Thermophysical Properties and Heat Transfer Coefficients for Flowing Packed Particle Beds
arxiv(2024)
摘要
Accurate determination of heat transfer coefficients for flowing packed
particle beds is essential to the design of particle heat exchangers and other
thermal and thermochemical processes. The discrete nature of granular materials
alters the thermal transport processes in both the near-wall and bulk regions
of flowing particle beds from their stationary counterparts. Heat transfer
correlations based on the stationary particle bed thermal conductivity could be
inadequate for flowing particles in a heat exchanger. Thermophysical properties
of the continuum were often obtained from measurements on stationary beds owing
to the difficulty of flowing bed measurements. In this work, we found that the
properties of a stationary bed are highly sensitive to the method of particle
packing and there is a decrease in the particle bed thermal conductivity and
increase in the near-wall thermal resistance, as measured by an air gap
thickness, on the onset of particle flow. These variations in the
thermophysical properties of stationary vs. flowing particle beds can lead to
large errors in heat transfer coefficient calculations. Therefore, we modelled
heat transfer coefficients for granular flows using the experimentally
determined flowing particle bed thermal conductivity and near-wall air gap for
ceramic particles - CARBO CP 40/100 (mean diameter=275 um), HSP 40/70 (404 um)
and HSP 16/30 (956 um); at velocities of 5-15 mms-1; and temperatures of
300-650 oC. These calculations, which show good agreement with experiments in
literature, can be used as a guide for heat exchanger designs.
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