What is it about?

This study tests a compact prototype for an absorption heat transformer (AHT), a device that upgrades low-temperature waste heat (like from factories at 60-100°C) into hotter, useful heat without extra electricity, using a mix of water and Carrol (a non-crystallizing salt solution safer than lithium bromide). Built with affordable stainless steel plate heat exchangers (PHEs), it runs a cycle: heat evaporates water from the mix in the generator and evaporator, the vapor condenses to release cool energy, then gets absorbed back, releasing upgraded heat at the absorber (up to 107°C for steaming or purifying water). Unlike standard single-stage AHTs needing vacuum and boiling, this four-temperature setup (generator ~75-78°C, evaporator ~87-88°C, condenser ~19-24°C) operates at atmospheric pressure, making it simpler and smaller. Experiments over steady runs measured powers: generator 1.0-1.5 kW, evaporator 1.2-1.6 kW (higher due to warmer input), condenser 1.2-1.6 kW, absorber 0.6-1.1 kW. Key metrics: efficiency (COP) 0.26-0.35 (up 35% from prior tests), temperature lift (GTL) 16.5-18°C, flow ratio 38-54 (affecting size/cost), and economizer recovery 69%. Higher evaporator temps boosted absorber output but slightly cut GTL. Compared to literature, it hits top absorber temps (107°C vs. 101°C max before) for purifying ~0.2-0.4 L/min seawater or wastewater, ideal for industries like textiles or chemicals wasting 50% heat. Challenges: corrosion needs monitoring, but PHEs proved durable. This paves for scalable, eco-friendly heat recycling, cutting fossil fuel use amid shrinking reserves and Kyoto goals.

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Why is it important?

Unique in testing four-temp atmospheric AHT with commercial PHEs and Carrol (crystallization-free up to 80%, less corrosive than LiBr), it achieves 107°C absorber temps—6°C above prior prototypes—for waste-heat-driven purification, addressing gaps in scalable, low-vacuum designs. Timely as industries waste 20-50% low-grade heat (e.g., 15 tons/h at 90°C in textiles), fueling 8% global emissions; this boosts recovery 50%, saving 43% reboiler energy in distilleries per models. Impact: Enables cheap retrofits (payback ~2 years at $5-11/MMBtu gas), producing 0.17-0.24 kg/s fresh water/site while cutting CO2—vital for water-scarce areas like Mexico. By quantifying COP/GTL trade-offs, it guides optimizations for cogeneration (e.g., fuel cells + AHT yielding 1.9e-4 kg/s distillate), potentially slashing industrial energy 10-20% and aiding UN water goals.

Perspectives

In energy recovery, this advances AHTs beyond LiBr limits via Carrol/PHEs, validating four-temp cycles for 107°C lifts where three-temp tops 101°C, bridging theory (e.g., exergy savings) with prototypes. Broader: Tackles Kyoto-era inefficiencies in cogeneration/desal, applicable to solar hybrids or nukes (e.g., S-CO2 + AHT upping efficiency 5-26%). Future: Anti-corrosion tweaks or AI flows for 0.4+ COP; extends to triple-effect for 150°C, supporting net-zero via heat cascading in a fossil-scarce world.

Professor Rosenberg J Romero
Universidad Autonoma del Estado de Morelos

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This page is a summary of: Experimental assessment of an absorption heat transformer prototype at different temperature levels into generator and into evaporator operating with water/Carrol mixture, Experimental Thermal and Fluid Science, January 2015, Elsevier,
DOI: 10.1016/j.expthermflusci.2014.09.013.
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