Session: 03-01 Low Temperature Thermal Storage

Paper Number: 142406

142406 - Revealing Predicted and Measured Tradeoffs Between Power Density and Energy Capacity of Composite Srbr2 Salt Hydrates for Thermochemical Energy Storage 

Abstract: 

With over 70% of the total energy use in U.S. residential house-holds is used for heating and cooling applications, it is crucial to decarbonize building energy sources with renewables. However, renewables cannot provide dispatchable power on demand, and therefore energy storage is crucial. Thermal energy storage is especially promising because of its projected low-cost (<40 $kWh target for ∼ 10 h storage) and its unique benefits of directly integrating with heating/cooling thermal loads. Further, thermochemical energy storage using salt hydrates promises high energy densities by storing heat in chemical bonds which is released by hydration with water vapor. Because this technology involves non-corrosive salts and largely benign water as reactants, it presents itself as an attractive candidate for energy storage in residential sectors such as space heating and heating up water. In this talk, we will present our recent findings from our theoretical and experimental work, where we developed models and experimental measurements with a through-flow, fixed bed reactor with strontium bromide impregnated in a porous vermiculite matrix. At the reactor-scale with ~100 g of the composite material, experiments were performed for a range of air flow rates at 22 ℃ and with a fixed humidity of 45%. A maximum hydration temperature rise of ~16 ℃ was achieved at a flow rate of 6 standard liters per minute, which corresponds to a specific power and energy storage capacity of 12 ± 0.38 W/kg and 160 ± 6 Wh/kg. These results are compared against materials-scale gravimetric measurements with ~1 g of the composite material, and also compared against predictions from a heat and mass transfer model. Comparisons with the materials-scale measurements highlight a near tenfold reduction in power densities during thermal discharge, and is primarily attributed to: (a) the differences in the specific surface area available for hydration reactions between the materials- and reactor-scale measurements, and (b) due to the possible reduction in the vapor pressure driving force for the hydration reaction related to local rises in reactor-scale temperatures. Model predictions were found to be most sensitive to the input kinetic parameters, and the equilibrium vapor pressure for the composite and its dependence on the thermodynamic state (pressure, temperature). Experimental data for the hydration reactions are expanded beyond the room temperature datasets for operating temperatures of 25°C-40°C to investigate tradeoffs between improved kinetic rate constants with the hydration reaction conditions inching closer to the equilibrium saturation curve. Overall, the performance of SrBr₂-vermiculite salt hydrates have been comprehensively characterized and interpreted at various length scales, and with models and measurements.

Presenting Author: Rohini Bala Chandran University of Michigan

Presenting Author Biography: Dr. Rohini Bala Chandran is an Assistant Professor in Mechanical Engineering at the University of Michigan since January 2018. At Michigan, Prof. Bala Chandran leads the Transport and Reaction Engineering for Sustainable Energy Lab (TREE Lab) to pursue multidisciplinary research in the areas of thermal, fluids and chemical sciences. She is a recipient of several early-career awards including the Bergles-Rohsenow Young Investigator Award in Heat Transfer (2023) and the NSF-CAREER award (2022).

Authors:

Bryan Kinzer University of Michigan
Durga Ghosh University of Michigan
Declan Crowley University of Michigan
Arijit Jatkar University of Michigan
Sunaad Gurajada University of Michigan
Rohini Bala Chandran University of Michigan