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ABSTRACT

Absorption refrigeration (ABR) systems are receiving increased attention worldwide in research ef forts aiming to enhance their performance. One major area of interest is the search for new combinations of refrigerant/absorbent pairs, which improve the ABR thermodynamic performance compared to the widely used ammonia-water or water-LiBr. In the present paper, the heat transfer and pressure drop characteristics of three binary mixtures namely water- LiBr, water-LiI and water-LiCl are investigated. Investigations focuses on the shell and tube type solution heat exchanger of the ABR process, where significant thermodynamic benefits can be obtained through internal heat recovery. Several operating parameters are varied over wide ranges for the three mixtures, including shell side absorbent concentration (0.45 - 0.75), shell side mass flow rate (0.5 (1.1) - 2 (4.4) kg/s (lb/s)), hot side solution inlet temperature (373 (211.7) - 403 (2657) K (°F)) and cold side solution inlet temperature (273 (31.7) - 293 (67.7) K (°F)). The tube side absorbent concentration (0.5) and mass flow rate (0.5 (1.1) kg/s (lb/s)) are held constant during the entire analysis. It is found that the absorbent concentration in the mixture has significant impact on shell side heat transfer coefficient and pressure drop and both are decreases with increase in the absorbent concentration. The shell side heat transfer coefficient affected slightly by increasing the hot solution inlet temperature, whereas the co ld so lu t ion inlet temperature has negligible ef fect over the tested range. At the same time, pressure drop remains almost constant in cases of both, inlet temperature o f hot and cold side solution. Among the tested mixtures, water-LiI exhibits better heat transfer performance and a lower pressure drop penalty followed by water-LiBr and water-LiCl.