The working process of a thermoelectric cooler (TEC) is not simply an ordinary heat absorption process or a process of consuming heat. After being powered on, one side of the TEC becomes cold while the other side becomes hot. A TEC can be thought of as a heat pump; it moves heat from one side to the other. 

Specifically, heat from the side being cooled is transferred to the other side—the hot side. This transfer process fully complies with thermodynamic principles. Since the cooling capacity of a TEC decreases as the temperature difference between its cold and hot sides increases, the hot side of the TEC must be attached to a suitable heat sink. This is necessary to dissipate both the heat transferred from the cold side and the Joule heat generated during the device's operation. 

Depending on the application, TECs require different types of heat sinks for optimal performance. Furthermore, various mechanical constraints often make the entire design process quite complex. Because application conditions vary significantly, it is difficult to recommend a single heat sink structure that satisfies most requirements. Many types of heat sinks are available on the market, which can generally be categorized into three types: natural convection, forced convection, and liquid cooling. 

Natural convection heat sinks can only be used in very low-power applications, particularly when small TECs operate below 2 A. For most applications, natural convection heat sinks cannot meet the requirement to dissipate all the necessary heat. In such cases, forced convection heat sinks or liquid cooling heat sinks are required.

1. Natural Convection Heat Sinks: Natural convection heat sinks are generally only suitable for low-power conditions. Most natural convection heat sinks have a thermal resistance greater than 0.5 °C/W, and in many cases, it can reach up to 10 °C/W. The placement of a natural convection heat sink must meet two conditions: a) The length direction of the fins should align with the direction of air flow; vertical orientation can enhance natural convection. b) There should be no significant physical obstructions hindering air flow. Additionally, consideration must be given to heat generated by other components around the heat sink, as a rise in ambient temperature will affect the overall performance.

2. Forced Convection Heat Sinks: Forced convection heat dissipation is the most common method used with TECs. A qualified forced convection cooling system typically maintains a thermal resistance in the range of 0.02 to 0.5 °C/W. Many standard extruded heat sinks, when paired with an appropriate fan, can form the basis of a complete cooling system. In practice, cooled air can be obtained using a fan or blower. The air can be directed to flow along the length of the heat sink, or it can be blown towards the center of the heat sink and exhausted from the two open ends.

2. Liquid Cooling Heat Sinks: Compared to the previous two types, a liquid cooling heat sink of the same volume offers the best performance. Through optimized design, very low thermal resistance can be achieved. Typical liquid cooling heat sinks usually have a thermal resistance as low as 0.01 to 0.1 °C/W. A simple liquid cooling heat sink can be made by soldering a copper turbulator onto a copper plate, or by drilling channels in a metal block for water to pass through. For more complex structures, and thus higher performance, intricate serpentine water channels can be machined into a copper or aluminum block, which is then sealed with a cover plate.

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