Jorge Llagostera - llagost@fem.unicamp.br
Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Departamento de Energia
Caixa Postal 6122 - 13083-970 - Campinas, SP, Brasil

Entropy generation in natural convection inside a porous two-dimensional cavity is calculated. The square cavity is isothermally heated from below and cooled from the top. Single-cell and multiple-cell steady-state solutions are considered. The non-dimensional formulation of the entropy balance applied for the calculation of entropy production is presented. The entropy generation related to heat transfer and the entropy generation related to fluid flow are calculated and reported for several cases. Contour level maps show entropy generation distributions. The main conclusion is that the entropy generation associated to heat transfer is much more important than the entropy generation associated to fluid flow, for the cases studied.

Keywords: Entropy generation, Natural convection, Porous cavity
 
 

Enildo A. Bernardes - obj.ura@ZAZ.COM.BR
Universidade Federal de Uberlândia - Faculdade de Engenharia Química - Av. João Naves de
Ávila, 2160 - 38408 100 - Uberlândia -MG

Moilton R. Franco Júnior - moilton@ufu.br
Universidade Federal de Uberlândia - Faculdade de Engenharia Química - Av. João Naves de
Ávila, 2160 - 38408 100 - Uberlândia -MG

The prediction of liquid-liquid equilibria (LLE) for systems involving compounds from chemical industry has been so much explored. Some methods which involve binary mixtures have been shown good performance for obtaining equilibrium data in low pressures. Some mixing rules such as Wong-Sandler and MHV1, connected with known equations used for representing excess Gibbs energy (G ex ) ,e.g., NRTL and UNIQUAC, show good agreement with experimental data. For systems which are under high pressures, Peng-Robinson equation matched to Wong-Sandler mixing rule and a suitable G ex , has been provided excellent results even for polar and self-associating components. In this work, we took the parameters from Escobedo & Sandler (1998), adjusted through Levenberg-Marquardt method (IMSL, 1979), to correlate LLE data of the systems containing alcohols, hydrocarbons and water. Good results were obtained for the systems under low pressure for which experimental data were available. Studies to apply this methodology for the systems under high pressures have being performed in our laboratory.

Keywords: Liquid-liquid equilibria, low pressures, mixing rules, cubic equation of state.
 
 

Pedro R. Fernandes - pedro@enq.ufrgs.br
Jorge O. Trierweiler - jorge@enq.ufrgs.br
Keiko Wada - keiko@enq.ufrgs.br
Argimiro R. Secchi - arge@enq.ufrgs.br
Universidade Federal do Rio Grande do Sul, Departamento de Engenharia Química
CEP 90040-040 - Porto Alegre, RS, Brasil

In this work one of the main benefits of the use of Local Thermodynamic Models Network (LTMN) for process dynamic simulation is discussed: the possibility of the development of efficient methods for the calculation of bubble point temperature of multicomponent mixtures. The LTMN are an evolution of the Local Thermodynamic Models already in use by commercial process simulators for the calculation of properties like 'volatilization equilibrium ratios' (or K_values) and enthalpies. Besides the reduction of the computational time spent in the evaluation of the thermophysical properties (TP), the use of the LTMN allows one to consider different models for accounting different behaviors of the system in the thermodynamic space. In this paper different methods for the approximation of bubble point temperature, such polynomials of several orders and rational approaches, are discussed. These methods are tested with some ternary systems.

Keywords: Local Thermodynamic Models Network, Bubble Point Temperature.
 
 

Antonio Garrido Gallego - e-mail: agallego@unimep.br
Faculdade de Engenharia Mecânica e de Produção - Universidade Metodista de Piracicaba
Est. Santa Bárbara/Iracemápolis, km 1, 13450-000 Santa Bárbara d'Oeste, S.P. - Brasil

Gilberto Martins - email: gmartins@unimep.br
Faculdade de Engenharia Mecânica e de Produção - Universidade Metodista de Piracicaba
Est. Santa Bárbara/Iracemápolis, km 1, 13450-000 Santa Bárbara d'Oeste, S.P. - Brasil

Silvia Azucena Nebra - e-mail: sanebra@fem.unicamp.bre
Faculdade de Engenharia Mecânica - Universidade Estadual de Campinas
P.O. box 6122, 13083-970, Campinas, S.P. - Brasil

No presente trabalho utiliza-se o método termoeconômico, como ferramenta para a análise da distribuição de custos em uma planta de cogeração proposta para uma cervejaria da região de Campinas. Para análise foram consideradas as demandas energéticas de calor de processo (em termos de vapor), refrigeração e eletricidade para produção de cerveja referente ao ano de 1997. O sistema de cogeração proposto possui duas turbinas a gás, cada uma com uma caldeira de recuperação e sistema de refrigeração por compressão de amônia. Na condição atual, a energia elétrica é fornecida pela concessionária de energia elétrica, o vapor é produzido em caldeiras que usam óleo combustível e o sistema de refrigeração é similar ao da proposta de cogeração. O desempenho da configuração atual e da proposta de cogeração foram simulados mês a mês, considerando a demanda mensal de vapor e refrigeração requerida pela planta. As turbinas a gás foram simuladas para trabalhar na carga nominal, sendo o excedente de energia vendido para a concessionária. Na análise termoeconômica de cada equipamento da configuração atual e da proposta de cogeração, foi
possível identificar a perda exergética de cada equipamento, sua contribuição no rendimento da planta e o custo exergético monetário para cada um dos fluxos envolvidos.

Palavras-chave: Cogeração, Cervejaria, Análise termoeconômica, Turbinas a gás
 
 

Felipe Raúl Ponce Arrieta - aponce@iem.efei.br
Electo Silva Lora - electo@iem.efei.br
Escola Federal de Engenharia de Itajubá (EFEI), Núcleo de Estudos de Sistemas Térmicos (NEST), Av. BPS, 1303 - Cx. P. 50, CEP 37500-000 Itajubá, MG, Brasil

Silvia Azucena Nebra de Pérez - sanebra@fem. unicamp.br
Universidade Estadual de Campinas (UNICAMP), Faculdade de Engenharia Mecânica, Departamento de Energia, Cidade Universitária Zeferino Vaz - Cx. P. Box 6122, CEP 13083-970, Campinas, SP, Brasil

Using Thermoeconomics as a tool to identify the location and magnitude of the real thermodynamic losses (energy waste, or exergy destruction and exergy losses) it is possible to assess the production costs of each product (electric power and heat) and the exergetic and exergoeconomic cost of each flow in a cogeneration plant to assist in decision-marketin procedures concerning to plant design, investment, operation and allocations of research funds.  Thermoeconomic analysis of Biomass Integrated Gasification Gas Turbine Combined Cycle (BIG GT CC) cogeneration plant for its applications in sugar cane mills brings the following results: (i) the global exergetic efficiency is low; (ii) the highest irreversibilities occur in the following equipment, by order: scrubber (38%), gas turbine (16%), dryer (12%), gasifier and HRSG (6%); (iii) due to the adopted cost distribution methodology, the unit exergetic cost of the heat (4,11) is lower than electricity (4,71); (iv) the lower market price of biomass is one of the most sensible parameter in the possible implementation of BIG-GT technology in sugar cane industry; (V) the production costs are 31 US$/MWh and 32 US$/MWh for electricity and heat, respectively.  The electricity cost is, after all, competitive with the actual market price.  The electricity and heat costs are lower or almost equal than other values reported for actual Rankine cycle cogeneration plants.

Keywords: Thermoeconomic analysis, Exergy, BIG-GT, Gas turbine, Biomass