Repositori URV

Identifier: TDX:1207

Handle: https://hdl.handle.net/20.500.11797/TDX1207

Authors:
Álvarez Bermúdez, Maria Eugenia

Abstract:
Despite its huge potential for energy savings and low environmental impact, the use of absorption refrigeration systems is well below its technical and economic potential. The conventional working fluid H2O/LiBr has serious problems regarding corrosion and thermal decomposition at temperatures above 150°C. For this reason, we propose the development of absorbents suitable to triple-effect absorption refrigeration cycles. These absorbents should be non-corrosive, thermally stable, and allow taking advantage of the thermal potential of high temperature heat sources. The objective of this work is to study the solutions of alkaline nitrates, LiNO3+KNO3+NaNO3 with a percentage mass composition in salts of 53, 28 and 19%, respectively, called “Alkitrate”, as a new working fluid for absorption chillers using water as refrigerant in triple-effect configurations that can operate up to temperatures of about 260°C. In a first stage, experimental measurement, estimation and modelling of the thermophysical properties of aqueous alkaline nitrate and nitrite solutions were carried out in order to create an experimental database of thermophysical properties. Subsequently, the absorption cycle configuration called 'Alkitrate topping cycle' was simulated using the ABSIM (Advanced Modular Simulation of Absorption Systems) program. The Alkitrate topping cycle showed a slightly higher efficiency as compared to the LiBr/H2O triple-effect cycle at generator temperatures above 180ºC, without the problems related to thermal stability and corrosion of H2O/LiBr at temperatures higher than 150ºC. Subsequently, an experimental set-up was designed and built-up to study the absorption process with Alkitrate as working pair in a horizontal falling film absorber at operating conditions of interest for