Computer cooling is required to remove the waste heat produced by computer components, to keep components within their safe operating temperature limits. Various cooling methods help to improve processor performance or reduce the noise of cooling fans. Components which produce heat and are susceptible to performance loss and damage include integrated circuits such as CPUs, chipset and graphics cards, along with hard drives. Overheated parts fail early and may give sporadic problems resulting in system freezes or crashes.
INTEGRAL MEANS OF COOLING
built in methods of temperature management such as energy efficiency
PERIPHERAL MEANS OF COOLING
heatsinks and fans etc… anything external that draws off heat.
CAUSES OF OVERHEATING
* Dust acting as a thermal insulator and impeding airflow, thereby reducing heat sink and fan performance.
* Poor airflow including turbulence due to friction against impeding components such as ribbon cables, or improper orientation of fans, can reduce the amount of air flowing through a case and even create localized whirlpools of hot air in the case.
* Poor heat transfer due to a lack of, or poor application of thermal compounds and sufficient surface area of heat sinks to radiate off the heat.
Thermal sensors in some CPUs and GPUs can shut down the computer when high temperatures are detected. However, reliance on such measures may not prevent repeated incidents from permanently damaging the integrated circuit.
Fans are most commonly used for air cooling. A computer fan may be attached to the computer case, or attached to a CPU, GPU, chipset, PSU, hard drive or PCI slot. Common fan sizes include 40, 60, 80, 92, 120, and 140 mm. Recently, 200mm fans have begun to creep into the performance market, as well as even larger sizes such as 230 and 240mm.
Desktop computers typically use one or more fans for cooling. Almost all desktop power supplies have at least one fan to exhaust air from the case. Most manufacturers recommend bringing cool, fresh air in at the bottom front of the case, and exhausting warm air from the top rear.
Data centers typically contain many racks of flat 1U servers. Air is drawn in at the front of the rack and exhausted at the rear. Because data centers typically contain such large numbers of computers and other power-consuming devices, they risk overheating of the various components if no additional measures are taken.
Another way of accommodating large numbers of systems in a small space are blade chassis. In contrast to the horizontal orientation of flat servers, blade chassis are often oriented vertically. This vertical orientation facilitates convection. When the air is heated by the hot components, it tends to flow to the top on its own, creating a natural air flow along the boards. This stack effect can help to achieve the desired air flow and cooling.
Most laptops use air cooling in order to keep the CPU and other components within their operating temperature range. Because the fan’s air is forced through a small port, the fan and heatsinks can be clogged by dust or be obstructed by objects placed near the port. This can cause overheating, and can be a cause of component failure in laptops.
An uncommon practice is to submerge the computer’s components in a thermally conductive liquid. Personal computers that are cooled in this manner do not generally require any fans or pumps, and may be cooled exclusively by passive heat exchange between the computer’s parts, the cooling fluid and the ambient air. Extreme component density supercomputers such as the Cray-2 and Cray T90 used additional liquid to chilled liquid heat exchangers in order to facilitate heat removal.
Several new 2GB and above DDR2 and DDR3 sticks of RAM, or system memory, are conductive cooled via a finned heatsink that is clipped onto the top edge of the memory stick. This also holds true for video cards that use a finned heatsink over the GPU for silent PC applications.
Some cooling solutions employ one or more methods of cooling, and may also utilize logic and/or temperature sensors in order to vary the power used in active cooling components.
Passive heat-sink cooling involves attaching a block of machined or extruded metal to the part that needs cooling. A thermal adhesive may be used. More commonly for a personal-computer CPU, a clamp holds the heat sink directly over the chip, with a thermal grease or thermal pad spread between. This block usually has fins and ridges to increase its surface area. The heat conductivity of metal is much better than that of air, and it radiates heat better than the component that it is protecting.
Dust buildup between the metal fins of a heat sink gradually reduces efficiency, but can be countered with a gas duster by blowing away the dust along with any other unwanted excess material.
Passive heat sinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers.
