ME415 THERMAL SYSTEM DESIGN Prof. Dr. Haşmet Türkoğlu Çankaya University Faculty of Engineering Mechanical Engineering Department Spring, 2017
INTRODUCTION Typical Professional Activities of Engineers: - Sale - Construction (Manufacturing) - Research and Development - Analysis - Design Engineering Analysis: The process of determining the behavior of an existing system or a trial system being designed for a prescribed task. - The determination of the behavior of a system implies calculation of its responds to specified inputs. For this reason, sizes of the parts and their configuration are given. Engineering Design: The process of devising a system, component, or process to meet desired needs. It is a decision-making process (often iterative), in which the basic sciences, mathematics, engineering sciences, standards, codes and safety factors are applied to convert resources optimally to meet a stated objective. (ABET) - In the design process, sizes and shapes of various parts are calculated considering the given requirements. Design of a system is an iterative process; we estimate a design and analyze it to see if it performs according to given specifications. If it does, we have an acceptable (feasible) design. We may still want to change it to improve its performance. If the trial design does not work, we need to change it to come up with an acceptable system. In both cases, we must be able to analyze designs to make further decisions. ME415 1 2
METHODOLOGY OF EVALUATING AND PLANNING AN EGINEERING ACTIVITY In recent years, an appreciable amount of attention has been given to the methodology of engineering activities. Certainly, the process and sequence of steps followed in each engineering activity is different. There is no universally applicable methodology. However, flow diagram of a typical steps followed in conception, evaluation and execution of an engineering activity is given in the figure: Technical engineering occurs mostly in activities 5 and 7, product and system design and research. Possible flow diagram in evaluating and planning an engineering activity. ME415 1 3
Step 1. Need or opportunity A need or opportunity is the reason for starting an engineering activity. - To provide enough water to a city during certain times of the year may be required. For this, solution may be enlargement of the water reservoir. - An opportunity may arise as a result of different situations, such as research and development, market potentials. Such an opportunity may lead to use of an existing product for other purposes. Step 2: Criteria of success - In commercial enterprises, the usual criterion of successes is the profit, i.e. providing a certain rate of the return on the investment. - In public projects, the criterion of success is the degree to which the need is satisfied in relation to the cost, monetary or otherwise. Step 3: Probability of success Plans and designs are always directed toward the future, for which only probability, not certainty, is applicable. There is no absolute assurance that the plan or design will meet the success criteria determined above. Therefore, probability of meeting the defined success criterion should be determined. Step 4: Market analysis Since the product or service must eventually be sold or lease to customers, an analysis of the market should be performed. This analysis show indications about the demand for the product or service, price that the potential customers may pay for. Step 5: Technical Design This step is where the largest portion of engineering time is spent. This step consist the majority of the topics of the course. Design consists of determining the sizes of the parts of the system, selecting an element of the system, etc. ME415 1 4
Step 6: Feasibility Feasibility refer to whether the project is possible. A project may be feasible, but not economical. Infeasibility may result from unavailability of investment capital, land, labor or favorable zoning regulations. Safety codes or other regulatory laws may prohibit the enterprise. If the project is infeasible, either alternatives must be found or the project must be dropped. Step 7: Research and development If the product or process is new to the organization, the results from research and development may be important input to decision process. Research efforts may provide origin and improvement of basic idea. ITERATION The loop in the above diagram emphasizes that the decision making process involves many iteration. Each pass through the loop improves the amount and the quality of information and data. Eventually a point is reached where the final decisions are made regarding the design, production, and marketing of the product. The substance that circulates through flow diagram is information, which may be in the form of reports, and conversations and may be both in verbal and pictorial. OPTIMIZATION OF OPERATION The above flow diagram terminates with the construction or beginning of manufacture of a product or service. At this point another stage takes over, which seeks to optimize the operation of given facility. The facility was designed on the basis of certain design parameters which almost inevitably change by the time the facility is in operation. The next challenge then is to operate the facility in the best possible manner in the light of such factors as actual cost and prices. A painful activity occurs when the project is not profitable and the objective becomes that of minimizing the loss. ME415 1 5
