Heat transfer in vertical perl mills |
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Authors: | A Heim T Maliszewski |
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Institution: | (1) Faculty of Process and Environmental Engineering, Department of Chemical Equipment, Technical University of ód , ul. Wolcza ska 175, 90-924 ód , Poland |
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Abstract: | A model of heat transfer during grinding in vertical multi-disk perl mills has been proposed. Heat transfer intensity in such mills depends on thermal resistance in a boundary layer formed at the inner surface of mill tank wall. The layer thickness changes depending on process variables. Results obtained are presented in the form of a dimensionless correlation equation.List of Symbols
C
ball filling of the mill,
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c
pw
specific heat of cooling water, kJ/(kg K)
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d
disk diameter, m
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d
k
ball diameter, m
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D
inner diameter of the mill tank, m
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G
w
mass flow rate of cooling water, kg/s
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h
distance between impeller disks, m
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n
revolutions frequency of the impeller shaft, s–1
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q
heat flux density, kW/m2
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Q
c
total heat energy emitted in the mill, W
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T
temperature, K
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T
w1
temperature of cooling water at the cooling jacket inlet, K
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T
w2
cooling water temperature at the outlet, K
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T
m
average temperature inside the mill, K
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T
s
average temperature of the tank wall, K
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u
peripheral speed of the impeller disk, m/s
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heat transfer coefficient, kW/(m2K)
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boundary layer thickness, m
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porosity of the lying bed,
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m
porosity of the suspended bed,
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c
liquid dynamic viscosity, Pa s
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cs
liquid dynamic viscosity at wall temperature, Pa s
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c
thermal conductivity coefficient of liquid, W/(mK)
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c
liquid density, kg/m3
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s
solid density, kg/m3
Dimensionless Numbers
Reynolds number for mixing process
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Reynolds number for liquid parameters
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Nusselt number for liquid parameters
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Prandtl number for liquid parameters
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modified Euler number |
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Keywords: | |
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