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In this review, the heat transfer characteristics of several pumped two-phase electronic cooling technologies are quantitatively examined and compared on the basis of heat flux, coolant temperatures, heat source area, base temperature, and coolant type. Cooling by parallel flow in mini/microchannels, pin fins, spray cooling, and jet impingement are discussed in detail. Chip powers up to 2.9 kW and heat fluxes 910 W/cm2 were demonstrated. The different surface modification techniques used to enhance heat transfer in all four technologies are also presented. Various coolants used in two-phase cooling applications are also quantitatively compared in terms of heat transfer coefficient (HTC), wall temperature, and heat source area. The current issues and potential research in two-phase cooling were also discussed. Water cooling has really high performance in terms of HTC. However, it is challenging for scientists and engineers to implement two-phase cooling with water at wall temperature lower than 100 °C due to high boiling point of water at atmospheric pressure. Therefore, two-phase cooling with water can be implemented in types of electronics that can tolerate higher junction temperature. Although having lower HTC, due to lower boiling point at atmospheric pressure, dielectric coolant can be a promising solution in two-phase cooling when lower chip temperatures are required. Geometry optimization of heat sinks is a promising research topic and has not been studied extensively considering the geometry parameters and solid–liquid interaction that affect thermal and hydraulic performance.

Growing demand for dense and high-performing IT compute capacity to support deep learning and artificial intelligence workloads necessitates data centers to look for more robust thermal management strategies. Today, data centers across the world are turning to liquid-based cooling solutions to keep up with the increased cooling demand for high power racks approaching 100kW of heat dissipation. Deploying direct-to-chip cold plate liquid cooling is one of the mainstream approaches which allows targeted cooling of high-power processors. This study provides the framework for a hybrid in row cooler (IRC) with liquid-to-air (L2A) heat exchanger (HX) system delivering chilled coolant to liquid-cooling cold plates mounted to the high heat dissipation electronics. This approach is useful for high heat density cooling of racks where no primary facility coolant is available at the data center. The present study aims to investigate the thermo-hydraulic performance of a distinct L2A IRC system that supplies cold secondary coolant (PG 25%) into the cooling loops of liquid-cooled servers in racks within an existing air-cooled data center. Thermal test vehicles (TTVs) are built to replicate actual high heat density servers. From the cold plate to data center level the proper choice of each level component was described based on their cooling performance and relevance. Three different cooling loop/rack designs are characterized experimentally, and detailed analytical and numerical (FNM) simulations are developed to analyze the heat exchanger performance. The FNM and CFD model of a data center are done in two steady and transient forms to study the performance of the L2A IRC in a data center.

More than ever before, data centers must deploy robust thermal solutions to adequately host the high-density and high-performance computing that is in high demand. The newer generation of central processing units (CPUs) and graphics processing units (GPUs) has substantially higher thermal power densities than previous generations. In recent years, more data centers rely on liquid cooling for the high-heat processors inside the servers and air cooling for the remaining low-heat information technology equipment. This hybrid cooling approach creates a smaller and more efficient data center. The deployment of direct-to-chip cold plate liquid cooling is one of the mainstream approaches to providing concentrated cooling to targeted processors. In this study, a processor-level experimental setup was developed to evaluate the cooling performance of a novel computer numerical control (CNC) machined nickel-plated impinging cold plate on a 1 in. × 1 in. mock heater that represents a functional processing unit. The pressure drop and thermal resistance performance curves of the electroless nickel-plated cold plate are compared to those of a pure copper cold plate. A temperature uniformity analysis is done using compuational fluid dynamics and compared to the actual test data. Finally, the CNC machined pure copper one is compared to other reported cold plates to demonstrate its superiority of the design with respect to the cooling performance.

The increased power consumption and continued miniaturization of high-powered electronic components have presented many challenges to their thermal management. To improve the efficiency and reliability of these devices, the high amount of heat that they generate must be properly removed. In this paper, a three-dimensional numerical model has been developed and experimentally validated for several manifold heat sink designs. The goal was to enhance the heat sink's thermal performance while reducing the required pumping power by lowering the pressure drop across the heat sink. The considered designs were benchmarked to a commercially available heat sink in terms of their thermal and hydraulic performances. The proposed manifolds were designed to distribute fluid through alternating inlet and outlet branched internal channels. It was found that using the manifold design with 3 channels reduced the thermal resistance from 0.061 to 0.054 °C/W with a pressure drop reduction of 0.77 kPa from the commercial cold plate. A geometric parametric study was performed to investigate the effect of the manifold's internal channel width on the thermohydraulic performance of the proposed designs. It was found that the thermal resistance decreased as the manifold's channel width decreased, up until a certain width value, below which the thermal resistance started to increase while maintaining low-pressure drop values. Where the thermal resistance significantly decreased in the 7 channels design by 16.4% and maintained a lower pressure drop value below 0.6 kPa.

