Design and Optimization of Thermal Systems, Third Edition

with MATLAB Applications

Yogesh Jaluria

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9781498778251
• Edition: 3
• Topic: Matematica
• Subtopic: Ottimizzazione

Design and Optimization of Thermal Systems, Third Edition: with MATLAB® Applications provides systematic and efficient approaches to the design of thermal systems, which are of interest in a wide range of applications. It presents basic concepts and procedures for conceptual design, problem formulation, modeling, simulation, design evaluation, achieving feasible design, and optimization. Emphasizing modeling and simulation, with experimentation for physical insight and model validation, the third edition covers the areas of material selection, manufacturability, economic aspects, sensitivity, genetic and gradient search methods, knowledge-based design methodology, uncertainty, and other aspects that arise in practical situations. This edition features many new and revised examples and problems from diverse application areas and more extensive coverage of analysis and simulation with MATLAB®.

1

Introduction

Design is generally regarded as a creative process by which new methods, devices, and techniques are developed to solve new or existing problems. Though many professions are concerned with creativity leading to new arrangements, structures, or artifacts, design is an essential element in engineering education and practice. Due to increasing worldwide competition and the need to develop new, improved, and more efficient processes and techniques, growing emphasis is being placed on design. Interest lies in producing new and higher quality products at minimal cost, while satisfying increasing concerns regarding environmental impact and safety. It is no longer adequate just to develop a system that performs the desired task to satisfy a recognized societal need. It is crucial to optimize the process so that a chosen quantity, known as the objective function, is maximized or minimized. Thus, for a given system, the output, profit, productivity, product quality, etc., may be maximized, or the cost per item, investment, energy input, etc., may be minimized.

The survival and growth of most industries today strongly depend on the design and optimization of the relevant systems. With the advent of many new materials, such as composites and ceramics, and new manufacturing processes, such as three-dimensional printing, several traditional industries, such as the steel industry, have diminished in importance in recent years, while many new fields have emerged. It is important to keep abreast of changing trends in these areas and to use new techniques for product improvement and cost reduction. Even in an expanding engineering area, such as consumer electronics, the prosperity of a given company is closely linked with the design and optimization of new processes and systems and the optimization of existing ones. Consequently, the subject of design, which had always been important, has become increasingly critical in today's world and has also become closely coupled with optimization.

In recent years, we have also seen tremendous growth in the development and use of thermal systems in which fluid flow and transport of energy play a dominant role. These systems arise in many diverse engineering fields such as those related to manufacturing, power generation, pollution, air conditioning, heating, and aerospace and automobile engineering. Therefore, it has become important to apply design and optimization methods that traditionally have been applied to mechanical systems, such as those involved with transmission, vibrations, controls, and robotics, to thermal systems and processes. In this book, we shall focus on thermal systems, considering examples from many important areas, ranging from classical and traditional fields like engines and heating/cooling to new and emerging fields like materials processing, data centers, nanomaterials, and alternative energy sources. However, many of the basic concepts presented here are also applicable to other types of systems that arise in different fields of engineering, for example, civil, chemical, electrical, and industrial engineering.

In this chapter, we shall first consider the main features of engineering design, its importance in the overall context of an engineering enterprise, and the need to optimize. We will also examine design in relation to analysis, synthesis, selection of equipment, and other important activities that support design. This discussion will be followed by a consideration of systems, components, and subsystems. The basic nature of thermal systems will be outlined, and examples of different types of systems will be presented from many diverse and important areas.

1.1ENGINEERING DESIGN

One of the most important tasks confronted by engineers is that of design. It may be the design of an individual component, such as a thermostat, flow valve, gear, or spring, or it may be the design of a system, such as a furnace, air conditioner, or an internal combustion engine that consists of several components or constituents interacting with one another. It is, therefore, fair to ask what design is and what distinguishes it from other activities, such as analysis and synthesis, with which engineers are frequently concerned. However, design has come to mean different things to different people. The perception of design ranges from the creation of a new device or process to the routine calculation and presentation of specifications of the different items that make up a system. However, design must incorporate some element of creativity and innovation, in terms of a new, different, and better approach to the solution of an existing engineering problem that has been solved by other methods or the solution to a problem that has not been solved before. The process by which such new, different, or improved solutions are derived and applied to engineering problems is termed design.

