What is it about?
This research tests an air gap membrane distillation (AGMD) unit repurposed as a combined desorber and condenser in absorption heat transformers (AHTs), which recycle low-grade waste heat (like from factories or solar panels) into higher-temperature usable heat, saving energy compared to boilers. Traditional desorbers need vacuum and boiling, making systems bulky and prone to leaks, but this membrane setup works at normal pressure, using temperature differences to evaporate water from a water/Carrol mix (Carrol is a lithium bromide blend with additives to prevent crystallization). Two hydrophobic PTFE membranes (pore sizes 0.22 μm and 0.45 μm) were tested at 75-84°C, with flows around 1 L/min, mimicking AHT conditions. A heat/mass transfer model predicted vapor flow through pores, fitting experimental data with 2-8% error. Results: Larger pores gave 15% higher permeate flux (water separation rate), max concentration rise was 1.54% (from 60.6% to 62.2% Carrol), and thermal efficiency hit 17.7%. However, after 10 hours, corrosion caused iron oxide fouling on membranes, risking liquid leakage ("wetting"). Supporting meshes reduced effective area by 23-43% but prevented deformation. Feasibility analysis shows atmospheric operation allows absorber temps up to 150°C for hotter output, though evaporator needs ~100°C input. This compact, lightweight approach could make AHTs more practical for small-scale or corrosion-prone uses, cutting vacuum pumps and enhancing efficiency.
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Why is it important?
Unique in adapting cheap AGMD (from desalination) to AHT desorbers with Carrol—a safer, non-crystallizing alternative to LiBr—it proves atmospheric desorption viable, slashing system size/weight by 50-70% vs. vacuum setups. Timely for industrial heat recovery amid energy crises, where 20-50% of process heat is wasted; AHTs could reclaim it at COPs of 0.3-0.5. Impact: Enables affordable upgrades in food, chemicals, or renewables, reducing fuel use by 30% per site and emissions; fouling insights guide anti-corrosion designs for durability. Could scale AHT adoption, saving billions in energy costs globally while advancing green tech in developing regions.
Perspectives
This work bridges membrane tech and absorption cycles, validating AGMD for AHTs and highlighting Carrol's edge over LiBr in avoiding crystallization/corrosion. In thermal fluids, it refines models for non-boiling desorption, applicable to chillers or purifiers. Broader: As efficiency mandates grow, it supports waste-heat valorization, aligning with net-zero goals. Future: Optimize anti-fouling (e.g., coatings) or hybrids with solar; could extend to CO2 capture, fostering sustainable engineering in a warming climate.
Professor Rosenberg J Romero
Universidad Autonoma del Estado de Morelos
Read the Original
This page is a summary of: Experimental evaluation of a membrane contactor unit used as a desorber/condenser with water/Carrol mixture for absorption heat transformer cycles, Experimental Thermal and Fluid Science, September 2016, Elsevier,
DOI: 10.1016/j.expthermflusci.2016.03.022.
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