An increasingly common power saving practice in data center thermal management is to swap out air cooling unit blower fans with electronically commutated plug fans, Although, both are centrifugal blowers. The blade design changes: forward versus backward curved with peak static efficiencies of 60% and 75%, respectively, which results in operation power savings. The side effects of which are not fully understood. Therefore, it has become necessary to develop an overall understanding of backward curved blowers and compare the resulting flow, pressure, and temperature fields with forwarding curved ones in which the induced fields are characterized, compared, and visualized in a reference data center which may aid data center planning and operation when making the decisions of which computer room air handler (CRAH) technology to be used. In this study, experimental and numerical characterization of backward curved blowers is introduced. Then, a physics-based computational fluid dynamics model is built using the 6sigmaroom tool to predict/simulate the measured fields. Five different scenarios were applied at the room level for the experimental characterization of the cooling units and another two scenarios were applied for comparison and illustration of the interaction between different CRAH technologies. Four scenarios were used to characterize a CRAH with backward curved blowers, during which a CRAH with forwarding curved was powered off. An alternate arrangement was examined to quantify the effect of possible flow constraints on the backward curved blower's performance. Then parametric and sensitivity of the baseline modeling are investigated and considered. Different operating conditions are applied at the room level for experimental characterization, comparison, and illustration of the interaction between different CRAH technologies. The measured data is plotted and compared with the computational fluid dynamics (CFD) model assessment to visualize the fields of interest. The results show that the fields are highly dependent on CRAH technology. The tile to CRAH airflow ratios for the flow constraints of scenarios 1, 2, 3, and 4 are 85.5%, 83.9%, 61%, and 59%, respectively. The corresponding leakage ratios are 14.5%, 16%, 38.9%, and 41%, respectively. Furthermore, the validated CFD model was used to investigate and compare the airflow pattern and plenum pressure distribution. Lastly, it is notable that a potential side effect of backward curved technology is the creation of an airflow dead zone.

The miniaturization of microelectronic devices and an increasing demand for faster computing results in high heat flux applications. By adopting direct liquid cooling, the high heat flux and high-power demands can be met. In this paper, thermo-hydraulic performance of a commercial hybrid micro-channel/multi-jet heat sink with water coolant was analyzed in detail. The copper microchannel heat sink with 3 mm fin height, fin thickness of 0.1 mm and channel width of 0.1 mm was used for removing heat flux from the chip surface area of 1″ × 1″(6.45 cm2). Water coolant was directed to microchannel fins by multiple slot jets, continuously providing impingement flow. A three-dimensional numerical simulation using commercial software 6sigmaET is carried out and validated with experimental results. The effects of the coolant inlet temperature and flow rate on the thermo-hydraulic performance was studied. CFD simulation was performed at inlet temperature of 29 °C, 36 °C, 50 °C and 60 °C. Flow rate was varied from 0.7 LPM to 3 LPM. Geometry optimization was performed, considering process of cutting the microchannel into pin fins. It was observed that the thermal resistance of pin-fins/multi-jet heat sink was reduced by 29.4 % as compared to original microchannel/multi-jet heat sink and without changing pressure drop significantly. In this specific heat sink design, the combination of multiple jets and pin fins leads to improvement of thermal performance as compared to micro-channel/multi-jet combination.

