Heat and mass transfer characteristics of a horizontal tube falling film absorber working with water/lithium bromide and ionic liquid as an anti-crystallization additive

Identifier:  imarina:9448916

Handle: https://hdl.handle.net/20.500.11797/imarina9448916

Authors:  Tariq, HA; Bourouis, M; Coronas, A

Abstract:
Absorption Heat Pumps (AHPs) become attractive when low-grade energy sources power them. The water/LiBr is a commonly used working solution in which water is used as a refrigerant which is economical, abundant, nontoxic and natural refrigerant. However, water/LiBr AHPs faces an inherent challenge in operating at higher concentrations, which restrict their capability for cooling at high heat sink temperatures or for heating applications. LiBr crystallizes in water/LiBr solution at high concentrations, limiting the operational range and affecting the performance of the absorption cycle. Ionic Liquid (IL) can be added as an anti-crystallisation additive to improve the solubility of LiBr in absorbent solution. In this work, 1,3-Dimethyl-1H-imidazolium chloride [DMIM][Cl] is used as an additive containing a 6 % mass fraction in absorbent (LiBr+[DMIM][Cl]). This paper aims to characterise the wettability and heat and mass transfer processes for water/(LiBr+[DMIM] [Cl]) and water/LiBr solutions at air- and water-cooling thermal conditions. A horizontal tube falling film absorber is used in the present investigation. The new solution shows no adverse effects on the heat and mass transfer processes compared to water/LiBr; thus, both solutions performed similarly. The increase of 3 %, 8 %, and 3 % on average is noted for water absorption mass flux, heat transfer coefficient and absorber heat duty, respectively, at a cooling water temperature of 50 degrees C, with solution inlet subcooling of -3 degrees C and an absorbent concentration of 64 %. Additionally, the new working solution water/LiBr+[DMIM][Cl]) shows better wettability of absorber tube than water/LiBr, which is favorable for the absorption process.