Abstract This paper presents simulations of discharges from pressure vessels that consistently account for non-ideal fluid behavior in all the required thermodynamic properties and individually considers all the chemical components present. The underlying assumption is that phase equilibrium occurs instantaneously inside the vessel and, thus, the dynamics of the fluid in the vessel comprises a sequence of equilibrium states. The formulation leads to a system of differential-algebraic equations in which the component mass balances and the energy balance are ordinary differential equations. The algebraic equations account for the phase equilibrium conditions inside the vessel and at the discharge point, and for sound speed calculations. The simulator allows detailed predictions of the condition inside the vessel and at the discharge point as a function of time, including the flow rate and composition of the discharge. The paper presents conceptual applications of the simulator to predict the effect of leaks from vessels containing mixtures of light gases and/or hydrocarbons and comparisons to experimental data.

Abstract The correlation of thermodynamic properties of nonaqueous electrolyte solutions is relevant to design and operation of many chemical processes, as in fertilizer production and the pharmaceutical industry. In this work, the Q-electrolattice equation of state (EOS) is used to model vapor pressure, mean ionic activity coefficient, osmotic coefficient, and liquid density of sixteen methanol and ten ethanol solutions containing single strong 1:1 and 2:1 salts. The Q-electrolattice comprises the lattice-based Mattedi-Tavares-Castier (MTC) EOS, the Born term and the explicit MSA term. The model requires two adjustable parameters per ion, namely the ionic diameter and the solvent-ion interaction energy. Predictions of osmotic coefficient at 298.15 K and liquid density at different temperatures are also presented.

This work compares two strategies to fit parameters of equations of state in parallel computers, emphasizing solutions that require few changes to existing sequential programs. One strategy uses the conventional Nelder-Mead algorithm coupled with parallel objective function evaluation (SSPO). The other strategy uses a parallel Nelder-Mead algorithm coupled with sequential objective function evaluation (PSSO). The PSSO strategy, which executes parallel one-dimensional searches during each iteration, is simpler to implement and converged to parameter sets with objective functions smaller than those obtained by the SSPO strategy. The SSPO strategy produced speedups consistent with the number of processes used and is more suitable when many processors are available. Both strategies are potentially useful and choosing between them is a matter of convenience, depending on the problem at hand. With parallel computers increasingly available, the easy implementation and convenience of these two strategies should appeal to developers and users of thermodynamic models.

This article proposes a new procedure to compute solid-liquid equilibrium in electrolyte systems that may form pure solid phases at a given temperature, pressure, and global composition. The procedure combines three sub-procedures: phase stability test, minimization of the Gibbs free energy with a stoichiometric formulation of the salt-forming reactions to compute phase splitting, and a phase elimination test. After the phase splitting calculation for a system configuration that has a certain number of phases, the phase stability test establishes whether including an additional phase will reduce the Gibbs free energy further. The criteria used for phase stability may lead, in some cases, to the premature inclusion of phases that should be absent from the final solution but, if this happens, the phase elimination sub-procedure removes them. It is possible to use the procedure with several excess Gibbs free energy models for liquid phase behavior. The procedure has proven to be reliable and fast and the results are in good agreement with literature data.

The procedure presented by Cabral et al. (2003) was used to predict the adsorption of multicomponent mixtures of methane, ethane, propane, and n-butane adsorbed on Silicalite S-115 at 300 K. The methodology employed uses the algorithm of molecular simulation for the grand canonical ensemble as an equation of state for the adsorbed phase. The adsorbent surface is modeled as a two-dimensional lattice in which solid heterogeneity is represented by of two kinds of sites with different adsorption energies. In all cases presented, the simulations described well the adsorption characteristics of the systems.

The dynamics of flash drums is simulated using a formulation adequate for phase modeling with equations of state (EOS). The energy and mass balances are written as differential equations for the internal energy and the number of moles of each species. The algebraic equations of the model, solved at each time step, are those of a flash with specified internal energy, volume and mole numbers (UVN flash). A new aspect of our dynamic simulations is the use of direct iterations in phase volumes (instead of pressure) for solving the algebraic equations. It was also found that an iterative procedure previously suggested in the literature for UVN flashes becomes unreliable close to phase boundaries and a new alternative is proposed. Another unusual aspect of this work is that the model expressions, including the physical properties and their analytical derivatives, were quickly implemented using computer algebra.

