Influence of crystal layer on the flow and heat transfer characteristics during TBAB CHS generation in a double-tube heat exchanger

The flow and heat transfer characteristics of tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) during its generation process in a double-tube heat exchanger (DHE) and the growth of crystal layer were investigated experimentally. During the generation, the formed crystals were easy to adhere to the heat transfer surface, and the present study was focused on the influences of such crystal layer on the pressure drop and heat transfer coefficient between the generating TBAB CHS and coolant in the heat exchanger. Pressure drops of TBAB CHS flowing through DHE without heat exchange were measured in advance to develop the corresponding friction factor correlations, and the comparison of the pressure drops during TBAB CHS generation process to those without heat exchange was conducted to obtain the effective thickness of the crystal layer. It was found that the thickness of the crystal layer increased as the heat transfer process going on. The crystal layer caused the enlargement of pressure drop and the drastic reduction of heat transfer performance due to the narrowing flow passage and large thermal resistance, respectively. The effective thermal conductivity of the crystal layer was also determined for the prediction of the heat transfer performance in the heat exchanger.