IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009
Exhaust
humid air
Regeneration hot
air
Outside
moist air
Dry air
Figure 3: Desiccant wheel
The desiccant wheel model used below is that proposed first by Banks [8] and also by
Maclaine-cross and Banks [7]. The following assumptions are made [3]:
• The state properties of the air streams are spatially uniform at the desiccant wheel
inlet
• The interstices of the porous medium are straight and parallel
• There is no leakage or carry-over of streams
• The interstitial air velocity and pressure are constant
• Heat and mass transfer between the air and the porous desiccant matrix is
considered using lumped transfer coefficients
• Diffusion and dispersion in the fluid flow direction are neglected
• No radial variation of the fluid or matrix states
• The sorption isotherm does not represent a hysteresis
• Air reaches equilibrium with the porous medium
Heat and mass conservation equations:
∂ha ∂ha
∂H
d
+ u + µ
∂t
∂z
∂t
= 0
(7)
∂wa ∂wa
∂Wd
+ u + µ
∂t
∂z
∂t
= 0
(8)
Heat and mass transfer equations:
∂H
d
∂ha
∂ha
µ + J
m
( Le(
Ta, eq
− Ta
) ) + ( wa,
eq
− wa
) = 0
(9)
∂t
∂T
∂w
a
w
∂Wd
µ + J
m
( wa, eq
− wa
) = 0
(10)
∂t
a
T
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