Thermal design and optimization bejan pdf

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Adrian Bejan, George Tsatsaronis, Michael Moran A comprehensive and rigorous introduction to thermal system designfrom a contemporary perspective. Thermal Design and Optimization offers readers a lucid introductionto the latest. Download >> Read Online >> thermal design and optimization pdf thermal design and optimization bejan pdf free download EXERGY. Bejan - Ebook download as PDF File .pdf), Text File .txt) or read book online. thermal design. THERMAL DESIGN AND OPTIMIZATION Adrian Bejan.

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Thermal design and optimization | 𝗥𝗲𝗾𝘂𝗲𝘀𝘁 𝗣𝗗𝗙 on ResearchGate | Thermal design and The plants were evaluated by applying the Bejan et al. method [7]. Workable, Optimal, and Nearly Optimal Designs / 3. Life-Cycle Design / 6. Overview of the Design Process / 6. Understanding the Problem. Thermal design and optimization of fin-and-tube heat exchanger using heat Bejan,. G. Tsatsaronis,. and. M. Moran,. Thermal. Design. and. Optimization,. Wiley.

The specific internal energy is symbolized by u or U. As these are needed to accommodate a plant expansion. Substituting Equation 2. Reliability is the probability that a system will successfully perform specified functions for specified environmental conditions over a prescribed operating life. The term Sgenis positive when internal irreversibilities are present during the process and vanishes when internal irreversibilities are absent. One-dimensional flow means that the flow is normal to the boundary at locations where mass enters or exits the control volume. The resultant force includes the forces due to pressure acting at the inlet and outlet.

The sources of background information cited in Section 1. Conceptual designers rely heavily on their practical experience and innate creativity. The second stage of the design process opens.

Sell the excess electricity to the utility. One is that an inferior concept will be retained only to be discarded later after considerable additional effort has been expended on it.

As the design of a thermal system is a significant undertaking involving considerable time and expense. Cogenerate steam and power. Another more serious. All ideas generated during a brainstorming session should be recorded. Evaluation occurs later. Generate more than the electricity requirement. Ideas may come quickly at first. The design team should keep working. The concept creation phase just considered can lead to a number of plausible alternative solutions to the primitive problem differing from one another in basic concept and detail.

Generate all of the steam required and: The goal should be to generate as many ideas as possible but not evaluate them.

Generate the full electricity requirement. Generate a portion of the electricity requirement. Purchase the remaining electricity needed from the utility.

Thermal Design and Optimization

Each cogeneration alternative may be configured using a steam turbine system. Concept screening is considered next. Generate all of the steam required in a boiler and purchase the required power from the local utility. Unproven technology may introduce many uncertainties about safe and reliable operation.

A positive total score for an alternative indicates that it is better overall in satisfying the criteria than the reference case. Decision Matrix. To illustrate its use. It should be stressed that such methods do not make the decisions but only allow for orderly interaction and decision making by the participants.

In the figure. The decision tree is another method that can be used to evaluate alternatives [2. Concepts judged as fundamentally unsafe or requiring highly toxic. In such an application. The reference case might be selected independent1. Note that the first alternative has been selected as a reference case and each of the other alternatives is evaluated on how well it competes against the reference case in satisfying the criteria.

Since the criteria employed are not equally important. The decision matrix is a formal procedure for evaluating alternative concepts. A sample decision matrix as might be prepared by an individual team member is shown in Figure 1.

This would conclude the preliminary screening of alternatives. An alternative is likely to be discarded if it is inferior to another concept under consideration. Screening Issues. The procedure would then be repeated and continued iteratively until all but the best of the alternatives remain. This method can be used for screening at any stage of the design process. During discussion of the decision matrices prepared by several evaluators. An alternative might also be replaced when on scrutiny it suggests a modification leading to an improved version.

An important screening issue is appropriate technology. In addition. These are just a few of the general considerations that may apply for screening alternatives. Let us suppose that after preliminary screening the following alternatives have been retained for further screening and evaluation: Produce all the steam required in a natural gas-fired boiler. Consider again the alternative cogeneration concepts for the sample problem listed in Section 1.

