Studies on fluidization. II—heat transfer

Abstract

In a small scale apparatus the heat transfer coefficient to the cylindrical wall of a fluidizing bed (“dense phase”) was measured under strongly varying conditions of gas and solids. The solids used were closely sized samples as well as mixtures of different sizes of carborundum, ironoxide (Fe 3O 4), coke, lead, Devarda's alloy, and fly ash. The gases used were air, mixtures of nitrogen and hydrogen, carbon dioxide, argon, town's gas and methane. For a correlation of the measuring result use is made of a system of dimensionless numbers that may be considered as a complete representation of all variables which may be expected to influence the value of the transfer coefficient. The gas rate is characterized by the reduced mass velocity G/ G 0 where G 0 is the mass velocity at which fluidization starts. A correlation based on this variable proves to be successful for Re < 5 and can be written as: ▪ when ψ( G/G 0) = 0,028( G/G 0) 0.45 for 2 < G/G 0 < 20; a larger region (1 < G/G 0 < 30) can be covered by ▪ With the aid of the generalized shape factor B introduced in Part I of this study, the above mentioned relationship can be transformed into a correlation restricted to the region 2 < G/G 0 < 20. This can be written as ▪ where for Re < 5, χ ( B Re) = 0,58 ( B Re) 0.45.