The rate of heat transfer to air flowing downward at low velocities through a heated tube was studied. The apparatus has been described in a previous work. The investigation covered a flow rate ranging from 85 to 930 lb./hr.ft.2, (NRc) from 380 to 6,900, (NGr) from 0.18 × 106 to 7.3 × 106 and nominal wall temperatures of 100, 500 and 950°C.The local Nusselt number could be correlated with the Grashof number independently of its axial position, over a range of Grashof numbers not previously investigated. In particular, it was noted that a marked change in the slope of the (NNu)‐vs‐(NGr) curve occurred around a Grashof number of 106.
In a pneumatic transport reactor, a dilute suspension of the reacting solid particles is conveyed by the gas stream through the reactor. The system is characterized by very short particle residence times. The relative flow rates of gas and solids are determined by the thermodynamic and kinetic requirements of the reacting conveyed systems.
Design considerations for co‐current gas and solids flows are presented and a comparison between co‐gravity and counter‐gravity flow reactors is discussed for the case of iron ore reduction by hydrogen. Kinetic data from single particle studies have been used to predict the performance of a pilot‐scale reactor.
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