Transient Heat Transfer Simulation of the Coupling 3-D Moving Piston Assembly-Lubricant Film-Liner System

Transient heat transfer model of the coupling 3-D moving piston assembly-lubricant film-liner system is successfully developed for predicting the temperature distributions in the component system of internal combustion chamber, in which the effect of the friction heat generated at the piston ring/cylinder liner interfaces has been taken into account. The finite element method (FEM) is employed in the model for establishing the heat transfer relation among the moving piston assembly-lubricant film-cylinder liner. The 3-D discrete model of the coupling system is obtained by hypothesizing the lubricant film as 1-D thermal resistances and the friction heat as heat flux boundary conditions. The allocation and distribution model of friction heat on piston ring pack and liner are also established. The 3-D coupling heat transfer model has been used to analyze the heat transfer of a gasoline engine.

Coupled Electro-Thermal-Phase Change Modeling of a Chalcogenide Switch

A coupled electro-thermal-phase change numerical model is developed to model the threshold and memory switching processes in a chalcogenide switch based on phase change memory (PCM) technology. Coupled electrical and thermal transport coupled to phase change and crystallization kinetics are solved. Charge transport has been implemented using simplified carrier continuity equations with a threshold switching model for electrical conductivity. Heat transfer is modeled using a Fourier model, accounting for latent heat through a fixed-grid enthalpy formulation. Phase change is modeled using the Johnson-Mehl equations for crystallization kinetics. Thermal conductivity and electrical resistivity changes due to phase change are modeled using a local percolation model. The charge transport and circuit equations are fully coupled with the heat transfer and phase change models to accurately simulate the switching process. SET and RESET pulses are simulated to demonstrate that the model is able to capture the underlying physics well.

Coupled Quantum-Scattering Madeling of Thermoelectric Properties of Si/Ge/Si Quantum Well Structures

Confined structures presumably offer enhanced performance of thermoelectric devices. 1) Interfaces and boundaries create scattering sites for phonons, which reduces the thermal conductivity. 2) Reduced dimensionality increases the local density of states near the Fermi level, which increases the Seebeck coefficient. From these two phenomena, the net effect should be an increase in ZT, the performance parameter used to evaluate different materials and structures. These effects have been measured and modeled, but none of the models attempts to quantify the electron-phonon coupled effects particularly in the regime where quantum and scattering influences are found. Using the non-equilibrium Green's function (NEGF) approach, quantum wells composed of Si and Ge are studied and the important physics isolated. Results show a competing effect between the decrease in the electrical conductivity due to scattering with the increase in electrical conductivity with doping, leading to 77% decrease in the value of the power factor for the case of electron-optical phonon scattering.

Approximate Analytical Model for a First Level Package With Non-Uniformly Powered Die

Microprocessors continue to grow in capabilities, complexity and performance. Microprocessors typically integrate functional components such as logic and level two (L2) cache memory in their architecture. This functional integration of logic and memory results in improved performance of the microprocessor as the clock speed increases and the instruction execution time has decreased. However, the integration also introduces a layer of complexity to the thermal design and management of microprocessors. As a direct result of function integration, the power map on a microprocessor is typically highly non-uniform and the assumption of a uniform heat flux across the chip surface is not valid. The active side of the die is divided into several functional blocks with distinct power assigned to each functional block. Previous work [1,2] has been done to minimize the thermal resistance of the package by optimizing the distribution of the non-uniform powered functional blocks with different power matrices. This study further gives design guideline and key pointers to minimized thermal resistance for any number of functional blocks for a given non-uniformly powered microprocessor. In this paper, initially (Part I) temperature distribution of a typical package consisting of a uniformly powered die, heat spreader, TIM 1 & 2 and the base of the heat sink is calculated using an approximate analytical model. The results are then compared with a detailed numerical model and the agreement is within 5%. This study follows (Part II) with a thermal investigation of non-uniform powered functional blocks with a different power matrices with focus on distribution of power over die surface with an application of maximum, minimum and average uniform junction temperature over a given die area. This will help to predict the trend of the calculated distribution of power that will lead to the least thermal gradient over a given die area. This trend will further help to come up with design correlations for minimizing thermal resistance for any number of functional blocks for a given non-uniformly powered microprocessor numerically as well as analytically. The commercial finite element code ANSYS® is used for this analysis as a numerical tool.

Submicron Thermal Imaging of High Power Slab Coupled Optical Waveguide Laser (SCOWL)

Nonradiative power dissipation within and near the active region of a high power single mode slab coupled optical waveguide laser is directly measured by CCD-based thermoreflectance, including its variation with device bias. By examining the high spatial resolution temperature profile at the optical output facets, we quantify heat spreading from the source in the active region both downward to the substrate and upward to the metal top contact.

