This paper presents the efficiency analysis of an experimental set-up double-pass V-corrugated solar air heater. All the experimental results were obtained with the developed solar air heater kept at an inclination angle of 23.5 degrees (Latitude Angle of Bhopal, India), facing due south, and using DC fans (for forced convection) with different air flow rates. The efficiency results, gathered on two consecutive typical Indian peak summer days, are presented taking into consideration the intermittent availability of sunlight at different times on these days. All the relevant design aspects of the developed double-pass V-corrugated solar air heater such as the material used for insulation, construction of the outer enclosure, and the solar air heater assembly, are discussed.

1. ICAER 2011
EFFICIENCY ANALYSIS FOR AN EXPERIMENTALLY SET-UP
DOUBLE-PASS V-CORRUGATED
SOLAR AIR HEATER
Nalin Deshpande1
, Aakanksha Dubey2
, Amrita Agrawal3
, Dr. Anil Kumar4
Department of Energy, Maulana Azad National Institute of Technology (MANIT), Bhopal, India 462051
Phone: +9199933197391
, +9194250054782
, +9199933655883
, +9194256804484
Email:1
nalin191189@yahoo.com, 2
aakanksha512@gmail.com,3
ambilavanya@gmail.com,4
anilkumar76@gmail.com
Abstract
This paper presents the efficiency analysis of an experimentally set-up double-pass V-corrugated solar air heater. All
the experimental results were obtained with the developed solar air heater kept at an inclination angle of 23.5
degrees (Latitude Angle of Bhopal, India), facing due south, and using DC fans (for forced convection) with
different air flow rates. The efficiency results, gathered on two consecutive typical Indian peak summer days, are
presented taking into consideration the intermittent availability of sunlight at different times on these days. All the
relevant design aspects of the developed double-pass V-corrugated solar air heater such as the material used for
insulation, construction of the outer enclosure, and the solar air heater assembly, are discussed.
Keywords: Solar Air Heater, Galvanised Iron, Absorber Plate Assembly, Fibre Reinforced Plastic
1. Introduction
Solar air heater (SAH) is a type of energy collector in which the energy from the sun is captured by an absorbing
medium and used to heat air. Solar air heating is a renewable energy heating technology used to heat or condition air
for buildings or process heat applications. According to Sukhatme (2008) et al, a conventional SAH generally
consists of an absorber plate with a parallel plate below forming a small passage through which the air to be heated
flows. As in the case of the liquid plate collector, transparent cover system is provided on the bottom and sides.
Various types of SAHs have been designed and used in space heating and cooling. Some of these designs include V-
corrugated, double pass, and finned types SAHs. For a finned type design, El-khawajah (2011) et al suggested that
the maximum efficiency was obtained by using 6 fins. They showed that the maximum efficiency obtained for the 2,
4, 6 fins of SAH were 75.0%, 82.1% and 85.9% respectively for the mass flow rate of 0.042 kg/s. In a V-corrugated
design, the absorber plate is made up of V-corrugated sheet to increase the effective absorption surface area. This
increased effective surface area results in raising the overall efficiency of the air heater. A double pass SAH consists
of two units, the first one comprising of a glass cover and an absorber plate through which the passed air is pre-
heated. The second unit, which is below the absorber plate, does additional heating of air.
Our developed solar air heater is a combination of a double pass and V-corrugated designs i.e. it is a double pass V-
corrugated SAH. El-Sebaii (2010) et al have shown that a double pass V-corrugated plate SAH is 9.3-11.9% more
efficient compared to double pass finned type SAH. In our double pass V-corrugated design the main absorber plate
is V-corrugated and a thermal storage unit, consisting of sand as storage medium, is used for absorbing solar
radiation. By forced convection air flows through the absorber plate assembly where it gets preheated by absorbing
energy from sand filled just below the secondary absorber plate. After getting preheated, air then turns and flows
between V-corrugated plate and glass. Glass is used to provide green house effect that helps in increasing the overall
efficiency of SAH.

2. 2. Experimental Set-Up
The developed SAH is a combination of two pass and V-corrugated design. Its assembly has the following six major
units or components: outer enclosure, absorber plate assembly, duct, insulation, transparent glass cover, and dc fans
for forced convection.
The outer enclosure, shown in Figures 1(a), provides a casing for all the internal units and prevents heat loss. We
used black colored fiber reinforced plastic (FRP) sheets of 3mm thickness for constructing this outer enclosure.
