Thermal Design Optimization Research Articles

Thermal Analysis of SOI Transistor Devices in LSI Chips.

Temperature distributions in SOI transistor devices with trench isolations in LSI chips were calculated using three-dimensional computer simulations. The relations between the maximum temperature increase in transistor devices and the geometric parameters (width and length of aluminum lines on the transistor devices, size of SOI regions, and spacing of two SOI devices) were calculated. We also calculated the effect of placing a heat dissipation layer on the SOI devices. Temperature increases in SOI devices were measured by placing a thermal sensor diode in the SOI region. The calculation results and experimental results agreed well. The calculation results can be used for optimal thermal design of SOI devices in LSI chips.

Thermal analysis of lithium polymer electrolyte batteries by a two dimensional model—thermal behaviour and design optimization

Thermal analysis of lithium polymer electrolyte batteries is carried out to examine the relationship between battery thermal behaviour and design parameters. By studying the effect of stack size and cooling/insulating conditions on battery temperature under different discharge rates, information is obtained as to how to maintain operating temperature by designing proper cell stacks and choosing proper cooling/insulating systems. Moreover, temperature distributions within cell stacks for different cell designs, including different thickness of cell components and different current collector materials, are calculated so as to carry out cell structure optimization from a heat transfer point of view. Finally, thermal characteristics of lithium polymer electrolyte batteries based on different positive electrodes ( eg V 6O 13, TiS 2 and redox polymer) are discussed.

Natural Convection Heat Transfer of a Spherical Lighting Fitting.

The surface temperatures of the inner lamp and the outer glove of a spherical lighting fitting, the surfaces of which are painted black, are measured. From the results the average cnonvective heat transfer coefficients between the inner lamp and the outer glove and on the outer surface of the glove are obtained. These data are correlated with the aid of existing equations for two concentric spheres and the outer surface of a single sphere. The relationships between the maximum and mean temperature on the lamp and the glove are also obtained. By the use of these equations a method for the optimal thermal design of spherical lighting fittings is proposed.

A feasibility study for the fabrication of planar silicon multichip modules using electron beam lithography for precise location and interconnection of chips : Andy Hopperet al. IEEE Trans. Compon. Hybrids mfg Technol.15, 97 (1992)

The study attempts to seek the optimal thermal design of planar multichip module (MCMs) under natural convection through optimal chip placement design. To attain the goal, a sequential metamodeling-based optimization approach is introduced. This approach incorporates a response surface methodology (RSM)-based design of experiment (DOE), three-dimensional (3D) thermal finite element analysis (FEA) and an updating scheme. Essentially, the RSM is used to construct, via quadratic polynomial approximation, the global RS of the chip junction temperature in terms of design variables. For speeding up the DOE and the solution of the optimization, several dynamic experimental design strategies using move limits and different proposed sampling techniques are introduced. The feasibility of the strategies is demonstrated, and their solution accuracy and efficiency are also compared with each other. By the explicit RS-based performance function together with geometry constraints, a constrained thermal optimization subproblem is formed. The optimum of the subspace optimization is sought, which is considered as the nominal starting point of next iteration. The iterative process continues with a new defined design subspace and factorial design plan until convergence is attained. The applicability of the proposed design optimization technique is demonstrated through several design case studies involving various planar MCMs.

Entropy generation in a high temperature superconducting current lead

The minimization of entropy generation has been used as a convenient thermal design tool in predicting the optimal temperature distribution in a cryogenic current lead. A vapour-cooled lead with non-ideal cooling has been modelled by a set of non-linear differential equations with corresponding boundary conditions. Highly non-linear temperature dependent thermophysical properties, typical for a high temperature superconducting YBCO compound, have been incorporated in a current lead model. Numerically obtained current lead temperature profiles have been used to calculate entropy generation within the lead as a function of the relevant physical and operational parameters. It has been shown that with respect to thermodynamic irreversibility as an objective function, in both resistive and superconducting modes of operation, there is an optimal thermal design.