1.1.1Design versus Analysis

We are all quite familiar with the analysis of engineering problems using information derived from basic areas such as statics, dynamics, thermodynamics, fluid mechanics, and heat transfer. The problems considered are often relevant to these disciplines and little interaction between different disciplines is brought into play. In addition, all the appropriate inputs needed for the problem are usually given and the results are generally unique and well-defined, so that the solution to a given problem may be carried out to completion, yielding the final result that satisfies the various inputs and conditions provided. Such problems are usually termed as closed-ended.

The calculation of the velocity profile for developed, laminar fluid flow in a circular pipe to yield the well-known parabolic distribution shown in Figure 1.1(a) is an example of analysis. Similarly, the analysis of steady, one-dimensional heat conduction in a flat plate results in the linear temperature distribution shown in Figure 1.1(b). Textbooks on fluid mechanics and heat transfer, such as Pritchard and Mitchell (2015) and Incropera and Dewitt (2001), respectively, present many such analyses for a variety of physical circumstances. Many courses are directed at engineering analysis and engineering students are taught various techniques to solve simple as well as complicated problems in fundamental and applied areas. Most students thus acquire the skills and expertise to analyze well-defined and well-posed problems in different engineering disciplines.

The design process, on the other hand, is open-ended; that is, the results are not well-known or well-defined at the onset. The inputs may also be vague or incomplete, making it necessary to seek additional information or to employ approximations and assumptions. There is also usually considerable interaction between various disciplines, particularly between technical areas and those concerned with cost, safety, and the environment. A unique solution is generally not obtained and one may have to choose from a range of acceptable solutions. In addition, a solution that satisfies all the requirements may not be obtained and it may be necessary to relax some of the requirements to obtain an acceptable solution. Therefore, trade-offs generally form a necessary part of design because certain features of the system may have to be given up in order to achieve some other goals such as greater cost effectiveness or smaller environmental impact. Individual or group judgment based on available information is needed to decide on the final design. Inverse problems, in which the desired outcome is known but the conditions that would lead to this outcome are to be determined, are also commonly encountered. Again, the solution obtained is not unique and optimization methods are needed to narrow the region of uncertainty and thus achieve a physically acceptable result.

FIGURE 1.1Analytical results for (a) developed fluid flow in a circular pipe and (b) steady-state one-dimensional heat conduction in a flat plate.

1.1.2A Few Examples

Consider the example of an electronic component located on a board and being cooled by the flow of air driven by a fan, as shown in Figure 1.2. The energy dissipated by the component is given. If the temperature distributions in the component, the board, and other parts of the system are to be determined, analysis or numerical calculations may be used for this purpose. Even though the numerical procedure for obtaining this information may be quite involved, the solution is unique for the given geometry, material properties, and dimensions. Different methods of solution may be employed but the problem itself is well-defined, with all the input quantities specified and with no variables left to be chosen arbitrarily. No trade-offs or additional considerations need to be included.

Let us now consider the corresponding design problem of finding the appropriate materials, geometry, and dimensions so that the temperature T_c in the component remains below a certain value, T_max, in order to ensure satisfactory performance of the electronic circuit. This is clearly a much more involved problem. There is no unique answer because many combinations of materials, dimensions, geometry, fan capacity, etc., may be chosen to satisfy the given requirement T_c < T_max. There is obviously considerable freedom and flexibility in choosing the different variables that characterize the system. Such a problem is, thus, open-ended and many solutions may be obtained to satisfy the given need and con...