The application of equilibrium thermodynamics in the study of thermal plant performance under real operating conditions is a constant challenge. In this paper, an analysis of a reservoir pressure piston working between two linear flow resistances is performed by considering the friction of the piston cylinder system on the walls. The proposed model is developed to obtain the optimum power output and speed of the piston in terms of first law efficiency. If the friction on the piston–cylinder assembly is neglected, the expressions obtained are consistent with those presented in the literature under laminar regime. It was also demonstrated that for both laminar and turbulent regimes with overall size constraints, the power delivered can be maximized by balancing the upstream and downstream flow resistances of the piston. This paper also evaluated the influence of the overall size constraints and flow regime on the performance of the piston cylinder. This analysis is equivalent to evaluate the irreversibilities in an endo-irreversible Carnot heat engine with heat loss resistance between the engine and its heat reservoirs. The proposed model introduced some modifications to the results obtained from the recent literature and led to important conclusions. Finally, the proposed model was applied to calculate the lost available work in a turbine operating at steady flow conditions with an ideal gas as working fluid.
This paper explores the feasibility of using Syngas with low methane number as fuel for commercial turbocharged internal combustion engines. The effect of methane number (MN), compression ratio (CR), and intake pressure on auto-ignition tendency in spark ignition internal combustion engines was determined. A nondimensional model of the engine was performed by using kinetics mechanisms of 98 chemical species in order to simulate the combustion of the gaseous fuels produced from different thermochemical processes. An error function, which combines the Livengood–Wu with ignition delay time correlation, to estimate the knock occurrence crank angle (KOCA) was proposed. The results showed that the KOCA decreases significantly as the MN increases. Results also showed that Syngas obtained from coal gasification is not a suitable fuel for engines because auto-ignition takes place near the beginning of the combustion phase, but it could be used in internal combustion engines with reactivity controlled compression ignition (RCCI) technology. For the case of high compression ratio and a high inlet pressure at the engine's manifold, fuels with high MN are suitable for the operating conditions proposed.
Background Use of clinical tests and ventilator weaning tests in conjunction with the spontaneous breathing test (SBT) can increase the predictive capacity of extubation success. Therefore, we assessed the predictive ability of SBT, cuff leak test, rapid-shallow-breathing-index, cough intensity, and velocity of diaphragmatic contraction (VDC) in successful weaning of mechanically ventilated patients. Methods A prospective multicenter observational study from in which consecutive adult patients admitted to 4 intensive care units. The performance of tests in discriminating between success and failure of the weaning process was assessed at different time points using ROC-curve in which the dependent variable was successful extubation. Results A total of 367 subjects who received invasive mechanical ventilation, 456 SBT were performed, with a success rate of 76.5%. The ROC curve of this model (0.52xCough)-(0.12xVDC) + 0.3 to predict a successful SBT was 0.63 (95%CI:0.60–0.65), a cut-off point > 0.84 had a sensitivity of 90.1% and a specificity of 25.3%. The ROC-curve of the model (5.7xSBT)+(0.75xCough)–(0.25xVDC)–4.5 to predict a successful extubation was 0.89 (95%CI:0.85–0.94), a cut-off point > 5.97 had a sensitivity of 98.9% and a specificity of 73.2%. The Hosmer-Lemeshow test showed no significant differences between observed and predicted values (p = 0.92). Conclusion Objective measures of cough and diaphragmatic function demonstrate excellent discriminatory ability to predict successful extubation with a cutoff of 5.97. The probability of having a successful extubation could be evaluated using the proposed model.
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