Experimental & Simulation Analysis of Convective Hot Air-Drying Chamber Used for Blood Bag Drying Operation

Abstract

This study aimed to analyse the convective heat transfer rate in a hot air-drying chamber (tray type) used for blood bag manufacturing. After steam sterilization in an autoclave, blood bags retain moisture in the form of water droplets inside and outside the Polypropylene (PP) covers. Currently, only 45-50% of the products are acceptable after the drying operation, with more than 50% still containing moisture. Experimental analysis was conducted to calculate the drying efficiency, temperature distribution, and Relative Humidity (RH) inside the drying chamber. Drying experiments were performed under different drying hold temperatures (60°C, 65°C, 70°C, and 75°C) with uniform air velocity. The optimal drying hold temperature for blood collecting bags was found to be 70°C, resulting in a 65.53% acceptance rate of the product. The convective heat transfer coefficient was calculated from experimental data and found to range from 35 to 45 W/m²K. The drying efficiency of the system for the optimum temperature cycle (70°C) is 66.42%. A simulation study was conducted to obtain the air flow pattern, air velocity, and temperature distribution inside the drying chamber and among the product trays. The case with baffles placed normally to the X-axis (case 1) showed non-uniform velocity distribution inside the chamber, with an average convective heat transfer coefficient (h) of 36.36 W/m²K and a total heat transfer rate (Q) of 5819 W for the entire tray. In case 2, where the baffles were positioned at a 45° angle, the values of h and Q were 39.42 W/m²K and 6422 W, respectively. Similarly, in case 3, where the baffles were positioned at a 45° angle in a zig-zag manner at the chamber's inlet, enhanced drying rates and more uniform velocity distributions were achieved, with h and Q values of 45.39 W/m²K and 7544 W, respectively. The energy consumed for one cycle of operation was determined as 752.48 kWh, and the Specific Energy Consumption (SEC) was calculated as 54.60 kWh/kg at 70°C, 68.60 kWh/kg at 65°C, and 80.47 kWh/kg at 60°C based on the moisture removal rate. In conclusion, this study suggests possible changes to the chamber settings to improve drying performance and velocity distributions, leading to higher product acceptance rates and more efficient drying processes.