Report on Solar Air heater by Hardik Ramani

ADVANCES IN SOLAR AIR HEATER
A
Seminar Report
Submitted In Partial Fulfilment of the Requirements
For The Degree Of
Master of Technology in Mechanical Engineering (Thermal Engineering)
Prepared by
HARDIK V.RAMANI
(13MMET16)
Guided by
PROF. S. V. JAIN
DEPARTMENT OF MECHANICAL ENGINEERING
INSTITUTE OF TECHNOLOGY
NIRMA UNIVERSITY
AHMEDABAD-382481
DECEMBER-2013
I

CERTIFICATE
This is to certify that the Seminar Report entitled “ADVANCES IN SOLAR AIR
HEATER” submitted by HARDIK V. RAMANI (13MMET16), towards the partial
fulfilment of the requirements for the degree of Master of Technology in Thermal
Engineering, Institute of Technology, Nirma University of Science and Technology,
Ahmedabad is the record of work carried out by him under my supervision and guidance. In
my opinion, the submitted work has reached a level required for being accepted for
examination. The results embodied in this Seminar work, to the best of my knowledge,
haven’t been submitted to any other university or institution for award of any degree.
Prof. S. V. Jain Dr R. N. Patel
Professor at ME Department, Professor and Head of ME Department,
Institute of Technology, Institute of Technology,
Nirma University, Ahmedabad Nirma University, Ahmedabad
II

APPROVAL SHEET
The Seminar entitled Advances in Solar Air Heater by HARDIK V. RAMANI
(13MMET16) is approved for the degree of Master of Technology in Mechanical
Engineering (Thermal Engineering).
III
Examiners
____________
--------------------
Date: __________
Place: Nirma University
Ahmedabad

ACKNOWLEDGEMENT
It gives me great pleasure in expressing thanks and profound gratitude for the dignitaries who
made this seminar work to complete. I would like to give my special thanks to my Guide,
Prof S. V. Jain, Professor, Department of Mechanical Engineering, Institute of Technology,
Nirma University, Ahmedabad for his valuable guidance and continual encouragement
throughout the Seminar work. I heartily thankful to him for his time to time suggestion and
the clarity of the concepts of the topic that helped me a lot during this study. And I am also
Thankful to Prof. N. K. Shah for their valuable guidance and support. I am also thankful to
Dr. R. N. Patel, Head of Department of ME, Institute of Technology, Nirma University,
Ahmedabad, for his continual kind words of encouragement and motivation throughout the
Project. I am also thankful to Dr K Kotecha, Director, Institute of Technology for his kind
support in all respect during my study.
IV
HARDIK V. RAMANI
(ROLL NO.13MMET16)

ABSTRACT
Given that the future of our planet is intricately entwined with the future choices of energy,
effective exploitation of non-conventional energy sources is becoming increasingly essential
for modern world as fossil fuels are hazardous to environment and cannot sustain supply for
long time as they are not renewable. Moreover, demand of energy is increasing rapidly. In
this scenario, solar energy is being seen as potential viable resource for ever increasing
hunger of the energy for the development of nation and by and large globe. In this seminar
work, effort has been made to demonstrate this reality with proof of statistics from reliable
sources. Furthermore numerous new designs of Solar Air Heater are emerging in various
aspects, in different number of roughness, in different cost. Extensive review of research
done in this field in recent past is covered with their design characteristics and their
suitability for specific conditions and applications with respect to their merits and demerits.
V

CONTENTS
CONTENT PAGE NO.
CERTIFICATE ........................................................................................................................ II
APPRROVAL SHEET ............................................................................................................ III
ACKNOWLEDGEMENT……..…………………………………………….………………IV
ABSTRACT ………………………………………………………………………………….V
CONTENTS………………………………………………………………………………….VI
LIST OF FIGURES .............................................................................................................. VIII
LIST OF TABLES .................................................................................................................... X
NOMENCLATURE ............................................................................................................... XI
CHAPTER 1: INTRODUCTION ........................................................................................... 1
1.1. Overview Of Solar Energy.............................................................................................. 1
1.2. Advantages...................................................................................................................... 1
1.3. Disadvantages ................................................................................................................. 1
1.4. Solar Air Heating ............................................................................................................ 2
1.5. Application ..................................................................................................................... 2
1.5.1 Heating ...................................................................................................................... 3
1.5.2 Cooling...................................................................................................................... 3
1.5.3 Ventilation & Moisture Control ................................................................................ 3
1.5.4 Filtration.................................................................................................................... 4
1.6.Saving with Solar Air Heater ........................................................................................... 4
CHAPTER 2: LITERATURE REVIEW ................................................................................ 5
2.1 Introduction ..................................................................................................................... 5
2.2 Principle ........................................................................................................................... 5
2.3 Types of Solar Air Heater. ............................................................................................... 6
2.2.1 Porous ....................................................................................................................... 6
2.2.2 Non-Porous ............................................................................................................... 7
CHAPER 3: LOW COST SOLAR HEATER ........................................................................ 8
3.1 Introduction. .................................................................................................................... 8
3.2. Experimention ................................................................................................................ 8
3.2.1. General ..................................................................................................................... 8
VI

3.2.2 Test at No-Load ....................................................................................................... 9
3.2.3 Test with Load .......................................................................................................... 9
3.3 Result and Discussion .................................................................................................. 10
3.3.1 Test at No - Load ................................................................................................... 10
3.3.2 Teat with Load ........................................................................................................ 12
3.3.2.1 During Summer Season ................................................................................ 12
3.3.2.1(A) Temperatura Rise ............................................................................ 12
3.3.2.1(B) Thermal Efficiency .......................................................................... 13
3.3.2.1(C) Instantaneous Thermal Efficiency ................................................... 15
3.3.2.2 During Winter Season ................................................................................... 17
3.3.2.2(A) Temperatura Rise ............................................................................ 17
3.3.2.2(B) Thermal Efficiency .......................................................................... 18
3.3.2.2(C) Instantaneous Thermal Efficiency ................................................... 20
3.3.3 Comparision .......................................................................................................... 22
3.4 Conclusion .................................................................................................................... 22
CHAPTER 4:EFFICIENCY IMPROVEMENT BY ROUGHNESS ................................. 25
4.1 General ........................................................................................................................... 25
4.2 Effective technique to enhance rate of heat transfer ...................................................... 25
4.3 Calculation. .................................................................................................................... 26
4.4 Experiment .................................................................................................................... 28
4.5 Experimentl Result......................................................................................................... 28
SUMMARY ............................................................................................................................. 30
REFERENCES ........................................................................................................................ 31
VII

