Study of a Natural Gas Combined Cycle with Multi-Stage Membrane Systems for CO2 Post-Combustion Capture

Abstract Carbon capture based on membrane process is receiving an increasing attention, due to advances in membrane performances. The aim of this paper is to investigate the integration of a post-combustion capture system based on membrane separation into a natural gas combined cycle (NGCC) power plant. A sensitivity analysis is carried out in order to evaluate the effect of membrane technology and operating conditions on permeate purity, membrane area and energy requirement for CO 2 capture. Hence, energy and environmental performances of the NGCC integrated with the separation unit are assessed and compared to a baseline power plant without carbon dioxide removal

Novità sul Pittore di Narce a Veio

Presentazione di due anfore inedite in depurata dipinta dalla necropoli di Casale del Fosso a Veio, con nuovi dati sull'ideologia funeraria della comunità protostorica veiente

A NUMERICAL PROCEDURE FOR THE EVALUATION OF THE ENGINE HEAD-CYLINDER GROUP COOLING EFFECTIVENESS

The purpose of this paper is to investigate the thermal flows and heat transfer phenomena occurring in the cooling circuit of a high specific power engine and to suggest a valid method to evaluate its effectiveness in keeping the temperature below a safety limit even in the highest thermal power points. This is a first work showing the analysis of the cooling circuit of a small single-cylinder, four-stroke, high power density gasoline engine carried out with a numerical three-dimensional CFD analysis by means of a CFD conjugate simulation, whose boundary conditions have been taken from a validated one-dimensional fluid dynamic engine model. Once its validity has been assessed by the comparison between the simulation results and data collected by literature and experiments, the interest for this procedure relies on the fact that heat fluxes are directly calculated by the CFD code through the knowledge of gas temperatures and convective heat transfer coefficients. Hence an arbitrary, a priori subdivision of the total heat flux released by fuel combustion into heat converted into mechanical work, heat released to the cooling system, heat rejected to the exhaust, etc. can be avoided; at the same time, the model provides the proper distribution of the heat rejected to the various surfaces constituting the water jackets. The evaluation of the effectiveness of the cooling system is then directly performed in terms of temperature distribution. By this way, once the engine has been designed from a fluid dynamic and mechanical point of view, the effectiveness of the cooling system can be immediately verified through the application of the described procedure. This study takes into consideration the evaluation of average and instantaneous heat transfer coefficient and in-cylinder gas temperature through the use of a validated 1D CFD model, the analysis of the temperature field by means of a conjugate heat transfer simulation of the whole head and cylinder group and an example of the application of this procedure for the evaluation of a simple modification of the cooling system

Risk Factors for Survival After Heart Transplantation in Children and Young Adults: A 22-Year Study of 179 Transplants

Background: This article reviews all patients who underwent heart transplantation (HTx) within a single institution (172 patients underwent 179 HTx [167 first-time HTxs, 10 second HTxs, 2 third HTxs]) to describe diagnostic characteristics, management protocols, and risk factors for mortality. Methods: Descriptive analysis was performed for the entire cohort using mean, standard deviation, median, interquartile range, and overall range, as appropriate. Univariable and multivariable Cox proportional hazards models were performed to identify prognostic factors for outcomes over time. The primary outcome of interest was mortality, which was modeled by Kaplan-Meier analysis. Results: Median age at HTx was 263 days (range, 5 days to 24 years; mean = 4.63 ± 5.95 years; 18 neonates, 79 infants). Median weight at HTx was 7.5 kg (range, 2.2-113 kg; mean = 19.36 ± 23.54). Diagnostic categories were cardiomyopathy (n = 62), primary transplantation for hypoplastic left heart syndrome (HLHS) or HLHS-related malformation (n = 33), transplantation after cardiac surgery for HLHS or HLHS-related malformation (n = 17), non-HLHS congenital heart disease (n = 55), and retransplant (n = 12). Operative mortality was 10.1% (18 patients). Cumulative total follow-up is 1,355 years. Late mortality was 18.4% (33 patients). Overall Kaplan-Meier five-year survival was 76.2%. One hundred twenty-one patients are alive with a mean follow-up of 7.61 ± 6.46 years. No survival differences were seen among the five diagnostic subgroups ( P = .064) or between immunosensitized patients (n = 31) and nonimmunosensitized patients (n = 141; P = .422). Conclusions: Excellent results are expected for children undergoing HTx with comparable results among diagnostic groups. Pretransplant mechanical circulatory support and posttransplant mechanical circulatory support are risk factors for decreased survival. Survival after transplantation for HLHS or HLHS-related malformation is better with primary HTx in comparison to HTx after prior cardiac surgery

Molecular simulation of CO2 adsorption in the presence of water in single-walled carbon nanotubes

The adsorption of carbon dioxide in the presence of water in single-walled carbon nanotubes is studied using Monte Carlo simulation, at 300, 325, and 350 K. We also investigate the influence of the diameter and chirality of the nanotubes on the adsorption isotherms of CO2. It is observed that increasing the nanotube diameter from 1.36 nm (10, 10) to 2.03 nm (15, 15) leads to enhanced CO2 capacity, while change in chirality has little effect on the adsorption capacity of carbon nanotubes. Our results show that the influence of preadsorbed water on CO2 adsorption is dependent on both the effects of excluded volume and H2O-CO2 interactions. The maximum adsorbed amount of CO2 decreases linearly with the loading of water, and drops more rapidly in narrower nanotubes. The structure of water in hydrophobic nanopores is in the form of hydrogen-bonded clusters, and its adsorption does not affect the arrangement and orientation of CO2 molecules (i.e., it does not affect the mechanism of CO2 adsorption). The average size of water clusters coexisting with CO2 depends strongly on the adsorbed amount of CO2; however, it is shown that splitting large water clusters into smaller ones can lead to significant enhancement of CO2 adsorption, due to the resulting stronger water-CO2 interaction. The maximum percentage increase in the excess adsorption of CO2 is as high as 53.4% when a single cluster is split into multiple smaller clusters. This finding demonstrates that the efficiency of CO2 capture from flue gas can be significantly improved by controlling the structure of coexisting water in carbon nanotubes