This paper focuses on two-phase flow boiling of dielectric coolant HFE 7000 inside a copper multi-microchannel heat sink for high heat flux chip applications. The heat sink is composed of parallel microchannels, 200 µm wide, 2500 µm high, and 20 mm long, with 200-µm-thick fins separating the channels. The copper heat sink consists of almost 100 channels connected by a longitude groove with a nearly trapezoidal cross section. Coolant impinges down to the base at the groove and then goes along the microchannels. A copper block heater arrangement was used to mimic a computer chip with a footprint of 1"x1" (6.45 cm2). The base heat flux was varied from 7.75 W/cm2 to 96.1 W/cm2 and the mass flux from 547.6 to 958.4 kg/m2s, at a nominal saturation temperature of 54 °C. Heat transfer coefficients as high as 57.5 Kw/m2K were reached, keeping the base temperature under 66 °C with a maximum of 21.9 kPa of pressure drop, for inlet subcooling of 5 degree and a coolant flow rate of 958.4 kg/m2. Effects of inner diameter of tubing on thermal performance and pressure drop are also discussed. It was observed that an increase of tubing inner diameter by 60 % can result in increase of heat transfer coefficient by 47.8 % and reduction in pressure drop by 63 %.

Data center cooling energy efficiency is critical to the successful operation of modern large data centers. In 2014, data centers in the U.S. consumed an estimated 70 billion kWh of electricity, representing about 1.8% of total U.S. electricity consumption. Given that the cooling infrastructure can average 40% of the total data center energy consumption, suggests the data center cooling energy consumed in 2014 can be approximated at 28 billion kWh. These numbers indicate that improving airflow management in order to improve the efficiency of cooling in data centers can significantly affect operating costs and allow for increased IT capacity, thereby extending the life of the data center. Some of the methods used to improve airflow include, but are not limited to, hot aisle and cold aisle containment, IT equipment alignment and configuration changes, bypass air management (e.g. cable penetrations), recirculation management (e.g. blanking panels). Other methods that can be deployed to improve cooling energy efficiency include air and/or waterside economization, variable frequency drives (VFD), and increased IT equipment inlet (supply air) temperatures, etc.Most of the above-mentioned thermal management technologies concentrate on managing airflow to achieve the desired server inlet temperature (supply air operating set point) and not to manage the amount of cool air (CFM) that each IT server should receive in order to remove the produced heat. However, airflow is equally important for quantifying adequate cooling to IT equipment, but it is more challenging to measure the airflow per server and hence per rack. Therefore, as a potential option for measuring this airflow an experimental based airflow measurement was performed in this study to quantify and compare between different devices including commercial flow hood, vane anemometer, and Mobile Temperature/Velocity Mesh (MTVM). Furthermore, the effect of measurement location (rack front/rear), type of IT equipment/rack, rack location and depth were investigated. On one hand, the results revealed that the rack airflow rate prediction using average inlet/outlet temperature across the rack was the most accurate and practical technique when compared to airflow reference value which was based on IT equipment pressure-flowrate curve. On the other hand, the measured flow rate using the flow hood at rack inlet face reported a 10% off from the reference value for rack C 1-8. Using flow hood for rack airflow is impractical to be used in real data centers. Therefore and based on the conducted comparison in this study, measuring air temperature across the rack inlet and outlet could be the easiest method to predict the actual rack airflow rate (i.e. supply at rack intake) and hence manage the airflow by compromising the supply to the IT equipment demand based on their flow curves.

It is well known that fans have been widely used in many applications for cooling and ventilation purposes. However, in a considerable portion of these applications, fans are being operated in highly resistive environments such as ITE (Information Technology Equipment) in which the fan will be installed in a narrow space surrounded by many obstacles. These obstructions lead to increased vibration and degradation in fan performance. As the fans’ pressure-flow rate (P-Q) curve is used to indicate the fan's performance, previous studies have investigated the blockage effect on the fan's P-Q curve using a flow test chamber. However, these studies measured the pressure from a considerable distance from the fan. Hence, developing a new technique that can measure the pressure closer to the fan will help in conducting a better understanding of how fans react to the presence of obstruction. In this work, pressure readings were taken through pressure taps that were drilled in a plexiglass sheet an experimental setup was designed to study the server chassis blockage effect on the fan performance by getting a multiple pressure reading right across the fans. These measurements were compared with pressure measurements that were collected from the flow test chamber at a considerable distance from the fan.