LIST OF FIGURES
LIST OF FIGURES PAGE NO
Fig. 1.1 Power of Sun 1
Fig. 1.2 Basic of Solar Air Heater 2
Fig. 1.3 Application 3
Fig. 2.1 Simple Solar Air Heater 5
Fig. 2.2 Principle 6
Fig. 2.3 Porous 6
Fig. 2.4 Non-Porous 7
Fig. 3.1 single glazed solar air heater 8
Fig. 3.2 double glazed solar air heater 8
Fig.3.3 (a) experimental set-up 10
Fig.3.3(b) schematic of experimental set-up 10
Fig.3.4 (a) Variation of ambient temperature, solar radiation intensity
and Stagnation temperature during the day at no load in single glazing
solar air heater
VIII
11
Fig.3.4 (b) Variation of ambient temperature, solar radiation intensity
and Stagnation temperature during the day at no load in double
glazing solar air heater
11
Fig.3.4 (a) Variation of ambient temperature, solar radiation intensity
and Stagnation temperature during the day at no load in packed bed
solar air heater
11
Fig 3.5(a) Rise in temperature of air during the day for summer
Season at different air flow rates in single glazing solar air heater
12
Fig 3.5(b) Rise in temperature of air during the day for summer
Season at different air flow rates in double glazing solar air heater
13
Fig 3.5(c) Rise in temperature of air during the day for summer
Season at different air flow rates in packed bed solar air heater
13
Fig 3.6(a) Thermal Efficiency for single glazing solar air heater
during the day for summer Season at different air flow rates
14
Fig 3.6(b) Thermal Efficiency for double glazing solar air heater
during the day for summer Season at different air flow rates
14
Fig 3.6(c) Thermal Efficiency for packed bed solar air heater during
the day for summer Season at different air flow rates
14

Fig 3.7 (a) Instantaneous Thermal Efficiency versus (To-Ta)/I for
single glazed solar air heater at different air flow rates for summer
season
IX
16
Fig 3.7 (b) Instantaneous Thermal Efficiency versus (To-Ta)/I for
double glazed solar air heater at different air flow rates for summer
season
16
Fig 3.7 (c) Instantaneous Thermal Efficiency versus (To-Ta)/I for
packed bed solar air heater at different air flow rates for summer
season
16
Fig.3.8 (a) Rise in temperature of air during the day for winter
season at different air flow rates in single glazed solar air heater
17
Fig.3.8 (b) Rise in temperature of air during the day for winter
season at different air flow rates in double glazed solar air heater
18
Fig.3.8 (c) Rise in temperature of air during the day for winter
season at different air flow rates in packed bed solar air heater
18
Fig.3.9 (a) Thermal Efficiency for single glazing solar air heater
during the day for winter season at different air flow rates
19
Fig.3.9 (b) Thermal Efficiency for double glazing solar air heater
during the day for winter season at different air flow rates
19
Fig.3.9 (c) Thermal Efficiency for packed bed solar air heater during
the day for winter season at different air flow rates
19
Fig. 3.10 (a) Instantaneous Thermal Efficiency versus (To-Ta)/I for
single glazed solar air heater at different air flow rates for winter
season
20
Fig. 3.10 (b) Instantaneous Thermal Efficiency versus (To-Ta)/I for
double glazed solar air heater at different air flow rates for winter
season
21
Fig. 3.10 (c) Instantaneous Thermal Efficiency versus (To-Ta)/I for
packed bed solar air heater at different air flow rates for winter
season
21
Fig.3.11 Variation of ambient temperature, solar radiation intensity on
aperture and outlet temperature in all three solar air heater for summer
season
22
Fig.3.12 Variation of ambient temperature, solar radiation intensity on
aperture and outlet temperature in all three solar air heater for winter
season
22
Fig 4.1 Absorber Plate Shapes 25
Fig.4.2 Energy Balance 26
Fig.4.3 Reynolds numbers vs Nusselt number 28
Fig.4.4 Reynolds numbers vs Friction factor 29
Fig.4.5 Reynolds numbers vs Thermo hydraulic performance 29

LIST OF TABLE
LIST OF TABLE PAGE NO
Table 1 Uncertainty in measurement of various equipment used
during experimentation.
X
9
Table 2 The average efficiency of each solar air heater during period
11:00–13:00 in summer and winter seasons for each flow rate.
15
Table 3 Heat removal factor based on air outlet temperature (Fo),
heat removal factor based on air inlet temperature (FR) and collector
efficiency factor (F0) for the three solar air heaters in summer and
winter season.
17
Table 4 Details of the cost (US$/m2) (material and fabrication cost)
of single glazed, double-glazed and packed bed solar air heaters.
23
Table 5 The Energy gain kJ/US$ of each solar air heater during
period 11:00–13:00 in summer and winter seasons for each flow rate.
23
Table 6 Observation Table 28

NOMENCLATURE
XI
Lower Cost Solar Air Heater
A aperture area of solar air heater (m2)
Cp specific heat of air (J/kg-_C)
Cd empirical-discharge coefficient (dimensionless)
d orifice diameter (m)
I solar radiation intensity (W/m2)
m mass flow rate of air (kg/s)
P1 upstream pressure of orifice plate (mm of water)
P2 downstream pressure of orifice plate (mm of water)
Ts stagnation temperature (0C)
Ta ambient temperature (0C)
To temperature of air at the outlet of solar air heater (0C)
Ti temperature of air at the inlet of solar air heater (0C)
UL overall heat loss coefficient (W/m2 K)
Gth thermal efficiency of the solar air heater (%)
FR collector heat removal factor depending on air inlet temperature (dimensionless)
Fo collector heat removal factor depending on air outlet temperature (dimensionless)
s transmissivity of glazing (dimensionless)
a absorptivity (dimensionless)
Wxi uncertainty in measurement of independent variable xi
WR uncertainty in result R

