Distributed Leakage Flow in Raised-Floor Data Centers

In raised-floor data centers, distributed leakage flow—the airflow through seams between panels on the raised floor—reduces the amount of cooling air available at the inlets of the computer equipment. This airflow must be known to determine the total cooling air requirement in a data center. The amount of distributed leakage flow depends on the area of the seams and the plenum pressure, which, in turn, depends on the amount of airflow into the plenum and the total open area (combined area of perforated tiles, cutouts, and seams between panels) on the raised floor. The goal of this study is to outline a procedure to measure leakage flow, to provide data on the amount of the distributed leakage flow, and to show the quantitative relationship between the leakage flow and the leakage area. It also uses a computational model to calculate the distributed leakage flow, the flow through perforated tiles, and the plenum pressure. The results obtained from the model are verified using the measurements. Such a model can be used for design and maintenance of data centers. The measurements show that the leakage flow in a typical data center is between 5–15% of the available cooling air. The measured quantities were used to estimate the area of the seams; for this data center, it was found to be 0.35% of the floor area. The computational model represents the actual physical scenarios very well. The discrepancy between the calculated and measured values of leakage flow, flow through perforated tiles, and plenum pressure is less than 10%.

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Perimeter Cooling Unit and Localized Row-Based Cooling Unit Transient Air Flow Effects Modeling and Characterization in Data Centers

Volume 8B: Heat Transfer and Thermal Engineering ◽

10.1115/imece2015-51012 ◽

2015 ◽

Author(s):

Tianyi Gao ◽

James Geer ◽

Bahgat G. Sammakia ◽

Russell Tipton ◽

Mark Seymour

Keyword(s):

Thermal Management ◽

Data Center ◽

Data Centers ◽

Cooling System ◽

Air Flow ◽

Cooling Systems ◽

Dynamic Thermal Management ◽

Hybrid Cooling ◽

Cooling Unit ◽

Cooling Air

Cooling power constitutes a large portion of the total electrical power consumption in data centers. Approximately 25%∼40% of the electricity used within a production data center is consumed by the cooling system. Improving the cooling energy efficiency has attracted a great deal of research attention. Many strategies have been proposed for cutting the data center energy costs. One of the effective strategies for increasing the cooling efficiency is using dynamic thermal management. Another effective strategy is placing cooling devices (heat exchangers) closer to the source of heat. This is the basic design principle of many hybrid cooling systems and liquid cooling systems for data centers. Dynamic thermal management of data centers is a huge challenge, due to the fact that data centers are operated under complex dynamic conditions, even during normal operating conditions. In addition, hybrid cooling systems for data centers introduce additional localized cooling devices, such as in row cooling units and overhead coolers, which significantly increase the complexity of dynamic thermal management. Therefore, it is of paramount importance to characterize the dynamic responses of data centers under variations from different cooling units, such as cooling air flow rate variations. In this study, a detailed computational analysis of an in row cooler based hybrid cooled data center is conducted using a commercially available computational fluid dynamics (CFD) code. A representative CFD model for a raised floor data center with cold aisle-hot aisle arrangement fashion is developed. The hybrid cooling system is designed using perimeter CRAH units and localized in row cooling units. The CRAH unit supplies centralized cooling air to the under floor plenum, and the cooling air enters the cold aisle through perforated tiles. The in row cooling unit is located on the raised floor between the server racks. It supplies the cooling air directly to the cold aisle, and intakes hot air from the back of the racks (hot aisle). Therefore, two different cooling air sources are supplied to the cold aisle, but the ways they are delivered to the cold aisle are different. Several modeling cases are designed to study the transient effects of variations in the flow rates of the two cooling air sources. The server power and the cooling air flow variation combination scenarios are also modeled and studied. The detailed impacts of each modeling case on the rack inlet air temperature and cold aisle air flow distribution are studied. The results presented in this work provide an understanding of the effects of air flow variations on the thermal performance of data centers. The results and corresponding analysis is used for improving the running efficiency of this type of raised floor hybrid data centers using CRAH and IRC units.

