BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI
buletinul institutului politehnic din iaşi - Universitatea Tehnică ...
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122 Petru Cârlescu et al<br />
air<br />
malt bed<br />
a<br />
b<br />
air inlet<br />
Fig. 1 – Geometry dryer: a – geometry; b – meshing.<br />
Processing the initial stage to impose conditions and calculation is<br />
performed in software FLUENT. The conditions chosen to study the effects of<br />
temperature and air flow on conditions within a bed of malt are presented in<br />
Table 2.<br />
Table 2<br />
Initial conditions<br />
W – initial moisture<br />
content,of the malt, %<br />
T – initial temperature<br />
of the malt, º C<br />
v – velocity of the<br />
air, m/s<br />
49 21 1<br />
The physical properties of the system investigated<br />
Specific heat of air c a – J/kg º C 1017<br />
Specific heat of liquid water c w – J/kg º C 4187<br />
Specific heat of malt c s - J/kg º C 2008<br />
Density of air ρ a – kg/m 3 1.169<br />
Density of malt ρ s – kg/m 3 639.2<br />
Temperature and humidity content in the input region are introduced as<br />
five order polynomial functions of time. Function of temperature is introduced<br />
in UDF code in Kelvin as follows<br />
−20 5 −16 4 −12 3 −8 2<br />
( ) = 10 −6⋅ 10 + 9⋅ 10 + 5⋅10<br />
f T τ τ τ<br />
+ 0.0012τ<br />
+ 303.22,<br />
τ +<br />
(13)<br />
where: τ – drying time between 0...25200 s.<br />
The UDF is introduced as a function of humidity content X kg vapor/kg<br />
dry air depending on time.<br />
−23 5 −18 4 −14 3 −10 2<br />
( ) 210 10 210 10<br />
f X = ⋅ τ − τ + ⋅ τ − τ +<br />
+ ⋅ +<br />
−7<br />
4 10 τ 0.0101,<br />
(14)