An experimental assessment of computational fluid dynamics predictive accuracy for electronic component operational temperature

Ever-rising Integrated Circuit (IC) power dissipation, combined with reducing product development cycles times, have placed increasing reliance on the use of Computational Fluid Dynamics (CFD) software for the thermal analysis of electronic equipment. In this study, predictive accuracy is assessed for board-mounted electronic component heat transfer using both a CFD code dedicated to the thermal analysis of electronics, Flotherm, and a general-purpose CFD code, Fluent. Using Flotherm, turbulent flow modelling approaches typically employed for the analysis of electronics cooling, namely algebraic mixing length and two-equation high-Reynolds number k-e models, are assessed. As shown, such models are not specific for the analysis of forced airflows over populated electronic boards, which are typically classified as low-Reynolds number flows. The potential for improved predictive accuracy is evaluated using candidate turbulent flow models more suited to such flows, namely a one-equation SpalartAllmaras model, two-layer zonal model and two equation SST k-co model, all implemented in Fluent. Numerical predictions are compared with experimental benchmark data for a range of componentboard topologies generating different airflow phenomena and varying degrees of component thermal interaction. Test case complexity is incremented in controlled steps, from single board-mounted components in free convection, to forced air-cooled, multi-component board configurations. Apart from the prediction of component operational temperature, the application of CFD analysis to the design of electronic component reliability screens and convective solder reflow temperature profiles is also investigated. Benchmark criteria are based on component junction temperature and component-board surface temperature profiles, measured using thermal test chips and infrared thermography respectively. This data is supplemented by experimental visualisations of the forced airflows over the boards, which are used to help assess predictive accuracy. Component numerical modelling is based on nominal package dimensions and material thermal properties. To eliminate potential numerical modelling uncertainties, both the test component geometry and structural integrity are assessed using destructive and non-destructive testing. While detailed component modelling provides the à priori junction temperature predictions, the capability of compact thermal models to predict multi-mode component heat transfer is also assessed. In free convection, component junction temperature predictions for an in-line array of fifteen boardmounted components are within ±5°C or 7% of measurement. Predictive accuracy decays up to ±20°C or 35% in forced airflows using the k-e flow model. Furthermore, neither the laminar or k-e turbulent flow model accurately resolve the complete flow fields over the boards, suggesting the need for a turbulence model capable of modelling transition. Using a k-co model, significant improvements in junction temperature prediction accuracy are obtained, which are associated with improved prediction of both board leading edge heat transfer and component thermal interaction. Whereas with the k-e flow model, prediction accuracy would only be sufficient for the early to intermediate phase of a thermal design process, the use of the k-co model would enable parametric analysis of product thermal performance to be undertaken with greater confidence. Such models would also permit the generation of more accurate temperature boundary conditions for use in Physics-of-Failure (PoF) based component reliability prediction methods. The case is therefore made for vendors of CFD codes dedicated to the thermal analysis of electronics to consider the adoption of eddy viscosity turbulence models more suited to the analysis of component heat transfer. While this study ultimately highlights that electronic component operational temperature needs to be experimentally measured to quality product thermal performance and reliability, the use of such flow models would help reduce the current dependency on experimental prototyping. This would not only enhance the potential of CFD as a design tool, but also its capability to provide detailed insight into complex multi-mode heat transfer, that would otherwise be difficult to characterise experimentally

A Combinatorial Method for Discovery of BaTiO3-based Positive Temperature Coefficient Resistors

