A Numerical Study on the Convective Heat Transfer Characteristics of Pulsed Impingement Drying

Abstract

Impinging jets issuing from the tailpipe of pulse combustors have been evaluated in recent studies for possible applications in rapid drying of continuous sheets such as grades of paper, textiles, etc. In order to further understand the effect of pulsed flows on the heat and mass transfer rates of impinging jets, a numerical study was performed on a two-dimensional pulsating impinging jet array. A computational fluid dynamics approach was used to examine the effect of periodic sinusoidal pulsation on the local Nusselt number distribution of the wet target surface being dried. Because a high temperature and large temperature difference between the jet flow and impingement surface are used to obtain high heat transfer rates in impingement drying, the thermophysical properties of jet flows were taken into account in the present mathematical model. A parametric study including phase angle and frequency as well as amplitude of pulsating flows was conducted for optimization and design of pulsating jet arrays. Examination of the velocity and thermal fields showed that the instantaneous heat transfer rate on the target surface was highly dependent on the mass transfer characteristic and development of the hydrodynamic boundary layer with time.

Keywords:

• CFD
• Impingement drying
• Nusselt number
• Pulsed flow

ACKNOWLEDGMENTS

This work was supported by the Zhejiang Provincial Natural Science Foundation of China through Grant nos. Y6110343 and Y6110304, the Qianjiang Program of Zhejiang Province of China through Grant nos. 2011R10092 and 2010R10022, and the Open Fund (PLN1116) of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University, China).