Miguel Torres García

Endocarditis infecciosa en el anciano

BACKGROUND: The influence of age on the clinical presentation and on the prognosis of infective endocarditis (IE) is unclear. Our aim was to analyse the epidemiologic, clinical and bacteriological characteristics of IE in the elderly compared with younger adult patients. PATIENTS AND METHODS A retrospective study of all patients with IE non intravenous drug users diagnosed in our hospital during the period from 1990 to 2000. We used the Duke criteria to compare the characteristics of 46 episodes of definitive IE in elderly patients (>65 years old ) and of 46 episodes in younger adult patients (20-64 years of age ). RESULTS: No significant differences were observed among the two groups with respect to the delay in diagnosed, possible source of infection, the frequency of positive blood cultures and the type of infective organism, clinical presentation and evolution of the IE. Elderly patients more often had risk factors predisposing (degenerative valvular disease, prosthetic valve and pacemaker ), which decreased the sensitivity of transthoracic echocardiography to 46.5% compared with 64.4% in the younger patients. Transesophageal echocardiography improved the diagnostic of IE in the 37.2% in elderly patients. The patients in the both groups underwent surgical therapy with similar frequency (36.9% in the elderly and the 39.1% in the younger adult patient ) and the mortality rate not was significantly higher in the elderly (19.5%) than in the younger adult patients (10.8%). CONCLUSIONS: The age itself is not a poor prognostic, and should not be used prejudicially in denying a early and aggressive treatment of the patients with IE.

Mechanical Analysis of Genoa 03 Stirling Engine

Due to the new technologies development based on renewable sources of energy, in recent years Stirling engines have become very important in the energetic sector. Many of them do not allow the use of fluid lubricants and, thus, the effect of friction losses is important. For this purpose, a mathematical model has been developed based on the force balance in the crankshaft using the pressure distribution in the cylinders. The aim of this work is to characterize the mechanical losses in a Genoa 03 Stirling engine using a numerical model and experimentally via the drag method. The results of this model have been compared with those obtained experimentally on Genoa 03 Stirling engine. In the experimental results, a proportional increase in friction torque due to the average pressure and the speed of the crankshaft is observed. The first of these is caused by an increase of dry friction forces and the second, by the viscous friction between the working fluid and the inner walls of the engine. Also in this paper, irreversible processes in a beta type Stirling engine have been investigated in order to highlight the impact of losses on mechanical power and its performance. This article develops the first study of the mechanical losses of Genoa 03 experimental Stirling engine, which has an output power of 3 kW. Although the model response follows the same trends as the experiments, those simplifications provide errors which become more significant as the engine speed increases.

Predictive Maintenance System for 2 Stroke Diesel Engines

Maintenance cost and unexpected failures can be drastically reduced in low speed diesel engines using vibro-acoustic condition monitoring. This methodology has presented as a reliable method for detection of manufacturing faults, running damages and other abnormalities in engine and its components. Continuous trending keeping deviations of monitored parameter allows also reduction of fuel consumption, optimize exhaust emissions, and increase components life time and increase safety. This paper describes a methodology for vibration monitoring and fault diagnosis based on time-windowing and frequency analysis. The effectiveness is demonstrated based on the results of two year operation on a large two stroke power plant diesel engine located in Mahon, Spain.Copyright

Analysis of Steam Turbine Instabilities of a 100 MW Combined Cycle Power Plant

An analysis of the vibration field of the steam turbine in a combined cycle power plant has been used to identify the causes of the plant rejection at commissioning. The steam turbine group consists of a high pressure turbine connected through a gear box to a medium and low pressure turbine. The high vibration level in the main steam turbine journal bearings caused the plant can’t reach nominal power 100 MW, and at approximately 43 MW the plant was rejected. Vibration is measured through proximity non-contact sensors (two per bearing at 90°), which give relative displacements between shafts and the bearing housing. Accelerometers are also located in the bearing housing. The analysis carried out included: • Field measurements; • Critical speeds dynamic model (API 684 guidelines); • Comparison with the API 684 stability test. As a result of this study, the authors found that excessive vibration was caused by a rotor instability phenomenon, “steam whirl”, and that it led to plant rejection. The main conclusions from this work are: • The vibration rejection of the combined cycle plant was due to an excess in the maximum permissible vibration value at synchronism speed, which always occurred at 43 MW. • The excessive vibration level was caused by rotor instabilities at the rotor shaft in the high-pressure steam turbine. The main vibratory energy was concentrated in a frequency range 0.38–0.41 × rpm. • The main instability phenomenon was identified as “steam whirl”. • The protocol used as a tool in the stability analysis of the turbine, defined in API 684, shows that the logarithmic decrement at the first modal frequency in the most dangerous situation (minimum gap in bearings) has a value of 0.149, which is higher than the stability threshold defined in the API 684 specification (0.1). In this way, and according to the stability analysis, the steam turbine design would be safe despite the fact that the instability problem appeared.Copyright