Solar air heaters are the cheapest and extensively
used solar energy collection devices employed to
deliver hot air at low to moderate temperature for space
heating, crop drying and many other domestic and
industrial applications. In solar air heaters, generally
poor convective heat transfer coefficient has been
observed during heat transfer from absorber plate to the
flowing air. This low heat transfer coefficient results in
relatively higher absorber plate temperature leading to
higher thermal losses to the environment and hence
lower thermal efficiency. Many attempts have been
made by the researchers for modifying the conventional
design of solar air heater in order to enhance thermal
efficiency of solar air heater. It is revealed from the
literature that applying artificial roughness on the
surfaces of absorber plate is a good technique for
Satcunanathan and Deonarine.  first time
investigated the concept of the DPSAH. These systems
gives better result than the SPSAH system.
Wijeysundera et al.  developed the model of heat
transfer for DPSAH system and compare with SPSAH
system. Naphon and Kongtragool  developed
mathematical models for the performance of the flat
plate solar air heater and heat transfer characteristics.
Naphon  studied the performance of double pass flat
plate solar air heater with or without porous media.
DPSAH with artificial roughened duct was used by
Dogra et al. . Tated et al.  investigated double pass
solar air heater duct roughened with W-shaped on both
sides. Limestone was used as the packing material in
DPSAH in the upper section by Ramadan et al. .
Ravi and Saini  reviewed the various investigations
conducted on performance enhancement of double pass
system. Ho et al.  used the wire mesh packing with
external recycling. So the main aim of present study is
to carry out experimental investigation on DPSAH duct
having zig-zag square shape protruded absorber plate.
Fig.1.Schematic of Experimental Setup.
1. Entry section 7. Pipe Fittings
2. Exit Section 8. Blower
3. Plenum 9. Selector Switch
4. Orifice Plate 10. Temprature Indicator
5. U-Tube Manometer 11. Electric motor
6. Flow Control Valve 12. Variac
A. Ampere meter
Fig.2. Photographic view of experimental setup.
Schematic diagram and photographic view of
experimental setup is shown in "Fig.2" and "Fig.1"
respectively. The aspect ratio of rectangular duct is 10.
The length of the test section, length of entry and exit
sections was taken as 1900 mm, 500 mm, 500 mm. The
width and depth of the rectangular duct was taken as
300 mm, 30 mm respectively and a gap of 30 mm (equal
to the depth of upper and lower channel) was kept at
one end of duct for flow of air into the lower section.
Therefore the total length of air duct was 2400mm
300mm 30mm. Galvanized iron sheet of 20SWG of
size 2370 300mm was used as absorber plate as
shown in Fig.4. Five halogen lamps each of 500W was
placed on the top of glass cover. The intensity of light
used for the experiment were constant and equal to
. Variac was used to control the intensity of
light for the experiment. Air was sucked through the
duct by means of a centrifugal blower provided at exit
side of the pipeline. Control valve was used to control
mass flow rate of air through duct. For measuring the
mass flow rate of air, an orifice plate was used in the
pipeline. Temperature was measured at various location
on the back plate, absorber plate and glass by using J-
type thermocouples. Photographic view of absorber
plate shown in Fig.3.
(a) Top view of absorber plate
(b) Bottom view of absorber plate
Fig.3. Schematic view of absorber plate.
Fig.4. View of roughness pattern on absorber plate.
The test was run to collect data under steady state
conditions. Five values of air mass flow rate were used
for each set of experimentation. Before starting each set
of experimentation, measuring instruments like digital
temperature indicator, selector switch, orifice meter,
variac and manometers were properly checked.
Pressure tapping and tubes were cleaned and checked
for leakage and blockage before each test run. Power to
centrifugal blower and halogen lamps was switched ON
and desired flow rate of air was set with the help of
control valves to start the experimentation. The system
took almost two hours to attain steady state condition
when starts from initial ambient state. However, for
subsequent runs for change of air flow rate, it took
almost 30 minutes to attain steady state. For each set of
experimentation data were collected for U-tube
manometer fluid column, micro-manometer fluid
column, temperature of absorber plate, glass and air at
various locations in test section of the duct.
To calculate the performance of DPSAH following
equations are used:
Mass flow rate
Pressure drop across orifice plate (
) was obtained
from the column of U-tube manometer (
was further used to obtain the mass flow rate of air by
using the following equations reported by Bhushan and
Pressure difference across test section was obtained by
using the following relationship;
P = g (
Heat transfer coefficients
Heat transfer coefficients was determined from
following relationship by Ravi and Saini ;
Overall heat transfer coefficient for the double pass
solar air heater by considering it as the composite wall
system is given by the following relationship;
Thermal efficiency of DPSAH was determined from
following relationship reported by Ravi and Saini ;
Thermohydraulic efficiency (
) for the DPSAH was
determined from following relationship reported by
Ravi and Saini ;
) is the flow pumping required for flowing the air
through the air heater duct is calculated as
Excerpt out of 5 pages
- Quote paper
- Barjinder Singh Gill (Author)Brij Bhushan (Author)Tarun Mahajan (Author), 2016, Performance investigation of double pass solar air heater duct having zig-zag square shape protruded absorber plate, Munich, GRIN Verlag, https://www.grin.com/document/338381