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1. Thermal and Exergy Analysis in UPS and Battery Rooms by Numerical Simulations

   Caceres, C; Ortega, A; Silva-Llanca, L; Jones, G; Sapia, N (May 2018, ITHERM)

   UPS (Uninterruptible Power Supply) units and batteries are essential subsystems in data centers or telecom industries to protect equipment from electrical power spikes, surges and power outages. UPS units handle electrical power and dissipate a large amount of heat, and possess a high efficiency. Therefore, cooling units (e.g., CRACs) are needed to manage the thermal reliability of this equipment. On the other hand, battery operating conditions and reliability are closely related to the ambient temperature according to battery manufacturers; reliability increases when the ambient room temperature is around 25ºC. This study analyzed different room configurations and scenarios using the commercial CFD software 6Sigma Room DCXTM. As a first approach, we evaluated the thermal behavior and cooling degradation using standard thermal performance metrics SHI (Supply Heat Index) and RHI (Return Heat Index). These are frequently implemented in data centers to measure the level of mixing between cold and hot air streams. The results from this evaluation showed that standard cooling practices are inefficient, as values for the two metrics differed considerably from industry recommendations. We also considered a metric from the second law of thermodynamics using exergy destruction. This technique allowed us to find the mechanisms that increase entropy generation the most, including viscous shear and air stream mixing. Reducing exergy destruction will result in lessening lost thermodynamic work and thus reduce energy required for cooling. Typically, UPS and batteries are located in different rooms due to the hydrogen generation by the batteries. The integration of both equipment in the same room is a new concept, and this study aims to analyze the thermal performance of the room. Adding controllability showed improvements by reducing the exergy destruction due to viscous dissipation while slightly increasing thermal mixing in the rooms. Ducting the return flows to avoid flow mixing increased pressure drop, but reduced heat transfer between the hot and cold air streams, which in turn, improved the thermal performance. In the study, we determined the optimal configuration and possible strategies to improve cooling while maintaining desirable battery temperatures. 

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2. Identification and Characterization of Particulate Contaminants Found at a Data Center Using Airside Economization

   https://doi.org/10.1115/1.4043481  

   Shah, Jimil M.; Misrak, Abel; Agonafer, Dereje; Kaler, Mike (September 2019, Journal of Electronic Packaging)

   Contamination due to the use of airside economizer has become a major issue that cost companies revenue. This issue will continue to rise as server components become smaller, densely packed, and as companies move into more polluted environments. Contaminants with small particles less than 10 μm are not noticeable; yet, these particles are most likely to get to areas where they can cause damage. Dust from different sources and suspended in air settles on surfaces of electrical components. The dust mainly contains two components: salts and metallic particles. The salts may be neutral or corrosive and the nature of the salt depends on the deliquescent humidity. For metallic particles, surveys are performed in various data centers in order to determine the limits in terms of weight per unit area and particle size distribution. It is necessary to first identify those contaminants that directly affect the information technology (IT) equipment in the data center. In this research, a real-world data center utilizing airside economization in an ANSI/ISA classified G2 environment was chosen for the study. Servers were removed and qualitative study of cumulative corrosion damage was carried out. The particulate contaminants were collected from different locations of a server and material characterization was performed using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and Fourier transform infrared spectroscopy (FTIR). The analysis from these results helps to explain the impact of the contaminants on IT equipment reliability. 

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3. Impact of Immersion Cooling on Thermomechanical Properties of Halogen-Free Substrate Core

   https://doi.org/10.1115/IPACK2023-111056  

   Bansode, Pratik; Ramalingam, Mohan Sai; Suthar, Rohit; Bhandari, Rabin; Lakshminarayana, Akshay Boovanahally; Gupta, Gautam; Simon, Vibin Shalom; Modi, Himanshu; Nair, Vivek; Sivaraju, Krishna Bhavana; et al (October 2023, American Society of Mechanical Engineers)

