MODEL OF HEAT SIMULATOR FOR DATA CENTERS

The aim of this paper is to present a design and a development of a heat simulator, which will be used for a flow research in data centers. The designed heat simulator is based on an ideological basis of four-processor 1U Supermicro server. The designed heat simulator enables to control the flow and heat output within the range of 10–100 %. The paper covers also the results of testing measurements of mass flow rates and heat flow rates in the simulator. The flow field at the outlet of the server was measured by the stereo PIV method. The heat flow rate was determined, based on measuring the temperature field at the inlet and outlet of the simulator and known mass flow rate

Toward high-efficiency hybrid (electricity and heat) high concentration photovoltaic systems

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Photovoltaic power generation is a growing renewable primary energy source, expected to assume a major role as we strive toward fossil fuel free energy production. However, the rather low photovoltaic efficiencies limit the conversion of solar radiation into useful power output. Hybrid systems extend the functionality of concentrating photovoltaics (CPV) from simply generating electricity, to providing simultaneously electricity and heat. The utilization of otherwise wasted heat significantly enhances the overall system efficiency and boosts the economic value of the generated power output. The system presented in this lecture is the outcome of collaborative research in my research group, with the IBM research lab in Zurich and the Fraunhofer Institute for solar energy systems in Freiburg, Germany. It consists of a scalable hybrid photovoltaic-thermal receiver package, cooled with an integrated high performance microchannel heat sink we initially developed and optimized for the efficient cooling of electronics. The package can be operated at elevated temperatures due to its overall low thermal resistance between solar cell and coolant. The effect of the harvested elevated coolant temperature on the photovoltaic efficiency is investigated. The higher-level available heat can be suitable for sophisticated thermal applications such as space heating, desalination or cooling (polygeneration approaches). A total hybrid conversion efficiency of solar radiation into useful power of 60% has been realized. The exergy content of the overall output power was increased by 50% through the exergy content of the extracted heat.dc201

System-Level Thermal-Aware Design of 3D Multiprocessors with Inter-Tier Liquid Cooling

Rising chip temperatures and aggravated thermal reliability issues have characterized the emergence of 3D multiprocessor system-on-chips (3D-MPSoCs), necessitating the development of advanced cooling technologies. Microchannel based inter-tier liquid cooling of ICs has been envisaged as the most promising solution to this problem. A system-level thermal-aware design of electronic systems becomes imperative with the advent of these new cooling technologies, in order to preserve the reliable functioning of these ICs and effective management of the rising energy budgets of high-performance computing systems. This paper reviews the recent advances in the area of systemlevel thermal modeling and management techniques for 3D multiprocessors with advanced liquid cooling. These concepts are combined to present a vision of a green data center of the future which reduces the CO2 emissions by reusing the heat it generates

A semi-analytical approach for optimized design of microchannel liquid-cooled ICs

The development of embedded and interlayer liquid cooling in integrated circuits (ICs) using silicon microchannels has gained interest in the recent years owing to the rise of on-chip heat uses that aggravate thermal reliability issues of the emerging 3D stacked ICs. Further development of such devices and their translation to commercial applications depend largely on the availability of tools and methodologies that can enable the "temperature-aware" design of liquid- cooled microprocessors and 2D/3D multiprocessor systems-on-chip (MPSoCs). Recently, two optimal design methods have been proposed for liquid-cooled microchannel ICs: one to minimize on-chip temperature gradients and the other, called GreenCool, to maximize energy eciency in the coolant pumping eort. Both these methods rely upon the concept of channel width modulation to modify the thermal behaviour of a microchannel liquid-cooled heat sink. At the heart of both these methods is a new semi-analytical mathematical model for heat transfer in liquid-cooled ICs. Such a mathematical model enables the application of gradient descent approaches, such as non-linear programming, in the search for the most optimally performing channel design in a huge multi-dimensional design space. In this paper, we thoroughly quantify the impact and efficiency of the semi-analytical model, combined with non-linear programming, when compared against several numerical optimization mechanisms. Our experimental evaluation shows that non-linear programming, alongside the semi-analytical model, is up to 23x faster than conventional randomized/heuristic design approaches such as genetic algorithms and simulated annealing using fully-numerical thermal models

3D-ICE: a Compact Thermal Model for Early-Stage Design of Liquid-Cooled ICs

Liquid-cooling using microchannel heat sinks etched on silicon dies is seen as a promising solution to the rising heat fluxes in two-dimensional and stacked three-dimensional integrated circuits. Development of such devices requires accurate and fast thermal simulators suitable for early-stage design. To this end, we present 3D-ICE, a compact transient thermal model (CTTM), for liquid-cooled ICs. 3D-ICE was first advanced by incorporating the 4-resistor model based CTTM (4RM-based CTTM). It was enhanced to speed up simulations and to include complex heat sink geometries such as pin fins using the new 2 resistor model (2RM-based CTTM). In this paper, we extend the 3D-ICE model to include liquid-cooled ICs with multi-port cavities, i.e., cavities with more than one inlet and one outlet ports, and non-straight microchannels. Simulation studies using a realistic 3D multiprocessor system-on-chip (MPSoC) with a 4-port microchannel cavity highlight the impact of using 4-port cavity on temperature and also demonstrate the superior performance of 2RM-based CTTM compared to 4RM-based CTTM. We also present an extensive review of existing literature and the derivation of the 3D-ICE model, creating a comprehensive study of liquid-cooled ICs and their thermal simulation from the perspective of computer systems design. Finally, the accuracy of 3D-ICE has been evaluated against measurements from a real liquid-cooled 3D IC, which is the first such validation of a simulator of this genre. Results show strong agreement (average error<10%), demonstrating that 3D-ICE is an effective tool for early-stage thermal-aware design of liquid-cooled 2D/3D ICs