Evaluation of Energy Usage for a Teaching and Research Complex

The evaluation of energy performance for a teaching and research complex located in South Florida was carried out by auditing the energy bills, on-site data monitoring, and numerical simulation by computer. To facilitate the process of on-site data monitoring, a remotely controlled, wireless thermal monitoring system was deployed in the building. The system can automatically collect the temperature, relative humidity ratio, illumination intensity, and building electricity usage data for analysis. The contribution and savings potential of each energy consumption component is analyzed for the whole building. From the audit result it is obvious that laboratory equipment is the dominant electricity consumption factor. The fluctuation pattern of electricity usage due to artificial lighting demonstrates the effectiveness of occupancy sensors for energy saving during evenings, weekends and holidays. The trend of HVAC chilled water consumption rate follows closely with the indoor and outdoor temperature difference. Since the HVAC coil load represents the building's total cooling requirement, the ratio between chilled water rate and temperature difference reflects the building's comprehensive thermal resistance. This coefficient can be used as a new building energy index for future energy audits of similar buildings. Finally, computer software simulates several proposed energy saving scenarios, e.g. reducing the HVAC fresh air percentage, adding energy wheel to recycle the wasted cooling, etc. The result shows that installing energy wheel can save more cooling load than other methods, however such benefit is compromised by its extra motor electricity usage.

Practical Study of Application of Thermal Network Method to Thermal Design of Electronic Equipment: An Example for the Thermal Design of a Compact Self-Ballasted Fluorescent Lamp

Thermal design is one of the most important issues in the development of compact self—ballasted fluorescent lamps as the demand for small yet powerful lamps is mounting. This paper proposes a simulation method that is based on a thermal network model for which a set of equations are developed. Some of the coefficients of the thermal network equations were determined experimentally using a simulated model lamp. The calculated temperatures are in good agreement with the measured temperatures. The work illustrates the usefulness of the proposed methodology in the design of compact self—ballasted fluorescent lamps.

Effect of 3D Diffusion Over Vertical Thin Rectangular Geometries in Natural Convection Heat Transfer

Natural convection over vertical plates is a very well known problem in heat transfer. There are many available correlations to predict Nusselt numbers for a wide range of Rayleigh numbers. These benchmark studies on natural convection for vertical plates were conducted on rather large surfaces leading to Rayleigh numbers in the range of 0.1 to 109. In natural convection the sole driving force of fluid motion is the change in fluid density, when the diffusive limit is small compared to convective heat transfer. However, conduction to air, as well as air entrainment from sides also contributes to the heat removal from heater surfaces. An experimental study has been carried out with small and large heaters compared to published data for 2×103<Ra<4×107. Square surfaces of 12.5 and 25.4 mm, and rectangular heaters of sizes 25.4×101.6 and 25.4×203.2 mm were tested for a range of heat inputs such that the surface temperatures are controlled between 30 °C and 80 °C. It is found that published correlations underpredict the Nusselt numbers as much as 20%. It is observed that widely known correlations underpredict the experimental values since the 3D conduction and side air drifts on heat transfer are not accounted for in these correlations. However, the cuboid model which includes the 3D diffusion term showed much better agreement with the experimental results.

Energy Flow in the Information Technology Stack: Introducing the Coefficient of Performance of the Ensemble

The information technology industry is in the midst of a transformation to lower the cost of operation through consolidation and better utilization of critical data center resources. Successful consolidation necessitates increasing utilization of capital intensive "always-on" data center infrastructure, and reducing the recurring cost of power. A need exists, therefore for an end to end physical model that can be used to design and manage dense data centers and determine the cost of operating a data center. The chip core to the cooling tower model must capture the power levels and thermo-fluids behavior of chips, systems, aggregation of systems in racks, rows of racks, room flow distribution, air conditioning equipment, hydronics, vapor compression systems, pumps and heat exchangers. Earlier work has outlined the foundation for creation of a "smart" data center through use of flexible cooling resources and a distributed sensing and control system that can provision the cooling resources based on the need. This paper shows a common thermodynamic platform which serves as an evaluation and basis for policy based control engine for such a "smart" data center with much broader reach - from chip core to the cooling tower. Computational Fluid Dynamics modeling is performed to determine the computer room air conditioning utilization for a given distribution of heat load and cooling resources in a production data center. Coefficient of performance (COP) of the computer room air conditioning units, based on the level of utilization, is used with COP of other cooling resources in the stack to determine the COP of the ensemble. The ensemble COP represents an overall measure of the performance of the heat removal stack in a data center.

A Remediation Scheme to Global Warming: Engineering Biodegradable Aerosols With Maximum Scattering Potential

This exploratory study evaluates the following moderation scheme against global warming: deploying nanoparticles in the atmosphere in order to scatter a tiny amount of sunlight (1% or 2W/m2) up to space. Such a strategy could be a last-resort method to counteract unbearable effects of global warming. For particles made of a wide range of known materials, the scattering ability is defined to quantify how efficient the particle is at scattering sunlight. This scattering ability is a function of the particle radius and index of refraction, and is calculated by an in-house numerical code solving the Mie scattering equations. The code is validated against scattering calculations for SO2 particles published by Schwartz[1]. Our calculations show that an optimum particle size exists, which would minimize the amounts to be deployed in the atmosphere. Also, we evaluate the deployment of biodegradable nanoparticles, which would counteract global warming and minimize dangers related to their redeposition.