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Adiabatic Effectiveness Measurements and Predictions of Leakage Flows Along a Blade Endwall

Journal of Turbomachinery ◽

10.1115/1.1929809 ◽

2005 ◽

Vol 127 (3) ◽

pp. 609-618 ◽

Cited By ~ 9

Author(s):

W. W. Ranson ◽

K. A. Thole ◽

F. J. Cunha

Keyword(s):

High Pressure ◽

Turbine Blades ◽

Leakage Flow ◽

Leakage Flows ◽

High Pressure Compressor ◽

Flow Through ◽

Cooling Air ◽

Low Speed Wind Tunnel ◽

Paper Address ◽

Good Agreement

Traditional cooling schemes have been developed to cool turbine blades using high-pressure compressor air that bypasses the combustor. This high-pressure forces cooling air into the hot main gas path through seal slots. While parasitic leakages can provide a cooling benefit, they also represent aerodynamic losses. The results from the combined experimental and computational studies reported in this paper address the cooling benefit from leakage flows that occur along the platform of a first stage turbine blade. A scaled-up, blade geometry with an upstream slot, a mid-passage slot, and a downstream slot was tested in a linear cascade placed in a low-speed wind tunnel. Results show that the leakage flow through the mid-passage gap provides only a small cooling benefit to the platform. There is little to no benefit to the blade platform that results by increasing the coolant flow through the mid-passage gap. Unlike the mid-passage gap, leakage flow from the upstream slot provides good cooling to the platform surface, particularly in certain regions of the platform. Relatively good agreement was observed between the computational and experimental results, although computations overpredicted the cooling.

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Design analysis and Work load characteristics of a Micro data Center

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/850/1/012018 ◽

2021 ◽

Vol 850 (1) ◽

pp. 012018

Author(s):

T Renugadevi ◽

D Hari Prasanth ◽

Appili Yaswanth ◽

K Muthukumar ◽

M Venkatesan

Keyword(s):

Data Storage ◽

Data Center ◽

Large Scale ◽

Data Centers ◽

Work Load ◽

Micro Data ◽

Air Gaps ◽

Cooling Unit ◽

Cooling Air ◽

Quantity Of Heat

Abstract Data centers are large-scale data storage and processing systems. It is made up of a number of servers that must be capable of handling large amount of data. As a result, data centers generate a significant quantity of heat, which must be cooled and kept at an optimal temperature to avoid overheating. To address this problem, thermal analysis of the data center is carried out using numerical methods. The CFD model consists of a micro data center, where conjugate heat transfer effects are studied. A micro data center consists of servers aligned with air gaps alternatively and cooling air is passed between the air gaps to remove heat. In the present work, the design of data center rack is made in such a way that the cold air is in close proximity to servers. The temperature and airflow in the data center are estimated using the model. The air gap is optimally designed for the cooling unit. Temperature distribution of various load configurations is studied. The objective of the study is to find a favorable loading configuration of the micro data center for various loads and effectiveness of distribution of load among the servers.

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Technologies for the Energy-Efficient Data Center

ASME 2007 InterPACK Conference, Volume 1 ◽

10.1115/ipack2007-33463 ◽

2007 ◽

Cited By ~ 1

Author(s):

Tahir Cader ◽

Levi Westra ◽

Andres Marquez

Keyword(s):

Pacific Northwest ◽

Data Center ◽

Data Centers ◽

Cost Ratio ◽

Typical Data ◽

The Pacific ◽

Power Usage Effectiveness ◽

Four Levels ◽

Broad Cross Section ◽

The Impact

Although semiconductor manufacturers have provided temporary relief with lower-power multi-core microprocessors, OEMs and data center operators continue to push the limits for individual rack power densities. It is not uncommon today for data center operators to deploy multiple 20 kW racks in a facility. Such rack densities are exacerbating the major issues of power and cooling in data centers. Data center operators are now forced to take a hard look at the efficiencies of their data centers. Malone and Belady (2006) have proposed three metrics, i.e., Power Usage Effectiveness (PUE), Data Center Efficiency (DCE), and the Energy-to-Acquisition Cost ratio (EAC), to help data center operators quickly quantify the efficiency of their data centers. In their paper, Malone and Belady present nominal values of PUE across a broad cross-section of data centers. PUE values are presented for data centers at four levels of optimization. One of these optimizations involves the use of Computational Fluid Dynamics (CFD). In the current paper, CFD is used to conduct an in-depth investigation of a liquid-cooled data center that would potentially be housed at the Pacific Northwest National Labs (PNNL). The boundary conditions used in the CFD model are based upon actual measurements on a rack of liquid-cooled servers housed at PNNL. The analysis shows that the liquid-cooled facility could achieve a PUE of 1.57 as compared to a PUE of 3.0 for a typical data center (the lower the PUE, the better, with values below 1.6 approaching ideal). The increase in data center efficiency is also translated into an increase in the amount of IT equipment that can be deployed. At a PUE of 1.57, the analysis shows that 91% more IT equipment can be deployed as compared to the typical data center. The paper will discuss the analysis of the PUE, and will also explore the impact of the raising data center efficiency via the use of multiple cooling technologies and CFD analysis. Complete results of the analyses will be presented in the paper.

