Date of Award

9-5-2017

Document Type

Thesis

Publisher

Santa Clara : Santa Clara University, 2017.

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Hohyun Lee

Abstract

Thermochemical energy storage has the potential to support the use of solar thermal energy collection in ways that traditional thermal energy storage, like sensible and latent heat storage, have fallen short. Thermochemical energy storage has been shown to have higher storage capacities than sensible and latent storage for dehumidifying applications and does not require insulation like sensible and latent heating do. Sensible heating is focused on maintaining an increased temperature of a storage medium while latent heat storage is focused on maintaining a phase of the storage material. Both sensible and latent heat storage have been shown to have lower storage capacities for the purposes of air cooling when compared to thermochemical energy storage, which allows for the conversion of heat energy to thermochemical energy. Liquid desiccants utilize heat in an endothermic reaction to concentrate the solution and create chemical bonds, resulting in a chemical potential that can later be released as heat with the addition of water or used to absorb water vapor with heat as the by product. Due to the fact that the energy is stored as a chemical potential, heat loss is minimal and insulation is not needed to store the majority of invested energy as much as other energy storage methods. However, current liquid desiccant energy storage systems focus on the dehumidification and cooling properties of desiccant materials and such systems face problems with desiccant carryover, corrosion, and are often expensive. This paper looks at using calcium chloride as a desiccant material to reduce costs, and examines the use of liquid desiccants for heating rather than cooling purposes. A test heat exchanger was built to evaluate the feasibility of heat extraction upon water addition and compare it to the theoretical prediction. A basic shell and tube heat exchanger was constructed, using copper piping, a plastic bin, a peristaltic pump and flexible hosing. The results from this experiment show the feasibility of a basic heat exchanger to extract significant heat from this reaction. The experiments done in this investigation reveal that a storage capacity of 19 kWh⁄m3 can be expected for the best-case scenario of a dilution reaction between 100% concentrated calcium chloride and water to a 20% solution.

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