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Device and Method of Intentional Airflow Recirculation for Enhanced Cooling in an Electronic Enclosure During an Airmover Replacement or Missing Airmover Disclosure Number: IPCOM000240106D
Publication Date: 2015-Jan-02
Document File: 5 page(s) / 880K

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Discussed is an unorthodox method of improving redundant cooling during the concurrent maintenance of a failed fan or missing fan.

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Device and Method of Intentional Airflow Recirculation for Enhanced Cooling in an

Electronic Enclosure During an Airmover Replacement or Missing Airmover

In most small electronic enclosures, air recirculation should be avoided. Loss of cooling, lowered fan efficiency, and limited cooling redundancy can occur from undetected or unaddressed airflow recirculation for nominal conditions. With small form factor fans, such as 40mm, 60mm and 80mm system fans, within 1U, 2U, and 4U electronic enclosures, all of the cooling for certain individual components can be significantly diminished because of recirculation problems, and common remedies include baffles, shrouds, foam blockages, or ducting systems to eliminate the majority of recirculation and direct it on to or toward hot spots. Having uniform airflow rates within the electronic enclosure helps mitigate hot spots and cooling challenges.

    As with electricity, the airflow will always take the path of least resistance. In densely packed systems, the removal of airmovers during concurrent maintenance or missing airmovers mistakenly left out of the system can cause the overheating and force a hard shutdown within minutes. Unlike previous generations of lower powered electronics, which would continue to operate for a comparatively longer time, today's systems are densely populated with high-powered subsystems. For many of late generation systems, airmovers such as counter-rotating fans are not only used for their high P-Q capabilities but is commonly thought to provide some level of redundant cooling because it contains two independent rotors within the same housing to produce airflow. Because of the system density, there's often not enough room within to allow for an adequate airflow sharing plenum. Such plenum would allow some airflow from one fan to provide airflow to components downstream of a neighboring fan when that fan is disabled or removed. Common practice it to use stacked fans or counter-rotating fans to provide the redundant airflow when one rotor fails. However, when a counter-rotating fan is removed, the localized cooling redundancy is temporarily removed because the functional rotor is also removed.

    The common practice regarding concurrent maintenance or missing airmovers results in requiring a limited time window which the system can continue to function until an orderly shutdown is initiated. For systems with compromised redundant cooling when one of the system's main counter-rotational fan is removed or goes missing, shown as the white square for Fan #4 in Figure 1, allows outside air to enter, bypassing the upstream components and also exit the system through the vacancy created by the fan, itself, when the cover is removed. This creates an airflow dead zone both upstream and downstream of the missing fan location. If there is no plenum space behind the fan try, there is also no mechanical method of channeling the airflow over to or from the areas now void of airflow.