The present work is focused on developing of operating characteristics of
adsorptive heat conversion units based on composites ‘silica gel – sodium sulphate’ for
heat supply systems.
Research results. Estimation operational parameters of adsorptive units based on
composites ‘salt in porous matrix’ for heat energy conversion involves multifactor
experiments of heat and mass transfer in these environments, which accompanies large
material costs. So, the development of an algorithm for calculation the operating
characteristics of adsorption heat storage devices is top-priority task. A system of
differential equations that describe the internal diffusion kinetics of adsorption in the
almost instantaneous establishment of equilibrium between the concentration of
adsorbate in the gas that fills the pores and its concentration in the adsorbed state
includes [6]:
1. material balance equation:
=
+
д
дс
D
д
д
дt
дс
дt
да
K
К
1
;
2. adsorption isotherm equation:
)
(c
f
a=
;
3. initial data:
0
)
0
,
(
)
0
,
(
=
=
c
a
;
4. boundary data:
()
0
,
c
t
R
c
=
,
0
0
=
→
д
дс
K
.
where a and c are the concentration of adsorbate in the mobile and stationary
phases. η equals x at the grain shape parameter K = 0 for a prismatic or cylindrical
grain of length 2R, the lateral surfaces of which are impermeable (plate);
r
=
corresponds to radial coordinate for cylindrical grain with impermeable ends (K = 1)
or spherical grain (K = 2); t is the time; D is the effective diffusion coefficient.
Saturation occurs from the outer surface of the granule, where a constant concentration
is maintained. The grains are assumed not to contain any amount of adsorbate at the
initial instant of time, and the diffusion coefficient D is supposed to be constant.
As heat storage media the composite adsorbents ‘silica gel – sodium sulphate’
synthesized from tetraethoxysilane, Na
2
SO
4
, ethanol (as a solvent), hydrochloric acid
(as a catalyst) and polyionenes served as organic modifiers [7]:
Diameters of composite sorbents granules are 0.5 – 1.5 mm.
O
C
O
CH
3
CH
3
CH
3
N
+
CH
2
CH
3
CH
2
CH
2
CH
2
CH
OH
R
CH
2
CH
2
CH
OH
CH
3
N
+
CH
3
CH
2
CH
OH
CH
2
R
m
Cl
Cl
n
R:
m=0,414
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