Abstract <p>A fin-fluidized bed heat exchanger was examined experimentally to improve the bed-to-surface heat transfer coefficient. The investigation was carried out in four stages (single tube heater, five internals equipped with a tube heater, single longitudinal fin tube heater, and five internals equipped with longitudinal fin tube heater) and was placed and moved at a different position in and around the center. The effect of vertical longitudinal fins with heat-exchanging tube bundles on the heat transfer coefficient (HTC) in a gas-solid fluidized bed has been studied locally and instantly. A sophisticated heat transfer technique and silica sand as a solid particle of 600 µm average size with a bulk density of 1570 kg/m³ were used. The experiments were performed in a Plexiglas fluidized bed reactor 0.13 m diameter with varied gas flow rates (0.215‒0.353 m/s). The study was initially without a fin, the tube heater was 0.012 m in diameter and 40 cm in length, then with a longitudinal fin (1.5 mm thickness, 7 mm height, and 400 mm length). The fluidized bed reactor with longitudinal fins and vertical tubes has been found to have a 47% lower local heat transfer coefficient than the reactor with bare vertical tubes. The findings show that even though using fins reduces the heat transfer coefficient, the overall heat transfer increases due to the increased surface area. It is observed that smooth and finned tube heat transfer coefficients increase as the fluidizing velocity increases.</p>