Optimal thermal design of air cooled forced convection finned heat sinks-experimental verification

D.B. Tuckerman and R.F.W. Pease (1981) showed that microchannels with water flow could be used to cool VLSI systems. Their work required the flow to be laminar, and the channel system, or fin array, was optimized analytically. Recently, it has been shown that, for some geometries and fluid pressure drops, a lower thermal resistance can be found if the channels are designed to allow turbulent flow. The current work uses the optimization scheme developed by R.W. Knight et al. (1991 and in this issue) to design three air-cooled aluminum finned arrays, which were built and tested experimentally. The thermal performances of the fin array designs, one containing 5 fins, one with 11 fins, and one with the predicted optimum of 8 fins, are compared. All arrays had turbulent flow and pressure drop across them, and all fins were the same length and width. The best thermal performance was obtained with the design predicted to be optimal. The scheme can be applied to a variety of heat sink design applications, including water-cooled microchannels. >

Optimal Thermal Design of Forced Convection Heat Sinks-Analytical

Abstract For fully developed flow in closed finned channels used to augment heat transfer, there exists an optimal geometrical design of the size and number of cooling channels. In this paper, the problem is generalized with a statement of dimensionless thermal resistance in terms of • the number of channels • a fin to channel thickness ratio • the length to width (planar dimensions) ratio of the heat source, and • a specified fin efficiency or fin length • a fluid to fin thermal conductivity ratio • the Prandtl Number of the coolant • a dimensionless pressure term, which incorporates the maximum allowable pressure drop through the cooling channels or alternatively, • a dimensionless work rate term, which incorporates the maximum allowable coolant pumping power required, An optimization scheme is described and used for comparison with two previously published cases wherein both designs were restricted to a fixed fin to channel thickness ratio and laminar flow; one by Goldberg (1984) using air and copper and a second one only by Tuckerman and Pease (1981) for water-cooled Silicon wafers. Results from the present optimization scheme show that upon reexamination of the first study by Goldberg, significant reduction of thermal resistance can be obtained by using fin/channel dimensions other than unity. A similar reduction is found in the second instance (Tuckerman and Pease) with the relaxation of the laminar limitation.

Heat-transfer considerations for large liquefied-natural-gas storage tanks

Natural gas is used worldwide as a practical energy source. In order to have a concentrated form of energy, natural gas is liquefied and stored under a pressure slightly above atmospheric and at a corresponding temperature just above its normal boiling point (112 K). This investigation presents a general steady-state study of the heat transfers into such a storage tank. Two mathematical models are proposed in order to help improve the thermal design process for such a tank. It is concluded that the aspect ratio (i.e. height-to-radius) of such a tank for the minimum rate of heat gains should be approximately unity. This value differs from the economically most favourable aspect ratio, i.e. that leading to the least total financial expenditure over the lifetime of the tank. However, the two models allow a complete simulation of the thermal costs. As the unit cost of fuel rises relative to other costs (e.g. for the construction of the tank), the overall most economic tank design approaches that of the optimal thermal design of tank as deduced in this investigation.

A Decomposition Strategy for Thermoeconomic Optimization

An optimal thermal design of a considered system configuration is conveniently decided when the system is modeled as made up of one thermodynamic subsystem and of the essential number of design subsystems. The thermodynamic subsystem decides the performance of the components and the design subsystems decide their best matching geometry and costs. An optimizer directs all decisions to an extremum of a given objective function. This decomposition strategy is illustrated by investigating the optimal values of seven decision design variables for a regenerative gas turbine power cycle when a cost-objective function is minimized. The results seen from the point of view of second law analysis and costing are discussed.

