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    Computer & CPU Cooling Experiments

    Computer & CPU Cooling

    Definition

    Computer cooling is the process of removing heat from computer components. Because a computer system's components produce large amounts of heat during operation, this heat must be dissipated in order to keep these components within their safe operating temperatures.

    Basics

    In addition to maintaining normative function, varied cooling methods are used to either achieve greater processor performance (overclocking), or else to reduce the noise pollution caused by typical (ie. cooling fans) cooling methods.

    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 (though excessive cooling of hard drives has been found to have negative effects). Overheated parts generally exhibit a shorter maximum life-span and may give sporadic problems resulting in system freezes or crashes.

    Both integral (manufacturing) and peripheral means (additional parts) are used to keep the heat of each component at a safe operational level. With regard to integral means, CPU and GPUs are designed entirely with energy efficiency, including heat dissipation, in mind, and with each advance CPUs/GPUs generally produce less heat (though this increased efficiency is always used to increase performance, producing similar heat levels as earlier models anyway). Cooling through peripheral means is mainly done using heat sinks to increase the surface area which dissipates heat, fans to speed up the exchange of air heated by the computer parts for cooler ambient air, and in some cases softcooling, the throttling of computer parts in order to decrease heat generation.

    Topics of Interest

    Causes of heat build up: The amount of heat generated by an integrated circuit (e.g., a CPU or GPU), the prime cause of heat build up in modern computers, is a function of the efficiency of its design, the technology used in its construction and the frequency and voltage at which it operates.

    In operation, the temperature levels of a computer's components will rise until the temperature gradient between the computer parts and their surroundings is such that the rate at which heat is lost to the surroundings is equal to the rate at which heat is being produced by the electronic component, and thus the temperature of the component reaches equilibrium.

    For reliable operation, the equilibrium temperature must be sufficiently low for the structure of the computer's circuits to survive.

    Additionally, the normal operation of cooling methods can be hindered by other causes, such as:

    • 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, or improper orientation of fans, can reduce the amount of air flowing through a case and even create localised whirlpools of hot air in the case.
    • Poor heat transfer due to a lack or poor application of thermal compounds.

    Damage prevention: It is common practice to include thermal sensors in the design of certain computer parts, e.g. CPUs and GPUs, along with internal logic that shuts down the computer if reasonable bounds are exceeded. It is, however, unwise to rely on such preventative measures, as it is not universally implemented, and may not prevent repeated incidents from permanently damaging the integrated circuit.

    The design of an integrated circuit may also incorporate features to shut down parts of the circuit when it is idling, or to scale back the clock speed under low workloads or high temperatures, with the goal of reducing both power use and heat generation.

    Air cooling: While any method used to move air around or to computer enclosures would count as air cooling, fans are by far the most commonly used implement for accomplishing that task. The term computer fan usually refers to fans attached to computer enclosures, but may also be intended to signify any other computer fan, such as a CPU fan, GPU fan, a chipset fan, PSU fan, HDD fan, or PCI slot fans. 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.

    Liquid submersion cooling: An uncommon practice is to submerse 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 density computers such as the Cray-2 may use additional radiators in order to facilitate heat exchange. The liquid used must have sufficiently low electrical conductivity in order for it not to interfere with the normal operation of the computer's components. If the liquid is somewhat electrically conductive, it may be necessary to insulate certain parts of components susceptible to electromagnetic interference, such as the CPU. For these reasons, it is preferred that the liquid be dielectric.Liquids commonly used in this manner include various liquids invented and manufactured for this purpose by 3M, such as Fluorinert. Various oils, including but not limited to cooking, motor and silicone oils have all been successfully used for cooling personal computers. Evaporation can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the computer's enclosure. Liquid may also slowly seep into and damage components, particularly capacitors, causing an initially functional computer to fail after hours or days immersed.

