2. INTRODUCTION
• Solar air heating is a solar thermal technology in which the energy from the sun, insolation, is captured by an absorbing
medium and used to heat air.
• It is a renewable energy heating technology used to heat or condition air for buildings or process heat applications.
• Solar collectors for air heat may be classified by their air distribution paths or by their materials, e.g
• Through-pass collectors
• Front-pass
• Back pass
• Combination front and back pass collectors
• Unglazed
• Glazed
• This report presents the analysis of an experimental investigation of the performance for a new flat plate solar air heater (SAH)
with several obstacles (type I, type II, and type III) and without obstacles (type Iv) and also highlights the other performance
tests.
3. CONT..
• It presents an analysis of efficiency evaluation of solar air heater supplied with
obstacles and those of the collector without obstacles.
• The experimental data along with the correlations obtained by linear regression
are presented.
• The optimal value of efficiency was determined for the solar air heater with type
ii absorbent plate in flow channel duct for all operating conditions; and the
collector supplied with obstacles appears significantly better than that without
obstacles.
5. LITERATURE REVIEW
• The main applications for solar air heaters (S.A.H) are space heating, drying and paint
spraying operations.
• The main drawback of an S.A.H is that the heat-transfer coefficient between the absorber
plate and the air stream is low, which results in a lower thermal efficiency of the heater.
• The efficiencies, the heat gain factors and heat loss coefficients were determined for four
types of solar air heaters and comparisons were made among them.
• There are different factors affecting the S.A.H efficiency, e.g.
• Collector length,
• Collector depth,
• Type of absorber plate,
• Glass cover plate and Wind speed.
7. CONT..
• Type 1: the triangular obstacles of 5×5 cm dimension was manufactured and
the obstacles were situated on the absorber plate at 10 cm intervals with 3.5 cm
distance
• Between successive lines (fig. 1a).
• Type 2: the leaf shaped obstacles of 5×5 cm dimension was situated on the
absorber plate at 10 cm intervals with 3.5 cm distance between successive lines
(fig. 1b).
• Type 3: the rectangular obstacles of 10×10 cm dimensions were situated at 2.5
cm intervals with at a 45° angle on the absorber plate (fig. 1c).
• Type 4: there are no obstacles on the absorbent surface (fig.1d)
8. SCHEMATIC VIEW OF SET UP
• Fig. 2. Schematic view of experimental set-up. 1) collector box, 2) glass cover, 3)
foot, 4) fan, 5) fan engine, 6) connection pipe, 7) channel selector, 8) digital
thermometer,9) thermocouples, 10) pyranometer, 11) pyranometer recorder, 12)
anemometer, 13) absorber plate (copper plate that's been painted black), 14)
absorber plate with obstacles
9. RESULTS AND DISCUSSIONS
• Four solar air heaters (types I–IV) were investigated in this study. Two air mass flow
rates of 0.0074 and 0.0052 kg/s were also investigated at the experiments.
• Fig. 3. Average values of hourly solar radiation and ambient temperatures.
10. CONT..
• Fig. 4. Variation of instantaneous solar radiation and temperature difference with
time at different air flow rates.
11. CONT..
• The highest temperature increase occurred at period of 12:00–14:00. The
maximum difference temperature increase through the four type solar air
heaters (I–IV) was 45.9, 50.5, 44.1, and 33.1 °C for 0.0074 kg/s, 47.4, 55.4,
48.5 and 38.3 for 0.0052 kg/s, respectively.
• The highest difference temperature increase occurred through type ii, while the
lowest through type iv.
12. CONT..
• Fig. 5. Variation of collector efficiency with the temperature parameters
13. CONT..
• Fig. 5 presents the collector efficiency versus the temperature parameter
(to−ta)/I for the four S.A.H at mass flow rate of 0.0074 and 0.0052 kg/s.
• The maximum efficiencies for type I, type ii, type iii, and type iv are determined
as 67% and 49%, 82% and 58%, 47% and 38%, and 35% and 29%, at ṁ=0.0074
kg/s and ṁ=0.0052 kg/s, respectively.
• The data in fig. 5 is fitted to straight lines using least squares data fitting
method
• The scatter of the data around the straight line is mainly attributed to the angle
of incidence variations, wind speed and the dependence of the heat loss on the
plate temperature.