In most data centers, performance reliability is often ensured by setting the amount of airflow provided by the cooling units to substantially exceed that which is needed by the IT equipment. This overly conservative strategy requires additional energy expenditure, which inevitably results in a huge amount of energy being wasted by the cooling system. To eliminate adopting such wasteful policies, conducting proper management of airflow, temperature, and energy is critical. To that end, this work proposes a novel approach to developing a compact IT equipment model at off-design conditions. This model is designed to support thermal and energy management functions in data centers. The benefit of this model is that it can accurately predict not only the IT equipment power consumption, but also the amount of flowrate required for the equipment and the air temperature leaving the equipment. While the compact model’s power consumption was derived as a function of CPU utilization, its flowrate demand and exhaust temperature were obtained from a dynamic detailed CFD model. Results from the compact model were validated with experiments where the maximum mismatch was found to be 5.7% in the outlet temperature field and 11.4% in flowrate. Compared to a state-of-the-art IT equipment compact model, the developed model was found to reduce the prediction error of the equipment’s flowrate and outlet air temperature by up to 5.2% and 9.3 % that of the state-of-the-art IT equipment compact model, respectively.

With the remarkable surge in IT power densities and energy consumption, the data center industry is starting to adopt energy and thermally-efficient single-phase cooling technologies. For many legacy data centers worldwide, the lack of a primary chilled water source is a substantial barrier to adopting single-phase technologies. In this study, the necessity of having a facility chilled water source for deploying liquid cooling solutions is eliminated by introducing a solution that does not require bringing in any modification of the data center layout. This simple solution proposes integrating liquid to air heat exchangers with the floor tiles to eject heat from the liquid-cooled IT equipment into the room air. An experimentally validated CFD modeling approach is used to investigate the performance of these heat exchangers. Results show that by installing two heat exchangers in different cold aisles, a significant amount of cooling load is handled at the design point conditions. When they are tested under different operational conditions, the cooling capacity of these heat exchangers is shown to be sensitive to the supply air temperature. To overcome the operational constraints stemming from the supply air temperature, an alternative configuration with just one heat exchanger installed in the hot aisle is considered and discussed. Results indicate that the second configuration shows superior performance to the first one in terms of sensitivity to supply air temperature and cooling capacity. Lastly, with this configuration, the data center utilizes energy extremely efficiently and achieves a power usage effectiveness of 1.06.

As the world is moving toward edge computing, the need for small scale, widely distributed data centers became more critical. The traditional raised floor cooling techniques might not be applicable in these data centers and it could be more efficient to use in-row coolers. Recently, a small-scale data center was built at Binghamton University. This data center consists of ten cabinets and six in-row air cooling units combined into a single cold aisle enclosure. In this study, a CFD model for this data center is built considering all components using Future Facilities CFD tool (6SigmaRoom). After that, this model is utilized to conduct a detailed computational heat transfer analysis. These analyses include: the data center heat load, IT-equipment different configurations, in-row coolers supply air temperature, in-row coolers airflow rate, the data center running cost and some instructions to improve the data center performance. Moreover, behaviors that could harm the IT-equipment were identified and proposed solutions to ensure the IT -equipment reliability were presented. Results showed that the data center heat load should be limited to 156 kW (15.6 kW per cabinet) and the supply air temperature should not exceed 23°C. In case of installing switches, cabinet load should be limited to 14 kW.

Miniaturization of microelectronic components comes at a price of high heat flux density. By adopting liquid cooling, the rising demand of high heat flux devices can be met while the reliability of the microelectronic devices can also be improved to a greater extent. Liquid cooled cold plates are largely replacing air based heat sinks for electronics in data center applications, thanks to its large heat carrying capacity. A bench level study was carried out to characterize the thermohydraulic performance of microchannel cold plates which uses warm De-Ionized (DI) water for cooling Multi Chip Modules (MCM). A laboratory built mock package housing mock chips and a heat spreader was employed while assessing the thermal performance of three different cold plate designs at varying coolant flow rate and temperature. The case temperature measured at the heat spreader for varying flow rates and input power were essential in identifying the convective resistance corresponding to the cold plates. The flow performance was evaluated by the measuring the pressure drop across cold plate module at varying flow rates. Cold plate with the enhanced microchannel design yielded better results compared to a traditional parallel microchannel design. The experimental results were validated using a numerical model which is further optimized for improved geometric designs. Finally, an estimation of chiller operating cost was obtained for a 100% air cooled facility and compared their performance to that of a 60% warm water cooled facility.

