On-site testing of crop drying fans

Abstract

The commercial peanut dryers used today were first conceived when energy was relatively inexpensive. Since then, energy costs have increased significantly, and more efficient peanuts dryers are desirable. To evaluate dryer efficiency, a mobile fan test facility was designed, built and calibrated for on-site fan airflow and energy measurements. Four-, six-, and eight-trailer peanut dryers were tested for performance. The characteristics observed were delivery of fan airflow as compared to manufacturers' ratings, air distribution to each of the trailer supply ports, plenum leaks, and energy savings achieved by the use of flow controls. For testing, air to the dryer fan was provided by a centrifugal supply fan, where the flowrate was determined by measuring the pressure drop across calibrated perforated plate positioned between the two fans. Airflow through each of the trailer supply ports was determined in a similar manner by measuring the pressure drop across calibrated resistance plates. Measured airflow to the trailers from dryer fans was found to be 75 to 100% of the airflow given by the manufacturers' ratings. Air distribution was poor in dryers with no baffle. However, the installation of a baffle resulted in significant improvement in air distribution. The baffle a pressure rise which reduced total airflow up to 5%. Based on a recommended airflow of 0.167 m³/s per m³ of peanuts, fan inlets were restricted to reduce airflow, and energy savings as high as 35% were achieved. Repairs on poorly maintained dryers increased flowrate from 3 to 7%.