A closed vessel is an apparatus with very thick walls, in which propellants under test are burnt. After ignition, gaseous products and heat are produced. The time history of pressures is measured by piezoelectric transducers, and recorded in either an analog or digital way. For the design and simulation of a gun performance, it would be rather important if one could use the thousands of P versus t points generated by a single shot for the estimation of as many as possible ballistic parameters. The present work is devoted to the development of predictive models for the closed vessel, comparing the performance to real experimental data. Using known regression procedures (Maximum Likelihood, for instance), ballistic parameters are fitted and lifetime of the propellant can be predicted. This can be done once such parameters are related to its ageing process, which consists of a loss of volatile components.

Most of the solids used in adsorption processes are heterogeneous and most isotherm models are not derived to use information about the solid structure and energy heterogeneity. A possible alternative is to use molecular simulation techniques, which turn the thermodynamic model more microscopic. Then, starting from information on the solid structure, it is possible to develop appropriate solid models for each type of real system. Therefore, the objective of this work is to use the grand canonical Monte Carlo technique of molecular simulation for correlating pure-component data and predicting adsorption of multicomponent mixtures. To decrease the computational effort, we use a simplified solid model that is represented by a two-dimensional square lattice. The solid heterogeneity is represented by a random distribution of different kinds of sites, characterized by distinct energy levels. The methodology developed by Cabral et al. (2003a) is used here to correlate pure components and for predicting binary mixtures of ethane, ethylene, isobutane, and carbon dioxide on zeolite 13X with good results.

OBJETIVO: A desnutrição é marcadora independente de óbito na cardiomiopatia dilatada idiopática. Foi analisada a repercussão da introdução da L-carnitina nos parâmetros nutricionais e ecocardiográficos em crianças com cardiomiopatia dilatada idiopática. MÉTODOS: Estudo prospectivo aberto de 11 crianças, comparadas com 40 controles, pareados para sexo e idade. Foi administrada L-carnitina oral (100 mg/kg/dia), além do tratamento padrão. Foram realizadas 118 pesagens no grupo L-carnitina e 264 nos controles, além de 65 ecocardiogramas no grupo L-carnitina e 144 nos controles. Análise estatística: qui-quadrado, teste t de Student, ANOVA e correlação de Pearson. Foi utilizado alfa = 0,05. RESULTADOS: Grupo L-carnitina: idade = 3,82 anos, 72,7% (p = 0,033) menores de 2 anos e do sexo feminino, e 90,9% (p = 0,001) em classe funcional III e IV. Não ocorreram óbitos no período. Não houve diferença no percentil de peso inicial (31,2±8,74 vs. 19,6±21,2) (p = 0,29) nem no índice z (-0,68±1,05 vs. -1,16±0,89) (p = 0,24). Ocorreu aumento do percentil (p = 0,026) e do índice z (p = 0,033) após a L-carnitina. Não houve diferença na fração de ejeção na apresentação (54,9%±3,8 vs. 49,3%±6,6) (p = 0,19), porém a massa VE/SC foi superior no grupo L-carnitina (169,12 g/m²±26,24 vs. 110,67 g/m²±15,62) (p = 0,0005). Após a L-carnitina, a ANOVA demonstrou aumento da fração de ejeção (48,3±7 para 67,2±7) (p = 0,044), e a massa do VE/SC foi reduzida (164,29g/m²±28,14 para 110,88g/m²±28,88), porém sem significância estatística (p = 0,089). CONCLUSÃO: Na cardiomiopatia dilatada idiopática na infância, a suplementação com L-carnitina pode auxiliar na recuperação nutricional e na melhora da fração de ejeção, facilitando a reversão do quadro de caquexia e da insuficiência cardíaca.

