Papers in Thermal MechanicsCopyright (c) 2018 University of Nebraska - Lincoln All rights reserved.
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Recent documents in Papers in Thermal Mechanicsen-usWed, 31 Jan 2018 19:31:20 PST3600Entropy generation in a rectangular packed duct with wall heat flux
https://digitalcommons.unl.edu/chemengthermalmech/12
https://digitalcommons.unl.edu/chemengthermalmech/12Wed, 30 May 2007 08:53:19 PDT
The entropy generation due to heat transfer and friction has been calculated for fully developed, forced convection flow in a large rectangular duct, packed with spherical particles, with constant heat fluxes applied to both the top (heated) and bottom (cooled) wall. An approximate analytical expression for the velocity profile developed for packed bed with H/dp > 5 has been used together with the energy equation of fully developed flow to calculate the non isothermal temperature profiles along the flow passage. The velocity profile takes into account the increase in the velocity near the wall due to the higher voidage in this region of the bed. The effect of the asymmetric heating on the velocity profile is neglected under the thermal conditions considered. The volumetric entropy generation rate and the irreversibility distribution ratios have been calculated and displayed graphically for the values of H/dp = 5 and 20. It was found that the irreversibility distributions are not continuous through the wall and core regions, hence the optimality criterion of equipartition of entropy generations should be considered separately for these regions of the packed duct.
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Yaşar Demirel et al.Review: Stability of Transport and Rate Processes
https://digitalcommons.unl.edu/chemengthermalmech/11
https://digitalcommons.unl.edu/chemengthermalmech/11Mon, 12 Mar 2007 09:57:54 PDT
About fifty years ago, the Turing instability demonstrated that even simple reaction-diffusion systems might lead to spatial order and differentiation, while the Rayleigh-Bénard instability showed that the maintenance of nonequilibrium might be the source of order in fluids subjected to a thermodynamic force above a critical value. Therefore, distance from global equilibrium in the form of magnitude of a thermodynamic force emerges as another constraint of stability; some systems may enhance perturbations, and evolve to highly organized states called the dissipative structures after a critical distance on the thermodynamic branch. Although the kinetics and transport coefficients represent short-range interactions, chemical instabilities may lead to long-range order and coherent time behavior, such as a chemical clock, known as Hopf bifurcation. Stability analyses of linear and nonlinear modes for stationary homogeneous systems are useful in understanding the formation of organized structures. This review presents the stability of equilibrium and nonequilibrium systems of transport and rate processes with some case studies. It underlines the relationships between complex behavior and stability of systems using the classical and nonequilibrium thermodynamics approaches.
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Yaşar DemirelThermoeconomics of seasonal latent heat storage system
https://digitalcommons.unl.edu/chemengthermalmech/10
https://digitalcommons.unl.edu/chemengthermalmech/10Mon, 12 Mar 2007 09:51:43 PDT
A simple thermoeconomic analysis is performed for a seasonal latent heat storage system for heating a greenhouse. The system consists of three units that are a set of 18 packed-bed solar air heaters, a latent heat storage tank with 6000 kg of technical grade paraffin wax as phase-changing material, and a greenhouse of 180m2. The cost rate balance for the output of a unit is used to estimate the specific cost of exergy for a yearly operation. Based on the cost rate of exergy, fixed capital investment, operating cost, and economic data, approximate cash-flow diagrams have been prepared. The systems feasibility depends on the cost rate of exergy, operating cost, internal interest rate, and rate of taxation strongly. A cash-flow diagram based on exergy considerations may enhance the impact of thermoeconomic analysis in feasibility studies of thermal systems.
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Yaşar Demirel et al.Effects of concentration and temperature on the coupled heat and mass transport in liquid mixtures
https://digitalcommons.unl.edu/chemengthermalmech/9
https://digitalcommons.unl.edu/chemengthermalmech/9Thu, 25 Jan 2007 13:58:44 PST
Using published experimental data on the thermal conductivity, mutual diffusivity, and heats of transport, the degree of coupling between heat and mass flows has been calculated for binary and ternary nonideal liquid n~ixtures. The binary mixtures consist of two types: the first is six systems of sis-to-eight-cai-boil straight and branchcd chain alkanes in chloroform and in carbon tetrachloride; and the second is mixtures of carbon tetrachloride with benzene. toluene, 2-propanone, n-hcxane, and 11-octane. The ternary mixture considered is toluene-chlorobenzeae-bromobenzene. The published data are available at 35OC. 30°C and 35OC and ambient pressurc. Using the linear nonequilibi-ium thern~odynainics( LNET) and the dissipation-pl~enon~enologicale quation (DPE) approach, the effects of concentration, temperature, molecular weight, chain-length, solute, solvent, and brailchiilg on the degree of coupling are examined. The extent of coupling and the thermal diffusion ratio are expressed in terms of the transport coefficients to obtain a better understanding of the interactions between heat and mass flows in liquid n~ixtures.I t is found that the compositioil of the heavy component bromobenzene changes the direction and magnitude of the two-flow coupling in the ternary mixture. O 2001 Elsevier Science Ltd. All rights reserved.