Usually a heat-sink is attached to the integrated heat spreader (IHS), essentially a large, flat plate attached to the CPU, with conduction paste layered between. This dissipates or spreads the heat locally. Unlike a heat sink, a spreader is meant to redistribute heat, not to remove it. In addition, the IHS protects the fragile CPU.
Passive cooling involves no fan noise.
Active heat-sink cooling uses the same principle as passive, with the addition of a fan that blows over or through the heat sink. The air movement increases the rate at which the heat sink can exchange heat with the ambient air. Active heat sinks are the primary method of cooling modern processors and graphics cards.
THERMO ELECTRIC COOLING
Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the temperature gradient (from cold to hot), with consumption of electrical energy. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). The Peltier device is a heat pump: when direct current runs through it, heat is moved from one side to the other. Therefore it can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.
As active heat pumps, TECs can cool the surface of components below ambient temperatures. This is impossible with common radiator cooled water cooling systems and heatpipe HSFs.
While originally limited to mainframe computers, water cooling has become a practice largely associated with overclocking in the form of either manufactured kits, or in the form of do-it-yourself setups assembled from individually gathered parts. The past few years has seen water cooling increasing its popularity with pre-assembled, moderate to high performance, desktop computers. Water has the ability to dissipate more heat from the parts being cooled than the various types of metals used in heatsinks, making it suitable for overclocking and high performance computer applications
A heat pipe is a hollow tube containing a heat transfer liquid. As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action, or, in earlier implementations, under gravitation). Heat pipes thus have a much higher effective thermal conductivity than solid materials. For use in computers, the heat sink on the CPU is attached to a larger radiator heat sink. Both heat sinks are hollow as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is expensive and usually used when space is tight (as in small form-factor PCs and laptops), or absolute quiet is needed (such as in computers used in audio production studios during live recording). Because of the efficiency of this method of cooling, many desktop CPUs and GPUs, as well as high end chipsets, use heat pipes in addition to active fan-based cooling to remain within safe operating temperatures.
PHASE CHANGED COOLING
Phase-change cooling is an extremely effective way to cool the processor. A vapor compression phase-change cooler is a unit which usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor of the same type as in a window air conditioner. The compressor compresses a gas (or mixture of gases) which condenses it into a liquid. Then, the liquid is pumped up to the processor, where it passes through an expansion device, this can be from a simple capillary tube to a more elaborate thermal expansion valve. The liquid evaporates (changing phase), absorbing the heat from the processor as it draws extra energy from its environment to accommodate this change (see latent heat). The gas flows down to the compressor and the cycle begins over again.
THEN THERE IS LIQUID NITROGEN AND LIQUID HELIUM
THEN THERE IS
SOFTWARE COOLING… THIS MEANS THE OS CONTROLS THE COOLING
UNDERVOLTING… RUNNING CHIPS BELOW VOLTAGE SPECS SO THEY DON’T HEAT UP AS FAST…
INTEGRATED COOLING TECHNIQUES
In micro-channel heat sinks, channels are fabricated into the silicon chip (CPU), and coolant is pumped through them. The channels are designed with very large surface area which results in large heat transfers. Heat dissipation of 3000W/cm2 has been reported with this technique. In comparison to the Sun power density of around 7400W/cm2. The heat dissipation can be further increased if two-phase flow cooling is applied. Unfortunately the system requires large pressure drops, due to the small channels, and the heat flux is lower with dielectric coolants used in electronic cooling.
Another local chip cooling technique is jet impingement cooling. In this technique, a coolant is flown through a small orifice to form a jet. The jet is directed toward the surface of the CPU chip, and can effectively remove large heat fluxes. Heat dissipation of over 1000W/cm2has been reported. The system can be operated at lower pressure in comparison to the micro-channel method. The heat transfer can be further increased using two-phase flow cooling and by integrating return flow channels (hybrid between micro-channel heat sinks and jet impingement cooling).
HEAT SINK LAPPING
Heat sink lapping is the smoothing and polishing of the contact (bottom) part of a heat sink to increase its heat transfer efficiency.