Heat naturally flows from hot to cold. This is a cardinal rule of Thermodynamics. As a result, heatsink fans and water-cooling systems that rely on convection cooling can never cool a CPU below the ambient air temperature. (In reality, the CPU will always be slightly warmer than the ambient air temperature.) However, as we all know, heat can be made to flow from cold to hot (i.e. refrigeration and air conditioning systems). To force heat to flow from cold to hot requires the input of energy and is referred to as active cooling. The following chart gives several examples of typical CPU full load temperatures using different types of cooling systems.
The Vigor Monsoon II Lite incorporates a Peltier device, which can be used to actively cool a computer’s CPU. In this configuration, electrical energy applied to the Peltier device is used to transfer heat from a relatively cool area (CPU/cold plate) to a warmer area (hot plate/heat pipes/aluminum fins). This implies that an active CPU cooler should be able to lower the temperature of the CPU below that of the ambient room air temperature.
The Monsoon II Lite cooler also uses heat pipes to efficiently transport heat from one area (the base plates) to another (aluminum fins). Heat pipes are passive, not active cooling devices as they require no additional energy input to make them work.
Thermoelectric Cooling – The Peltier Device
A Thermoelectric Cooler (TEC) is a solid state device that operates on the Peltier effect. When a DC voltage is applied to an array of tiny thermocouples sandwiched between two ceramic plates, one side of the device becomes hot while the other side becomes cold. The TEC acts like a solid state heat pump and can be used to actively cool (or heat) an object it is attached to. In the Monsoon II CPU cooler, the TEC is used to actively transport heat away from the cooler’s base and into an array of cooling fins via heat pipes.
Peltier devices are pretty cool little bits of technology but they are not without their disadvantages. One problem with incorporating a TEC into a HSF is that Peltier devices are not very efficient. This means they consume more electrical energy than they can pump – two or three times more, which is converted directly into waste heat that must be dissipated on the hot side along with the heat being pumped. This can be a real problem for an air-cooled heatsink and is why many TEC coolers use water-cooling to keep the hot side cool.
Another potential problem when using a TEC in a HSF is that as the CPU load changes the temperature may change dramatically. At light idle loads the cooler base and surrounding socket area may become so cold that condensation and even frost may form – not good. As the heat being generated by the CPU increases the TEC becomes less effective. If the heat pumping capacity of the TEC (Qmax) isn’t sized to handle the maximum CPU heat generation it won’t be able to keep up resulting in over heating and instability.
By nature, a solid state Peltier device is generally very reliable but if something does happen (loose connection, broken wire, or loss of power) the TEC will immediately stop pumping heat and become a very good insulator, quickly causing a CPU core meltdown.
However, the Vigor Monsoon II has taken all of these potential weaknesses into account and found ways to eliminate or manage them… 🙂
Heat Pipe Technology
The Vigor Monsoon II Lite cooler uses four, U-shaped, copper heat pipes to transport heat from the heatsink base up to the large surface area provided by the aluminum fins. A heat pipe is a highly efficient conductor of heat. A properly constructed heat pipe has a very low thermal resistance, which is roughly independent of its length (unlike ordinary metal rods whose thermal resistance increases with length). Heat pipes are commonly used to transport heat from one location to another.
Heat pipes work on the principle of evaporation and condensation. A working fluid (frequently distilled water) evaporates inside one end of the heat pipe (the hot-end) absorbing heat in the process. A partial vacuum inside the heat pipe allows the water to evaporate at low temperatures. Once formed, the water vapor diffuses from an area of high vapor pressure (where it is being generated) to the other end of the tube where the vapor pressure is lower.
The vaporized fluid then condenses back to liquid (cold-end) and the heat is dissipated into the air from the metal cooling fins. The working fluid returns to the hot end via capillary action thru an internal wicking structure (sintered metal coating, fine wire mesh, or grooves) so the heat pipe does not have to rely on gravity to recycle the working fluid. The key to a heat pipe’s high efficiency is the latent heat of vaporization.