(697c) High Temperature Latent Heat Transportation by Use of Hydrate Slurry Treated with Surfactants

Improvement of fluidity of non-organic hydrate slurries has been investigated. Ammonium alum, a kind of non-organic hydrates, has high latent heat and high phase change temperature. This material can be a candidate of materials for latent heat transportation. Latent heat transportation causes flow rate reduction in heat devices and then miniaturizes heat devices. However, ammonium alum has two disadvantages as a heat media. It has high solubility in high temperature around phase change temperature. About 300g of ammonium alum dissolve into 100g water at 80 degree Celsius. The dissolved material has no latent heat. Then, more than 300g of ammonium alum is required for latent heat transportation. In this situation, no fluidity can be expected at the normal temperature when solubility of ammonium alum becomes very low. In the present study, mixture of water and ethylene glycol is used for a solvent in order to reduce solubility of ammonium alum at high temperature. Ammonium alum shows no solubility against ethylene glycol. The solubility of ammonium alum to the mixture in which the concentration of ethylene glycol was changed from 0 to 80% was examined. From this, it was found that the solubility of ammonium alum effectively decreases at high temperature. Then, the fluidity of hydrate slurry was improved in the normal temperature. However, the flow drag became higher because the viscosity of solvent becomes higher and particles of ammonium alum hydrate showed agglomeration. In order to prevent this agglomeration, surfactant additives were tested. Behenyltrimethylammonium chloride were tested as dispersants. This material can also be a drag reducing additives. From the results, it is found that flow drag of ammonium alum hydrate slurry shows effective drag reduction for a solvent mixed with 30 % ethylene glycol. However, drag reduction effect disappears at 50% and higher of ethlene glycol concentration. On the other hand, the particle size becomes much smaller that that in the case without surfactants even at high concentration of ethylene glycol in solvent. From this, it is concluded that the present surfactants has an advantage as dispersants of ammonium alum hydrates in mixture solvent.