These FRP sheets are held together with the help of L-shaped aluminum angles and the corners are sealed using
white cement. The effective dimensions of the outer enclosure are 1m x 1m x 0.2m as shown in figure 1(b).
(a) (b)
Figure 1(a) Picture of experimentally set-up Outer Enclosure (b). Dimensions of the outer enclosure
Absorber Plate Assembly (APA) absorbs the incoming solar radiations and transfers the heat energy to the incoming
low temperature air to raise its temperature to an optimum level. In our SAH design, the absorber plate assembly is
painted black with selective coating to reduce reflective losses and for absorption of maximum incoming solar
radiations. Additionally, an enclosed volume of sand was placed below the absorber plate to increase the thermal
storage capacity. Air cavities in the sand absorb heat during peak sunshine hours and dissipate it during low
sunshine hours. Galvanized iron (GI) sheets were used to obtain dimensions of 0.9 m x 0.85 m x 0.1m (volume).The
other relevant specifications are given in Table 1.The V-corrugated sheet, shown in Figure 2, was sandwiched
between two flat plate absorbers and this assembly, being 0.065m in height, was held at a height of 0.05m from the
bottom that constitutes the thermal storage unit.
Table 1: Dimensions of Absorber Plate Assembly
Top-GI-sheet area 0.8m x 0.85m
V-corrugated sheet area 8800 mm2
Bottom-GI-sheet area 0.9m x 0.85m
Thermal Storage Volume 0.9m x 0.85m x 0.05m
Figure 2 (a).Picture of experimentally set-up sandwiched V-corrugated APA (b).Dimensions of cross section.
A partitioned duct was created for the circulation of air and this is shown in Figure 3. The partitioned duct prevents
heat loss to the surrounding and allows low temperature incoming air enter the system.FRP sheet of thickness 1 mm

3. was used for its fabrication. The above shape was adopted for uniform pressure drop. The duct, as shown in Figure
3(b), has a height to width ratio of 7:3.
Figure 3(a). Duct Dimensions (b.) Cross sectional view & dimensions (c).Three dimensional view of the Duct.
Glass wool layers, for insulation and to minimize the heat loss, were laid till a height of 0.05m from the bottom.
Similarly, side insulations were also provided. A transparent glass cover, made up of toughened glass of thickness
4mm to create green house effect, was used within the air heater. To create air flow, by the means of forced
convection, a 12 volts DC fan was used.
3. Experimental Results
All the experimental results were obtained with the developed solar air heater kept at an inclination angle of 23.5
degrees (Latitude Angle of Bhopal, India), facing due south, and using DC fans (for forced convection) with
different air flow rates. The efficiency results, gathered on two consecutive typical Indian peak summer days, are
presented taking into consideration the intermittent availability of sunlight at different times on these days. The
relevant experiment parameters, such as the ambient air temperature, and relative humidity, etc., are given below.
Day 1:
Date of Experiment Performance: 18.04.2011
Average Mass Flow Rate: 0.01056 kg/s
Average Ambient Air Temperature: 38.5430C
Average Ambient Air Relative Humidity: 21.4714%
Day 2:
Date of Experiment Performance: 19.04.2011
Average Mass Flow Rate: 0.004839 kg/s
Average Ambient Air Temperature: 38.2140
C
Average Ambient Air Relative Humidity: 21.1286%
The instantaneous efficiency (ᶯc) of a solar collector can be calculated as:
ᶯc = mCp (T2-T1) (1)
Ac It
Where,
m mass flow rate of the air, kg/s
Cp specific heat of air, J/kgK
T2 temperature of the air leaving the collector, K
T1 temperature of the air entering the collector, K
Ac area of collector, m2
It total solar energy incident upon the plane of the collector per unit time per unit area, W/m2
The parameters considered for performing the thermal analysis are as follows:
Ig total global radiation falling on the tilted surface per unit area per unit time, W/m2
Id total diffused radiations falling on a tilted surface per unit area per unit time, W/m2

4. Ta ambient air temperature, 0
C
Rha relative humidity of ambient air, %
Ti inlet air temperature , 0
C
Rhi relative humidity of inlet air, %
To outlet air temperature , 0
C
Rho relative humidity of outlet air, %
vi inlet air velocity, m/s
vo outlet air velocity, m/s
Tab absorber plate temperature, 0
C
Tig inner glass temperature, 0
C
Tog outer glass temperature, 0
C
Table 2: Efficiency of the developed SAH for Day1
Table 3: Efficiency of the developed SAH for Day 2
As seen from Table 2(for Day 1), the efficiency of the developed SAH lies in the range of 28-70% with a maximum
attained outlet air temperature of 85.80
C. On Day2, the efficiency lies in the range of 17-47% while the maximum
temperature reached on this day was lower, 78.10
C. During the evening hours when solar insolation is quite low, due
to the thermal energy storage effect, the efficiency of the air heater does not drop below 20%.
