1991 journal article

Extraction of energy from crop dryer exhaust

Applied Engineering in Agriculture, 7(2), 223.

By: C. Suggs*, T. Seaboch & C. Abrams

Source: NC State University Libraries
Added: August 6, 2018

Depending on difference between ambient and exhaust air temperatures, considerable amounts of heat energy can be recovered from the exhaust of a crop dryer by means of a heat exchanger which keeps the inlet and exhaust air streams separate but conducts the heat through the barrier from the hot exhaust to the cold intake. A flat plate, turbulent flow heat exchanger was attached to a bulk curing tobacco barn with appropriate ducts to channel the exhaust and intake through alternate channels of the heat exchanger. Wet and dry bulb temperatures were measured in both streams at the inlet and outlet ends of the exchanger along with air flow rate through the exhaust and intake ducts. Values of the heat transfer coefficient determined from experimentally observed temperature differences and the amount of heat transferred were larger than values calculated directly. At least part of the difference was due to condensation which delayed cooling of the hot exhaust stream and enhanced heat recovery. Values of observed and calculated heat exchanger effectiveness were similar. Measurements were made of six cures of tobacco spaced over two years. The heat exchanger used in these experiments saved approximately six to 12% of the curing fuel. For typical tobacco barn operations, recoverable costs for a heat exchanger with a 20-year life and interest at 10% would be about $400 to $800, depending on fuel costs, barn usage, weather conditions and the manner in which the barns are operated.