저온잠열축열을 위한 TMA-물계 포접화합물의 냉각특성에 대한 연구

Abstract

Low temperature latent heat storage systems are supplied more and more so that power load in the daytime due to refrigeration demand in the summer is moved into the nighttime and the equalization of the whole power load. However, in the case of ice storage systems that water is used as low temperature latent heat storage material, refrigerator capacity is increased and COP (performance factor) is decreased because the refrigerator is operated at low temperature due to supercooling of water in the course of the phase change from liquid to solid. Materials that can store low temperature solidification latent heat are organic/inorganic chemicals, eutectic salt systems and clathrate compounds. A clathrate compound is a material that host (water; H2O) molecule of hydrogen bond forms cage and guest (Gas) molecule is included into it and combined. Crystallization of hydrate is generated at higher temperature than that of ice from pure water. And physical properties according to temperature are stable and congruent melting phenomenon occurs without phase separation and it has a relatively high latent heat. But clathrate compound still has supercooling problems. TMA (Tri-methyl-amine, (CH3)3N), the third amine series, is a colorless gas and soluble in water, ether and alcohol. A TMA gaseous molecule that is mixed with water is included by water molecule in the hydrogen bond at a temperature of phase change and forms a clathrate compound of cluster type. This study was investigated the thermal characteristics of the TMA-water clathrate compound including TMA of 20∼25wt% as a low temperature latent heat storage material at -5℃, cooling source temperature. And 0.1wt%, 0.3wt% and 0.5wt% of ethanol(CH3CH2OH) was added to TMA 25wt%-water clathrate compound and its cooling characteristics were studied experimentally to restrain supercooling at cooling source temperature of -6℃, -7℃ and -8℃. The next study was investigated operating characteristics and performance factor (COP) of the low temperature latent heat storage system in the case of TMA 25wt%-water clathrate compound with ethanol as storage material. The conclusion of above studies are as following ; 1. The phase change temperature was average 5.1℃ according to cooling source temperatures in the case in which 0.5wt% of ethanol was added to TMA 25wt%-water clathrate compound. 2. The supercooling degree was average 2.0∼2.4℃ according to cooling source temperature and it was minimum in the case in which 0.5wt% of ethanol was added, in addition the time of liquid phase retention was 328∼406 sec and it had the effect of restraining supercooling.ㅁ 3. The specific heat was average 3.013∼3.048 kJ/kgK according to cooling source temperature in the case in which 0.5wt% of ethanol was added, and it was lower 0.506∼0.600 kJ/kgK than TMA 25wt%-water clathrate compound. 4. The volume was decreased after phase change from liquid to solid in the case of TMA 25wt%-water clathrate compound with ethanol. And the rate of volume change was average 1.77∼2.26% according to cooling source temperature and it was minimum in the case in which 0.5wt% of ethanol was added. 5. The performance factor(COP) was average 3.458 while system was operated in the case in which TMA 25wt%-water clathrate compound with ethanol 0.5wt% was applied low temperature latent heat storage material. Its COP was higher 0.105 and 1.163 than in the case of pure water and TMA 25wt%-water clathrate compound. The phase change temperature higher than water and restraint effect of the supercooling by ethanol 0.5wt% can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound. This can lead reduction of operation time of refrigerator in low temperature latent heat storage system and efficiency improvement of refrigerator COP and overall system. Therefore, energy saving and improvement of utilization efficiency are expected.