• Also, the variations of the relative proportions of beam diffuse and ground
reflective components of solar radiation are participating in the data scattering.
14. CONT..
• The higher the temperature parameter the less the efficiencies are resulted.
Thus at higher temperature parameters, the overall loss is lower.
• From the figure, it can be seen that, the collector efficiency increases with
increasing air mass flow rate considerably. The reason for the significant
increase in efficiency from 0.0052 kg/s to 0.0074 kg/s can be attributed to
changes in flow condition from laminar to turbulent.
• The heat-transfer rate has largest value in type ii due to this collector having
more efficient heat transfer rate than the other three collectors.
16. CONT..
• The heat gain factors, which are computed using regression lines in fig. 5, are
depicted in fig. 6 for all SAH. The values of FR, FO, F′ and UL were calculated from
the slopes and intercepts of the best lines in fig. 5.
• The highest FR, FO and F′ Values are obtained by SAHs with leaf obstacles (type
II), whereas the lowest values are obtained by the SAH without obstacles (type
IV), i.e. Flat plate collector. All the relevant factors of type II are higher than that
of type I, type III and also that of type IV, respectively. The FR, FO and F′ values
increased with increasing air mass flow rate of air
18. CONT..
• The heat loss factors shown in fig. 7 for all the SAH. The heat loss coefficients for type I, type II, type III,
and type IV are determined as 6.88 and 5.45 W/m2 K, 4.2 and 3.1 W/m2 K, 14.36 and 11.75 W/m2 K,
and 24.17 and 19.3 W/m2 K, at ṁ=0.0074 kg/s and ṁ=0.0052 kg/s respectively.
• The heat loss coefficients increased with increasing air mass flow rate of air. However, the heat loss
factors are especially much lower than those found for type IV at two mass flow rates.
• It can, also, be seen that slope of the efficiency curves decreases, meaning decrease in loss coefficient,
with increase of mass flow rates. The efficiency of type II (great turbulence) is higher than that of type I
(middle turbulence), than that of type III (little turbulence) and also that of type IV (no turbulence, without
obstacles), respectively. The study has shown that the solar collector supplied with type II than type I and
type III leads to a very significant improvement in the efficiency–temperature rise couple. It's because type
II leads to very great turbulence in the collector unit
• These results show that the enhancements in heat gain have resulted mainly from more efficient
absorption of solar radiation and heat-transfer between air and absorbing surfaces inside the type II,
which eventually reduce radiation and heat losses.
21. CONT..
• This experiment was conducted by Abd Elnaby Kabeel of Tanta university and
observed the following;
• The shape absorber factor is the most important parameter in the design of the solar
air heaters.
• The heat transfer to the flow in the heater and the pressure drop in the solar air
heater increase with increase of the triangular angle of the triangular collector.
• The collector efficiency factor for the triangular solar air heater is higher than the
longitudinal fins solar air heater
22. b) EFFECT OF PASS NUMBER ON COLLECTOR
EFFICIENCY IN DOWNWARD-TYPE MULTI-
PASS SOLAR AIR HEATERS
23. CONT..
• The experiment was carried at energy and opto-electronic materials research
center, department of chemical and materials engineering, Tamkang university,
Tamsui, Taiwan and concluded that considerable improvement in collector
efficiency is obtainable if the operation is carried out with multi-pass operation,
while the undesirable effect is still small and may be ignored. The enhancement
increases with increasing pass number, especially for operating at lower air flow
rate with higher inlet air temperature.
24. CONCLUSION
• The efficiency of the solar air collectors depends significantly on the solar radiation,
surface geometry of the collectors and extension of the air flow line. The efficiency
of the collector improves with increasing mass flow rates due to an enhanced heat-
transfer to the airflow.
• The efficiency increases as the temperature parameter increases, meaning, at higher
temperature parameter, the overall loss is lower.
• The highest collector efficiency and air temperature rise were achieved by SAHs with
leaf obstacles (type ii), whereas the lowest values were obtained for the SAH without
obstacles (type iv), i.e. Flat plate collector. In addition, this study has allowed to
show that the use of obstacles in the air flow duct of the collector is an efficient
method of adapting air exchanger according to user needs.
• Test results always yield higher efficiency values for type II than for type IV (without
obstacles) flat plate collector. The obstacles ensure a good air flow over and under
the absorber plates, create the turbulence, and reduce the dead zones in the
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