Title

The use of ammonium carbamate as a high specific thermal energy density material for thermal management of low grade heat

Date of Award

2011

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Kevin J. Myers

Abstract

The specific energy storage capacities of phase change materials (PCMs) increase with temperature, leading to a lack of thermal management (TM) systems capable of handling high heat fluxes in the temperature range from 20°C to 100°C. State of the art PCMs in this temperature range are usually paraffin waxes with energy densities on the order of a few hundred kJ/kg or ice slurries with energy densities of the same magnitude. However, for applications where system weight and size are limited, it is necessary to improve this energy density by at least an order of magnitude. The compound ammonium carbamate (AC), [NH4 ][H2NCOO], is a solid formed from the reaction of ammonia and carbon dioxide which endothermically decomposes back to ammonia and carbon dioxide in the temperature range of 20°C to 100°C with an enthalpy of decomposition of 2,010 kJ/kg. Various methods to use this material for TM of low-grade, high-flux heat have been evaluated including: bare powder, thermally conductive carbon foams, thermally conductive metal foams, hydrocarbon based slurries, and a slurry in ethylene glycol or propylene glycol. A slurry in glycol is a promising system medium for enhancing heat and mass transfer for TM. Small-scale system level characterizations of AC in glycol have been performed and results indicate that AC is indeed a promising material for TM of low-grade heat. It has been shown that pressures on the order of 200 torr will achieve rapid decomposition and thermal powers of over 300 W at 60°C have been found, demonstrating the capability of AC.

Keywords

Ammonium compounds Thermal properties, Heat storage Research, Energy storage Research, Thermochemistry Research

Rights Statement

Copyright 2011, author

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