   Abstract The data center’s server power density and heat generation have increased exponentially because of the recent, unparalleled rise in the processing and storing of massive amounts of data on a regular basis. One-third of the overall energy used in conventional air-cooled data centers is directed toward cooling information technology equipment (ITE). The traditional air-cooled data centers must have low air supply temperatures and high air flow rates to support high-performance servers, rendering air cooling inefficient and compelling data center operators to use alternative cooling technology. Due to the direct interaction of dielectric fluids with all the components in the server, single-phase liquid immersion cooling (Sp-LIC) addresses mentioned problems by offering a significantly greater thermal mass and a high percentage of heat dissipation. Sp-LIC is a viable option for hyper-scale, edge, and modular data center applications because, unlike direct-to-chip liquid cooling, it does not call for a complex liquid distribution system configuration and the dielectric liquid can make direct contact with all server components. Immersion cooling is superior to conventional air-cooling technology in terms of thermal energy management however, there have been very few studies on the reliability of such cooling technology. A detailed assessment of the material compatibility of different electronic packaging materials for immersion cooling was required to comprehend their failure modes and reliability. For the mechanical design of electronics, the modulus, and thermal expansion are essential material characteristics. The substrate is a crucial element of an electronic package that has a significant impact on the reliability and failure mechanisms of electronics at both the package and the board level. As per Open Compute Project (OCP) design guidelines for immersion-cooled IT equipment, the traditional material compatibility tests from standards like ASTM 3455 can be used with certain appropriate adjustments. The primary focus of this research is to address two challenges: The first part is to understand the impact of thermal aging on the thermo-mechanical properties of the halogen-free substrate core in the single-phase immersion cooling. Another goal of the study is to comprehend how thermal aging affects the thermo-mechanical characteristics of the substrate core in the air. In this research the substrate core is aged in synthetic hydrocarbon fluid (EC100), Polyalphaolefin 6 (PAO 6), and ambient air for 720 hours each at two different temperatures: 85°C and 125°C and the complex modulus before and after aging are calculated and compared. 

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4. Identification and Characterization of Particulate Contaminants Found at a Data Center Using Airside Economization

   Shah, J.M. (May 2019, Journal of electronic packaging)

   Contamination due to the use of airside economizer has become a major issue that cost companies revenue. This issue will continue to rise as server components become smaller, densely packed, and as companies move into more polluted environments. Contaminants with small particles less than 10lm are not noticeable; yet, these particles are most likely to get to areas where they can cause damage. Dust from different sources and suspended in air settles on surfaces of electrical components. The dust mainly contains two components: salts and metallic particles. The salts may be neutral or corrosive and the nature of the salt depends on the deliquescent humidity. For metallic particles, surveys are performed in various data centers in order to determine the limits in terms of weight per unit area and particle size distribution. It is necessary to first identify those contaminants that directly affect the information technology (IT) equipment in the datacenter. In this research, a real-world data center utilizing airside economization in an ANSI/ISA classified G2 environment was chosen for the study. Servers were removed and qualitative study of cumulative corrosion damage was carried out. The particulate contaminants were collected from different locations of a server and material characterization was performed using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and Fourier transform infrared spectroscopy (FTIR). The analysis from these results helps to explain the impact of the contaminants on IT equipment reliability. 

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5. Thermal Performance Evaluation of Three Types of Novel End-of-Aisle Cooling Systems

   https://doi.org/10.1115/IPACK2017-74016  

   Sahini, Manasa; Agonafer, Dereje; Pandiyan, Vijayalan (August 2017, ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems)

   Data centers house a variety of compute, storage, network IT hardware where equipment reliability is of utmost importance. Heat generated by the IT equipment can substantially reduce its service life if Tjmax, maximum temperature that the microelectronic device tolerates to guarantee reliable operation, is exceeded. Hence, data center rooms are bound to maintain continuous conditioning of the cooling medium becoming large energy consumers. The objective of this work is to introduce and evaluate a new end-of-aisle cooling design which consists of three cooling configurations. The key objectives of close-coupled cooling are to enable a controlled cooling of the IT equipment, flexible as well as modular design, and containment of hot air exhaust from the cold air. The thermal performance of the proposed solution is evaluated using CFD modeling. A computational model of a small size data center room has been developed. Larger axial fans are selected and placed at rack-level which constitute the rack-fan wall design. The model consists of 10 electronic racks each dissipating a heat load of 8kw. The room is modeled to be hot aisle containment i.e. the hot air exhaust exiting for each row is contained and directed within a specific volume. Each rack has passive IT with no server fans and the servers are cooled by means of rack fan wall. The cold aisle is separated with hot aisle by means of banks of heat exchangers placed on the either sides of the aisle containment. Based on the placement of rack fans, the design is divided to three sub designs — case 1: passive heat exchangers with rack fan walls; case 2: active heat exchangers (HXs coupled with fans) with rack fan walls; case 3: active heat exchangers (hxs coupled with fans) with no rack fans. The cooling performance is calculated based on the thermal and flow parameters obtained for all three configurations. The computational data obtained has shown that the case 1 is used only for lower system resistance IT. However, case 2 and Case 3 can handle denser IT systems. Case 3 is the design that can consume lower fan energy as well as handle denser IT systems. The paper also discusses the cooling behavior of each type of design. 

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