Thermoelectric Cooling

Thermoelectric Cooling

Thermoelectic Cooler

Courtesy of Wikipedia

When a passive heat sink is at its cooling limits, a great option is to to enhance the performance through Thermoelectric cooling. A Thermoelectric system uses the Peltier effect and uses a Thermoelectric cooler (TEC) that is semiconductor device that functions as a small heat pump. In the 1800's Thomas Seebeck discovered that an electric current would flow continuously in a device made up of two dissimilar metals provided that the junctions of the metals were maintained at two different temperatures. peltier effect  Enhancing this discovery, in 1834 Jean Charles Athanase Peltier determined that heat could be generated when a current is generated between two conductors. Peltier also found the Thermoelectric device can create a voltage when there is a different temperature on each side. A typical Peltier heat pump involves multiple junctions in series, through which a current is driven. Some of the junctions lose heat due to the Peltier effect, while others gain heat. Thermoelectric heat pumps exploit this phenomenon, as do thermoelectric cooling devices found in refrigerators. There are many articles online about this effect, and  a great starting point is at Northwestern University Materials Science and Engineering

Adding heat sinks to the Thermoelectric Cooler increases the peltier effect. Radian Thermal Products has been optimizing the heat sink design for many of our customers using a thermoelectric cooler through thermal simulation that can also take into account other factors such as a fan, cold plate, and the packaging. We can offer just the heat sink, or supply the complete assembly to create an Active Cooling System.

Peltier Heat Pump

A Thermoelectric Cooler (TEC) can be used as a heat pump using Peltier effect. This occurs when a n-type and p-type semiconductor are joined in series with a thermally conducting plate on each side. When the power is applied the electrical current flows through the junctions which creates a temperature difference. The energy is absorbed on the cold side, and released is in the form of heat on  the opposite plate. The net cooling or heating effect is proportional to the electric current and Peltier coefficient.

Peltier Heat Pump

Seebeck Power Generator

A Thermoelectric module can also be be used as a Seebeck power generator known as a Thermoelectric Generator (TEG). By applying heat to one plate the device converts heat flux  directly into electrical energy through a phenomenon called the Seebeck effect. The Seebeck effect occurs when a temperature difference occurs causing a direct current (DC) to flows through the circuit. The voltages produced by Seebeck effect are small, but by connecting many devices in series the output voltage can be increased.

Peltier Heat Pump

Single Stage Thermoelectric Cooler

A single Stage Thermoelectric Cooler (TEC) is typically manufactured between two ceramic substrates with rows of the P and N type material connected in series so that there is just two terminal wires. The most commonly used semiconductor is Bi2Te3. The performance of this material is relatively low and alternate materials are being investigated such such as super-lattice structures, quantum wires and quantum wells, thin films using SiGe/Si.

When the temperature difference between the cold and hot side cannot be achieved with a single stage module, a Multistage Thermoelectric module can be used. Multistage Thermoelectric modules are essentially single stage modules stacked up in a vertical pyramid-shaped array. As the number of layers increases, the cold side minimum temperature will decrease. Increasing the number of stages increases the coefficient of performance for a given cold side temperature (Goldsmid,1986).

Thermoelectric Cooler internals

The cold facts about Thermoelectric Coolers

Thermoelectric Cooler

There a many advantages of Thermoelectric Coolers: 

  • Thermoelectric Coolers can cool to -100°C  using a 6 stage device
  • Thermoelectric Coolers can pump up to 600W using multiple devices
  • Thermoelectric Coolers range from 2mm to over 60mm
  • Thermoelectric Coolers are typically RoHS compliant
  • Thermoelectric Coolers have the ability to alternate between heating and cooling offering precise temperature control
  • Thermoelectric Cooler temperature stability has been reported at ±.0003 degrees celcius
  • Thermoelectric Coolers have no moving parts make them very reliable
  • Thermoelectric Coolers are a good choice for equipment sensitive to mechanical vibration

Air-Air Thermoelectric Cooler system (A-A TEC)

Air-Air Thermoelectric Cooler system

In an Air-Air Thermoelectric Cooler system the simpliest version is a Thermoelectric cooler connected to two passive heatsinks.

Air-Air Thermoelectric Cooler system

The addition of fans to an Air-Air Thermoelectric Cooler system improves efficiency as there is forced air to create a temperature difference.

Air-Liquid Thermoelectric Cooler system (A-L TEC)

Air-Liquid Thermoelectric Cooler systemAn Air-Liquid Thermoelectric Cooler system is ideal when high thermal performance is required in a compact design. The heat is absorbed by a heat sink with fan on the cold side and then dissipated to a liquid on the warm side. The liquid circuit typically uses a recirculator to remove the heat into the ambient air. This Air-Liquid Thermoelectric Cooler system allows for precise temperature control of the fluid, and has been solution for many devices including cooling lasers, and medical applications such as blood preservation, patient rehabilitation pads and blankets.

Liquid-Liquid Thermoelectric Cooler system (L-L TEC)

Liquid to Liquid Thermoelectric Cooler systemWith a Liquid-Liquid Thermoelectric Cooler system heat is dissipated to a liquid on the warm side. The liquid circuit is normally of a recirculating type with a pump and a liquid-to-air heat exchanger to remove the heat into the ambient air. By using an efficient heat exchanger and one or more LL-assemblies, a powerful yet compact system is created. To improve heat transfer, turbulators are inserted into the liquid channels.