Thermophysical properties and reaction rate of composite reactant of calcium chloride and expanded graphite

• Published in: Applied thermal engineering Vol. 50; no. 2; pp. 1627 - 1632
• Main Authors: Fujioka, Keiko, Suzuki, Hiroshi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2013
• Subjects: Calcium chloride; Gas–solid reaction; Graphite; Heat transfer; Hydration reaction; Permeability; Reactors; Thermal conductivity; Thermophysical properties; Void fraction; Gas–solid reaction; Permeability; Hydration reaction; Heat transfer
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2011.08.024

Experimental studies have been conducted in order to obtain information on thermophysical properties and reaction characteristics of composite reactant of calcium chloride and expanded graphite, which has been developed to improve the performance of a reactor bed used for gas–solid chemical heat pumps. Effective thermal conductivity, permeability and reaction rate of the composite reactant have been measured. From the results of heat transfer experiments it was found that the effective thermal conductivity of the composite reactant is more than ten times larger than granular calcium chloride and strongly affected by void fraction. Permeability measurements show that the Darcy number increases rapidly with decreasing void fraction in the range of the void fraction from 0.4 to 0.6. The rate of reaction of composite reactant with water has been measured using a small cell which simulates a part of reactor bed where the reactant is packed between fins of plate-fin heat exchanger. The measured overall reaction rate has been analyzed using a model which is developed by taking account of the influence of adsorption of water molecules on hydration rate. ► CaCl2-expanded graphite composite is used to enhance heat and mass transfer. ► We measure thermal conductivity, permeability and hydration rate of the composite. ► Its thermal conductivity is 10 times larger than granular CaCl2. ► Darcy number increases rapidly with increasing void fraction. ► Overall hydration rate is controlled by mass transfer with void fraction up to 0.95.