Latent heat recovery from supercooled sodium acetate trihydrate using a brush heat exchanger
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Helsinki University of Technology |
Diplomityö
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Date
2007
Department
Major/Subject
Lämpötekniikka ja koneoppi
Mcode
Ene-39
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Language
en
Pages
104
Series
Abstract
This study is a part of a research project developing heat storages for warming automobile combustion engines. Thermal storage is charged with engine waste heat, which is discharged in order to maintain proper engine temperature or used for preheating. The supercooling phenomenon intrigued us because of its ability to store the latent heat of phase change material (PCM) without any losses for long periods of time and release it when desired. In this work, heat recovery as supercooled liquid sodium acetate trihydrate (SAT) encounters rapid phase change in the various brush heat exchangers is studied. Laboratory experiments uncover the suitability of supercooled sodium acetate trihydrate as a latent heat storage medium by output capacities and repeatability of the freeze-thaw cycles. An effect that the degree of supercooling and coolant flow rate has on the heat recovery is also considered. Curved pipe heat transfer characteristics and optimal curvature for efficient heat transfer with adequate pressure losses was studied by minimizing the entropy generation rate in heat transfer pipe. Results revealed an exiguous relation between brush density and output capacities and heat recovery rate. For low power requirements, coarser brushes should be utilized, as the heat release rate is moderate. Crystallization experiments conducted in glass vessels compared to the ones performed in the brush heat exchangers showed a significant difference of the stability of the supercooled metastable state and the degree of supercooling. Thus, major work has to be pursued in developing stable and reliable supercooled phase change material, as spontaneous crystallization must be prevented.Description
Supervisor
Lampinen, MarkkuThesis advisor
Seppälä, AriKeywords
heat recovery, lämmöntalteenotto, latent heat storage, faasimuutosvarasto, supercooling, alijäähtyminen, brush heat exchanger, harjalämmönvaihdin, sodium acetate trihydrate, natriumasetaatti trihydraatti, curved pipe heat transfer, lämmönsiirto kierreputkessa