1
CHAPTER 1
Introduction
1.1 Overview Of Solar Energy
Solar power is energy from the sun and without its presence all life on earth would end. Solar
energy has been looked upon as a serious source of energy for many years because of the vast
amounts of energy that are made freely available, if harnessed by modern technology.
As shown in fig1.1,simple example of the power of the sun can be seen by using a
magnifying glass to focus the sun’s rays on a piece of paper. Before long the paper ignites
into flames.
Fig.1.1 Power Of The Sun[1]
The simplest and the most efficient way to utilize solar energy are to convert it into thermal
energy for heating applications. The most important and basic components of the system
required for conversion of solar energy into thermal energy are called solar collector.
1.2 Advantages[1]
1. Solar energy is free although there is a cost in the building of ‘collectors’ and other
equipment required to convert solar energy into electricity or hot water.
2. Solar energy does not cause pollution. However, solar collectors and other associated
equipment / machines are manufactured in factories that in turn cause some pollution.
3. Solar energy can be used in remote areas where it is too expensive to extend the electricity
power grid.
4. Many everyday items such as calculators and other low power consuming devices can be
powered by solar energy effectively.
5. It is estimated that the world’s oil reserves will last for 30 to 40 years. On the other hand,
solar energy is infinite (forever).
1.3 Disadvantages[1]
1. Solar energy can only be harnessed when it is daytime and sunny.
2. Solar collectors, panels and cells are relatively expensive to manufacture although prices
are falling rapidly.

3. Solar power stations can be built but they do not match the power output of similar sized
conventional power stations. They are also very expensive.
4. In countries such as the UK, the unreliable climate means that solar energy is also
unreliable as a source of energy. Cloudy skies reduce its effectiveness.
5. Large areas of land are required to capture the suns energy. Collectors are usually arranged
together especially when electricity is to be produced and used in the same location.
6. Solar power is used to charge batteries so that solar powered devices can be used at night.
However, the batteries are large and heavy and need storage space. They also need replacing
from time to time.
1.4 Solar Air Heating[1,7]
As the name suggests, Solar Air Heating is the conversion of solar radiation to thermal heat.
The thermal heat is absorbed and carried by air which is delivered to a living or working
space. The transparent property of air means that it does not directly absorb effective amounts
of solar radiation, so an intermediate process is required to make this energy transfer possible
and deliver the heated air into a living space. The technologies designed to facilitate this
process are known as Solar Air Heaters.
Solar Air Heaters operate on some of the most fundamental and simple thermodynamic
principles:
Fig.1.2 Basic of Solar Air Heater
Absorption of the solar radiation by a solid body results in the body heating up. In broad
terms this solid body is known as the 'collector'. Some bodies are better at absorption than
others, such as those with black non-reflective surfaces.
Convection of heat from the heated solid body to the air as it passes over the surface.
Typically a fan is used to force the air across the heated body, the fan can be solar powered or
mains powered.
Different types of Solar Air Heater Technology achieve this process using the same basic
principles but through the use of different solid bodies acting as the collector. The fan that
transfers the air across the heated surface is also used as part of a ducting system to direct the
heated air into the dwelling space. In addition to heating the air within that space, the heat
can further be absorbed by thermal mass such as walls, flooring, furniture and other contents.
Such heat is effectively 'stored' and slowly dissipates beyond sunlight hours.
1.5 Applications [1,7]
The benefits of Solar Thermal Air are often more than just heating.
2

Fig.1.3 Application
3
1.5.1 Heating
The primary function of a solar air heating system is to provide home heating. The heat
generated is extremely energy efficient and as a result there are several significant benefits:
 a higher level of comfort
 lower power bills
 lower carbon emissions
Space heating accounts for 38% of residential energy usage in Australia, with some states
such as Victoria as high as 55% (hot water accounts for 23%). Although results vary, case
studies have shown some homes to reduce the heating component of their annual energy bills
by around 50%, resulting in a total household reduction of around 20% per annum. The
amount of savings achieved depends on several factors:
 The size and type of Solar Air Heating System installed.
 The size and type of existing conventional heater.
 The habits of the occupants (e.g. thermostat setting).
 The thermal properties of the dwelling (e.g. insulation, draft sealing, size).
 The local climate.
1.5.2 Cooling
Many solar air heating systems can also be used to help cool homes by:
 Transferring cool outside air into the home, especially after sunrise during summer;
and/or
 Expelling hot air out of the roof cavity to reduce the transfer of heat from ceiling to
inside air.
The cooling effect is often likened to an evening breeze bringing in cool air after sunset. The
same fan that is used to transfer warm air into the home for heating can be used to transfer air
via one of the methods above. The same ducting and thermostat control used to control the
heating system can also be utilized, often with no or very little additional hardware.
1.5.3 Ventilation & Moisture Control
Modern Australian homes are designed and built to seal tight to minimize the amount of heat
loss (or heat gain in summer) for the purpose of energy efficiency. While this helps with

heating and cooling bills, it can also introduce humidity related problems as it restricts the
amount of fresh air entering the dwelling. Moisture from showers, cooking and even
breathing can become trapped and lead to condensation on internal surfaces and mound.
4
1.5.4 Filtration
Many Solar Thermal Air systems incorporate a high grade air filter to ensure that not only is
the incoming air fresh, but well filtered from dust, pollen and larger particles from wood fires
and transport emissions. The majority of the air enters the house in this controlled manner,
rather than entering randomly through windows and doors.
1.6 Saving With Solar Air Heater[7]
Case studies and university investigations have shown installations to reduce the reliance on
conventional heating & cooling systems by over 50%. Naturally results do vary depending
on the local climate, size & type of system installed, size & type of existing heating/cooling,
size of dwelling and the thermal properties of the house (insulation, draft protection).