Employ a coal-fired steam turbine cogeneration system. Cost is another important way to decide among alternatives. Purchase the electricity from the local utility. The concept development stage is idealized in Figure 1. In this step the particular equipment items making up the overall thermal system and their interconnections are specified.

In parameter optimization the pressures. Synthesis is considered in more detail later in the present section. At this juncture. The objective of the analysis and optimization steps is to identify the preferred configuration from among the configurations synthesized. Each cogeneration system might be sized to provide the required steam. Employ a natural gas-fired combined steam and gas turbine cogeneration system.

The final flow sheets fully specify the equipment items and the interconnections among them required to meet all specifications. The schematics of Figure 1. Optimization can take two general forms: Analysis generally entails thermal analysis solving mass. Structural optimization is indicated in Figure 1. This is known as the base-case design. Synthesis is concerned with putting together separate elements into a whole.

If less than the required power would be produced. Although the goal of the concept development stage is clear. There are. Steam Users. I Return Condensate t L-Steam!..

A great many design guidelines have been reported in the literature. With this approach a flow sheet evolves in a step-by-step manner. To avoid the need to consider all possible alternatives.

Each flow sheet would be described in terms of numerous equations. To reduce the chance of a fundamentally flawed design. In selecting processes and equipment. The table entries are organized under two headings: Such design guidelines are drawn from the experience of designers who have solved similar problems and recorded common features of their solutions. Ideally a hierarchy o levels is traversed. Additional design guidelines are provided in Sections 3.

Proces synthesis has an inherently combinatorial nature. The use of design guidelines does not assure the discovery of a satisfactory design.

Table 1. Each decision level should involve an economic evaluation so that later decisions rest on and are guided by the economic evaluations at earlier levels. Such selections should not introduce glaring design errors: Engineers have traditionally approached such daunting design problems using experience.

The number of possible flow sheets for such a system might be considerable: For complex systems the number of flow sheets might be of the order of lo6. For systems of practical interest this combinatorial aspect soon becomes challenging. Within the system the streams may interact in various ways. Do not overlook the impact of a modification of that process on other processes. Notice that in accordance with one.

The objective now is to identify the alternative that serves as the focus of the detailed design stage. By comparing the results from such economic evaluations. Minimize the mixing of streams with different temperatures. Consider the use of expanders if the power available is greater than kW. Avoid unnecessary heat transfer: When assessing the possibility of improving a particular process.

This crucial concept development step requires. See Section 9. Maximize the use of cogeneration of power and process steam or hot water. Let us suppose that appropriate component descriptions and preliminary costing evaluations also have been obtained. Avoid heat transfer at high temperatures directly to the ambient or cooling water.

When assessing the possibility of improving performance. Minimize the use of throttling. Consider state-of-the-art technology. Use efficient pumps.

When using combustion. Consider standard equipment whenever possible. For heat exchanger networks. The concept development stage then continues for this alternative until the base-case design provided in Figure 1. Minimize the use of combustion. Do not heat refrigerated streams with a stream at a temperature above ambient. See Sections 2. Widely used heat exchanger programs stem from the large-scale research efforts of Heat Transfer Research.

Software for numerous other types of equipment. Although not realized uniformly in each instance. Many companies also have developed proprietary software. One respected source of property data is a program developed by the Design Institute for Physical Properties under the auspices of the American Institute of Chemical Engineers. This section provides a brief overview of computer-aided thermal system design.


This configuration is analyzed from the exergy viewpoint in Section 3. The configuration of Figure 1. The extent to which computer-aided thermal design can be applied is limited by the availability of property data in suitable forms. Libraries of programs are available for designing or rating one of the most common thermal system components: Computer-aided design also relies heavily on suitable process equipment design programs.

It combines qualitative knowledge in the form of heuristics with quantitative knowledge in the form of design and cost models.

The output of these procedures can be used as part of the input to one of the conventional simulators considered next. The design guidelines are drawn from the second law of thermodynamics and correspond closely to those listed in Reference 8. In their present states of development such expert systems provide plausible means for synthesizing flow sheets. This procedure aims at synthesizing a flow sheet starting from a list of components stored in a database.

