Investigation of the heat transfer coefficient in a plate heat exchanger for cooling product before storage: Based on a biodiesel plant case

Plate heat exchangers (PHE) are essential for efficient heat transfer in biodiesel production, but the performance can decline due to silica scaling. In this paper, heat transfer in PHE before and after cleaning was experimentally investigated. The CIP process using 5% citric acid was applied to fouled PHE from biodiesel plant at various cleaning durations of 2, 4, 6, and 8 h, targeting silica scale removal on the cooling side. The heat transfer performance was evaluated before and after cleaning by calculating the overall heat transfer coefficient, LMTD, and relevant dimensionless numbers based on experimental data. The results show after 8 h cleaning process, the temperature on the cooling side decreased from 39 O C to 31.5 O C, while the hot side temperature dropped from 85 O C to 55 O C. Heat transfer coefficient increased from 32.669 W/m 2. K to 53.9083 W/m 2. K. Heat load increased from 217,445.95 W to 434,984.00 W. The LMTD on cooling water side decreased from 48.1928 to 43.6012. The Reynolds number increased, the Nusselt number decreased, and The Prandtl number decreased. Pump pressure increased from 2.8 bar to 5.2 bar. These changes indicate enhanced system performance following citric acid cleaning, attributed to effective contaminant removal and improved surface conditions.