OBJECTIVES: Malnutrition is an independent predictor of death in idiopathic dilated cardiomyopathy. An analysis was performed of the impact of L-carnitine supplementation on the nutritional status and echocardiogram parameters of children with idiopathic dilated cardiomyopathy. METHODS: This was an open label cohort of 11 patients who received L-carnitine (100 mg/kg/day) plus the conventional medical treatment, compared with 40 controls, matched for gender and age. The L-carnitine group was weighed 118 times and the controls 264 times. Additionally, the L-carnitine group underwent 65 two-dimensional echocardiograms and the controls 144. Chi-square, Student's t test, Pearson correlation and ANOVA were calculated with alpha = 0.05. RESULTS: For the L-carnitine group: age at presentation = 3.82 years old, 72.7% (p = 0.033) were females younger than 2 years and 90.9% (p = 0.0001) were in functional classes III and IV. There were no deaths during this period. At presentation, no differences were observed in weight percentile (31.2±8.74 vs. 19.6±21.2) (p = 0.29) or z score (-0.68±1.05 vs. -1.16±0.89) (p = 0.24). Increases were observed in both the percentile (p = 0.026) and z score (p = 0.033) after the introduction of L-carnitine. At presentation, there were no differences in ejection fraction (54.9%±3.8 vs. 49.3%±6.6) (p = 0.19), but LV mass/BSA were greater in the L-carnitine group (169.12 g/m²±26.24 vs. 110.67 g/m²±15.62) (p = 0.0005). After the introduction of L-carnitine an increase in ejection fraction (48.3±7 to 67.2±7) (p = 0.044) was observed. LV mass/BSA decreased (164.29g/m²±28.14 to 110.88g/m²±28.88), but without significance (p = 0.089) CONCLUSION: In children with idiopathic dilated cardiomyopathy, supplementation of L-carnitine may be helpful for nutritional and echocardiographic improvement.

Phase equilibrium calculations for fluids confined inside capillary tubes or porous media are formulated using the isofugacity equations. In this situation, the phase pressures are not equal and it is assumed that they are related by the Laplace equation. With this formulation, existing procedures for phase equilibrium calculations can be readily modified to include capillary effects. In this paper, we review some of the main authors who have studied the behavior of fluids inside porous media and perform bubble- and dew-point calculations for pure components and mixtures, using the Peng-Robinson equation of state to model the coexisting phases and several planar surface tension models. Comparisons with results from the literature indicate that the proposed formulation is adequate for representing phase equilibrium inside capillary tubes.

The behavior of binary mixtures of carbon dioxide+alkanol (1-butanol, 2-butanol, 1-pentanol, or 2-pentanol) at high pressures was modeled using the Stryjek-Vera version of the Peng-Robinson equation of state. Two mixing rules were compared for this purpose: the classical one-fluid van der Waals and the Wong-Sandler mixing rules. In the case of the latter mixing rule, the NRTL model for the excess Gibbs free energy was used. We observed that both mixing rules can reproduce the qualitative aspects of the critical diagrams of these binary mixtures. A comparison of the results shows that there is no clear superiority of one mixing rule over the other in terms of the ability to predict the critical behavior of these mixtures.

OBJETIVO: Determinar a importância da desnutrição como marcadora e preditora do óbito na cardiomiopatia dilatada idiopática na infância. MÉTODOS: Este é um estudo retrospectivo envolvendo 165 pacientes (setembro de 1979 a março de 2003). As variáveis analisadas foram sexo, idade e história de infecção viral nos últimos 3 meses, classe funcional da New York Heart Association (NYHA), percentil e desvio padrão do peso (índice z) e avaliação do estado nutricional. Foram realizadas 744 pesagens nos primeiros 72 meses e 93 no primeiro mês de evolução. Análise estatística: qui-quadrado, teste t de Student e análise de variância. Foram utilizados o valor alfa de 0,05 e o valor beta de 0,80. RESULTADOS: A idade no diagnóstico foi de 2,1±3,2 anos, com maior incidência nos menores de 2 anos (75,8%; IC95 = 68,5-82,1%) (p < 0,0001). A classe funcional III e IV foi observada em 81,2% (IC95 = 74,4-86,9%) (p < 0,0001), tendo todos os 40 óbitos ocorrido neste grupo (p = 0,0008). Na apresentação, a miocardite ocorreu em 39,4% (IC95 = 31,9-47,3%) (p = 0,0001). Houve forte associação entre miocardite e doença viral prévia (p = 0,0005) (RC = 3,15; IC95 = 1,55-6,44). A desnutrição na apresentação não influenciou o óbito (p = 0,10), porém a desnutrição evolutiva foi marcadora de óbito (p = 0,02) (RC = 3,21; IC95 = 1,04-9,95). Não houve diferença significativa no percentil de peso (p = 0,15) ou no índice z (p = 0,14) na apresentação. A média do percentil de peso e do índice z foram superiores nos sobreviventes (34,9+32,6 versus 8,6+16,0 e -0,62+1,43 versus -2,02+1,12) (p < 0,0001). A análise de variância demonstrou diferença significativa na evolução para o percentil de peso (p = 0,0417) e para o índice z (p = 0,0005) desde o primeiro mês de evolução. CONCLUSÃO: A avaliação do estado nutricional é de fácil execução, não implica ônus adicional e deve tornar-se rotina no seguimento do paciente com insuficiência cardíaca crônica.

