Method of reducing/eliminating airflow recirculation in server with selective rotor shutdown
Publication Date: 2015-Dec-09
The IP.com Prior Art Database
Described is a method of reducing/eliminating airflow recirculation in a server with selective rotor shutdown.
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Method of reducing / shutdown
A novel scheme for airflow control in a server is described herein. If a counter-rotating fan experiences a single rotor failure, the other fans (which remain fully functional) throttle back to prevent overpressure and allow acceptable airflow from the failed fan. This modeling shows a 14% airflow improvement to components behind a failed fan in a reference system. Thus, this scheme may help components directly downstream from the failed fan maintain their performance/reliability, avoid shutdown, etc.
Servers using counter-rotating fans tend to leverage their high-pressure characteristics to improve airflow. However, the high pressures these fans generate can become a problem if one of them loses function in a single rotor -- if the server plenum is small, the good fans will overwhelm the failed fan, causing stagnation behind the failed fan or even recirculation through the failed fan's channel. However, the output of the good fans to match the failed fan by reducing fan speeds opposed to just a default to maximum fan speeds, thus the pressures from each fan would be equalized again. Overall system flow would be weakened, but the components behind the failed fan would be less compromised.
The following invention prevents pressure differentials across fan outlets. Pressure differentials across fan outlets may lead to a situation wherein the good fans' pressure causes their higher-pressure airflow to overwhelm the lower-pressure airflow of the failed fan. Therefore, reducing pressure output from the remaining good fans allows equalized cooling capacity from all fans. This decreases cooling for components behind the non-failed fans, but improves cooling for components behind the failed fan. Depending on the situation, the components behind the failed fan may be critically affected by the failure if the good fans stay at capacity. Therefore, it could be critical to reduce the good fans' performance to preserve such sensitive components.
A simulation models a server with 5x fans and 10x generic zones of airflow impedance and power generation. Note that Zones 1 to 10 are left-to-right/top-to-bottom in the figures shown. Each zone uses the following P-Q impedance curves in the Z (axial) and X/Y directions. The five fans are mounted 1cm from the zones. This simulates a system with a minimal plenum, which would experience the greatest degradation of cooling capacity in affected zones if a fan loses a rotor (see Figure 1 below).
/eliminating airflow recirculation in server with selective rotor