Instantaneous local heat transfer coefficients and related frequency spectra for a horizontal cylinder in a high temperature fluidized bed

Abstract

Experimental data are reported for instantaneous local heat transfer coefficients on the surface of an immersed 50.8 mm diameter horizontal cylinder in a high temperature (562° C) fluidized bed of particles with 1 mm mean size using air as the fluidizing gas. Comparison of the reported data with analytical models of bed-to-surface heat transfer shows good agreement for heat transfer near particle contact points and in the interstitial channels between particles. The shallow bed height above the instrumented cylinder (0.10 m) allowed bubbles to erupt to the surface while still in contact with the cylinder. Heat transfer during periods of bubble phase contact increased, compared to the case of fully immersed bubbles, by a factor of 2 or 3 due to erupting bubbles contacting the cylinder. The frequency spectra related to the instantaneous local heat transfer coefficients displayed sharp maxima at low frequencies (0.36–1.46 Hz). Based on these frequency spectra, it is suggested that instrumentation for similar measurements be designed for a bandwidth of at least 100 Hz.