OBJECTIVE: To analyze the prognostic value of malnutrition in children with idiopathic dilated cardiomyopathy. METHODS: This is a retrospective study of 165 patients with idiopathic dilated cardiomyopathy, diagnosed from September 1979 to March 2003. It analyzed the following variables: gender, age, previous viral illness in the preceding 3 months, functional class according to the New York Heart Association (NYHA), evaluation of nutritional status (normal vs malnutrition), percentile and standard deviation (z index) of weight. Weight was measured 744 times during the first 72 months, 93 during the first month. Statistical analysis was performed by chi-squared, Student t test and analysis of variance for repeated measures (ANOVA). Ninety-five percent confidence intervals (CI95) and odds ratios (OR) were calculated. An alpha value of 0.05 and beta of 0.80 were used. RESULTS: Mean age at presentation was 2.2±3.2 years with higher incidence in those younger than 2 years (75.8%-CI95 = 68.5% to 82.1%) (p < 0.0001). NYHA classes III and IV were observed in 81.2% (CI95 = 74.4% to 86.9%) (p < 0.0001) and all 40 deaths were this group (p = 0.0008). At presentation, myocarditis occurred in 39.4% (CI95 = 31.9% to 47.3%) (p = 0.0001) and a high level of association between myocarditis and previous viral illness was observed (p = 0.0005) (OR = 3.15-CI95 = 1.55 to 6.44). Malnutrition at presentation did not influence death (p= 0.10), however progressive malnutrition was a marker for death (p = 0.02) (OR = 3.21-CI95 = 1.04 to 9.95). No significant differences weight percentiles (p = 0.15) or in z scores (p = 0.14) were observed. Observed mean weight percentiles (34.9+32.6 vs 8.6+16.0) (p < 0.0001) and z scores (-0.62+1.43 vs -2.02+1.12) (p < 0.0001) during the study period were greater among survivors. ANOVA demonstrated significant differences in weight percentile progression (p = 0.0417) and z scores (p = 0.0005) from the first month onwards. CONCLUSION: The evaluation of nutritional status. is easy to performer, it does not imply additional costs and should become routine for children with chronic heart failure.

OBJETIVOS: Analisar o valor prognóstico da cardiomegalia, da congestão pulmonar e do índice cardiotorácico como marcadores de óbito e sobrevida em crianças com cardiomiopatia dilatada. MÉTODOS: Estudo retrospectivo de 152 pacientes entre setembro de 1979 e março de 2003. Foram realizados 722 exames nos primeiros 72 meses e 100 nos primeiros 15 dias de evolução. Análise estatística: qui-quadrado, teste t de Student, análise de variância para medidas repetidas e método de Kaplan-Meier. Foram utilizados os valores alfa = 0,05 e beta = 0,80. RESULTADOS: Idade no diagnóstico de 2,2±3,2 anos. Incidência maior nos menores de 2 anos (76,3%; IC 95% = 68,7% a 82,8%) (p < 0,0001). Sexo (p = 0,07) e etnia (p = 0,11) não foram significantes, e a mortalidade não foi influenciada pela faixa etária (p = 0,73), sexo (p = 0,78) e etnia (p = 0,20). A maioria dos pacientes (84,2%; IC 95% = 77,4% a 89,6%) era grave, classe funcional III e IV (p < 0,0001), e todos os 43 óbitos ocorreram neste grupo (p = 0,0008). Cardiomegalia inicial foi observada em 94,1% (IC 95% = 89,1% a 97,2%) (p < 0,0001) e congestão pulmonar em 75,6% (IC 95% = 68,0% a 82,2%)(p < 0,0001), sendo mais freqüente na classe funcional III/IV (RC = 8,03; IC 95% = 2,85% a 23,1%)(p < 0,0001). A congestão pulmonar foi marcadora de óbito (RC = 3,16; IC 95 %= 1,06% a 10,07) (p = 0,0222), o mesmo não ocorrendo com a cardiomegalia (p = 0,1185). A sobrevida foi influenciada pela cardiomegalia (p = 0,0189) e pela congestão pulmonar (p = 0,0050). O índice cardiotorácico máximo e médio foram superiores no grupo óbito (0,749+0,053 versus 0,662+0,080) (p < 0,0001) e (0,716+0,059 versus 0,620+0,085) (p < 0,0001). A análise de variância demonstrou diminuição progressiva do índice cardiotorácico no grupo que sobreviveu (p < 0,0001). CONCLUSÃO: Em crianças com diagnóstico de cardiomiopatia dilatada Idiopática, a presença de congestão pulmonar no exame inicial e o aumento do índice cardiotorácico, são achados associados a menor sobrevida.

