Passive intensification of the ammonia absorption process with NH3/LiNO3 using carbon nanotubes and advanced surfaces in a tubular bubble absorber

The present study aims to quantify experimentally the individual and simultaneous effects of CNTs (carbon nanotubes) and advanced surfaces on the performance of an NH3/LiNO3 tubular bubble absorber. Operating conditions are those of interest for use in air-cooled absorption chillers driven by low temperature heat sources. Firstly, experimental tests were performed with the tubular absorber fitted with an inner smooth surface to analyze the effect of adding carbon nanotubes (0.01 wt%) to the base mixture NH3/LiNO3. Then, the tubular absorber was tested using an inner advanced surface tube both with and without adding carbon nanotubes to the base mixture NH3/LiNO3. The advanced surface tube is made of aluminum and has internal helical micro-fins measuring 0.3 mm in length. Results show that the maximum absorption mass flux achieved with the CNT binary nanofluid and the smooth tube is up to 1.64 and 1.48 times higher than reference values at cooling-water temperatures of 40 and 35 degrees C, respectively. It is also found that simultaneous use of CNT nanoparticles and advanced surfaces resulted in a more pronounced increase in the absorption mass flux and solution heat transfer coefficient with respect to the smooth tube absorber with NH3/LiNO3 as a working pair. (c) 2014 Elsevier Ltd. All rights reserved.