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Improving Cooling Efficiency by Using Mixed Tiles to Control Airflow Uniformity of Perforated Tiles in a Data Center Model

Volume 1: Aerospace Heat Transfer; Computational Heat Transfer; Education; Environmental Heat Transfer; Fire and Combustion Systems; Gas Turbine Heat Transfer; Heat Transfer in Electronic Equipment; Heat Transfer in Energy Systems ◽

10.1115/ht2017-5022 ◽

2017 ◽

Author(s):

Long Phan ◽

Sadhana Bhusal ◽

Cheng-Xian Lin

Keyword(s):

Power Density ◽

Simulation Study ◽

Data Center ◽

Data Centers ◽

Industrial Sector ◽

Cooling Efficiency ◽

Direct Impact ◽

Flow Through ◽

Energy Consumptions ◽

Heat Loads

Data centers in recent years have grown so fast so that their energy consumptions become a big issue in the industrial sector. One of the strategies to make better use of energy in data centers is to improve the efficiency in cooling. As the load density in data centers increases dramatically over the years, the number of computer room air handlers (CRAHs) are also increased to accommodate the high cooling demands. However, the number of CRAH units and their layouts really affect the air flow through the perforated tiles. Non-uniform airflow distributions in the perorated tiles in the cold aisles cause inefficient cooling of all the servers mounted in racks in data centers. Application of necessary strategies to minimize airflow non-uniformity is therefore very important because of its direct impact on the power density capacity. In this paper, a simulation study to examine how computer room air handler (CRAH) positions, the number of operating units, and tile types affect the airflow uniformity in selected data center models. Also, the placement of mixed tiles in cold aisles to regulate the airflow through the perforated tiles to accommodate greater heat loads from server racks is evaluated.

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Adiabatic Effectiveness Measurements and Predictions of Leakage Flows Along a Blade Endwall

Heat Transfer, Volume 2 ◽

10.1115/imece2004-62021 ◽

2004 ◽

Cited By ~ 4

Author(s):

W. W. Ranson ◽

K. A. Thole ◽

F. J. Cunha

Keyword(s):

High Pressure ◽

Turbine Blades ◽

Leakage Flow ◽

Leakage Flows ◽

High Pressure Compressor ◽

Flow Through ◽

Cooling Air ◽

Low Speed Wind Tunnel ◽

Paper Address ◽

Good Agreement

Traditional cooling schemes have been developed to cool turbine blades using high-pressure compressor air that bypasses the combustor. This high pressure forces cooling air into the hot main gas path through seal slots. While parasitic leakages can provide a cooling benefit, they also represent aerodynamic losses. The results from the combined experimental and computational studies reported in this paper address the cooling benefit from leakage flows that occur along the platform of a first stage turbine blade. A scaled-up, blade geometry with an upstream slot, a mid-passage slot, and a downstream slot was tested in a linear cascade placed in a low speed wind tunnel. Results show that the leakage flow through the mid-passage gap provides only a small cooling benefit to the platform. There is little to no benefit to the blade platform that results by increasing the coolant flow through the mid-passage gap. Unlike the mid-passage gap, leakage flow from the upstream slot provides good cooling to the platform surface, particularly in certain regions of the platform. Relatively good agreement was observed between the computational and experimental results although computations overpredicted the cooling.

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Optimization of Cold Aisle Isolation Designs for a Data Center With Roofs and Doors Using Slits

ASME 2009 InterPACK Conference, Volume 2 ◽

10.1115/interpack2009-89203 ◽

2009 ◽

Cited By ~ 10

Author(s):

Srujan Gondipalli ◽

Bahgat Sammakia ◽

Siddarth Bhopte ◽

Roger Schmidt ◽

Madhusudan K. Iyengar ◽

...

