Abstract Transistor density trends till recently have been following Moore's law, doubling every generation resulting in increased power density. The computational performance gains with the breakdown of Moore's law were achieved by using multicore processors, leading to nonuniform power distribution and localized high temperatures making thermal management even more challenging. Cold plate-based liquid cooling has proven to be one of the most efficient technologies in overcoming these thermal management issues. Traditional liquid-cooled data center deployments provide a constant flow rate to servers irrespective of the workload, leading to excessive consumption of coolant pumping power. Therefore, a further enhancement in the efficiency of implementation of liquid cooling in data centers is possible. The present investigation proposes the implementation of dynamic cooling using an active flow control device to regulate the coolant flow rates at the server level. This device can aid in pumping power savings by controlling the flow rates based on server utilization. The flow control device design contains a V-cut ball valve connected to a microservo motor used for varying the device valve angle. The valve position was varied to change the flow rate through the valve by servomotor actuation based on predecided rotational angles. The device operation was characterized by quantifying the flow rates and pressure drop across the device by changing the valve position using both computational fluid dynamics and experiments. The proposed flow control device was able to vary the flow rate between 0.09 lpm and 4 lpm at different valve positions.
more »
« less
Design and Optimization of Control Strategy to Reduce Pumping Power in Dynamic Liquid Cooling
Abstract Data centers are a large group of networked servers used by organizations for computational and storage purposes. In 2014, data centers consumed an estimated 70 billion kWh in the United States alone. It is incumbent on thermal engineers to develop efficient methods in order to minimize the expenditure at least toward cooling considering the limited available power resources. One of the key areas where electronic cooling research has been focusing, is addressing the issue of nonuniform power distribution at the rack, server and even at package levels. Nonuniform heating at the chip level creates hotspots and temperature gradients across the chip which in turn significantly increases the cost of cooling, as cooling cost is a function of the maximum junction temperature. This challenge has increased the use of temperature sensing mechanisms to help in finding ways to mitigate the gradients. A very effective way to conserve pumping power and address hotspots on the single or multichip modules is by targeted delivery of liquid coolant. One way to enable such targeted delivery of coolant is by using dynamic cold plates coupled with self-regulating flow control device that can control flow rate based on temperature. This novel technology will have more effective implementation coupled with a good control strategy. This paper addresses the development and testing of such control strategy with minimal sensors along with less latency and optimization of the same.
more »
« less
- Award ID(s):
- 1738811
- NSF-PAR ID:
- 10276340
- Date Published:
- Journal Name:
- Journal of Electronic Packaging
- Volume:
- 143
- Issue:
- 3
- ISSN:
- 1043-7398
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
As the demand for faster and more reliable data processing is increasing in our daily lives, the power consumption of electronics and, correspondingly, Data Centers (DCs), also increases. It has been estimated that about 40% of this DCs power consumption is merely consumed by the cooling systems. A responsive and efficient cooling system would not only save energy and space but would also protect electronic devices and help enhance their performance. Although air cooling offers a simple and convenient solution for Electronic Thermal Management (ETM), it lacks the capacity to overcome higher heat flux rates. Liquid cooling techniques, on the other hand, have gained high attention due to their potential in overcoming higher thermal loads generated by small chip sizes. In the present work, one of the most commonly used liquid cooling techniques is investigated based on various conditions. The performance of liquid-to-liquid heat exchange is studied under multi-leveled thermal loads. Coolant Supply Temperature (CST) stability and case temperature uniformity on the Thermal Test Vehicles (TTVs) are the target indicators of the system performance in this study. This study was carried out experimentally using a rack-mount Coolant Distribution Unit (CDU) attached to primary and secondary cooling loops in a multi-server rack. The effect of various selected control settings on the aforementioned indicators is presented. Results show that the most impactful PID parameter when it comes to fluctuation reduction is the integral (reset) coefficient (IC). It is also concluded that fluctuation with amplitudes lower than 1 ᵒC is converged into higher amplitudesmore » « less
-
Recent commercial efforts have reestablished the benefits of cooling server modules using direct liquid cooling (DLC) technology. The primary drivers behind this technology are the increase in chip densities and the absolute need to reduce the overall data center power usage. In DLC technology, a cold plate is situated on top of the chip with thermal interface material between the chip and the cold plate. The low thermal resistance path facilitates the use of warm water which helps data centers in replacing the chilled water system by a water side economizer utilizing ambient temperature. This work describes the effort to leverage DLC by employing microchannel cold plates to cool multi-chip modules. The primary objective of this work is to build a sophisticated test rig to characterize the flow and thermal performance of a microchannel cold plate for cooling a two-die chip. This study highlights the challenges of building an experimental setup which simulates a two-die chip package and the approaches taken to overcome the challenges. A parallel channel cold plate is used to benchmark the performance. Tests were conducted for a set of independent variables like flow rate, input power to dice, coolant temperature, flow direction and TIM resistance. The results are presented as PQ curves, specific thermal resistance curves and case temperature distribution reflecting the effect of changing the input variables.more » « less
-
Increasing power densities in data centers due to the rise of Artificial Intelligence (AI), high-performance computing (HPC) and machine learning compel engineers to develop new cooling strategies and designs for high-density data centers. Two-phase cooling is one of the promising technologies which exploits the latent heat of the fluid. This technology is much more effective in removing high heat fluxes than when using the sensible heat of fluid and requires lower coolant flow rates. The latent heat also implies more uniformity in the temperature of a heated surface. Despite the benefits of two-phase cooling, the phase change adds complexities to a system when multiple evaporators (exposed to different heat fluxes potentially) are connected to one coolant distribution unit (CDU). In this paper, a commercial pumped two-phase cooling system is investigated in a rack level. Seventeen 2-rack unit (RU) servers from two distinct models are retrofitted and deployed in the rack. The flow rate and pressure distribution across the rack are studied in various filling ratios. Also, investigated is the transient behavior of the cooling system due to a step change in the information technology (IT) load.more » « less
-
Characterization of an Isolated Hybrid Cooled Server With Failure Scenarios Using Warm Water CoolingModern day data centers are operated at high power for increased power density, maintenance, and cooling which covers almost 2 percent (70 billion kilowatt-hours) of the total energy consumption in the US. IT components and cooling system occupy the major portion of this energy consumption. Although data centers are designed to perform efficiently, cooling the high-density components is still a challenge. So, alternative methods to improve the cooling efficiency has become the drive to reduce the cooling cost. As liquid cooling is more efficient for high specific heat capacity, density, and thermal conductivity, hybrid cooling can offer the advantage of liquid cooling of high heat generating components in the traditional air-cooled servers. In this experiment, a 1U server is equipped with cold plate to cool the CPUs while the rest of the components are cooled by fans. In this study, predictive fan and pump failure analysis are performed which also helps to explore the options for redundancy and to reduce the cooling cost by improving cooling efficiency. Redundancy requires the knowledge of planned and unplanned system failures. As the main heat generating components are cooled by liquid, warm water cooling can be employed to observe the effects of raised inlet conditions in a hybrid cooled server with failure scenarios. The ASHRAE guidance class W4 for liquid cooling is chosen for our experiment to operate in a range from 25°C – 45°C. The experiments are conducted separately for the pump and fan failure scenarios. Computational load of idle, 10%, 30%, 50%, 70% and 98% are applied while powering only one pump and the miniature dry cooler fans are controlled externally to maintain constant inlet temperature of the coolant. As the rest of components such as DIMMs & PCH are cooled by air, maximum utilization for memory is applied while reducing the number fans in each case for fan failure scenario. The components temperatures and power consumption are recorded in each case for performance analysismore » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1115/1.4049018
