Enrico Sciubba

The optimal spacing of parallel plates cooled by forced convection

This paper reports the optimal board-to-board spacing and maximum total heat transfer rate from a stack of parallel boards cooled by laminar forced convection. The optimal spacing is proportional to the board length raised to the power 1/2, the property group (μα)14, and (ΔP)−14, where ΔP is the pressure head maintained across the stack. The maximum total heat transfer rate is proportional to (ΔP)12, the total thickness of the stack (H), and the maximum allowable temperature difference between the board and the coolant inlet. Board surfaces with uniform temperature and uniform heat flux are considered. It is shown that the surface thermal condition (uniform temperature vs uniform heat flux) has a minor effect on the optimal spacing and the maximum total heat transfer rate.

Exergy use in the Italian society

The exergy concept is reviewed as a tool for resource accounting. Conversions of energy and material resources in Italian society are described in terms of exergy. Necessary concepts and conventions are introduced. Exergy losses in transformations of material resources and in the conversion of various forms of energy are described in some detail.

Extended exergy accounting applied to energy recovery from waste: The concept of total recycling

A novel systematic approach to the evaluation of energy conversion processes and systems, based on an extended representation of their exergy flow diagram is presented and discussed in this article. The method constitutes a substantial generalisation of Szargut’s cumulative exergy consumption procedure, and provides a coherent and consistent framework for including non-energetic quantities like capital, labour and environmental impact into an engineering optimisation procedure (the apposition ‘extended’ refers to these enhanced capabilities). It is argued that some of the issues that are difficult to address with a purely monetary or even with a thermo-economic approach can be resolved in a straightforward manner by extended exergy accounting (‘EEA’ in this article). As an indication of the potential of the method, a general, qualitative example is offered of the application of EEA to the evaluation of a technical alternative between a non-integrated waste recycling and an integrated waste recycling and incineration facility.

From engineering economics to extended exergy accounting: A possible path from monetary to resource-based costing

The article describes the extended exergy accounting technique (EEA), a novel method for computing the cost of a commodity based on its resource-base equivalent value (as opposed to its monetary cost) that enables the analyst to perform more complete and meaningful assessments of a complex system. The claim made here is that the novelty, as well as the decisive advantage, of EEA consists in its being entirely and uniformly resource based, thanks to the inclusion in the system balance of exergetic fluxes equivalent to labor, capital, and environmental remediation costs. In this respect, EEA owes some of its structural formalism to Sraffas network representation of the economic production of commodities by means of other commodities, which it extends by accounting for the unavoidable energy dissipation in the productive chain (whose economic implications were first discussed by Georgescu-Roegen), to Dalys pioneering work in resource-oriented economics, and to Szarguts cumulative exergy consumption method. The representation of a process by means of its extended exergy flow diagram is discussed in this article, and it is argued that some of the issues that are difficult to address with a purely monetary approach can be properly resolved by EEA. The main shortcomings of EEA are its intrinsic locality in time and space: They are demonstrated to be necessary and not casual consequences of its very definition and of the nonuniformity of societal conditions. In the conclusions, some indications are given as to the possibility of using this new technique to complement (and extend) other current tools, such as life-cycle assessment or environmental footprint analysis.

Cost analysis of energy conversion systems via a novel resource-based quantifier

The paper presents a new formalism for the costing of production chains, with special emphasis on energy conversion systems. From a mathematical point of view, this method can be described as a standard Leontiev-type input-output technique, in the formulation commonly adopted by most costing theories, including Thermoeconomics. Any complex production chain can be decomposed into modules, to each one of which mass and energy balances are applied. The resulting flow diagram is then examined from an exergetic point of view, and a cost analysis is performed. The costing paradigm is the novel feature here: rather than monetary units, a resource-based quantifier, called “extended exergy”, is employed. It is argued that both labour and financial costs can be properly linked to an equivalent resource consumption through a back-to-resource accounting procedure that expresses the total exergy consumption required to “generate” one man-hour of work or one monetary unit of currency circulation. Environmental remediation costs are similarly taken into account by computing the equivalent cumulative exergy expenditures required to achieve zero impact. It is argued, and discussed on the basis of an example of application to a cogeneration plant, that the new technique, called Extended Exergy Accounting (EEA), is a substantial improvement with respect to current engineering economic techniques, including Thermoeconomics. It is shown that EEA calculates the real, resource-based “value” of a commodity (which is not necessarily equal to its monetary cost) thus enabling Analysts and Energy Planners to perform a more complete and meaningful assessment of an Engineering Complex System. The decisive advantage of EEA consists in its being entirely and uniformly resource-based: in this respect, it owes some of its structural formalism both to the economic theory of production of commodities, which it extends by accounting for the unavoidable energy dissipation in the productive chain, and to resource-oriented economics. It must be acknowledged as well that EEA follows a path originally proposed by Szargut in his “Cumulative Exergy Consumption” method, which it extends by providing a rational and uniform treatment for all non-externalities.

The optimal cooling of a stack of heat generating boards with fixed pressure drop, flowrate or pumping power

Abstract In this paper, we show analytically how to optimize the spacing between heat generating boards in a stack cooled by single-phase laminar forced convection. The thickness of each board is not negligible. The theoretical results for optimal spacing and maximum overall thermal conductance between stack and coolant are validated by means of numerical simulations of the complete flow and temperature fields. Results are reported for three different situations, which are dictated by the way in which the stack is attached to the rest of the cooling network of the electronics package : (1) fixed pressure drop, (2) fixed mass flowrate, and (3) fixed pumping power.