In the sequential-modular approach. Such software has become popular because of its availability for microcomputers at reasonable cost. A knowledge-based approach to flow sheet synthesis of thermal systems with heat-power-chemical transformations is presented in Reference They allow for rapid screening of alternatives and obtaining first estimates of design conditions.

They aim at inventing feasible designs but not necessarily a final design. Spreadsheet software is a less sophisticated but still effective approach for a wide range of applications.

This type of application is commonly called Jlowsheeting or process simulation. With the advent of very high speed computers and rapidly improving software. Another expert system for the design of thermal systems is discussed in Reference Flowsheeting has developed along two lines: The process invention procedure is a hierarchical expert system for the synthesis of process flow sheets for a class of petrochemical processes [ 2 3 ].

Though still in its infancy. Flowsheeting Software Greater success has been achieved thus far in applying computer aids to analysis and parameter optimization than to process synthesis.

Flowsheeting software allows the engineer to model the behavior of a system. The method of thermoeconomics may then provide a better approach. Vendors should be contacted for up-to-date inlormation concerning the features of flowsheeting software. Optimization deserves a special comment.

A brief description of the features of each simulator is given. Most of the more widely used flowsheeting programs: Many of the leading sequential-modular amd equation-solving programs have optimization capabilities. Chapters 8 and 9 present the fundamentals of thermoeconomics. Thermoeconomics aims to facilitate feasibility and optimization studies during the design phase of new systems and process improvement studies of existing systems.

And for complex thermal systems described in terms of a large number of equations. Of these. Conventional optimization procedures may suffice for relatively simple thermal systems.

A survey of the capabilities of 15 commercially available process simulators is reported in Reference Knowledge developed via thermoeconomics assists materially in improving system efficiency and reducing the product costs by pinpointing required changes in structure and parameter values. National Academy Press. New York. Such modeling is often an important element of the concept development stage of design. Conceptual Design of Chemical Processes.

These methods identify the real cost sources at the component level. E Love. The optimization of the design of thermal systems is based on a careful consideration of these cost sources. New York..

Nevins and D. Taguchi on Robust Technology Development. Concurrent Design of Products and Processes. These presentations are intended to illuminate the design process by gradually introducing first-level design notions such as degrees of freedom.

Elementary models can also highlight key design variables and relations among them. In some instances. ASME Press. Engineering Design Methods. Designing for Competitive Advantage U. Total Design: Integrated Methods for Successful Product Engineering. Improving Engineering Design. Achieving Problem Free Project Management.

Avallone and T. Version 3. The Engineering Design Process. A Wealth of Information Online. Process modeling on spreadsheet. Chemical process simulation. Introductory Management Science. Gtis Turbines and Powes Vol. Could and G. Least-Cost Electric Utility Planning. Electric Power Research Institute. Van Nostrand Reinhold. Englewood Cliffs. Pa10 Alto. Chemical Engineering Economics. Institution of Chemical Engineers. Peters and K. Computer-aided process engineering: The evolution continues. The use of the second law of thermodyriamics in the design of heat exchangers.

Chem Eng. Plant Design and Economics for Chemical Engineers. An autonomous artificial designer of thermal energy systems: Part 1 and Part 2. Design and functional optimization of thermo-mechanical plants via an interactive expert system.

American Society of Heating. July Ertas and J. Perry and D. A prototype expert system for synthesizing chemical process flow sheets.

Tsatsaronis et al. Explain how the inventor presented proof of his or her claims. Using the format listed in Section 1.

Also prepare a Gantt chart and budget. Identify the pipe diameter giving the least total cost per year. Obtain federal. Contact a company regularly doing engineering design work. Who are the customers that should be consulted? How might a design team be set up for this purpose? What are the health risks associated with these substances? Contact your state environmental protection agency for regulations relating to liquid effluents discharged from industrial plants into lakes.

An engineering college at a large university is considering a major revision of its curricula. For this project. Sketch curves giving qualitatively a the cost for pumping the water. Together with two co-workers you have agreed to refinish the exterior of a two-story family dwelling.

Outline the claims presented in the patent. List five words you often misspell and three grammatical errors you occasionally make in report writing. Repeat using a decision tree approach.

