Koren Antun, Saifert Danijel, Jurum Kipke Jasna

Abstract :

The cooling of the computer system is one of the elements which has the key importance for the stability of the whole computer system. The majority of the computer processors emit by dissipation a great quantity of heat on a small surface, which makes the cooling of the computer system a very complex process. During the development of the new versions of the processors for computer systems the demands in producing qualitative coolers, which remove the problems of heating and instability of the whole computer system, grow also.

The cooling process itself is influenced by the composition of metals, which were used in the production of a cooler. In this sense there are several approaches in the construction of the coolers. The metal, which is mostly used in the manufacturing of coolers, is aluminium, which is used because if its small mass and good conductivity. Copper which has even better conductivity but a greater mass is used with aluminium very often. The combination of these two metals gives the best results in regard to the economic parameters of the coolers production.

The aim of this work is to find out how much the different materials influence the cooling of the computer system in regard to the various approaches of the usage of different materials in production of the coolers, and to explain the influence of the usage of the different materials on the stability of the whole computer system.

Key words : Cooler, processors, conductivity, alternate ways of cooling

1 Introduction

Cooling of the computer processors is the necessary process during the work of any computer system. The first computers did not demand special cooling because of insignificant heating of the processor (or processors) core and because of the low speed in performing the given mathematical processes. The basic cooling of the processors by means of the passive coolers (those without the fan) has not effect any more with the fifth generation of the coolers, so the cooling of the processors must be perfectly performed in order to be efficacious. The cooling can be done by air or in the combination with water. A great problem in cooling the computer processors is the surface of the cooler leaning on the processor core. As the surface of the cooler is obtained by mechanical way, there are numerous microscope holes, which are filled with air during the process of the leaning on the core, which has the opposite effect in the cooling process. To avoid this various pastes based on silicon and silver have been used which partially decrease this disadvantage.

2 Development of the processors coolers

By appearance of the computers driven by Intel 286 processor and its clones, it was possible to see the coolers in PCs, which were mounted on the system processors and co-processors. The passive coolers of small dimensions made from aluminium alloy with a small thermal permeability were put on Intel 286 and 386 processors from 16 to 33 MHz. By appearance of Intel 486 and later AMD versions of 486 processors, the classical cooling by a piece of “metal sheet” was not enough because the later versions of that processor working with the speed of 133MHz emitted considerable quantity of heat into the environment and the coolers with perforated surface started to be build in. The perforation of the upper part of the cooler increases the surface emitting the heat in the environment.

Figure 1. The design of a cooler

The perforations on the coolers have been used up today. They considerably increase the efficacy of the cooling process. The perforations on the coolers for 486 processors were performed so that the cooler was extended in the height for about 3 cm in a form of a box whose interior was made of ten upright metal sheets of aluminium alloy with the rectangular cross-section of about 5-6 mm. With the further development of the processors the first Pentium and Pentium MMX processors with the greater velocity of the inner core and greater number of transistors appeared on the market, and as such they emit greater quantity of heat. Their speed is in the limits from 780 – 233 MHz. At that time the coolers with the built in fans on the top of the coolers base appeared as well. The first fans on the coolers were not very efficacious firstly because of the small cross-section of the blade and of the small rotation speed. The coolers without fans have been used further on. The next generation of the processors in PCs demanded the new construction in the cooler production. Pentium II processors abandon the horizontal socket construction and use the vertical slot construction. It differs in the fact that the processor is implemented into the master plate and as such it is inserted into the slot on the matrix plate.

The velocity of the processor grows up to 459 MHz and passive and active coolers have been used further on, depending on the manufacturers of the PC platforms. Both kinds of coolers have greater surfaces and volume and their efficacy has increased. It is important to stress that the construction of the Pentium II core itself consumes less energy then its predecessor and it is less heated. Pentium II has the heir in Pentium III processor. The velocities in Pentium III processor grow up to 1400 MHz. For the first time the magic boundary of 1 GHz has been broken through. Pentium III processors use the slot and socket solutions and 3 versions of the processor core. Passive coolers have been slowly abandoned because they cannot give the satisfactory cooling of the processors above 1 GHz. Pentium II as well as Pentium III get their “m” solutions, which have been built, in portable computers. They have considerably smaller energy consumption and the have been heated very little.

In accordance to Intel the firsts AMD Athlon processors with different construction of the processor core appear. They have identical speed as Intel Pentium III processors but they are heated extremely because of the construction of the processor core. Because of that the new constructions of the active coolers appear on the market, which have greater surface, mass and greater rotation speed of the fan. On the bottom of the cooler, the small copper disc is implemented which increases the heat conducting from the processor core in the environment.

At the beginning of 21st century the new Intel Pentium IV processors come to the market as well as AMD Athlon II (Palomino and Barton) processors. Their speed exceeds 3 GHz so they are heated extremely. Consequently, the complete sets of water coolers as well as advanced active coolers with the implemented gas in the inside of the coolers appear. Cooling by means of water is done in the closed system in which the silent pressure pump sets the water in motion in the circular system. Water flows through the copper block (which is in the processor core) and takes over the heat from the core and transports it to the additional cooler which is in the housing of the computer. Special cooling systems are used which work on the basis of exchange of the electric charge on the metal surface, which cools the processor. Such a system is called Peltier and it has very good results in cooling of modern processors. The disadvantage is its high price and great consumption of electric current in the computer, so the purchase of more expensive housings with the better electrical charging is necessary. The great problem of those coolers is the price, which approximates the half price of the processor itself. Experiments have been made in cooling with freon and similar gasses in the closed system implemented in computer housing.

