Experimental investigation of an ammonia-water-hydrogen diffusion absorption refrigerator

Diffusion absorption refrigeration (DAR) is a small-scale cooling technology that can be driven purely by thermal energy without the need for electrical or mechanical inputs. In this work, a detailed experimental evaluation was undertaken of a newly-proposed DAR unit with a nominal cooling capacity of 100~W, aimed at solar-driven cooling applications in warm climates. Electrical cartridge heaters were used to provide the thermal input which was varied in the range 150-700 W, resulting in heat source temperatures of 175--215 C measured at the generator. The cooling output during steady-state operation was determined from the power consumed by an electric heater used to maintain constant air temperature in an insulated box constructed around the evaporator. Tests were performed with the DAR system configured with the default manufacturer's settings (22 bar charge pressure and 30 % ammonia concentration). The measured cooling output (to air) across the range of generator heat inputs was 24--108 W, while the coefficient of performance (COP) range was 0.11--0.26. The maximum COP was obtained at a generator heat input of 300 W. Results were compared to performance predictions from a steady-state thermodynamic model of the DAR cycle, showing a reasonable level of agreement at the nominal design point of system, but noteworthy deviations at part-load/off-design conditions. Temperature measurements from the experimental apparatus were used to evaluate assumptions used in the estimation of the model state point parameters and examine their influence on the predicted system performance

Spectrometric characterization of amorphous silicon PIN detectors

During the last years, much interest has been dedicated to the use of amorphous silicon PIN diodes as particle and radiation detectors for medical applications. This work presents the spectrometric characterization of PECVD high deposition rate diodes fabricated at our laboratory, with thickness up to 17.5 μm. Results show that the studied devices detect the Am^(241) alpha particles and the medical X-rays generated by a mammograph model Senographe 700T from General Electric. Possible reasons of the observed energy losses are discussed in the lest. Using the SRIM2000 program, the transit of 5.5 MeV alpha particles through a diode was simulated, determining the optimum thickness for these particles to deposit their energy in the intrinsic layer of the diode

Generación automática de pruebas de validación de prácticas de sistemas distribuidos

La corrección de prácticas de sistemas distribuidos es una tarea costosa para el profesor que evalúa dichos ejercicios. Esta tarea puede ser sistematizada mediante la ejecución de tests automatizados cuya elaboración representa una alta inversión de tiempo para cada práctica a corregir. Así surge la necesidad de desarrollar una herramienta que, a partir de pequeñas especificaciones proporcionadas por el usuario, genere fácil y rápidamente dichos scripts libres de errores de sintaxis. Con este fin, se ha desarrollado una herramienta web flexible, sencilla de utilizar y que permite ahorrar tiempo dedicado a la elaboración de scripts.Peer Reviewe

Deposition reactors for solar grade silicon: a comparative thermal analysis of a Siemens reactor and a fluidized bed reactor

Polysilicon production costs contribute approximately to 25-33% of the overall cost of the solar panels and a similar fraction of the total energy invested in their fabrication. Understanding the energy losses and the behaviour of process temperature is an essential requirement as one moves forward to design and build large scale polysilicon manufacturing plants. In this paper we present thermal models for two processes for poly production, viz., the Siemens process using trichlorosilane (TCS) as precursor and the fluid bed process using silane (monosilane, MS).We validate the models with some experimental measurements on prototype laboratory reactors relating the temperature profiles to product quality. A model sensitivity analysis is also performed, and the efects of some key parameters such as reactor wall emissivity, gas distributor temperature, etc., on temperature distribution and product quality are examined. The information presented in this paper is useful for further understanding of the strengths and weaknesses of both deposition technologies, and will help in optimal temperature profiling of these systems aiming at lowering production costs without compromising the solar cell quality