Optimal Thermo Hydraulic Performance Of Three Sides Artificially Roughened Solar Air HeatersOptimal Thermo Hydraulic Performance Of Three Sides Artificially Roughened Solar Air Heaters

1. Presentation forthepositionof associateprofessor
on
Optimal Thermo Hydraulic Performance Of Three Sides Artificially
Roughened Solar Air Heaters
by
Dr.ASHWINIKUMAR
PhD(MechanicalEngineering)
NITJAMSHEDPUR
&
Currentlyworkingas
seniortechnicalconsultant at praxisvalues,Bengaluru
With Total working Experience in Teaching, Research and Industry
of
10 years 7 Months

2. Major Contents of My Presentation
 What is Solar Energy
 Solar Air Heaters- Introduction
 Concept of Artificial Roughness- Literature Survey
 Introduction to Three sides Roughened Collectors and
My Original Work
 Effect of Three sides collectors on Thermal and
Thermohydraulic Performance
 Effect of number of Glass covers on the Performance of
Solar Air Heaters with Smooth Collectors
 Development of Correlations of Such Types of Solar Air
Heaters
 Heat Transfer Mechanism
 Concept of Booster Mirrors for Future Prospects

3. What is Solar Energy?
Solar Energy originates with the thermonuclear fusion
reactions occurring in the sun.
The spectrum of solar light at the Earth's surface is mostly
spread across the visible and near infrared ranges with a small
part in the ultraviolet region.

5. Producing Electricity using Solar Energy
Solar Energy can be used to generate electricity in 2 ways:
 Thermal Solar Energy:
Using solar energy for heating fluids
which can be used as a heat source or
to run turbines to generate electricity.
 Photovoltaic Solar Energy:
Using solar energy for the direct generationof
electricity using photovoltaic phenomenon.

6. Solar Air Heaters- Introduction and Survey
 Solar air heaters find application in space heating, artificial crop
and grain drying and many systems requiring low grade thermal
energy.
 Inspite of the lower manufacturing cost and simple design,
operation and maintenance; their application has been limited in
contrast to solar water collectors, mainly because of lower heat
transfer coefficient between the absorber plate and carrier fluid.
 Solar energy is radiant light and heat from the Sun that is
harnessed using a range of ever-evolving technologies such
as solar heating, photovoltaic's, solar thermal energy, solar
architecture and artificial photosynthesis.
 It is an important source of renewable energy and its
technologies are broadly characterized as either passive
solar or active solar depending on how they capture and
distribute solar energy or convert it into solar power.
 Active solar techniques include the use of photovoltaic
systems, concentrated solar power, solar air heating and solar

7. Concept of Artificial Roughness
 Use of artificial roughness of different configurations has been used in plenty
of studies to enhance the heat transfer rate in solar air heaters during the last
decades.
 Varying magnitudes of roughness results in varying values of heat transfer
and friction factor enhancement.
 Artificial roughness provided on absorber plates invariably enhances heat
transfer associated with increase in friction factor. Increase in heat transfer
increases the thermal performance but increase in friction factor affects the
thermo hydraulic performance.

8. Sl. No. Reference Roughness Geometry Parameter
Investigated
1 Prasad and Saini
(1988)
Small diameter protrusion
wire
e/D=0.020-0.033
p/e=10-20
Re=5000-50000
2 Gupta et al., (1993) Transverse ribs e/D=0.018-0.052
Re=3000-18000
W/H=6.8-11.5
3 Gupta et al., (1997) Inclined ribs e/D=0.020-0.053
p/e=7.5 & 10
=30-90
Re=5000-30000
4 Saini and Saini (1997) Wire mesh roughness
e/D=0.012-0.039
S/e=15.62-46.87
L/e=25.00-71.87
Re=1900-13000

9. Introduction to Three sides Roughened Collectors
 In all the above cases, the provision of artificial roughness and
glass cover has remained limited to only one side (top side) of
the solar air heater duct.
 In my research three sides artificially roughened ducts were
used, wherein it has been concluded that three sides roughened
and glass covered solar air heaters perform even better than
those of one side roughened and glass covered solar air
heaters, but friction factor also increases.