Most of the thermal management technologies concentrate on managing airflow to achieve the desired server inlet temperature (supply air operating set point) and not to manage/improve the amount of cool air (CFM) that each computer rack (i.e. IT servers) should receive in order to remove the produced heat. However, airflow is equally important for quantifying adequate cooling to IT equipment, but it is more challenging to obtain a uniform airflow distribution at the inlet of computer racks. Therefore, as a potential option for improving airflow distribution is to eliminate the sources of non-uniformities such as maldistribution of under-floor plenum pressure field caused by vortices. Numerous researchers focus on the adverse effects of under-floor blockages. This study focused to numerically investigate the positive impact of selectively placed obstructions (on-purpose air-directors); referred as partitions; Quantitative and qualitative analysis of underfloor plenum pressure field, perforated tiles airflow rate and racks inlet temperature with and without partitions using two Computational Fluid Dynamics (CFD) models, which were built using Future Facilities 6SigmaRoom CFD tool. First, a simple data center model was used to quantify the partitions benefits for two different systems; Hot Aisle Containment (HAC) compared to an open configuration. Second, the investigation was expanded using a physics-based experimentally validated CFD model of medium size data center (more complicated data center geometry) to compare different types of proposed partitions. Both models results showed that partition type I (partitions height of $\frac{2}{3}$ of plenum depth measured from the subfloor) eliminates the presence of vortices in the under-floor plenum and hence, more uniform pressure differential across the perforated tiles that drives more uniform airflow rates. In addition, the influence of proposed partitions on the rack inlet temperature was reported through a comparison between open versus hot aisle containment. The results showed that the partitions have a minor effect on the rack inlet temperature for the hot aisle containment system. However, the partitions significantly improve the tiles flowrate. On the other hand, for the open system, the presence of partitions has improved the tiles airflow rate, rack inlet temperature and hence eliminate the hot spots formation at computer rack inlet.

The role of data centers in modern life has expanded rapidly over the past decades. In addition, this expansion has resulted in a significant increase in the share of data centers in total energy consumption of the world. Thus, reliability and energy efficiency have become a common concern in data centers. Information technology equipment (ITE) and cooling infrastructure are the largest power consumer in data centers. The cooling power in a data center depends on the amount of heat dissipated by ITE. Therefore, the thermal design of the ITE impacts not only the ITE power but also affects the infrastructure power and has a significant role in the overall efficiency of data centers. This paper studies the impact of fans location and airflow balancing on the thermal performance and power of a server. A detailed computational fluid dynamic (CFD) model of the server is built, calibrated and validated using experimental test results. Next, impacts of moving fans to the rear side of the chassis on the flow rate and temperature of components are investigated. Special attention is given to controlling airflow through power supplies.

This study reports on the essential forced air-cooled electronics issue of fan performance deterioration caused by the presence of obstructions inside Information Technology Equipment (ITE). Fan performance was characterized based on the fan's static pressure and flowrate. Three different experimental techniques (flow test chamber, pressure probe, and pressure taps) were used to measure the fan static pressure at different locations. Moreover, Computational Fluid Dynamics (CFD) models were built considering different fan working environments. Multi Reference Frame (MRF) and Lumped Fan (LF) model CFD techniques were employed. The experimental results were used to evaluate the modeling techniques whilst implemented in different working environments and to better understand how fans react to blockages inside ITE. Experiments showed that compared to the Free Environment (FE) readings, placing the fan inside a specific ITE reduced the flowrate delivered by the fan by 57.2% and decreased static pressure by 76.3%, which affects the thermal performance of the ITE cooling system. Moreover, comparing numerical results with the experimental ones showed that the MRF approach predicted the flowrate delivered by the fan with a relative error of 3.9%, while the LF approach overestimated the flowrate by 70.3%. The results and conclusions reported in this work can be expanded to cover many other applications in which fans are operating inside enclosed environments and surrounded by many obstructions.

This investigation focuses on improving the airflow distribution in data centers. In many data centers vortices form in the plenum during operations. These vortices cause spatial and temporal non-uniformities and may give rise to hot regions in the data center which in turn impacts performance and reliability of the IT equipment. The current study identifies a novel approach using porous partitions in the plenum and demonstrates a significant generalized approach that is easily adoptable in existing and future data centers. For improving the overall data center energy efficiency and the cooling system effectiveness by eliminating a critical source of inefficiency. The results of quantitative and qualitative analyses of the underfloor plenum pressure field, perforated tiles airflow rate, and air temperature at the rack intake side with and without partitions are presented. Different data center configurations are studied using physics-based experimentally validated Computational Fluid Dynamics (CFD) model. The CFD model results showed that the partitions eliminated the presence of vortices in the underfloor plenum and thus enabled a more uniform pressure distribution and tile airflow delivery. Regarding rack inlet temperature, the results showed that the partitions significantly improved the air temperature at the rack inlet. Finally, a geometrical parametric study is performed. An ideal design is and demonstrated to improve the Supply Heat Index (SHI) by about 10%, while the amount of IT equipment that exceeded the ASHRAE recommended supply air temperature (SAT) was reduced by about 40%, and the floor leakage was cut in half.

