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

Abstract

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 44K between desorber and condenser is reached.In relation to the concentration difference, a theoretical energy density of 435 kWh/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. Nomenclature a Coefficients in equation 2 b Coefficients in equation 1 ρ Density [g/m 3 ] k Constant in equation 1 and 2 l Constant in equation 1 and 2 m Constant in equation 1 and 2 ṁ Mass flow [g/min] p Pressure [kPa] ϑ Temperature [°C] X Mass fraction [kg/kg] This document is the accepted manuscript version of the following article: Fumey, B., Weber, R., & Baldini, L. (2017). Liquid sorption heat storage -a proof of concept based on lab measurements with a novel spiral fined heat and mass exchanger design.

Design and functionality of a segmented heat-storage prototype utilizing stable supercooling of sodium acetate trihydrate in a solar heating system

“…To charge the PCM units, the pump P PCM was used to circulate water via V 15 , V 13 , the HX and V 11 to the segmented PCM heat storage. Heat transfer from the PCM heat storage to the water tank was realized via V 15 , V 14 and V 17 when P PCM was switched on.…”

“…Promising heat storage concepts are based on solid sorption materials which utilize the adsorption of water vapour [9]- [11], the principle of absorption (e.g. with sodium-hydroxide and water [12] as demonstrated by Fumey et al [13] and Daguenet-Frick et al [14]), thermochemical reactions (as demonstrated by Zondag et al [15]), and phase-change materials (PCMs). Salt hydrate reactions have been considered for their high potential energy storage density [16].…”

Comparison of Direct and Indirect Active Thermal Energy Storage Strategies for Large-Scale Solar Heating Systems

“…The storage temperature differs from that of ambient and as a result heat loss should be considered. Advanced TES systems by latent heat using PCM [23] or chemical-or physical-bond related energy, so called thermochemical techniques, have also been studied extensively [24]. PCM and thermochemical storages are usually more compact than sensible TES.…”

Identification of best available thermal energy storage compounds for low-to-moderate temperature storage applications in buildings

“…Another test carried out by Weber et al (135) showed that, including tanks and heat exchangers, the total energy density could be three times higher compared to traditional hot water storage at 70 °C, and about six times higher for a tap temperature of 40 °C for low-temperature space heating. Fumey et al (140) tested at lab-scale a conventional spiral fined tube heat exchanger where the absorbent (NaOH) flows along the fin from top to bottom. A temperature lift of 35 °C between the maximum absorbent temperature and the absorbate was measured, with a dilution from 50wt% to 27wt%.…”