A new tri-generation system: thermodynamical analysis of a micro compressed air energy storage

There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers’ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network (peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). CAES (compressed air energy storage systems) are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink® environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device

Correlations for the double-diffusive natural convection in square enclosures induced by opposite temperature and concentration gradients

Double-diffusive natural convection in vertical square enclosures induced by opposite horizontal temperature and concentration gradients is studied numerically. A computational code based on the SIMPLE-C algorithm for pressure–velocity coupling is used to solve the system of the conservation equations of mass, momentum, energy and species. Simulations are performed using the thermal Rayleigh number, the buoyancy ratio, the Prandtl number, and the Lewis number, as independent variables. It is found that both heat and mass transfer increase as the thermal Rayleigh number and the Prandtl number are increased, while exhibit a minimum at a value of the buoyancy ratio which increases with increasing the thermal Rayleigh number and the Lewis number. Finally, the mass transfer rate increases with the Lewis number. Conversely, the heat transfer rate is practically independent of the Lewis number as long as the buoyancy ratio is lower than the value at which the minimum heat transfer occurs, whereas it decreases significantly with the Lewis number for higher values of the buoyancy ratio. Based on the results obtained, suitable correlations are developed for the Nusselt and Sherwood numbers of the enclosure

Ulcere Cutanee:etiopatogenesi,diagnosi,terapia e tecniche chirurgiche

Contenuti del volume: Anatomia della cute. Fisiologia del processo di cicatrizzazione. Le ulcere. Terapia medica. Preparazione del letto dell'ulcera (TIME). Medicazioni avanzate. Medicina rigenerativa. Terapia a pressione negativa. Ulcere vascolari agli arti inferiori. Ulcere del piede diabetico. Terapia chirurgica. Decubito. PRP autologo

Optimal inclination for maximum convection heat transfer in differentially-heated enclosures filled with water near 4 degrees C

Natural convection in water-filled square cavities inclined with respect to gravity, having one wall cooled at 0°C and the opposite wall heated at a temperature ranging between 4°C and 30°C, is studied numerically for cavity widths spanning from 0.02 m to 0.1 m in the hypothesis of temperaturedependent physical properties, with the main aim to determine the optimal tilting angle for maximum heat transfer. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. Once the vertical configuration, in which the cavity is differentially heated at sides, is identified by the zero tilting angle, and positive angles denote configurations with the heated wall facing upwards, it is found that the optimal tilting angle is positive if the heating temperature is equal or higher than 8°C, whereas it is negative whenever the heating temperature is lower than 8°C. Moreover, the optimal tilting angle is found to increase as the cavity width is decreased and the temperature of the heated wall is either decreased or increased, according as it is higher or lower than 8°C. Sets of dimensionless correlating equations are developed for the prediction of both the optimal tilting angle and the heat transfer rate across the enclosure

Heat transfer correlations for natural convection in inclined enclosures filled with water around its density-inversion point

Abstract Natural convection in tilted square cavities filled with water, having one side cooled at 0 °C and the opposite side heated at a temperature ranging between 8 °C and 40 °C, is studied numerically for different cavity widths in the hypothesis of temperature-dependent physical properties, exploring the full range of inclination angles. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. It is found that, as the inclination angle is increased starting from the cooling-from-below configuration, the heat transfer rate keeps substantially constant until the breakdown of the upper fluid stratification occurs. Thereafter, the heat transfer performance increases steeply up to reaching a peak at an optimal tilting angle, which increases with decreasing both the cavity width and the temperature of the heated wall. Furthermore, when the combination of the cavity width and the temperature of the heated wall is such that at small tilting angles the buoyancy force in the water layer confined between the cooled bottom wall and the density-inversion isotherm is that required for the onset of convection, or just higher, the asymptotic solution is periodical. A number of dimensionless correlations are developed for the prediction of both the optimal tilting angle and the heat transfer rate across the enclosure