During the lifespan of a data center, power outages and blower cooling failures are common occurrences. Given that data centers have a vital role in modern life, it is especially important to understand these failures and their effects. A previous study [16] showed that cold aisle containment might have a negative impact on IT equipment uptime during a blower failure. This new study further analyzed the impact of containment on IT equipment uptime during a CRAH blower failure. It also compared the IT equipment performance both with and without a pressure relief mechanism implemented in the containment system. The results show that the effect of implementing pressure relief in containment solution on the IT equipment performance and response could vary and depend on the server’s airflow, generation and hence types of servers deployed in cold aisle enclosure. The results also showed that when compared to the discrete sensors, the IPMI inlet temperature sensors underestimate the Ride Through Time (RTT) by 32%. This means that the RTT calculations based on the IPMI inlet sensors may be inaccurate due to variations in the sensor readings; as they exist today; in these servers. as discussed in a previous study [26]. Additionally, it was shown that all Dell PowerEdge 2950 servers have a similar IPMI inlet temperature reading, regardless of mounting location. As external system resistance increases during cooling failure, the servers exhibit internal recirculation through their weaker power supply fans, which is reflected in the high IPMI inlet temperature readings. For this server specifically, a pressure relief mechanism reduces the external resistance, thereby eliminating internal recirculation and resulting in lower IPMI inlet temperature readings. This in turn translates to a lower RTT. However, pressure relief showed conflicting results where the discrete sensors showed an increase in inlet temperature when pressure relief was introduced, thereby reducing the RTT. The CPU temperatures conformed with the discrete sensor data, indicating that containment helped increase the RTT of the servers during failure.

In raised floor data centers, tiles with high open area ratio or complex understructure are used to fulfill the demand of today's high-density computing. Using more open tiles reduces the pressure drop across the raised floor with the potential advantages of increased airflow and lower noise. However, it introduces the disadvantage of increased nonuniformity of airflow distribution. In addition, there are various tile designs available on the market with different opening shapes or understructures. Furthermore, a physical separation of cold and hot aisles (containment) has been introduced to minimize the mixing of cold and hot air. In this study, three types of floor tiles with different open area, opening geometry, and understructure are considered. Experimentally validated detail models of tiles were implemented in computational fluid dynamics (CFD) simulations to address the impact of tile design on the cooling of information technology (IT) equipment in both open and enclosed aisle configurations. Also, impacts of under-cabinet leakage on the IT equipment inlet temperature in the provisioned and under-provisioned scenarios are studied. In addition, a predictive equation for the critical under-provisioning point that can lead to a no-flow condition in IT equipment with weaker airflow systems is presented. Finally, the impact of tile design on thermal performance in a partially enclosed aisle with entrance doors is studied and discussed.

The constant increase in data center computational and processing requirements has led to increases in the IT equipment power demand and cooling challenges of high-density (HD) data centers. As a solution to this, the hybrid and liquid systems are widely used as part of HD data centers thermal management solutions. This study presents an experimental based investigation and analysis of the transient thermal performance of a stand-alone server cabinet. The total heat load of the cabinet is controllable remotely and a rear door heat exchanger is attached with controllable water flow rate. The cooling performances of two different failure scenarios are investigated. One is in the water chiller and another is in the water pump for the Rear Door Heat eXchanger (RDHX). In addition, the study reports the impact of each scenario on the IT equipment thermal response and on the cabinet outlet temperature using a mobile temperature and velocity mesh (MTVM) experimental tool. Furthermore, this study also addresses and characterizes the heat exchanger cooling performance during both scenarios.