Use a decision matrix to evaluate three alternative automobiles. Obtain two vendor quotes for the installed cost of a gas turbine-electric generator system for this application. Is this claim correct? Design analysis simply refers to the reasoning and evaluations that are a normal adjunct of engineering design.

The current presentation is introductory. Later chapters of the book provide further illustrations of modeling and design analysis. Most concepts are discussed only briefly in the belief that this is adequate to spark recall. In Section 2.

If further elaboration is required. The microstructure of matter is studied in kinetic theory and statistical mechanics including quan A premise underlying this presentation is that the reader has had an introduction to engineering thermodynamics and fluid flow. The term model refers here to a description. Fundamentals are surveyed in Sections 2.

It addresses the gross characteristics of large aggregations of molecules and not the behavior of individual molecules. An overbar is used to distinguish an extensive property written on a per mole basis from its value expressed per unit mass. The term phase refers to a quantity of matter that is homogeneous throughout in both chemical composition and physical structure.

When any property of a system changes in value. When an extensive property is reported on a unit mass or a unit mole basis. Pressure and temperature are examples of intensive properties. The defining surface is known as the control surjiace or system boundary. A property is any quantity whose numerical value depends on the state but not the history of the system.

The condition of a system at any instant of time is called its state. Normally the system is a specified region that can be separated from everything else by a well-defined surface.

In this book. A system can contain one. Everything external to the system is the surroundings. Phase and Pure Substance.

Pdf bejan optimization design thermal and

The value of a property is determined in principle by some type of physical operation or test. The control surface may be movable or fixed. A mole is a quantity of substance having a mass numerically equal to its molecular weight. An extensive property is additive in the sense that its value for the whole system equals the sum of the values for its parts. One kilogram mole. Designating the molecular weight by M and the number of moles by n.

A system of fixed mass is referred to as a control mass or as a closed system. Extensive properties depend on the size or extent of the system. When a system in a given initial state goes through a sequence of processes and finally returns to its initial state. In a thermodynamic analysis. The state at a given instant of time is described by the properties of the system. Intensive properties are independent of the size or extent of the system. Homogeneity in physical structure means that the matter is all solid or all liquid or all vapor or equivalently all gas.

Two states are identical if. When there is flow of mass through the control surface. A pure substance can exist in more than one phase. The definition of an absolute temperature following from the second law is valid over all temperature ranges and provides an essential connection between the several empirical measures of temperature. A pure substance is one that is uniform and invariable in chemical composition.

When a system is isolated. Equilibrium means a condition of balance. Such a scale is called a thermodynamic temperature scale. In thermodynamics the concept includes not only a balance of forces but also a balance of other influences. When all such changes cease. Each kind of influence refers to a particular aspect of thermodynamic. Chemical equilibrium is also established in terms of chemical potentials. At equilibrium. The establishment of a scale of temperature independent of the working substance is clearly desirable.

Thermal equilibrium refers to an equality of temperature. The familiar mercury-in-glass thermometer relates the variation in length of a mercury column with the variation in temperature. The dependence of temperature measurements on a thermometric substance such as mercury is not satisfactory.

For complete equilibrium the several types of equilibrium must exist individually. As discussed in Section 2. If there are no changes. The system can be said to be at an equilibrium state. Isolate the system from its surroundings and watch for changes in its observable properties.

To determine if a system is in thermodynamic ecluilibrium. Using the symbol W to denote work. Energy Energy is a fundamental concept of thermodynamics and one of the most significant aspects of engineering analysis. Energy can also be transformed from one form to another and transferred between systems. In thermodynamics. Work is done by a system on its surroundings if the sole effect on everything external to the system could have been the raising of a weight.

Work done by a system is considered positive in value. Energy can be stored within systems in various macroscopic forms: The absolute temperature at the triple point of water is fixed by international agreement to be Notice that the raising of a weight is in effect a force acting through a distance.

We now organize these ideas into forms suitable for engineering analysis. Work is an effect of one system on another. For closed systems. The total amount of energy is conserved in all transformations and transfers. The magnitude of the work is measured by the number of standard weights that could have been raised. WO states in terms of the work in an adiabatic process between these states is. That is. One is the change in kinetic energy KE associated with the motion of the system as a whole relative to an external coordinate frame.