5
CHAPTER 2
Literature review
2.1 Introduction
Solar energy striking the collector(s) passes through the high-transmittance solar glazing and
heats the highly efficient absorber plate. When there is heat available in the collector(s) and
the building requires heat, simple controls automatically activate the fan. The fan moves air
through the collector(s), where it is heated, and then redistributed to the building using
conventional, off-the-shelf, HVAC ducting and air handling equipment.
Fig.2.1 Simple Solar Air Heater[7]
Check valves prevent reverse thermo-siphoning and uncalled-for heat, so you get clean, free,
solar heat only when you want. Solar air heat is often the most efficient and cost competitive
solar technology available in colder climates, saving clients many thousands of dollars and
eliminating toxic emissions.
2.2 Principle[5]
A conventional solar air heater is essentially a flat plate collector with an absorber plate. It is
a transparent cover system at the top and insulation at the bottom and on the sides. The whole
assembly is enclosed in a sheet metal container.
As shown in fig.2.2 cold air of inside home is drawn by fan in to duct which is covered by
solar collector. The heat absorbing by solar collector is transfer to the air in duct and so air

become warm. Warm air has low density as compare to cold air so it flow to upward and thus
natural convection current is being set. Air has low co-efficient of heat convection so for
increasing velocity blower is used.
Fig.2.2 Principle[7]
6
2.3 Types of Solar Air Heater
2.3.1.Porous Type
Fig.2.3 Porous [5]

It has porous absorber which may include slit and expanded metal, overlapped glass plate
absorber.
7
2.3.2 Non-Porous Type
Fig.2.4 Non-Porous [5]
In this type air does not passing through below the absorber plate but air may flow above the
plate.

8
CHAPTER 3
Low Cost Solar Air Heater
3.1 Introduction
Two low cost solar air heaters viz. single glazed and double glazed were designed, fabricated
and tested. Thermo Cole, ultraviolet stabilised plastic sheet, etc. were used for fabrication to
reduce the fabrication cost. These were tested simultaneously at no load and with load both in
summer and winter seasons along with packed bed solar air heater using iron chips for
absorption of radiation. The initial costs of single glazed and double glazed are 22.8% and
26.8% of the initial cost of packed bed solar air heater of the same aperture area. It was found
that on a given day at no load, the maximum stagnation temperatures of single glazed and
double glazed solar air heater were 43.5 C and 62.5 C respectively. The efficiencies of
Single glazed, double glazed and packed bed solar air heaters corresponding to flow rate of
0.02 m3/ s-m2 were 30.29%, 45.05% and 71.68% respectively in winter season. The collector
efficiency factor, heat removal factor based on air outlet temperature and air inlet temperature
for three solar air heaters were also determined.
3.2. Experimentation
3.2.1 General
An experimental set up was constructed and tested in Punjab Agricultural University,
Ludhiana (310 N), India. The experiments were conducted at no load and with load in both
summer and winter seasons to do the thermal analysis and to compare the performance
of these three solar air heaters.
Fig. 3.1 single glazed solar air heater.[6]
Fig. 3.2 double glazed solar air heater.[6]

3.2.2 Test at no load
The test set-up comprises of single glazed solar air heater, double glazed solar air heater and
conventional packed bed solar air heater. Solar irradiation on the aperture of the solar air
heaters, ambient temperature and stagnation temperature in the solar air heaters was recorded
after every half an hour. The values of overall heat loss coefficient was calculated every half
an hour from 11:00 to 14:00 by using the following equation:
I(ατ) = UL(Ts-Ta)
The transmissivity of glazing of single glazed, double glazed and packed bed solar air heater
was 0.86,
3.3.3 Test with load
A photograph and schematic diagram of experimental set up are shown in Fig.3.3 (a) and (b)
respectively. The test set-up comprises of single glazed solar air heater, double glazed solar
air heater, conventional packed bed solar air heater, electric blower, orifice meters, gate
valves and pipe network. To control and measure the flow rate of air in each solar air heater,
valve and orifice meter are installed after each solar air heater. Electric blower is used to pass
the air in solar air heaters.
Tests were conducted during summer and winter under normal weather conditions. Ambient
temperature and temperatures at outlet of each solar air heaters were recorded for each flow
rate. Ambient air was sucked into the solar air heaters, so the inlet air temperature was taken
equal to ambient temperature. Solar radiation intensity on the aperture was recorded with the
Silicon pyranometer by placing it adjacent to the glazing cover of solar air heater, in the same
plane i.e. facing due south.
All these observations were recorded every half an hour during the day for each flow rate.
All the tests started at 10:30 and ended at 14:30. Observations were started after 30 min when
solar air heater reached steady state condition.
Wind speed data for the experimental days was recorded from the Department of Agricultural
Meteorology, Punjab Agricultural University, Ludhiana, India. The instantaneous thermal
efficiency of solar air heaters was calculated from the experimental data for each flow rate
from the daytime measurements between 11:00 and 13:00, using following relation:
Solar air heater performance parameters viz. heat removal factor depending on air outlet
temperature (Fo), heat removal factor depending on air inlet temperature (FR) and collector
efficiency factor (F0) were also determined. These parameters depend on construction
materials, flow conditions and design type of the collector. The instantaneous thermal
efficiency of a solar air heater, in which useful energy is expressed in the form of the energy
gain by the absorber and energy lost from the absorber, can be expressed as
9

Fig.3.3 (a) experimental set-up [2]
Fig.3.3 (b) schematic of experimental set-up [2]
10
3.3 Results And Discussion
3.3.1. Test At No Load
Fig.3.4 shows the variation in ambient temperature, solar radiation intensity and stagnation
temperature in the single glazed, double glazed and packed bed solar air heaters, respectively,
during the day.