Optimisation of ‘radiator’ shelf design in order to achieve energy thrift

The traditional hot-water-filled ‘radiator’, i.e. a vertical, flat heat emitter, fitted below a window, can often lose > 10% of its heat output through the window (i.e. without making any useful direct contribution to heating the main body of the room in which it is placed). A reduction in this rate of heat loss can be achieved by replacing the single glazing by double glazing. However, a much lower capital-cost, energy-thrift option, which is considered here, merely requires installing a suitably designed horizontal shelf between the radiator and the window. By optimising the geometry of this shelf, placed between the two buoyancy-driven air flows, i.e. downwards from the window and upwards from the radiator, a reduction in the steady-state rate of heat loss through an experimental window of ∼14% of the radiator output has been achieved, resulting in a simple pay-back period for the installation of the shelf of ∼2 years. The wide variations in the dimensions of windows and radiators as well as their relative placements and surface temperatures preclude a simple optimal thermal design of the horizontal shelf, which is suitable for all occasions, being proposed. However, significant improvements in the system's energy performance (i.e. lower rates of heat loss through the window) will be achieved when the following are employed: either (1) a straight horizontal shelf, protruding from the wall by 84 mm; or (2) a horizontal shelf, with a curved underside of radius 98 mm, when the protrusion from the wall is 98 mm.

Evaluation of thermal efficiency and cost of high temperature solar heat from central receiver systems to use in hydrogen producing thermochemical processes

The thermal efficiency and cost evaluation of high temperature solar heat, for hydrogen producing processes, from central receiver systems has been carried out using the DELSOL2 code program developed at Sandia laboratories. The thermal performance and design optimization runs were performed for various locations with different levels of yearly direct insolation at normal incidence. The study has been carried out with an external vertical cylindrical receiver and for plant sizes ranging from 100 MW to 900 MW. It has been found that the overall thermal efficiency of the system varies from 51.3% to 56.1% and that the typical levelized thermal energy cost is in the range of 10 $ GJ −1 for favorable locations. The results for small size systems have been verified using the CRS code developed at Ecole Polytechnique and the published results are in the literature. It has also been determined that for a system with a cavity type receiver, the levelized thermal energy cost is higher although the overall system thermal efficiency is improved.

An Approach to Optimal Thermal Design of Superconducting Generator Rotor

An Approach to Optimal Thermal Design of Superconducting Generator Rotor

An Approach to Optimal Thermal Design of Superconducting Generator Rotor

To stabilize the superconducting condition of field winding of a superconducting generator and to ensure high-efficiency operation of the machine, heat penetrating the inner rotor of the superconducting rotor must be suppressed. This makes it necessary to recognize quantitatively and accurately heat penetrating from such parts as current leads, torque tubes, and radiation shields. Since the temperatures of such structures and the coolant rise from around 4K to 300K, such physical quantities as density of the coolant and thermal conductivities of the structures depend nonlinearly on temperatures. This prevents adequate accuracy from being obtained simply by the analysis of penetrating heat by using the mean values of properties. To improve this inaccuracy, we developed nonlinear thermal analysis methods. Many experiments, including those with a 3000kVA superconducting generator, have proved that this technique accurately estimates the temperature distribution in structures and the heat penetrating an inner rotor. The technique enabled us to obtain important knowledge on parameters concerning heat penetrating from current leads, torque tubes, and radiation shields for trial designing of a 1000MVA machine.

Optimal thermal design of injection molds for filled thermosets

AbstractSince the cure rate of injection molded thermosets is usually very sensitive to cavity surface temperature, spatial variations in these temperatures can lengthen the necessary cure time for the entire part and cause distortion and residual stress in the molded article. This problem is addressed in the present paper by combining an optimization algorithm with a quasi‐steady heat conduction analysis in the mold to determine the heating line positions and operating temperatures that minimize the spatial variation in cavity surface temperature. The method is applied to an example mold for a flat panel of uniform thickness, using two different gate locations. At a one‐minute cycle, the optimal designs for each gate location dramatically reduce the variation in cavity surface temperature compared with corresponding results using a conventional heating system. These results are made more significant by the fact that the optimal designs use considerably fewer heating lines. In spite of their simplicity, the optimal designs still have enough flexibility to adjust to a changing cycle without sacrificing uniformity in cavity surface temperature.

