Heat transfer between materials and unsteady airflow from a Helmholtz typecombustor

Although pulse combustion devices exhibit a high thermal efficiency and low pollutant emission when used in a drying process, a broad application of t hese dryers has been limited because of a lack of understanding of the fund amental controlling heat and mass transfer. This paper reports the results of an experimental investigation of heat transfer between unsteady airflow and a brass sphere under various oscillating frequencies. In order to gener ate an unsteady flow, we constructed a gas-fired, water-cooled pulse burner . The burner is of a Helmholtz type and its operating frequency can be adju sted by changing the tailpipe length. The heat transfer coefficient between unsteady air outflow and brass was determined by the lumped capacity metho d. The effect of airflow oscillating frequency on heat transfer coefficient was investigated and their correlation was established. Refractory clay pa rticles in the oscillating airflow were dried and the effect of the frequen cy on the drying process was predicted using the heat transfer coefficients obtained.