THE DESIGN PROCESS Design process starts with accepting the job and ends with a final report. Design process is not just finding a solution. There are many aspects of a design process. Design is not necessarily a single task but a complex process. Design is an activity that can include gathering information, attending meetings, considering alternatives, making calculations, making decisions, etc. An engineer goes through these processes to determine how best to use the resources to accomplish a required job. An unfortunate aspect of design is that, in most cases, what the client wants may be unclear to the engineer and to the client. It is for this reason, a good design engineer will spend much time in defining the problem and in planning the way in which it will be solved. One unique feature of design problems is that there is no one correct answer. For example, in sizing a heat exchanger to provide specific outlet temperatures, one would find that several heat exchangers will work. Each solution will have good and poor aspects associated with it. A rather large group of interrelated and complex factors must be usually considered and some good points may have to be neglected to satisfy other needs. ME415 1 6
Design Phases There are phases in design processes. These include: - recognizing (defining) a need - identifying the problem - synthesizing a solution - redesigning if necessary for optimizing the design - evaluating the design - communicating the results In the figure, one way that the steps in a design can be synthesized: ME415 1 7
Define the Need: Design begins when a client recognizes a need and stars working on satisfying that need. The need can be something obvious or merely a sense that something is not right. Identify the Problem: Defining the problem must include all specifications for the thing to be designed. This includes its dimensions, characteristics, location, cost, expected life, operating conditions, limitations, etc. Restrictions often include available manufacturing processes, available skills, materials to be used, sizes in the stock, etc. Synthesis of the optimum solution: This requires analysis and optimization. This part of the process is iterative in nature and continues until the best solution is found. Evaluation of the design: Evaluation of the design is a significant part of the design process. Evaluation is the proof that the design is successful. Communicating the results: Communicating the results is the final step in the design process. Communication is done orally and/or means of written detailed report. Presenting the results is a selling job where the engineer tries to convince the client that this solution is the best one. Other Aspects of Design Process Product Safety: Every effort should be made on the part of the engineer to assure that the design is safe and has no defects. Public safety is the engineer s chief concern. Economics: Cost considerations play an important role in the design process. Cost must be considered as through as possible in the design process. Using the standard size is almost a necessity in keeping costs low. Codes and Standards Engineering design should comply with the related codes and standards. - Standard is a specification for sizes of part, types of materials or manufacturing processes. The purposes of a standard is to provide the public or customer with uniformity in size and quality. - A code is a specification for the analysis, design or construction of something. The purpose of a code is to guarantee a certain degree of safety, performance and quality. ME415 1 8
The Report After completing the engineering phases of the project, the results should be communicated. Usually a written report and an oral presentation are given. The written report should contain the followings: Letter of transmittal (cover letter): - States that the project has been completed and results are given in the accompanying report. Title Page: - Contains project title, finished date, engineers worked on the project. Problem statement: - Problem considered in the project is clearly explained. Summary of the results: Summarizes the details of the solution. This section might present a list as follows: - what pump to buy - what size pipe to use - what heat exchanger to use, etc. - cost of all components. Narrative: - Presents the details of all components specified in the summary and why these components was selected. Bibliography/References - Shows publications used to arrive at specifics of the design. The written report and oral presentation should be professional in every way. ME415 1 9
Thermal System: Systems that involve fluid flow and/or heat transfer are called thermal system. Examples - Pump and pipe combination - Air conditioner and heating systems - Electric power plants - Combustion fired - Hydraulic power plant - Nuclear power plant - Renewable sources (wind, solar, biomass, geothermal, etc.) - Transportation power systems - Automobiles - Airplanes - Trains - Ship - Processing facilities - Chemical processing plants - Food processing units - Manufacturing facilities - Many other industrial facilities These systems are rather complex. These large systems consist of components and/or small systems as follow: - Pipes, ducts, or channels - Refrigerators, air conditioners, heat pump, dryers - Compressors, pumps or blowers - Furnaces, boilers, gas turbines, steam turbines, - Heat exchangers, cooling towers, internal combustion engines, humidifiers, thermal storage systems, solar collector systems. ME415 1 10