Closed‐Loop Adsorption‐Based Upgrading of Heat from 90 to 110 °C: Experimental Demonstration and Insights for Future Development

Abstract

Industrial energy efficiency can be increased by recovering waste heat, mainly available below 100 °C. This low‐temperature waste heat can drive adsorption heat transformers (AdHTs) to upgrade waste heat to industrially relevant temperatures above 100 °C. Flexible process integration can be achieved by decoupling adsorptive and heat transfer fluid in closed‐loop cycles. However, the experimental feasibility of closed‐loop AdHTs has not been shown yet. Hence, this work studies an experimental one‐bed setup of an AdHT based on a closed‐loop cycle using silica gel 123 and water as the working pair. Experimental feasibility is demonstrated for heat transformation from 90 to 110 °C with waste heat released at 25 °C. The highest coefficient of performance (COP) is 0.183 J J−1 (23% of the maximum Carnot efficiency), and the highest specific heating power (SHP) is 168 W kg−1. A systematic variation of the operating conditions shows that efficiency COP and power density SHP strongly depend on the operating temperatures, volume flows, and phase times. Furthermore, avoiding condensation inside the adsorber casing and heat losses are identified to be crucial for the design of AdHTs. In summary, AdHTs based on a closed‐loop cycle show a promising performance to recover low‐temperature waste heat.

Review on Salt Hydrate Thermochemical Heat Transformer

“…The heat of adsorption in physisorption is lower than in chemisorption [86]. The heat transformer application employing adsorption materials is referred to as Adsorption Heat Transformer (AHT or AdHT) [87,88]. A recent AHT experiment reported a thermal upgrade of 20 • C was achieved for a silica gel-water vapour closed system [88].…”

“…The heat transformer application employing adsorption materials is referred to as Adsorption Heat Transformer (AHT or AdHT) [87,88]. A recent AHT experiment reported a thermal upgrade of 20 • C was achieved for a silica gel-water vapour closed system [88]. A theoretical work analyzing the thermodynamic performance of multiple adsorption working pairs was performed by Frazzica et al [89], including silica gel/water vapour, AQSOA Zeolite/water vapour, MWCNT-LiCl/water vapour, and silica gel-LiCl/water vapour.…”