Search

Waste heat recovery (WHR) can represent a solution to improve the efficiency of ships' propulsion, helping to exceed stringent greenhouse gas emission limits. This is particularly suitable in the case of propulsion based on gas turbines due to their medium-high temperature level of the exhaust gases. This study analyzes the performance of a hybrid energy grid, in which the heat is recovered by the exhaust gases of an aeroderivative gas turbine, a GE LM2500+, when the bottoming system is a supercritical CO2 gas turbine. Given the issues and peculiarities related to the onboard installation, where size and weight are fundamental concerns, six WHR schemes have been analyzed. They span from the simple cycle to partial preheated and regenerative, to a cascade layout in which an ORC system receives thermal power by the sCO2 GT. The influence of the seawater temperature on the performance of the hybrid energy system has been also considered. The energetic and exergetic performance comparison of the different schemes has been carried out by using the commercial software Thermoflex. The results showed that an increase in overall performance by up to 29% can be obtained and that the increase in seawater temperature can lead to a decrease in the overall performance. [ABSTRACT FROM AUTHOR]

Reliability-growth models have become popular because of the need to ensure systems reliability even during the development stage of a system. In light of the inadequacies of existing models, a nonparametric reliability-growth model based on the Bayes-decision framework has been developed. The model tracks the number of failures at each testing stage and makes decisions about system reliability.

Transformations inside emulsion droplets of 82 µm have been studied by using laser diagnostics. Arrays of calibrated droplets of emulsion 70/30 w/w diesel oil/pyrolysis oil were injected in pre-heated air flow inside a tubular reactor. Four thermal regimes have been studied: room temperature, 150°C, 250°C, and 350°C. For comparison, droplets of the diesel oil used to form the emulsion were studied in the same experimental conditions. The investigation has been performed by applying the Generalized Scattering Imaging laser technique that allows the simultaneous determination of size and optical properties of droplets. This optical diagnostic technique permitted to infer the chemical-physical changes inside the emulsion droplet by measuring the imaginary part of their refractive index. At 150°C and 250°C, the emulsion droplets suffered progressive depletion of the diesel oil phase. The pyrolysis oil, dispersed in the diesel oil matrix in the form of microdroplets 2 µm sized, underwent partial evaporation, liquid phase pyrolysis, and polymerization. At 350°C almost all the diesel oil had evaporated and the pyrolysis oil microdroplets dispersed in the emulsion droplet had merged to form a single droplet. These residual droplets showed a very narrow size distribution and an absorption coefficient greater than that of the original PO in agreement with the assessment that they represent the combined outcome of evaporation, liquid phase pyrolysis and polymerization of the pyrolysis oil. Samples of residual droplets were captured at the exit of the reactor and analyzed by means of optical microscopy. The microscope analysis was consistent with the laser diagnostics results. [ABSTRACT FROM AUTHOR]

Dependability has been recognized in the transportation reliability literature as an effective measure of transit system service quality. Dependability models link system dependability with reliability and maintainability characteristics of subsystems, incorporating special operating characteristics and recovery policy from failure of each particular transit system. In this paper a new transit system dependability model is proposed, which considers the possibility that a passenger may be delayed by the occurrence of more than one failure in a trip. The mathematical difficulties associated with the algebra of random variables are overcome by using the Monte Carlo method. The results of the proposed model are compared with those relative to different modelling approaches in the literature, by applying the model to a common test scenario. [ABSTRACT FROM AUTHOR]