Z. M. Zulfattah Procedia Engineering 00 2013 000–000
2.2. Presetting the shifted configuration
The operation temperature and also the set of wire mesh of the absorber are set primarily to follow the values given by Prasad et. al. [2] in order to examine the formula. After confirming that the formulas are giving the correct values the
parameter of the wire mesh is then changed to the desired value for the CST absorber. The best heat transfer occurs in the least porous structure. Therefore, calculations started at fraction of hollow space of
only 0.1 which means 90 percent of the cup volume is empty. Relative mass flow rate G0 of 0.5455 kgm.s
2
as well as other parameters listed on the left of the table below are the actual air parameters during operation. The corresponding air
properties are listed on the right Table 2.
Table 2. Operating condition and the corresponding air properties
G0 0.5455 rel. mass flow kgm².s
v 6.45E-05
by m m²s m
0.01069 mass flow kgs 0.04996
by m Wm.K in
20 inlet air temp. °C 0.517
by m kgm³ out
780 outlet air temp. °C Cp
1069 by m Jkg.K
m 400
average air temp. °C Pr
0.7137 by m
w 800
average absorber temp °C PrW
0.7342 by w
2.3. Other setting
Flow characteristics like Reynolds number, Nusselt number and also Prandtl number have been inserted into the program to calculate and simulate the real condition.
3. Results and discussion
a
100 200
300 400
500 600
700 800
900
1.00E-03 1.10E-03
1.20E-03 1.30E-03
1.40E-03 1.50E-03
1.60E-03 1.70E-03
H e
a t
tr a
n sf
e r
co e
ff ic
ie n
t α
, W
m
2
.K
Wire diameter da [m]
0.100 0.200
0.300 0.400
0.500
b
620.00 640.00
660.00 680.00
700.00 720.00
740.00 760.00
780.00 800.00
820.00 840.00
500 1000
1500 2000
2500
0.0010 0.0011
0.0012 0.0013
0.0014 0.0015
0.0016 0.0017
H e
a t
tr a
n sf
e r
co e
ff ic
ie n
t α
[W m
2
.K ]
R e
y n
o ld
s n
u m
b e
r, R
e
ψ ,1
Wire diameter da [m]
ReΨ,1 αWm²K
Fig. 2. Results using six layers of wire mesh with porosity from 0.1 to 0.5 for a wire diameter versus heat transfer coefficient and b wire diameter versus Reynolds number with corresponding .
Fig 2a shows that the increasing amount of wire inside the absorber cup leads to a less porous structure which reduces the heat transfer ability. Increasing the layer leads to a higher which is good for the absorber cup. The best of 1111
Wm
2
.K has been recorded for 1mm wire diameter with 24 mesh layers and equals to 0.1, see Fig 3. Reynolds number is recorded increasing with the diameter of the wire mesh used. Bigger wire reduces the porosity and
thus intensifies the air-to-wall friction creating turbulence Fig 2b. This friction increases the pressure inside the absorber and reducing the air flow rate through the cup. This situation will put unnecessary burden to the pump, create hotspot on the
absorber surface and further eliminate a smooth heat transfer from the mesh to the air.
Z. M. Zulfattah Procedia Engineering 00 2013 000–000
a
200 400
600 800
1000 1200
1.00E-03 1.10E-03
1.20E-03 1.30E-03
1.40E-03 1.50E-03
1.60E-03 1.70E-03
H e
a t
tr a
n sf
e r
co e
ff ic
ie n
t α
, W
m
2
.K
Wire diameter da [m]
0.100 0.200
0.300 0.400
0.500
b
0.00 200.00
400.00 600.00
800.00 1000.00
1200.00
200 400
600 800
1000 1200
1400
0.0010 0.0011
0.0012 0.0013
0.0014 0.0015
0.0016 0.0017
H e
a t
tr a
n sf
e r
co e
ff ic
ie n
t α
[W m
2
.K ]
R e
y n
o ld
s n
u m
b e
r, R
e
ψ ,1
Wire diameter da [m]
ReΨ,1 αWm²K
Fig. 3. Results using 24 layers of wire mesh with porosity from 0.1 to 0.5 for a wire diameter versus heat transfer coefficient and b wire diameter versus Reynolds number with corresponding .
4. Conclusion