    Spot cooling: In addition to system cooling, various individual components usually have their own cooling systems in place. Components which are individually cooled include, but are not limited to, the CPU, GPU and the Northbridge chip. 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: Passive heatsink fitted on a Intel GMA graphics chipPassive heat sink cooling involves attaching a block of machined or extruded metal to the part that needs cooling. A thermal adhesive may be used, or more commonly for a personal computer CPU, a clamp is used to affix the heat sink right over the chip, with a thermal grease or 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 its ability to radiate heat is better than that of the component part it is protecting (usually an integrated circuit or CPU). Until recently, fan cooled aluminium heat sinks were the norm for desktop computers. Today many heat sinks feature copper base-plates or are entirely made of copper, and mount fans of considerable size and power.

    Active heat sink cooling: Active heat sink cooling uses the same principle as passive, with the addition of a fan that is directed to blow over or through the heat sink. The moving air increases the rate at which the heat sink can exchange heat with the ambient air. Active heat sinks are the primary method of cooling a modern processor or graphics card.

    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 diode, cooling diode, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). Because heating can be achieved more easily and economically by many other methods, Peltier devices are mostly used for cooling. However, when a single device is to be used for both heating and cooling, a Peltier device may be desirable. Simply connecting it to a DC voltage will cause one side to cool, while the other side warms. The effectiveness of the pump at moving the heat away from the cold side is dependent upon the amount of current provided and how well the heat can be removed from the hot side.

    Water cooling: 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 cooled parts than the various types of metals used in heatsinks, making it suitable for overclocking and high performance computer applications. Advantages to water cooling include the fact that a system is not limited to cooling one component, but can be set up to cool the central processing unit, graphics processing unit, and/or other components at the same time with the same system. As opposed to air cooling, water cooling is also influenced less by the ambient temperature. Water cooling's comparatively low noise-level is also favorable to that of active cooling, which can become quite noisy. One disadvantage to water cooling is the potential for a coolant leak. Leaked coolant can damage any electronic components it comes in contact with. Another drawback to water cooling is the complexity of the system; an active heat sink is much simpler to build, install, and maintain than a water cooling solution.

    Heat pipe: 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 CPU's and GPU's, as well as high end chipsets, use heat pipes in addition to active fan-based cooling to remain within safe operating temperatures.

    Phase-change 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. The evaporation can produce temperatures reaching around −15 to -150 degrees Celsius. The gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from −15 to −150 degrees Celsius, depending on the load, wattage of the processor, the refrigeration system and the gas mixture used. This type of system suffers from a number of issues but mainly one must be concerned with dew point and the proper insulation of all sub-ambient surfaces that must be done (the pipes will sweat, dripping water on sensitive electronics).

    Undervolting: Undervolting is a practice of running the CPU or any other component with voltages below the device specifications. An undervolted component draws less power and thus produces less heat. The ability to do this varies by manufacturer, product line, and even different production runs of the same exact product (as well as that of other components in the system), but modern processors are typically shipped with voltages higher than strictly necessary. This provides a buffer zone so that the processor will have a higher chance of performing correctly under sub-optimal conditions, such as a lower quality mainboard (motherboard). However, too low a voltage will not allow the processor to function correctly, producing errors, system freezes or crashes, or the inability to turn the system on. (Undervolting too far does not typically lead to hardware damage, though in worst-case scenarios, program or system files can be corrupted). This technique is generally employed by those seeking low-noise systems, as less cooling is needed because of the reduction of heat production.

    Cooling and overclocking: Extra cooling is usually required by those who run parts of their computer (such as the CPU and GPU) at higher voltages and frequencies than manufacturer specifications call for, called overclocking. Increasing performance by this modification of settings results in a greater amount of heat generated and thus increasing the risk of damage to components and/or premature failure. The installation of higher performance, non-stock cooling may also be considered modding. Many overclockers simply buy more efficient, and often, more expensive fan and heat sink combinations, while others resort to more exotic ways of computer cooling, such as liquid cooling, Peltier effect heatpumps, heat pipe or phase change cooling.

    Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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