Liquid sorption heat storage - A proof of concept based on lab measurements with a novel spiral fined heat and mass exchanger design

This paper presents a practical study towards the development of a heat and mass exchanger fitting to liquid absorption heat storage for building application. Results of a lab scale setup are shown. To reach high heat capacity in absorption storage, a maximum temperature gain and concentration difference is mandatory. A conventional spiral fined tube heat exchanger is employed as heat and mass exchanger, whereby the tube is installed vertically and the absorbent flows slowly along the fin from top to bottom due to gravitational force. Sufficient time is given for absorption and heat release. Operating with sodium hydroxide as absorbent, a temperature lift of 35 K measured between maximum absorbent temperature and absorbate temperature as well as dilution from 50 wt% to 27 wt% in one continuous process step is attained in absorption. During desorption, a concentration lift from 25 wt% to 53 wt% at a temperature spread of 44 K between desorber and condenser is reached. In relation to the concentration difference, a theoretical energy density of 435 kW h/m3 in respect to the discharged absorbent is reached. This development enables compact, lossless, long term heat storage suitable for space heating and domestic hot water.