Figure 4: Efficiency curves for Day 1 and Day 2.
On Day1, when the mass flow rate is larger, the efficiency is higher than that on Day2.The highest observed
efficiency in our 2-day experiment period was 67.56%, observed between 1:00-2:00 pm on Day 1, while the lowest
being 17.81%noted between 11:00 am- 12:00 pm on Day 2.For both the days, the efficiency generally reaches its
peak value somewhere between 12pm to 1 pm when the solar radiation is maximum. The morning and evening
S.No. TIME Ig Id Ta Rha Ti To Vi Vo Rhi Rho Tab Tig Tog ᶯ
(W/m²) (W/m²) (°C) (%) (°C) (°C) (m/s) (m/s) (%) (%) (°C) (°C) (°C) (%)
1 11:00am 864 258 36.7 26.9 39 73.2 3.11 0.5 23.1 10.3 81.6 85.7 59.2 55.19761
2 12:00pm 998 287 39.5 24.5 38.3 78.4 3.37 0.44 23.5 5.8 89.3 88.2 61.5 60.8508
3 1:00pm 961 221 38.2 21.8 40.6 85.8 3.22 0.33 18.2 4.2 88.8 89.8 51.8 67.56131
4 2:00pm 904 326 38.6 19.6 40.4 80.5 3.27 0.23 17 4.4 87.7 89 50.9 64.74821
5 3:00pm 802 215 39.7 19.4 42.5 71.1 3.08 0.48 16.8 5.9 81.8 78.1 49.1 48.70208
6 4:00pm 635 241 38.2 18.8 42.5 66.1 2.83 0.27 17 6.3 74.1 67.8 55.6 46.63691
7 5:00pm 334 156 38.9 19.3 37.9 45 2.96 0.22 21.9 14.8 55.2 48.3 43 28.31289
S.No. TIME Ig Id Ta Rha Ti To Vi Vo Rhi Rho Tab Tig Tog ᶯ
(W/m²) (W/m²) (°C) (%) (°C) (°C) (m/s) (m/s) (%) (%) (°C) (°C) (°C) (%)
1 11:00am 920 180 39.1 20.6 42 67.8 1.43 0.29 16.7 6.6 86.3 82 54.7 17.8099
2 12:00pm 1063 246 36.6 24.2 44.3 78.1 1.57 0.28 18.2 5.5 86.5 86.4 60.2 22.00993
3 1:00pm 257 217 35.6 24.2 37.2 56.2 1.4 0.48 21.6 9.8 60.5 60.6 54.7 46.67751
4 2:00pm 947 205 43.6 21.5 38.7 73.8 1.45 0.62 17.1 5.7 78.8 81 54.1 24.12072
5 3:00pm 177 120 36.7 21.6 37 47.3 1.23 0.6 21.7 13 52.2 55.1 42.8 32.30042
6 4:00pm 557 162 37.2 19.4 41.3 59.9 1.71 0.52 17.1 8.7 65.1 64.8 46.7 25.41635
7 5:00pm 284 108 38.7 16.4 39.8 52.5 1.22 0.29 17.3 10.8 53.8 51.6 43.2 24.39951
0
50
100
11 12 13 14 15 16 17
Efficiency(%)
Time of the day (Hours)
InstantaneousEfficiency of Solar Air Heater
Day1
Day2

5. hours showed low efficiencies due to less heat gain by the air and comparatively colder climatic conditions. On
Day2, an abrupt change in the instantaneous efficiency was observed between 1 pm and 2 pm, owing to the cloudy
conditions prevailing in this period. From this experimentation it can be deduced that cloud cover and weather
conditions play a major role in determining the extent of temperature rise and thus efficiency of the air heater.
Figure 5: Variation of temperatures Ta,, Ti & To with time for the experimentation days.