Development of Micro-Grippers for Tissue and Cell Manipulation with Direct Morphological Comparison

Although tissue and cell manipulation nowadays is a common task in biomedical analysis, there are still many different ways to accomplish it, most of which are still not sufficiently general, inexpensive, accurate, efficient or effective. Several problems arise both for in vivo or in vitro analysis, such as the maximum overall size of the device and the gripper jaws (like in minimally-invasive open biopsy) or very limited manipulating capability, degrees of freedom or dexterity (like in tissues or cell-handling operations). This paper presents a new approach to tissue and cell manipulation, which employs a conceptually new conjugate surfaces flexure hinge (CSFH) silicon MEMS-based technology micro-gripper that solves most of the above-mentioned problems. The article describes all of the phases of the development, including topology conception, structural design, simulation, construction, actuation testing and in vitro observation. The latter phase deals with the assessment of the function capability, which consists of taking a series of in vitro images by optical microscopy. They offer a direct morphological comparison between the gripper and a variety of tissues.

A computational, modular approach to the simulation of powerplants

Abstract The paper describes the development, the implementation and the practical application of a new modular procedure for the numerical simulation of thermal powerplants. The procedure has resulted in a FORTRAN code, named “CAMEL” (Italian acronym for “Modular Elemental Plant Calculation), which is also described in detail. The plant -any plant, but application of the procedure is presently limited to thermal powerplant- is described in terms of three matrices, named the Interconnection matrix IM , the plant matrix PM and the Topographic matrix TM , which contain in an orderly fashion all of the design data and the6“topological” description of the plant configuration. The Interconnection matrix is equivalent to a structured list of the flows (of matter and energy) which are fed to or extracted from any of the “n” plant components; the plant matrix is a table of the design values of all the fluxes in the plant, and the Topographic matrix is a reference table which allows the logical location of any component to be found both in PM and in IM . Starting from a set of design input data, CAMEL calculates, component bby component, all the values of the thermodynamic variables of interest which do not already appear in PM ; more precisely, CAMEL can calculate the numerical value of all the parameters needed to uniquely determine the thermodynamic and/or energetic state of whatsoever flux in the plant by calling for each component the corresponding routine, which returns the numerical value of all the variables it can calculate at the “present” stage of the simulation. It is important to underscore that these routines can calculate a component not as whole machine but equation by equation, i.e., the routine must not necessarily calculate all of the operating parameters of the component at the same stage of the simulation, but only those which can be calculated with the data known at the current stage of the simulation and that are involved in the same physical event described by one of the equations included in the set which pertains to that component. CAMEL can perform, at the users request, either a single plant simulation or a sensitivity analysis of the behaviour of the plant. At present, CAMEL is only capable of performing sensitivity analysis of plants at design conditions and in a limited number of (steady state) off-design conditions (i.e., the analysis is aimed at the optimization of the design operating conditions of the plant): in principle it is possible to implement a transient computation, but this has not yet been done. CAMEL has been implemented for powerplant simulation, but the core has been structured to allow the code to handle with any kind of processor-plant, provided the codes component library is large enough. The paper reports the philosophy of the approach, describes the details of the algorithm, discusses the flow chart of the numerical code and presents detailed results for an industrial case-study: a combined-cycle power station for electrical generation.

A prototype expert system for the conceptual synthesis of thermal processes

Abstract An expert system capable of assisting the process engineer in thermal processes design selection can improve both the quality and the variety of the solutions proposed. Conceptual design is part of the engineering design process which converts design requirements into an acceptable design solution. Nowadays, engineering design problems have become more and more complex and the increasing complexity has made synthesis a very difficult task: it is during this stage of the design process that the creativity and experience of an engineer are most needed. Inappropriate component requirements and/or coupling can significantly reduce the capability of a process to meet design demands. The prototype presented in this paper (COLOMBO) is an attempt to show that an expert system can be of valid help in finding answers to conceptual process selection. An exhaustive search across the data base allows the user to evaluate plant configuration constituted by virtually every technically feasible combination of components. Generally, the problems under exam result in a goal-driven search process and, therefore, a backward chaining approach is used here. The data base has been subdivided into two main classes: equipment and resources. Each “equipment” object has in-flows and out-flows (energy, matter,…) which define its operational capabilities. Interconnection of these objects is possible when there is compatibility between the out-flows of one and the corresponding in-flows of the next object. Of course, connectivity must satisfy all the constraints imposed to the problem domain. Presently only a few components have been included in the data base and, therefore, only few conventional configurations are produced by the expert system. Nevertheless COLOMBO produced four configurations for a power generation plant and three process configurations for a cogeneration plant which resolve to be equivalent to the human expert choices.

Coupling BEM, FEM and analytic solutions in steady-state potential problems

Problems solved by using different steady-state solution techniques in adjacent subregions are discussed. The computational domain typically consists of two subregions, with a linear boundary value problem in one of them. BEM or analytical methods are used to solve the problem in this subregion. Static condensation of the off-interfacial degrees of freedom in this subdomain produces a linear set of equations linking nodal potentials and fluxes on the interface. This set of equations is generated by solving a sequence of boundary value problems in the linear subregion. Access to the source version of the software used to solve these boundary value problems is not required. Thus, the condensation can be accomplished using any commercial BEM code. The resulting set of equation is then treated as a boundary condition attached to the second subregion. In the latter, any numerical technique can be used and both linear and nonlinear problems may be considered. The paper addresses coupling of BEM and FEM, BEM and BEM and analytical solutions with BEM and FEM. Numerical examples are included.