Fig.3.4 (a) Variation of ambient temperature, solar radiation intensity on aperture and
Stagnation temperature during the day at no load in single glazing solar air heater[2]
Fig.3.4(b) Variation of ambient temperature, solar radiation intensity on aperture and
Stagnation temperature during the day at no load in double glazing solar air heater[2]
Fig.3.4 (c) Variation of ambient temperature, solar radiation intensity on aperture and
Stagnation temperature during the day at no load in packed bed solar air heater[2]
11

The maximum stagnation temperature achieved for single glazed, double glazed and packed
bed solar air heaters was 43.50C, 62.50C and 85.70C respectively. The corresponding values
of solar radiation and ambient temperature were 740 W/m2 and 19 0C respectively for single
glazed and double glazed solar air heaters and 560 W/m2 and 35 0C respectively for packed
bed solar air heater.
The overall heat loss coefficients of solar air heaters based on aperture area were calculated
by putting the experimental data given in Fig.3.5 into Eq. (1). The values of overall heat loss
coefficient varied from 23.38 to 28.75 W/m2*K for single glazed,11.23 - 14.68 W/m2*K for
double glazed solar air heater and 7.55-9.60 W/m2*K for packed bed solar air heater.
Therefore the average overall heat loss coefficient of single glazed solar air heater, double
glazed solar air heater and packed bed solar air heater is 25.66 W/m2*K,12.33 W/m2*K and
7.97 W/m2*K respectively.
12
3.3.2 Test with Load
3.3.2.1 Results of Testing During Summer Season
3.3.2.1(A) Rise in Temperature
The curves for rise in air temperature from inlet to outlet of each solar air heater for each flow
rate are plotted in Fig.3.5. The maximum rise in air temperature in single glazed solar air
heater and double glazed solar air heater was found to be 18 0C and 12 0C, respectively, for
flow rate of 0.020 m3/s per m2 aperture area while maximum rise in temperature in packed
bed solar air heater was 35 0C, for flow rate of 0.011 m3/s per m2 aperture area.
Fig 3.5(a) Rise in temperature of air during the day for summer
Season at different air flow rates in single glazing solar air heater[2]

Fig 3.5 (b) Rise in temperature of air during the day for summer
Season at different air flow rates in double glazing solar air heater[2]
Fig 3.5(c) Rise in temperature of air during the day for summer
Season at different air flow rates in packed bed solar air heater[2]
It was observed that as the air flow rate increased the rise in air temperature from inlet to
outlet increased in case of single and double glazed solar air heaters whereas it decreased in
case of packed bed solar air heaters. This is so because in flat plate absorber, convective heat
transfer coefficient increases with increase in flow rate thereby increasing the heat gain of the
air. While in case of packed bed absorber turbulence is created even at low air flow velocity
resulting in increased value of convective heat transfer coefficient. So increase in velocity
does not result in increase in convective heat transfer coefficient. Hence heat gain does not
increase and temperature of outlet air decreases.
3.3.2.1(B) Thermal Efficiency
The thermal efficiency of the each solar air heater during day for each flow rate is shown in
Fig. 3.6 The maximum efficiency of single glazed, double glazed and packed bed solar air
heater was 37.45%, 24.07% and 66.23%, respectively, for the flow rate of 0.020 m3/s per m2
aperture area.
An increase in efficiency with increase in flow rate was observed in all solar air heaters
because of changes in flow conditions [8,9]. Table 2 shows the average efficiency of each air
heater during the period 11:00–13:00 for each flow rate. The maximum average efficiency
was observed in packed bed solar air heater for each flow rate because of better heat transfer
and lesser thermal losses [9,10].
13

Fig 3.6(a) Thermal Efficiency for three solar air heaters during the day for summer
Fig 3.6 (b) Thermal Efficiency for three solar air heaters during the day for summer
Fig 3.6(c) Thermal Efficiency for three solar air heaters during the day for summer
Season at different air flow rates in packed bed solar air heater[2]
14

During period 11:00–13:00, the maximum average efficiency in packed bed solar air heater
was 50.30, 56.20, 64.56 and 66.23 for the flow rate of 0.011, 0.014, 0.017 and 0.020 m3/s per
m2 aperture area respectively.
It is observed that for all flow rates, the efficiency of single glazed solar air heater is more
than double glazed solar air heater as single glazing allows more radiation to pass than double
glazing and due to higher temperature in summer there is not much reduction in heat loss.
The average thermal efficiency of single glazed solar air heater for 17.5 0C temperature rise
was found to be 37.5%, and it was 24.0% for 11 0C temperature rise in double glazed solar air
heater.
Whereas for previous designs of low cost solar air heaters i.e. black porous textile absorber
solar air heater and plastic wrapping film with air bubbles solar air heater, the thermal
efficiency was 18% and 12.5%, respectively for air temperature rise of 10 0C. This indicates
that with the present low cost solar air heater higher efficiency can be achieved even for
higher air temperature rise.
3.3.2.1(C) Instantaneous Thermal Efficiency
The instantaneous thermal efficiency at noon as a function of temperature parameter (To-
Ta)/I for the three solar air heaters at different flow rates are shown in Fig.3.7. The empirical
relations and regression coefficient of the best fit line are also shown in Fig.3.7. The scatter
of the data around the straight line is mainly attributed to wind speed and the dependence of
the heat loss on the data are to be expected [8,9]. It can be seen from Fig.3.7 that the thermal
efficiency increases with increase in air mass flow rate as was discussed earlier in Fig.3.7
[8,9]. It can also be seen that the thermal efficiency decreases with increase in temperature
parameter (To-Ta)/I. This is because increase in temperature parameter causes increase in
absorber temperature that causes increase in heat losses hence decrease in efficiency
15

Fig 3.7 (a) Plot of instantaneous thermal efficiency versus (To-Ta)/I for single glazed solar
air heater at different air flow rates for summer season[2]
Fig 3.7 (b) Plot of instantaneous thermal efficiency versus (To-Ta)/I for double glazed solar
air heater at different air flow rates for summer season[2]
Fig 3.7 (c) Plot of instantaneous thermal efficiency versus (To-Ta)/I for Packed bed solar air
heater at different air flow rates for summer season[2]
16