All other energy changes are lumped together in the internal energy U of the system. In engineering thermodynamics the change in the energy of a system is considered to be made up of three macroscopic contributions. This property is called energy.

The specific energy energy per unit mass is the sum of the specific internal energy u. As the work in an adiabatic process depends on the initial and final states only.

Collecting results. A closed system undergoing a process that involves only work in- teractions with its surroundings experiences an adiabatic process. Only changes in the energy of a system have significance. Like kinetic energy and gravitational potential energy. On the basis of experimental evidence. Since any arbitrary value can be assigned to the energy of a system at a given state 1.

The specific internal energy is symbolized by u or U. This postulate. A property related to internal energy u. This expression can be rewritten as U. This means of energy transfer is called an energy transfer by heat. These methods recognize two basic transfer mechanisms: On the basis of experiment it is known that such an energy transfer is induced only as a result of a temperature difference between the system and its surroundings and occurs only in the direction of decreasing temperature.

Closed systems can also interact with their surroundings in a way that cannot be categorized as work. The following sign convention applies: This type of interaction is called a heat interaction.

It follows that heat interactions also involve energy transfer. A fundamental aspect of the energy concept is that energy is conserved.

The quantity denoted by Q in Equation 2. Power Cycles. It follows from Equation 2. This less formal approach is commonly used in engineering practice. A power cycle. Work and heat are not properties. The terms work and heat denote different means whereby energy is transferred and not what is transferred. This equals the net amount of energy received through heat interactions.

Since energy is a property. From experience it is found that power cycles are characterized both by an addition of energy by heat transfer and an inevitable rejection of energy by heat transfer: Wand Q are often referred to simply as work and heat transfer.

Combining the last two equations The thermal efficiency of a heat engine is defined as the ratio of the net work developed to the total energy added by heat transfer: Consider a closed system undergoing a thermodynamic cy- cle. The quantities symbolized by W and Q account for transfers of energy. Further discussion of heat transfer fundamentals is provided in Chapter 4. A thermal reservoir is a system that always remains at a constant temperature even though energy is added or removed by heat transfer.

In other words. The Kelvin-Planck statement refers to the concept of a thermal reservoir. A reservoir is an idealization. A process is said to be reversible if it is possible for its effects to be eradicated in the sense that there is some way by which both the system and its surroundings can be exactly restored to their respective initial states. The Kelvin-Planck statement of the second law may now be given as follows: It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy by heat transfer from a single thermal reservoir.

Expressed analytically. The less than sign of Equation 2. Given this fact. Extensive properties of thermal reservoirs. In every instance where a consequence of the second law has been tested directly or indirectly by experiment it has been verified. The concept of irreversibilities is considered next.

Thermal Design and Optimization : Adrian Bejan :

Each of these can be called a statement of the second law or a corollary of the second law: If one is not valid. Among the many alternative statements of the second law. Kelvin-Planck Statement.

A process is irreversible if there is no way to undo it. It might be expected that the importance of this irreversibility diminishes as the temperature difference narrows. These include but are not limited to the following: Heat transfer through a finite temperature difference Unrestrained expansion of a gas or liquid to a lower pressure Spontaneous chemical reaction Mixing of matter at different compositions or states Friction-sliding friction as well as friction in the flow of fluids Electric current flow through a resistance Magnetization or polarization with hysteresis Inelastic deformation - The term irreversibility is used to identify effects such as these.

A system that has undergone an irreversible process is not necessarily precluded from being restored to its initial state. With a Jinite temperature difference between them. As this division depends on the location of the boundary. Internal irreversibilities are those that occur within the system. When internal irreversibilities are absent during a process.

As an illustration. Engineers should be able to recognize irreversibilities. There are many effects whose presence during a process renders it irreversible. Although improved thermodynamic performance can accompany the reduction of irreversibilities.

Irreversibilities can be divided into two classes. The maximum theoretical efficiency for systems undergoing power cycles while communicating thermally with two thermal reservoirs at different temperature levels can be evaluated with reference to the following two corollaries of the second law.

Carnot Corollaries. All reversible power cycles operating between the same two thermal reservoirs have the same thermal efficiency. Corollary 2. The words rev cycle emphasize that this expression applies only to systems undergoing reversible cycles while operating between the two reservoirs.

