Number 228 - May 2002

PC Cooling and Power
by Herbert Wong, Jr., (NOCCC - February 2002)
Heat is the biggest enemy of electronic components. Without a complete strategy for dispersing and venting this excess energy (heat), a literal component meltdown can occur in seconds. It is in your best interest to prevent this from happening in the computer you own or build. In Theory     The American Heritage Dictionary defines heat as "A form of energy associated with the motion of atoms or molecules in solids and capable of being transmitted through solid and fluid media by conduction, through fluid media by convection and through empty space by radiation."     The flow of an electric current through a resistance will produce heat. This is true whether you are looking at a single transistor in a circuit or a complex integrated circuit (a dense collection of, commonly, millions of transistors). Increases in current, voltage, resistance, and frequency can cause heat to increase.     A properly designed component disperses heat through conduction (transfer of kinetic energy from one molecule to another). The component's mounting and case spread the heat away from a tiny area. In a small but important way, this will help prevent the excessive heat disaster that we try to avoid. If the component continues to produce heat and it builds up, bad things can happen. Melting or even fire can result.     A few years ago, Intel designed a microprocessor that had a particular layout that placed frequently used transistors too close together. After extensive testing, the design was declared unsatisfactory. Commonly executed code repeatedly used the same transistors, which resulted in a heat buildup. Unfortunately, that version was already shipping and those units had to be replaced by a similar circuit with a different layout without the hot spots.     Where does the heat go? There is always electromagnetic radiation via photons. No physical contact or circulating fluids or gases are required. Radiation even occurs in a vacuum. However, radiation is not very efficient or fast enough to be of much use in electronics.     The greatest cooling occurs by convection. Heat, transferred to a moving liquid or gas, moves away from the component. So far, so good. However, in a closed system, the heat has nowhere to go and the liquid or gas can become excessively hot.     For a computer, the processor wastes electricity in the form of heat. The chip radiates (electromagnetic radiation) and conducts heat to a heat sink. A fan forces air through the heat sink. The air takes the heat away from the heat sink by convection. The warm air is now forced out of the computer case by a fan. Needless to say, if there is a breakdown in the process, the system is in jeopardy.     A seven-watt night-light in a bedroom seems innocuous. However, a stray blanket can easily trap in this small source of heat. Given enough time, a fire will break out.     A computer power supply is rated at between two hundred and four hundred watts of electricity. The energy consumed is mostly transformed to heat and released into the case. Now you can see why proper cooling is so critical. Ins And Outs Of Airflow     Heat rises. It's that simple. The strategy for cooling a computer case should be to let heat rise. However, it is not that simple.     Some geniuses at the other half of the Wintel team decided that the ATX computer power supply should blow cool external air through the power supply into the computer case. The now warm air is forced over the microprocessor. Ultimately, the hot air escapes through any perforations in the case. Since power supplies are always at the top of the case, this means that the hot air must be forced down through the case.     Because hot air from the power supply is blown across the microprocessor and hot air is forced down through the case, many manufacturers have rejected the ATX specifications for power supply airflow. Instead, many ATX power supplies force air out of the case.     Most cases allow the installation of a small fan in the front at the base. This fan should blow air into the case when the power supply is configured to blow air out of the case. This combination will establish the best airflow.     If the power supply forces air into the case, you must make a decision. You could go with the flow (sorry about that) or you could change it. Common sense would dictate that the airflow in the power supply should be reversed to conform to the previously described two-fan configuration. A	qualified technician can unplug the power cord, open the power supply, and turn the fan around. Simply reversing the electrical polarity will not work and may actually damage the fan. Obstacles     The average computer case is full of wide, flat, and gray ribbon cables. Floppy disk drive, hard disk drive, CD/DVD drive, and SCSI (small computer system interface) drive cables are commonly used. In addition, power supply, audio, and video cables run throughout the case. This awful mess of cables is like a mixture of spaghetti and lasagna leftovers. All of these cables interfere with each other and block the crucial airflow.     For years, overclockers have been custom modifying their ATA66/ATA100 ribbon cables with razor knives and heat-shrink tubing. The resulting round cables are labor intensive and costly (especially when cutting errors are made). The introduction of commercial machine-manufactured round ATA66/100 cables means you can easily (as in easy installation) reduce the internal computer case temperature by one or two degrees.     By specification, ATA100 (a.k.a. - Ultra DMA100) cables should be between ten and eighteen inches. As cable lengths increase, the chances of introducing undetected data errors increases (to the point of overt data errors). That does not stop manufacturers from producing cables that are 18", 24", 30", and 36" in length. Problems can also occur when trying to use ATA66/ATA100 cables with older controllers and devices (ex. - ATA33). Verify the manufacturer's specifications before proceeding to spend your time and money. Caveat emptor.     In the future, Serial ATA will replace the current generation of round-and-fat or flat-and-wide ATA cables with thin round cables (think of angel hair pasta). Bandwidth will be, initially, 150 megabytes per second. Later versions will go up to 600 megabytes per second.     Here is one final obstacle for your consideration. Typically, thermal compound (a.k.a. heat sink grease, silicone compound, etc.) is made from silicone mixed with zinc oxide. Newer designer concoctions made from aluminum oxide (or other compounds including silver alloys) may yield a decrease of a couple of degrees in microprocessor temperature.     The problem is that excessive thermal compound can actually act as a thermal barrier since silicone is not a good thermal conductor. The zinc oxide is added to improve the conductivity. One Web site recommends using a paper-thin layer of thermal compound. I think that may be too much.     The two interface surfaces (microprocessor and heat sink) are manufactured to be very flat but not perfectly smooth. The microscopic ridges and imperfections provide contact surfaces. The valleys allow the thermal compound means of flowing out of the way.     Uniformly apply the smallest possible film of thermal compound to only one surface. The interface should be completely covered when the two surfaces are rubbed together. Ideally, however, the ridges on the two surfaces should be touching.     Think of it as joining the two surfaces together (metal to metal) and replacing the molecules of air with molecules of thermal compound. In this case, the air molecules are insulators and the thermal compound is a slightly better thermal conductor (and electrical insulator). References     Check out the usual sites: www.over clockers.com, www.dansdata.com/, www.sysopt.com/, www.heat sink-guide.com/, www.toms hardware.com, etc. Conclusion     Some newer commercially designed and manufactured computer systems are taking efforts to scientifically ventilate and duct their cases. Some hobbyists (overclockers in particular) take elaborate steps to improve processor cooling and ventilate their home built computer cases.     Everyone must recognize that newer high-powered systems require particular attention to adequate system cooling. A little common sense and advanced planning are all that needs to be done.     One last thought on this. Dust acts as a thermal insulator. Clean the dust off the surfaces of the filters, fan blades, case holes, cards, microprocessors, heat sinks, memory, hard disk drives, etc. While your at it, clean the dust off of your refrigerator coils, too.     The latest version of this article www.singularity technology.com/ articles/ PCCooling And Power.html     Copyright (c) 1995-7 by North Orange County Computer Club. All rights reserved.
Number 228 - May 2002