Bio-Analysis of Cross-Mixed Coolants in High Powered Liquid Cooled Data Center
Authors: Shahi Pardeep , Heydari Ali , Chinthaparthy Lochan Sai Reddy , Modi Himanshu , Barigala Anto , Sivapalan Sean , Miyamura Harold , Agonafer Dereje , Tradat Mohammad , Rodriguez Jeremy 
Published: November 2024

The growing need for high-performance liquid-cooled data centers emphasizes the need to ensure the reliability of coolant solutions, namely propylene glycol. This abstract aims to examine the significance of employing reliability testing methods recommended by the Open Compute Project (OCP) and ASTM testing procedures, including ASTM D1384 and D8040. These standardized testing procedures may be used to confirm the effectiveness and long-lasting nature of propylene glycol’s corrosion inhibitors in data center cooling systems, which operate under challenging conditions.

In the context of liquid cooling methods, the use of cold plates and cooling loops is crucial for ensuring effective heat transfer. Prior to installation in data centers, vendors subject these components to rigorous testing using specifically formulated coolants. Following the flushing of TCS (technology cooling system) loops and equipment such as CDU (Coolant distribution units) and manifolds, any remaining coolant will be drained. However, it is important to note that achieving a complete removal of coolant is not possible, as there will always be residual amounts left behind. These residuals can contaminate the loop when a different type of coolant is introduced at data center sites. This can lead to performance issues and a reduction in the reliability of the coolant, potentially resulting in the growth of biological organisms.

Bio growth, resulting from cross-contamination of multiple coolants in a liquid-cooled data centers, poses a significant threat to their reliability and efficiency. The presence of bacterial variants in the coolant can lead to fouling, corrosion, and inefficient heat transmission, ultimately jeopardizing the functionality of critical information technology infrastructure. To avoid this risk, it is necessary to design reliability testing procedures that focus on evaluating the resistance of coolants to bio-growth in real-world operating conditions.

In the first test, a coupon set made up of the wetted materials used in a data center TCS loop will be submerged for a considerable amount of time at a temperature that is suitable for bio-growth in a known concentration of cross-contaminated solution. Sampling will be conducted at thirty-day intervals to analyze microbial growth. This test simulates the stagnant condition of cooling loops and data center equipment that will be stored in storage rooms. For the second test, we employed a cooling loop including a micro-fin channeled cold plate and utilized a flushing approach often employed by data center facilities and equipment suppliers. During the test, a water-based coolant was continuously circulated in the loop at a desired inlet temperature. A heat load is constantly provided to the heater which mimics the CPU/GPU in a data center. Subsequently, a sample was collected at regular intervals and analyzed to determine the existence of microbial growth. The test mimics a data center site, employing various coolants based on the required degree of thermal efficiency.

Data center operators can ensure the reliability of the coolant by conducting simulations, complying with standards, and doing thorough testing. Testing evaluates the coolant’s resistance to bio-growth and contamination to guarantee that it does not impact the functioning of the IT (Information Technology) systems. Assessing coolant’s reliability in liquid-cooled facilities enhances the system’s durability and effectiveness. Adhering to OCP standards and ASTM protocols guarantees the suitability of coolant, so safeguarding data centers from the constantly changing challenges they encounter. By using this comprehensive strategy, both reliability and performance are upheld, effectively meeting the demands of contemporary computing.