Each of these options clearly have cost implications. From the study of heat transfer we know that the transfer of a finite amount of energy by heat between bodies whose temperatures differ only slightly requires a considerable amount of time. Corollary 1. A cycle is considered reversible when there are no irreversibilities within the system as it undergoes the cycle and heat transfers between the system and reservoirs occur ideally i.

The Carnot corollaries can be demonstrated using the Kelvin-Planck statement of the second law [I]. Kelvin Temperature Scale. The thermal efficiency of an irreversible power cycle is always less than the thermal efficiency of a reversible power cycle when each operates between the same two thermal reservoirs.

Using Equation 2. That is where QH is the energy transferred to the system by heat transfer from a hot H on a temperature scale to be defined and Q. Carnot Corollary 2 suggests that the thermal efficiency of a reversible power cycle operating between two thermal reservoirs depends only on the temperatures of the reservoirs and not on the nature of the substance making up the system executing the cycle or the series of processes.

To approach ideality. Primary consideration has been given thus far to the case of systems undergoing cycles while communicating thermally with two reservoirs.

The specification of the Kelvin scale is completed by assigning a numerical value to one standard reference state. As temperatures on the Rankine scale differ from Kelvin temperatures only by the factor 1.

In the present discussion a. Clausius Inequality. By invoking the two Carnot corollaries. For the special case of a reversible power cycle operating between thermal reservoirs at temperatures THand Tc. If a reversible cycle is operated between a reservoir at the reference state temperature and another reservoir at an unknown temperature T.

The Rankine scale. Carnot Efficiency. Over their common range of definition the Kelvin and gas scales are equivalent. The state selected is the same used to define the gas scale: At the triple point of water the temperature is specified to be Equation 2.

The equality applies when there are no internal irreversibilities as the system executes the cycle.. The property entropy and the entropy generation concept play prominent parts in these considerations. In the next section. The significance of the inequality of Equation 2.

The value of S. The Clausius inequality can be demonstrated using the Kelvin-Planck statement of the second law [l]. Means are now introduced for analyzing systems from the second-law perspective as they undergo processes that are not necessarily cycles. Sgen is a measure of the effect of the irreversibilities present within the system executing the cycle.

The subscript b serves as a reminder that the integrand is evaluated at the boundary of the system executing the cycle. For subsequent applications. The Clausius inequality provides the basis for introducing two ideas instrumental for quantitative evaluations of systems from a second-law perspective: The Clausius inequality states that The symbol S is used to distinguish the differentials of nonproperties.. The other cycle consists of an internally reversible process B from state 1 to state 2.

Subtracting these equations leaves 1? Since A and B are arbitrary. Consider two cycles executed by a closed system. It can be concluded. Equation Entropy is an extensive property. Selecting the symbol S to denote this property. Since entropy is a property.

For these cycles. This property is called entropy.

And bejan design pdf optimization thermal

One cycle consists of an internally reversible process A from state I to state 2. The evaluation of entropy changes is discussed further in Sections On rearrangement. In an adiabatic internally reversible process of a closed system the entropy would remain constant. Entropy Balance. Since no irre-. Consider next a cycle consisting of process I from state 1 to state 2. The subscript is not required in the second integral because temperature is uniform throughout the system at each intermediate state of an internally reversible process.

The subscript b in the first integral emphasizes that the integrand is evaluated at the system boundary. The area interpretation of heat transfer is not valid for irreversible processes. A constant-entropy process is called an isentropic process. The direction of the entropy transfer is the same as that of the heat transfer. We can interpret this to mean that an entropy transfer is associated with or accompanies heat transfer.

For this cycle. This can be brought out using the definition of entropy change on a differential basis 2. On such a plot. The term Sgenis positive when internal irreversibilities are present during the process and vanishes when internal irreversibilities are absent. This term can be interpreted as the entropy transfer associated with or accompanying heat transfer. The first term on the right side is associated with heat transfer to or from the system during the process.

The second law of thermodynamics can be interpreted as specifying that entropy is generated by. The entropy change of a system is not accounted for solely by the entropy transfer but is due in part to the second term on the right side of Equation 2. Applying the definition of entropy change. This can be described by saying that entropy is generated or produced within the system by action of irreversibilities..