PhDThe conventional materials discovery is a kind of empirical (“trial and error”) science that of handling one sample at a time in the processes of synthesis and characterization. However, combinatorial methodologies present the possibility of a vastly increased rate of discovery of novel materials which will require a great deal of conventional laboratory work. The work presented in this thesis, involved the practice of a conceptual framework of combinatorial research on BaTiO3-based positive temperature coefficient resistor (PTCR) materials. Those including (i) fabrication of green BaTiO3 base discs via high-throughput dip-pen printing method. Preparation and formulation of BaTiO3 inks (selection of dispersant and binder/volume fraction) were studied. The shape of drying residues and the morphogenesis control of droplet drying were discussed. (ii) investigation of a fast droplet-doping method, which induced the dopant precursor solution infiltrating into the porous BT base disc. Various characterization methods were used to examine the dopant distribution in the body of disc. (iii) devising a high-throughput electrical measurement system including an integrated unit of temperature control and automatic measurement operation, and an arrayed multichannel jig. (iv) synthesis of donor-doped BaTiO3 libraries, which involved lanthanum, erbium, yttrium as donor elements and manganese as an acceptor dopant element respectively. Their temperature dependant resistivities were also explored. The work successfully developed an integrated tool including high-throughput synthesis of a large batch of libraries and high-throughput electrical property measurement for combinatorial research on BaTiO3-based PTCR ceramics. The Abstract ii combinatorial method, thus validated, has the potential to deliver dopant-doped BTbased PTCR libraries rapidly with a very wide range of dopant mixtures and concentrations for electrical property measurement and deserves to be applied to other low level dopant ceramic systems. These approaches are novel and paving the way for other new materials selection and materials research

Low cost attitude control system scanwheel development

In order to satisfy a growing demand for low cost attitude control systems for small spacecraft, development of low cost scanning horizon sensor coupled to a low cost/low power consumption Reaction Wheel Assembly was initiated. This report addresses the details of the versatile design resulting from this effort. Tradeoff analyses for each of the major components are included, as well as test data from an engineering prototype of the hardware

An in situ investigation of the physical properties of rock salt with special reference to underground gas storage

PhD ThesisIntroduction The rate of production of any consumable, whether it be raw materials or a finished product, rarely equals the rate of its consumption. Manufacturing industries cannot produce at a rate equalling the peak consumption rate without over-capitalisation of plant. The disparity between production and consumption rates necessitates the creation of a buffer which will enable the manufacturer to produoo at an economical rate and yet provide the consumer with an uninterupted supply at peak demand. The problems of varying production and consumption rates are experienced in the energy supply industries. Solid fuels, oil and gas are all stockpiled at many links in the chain from producer to consumer. The storage of fuel is necessary to accommodate the diurnal and seasonal variation in demand occasioned by the working hours of industry and commerce and the domestic habits of householders. Solid fuels and oils are normally subject to only seasonal variations in demand but gas and electricity suffer from high diurnal variations in demand from both industrial and domestic consumers. In its early drays gas was chiefly used as an illuminant and the demand was low in suer and in daylight hours. Towards the onä of the nineteenth century other uses for gas were developed, making the demands more even. A sharp return to the former annual cycle has now arisen as a result of the tremendous success of gas spaoo heating, and it can be but a few years before the seasonal ratio midwinter: midsummer reaches the proportion 5: 1 (1,2) The gas industry can meet this challenge in two possible ways; additional gas production plant for winter use only or by increasing gas storage facilities. As both of these solutions result in under-employment of capital, the gas industry has been investigating over the last twenty years various gas storage techniques which do not steriliso as much capital as the conventional low-pressure holder. High-pressure gas storage, when allied to high pressure distribution times can effect several economics in this field.Imperial Chemical Industries Limite

A Study of the Change in the Temperature of Maximum Density of Water and Aqueous Solutions as a function of Pressure

