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Cooling: Heat is a Processor's Worst Enemy

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What Makes Cool Cooler?



Heat has always been a computer's worst enemy. Not just the processor, like you always here, but the whole computer is at risk, especially today, when graphics systems alone can require nearly as much power as an entire system might have just over 20 years ago. Dual core processors, larger power supplies, huge hard drives, DVD burners and even physics cards now add to the burden. Imagine all that plus overclocking. Suddenly there is a market for all kinds of strange looking heatsink/fan combos, phase change coolers, Peltier coolers, and water coolers. This page merely provides a loose explanation of the technologies and suggests why these methods might be important to you.




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Heatsink/Fan combinations come in all sizes and shapes. AMD HSF CombosIt has been a few years, but there was a time when most processors were passively cooled, meaning that all that was necessary was a lowly heatsink. But as processors grew larger and faster, and transistor counts increased, more power was required. That power is the source of heat. Heatsinks work by transferring heat through a plate on the bottom of the device to fins attached to the base.zTherm HSF The fins provide increased surface area through which the heat is wicked away. Intel HSF The fan provides a constant flow of cooler air to be moved over the sufaces of the fins and extract the maximum possible amount of heat. The warmed air is then moved by fan or convection to a point where it can be vented from the Zalman HSFcase to the outside air. The number of configurations of these devices seems endless, and they run from very cheap to very expensive. Most of them are made of either copper or aluminum. Some add heat pipes, which contain liquid and a wick to extract heat from the base and move it through the liquid in the pipes up to a heatsink attached to the tops of the pipes. These also have fans to complete the heat extraction process.
Phase Change cooling has four major parts in the system. These parts form a closed loop of tubing of varying diameters which is filled with refrigerant to transport heat away from the processor or other part being cooled. The image below illustrates the phase change process. This is a brief description of each piece of the system and what it does.
(image courtesy of Asetek)
Refrigerate!
A phase change system works by using a process called latent heat of vaporization. Refrigerant absorbs a huge amount of heat as it changes from a liquid to a gas (changes phase). For about the past 20 years, refrigerants have had to be environmentally friendly. Thus, a newer refrigerant called R134a came into being. Most phase change units use this or another variation of this refrigerant such as R404a or R507 refrigerant. Some, such as R404a, are actually blends of several refrigerants. Phase ChangeOnce in the system, the compressor takes the refrigerant and compresses it into a high pressure gaseous state before sending it to the condenser.
Condense!
A condenser is just a radiator with a cooling fan. This is where the refrigerant releases the heat absorbed during the previous stage. This is also where the heat is extracted and exhausted from the system. While the condenser, the refrigerant condenses from high-pressure gas into a high pressure liquid state.
Pressurize!
The capillary tube is a very small diameter copper tube that createa a restriction in the system. This restriction keeps the refrigerant in a high pressure liquid state on one side and a low pressure gaseous state on the other side of the tube. This is where the actual "phase change" takes place.
Evaporate!
In a phase change cooler for a PC processor, the block that attaches to the processor is actually the evaporator. As the refrigerant enters the evaporator there is a huge drop in pressure, which allows the refrigerant to "change phase" from a liquid to a gaseous state. During this process is when the heat from the processor is extracted into the gaseous refrigerant and passed into the compressor to start the cycle all over again. It si in the evaporator that the real work of removing heat from the processor occurs. If it were not for the drop in pressure and gasifying of the liquid, no heat would be removed.
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Peltier devices (sometimes referred to as thermoelectric (TE) modules) are solid-state devices that function as heat pumps. They are very compact for the amount of work that they do, measuring on average only a few millimeters Peltier coolerthick and a couple of centimeters square. However, that does not mean that they are electrically efficient, since they are capable of consuming large amounts of power in return for the heat that is dispelled. Still, with no refrigerant necessary and no noise or moving parts, the extra draw on the electric bill may be tolerable. With the lack of moving parts, Peltierthey are very durable, last for years, and allow for extremely tight control of temperatures in small spaces. Each unit consists of an array of small Bismuth Telluride cubes (aka "couples") between two ceramic plates. When a DC current is applied, one of the plates will become very cold as heat is transferred from one plate to the other. Once on the "hot" side, heat is then extracted by way of a heatsink. This arrangement is excellent for cooling such devices as computer chips. Reversing the electrical connection causes the device to preform like a tiny electric heater. But you wouldn't want to attach it to your processor that way!
coolWater Cooling is the most popular form of exotic cooling, with a wide variety of devices available to fill the bill. Though most people shake in their boots at the thought of getting water near a processor or motherboard, it can actually be done rather safely. There are a number of manufacturers of water cooling kits now, and installation may not be as bad as you'd think, but you have to do your homework before you buy. Water coolers are simple devices that work by passing water through a hose to a copper block that is mounted on the CPU (or other chip). waterblockThe CPU transfers heat from itself to the water block attached to it by convection. Water passing through the block removes the heat from the copper and carries it to a radiator mounted either inside or outside the computer. A fan attached to the radiator radiatorpasses air over the fins in the radiator to remove the heat deposited there by the water. The water then returns to a reservoir, where a pump continuously circulates the water to keep things cool. Though a water cooled system is not silent, it is much quieter than a standard heatsink/fan combination, pumpbecause the fan attached to it is larger and turns at a slower speed. Water coolers do a better job of cooling in extreme conditions than standard hardware, but the best it is capable of is room temperature. Still, if a PC is overclocked there will be far more heat than normal, and room temperature will be a huge improvement. Other drawbacks to water cooling are that the hardware involved requires an enormous amount of space in a computer case. The hoses are measured by inside diameter, and a hose with a 3/8" diameter will measure over 1/2" outside. The size may make it very awkward to bend, and crimps provide resistance to flow, which reduces efficiency, and may become leaks in the future. Zalman ReseratorAnywhere there is a tank of water near a computer, there is room for worry. Water tanks for these units are sealed, and some mount in an empty drive bay, but extreme care is necessary. Also, there is the consideration of what to use for coolant. Water must be distilled, and it must contain additives to help remove heat and prevent rust and corrosion, as well as the build-up of algae in the system. There are many excellent products on the market that take care of these problems. Many of them are also ultraviolet reactive, which means if you put a black light in your case, you will have attained an all new level of coolness, as the tubes glow like an alien force waiting to take over! Water cooling can create some beautiful modding effects.
Ferrell-PC · ·Franklinton, NC
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