13. Effect of Three sides collectors on Thermal and
Thermohydraulic Performance
5 10 15 20 25 30 35 40 45 50 55 60 65 70
0
2
4
6
8
10
(1) p/e=10(Preasent case)
(2) p/e=10(Prasad and Saini,1991)
(3) p/e=20(Present case)
(4) p/e=20(Prasad and Saini,1991)
(5) p/e=30(Present case)
(6) p/e=30(Prasad and Saini,1991)
(1)
(2)
(3)
(4) (5)
(6)
B
-1
e/D=0.0225 (Preseant Case)
e/D=0.0205 (Prasad and Saini,1991)
20000
4000
Re 

Re
2
/
/ r
f
D
e
e 


14. 5 10 15 20 25 30 35 40 45 50 55 60 65 70
2
4
6
8
10
12
14
(1) p/e=10(Present Case)
(2) p/e=10(Prasad and Saini,1991)
(3) p/e=20(Present Case)
(4) p/e=20(Prasad and Saini,1991)
(5) p/e=30(Present Case)
(6) p/e=30(Prasad and Saini,1991)
(1)
(2)
(3)
(4)
(5)
(6)
e/D=0.0225 (Present Case)
e/D=0.0205 (Prasad and Saini,1991)
C
-1
20000
4000
Re 

Re
2
/
/ r
f
D
e
e 


15. Sl.No. References Roughness and flow duct geometry p/e e/D Re
1. Sheriff and Gumley, (1966) Annulus with wires 10 0.018-0.035 1×104–2×103 35
2. Webb and Eckert, (1971) Rectangular with ribs 10-40 0.01-0.04 6×103–10×103 20
3. Lewis, (1975 b) Circular tubes with ribs 2-60 0.02-
0.10
1×104–1×107 20
4. Prasad and Saini, (1991) Rectangular with top side wires 10-40 0.020-0.033 3×103–20×103 24
5. Verma and Prasad, (2000) Rectangular with top side wires 10-40 0.010-0.030 5×103–20×103 24
7. Present case Rectangular with three sides wires 10-30 0.013 – 0.025 4×103–20×103 23

16. 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
40
45
50
55
60
65
70
75
80
85
90
e/D=0.0130
e/D=0.0225
e/D=0.0250

thermo
% Re=4000-20000
Re
2
/
/ r
f
D
e
e 

p/e=20

19. 0.000 0.004 0.008 0.012 0.016 0.020
0
10
20
30
40
50
60
70
80
90

th
%
(T0
-Ti
)/I,
0
C-m
2
/W
m7
m6
m5
m4
m3
m2
m1
p/e=10
e/D=0.0247
m1
0.0085
m2
0.0118
m3
0.0175
m4
0.0187
m5
0.0271
m6
0.0282
m7
0.0375
3r,3G(Present case) 1r,1G(Prasad, 2013) S,3G(Present case) S,1G(Prasad, 2013)
m kg/s
B3r,3G
A
C
D1r,1G
(Prasad, 2013)
E
G
FS,3G
HS,1G
(Prasad, 2013)

20. Effect of Number of Glass Covers on the
Performance of Solar Air Heaters with Smooth
Collectors

23. Development of Correlations for Solar Air
Heaters
 On the basis of experimental data of heat
transfer and friction factor, the correlations for
three sides roughened and glass covered solar
air heaters, have been developed by using the
method of regression analysis, as a function of
roughness and flow parameters.
 A correlation for heat transfer of three sides
glass covered smooth solar air heater has also
been developed.

24. 0 4000 8000 12000 16000 20000
0
30
60
90
Nusselt
number
Reynolds number
Nu3r
=A0
(Re)
0.946

25. 8 12 16 20 24 28 32
0.00005
0.00010
0.00015
0.00020
0.00025
0.00030
0.00035
0.00040
0.00045
Nu
3r
/(Re)
0.946
p/e
Nu3r
=B0
(Re)
0.946
(p/e)
-0.0713

26. 0.015 0.020 0.025 0.030 0.035 0.040
0.0006
0.0008
0.0010
0.0012
0.0014
0.0016
[{Nu
3r
/(Re)
0.946
}/(p/e)
-0.0713
]
e/D
Nu3r
=C0
(Re)
0.946
(p/e)
-0.0713
(e/D)
0.0871

27. 3000 6000 9000 12000 15000 18000 21000
10
20
30
40
50
60
70
S
Nu
Re
NuS
=A1
(Re)
0.932

28. 0.690 0.692 0.694 0.696 0.698 0.700
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
0.0016
0.0018
Nu
S
/(Re)
0.932
Pr
NuS
=B1
(Re)
0.932
(Pr
)
0.5

29. 0.025 0.026 0.027 0.028 0.029 0.030 0.031 0.032
0.0030
0.0031
0.0032
0.0033
0.0034
0.0035
0.0036
0.0037
[{Nu
S
/(Re)
0.932
}/(P
r
)
0.5
]
fS
NuS
=C1
(Re)
0.932
(Pr
)
0.5
(fS
)
0.7

30. Concept of Booster Mirrors for Future
Prospects
 Use of booster mirror in such solar air heaters
may be the reason behind better performance.
 In a flat plate solar collector, there is a provision
of only one side absorber plate and the rear
portion is insulated to reduce thermal losses.
 If the insulated portion is replaced by a glass
cover along with a booster mirrors used for the
reflection of the solar radiation onto the rear
side of the collector, such a system is known as
double exposure collector system.

34. The intensity of radiation falling on the absorber plate increases by 40% due to boosting
of radiation.