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Y. Demirel et al.Thermodynamics and bioenergetics
https://digitalcommons.unl.edu/chemengthermalmech/8
https://digitalcommons.unl.edu/chemengthermalmech/8Fri, 12 Jan 2007 14:04:20 PST
Bioenergetics is concerned with the energy conservation and conversion processes in a living cell, particularly in the inner membrane of the mitochondrion. This review summarizes the role of thermodynamics in understanding the coupling between the chemical reactions and the transport of substances in bioenergetics. Thermodynamics has the advantages of identifying possible pathways, providing a measure of the efficiency of energy conversion, and of the coupling between various processes without requiring a detailed knowledge of the underlying mechanisms. In the last five decades, various new approaches in thermodynamics, non-equilibrium thermodynamics and network thermodynamics have been developed to understand the transport and rate processes in physical and biological systems. For systems not far from equilibrium the theory of linear non-equilibrium thermodynamics is used, while extended nonequilibrium thermodynamics is used for systems far away from equilibrium. All these approaches are based on the irreversible character of flows and forces of an open system. Here, linear non-equilibrium thermodynamics is mostly discussed as it is the most advanced. We also review attempts to incorporate the mechanisms of a process into some formulations of non-equilibrium thermodynamics. The formulation of linear non-equilibrium thermodynamics for facilitated transport and active transport, which represent the key processes of coupled phenomena of transport and chemical reactions, is also presented. The purpose of this review is to present an overview of the application of nonequilibrium thermodynamics to bioenergetics, and introduce the basic methods and equations that are used. However, the reader will have to consult the literature reference to see the details of the specific applications.
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Y. Demirel et al.Thermodynamics and bioenergetics
https://digitalcommons.unl.edu/chemengthermalmech/7
https://digitalcommons.unl.edu/chemengthermalmech/7Fri, 12 Jan 2007 13:47:53 PST
Bioenergetics is concerned with the energy conservation and conversion processes in a living cell, particularly in the inner membrane of the mitochondrion. This review summarizes the role of thermodynamics in understanding the coupling between the chemical reactions and the transport of substances in bioenergetics. Thermodynamics has the advantages of identifying possible pathways, providing a measure of the efficiency of energy conversion, and of the coupling between various processes without requiring a detailed knowledge of the underlying mechanisms. In the last five decades, various new approaches in thermodynamics, non-equilibrium thermodynamics and network thermodynamics have been developed to understand the transport and rate processes in physical and biological systems. For systems not far from equilibrium the theory of linear non-equilibrium thermodynamics is used, while extended nonequilibrium thermodynamics is used for systems far away from equilibrium. All these approaches are based on the irreversible character of flows and forces of an open system. Here, linear non-equilibrium thermodynamics is mostly discussed as it is the most advanced. We also review attempts to incorporate the mechanisms of a process into some formulations of non-equilibrium thermodynamics. The formulation of linear non-equilibrium thermodynamics for facilitated transport and active transport, which represent the key processes of coupled phenomena of transport and chemical reactions, is also presented. The purpose of this review is to present an overview of the application of nonequilibrium thermodynamics to bioenergetics, and introduce the basic methods and equations that are used. However, the reader will have to consult the literature reference to see the details of the specific applications.
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Y. Demirel et al.Thermodynamic Analysis Of Separation Systems
https://digitalcommons.unl.edu/chemengthermalmech/2
https://digitalcommons.unl.edu/chemengthermalmech/2Mon, 11 Dec 2006 10:50:52 PST
Separation systems mainly involve interfacial mass and heat transfer as well as mixing. Distillation is a major separation system by means of heat supplied from a higher temperature level at the reboiler and rejected in the condenser at a lower temperature level. Therefore, it resembles a heat engine producing a separation work with a rather low efficiency. Lost work (energy) in separation systems is due to irreversible processes of heat, mass transfer, and mixing, and is directly related to entropy production according to the Gouy-Stodola principle. In many separation systems of absorption, desorption, extraction, and membrane separation, the major irreversibility is the mass transfer process. In the last 30 years or so, thermodynamic analysis had become popular in evaluating the efficiency of separation systems. Thermodynamic analysis emphasizes the use of the second law of thermodynamics beside the first law, and may be applied through (i) the pinch analysis, (ii) the exergy analysis, and (iii) the equipartition principle. The pinch analysis aims a better integration of a process with its utilities. It is one of the mostly accepted and utilized methods in reducing energy cost. Exergy analysis describes the maximum available work when a form of energy is converted reversibly to a reference system in equilibrium with the environmental conditions; hence, it can relate the impact of energy utilization to the environmental degradation. On the other hand, the equipartition principle states that a separation operation would be optimum for a specified set of fluxes and a given transfer area when the thermodynamic driving forces are uniformly distributed in space and time. Thermodynamic analysis aims at identifying, quantifying, and minimizing irreversibilities in a separation system. This study presents an overview of the conventional approaches and the thermodynamic analysis to reduce energy cost, thermodynamic cost, and ecological cost in separation systems with the main emphasis on distillation operations. Some case studies of cost reduction based on the thermodynamic analysis are also included.
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Y. Demirel