Keyword(s):

Data Center ◽

Data Centers ◽

Heat Fluxes ◽

Low Velocity ◽

Cold Air ◽

Average Temperature ◽

Hot Air ◽

Large Numbers ◽

Typical Data ◽

Air Streams

Data centers are facilities that house large numbers of computer servers that typically dissipate high power. With the rapid increase in the heat flux of such systems, their thermal management represents an economic and environmental challenge that needs to be addressed [2]. Considering the trends of increasing heat loads and heat fluxes, the focus for users is in providing adequate airflow through the equipment at a temperature that meets the manufacturers’ requirements. Data centers house IT equipment in racks typically arranged in rows which face one another. Alternating cold and hot aisles are formed and this pattern is repeated across the data center. This approach helps to separate cold and hot air streams; but this does not always suffice in the separation of cold and hot air. The mixing of hot rack exhaust air with cold supply air, short-circuiting of cold air to the coolers and the recirculation of hot air to racks’ inlet are the common phenomena that lead to thermal inefficiencies in a typical data center. Typically in a raised floor data center, increase in rack inlet air temperature is seen because of the infiltration of hot air into the cold aisle from the top (ceiling of the cold aisle) and from edges or sides. Infiltration can be reduced to a certain extent if cold aisles are isolated from ceiling and hot aisles using partially or fully closed doors with slits to manage the airflow. The key is to redistribute the cold air entering the cold aisle along with any infiltration such that the overall average temperature at the rack inlets is below a predefined level. In this paper, different designs were generated with the criteria of achieving no hotspots, a relatively low pressure drop across the servers and low velocity of the air in the cold aisle based on an actual data center model. Several designs are proposed that meet all of the defined constraints.

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Optimization of Enclosed Aisle Data Centers Using Bypass Recirculation

Journal of Electronic Packaging ◽

10.1115/1.4005907 ◽

2012 ◽

Vol 134 (2) ◽

Cited By ~ 18

Author(s):

Dustin W. Demetriou ◽

H. Ezzat Khalifa

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Energy Consumption ◽

Data Center ◽

Data Centers ◽

Total Power ◽

Total Energy Consumption ◽

Air Conditioners ◽

Data Center Cooling ◽

Flow Through

The work presented in this paper describes a simplified thermodynamic model that can be used for exploring optimization possibilities in air-cooled data centers. The model is used to evaluate parametrically the total energy consumption of the data center cooling infrastructure for data centers that utilize aisle containment. The analysis highlights the importance of reducing the total power required for moving the air within the computer room air conditioners (CRACs), the plenum, and the servers, rather than focusing primarily or exclusively on reducing the refrigeration system’s power consumption. In addition, the benefits of introducing a bypass recirculation branch in enclosed aisle configurations are shown. The analysis shows a potential for as much as a 60% savings in cooling infrastructure energy consumption by utilizing an optimized enclosed aisle configuration with bypass recirculation, instead of a traditional enclosed aisle in which all the data center exhaust is forced to flow through the CRACs. Furthermore, computational fluid dynamics is used to evaluate practical arrangements for implementing bypass recirculation in raised floor data centers. A configuration where bypass tiles, with controllable low-lift fans, are placed close to the discharge of CRACs results in increased mixing and is shown to be a suitable method for providing nearly thermally uniform conditions to the inlet of the servers in an enclosed cold aisle. Other configurations of bypass implementation are also discussed and explored.

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Data Center Equipment Reliability Concerns—Contamination Issues, Standards Actions, and Case Studies

ISTFA 2013: Conference Proceedings from the 39th International Symposium for Testing and Failure Analysis ◽

10.31399/asm.cp.istfa2013p0438 ◽

2013 ◽

Author(s):

Chris Muller ◽

Chuck Arent ◽

Henry Yu

Keyword(s):

Case Studies ◽

Data Center ◽

Data Centers ◽

Electronic Equipment ◽

Circuit Board ◽

Lead Free ◽

Reliable Operation ◽

Contamination Assessment ◽

Equipment Reliability ◽

Equipment Failures

Abstract Lead-free manufacturing regulations, reduction in circuit board feature sizes and the miniaturization of components to improve hardware performance have combined to make data center IT equipment more prone to attack by corrosive contaminants. Manufacturers are under pressure to control contamination in the data center environment and maintaining acceptable limits is now critical to the continued reliable operation of datacom and IT equipment. This paper will discuss ongoing reliability issues with electronic equipment in data centers and will present updates on ongoing contamination concerns, standards activities, and case studies from several different locations illustrating the successful application of contamination assessment, control, and monitoring programs to eliminate electronic equipment failures.

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