Heat pipe—An instrumental component for heat dissipation
in consumer electronic products
With the miniaturization trend of consumer electronic products, engineers are faced with new safety and performance challenges—how to fit more components into limited space while facilitating heat dissipation during product operation.
Heat pipe was an invention by Mr. George Grover at the Los Alamos Laboratory of University of California
in 1963. It was originally developed as a component for dissipating the high-temperature waste heat so as to ensure that a machine can operate smoothly in a normal temperature environment. With its unique features of high heat-conduction, fast heat-transfer, operating noise-free, and light in weight, heat pipe is widely used for heat dissipation in consumer electronic products today.
Do you know how a heat pipe works in such a small space? How does it facilitate heat dissipation in electronic products?
Before learning about the operating principles of a heat pipe, let's first understand the basic concept of "heat transfer". Heat transfer happens when heat flows from a high temperature environment to a lower temperature environment. There are three different ways that heat can spread, namely, conduction, convection and radiation.
Conduction: The transfer of heat energy from an object of a higher temperature to an object of lower temperature when the two objects come into direct contact.
Convection: The transfer of heat by the movement of a fluid. Heat flow occurs when a solid and fluid, or fluids of different temperatures, come into direct contact. Radiation: Heat moves directly from a hotter object as a form of electromagnetic energy, which can be absorbed by another object. No direct contact between the hotter object and the colder object is required.
In addition, heat transfer occurs when a substance changes state. During a change of state—from solid to liquid and vice versa, or from liquid to gas and vice versa, heat energy is either absorbed or released. For examples, the amount of heat required to convert a substance from the liquid to the gaseous state is called the Latent Heat of Vaporization. Conversely, the amount of heat required to convert a substance from its gaseous state back into its liquid state is called the Latent Heat of Condensation.
Operating principle of heat pipe
A heat pipe dissipates energy through conduction, evaporation, convection and condensation. Leveraging the change of state of a substance, heat pipe has demonstrated a very high level of thermal conductivity through efficient absorption and dissipation of heat energy.
A heat pipe has a very simple structure. It is a long and narrow metal container closed at both ends. Filled with working fluid, a heat pipe has capillary wicking material covering its inner surfaces. Depending on actual applications, different types of heat pipes comprise different types of metal materials and working fluids. The shell of the pipe is usually made up of copper, nickel, steel, tungsten or alloy, while working fluids may consist of potassium, sodium, or lithium, to meet the requirements of the actual operating temperature.
A heat pipe can transfer heat from one point of higher temperature to a point of lower temperature:
- Heat starts to transfer from the high-temperature area through the shell to the wick of the heat pipe.
- At that time, the working fluid at the wick boils and enters the vapor state. The part of high temperature of the heat pipe is called the Evaporator section.
- While vapor accumulates at the Evaporator section of the heat pipe, it moves to the colder end of the heat pipe and then condenses into liquid again. The part of low temperature of the heat pipe is called the Condenser section.
- When the working fluid is in a gaseous state and travels through the wick and the metal shell, thermal energy transfers to the external part of the heat pipe that is of lower temperature.
- The heat pipe operates continuously in a condensation and evaporation cycle. Owing to the "capillary pumping" force, the working fluid is driven from the Condenser section to the Evaporator section.
In fact, heat energy flowing from a high temperature point to a low temperature point is the fundamental operating principle of the heat pipe. The heat pipe is essentially a heat transfer device with highly effective thermal conductivity. Provided the same temperature difference between both ends, a heat pipe can transfer more than a thousand times of heat energy than a metal rod of equivalent volume.
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