Determination of Heat Transfer Coefficients of Farm Products by Transient Method using Lead Model

Abstract

The heat transfer coefficients of the apple (Kokko), eggs (Leghorn and Gifu-Jitori), the Citrus (Unshu) and carrots in an air stream were determined from the cooling rate of the lead models of the products placed in the flow of air through a 20cm-diam poly vinyl chloride duct with a centrifugal blower.
The transient temperature change of the model was measured and recorded with a recording potentiometer (Shinkoh co., AS-11) employing copper-constantan thermocouples. The air velocity was determined by measuring the dynamic pressure at the head of the products with a manometer. The manometer was connected by a rubber tube with a 2.5mm glass pipe which was placed the model parallel to the air flow.
The results were expressed as the empirical formuras of the relation between Nusselt and Reynolds numbers.
The errors of this method which assumed no thermal resistance in the model were estimated for the lead model by using the solution to the equation of conduction of heat. It was found that the er rors were within 1.0 percent in the range of the experiment.