超電導ケーブル用ブッシング導体の最適熱設計

Superconducting cable is one of the promising ways for transmitting the huge electric power in the future. In the terminal bushing of superconducting cable, huge heat influx flows from the ambient temperature region into the cold region through conductor. Huge Joule heat arises because of large electric current in the normal conducting part. To minimize the refrigerator load of terminal bushing in superconducting cable system under steady operation, the sum of Joule heat and heat influx should be minimized. In this paper we discuss the optimum thermal design of the bushing conductor for superconducting cable system.The conclusions are(1) It was shown that, to minimize the sum of Joule heat and heat influx in the terminal bushing with constant cross section along the length, it is required that heat influx is equal to the Joule heat in each part of bushing conductor.(2) We obtained the optimum cross section and optimum temperature distribution from the optimum conductor design based on the above condition. The sum of heat was compared with ones from other design to show the validity of this optimum design.(3) By the design technique combining the optimum design and simulation of temperature distribution, it is possible to take account of temperature dependences of electric resistivity and thermal conductivity, and heat transfer coefficient between gas helium and bushing conductor.(4) With regard to conductor configuration, configuration with high heat transfer coefficient, as braid conductor, makes conductor dimension and helium consumption small.

Optimal arrangement of holes in a two‐dimensional heat conductor by a special boundary integral method

AbstractThe position, size and surface temperature of circular holes inside a two‐dimensional heat conductor are optimized to produce a minimum variation in surface temperature over a portion of the outer boundary. This problem, whic arises in thermal desing of moulds and dies, resembles those encountered in structural shape optimization because the internal geometry of the heat conductor depends on the design variables. In this paper, some of the traditional difficulties associated with shape optimization are overcome by analysing steady heat conduction with a special boundary integral method developed for two‐dimensional regions with circular hole. This approach eliminates the need to regenerate a finite element mesh over the interior of the region each time the geometry is changed during the design process. It also increases the efficiency of the analysis by reducing the number of unknowns in the numerical discretization of the region. Since the objective function depends only on the boundary temperatures, there is no need to determine temperatures in the interior.The analysis method is applied to two problems arising in optimal thermal design of compression moulds. These examples show that the number of holes choson for the design strongly affects their resulting optimal arrangement as well as the ultimate uniformity of the cavity surface temperature.

An approach to the optimum thermal design of office buildings

The paper describes a method for determining a thermal design for an office building which minimizes the sum of initial costs and running costs discounted over the life of the building whilst satisfying constraints deriving from technological and comfort requirements. A thermal model of an office building is described in terms of heat supply and heat losses and some ingenious features of the modelling are presented. Costing techniques for heating and insulating the building are also described. An optimization algorithm based on geometric programming is then applied to the thermal model and typical results are presented. The importance of sensitivity analyses of the results is stressed.

Optimum Thermal Design of Radiative-Conductive Systems

In applying nonlinear programming to optimization of temperatures in a system with radiation and conduction heat transfer, design requirements on the temperatures are translated into mathematical functions in which the design variables are the radiation surface properties, infrared emmittance and solar absorptance. Physical limitations in the surface properties and design objectives form the constraints of the nonlinear programming problem. A mathematical model of a radiative-conductive system employs a nodal analysis. Radiative heat transfer is treated under the semi-gray assumption and a total exchange factor allows surfaces to be specular-diffuse reflectors. Two types of design problems formulated consider (a) the case in which components of a system must operate within certain temperature limits and (b) a system in which uncertainty in the parameters produces uncertainty in the temperatures.

A systematic approach to optimum thermal design

This paper presents the philosophy underlying a mathematical model for optimum thermal design of residential or office buildings. The criterion of performance is chosen to be minimum discomfort in the absence of custom-designed environmental control systems. An optimization method based on systematic search procedures has been coupled to the thermal analysis of buildings subjected to time-varying excitations, both climatic and operational. The design model considers siting, insulation, massing, shading, and glazing parameters, and is open and flexible to allow for linking interacting systems such as acoustics and lighting. Provision has been made for the subjectivity of design climatic data and comfort levels. The investigations are ultimately intended to provide suitable thermal design standards for different climatic regions.

Optimization of steady-state thermal design of space radiators

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.