In raised floor data centers, tiles with high open area ratio or complex understructure are used to fulfill the demand of today’s high-density computing. Using more open tiles reduces pressure drop across the raised floor with the potential advantages of increased airflow and lower noise. However, it introduces the disadvantage of increased non-uniformity of airflow distribution. In addition, there are various tile designs available on the market with different opening shapes or understructures. Furthermore, a physical separation of cold and hot aisles (containment) has been introduced to minimize the mixing of cold and hot air. In this study, three types of floor tiles with different open area, opening geometry, and understructure are considered. Experimentally validated detail models of tiles were implemented in CFD simulations to address the impact of tile design on the cooling of IT equipment in both open and enclosed aisle configurations. Also, impacts of under-cabinet leakage on the IT equipment inlet temperature in the provisioned and under-provisioned scenarios are studied. Finally, a predictive equation for the critical under-provisioning point that can lead to a no-flow condition in IT equipment with weaker airflow systems is presented.

The operation of today’s data centers increasingly relies on environmental data collection and analysis to operate the cooling infrastructure as efficiently as possible and to maintain the reliability of IT equipment. This in turn emphasizes the importance of the quality of the data collected and their relevance to the overall operation of the data center. This study presents an experimentally based analysis and comparison between two different approaches for environmental data collection; one using a discrete sensor network, and another using available data from installed IT equipment through their Intelligent Platform Management Interface (IPMI). The comparison considers the quality and relevance of the data collected and investigates their effect on key performance and operational metrics. The results have shown the large variation of server inlet temperatures provided by the IPMI interface. On the other hand, the discrete sensor measurements showed much more reliable results where the server inlet temperatures had minimal variation inside the cold aisle. These results highlight the potential difficulty in using IPMI inlet temperature data to evaluate the thermal environment inside the contained cold aisle. The study also focuses on how industry common methods for cooling efficiency management and control can be affected by the data collection approach. Results have shown that using preheated IPMI inlet temperature data can lead to unnecessarily lower cooling set points, which in turn minimizes the potential cooling energy savings. It was shown in one case that using discrete sensor data for control provides 20% more energy savings than using IPMI inlet temperature data.

Today's data centers increasingly rely on environmental data collection and analysis to operate the cooling infrastructure as efficiently as possible and to maintain the reliability of IT equipment. This in turn emphasizes the importance of the quality of data collected and its relevance to the overall operation of the data center. This study presents an experiment based analysis and comparison of environmental and power data collection using two different approaches; one uses a discrete sensor network and smart PDUs, and another uses available data from the installed IT equipment (IPMI data). The comparison looks deeply into the effect of both approaches that are adopted to control data center cooling. In addition, the effect that the Supply Air Temperature (SAT) from the Computer Room Air Handler (CRAH) unit had on the IT equipment was investigated in fully sealed Cold Aisle Containment (CAC) with 100% CPU utilization. It can be observed that the difference between the discrete and IPMI inlet temperature of the IT equipment increased as SAT increased due to the IT fans increasing speed in an attempt to get more cooling and the resulting in negative pressure differential build up inside the containment. Furthermore, the authors identified a value of the supply air temperature at which IT equipment started to ramp up for both approaches of data center cooling and control. The novelty of this study may aid data center operators when making the decision of what monitoring or control scheme to use.

In most air cooled data centers the required air for cooling of IT equipment is supplied from a raised floor to server racks through perforated tiles; therefore, an understanding of tile impact on flow features is an essential step for designing an efficient air delivery scheme. In recent years, different approaches have been implemented to increase the efficiency of air delivery through tiles such as the use of directional tiles or adding understructure scoops. In such tiles, the approaching angle of the cross flow to the tile, the angle of approach, becomes very important, since it may result in different velocity stratification patterns. Although many studies have focused on the use of computational fluid dynamics (CFD) for predicting tile airflow delivery to the racks, very few controlled experimental results are available. An important factor that has been often ignored in perforated tile modeling is the direction of the flow approaching the tile. In this study, an experimental setup has been designed and built to examine the effects of the direction of the approaching airflow to the tile on the airflow rate and resulting jet of coolant for different types of perforated tiles. In the designed setup, rotating the tile on a horizontal surface changes the angle of approaching airflow. The effect of angle of approach (AoA) on the direction of the jet is visualized by creating a laser sheet and performing airflow smoke visualization tests for four different types of tiles. Visualizations showed that the airflow direction changes significantly with AoA. Furthermore, the velocity distribution of air after the tiles at various AoA are measured, presented, and compared using a vane anemometer and a velocity sensor grid. Finally, the airflow rates for each case is calculated from the measured velocities by a grid of velocity sensors and a vane anemometer, which are then compared with flow rates measured by a commercial flow hood.