condenser, and the condensed liquid is pumped back through microporous structure call the wick.

Performance Strongly Dependent on

Geometry,

Working Fluid,

Microstructure of wick

Baknor’s world-class engineering, manufacturing, and testing capabilities ensure that solutions provided are of the highest performance. There are numerous applications of two-phase fluid flow technologies in a variety of industries. They are also are a key component of most thermal management solutions. These technologies feature much higher thermal conductivity than solid copper and near-uniform temperature gradients, essential for effective thermal management devices. Two-Phase Heat Transfer Technologies are differentiated across their numerous applications by the structure of their wick, the working fluid used, and their shape. Application are also used in medical, space and maritime devices in addition to consumer devices.

We offer a very broad range of solutions, from simple heat pipes to embedded heat pipes to two-phase thermal systems which include several different types of advanced technologies and materials. We offer a full range of integrated solutions.

The wick is a microporous structure made of metal and is attached to the inner surface of the envelope. The working fluid is located in the void space inside the wick. When the heat is applied at the evaporator by an external heat source, the applied heat vaporizes the working fluid in the heat pipe. The generated vapor of working fluid elevates the pressure and results in pressure difference along the axial direction. The pressure difference drives the vapor from evaporator to the condenser, where it condenses, releasing the latent heat of vaporization to the heat sink. In the meantime, depletion of liquid by evaporation at the evaporator causes the liquid–vapor interface to enter into the wick surface, and thus a capillary pressure is developed there. This capillary pressure pumps the condensed liquid back to the evaporator for re-evaporation of working fluid. Likewise, the working fluid circulates in a closed loop inside the envelope, while evaporation and condensation simultaneously take place for heat absorption and dissipation, respectively. The high thermal performance of the heat pipe is originated from the latent heat of vaporization, which typically amounts to millions of Joules per 1 kg of fluid.

The flow in the wick is attributable to the same mechanism with the suction of water by a sponge. The micro sized pores in the sponge (or wick) can properly generate the meniscus at the liquid–vapor interfaces, and this yields the capillary pressure gradient and resulting liquid movement. It should be noted that the wick provides the capillary pumping of working fluid, which must be steadily supplied for the operation of heat pipe as well as the flow passage of the working fluid. In addition, the wick also acts as a thermal flow path because the applied heat is transferred to the working fluid through the envelope and wick. Therefore, the thermal performance of the heat pipe is strongly dependent on the wick structure.

Various types of wick structures have been used for enhancing the thermal performance of heat pipes.

Three representative types of wick structures:

Mesh screen wick

Grooved wick, and

Sintered particle wick.

The mesh screen wick is the most common wick structure, which made of wrapped textiles of metal wires.

The grooved wick utilizes axial grooves directly sculptured on the envelope inner surface as the flow channel.

About Phase Change Cooling A Two-Phase Heat Transfer Technology

Phase Change Cooling