The aim of this research is to study the shift in the temperature of maximum density of water and aqueous solutions as a function of pressure. One of the many anomalous properties of water is that it passes through a maximum in density in the liquid state. In order to accurately measure the temperature of maximum density (Tmd), convective flow is monitored in a rectangular container containing the fluid. A temperature gradient is held across the chamber and it is cooled and heated in a quasi-steady state manner. A double cell convection pattern forms in the vicinity of the density maximum. This double cell is tracked by monitoring the temperature at selected points in the fluid. The change in temperature of maximum density due to concentration and applied pressure can be investigated using this technique. At a pressure of one atmosphere, this density maximum occurs in pure water at a temperature of 3.98 C. It is known that the temperature of maximum density decreases as the pressure increases; for pure water this occurs at a rate of 1 C per 50 bar. Experimentally the shift in the temperature of maximum density of aqueous solutions is tracked over the pressure range 1 to 100 bar. It is found that the temperature of maximum density drops as the pressure rises for all solutes studied, but that the rate of decrease changes depending on the nature of the solute. For ionic salts, the rate of decrease is steeper than that for pure water, whereas for monohydric alcohols the rate of decrease is less that that for pure water. These divergent trends become more apparent as solute concentrations increase. The behaviour of the temperature of maximum density is modelled on both macroscopic and microscopic levels. A simple macroscopic model is proposed by combining state functions for water with those of solutes. This approach predicts that the rate of decrease of the temperature of maximum density for ideal (noninteracting) mixtures as a function of pressure is less than for pure water (but not as pronounced as the change observed in the alcohol solutions). Microscopic modelling at the molecular level is done using Monte Carlo methods. Non-ideal mixtures are studied by introducing molecules whose interactions with water are either stronger or weaker than the water-water interactions. In all cases it is found that the rate of change of the temperature of maximum density as a function of pressure lessens compared to the rate for pure water. The models thus help in understanding some, but not all, of the experimental observations

Towards High-Throughput, Simultaneous Characterization of Thermal and Thermoelectric Properties

The extension of thermoelectric generators to more general markets requires tha

Thermal Analysis of Cryoprotectants for Cryopreservation

University of Minnesota M.S.M.E. thesis. February 2017. Major: Mechanical Engineering. Advisor: John Bischof. 1 computer file (PDF); viii, 65 pages.Cryopreservation by vitrification is a promising technique for preservation of biomaterials such as organs for long term storage. Crystallization while cooling and warming is an important hurdle for a successful cryopreservation. This problem can be addressed by the use of cryoprotectant solutions (CPAs) which help in inhibiting crystallization. The cooling and warming rates needed to prevent crystallization in these CPAs are called Critical Cooling Rate (CCR) and Critical Warming Rate (CWR) respectively. Thermal modeling is an important tool which can help to study this process and predict subsequent cooling and warming rates needed to avoid crystallization. Temperature dependent thermal properties such as thermal conductivity, specific heat capacity and density are needed in order to develop an accurate model. This work involved the measurement of specific heat capacity (Cp) of high concentration CPAs (> 6M) that are used to study vitrification. The thermal properties were then used in a numerical model to predict cooling and warming rates encountered in a cylindrical geometry of CPAs. Chapter 1 provides a review of the thermal properties (thermal conductivity and specific heat capacity) of various biomaterials available in the literature in the sub-zero and supra-zero temperature ranges. Thermal properties of biomaterials are highly temperature dependent. In addition to dependence on temperature, these properties are affected by crystallization and vitrification at sub-zero temperatures (0°C). Finally, a modeling case study (Bischof and Han 2002) has been provided to highlight the significance of using temperature dependent thermal properties for accurately predicting thermal history. Chapter 2 focusses on experimental measurements of specific heat capacity (cp) of five high concentration CPAs (> 6M) — VS55 (with and without sucrose), DP6 (with and without sucrose) and M22. Further, the effect of cooling / warming rate (1, 5 and 10 °C/min) on crystallization and vitrification has been studied. It was observed that the addition of 0.6 M sucrose to two CPAs viz., VS55 and DP6 suppressed their crystallization for all the three cooling and warming rates. Chapter 3 involves thermal modeling of cooling and warming in a COMSOL Multiphysics package. Thermal properties from Chapters 1 & 2 were used in order to predict the cooling and warming rates for three conditions, viz. convective cooling, convective warming and nano warming. These simulations were carried out in a cylindrical geometry for an increasing size, i.e. the radius of the cylinder. The objective was to find the size limit beyond which cooling and warming rates would not exceed the CCR and CWR respectively