A positive value means that entropy is transferred into the system. The direction of entropy transfer is the same as the direction of the heat transfer. The entropy balance can be expressed in alternative forms that may be convenient for particular analyses. This allows attention to be focused on the components that contribute most heavily to inefficient operation of the overall system.

For a system isolated from its surroundings. The variable S. Since Sgenmeasures the effect of irreversibilities present within a system during a process. One of these is the rate form. The term Sgenaccounts for the time rate of entropy generation due to irreversibilities within the system.

By comparing entropy generation values. The significance is normally determined through comparison: The entropy generation within a given component might be compared to the entropy generation values of the other components included in an overall system formed by these components. To evaluate the entropy transfer term of the entropy balance requires information regarding both the heat transfer and the temperature on the boundary where the heat transfer occurs.

When applying the entropy balance. The entropy transfer term is not always subject to direct evaluation. In practical applications. An important case for subsequent developments is one for which inward and outward flows occur.

The volurnetricjow rate through a portion of the control surface with area dA is the product of the velocity normal to the area times the area: The time rate of accumulation of mass within the control volume equals the difference between the total rates of mass flow in and out across the boundary. For this case the conservation of mass principle takes the form dm. As systems left to themselves tend to undergo processes until a condition of equilibrium is attained.

The massflow rate through dA is found by multiplying the volume flow rate by the local fluid density: Equations of change for mass. These are given in the present section in the form of overall balances.

When applied to a control volume. The increase of entropy principle is sometimes adopted as a statement of the second law. The mass rate of flow through a port of area A is then found by integration over the area.

This is known as the increase of entropy principle. One contribution is the work associated with the force of the fluid pressure as mass is introduced at the inlet and removed at the exit. Energy can enter and exit a control volume by work and heat transfer. Energy also enters and exits with flowing streams of matter. Control Volume Energy Balance. For one-dimensional flow. The work rate concept of mechanics allows the first of these contributions to be evaluated in terms of the product of the pressure force and velocity at the point of application of the force.

Because work is always done on or by a control volume where matter flows across the boundary. The terms Q and W account. The other contribution.. One-dimensional flow means that the flow is normal to the boundary at locations where mass enters or exits the control volume.

The time rate of accumulation of energy within the control volume is equal to the excess of the incoming rate of energy over the outgoing rate of energy. The terms mi pp. Substituting Equation 2. The previously stated sign convention for work applies to Equation 2. With these considerations. The term Qj represents the time rate of heat transfer at the location on the boundary where the instantaneous temperature is T..

Thermal design and optimization

The term s. The mechanisms of energy transfer are heat and work. To demonstrate the application of important design principles introduced, a single case study involving the design of a cogeneration system is followed throughout the book. In addition, Thermal Design and Optimization is one of the best new sources available for meeting the recommendations of the Accreditation Board for Engineering and Technology for more design emphasis in engineering curricula.

Supported by extensive reference lists, end-of-chapter problem sets, and helpful appendices, this is a superb text for both the classroom and self-study, and for use in industrial design, development, and research. A detailed solutions manual is available from the publisher. Flap copy Th ermal Design and Optimization offers engineering students, practicing engineers, and technical managers a comprehensive and rigorous introduction to thermal system design and optimization from a distinctly contemporary perspective.

Back cover copy A comprehensive and rigorous introduction to thermal system design from a contemporary perspective Thermal Design and Optimization offers readers a lucid introduction to the latest methodologies for the design of thermal systems and emphasizes engineering economics, system simulation, and optimization methods.

Table of contents Introduction to Thermal System Design. Thermodynamics, Modeling, and Design Analysis. Exergy Analysis. Heat Transfer, Modeling, and Design Analysis. Applications with Heat and Fluid Flow. Applications with Thermodynamics and Heat and Fluid Flow.

Economic Analysis. Thermoeconomic Analysis and Evaluation. Thermoeconomic Optimization. He is coauthor with Howard N. Shapiro of Fundamentals of Engineering Thermodynamics, now in its third edition and published by Wiley. He is also the author of Availability Analysis: A Guide to Efficient Energy Use.

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