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MEASUREMENTS OF INSTANTANEOUS LOCAL HEAT TRANSFER COEFFICIENTS AROUND A TUBE IMMERSED IN A HIGH TEMPERATURE FLUIDIZED BED

Heinz Jorg Rottger
Lehrstuhl fur Warmeubertragung und Klimatechnik, RWTH Aachen, 52056 Aachen, Germany

Ulrich Renz
Lehrstuhl für Warmeübertragung und Klimatechnik, RWTH Aachen, Germany

Abstract

A novel probe was developed to measure the instantaneous local heat transfer coefficient around a tube immersed in a high temperature fluidized bed. The probe is explained and experimental data are reported for a 50 mm diameter horizontal cylinder. The fluidizing gas is air and the heat source is coal burning in the bed at a maximum temperature level in the bed of 900 °C. The results show that heat transfer values obtained with a sampling rate of 1000 Hz are comparable with results found with a 100 Hz sampling rate which indicates, that the time resolution of the probe is far beyond, what is really needed. No calibration of the probe is necessary as consistency checks are integrated in both, the probe and the evaluation algorithm.
The time averaged heat transfer coefficient is evaluated from the instantaneous measurement. It compares favourably with the transfer coefficient calculated from the energy balance and data published in literature.

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