The heat removal factor based on air outlet temperature (Fo), heat removal factor based on air
inlet temperature (FR) and collector efficiency factor (F0) computed from Fig.3.7
respectively for each solar air heater are given in Table 3.
The value of FR, FO and F0 for packed bed solar air heater was the highest followed by
single glazed solar air heater and double glazed solar air heater. These results shows that the
packed bed is most efficient solar air heater due to higher heat removal factor mainly because
of better heat transfer between air and packing material (iron chips) in the packed bed solar
air heater, which eventually reduced heat losses [8].
3.3.2.2. Results of testing during winter season
3.3.2.2(A) Rise in Temperature
The curves for rise in air temperature from inlet to outlet of each solar air heater for each flow
rate are shown in Fig.3.8. The maximum rise in air temperature in single glazed, double
glazed and packed bed solar air heater was observed to be 19.5 0C, 33.5 0C and 50.5 0C
respectively at flow rate of 0.011 m3/s per m2 aperture area.
Fig3.8 (a) Rise in temperature of air during the day for summer
season at different air flow rates in single glazed solar air heater[2]
17

Fig.3.8 (b) Rise in temperature of air during the day for winter
season at different air flow rates in double glazed solar air heater[2]
Fig3.8 (c) Rise in temperature of air during the day for winter
season at different air flow rates in packed bed solar air heater[2]
It was observed that as the air flow rate decreased the rise in air temperature in single glazed,
double glazed and packed bed solar air heaters increased.
3.2.1.2(B) Thermal Efficiency
The thermal efficiency of the each solar air heater during day for each flow rate is shown in
Fig.3.9. The maximum average efficiency of single glazed, double glazed and packed bed
solar air heater was 30.29, 45.05 and 71.68%, respectively, for the flow rate of 0.020 m3/s per
m2 aperture area. An increase in efficiency with increase in flow rate was observed in all
solar air heaters due to change in flow conditions [8,9].
18

Fig.3.9 (a) Thermal Efficiency for single glazing solar air heater during the day for winter
season at different air flow rates[2]
Fig.3.9 (b) Thermal Efficiency for double glazing solar air heater during the day for winter
Fig.3.9 (c) Thermal Efficiency for packed bed solar air heater during the day for winter
19

Table 2 shows the average efficiency of each solar air heater during the period 11:00–13:00
for each flow rate. The maximum average efficiency was observed in packed bed solar air
heater for each flow rate because of better heat transfer and lesser thermal losses [8,10].
During period 11:00–13:00, the maximum average efficiency in packed bed solar air heater
was 60.46%, 62.02%, 66.21% and 71.68% for the flow rate of 0.011, 0.014, 0.017 and 0.020
m3/s per m2 aperture area respectively. It is observed that during winter for all flow rates, the
efficiency of double glazed solar air heater is more than single glazed solar air heater because
reduction in input is less than saving in heat loss due to lower ambient temperature in winter.
There is change in trend of air temperature rise in single and double glazed solar air heaters
during summer and winter season. This is so because due to increase in air flow rates the
value of convective heat transfer coefficient from absorber increases resulting in more heat
gain by air irrespective of season. Simultaneously, the hot air flowing in the air heater loses
heat to the ambient. This heat loss is more in winter than in summer. Hence during summer
heat gain due to higher convective heat transfer coefficient is predominant while during
winter heat loss from hot air to ambient becomes predominant.
The thermal efficiency was found to be 30.9% for 12.5 0C temperature rise for single glazed
solar air heater. Whereas for double glazed solar air heater the thermal efficiency was 45.1%
for 18 0C temperature rise. These efficiency values are higher than the earlier low cost solar
air heaters [11].
3.3.2.2(C) Instantaneous Thermal Efficiency
In Fig.3.10 the plots of instantaneous thermal efficiency at noon as a function of temperature
parameter (To-Ta)/I for the three solar air heaters at different flow rates are shown. The
trends of variation in thermal efficiency with temperature parameter and flow rate were found
to be similar to that of summer season as seen in Fig.3.6
Fig. 3.10 (a) Plot of instantaneous thermal efficiency versus (To-Ta)/I for single glazed solar
air heater at different air flow rates for winter season[2]
20

Fig. 3.10 (b) Plot of instantaneous thermal efficiency versus (To-Ta)/I for double glazed solar
Fig. 3.10 (c) Plot of instantaneous thermal efficiency versus (To-Ta)/I for Packed bed solar
For winter season, the heat removal factor based on air outlet temperature (Fo), heat removal
factor based on air inlet temperature (FR) and collector efficiency factor (F0) for each solar
air heater are given in Table 3. The values of FR, FO and F0 for packed bed solar air heater
were highest followed by double glazed solar air heater and single glazed solar air heater.
The variation of ambient temperature, solar radiation intensity on aperture and outlet
temperature in single glazed solar air heater, double glazed solar air heater and packed bed
solar air heater for a typical day of summer and winter season at flow rate of 0.011 m3/s per
m3 aperture area are shown in Figs.3.11 and 3.12 respectively.
21

