Thermal Conductivity of Sludge Generated at Waste Water Treatment Plant

Abstract

The thermal conductivity of the sluge generated at a waste water treatment plant was measured by means of a hot wire method to get information needed for designing effective multi-hearth furnaces.
The results are summarized as follows;
(1) The relation between the thermal conductivity of the sludge λ (kcal/m.h.°C) and water content Φ (wt%) was expressed by the experimental formula
λ=(2.32Φ+60.4)×10^-3 (0≤Φ≤20)
λ=0.00045Φ^1.75 (20<Φ≤60)
(2) The effect of the solid volume fraction (φ) on the thermal conductivity of the dried sludge (λ) in the atmosphere of air, nitrogen or carbon monoxide was given by the experimental formula
λ=0.25φ+0.015 (kcal/m.h.°C)
irrespective of the atmosphere.
(3) The thermal conductivity (λ) of the ash bed obtained by burning the sludge increased linearly with increasing temperature T(°C) and was given by the experimental formula
λ=(1.37T+955)×10^-4 (kcal/m.h.°C)
This temperature dependency is due mainly to that of air in the pores of the ash bed.
(4) The thermal conductivity of the ash particle was estimated to be about 1kcal/m.h.°C by using de Vries' equation.