A Comparison of Heat Transfer Enhancement in Medium Temperature Thermal Energy Storage Heat Exchanger Using Fins and Multitubes

English

Experimental studies using a medium temperature phase change material (PCM) Erythritol, melting point 117.7°C, in a horizontal shell and tube system have been undertaken. The experimental programme investigated the suitability of Erythritol (a sugar based material) to deliver a near constant thermal energy to be used for the hot side of LiBr/water absorption cooling system. Four experimental configurations, consisting a base model with no heat enhancement (control system), systems enhanced with circular and longitudinal fins and a multitube system were studied. Experiments were conducted at the same inlet heat transfer fluid temperature of 140°C and mass flow rate of 30 kg min?1 for the different configurations. The results presented include experimentally determined isotherm plots for the final melt illustrating the heat transfer characteristics of the systems and quantitative information relating to the transient change in temperature during the charging and discharging processes. The experimental results indicate that the multitube system achieved the best charging performance with the shortest melt time due to the presence of convection but showed large subcooling during the discharge process. The presence of longitudinal fins improved the conduction heat transfer significantly during the charging process due to increased heat transfer surface area and also reduced the level of subcooling during the discharge process. The circular finned system showed no significant improvement in melt time and size and as such would not be worthy of further development.

Agyenim, F.; Smith, M.; Eames, P.C.