3 The basic function of a cooler in the process of cooling

The basic function of the cooler is to lead away the high temperature from one medium to another in the shortest possible time, i.e. to do the greatest dissipation of the heat into the environment. Contemporary cores of the quickest processors spend over 100W current while they work at full load. The core temperature increases then from 0 – 360oC in 2-3 seconds and they burn through if they have no adequate solution for cooling. The function of a cooler is to keep the temperature in normal limits. The greatest majority of today's coolers is built of the body made from aluminium (Al) with addition of copper (Cu) because of better conductivity, and the fan which is placed on the top of the cooler and is bonded to the source of electricity on the master plate of the computer . Their mass ranges from 150 – 770 g. The essential characteristic of the cooler is the rotation speed of the fan. The speeds of the fans range from the silent ones with 1400 revolutions per minute (RPM) to the very noisy ones of 7000 revolutions per minute (RPM) Where the noise is from 40-45 db.

The surface of the cooler leaning on the processor's core is flat and its size is 60 x 60 mm up to 80 x 80 mm. This surface is mechanically finished and it is not perfectly flat. When the cooler surface leans on the processor surface numerous microscopically visible vacuoles filled with air remain there on the surface of the cooler. This airs in vacuoles cancels the effect of heat acceptance from the processor core on the cooler base, because the heat is not transferred uniformly onto the cooler surface. Great efficacy is lost and pastes based on silicon and silver have been deposited in a thin layer on the cooler base. The paste fills in vacuoles on the cooler and increases the cooling effect of the processor core. The more vacuoles have been filled with the paste the more efficient cooling there is and the results of cooling are better.

In the industrial production of computers coolers the metals with good conductivity are leading in usage. The most often represented metal is aluminium (Al) because of its good conductivity, small mass and good price. The second in usage after aluminium is copper (Cu). Metals with even greater conductivity are silver (Ag) and gold (Au). They are not used for commercial purposes in coolers production because of their great mass and high price. However the combination of the mentioned metals as the coating on the lower surface of the cooler's base with aluminium would be financially profitable and efficacious. The problem appears when the coating of one micron thickness has to be applied chemically on aluminium because of the not binding the mentioned metals without additives and production of alloys. The only way is the mechanical one which is in fact filling the aluminium surface with the atomic particles of silver. Such approach was accepted in this article.

4 Experimental

The PC platform driven by PIV processor on 2667MHz (2,66 GHz) has been used for the research. The computer was formatted before the tests and the Windows XP Professional SP1 system with the necessary drivers and testing programs were installed. It is important to stress that the computer was placed into Cieftec Dragon Series Big Tower because of better cooling of the whole computer system. The system was composed of MSI 875p master plate, PIV 2,667 GHz, Geil 2 x 256 Mb 3500 ddr memory, which worked in synchrone dual channel mode, Saphire Ati Radeon 9800 pro graphic adapter, HDD Seagate Baracuda IV 120 Gb SAT. The cooler used for testing was Spire 9T291B1M3 EasyStream III™ Cooler assigned for PIV processors. Its technical characteristics are:

Dimensions 78×90×47 mm

Rotation speed of the fan - 3700 RPM +/-10%

Consumption of electric current - 2,4 W

Strength of noise produced by the fan - 29.7 db

Air flow - 27.8 CFM at 3700 RPM

Period without errors - 50.000 working hours

Figure 2. Spire 9T291B1M3 EasyStream III™

The cooler Zalman CNPS7000A-Cu was also used. Its technical characteristics are:

Dimensions - 109×109×62 mm

Rotation speed of the fan - 1350 - 2400 RPM +/-10%

Consumption of electric current - 6 W

Strength of noise produced by the fan - 20-25 db +-10%

Mass – 773 g

Period without errors - 70.000 working hours

Figure 3. Zalman 7000A-Cu

The layer of silver in thickness of 0.8 to 1.2 microns was applied on the Spire cooler, i.e. on its surface leaning on the processor's core. The other bases of the cooler were isolated during the silver application in order to obtain the aimed application of the metal. The further testing was performed in the program Prime 95. Prime is the program which calculates the primary numbers by means of several mathematical functions and algorithms. It is important to stress that the loading of the processor during performing the series of the Prime tests is always over 95%. Each Prime test has lasted for 10 hours to avoid the oscillations in temperature. Each test has been repeated for 15 times in order to avoid the possible error. The measuring results were added and the middle value was calculated. After the each test the computer was switched off and it was left to cool down for one hour to obtain the optimal temperature of the processor. The same principle was repeated at test computer without the running of the Prime 95 program. Each process was identical for each cooler.

4 Results

Table 1. Testing results

The results show that the usage of a particular metal in the construction of the modern coolers for PC processors results in different ways of cooling. In this sense, the results show further that the modification on an ordinary aluminium cooler with the addition of the silver particles has better results for 4% than the reference cooler. The progress is visible but it is still less than the result obtained with the cooler made of Copper.

6 Conclusion

The development of contemporary computer component, the development of the computer processors and coolers for the mentioned processors have been presented in the article. The testing results of the cooler show that it is possible to improve cooling by adding silver to aluminium cooler. This fact determines in a way the further possible researches and gives directions to enable the development of the adequate coolers for contemporary computer systems.

Because of the continuous and quick development of processors for PC computer platforms, one can expect the progress in the development of the alternative ways of cooling which could give better performances and secure and undisturbed work of the proccesors.

7 References

1. Dave S. Steinberg ,Cooling Techniques for Electronic Equipment, 2nd Edition, Wiley-Interscience (1991)