Enhancing evaporation in vacuum freeze drying: Optimizing airflow in horizontally-connected chambers

Abstract

Efforts to enhance the evaporation rate in a vacuum freeze-drying system were carried out by adding a fan between the drying chamber and the cold trap, which are horizontally connected. The fan was installed to accelerate the vapor movement from the drying chamber to the cold trap. In this study, distilled water was used as a test material, placed in a container inside a horizontally configured drying chamber. A low-power axial fan was installed in the connecting pipe to induce forced vapor flow, and the system employed electric heaters mounted on the chamber walls to provide convective heating. The experimental setup tested four different drying chamber temperatures (20 degrees C, 25 degrees C, 30 degrees C, and 35 degrees C), with each condition repeated under fan-on and fan-off states. The experimental results showed that the use of a fan in the drying chamber significantly enhanced the sublimation rate compared to the tests without the fan. The highest evaporation rate increased by up to 42.9 % was achieved at 35 degrees C with the fan, reaching 27.47 x 10-7 kg/s. On average, the evaporation rate with the fan increased by 27.3 %. The average specific energy consumption of vacuum freeze drying decreased when using a fan proportionally with the 20.8 %. This research confirmed that the fan significantly improved the evaporation rate. The obtained evaporation rate data using the convective heating method with electric heaters can serve as a preliminary reference for those seeking a simpler alternative in operational complexity and initial investment compared to microwave or infrared vacuum freeze-drying systems.