OBJECTIVE: To analyze the prognostic value of cardiomegaly, pulmonary congestion and cardiothoracic ratio as indicators of death and survival in children with idiopathic dilated cardiomyopathy. METHODS: We carried out a retrospective review of 152 patients with IDCM diagnosed between September 1979 and March 2003. In the first 72 months, 722 exams were performed (100 in the first 15 days). Statistical analysis: chi-square, Student's t test, ANOVA and Kaplan-Meier curves. Alpha = 0.05; beta = 0.80. RESULTS: The mean age at presentation was 2.2±3.2 years. ICDM incidence was higher in children younger than 2 years (76.3% - 95% CI = 68.7% to 82.8%) (p < 0.0001). Sex (p = 0.07) and color (p = 0.11) were not significant and mortality was not influenced by age (p = 0.73), sex (p = 0.78) or color (p = 0.20). Most patients were severely ill (84.2% - 95% CI = 77.4% to 89.6%; functional class III and IV; p < 0.0001). All 43 deaths occurred in this group (p = 0.0008). Cardiomegaly at presentation was observed in 94.1% (95% CI = 89.1% to 97.2%) (p < 0.0001), and pulmonary congestion in 75.6% (95% CI = 68.0% to 82.2%) (p < 0.0001). Pulmonary congestion and cardiomegaly were more frequent in functional class III/IV patients (RC = 8.03 - 95% CI = 2.85% to 23.1%) (p < 0.0001). Pulmonary congestion was a marker of death (RC = 3.16 - 95% CI = 1.06% to 10.07) (p = 0.0222), but not cardiomegaly (p = 0.1185). Survival was influenced by both cardiomegaly (p = 0.0189) and pulmonary congestion (p = 0.0050). Mean and maximum cardiothoracic ratio were higher in the death group (0.749±0.053 vs. 0.662±0.080) (p < 0.0001) and (0.716±0.059 vs. 0.620±0.085) (p < 0.0001). ANOVA revealed a progressive decrease in cardiothoracic ratio in the survival group (p < 0.0001). CONCLUSION: In children with idiopathic dilated cardiomyopathy, the presence of pulmonary congestion at presentation and increased cardiothoracic ratio are associated with poor survival.

Molecular simulation data were used to study the performance of equations of state (EoS) and combining rules usually employed in thermodynamic property calculations. The Monte Carlo method and the Gibbs ensemble technique were used for determining composition and densities of vapor and liquid phases in equilibrium for binary mixtures of Lennard-Jones fluids. Simulation results are compared to data in the literature and to those calculated by the t-PR-LJ EoS. The use of adequate combining rules has been shown to be very important for the satisfactory representation of molecular simulation data.

A modified form of the Hicks and Young algorithm was used with the Mattedi-Tavares-Castier lattice equation of state (MTC lattice EOS) to calculate critical points of binary mixtures that exhibit several types of critical behavior. Several qualitative aspects of the critical curves, such as maxima and minima in critical pressure, and minima in critical temperature, could be predicted using the MTC lattice EOS. These results were in agreement with experimental information available in the literature, illustrating the flexibility of the functional form of the MTC lattice EOS. We observed however that the MTC lattice EOS failed to predict maxima in pressure for two of the studied systems: ethane + ethanol and methane + n-hexane. We also observed that the agreement between the calculated and experimental critical properties was at most semi-quantitative in some examples. Despite these limitations, in many ways similar to those of other EOS in common use when applied to critical point calculations, we can conclude that the MTC lattice EOS has the ability to predict several types of critical curves of complex shape.