Figure 5 shows the variations of the ambient, input, and output air temperatures with time for the two experimental
days. As seen, the ambient and inlet temperatures were approximately equal for both days. The small difference in
these temperatures is due to the ambient temperature being measured in a shaded region while the inlet temperature
being measured under the working conditions. On Day1, the output air temperature rose to its highest value
approximately at 1pm and started to decline with time. On Day2, the output air temperature kept fluctuating with a
maximum of 78.10
C.
The variation of the ambient, absorber plate, inner glass and outer glass temperatures with time of the day is shown
in Figure 6. The following observations were drawn from the recorded data:
 Tab, Tig and Tog are significantly above the ambient air temperature.
 Tab and Tig are approximately at the same temperature throughout.
 Tog lies between Tab or Tig and the ambient air temperature.
Figure 6: Variation of temperatures Ta, Tab, Tig & Tog with time for the experimentation days.
The graphs (Figure 7) show the relation between relative humidity and time of the day. Following are the inferences
drawn from the graph:
 Rha and Rhi are relatively at the same level with Rhi being lower due to higher temperature.
 On Day1, Rho decreases initially as temperature rises and then it increases in the evening hours.
 On Day2, Rho fluctuates with time due to the weather conditions. Maximum humidity being at 3pm and
minimum at 12 noon.
0
20
40
60
80
100
11 12 13 14 15 16 17
Temperature(°C)
Time of the day (Hours)
Ta
Ti
To
0
20
40
60
80
100
11 12 13 14 15 16 17
Temperature(°C)
Time of the day (Hours)
Ta
Tab
Tig
Tog 0
20
40
60
80
100
11 12 13 14 15 16 17
Temperature(°C)
Time of the day (Hours)
Ta
Tab
Tig
Tog

6. Figure 7: Variation of relative humidity parameters with time.
4. Practical applications of solar air heaters
The important applications of SAHs are heating and cooling of buildings, greenhouse heating, and industrial
processes such as drying of agricultural crops and timber. Various types of SAHs have been designed and used in
space heating and cooling. Air Heaters (AHs) are not only used in actively heated or cooled buildings but also can
be used with desiccant beds for solar air conditioning. The heat from the air heaters can also be used to heat the
generator of an absorption air conditioner for cooling purpose. Drying is a promising area for the application of
AHs. Dilip Jain (2004) et al suggested that the humidity of the air and the drying rate increases with the increase in
the depth of drying bed. Hot air from SAH is circulated through the crop to reduce its moisture content. The air can
be circulated either by a fan or by natural convection; correspondingly, the heaters are called active or passive dryers
depending on the mode of circulating air, a number of designs are possible. One such design is two-pass air heater
connected to a drying chamber. In this design, the hot air passes through the crops immediately after it leaves
through the collector. The moist air escapes into the atmosphere through an opening at the bottom of the dryer.
5. Conclusions
This paper described the experimental set-up of a double pass V-corrugated solar air heater and presented its
efficiency analysis for two peak summer days. The developed SAH attained a highest efficiency value of 67.56%.
The effect of the ambient temperature, and the relative humidity, on the efficiency was discussed. The developed
solar air heater showed higher efficiency when the temperature fluctuation was less and the relative humidity was
higher.
6. References
Dilip Jain, Rajeev Kumar Jain, 2004, Performance evaluation of an inclined multi-pass Solar Air Heater with in-
built thermal storage on deep-bed drying application.
Duffie J.A and Beckman W.A, 1991, Solar Engineering of Thermal Processes
El-khawajah M.F, Aldabbagh L.B.Y, Egelioglu F, 2011, The effect of using transverse fins on a double pass flow
solar air heater using wire mesh as an absorber.
El-Sebaii A.A, Aboul-Enein S., M.R.I. Ramadan, Shalaby S.M, Moharram B.M, 2010, Thermal performance
investigation of double pass finned plate Solar Air Heater..
Garg H.P, 2000, Solar Energy Fundamentals & Applications
Sukhatme S.P and Nayak J.K, 2008, Solar Energy Principles of thermal collection & Storage
Tiwari G.N, May 2000, Solar Energy Fundamentals, Design, Modeling & Applications.
0
10
20
30
11 12 13 14 15 16 17
RelativeHumidity(%)
Time of the day (Hours)
Relative Humidity v/s Time Plot (Day1)
Rha
Rhi
Rho 0
10
20
30
11 12 13 14 15 16 17
RelativeHumidity(%)
Time of the day (Hours)
Relative Humidity v/s Time Plot (Day2)
Rha
Rhi
Rho