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Know-How Silverstone : positive pressure and stack effect


What is meant by positive and negative pressure inside a cabinet?

 

The following videos are related to the first model of Raven 1, where a smoke machine is used to show what the commonly called "stack effect" is. The stack effect in a cabinet means the natural movement of the warm air from bottom to top. In the Raven 1, the presence of a 180mm fan in the lower position, combined with the rotation of 90 degrees clockwise of the plate of the motherboard, as shown in the video, allows a better management of the internal airflows and lower temperatures on all the components, removing at the root also the potential internal recirculation of hot air. With this cabinet, the RV01, Silverstone debuted for the first time with this very special interior layout, revolutionizing the common conception of chassis for PC:

 

http://www.youtube.com/watch?v=douRh490E3I&list=UUig-yfqTR5tHwdxuxpmPK7w&feature=plcp

http://www.youtube.com/watch?v=q1Xgjvf0SDc&list=UUig-yfqTR5tHwdxuxpmPK7w&feature=plcp

 

In the next videos the analyzed phenomenon is the positive pressure inside the Fortress FT01 (a windowed black version). It’s very interesting to see the SilverStone continuous research for innovation from the thermal point of view. We can assure that a case like this is still a jewel of innovation, process, technique, style and functionality. Thanks to this innovative system we managed to keep a Macho HR02 heatsink in passive configuration on an Intel Core i7 920 at default and slightly overclocked settings. As shown in a previous review, temperatures of such a fanless configuration are just slightly higher than fan-equipped coolers. Impressive at least!


http://www.youtube.com/watch?v=DLOg9yI3rjs&list=UUig-yfqTR5tHwdxuxpmPK7w&feature=plcp

http://www.youtube.com/watch?v=Qe-2ZqmSGug&list=UUig-yfqTR5tHwdxuxpmPK7w&feature=plcp

 

Next video shows the SilverStone SG03 SSF case, with a positive pressure system too, together with the Silverstone NT-06 cooler. As previously stated, this system allows an optimization of the fresh air flow really remarkable. Let’s see the smoke machine test:


http://www.youtube.com/watch?v=VsmKHJq2aTs&list=UUig-yfqTR5tHwdxuxpmPK7w&feature=plcp

 

General purpose cabinets usually have many fans, some fans are designed for extraction and other for intake. When the combined air flow of intake fans is higher than the combined air flow of exhaust fans, positive pressure is created inside the cabinet. Instead, when the airflow is greater for exhaust fans, then a negative pressure is created.
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How do the positive and negative pressure influence the air flow in a cabinet? The main difference between positive and negative pressure is the way they affect vents and other ventilation slots of the chassis. This picture shows an example of a modern high-performance case, with additional air intakes that aren’t occupied by the cabinet fans. These openings can work either as exhaust or intake depending on whether the cabinet has a positive or negative air pressure, respectively.

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The ventilation grilles are not the only place in the chassis that can be affected by the dynamics of incoming and outgoing flows: also fissures, shown in this photo, may be called into question. This is a first benefit from positive air pressure: dust removal. New models of cases usually include filters to avoid accumulation of dust inside the cabinet. If the case has a positive pressure, only the dedicated intake fans will require filters to reduce the total quantity of dust.

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The diagram shows clearly that the cabinet with a positive pressure can prevent the accumulation of dust, thanks to dedicated filters placed in front of fans, which push the air out through openings where there are no appropriate filters. The idea is to use positive air pressure to build dust-proof cabinets, similar to the concept of cleanrooms, where filtered air pumped in with positive pressure helps keeping out the dust from the room. These rooms are used in fields like Hi-tech, medical and food processing systems, to prevent contamination or dust. Regardless of their size and their level, they are built to maintain a positive air pressure to remove dust.

The other benefit of positive air pressure is maximizing the efficiency of the heat sink video card.

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Left, partially closed cooler - Right, totally closed cooler

Generally all the video cards are studied to exhaust hot air outside of the case, to limit the reintroduction of hot air inside the cabinet itself.

Partially closed cooler:

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Totally closed cooler:

4ss

 

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Taken from: http://www.silverstonetek.com/techtalk_cont.php?area=usa&tid=wh_positive

We also thank SilverStone for providing materials and pamphlets.

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