HEAT TRANSFER BETWEEN MATERIALS AND UNSTEADY AIRFLOW FROM A HELMHOLTZ TYPE COMBUSTOR

Abstract

Although pulse combustion devices exhibit a high thermal efficiency and low pollutant emission when used in a drying process, a broad application of these dryers has been limited because of a lack of understanding of the fundamental 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 generate 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 adjusted by changing the tailpipe length. The heat transfer coefficient between unsteady air outflow and brass was determined by the lumped capacity method. The effect of airflow oscillating frequency on heat transfer coefficient was investigated and their correlation was established. Refractory clay particles in the oscillating airflow were dried and the effect of the frequency on the drying process was predicted using the heat transfer coefficients obtained.

Keywords:

• Heat transfer
• Pulse combustion
• Drying
• Refractory clay
• Oscillating frequency

ACKNOWLEDGMENT

The work was carried out as a part of the research project No. 59776037 sponsored by the National Natural Science Foundation of China in the year 1997.