Research Papers: Energy Systems Analysis

Study of Heat and Mass Transfer in MgCl2/NH3 Thermochemical Batteries

[+] Author and Article Information
Seyyed Ali Hedayat Mofidi

Sustainable Energy Laboratory,
Department of Mechanical Engineering,
University of Utah,
Salt Lake City, UT 84112
e-mail: Ali.Hedayat@Utah.edu

Kent S. Udell

Department of Mechanical Engineering,
University of Utah,
Salt Lake City, UT 84112
e-mail: Udell@mech.Utah.edu

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received August 12, 2016; final manuscript received January 11, 2017; published online February 14, 2017. Assoc. Editor: Antonio J. Bula.

J. Energy Resour. Technol 139(3), 032005 (Feb 14, 2017) (10 pages) Paper No: JERT-16-1339; doi: 10.1115/1.4035750 History: Received August 12, 2016; Revised January 11, 2017

Intermittency of sustainable energy or waste heat availability calls for energy storage systems such as thermal batteries. Thermochemical batteries based on a reversible solid–gas (MgCl2–NH3) reactions and NH3 liquid–gas phase change are of specific interest since the kinetics of absorption are fast and the heat transfer rates for liquid–vapor phase change are high. Thus, a thermochemical battery based on reversible reaction between magnesium chloride and ammonia was studied. Two-dimensional experimental studies were conducted on a reactor in which temperature profiles within the solid matrix and pressure and flow rates of gas were obtained during discharging processes. A numerical model based on heat and mass transfer within the salt and salt–gas reactions was developed to simulate the NH3 absorption processes within the solid matrix, and the results were compared with experimental data to determine dominant heat and mass transfer processes within the salt. It is shown that for high permeability salt beds, the reactor uniformly adsorbs gaseous ammonia until the bed reaches the equilibrium temperature, then adsorbs gas near the cooled boundaries as the reaction front moves inward. In that mode, the heat transfer is the dominant factor in determining reaction rates.

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Fig. 1

Equilibrium line for magnesium chloride–ammonium reaction. Numbers after / indicate the number of ammonia molecules absorbed by the salt. Constants are reported from Ref.[3].

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Fig. 2

Schematic of the experiment setup

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Fig. 3

The method used to measure thermal conductivity: (a) central heater is on for short period of time and (b) slope of the curve at the left can be used to measure thermal conductivity

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Fig. 4

Geometry and boundary conditions used in numerical simulations

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Fig. 5

Mass flow rate of ammonia during absorption process in case 1

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Fig. 6

Pressure of reactor inlet and exit during absorption process

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Fig. 7

Variation of temperatures within salt–graphite complex during absorption process at location 6

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Fig. 8

Comparison of global reaction rate obtained by numerical simulation and experiment

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Fig. 9

Comparison of global reaction progress (based on mass of ammonia absorbed obtained by integration of flow rate of ammonia)

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Fig. 10

Temperature profiles of absorption process of case 1: (a), (c), (e), (g), and (i) obtained from experiment and (b), (d), (f), (h), and (j) obtained from numerical model

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Fig. 11

Radial profiles of reaction progress and temperature from numerical simulations

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Fig. 12

Contours of propagation of reaction. Each line shows Xm = 0.95 at different values for Xg. Note: R scale is different than x scale.




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