In the research work, energy transport between dense fluidized bed and submerged horizontal tube bundle is analysed in the commercial external heat exchanger (EHE). In order to investigate the heat transfer behaviour, Authors carried out seven performance tests in a fluidized bed heat exchanger chamber with the cross-section 2.7mx2.3m in depth and width and the height up to 1.3m. Authors have been developed mechanistic model for the prediction of average heat transfer coefficient which includes the effect of the geometric structure of tube bundle and the location of heat transfer surface on heat transfer rate. The computational results depict that the average heat transfer coefficient is essential affected by superficial gas velocity, suspension density rather than bed particle size. The empirical correlations have been proposed for predicting heat transfer data since the existing literature data is not sufficient for industrial fluidized bed heat exchangers. On the basis of evaluated operating conditions of an external heat exchanger, it could be deduced an optimal conditions where heat transfer occurs. The developed mechanistic heat transfer model is validated by experimental data under examined conditions.