Fig.3.11 Variation of ambient temperature, solar radiation intensity on aperture and outlet
temperature in all three solar air heater for day of summer season at flow rates of 0.011 m3/s
per m2 aperture area.[2]
Fig.3.12 Variation of ambient temperature, solar radiation intensity on aperture and outlet
temperature in all three solar air heater for a typical day of winter season at flow rates of
0.011 m3/s per m2 aperture area.[2]
3.3.3 Comparison of solar air heaters based on energy per unit cost
To compare the thermal performance of solar air heaters, their average thermal efficiencies
between 11:00 and 13:00 were calculated and compared in summer and winter seasons for
each flow rate. The ratio of average thermal efficiency of single glazed solar air heater to
packed bed solar air heater and double glazed solar air heater to packed bed solar air heater
during period 11:00–13:00 in summer and winter seasons for each flow rate are shown in
Table 2. The ratio of average thermal efficiency remains almost constant at all the flow rates
for both the solar air heaters. The ratio of average thermal efficiency of single glazed solar air
heater to packed bed solar air heater for summer and winter seasons are 0.5 and 0.4
22

respectively, and the ratio of average thermal efficiency of double glazed solar air heater to
packed bed solar air heater for summer and winter seasons are 0.33 and 0.65 respectively.
The cost of single glazed solar air heater, double glazed solar air heater and packed bed solar
air heater is estimated. The bill of material of these solar air heaters are given in Table 4. The
capital cost of single glazed, double glazed and packed bed solar air heater turns out to be
27.34, 32.11 and 120.00 respectively.
The energy gain kJ per US$ of each solar air heater during period 11:00–13:00 in summer
and winter seasons for each flow rate are given in Table 5. Energy gain kJ/US$ for both
single glazed solar air heater and double glazed solar air heater is more than packed bed solar
air heater.
Thus, for the same money spent, low cost solar air heaters collect more energy than packed
bed solar air heater. This shows that one can install large area of single/double glazed solar
air heaters to get the same energy output as of packed bed solar air heater at a lesser cost than
packed bed solar air heater. Other advantage of low cost solar air heater is that single person
can easily carry these due to its light weight and these can be stored indoor during off-season.
3.4 Conclusions[2]
Single glazed low cost solar air heater gives better thermal efficiency during summer while
double glazing is better during winter for all flow rates. For flow rate of 0.020 m3/s per m2
aperture area, the maximum average thermal efficiency was 37.45% for single glazed and
24.07% for double glazed solar air heater during summer. Corresponding figures for winter
were 30.29% and 45.05% respectively.
23

For flow rate of 0.020 m3/s per m2 aperture area, the maximum rise in air temperature was
180C for single glazed and 12 0C for double glazed solar air heater during summer.
Corresponding figures for winter were 19.50C and 33.50C respectively.
The heat removal factor based on air outlet temperature (Fo), heat removal factor based on air
inlet temperature (FR) and collector efficiency factor (F0) were found to be higher for packed
bed solar air heater as compared to single and double glazed solar air heaters for summer as
well as winter season. These factors for single glazed solar air heater were more during
summer, whereas in winter values of double glazed solar air heater were more.
For the same initial investment, low cost solar air heaters collect more energy than packed
bed solar air heater. For flow rate of 0.020 m3/s per m2 aperture area, the solar energy gain
per unit investment was 0.13 kJ per US$ for single glazed, 0.10 kJ per US$ for double glazed
and 0.03 kJ per US$ for packed bed solar air heater during summer. Corresponding figures
for winter were 0.08 kJ per US$, 0.07 kJ per US$ and 0.02 kJ per US$ respectively.
24

25
CHAPTER 4
EFFICIENCY IMPROVEMENT BY ARTIFICIAL ROUGHNESS
4.1 General
It is well known, that, the heat transfer coefficient between the absorber plate and working
fluid of solar air heater is low. It is attributed to the formation of a very thin boundary layer
at the absorber plate surface commonly known as viscous sub-layer The heat transfer
coefficient of a solar air heater duct can be increased by providing artificial roughness on the
heated wall (i.e. the absorber plate) The use of artificial roughness on the underside of the
absorber plate disturbs the viscous sub-layer of the flowing medium. It is well known that in
a turbulent flow a sub-layer exists in the flow in addition to the turbulent core. The purpose
of the artificial roughness is to make the flow turbulent adjacent to the wall in the sub-layer
region. Experiments were performed to collect heat transfer and friction data for forced
convection flow of air in solar air heater rectangular duct with one broad wall roughened by
discrete v –groove & v- shape ribs. The range of parameters used in this experiment has been
decided on the basis of practical considerations of the system and operating conditions. The
range of Reynolds number of 3000-14000, Relative Roughness Height ( eh/D ) of height
0.030 to 0.035, Rib angle of attack 600, heat flux 720 W/m2 and pitch of relative roughness
pitch 10 the Result has been compared with smooth duct under similar flow and boundary
condition It is found from the investigation that on increasing the roughness of a roughened
plate the friction factor and heat transfer performance of solar air heater increase and the rate
of increase of heat transfer performance of solar air heater get reduced as the roughness of
plate increases.
4.2 Effective technique to enhance the rate of heat transfer
• The Thermal efficiency of solar air heater has been found to be poor.
• The reason behind it is low heat transfer capability between the absorber and air
flowing in the duct.
• So, by providing the artificial roughness on the underside of the absorber plate the
heat transfer coefficient
Fig 4.1 Absorber Plate Shapes[3]
A conventional solar air heater generally consists of an absorber plate with a parallel plate
below forming a passage of high aspect ratio through which the air to be heated flows. As in
the case of the liquid flat-plate collector, a transparent cover system is provided above the
absorber plate, while a sheet metal container filled with insulation is 'provided on the bottom
and sides. The arrangement is sketched in fig. 4.1 Two other arrangement, which are not so
common are also shown in fig 4.1 In the arrangement shown in fig 4.1, the air flows between
the cover and absorber plate; as well as through the passage below the
absorber plate.