Green Cooling of High Performance Micro Processors: Parametric Study between Flow Boiling and Water Cooling

Due to the increase in energy prices and spiralling consumption, there is a need to greatly reduce the cost of electricity within data centers, where it makes up 50% of the total cost of the IT infrastructure. A technological solution to this is using on-chip cooling with a single-phase or evaporating liquid to replace energy intensive air-cooling. The energy carried away by the liquid or vapour can also potentially be used in district heating, as an example. Thus, the important issue here is “what is the most energy efficient heat removal process?” As an answer, this paper presents a direct comparison of single-phase water, a 50% water ethylene glycol mixture and several two-phase refrigerants, including the new fourth generation refrigerants HFO1234yf and HFO1234ze. Two-phase cooling using HFC134a had an average junction temperature 9 to 15˚C lower than for single-phase cooling, while the required pumping power for the CPU cooling element for single-phase cooling was on the order of 20-130 times higher to achieve the same junction temperature uniformity. Hot-spot simulations also showed that two-phase refrigerant cooling was able to adjust to local hot-spots because of flow boiling's dependency on the local heat flux, with junction temperatures being 20 to 30˚C lower when compared to water and the 50% water-ethylene glycol mixture, respectively. An exergy analysis was developed considering a cooling cycle composed by a pump, a condenser and a multi-microchannel cooler. The focus was to show the exergetic efficiency of each component and of the entire cycle when the subject energy recovery is considered. Water and HFC134a were the working fluids evaluated in such analysis. The overall exergetic efficiency was higher when using HFC134a (about 2%) and the exergy destroyed, i.e. irreversibilities, showed that the cooling cycle proposed still have a huge potential to increase the thermodynamic performance

Experimental Evaluation and Control of Two-Phase Multi-Microchannel Evaporator Cooling Systems for High Efficiency Data Center

Thermal designers of data centers and server manufacturers are showing a greater concern regarding the cooling of the new generation data centers, which consume considerably more electricity and dissipate much more waste heat, a situation that is creating a re- thinking about the most effective cooling systems for the future beyond conventional air cooling of the chips/servers. Potentially, a significantly better solution is to make use of on- chip two-phase cooling, which, besides improving the cooling performance at the chip level while also consuming less energy to drive the cooling process, also adds the capability to reuse the waste heat in a convenient manner, since higher evaporating and condensing temperatures of the two-phase cooling system (from 60-95 °C) are possible with such a new “green” cooling technology. In the present thesis, three such two-phase cooling cycles using micro-evaporation technology were experimentally evaluated with specific attention being paid to (i) controllability of the two-phase cooling system, (ii) energy consumption and (iii) overall exergetic efficiency, with the emphasis on (i). The controllers were evaluated by tracking and disturbance rejection tests, which were shown to be efficient and effective. The average temperatures of the chips were maintained below the upper limit of 85 °C of computer CPU’s for all tests evaluated in steady state and transient conditions. In general, simple SISO and SIMO strategies were sufficient to attain the requirements of control. Regarding energy and exergy analyses, the experimental results showed that all these systems can be thermodynamically improved since only about 6% of the exergy supplied is in fact recovered in the condenser in the present setup. Additionally, a series of tests covering a wide range of operating conditions under steady state regime were done. The main idea was to generate a “map of performance” of the different cooling systems in terms of energy consumption, energy recovery at the condenser and heat exchanger performance. A total of 120 tests were done which considered all combinations of the variables involved. Finally, empirical and semi-empirical correlations for overall thermal conductance and performance of all components and piping of all these systems were developed based on the experimental results obtained, which can be used for simulations and validations of potential codes developed to design and/or evaluate performance of cooling systems. An overall energy balance analysis for each system using the correlations developed showed that 99.17% of the experimental data were bounded within ± 10%

Contextual information quality assessment methodology in data processing using the manufacturing of information approach

Studies have shown that data-quality (DQ) and information-quality (IQ) assessment are essential activities in organizations that want to improve the efficiency of communication and information systems. So far, research on the evaluation of DQ and IQ has focused on approaches, models or classification of attributes. However, context-specific DQ and IQ assessment methodologies are difficult to find in the literature. While assessment methodologies do exist for office document processing in general, there are none for forms. The focus of this thesis is the need for a context-specific tool with which to assess the DQ input and the IQ output in communication and information systems. The channel analysed for this purpose is the form. This thesis proposes a novel methodology based on: 1) an adaptation of the “manufacturing of information” approach, which adopts the communication-system point of view; 2) an existing DQ classification system that classifies attributes as intrinsic, contextual, representational or accessible; and 3) a new conceptual model which provides the guidelines for assessment of forms. This evaluation only takes into consideration established contextual attributes, such as completeness, appropriate amount of data (here called “sufficiency”), relevance (which emphasises content), timeliness (which emphasises process) and actual value. To present the applicability of the contextual-information quality assessment (CIQA) methodology, two representative forms were used as case studies. The main results suggest that a novel data representation allows data to be classified by type (indispensable or verification) and composition (simple or composite). In one of the two case studies, the data quantity was reduced by 50%, resulting in a 15% improvement of IQ and a more efficient document processing system. The streamlining and new structure of the form led not only to a reduction in data quantity but also to increased information quality. This suggests that data quantity is not directly correlated to IQ, as IQ may increase in the absence of a corresponding increase in data quantity. In addition, the design of the forms requires particular attention to content, not simply aesthetics. Furthermore, in data processing, there could be great benefits in combining IQ assessment and computerization processes, in order to avoid problems such as data overload; of course, data security would need to be considered as well