However, the value of the heat transfer coefficient between the absorber plate and air is low
and this result in lower efficiency. For this reason, the surfaces are sometimes roughened or
longitudinal fins are provided in the airflow passage. A roughness element has been used to
improve the heat transfer coefficient by creating turbulence in the flow. However, it would
also result in increase in friction losses and hence greater power requirements for pumping air
through the duct. In order to keep the friction losses at a low level, the turbulence must be
created only in the region very close to the duct surface, i.e. in laminar sub layer.
4.3 Calculation
Solar air heaters, because of their inherent simplicity, are cheap and most widely used as
collection device. The thermal efficiency of solar air heaters has been found to be generally
poor because of their inherently low heat transfer capability between the absorber plate and
air flowing in the duct. In order to make the solar air heaters economically viable, their
thermal efficiency needs to be improved by enhancing the heat transfer coefficient. In order
to attain higher heat transfer coefficient, the laminar sub-layer formed in the vicinity of the
absorber plate is broken and the flow at the heat-transferring surface is made turbulent by
introducing artificial roughness on the surface.
Fig.4.2 Energy Balance[4]
The useful heat gain of the air is calculated as: Qu = m’Cp ( Tfo - Tfi) (4.1)
The heat transfer coefficient for the test section is: h = Qu/A ( Tpm - Tfm ) (4.2)
Where,
Tpm is the average value of the heater surface temperatures,
Tfm is the average air temperature in the duct = (Tfi + Tf0)/2
The Nusselt number: Nu = h Dh / Kair (4.3)
Where,
Dh is hydraulic mean diameter of test duct
h is convective heat transfer coefficient
Kair is thermal conductivity of air
The friction factor was determined from the measured values of pressure drop across the
test length: f =( ΔP)Dh/(2ρairLV2
26
air) (4.4)
Where,
ΔP is pressure drop in the test duct
ρ is density of air
L is test duct length
V air is average velocity of air
Thermal Performance (overall enhancement ratio) (Nur/Nus)/ (fr/fs) 1/3 (4.5)
Mean Air & Plate Temperature
Tile mean air temperature or average flow temperature flow is the simple arithmetic mean of
the measure values at the inlet and exit of the test section.

Thus Tfav = (ti + toav) /2 (4.6)
The mean plate temperature, tpav is the weighted average of the reading of 6 points located on
the absorber plate.
Pressure Drop Calculation
Pressure drop measurement across the orifice plate by using the following relationship:
Po = ρm x h x 9.81 x 1 (4.7)
Where,
Po = Pressure diff.
ρm = Density of the fluid (kerosene) i.e. 0.8x103
h = Difference of liquid head in U-tube manometer, m
Mass Flow Measurement
Mass flow rate of air has been determined from pressure drop measurement across the orifice
plate by using the following relationship: m = Cd x A0 x [2 ρ0 / (1 - 4)] (0.5) (4.8)
Where
m = Mass flow rate, kg / sec.
Cd = Coefficient of discharge of orifice i.e. 0.62
A0 = Area of orifice plate, m2
ρ0 = Density of air in Kg/m3
r = Ratio of dia. (do / dp) i.e. 26.5/53 = 0.5
Velocity Measurement
V=m/ρWH
Where,
m = Mass flow rate, kg / sec3
H = Height of the duct in m
W= Width of the duct, m
ρ =Density of the air kg / m3
Reynolds Number
The Reynolds number for flow of air in the duct is calculated from:
Re
Where,
of air at tfav in m2/sec
Dh = 4WH / 2 (W+H) =0.04444
Heat Transfer Coefficient
Heat transfer rate, Qa to the air is given by: Qa = m cp (t0 – ti) (4.8)
The heat transfer coefficient for the heated test section has been calculated from:
h = Qa / Ap (tpav – tfav) (4.9)
Ap is the heat transfer area assumed to be the corresponding smooth plate area.
Nusselt Number
Tile Heat Transfer Coefficient has been used to determine the Nusselt number defined as;
Nusselt No. (Nu) = h Dh/ K
Where k is the thermal conductivity of the air at the mean air temperature and Dh is the
hydraulic diameter based on entire wetted parameter.
Thermo hydraulic performance
Heat transfer and friction characteristic of the roughened duct shows that enhancement in
heat transfer is , in general , accompanied with friction power penalty due to a corresponding
increase in the friction faceted. Therefore it is essential to determine the geometry that will
result in maximum enhancement in heat transfer with minimum friction penalty. In order to
27

achieve this object of simultaneous consideration of thermal as well hydraulic performance,
i.e. thermo hydraulic performance,
hp = (Nu /Nus) / (fr/fs)1/3 (4.9)
4.4 Experiment
A value of this parameter higher then unity ensure the fruitfulness of using an enhancement
device and can be used to compare the performance of a number of arrangement to decide the
best among these. The value of this parameter for the roughness geometries are investigated.
28
Table 6 Observation[4]
S.
No.
Reynol
ds no.
(Re)
Inlet
tempera
ture of
air (ti)
OC
Average
outlet
Tempera
ture
(toav)
OC
Average
air
temperat
ure (tfav)
OC
Average
plate
temperat
ure (tpav)
OC
Heat
transf
er
Q
(W)
Convectiv
e heat
transfer
coffecient
(h)
W/m2-oK
Nusselt
no.
(Nu)
Friction
Factor
(f)
Thermo
hydraulic
performa
nce
1 5387 34.00 46.00 40.00 72.28 136.8 14.12 22.57 0.032 0.5
2 7604 33.50 44.00 38.75 70.48 169.0 17.75 28.37 0.0275 0.69
3 9315 33.00 42.00 37.50 66.00 178.0 20.81 33.23 0.025 0.853
4 10788 33.00 41.00 37.00 63.00 182.0 23.33 37.26 0.023 1.0
5 12051 32.00 39.50 36.00 61.20 191.3 25.26 40.37 0.022 1.1
6 13211 31.50 39.00 35.2 60.00 209.0 27.80 44.40 0.021 1.07
4.5 Experimental Results
The effect of various flow and roughness parameters on heat transfer characteristics for flow
of air in rectangular ducts of different relative roughness height in the present investigation
are discussed below. Results have also been compared with those of smooth ducts under
similar flow and geometrical conditions to see the enhancement in heat transfer coefficient.
Fig.4.3 Reynolds numbers vs Nusselt number[4]

Figure shows the values of Nusselt Number increases with increases in Reynolds Numbers
because it is nothing but the ratio of conductive resistance to convective resistance of heat
flow and as Reynolds Number increases thickness of boundary layer decreases and hence
convective resistance decreases which in turn increase the Nusselt Number.
Fig.4.4 Reynolds numbers vs Friction factor[4]
Figure shows the plots of experimental values of the friction factor as the function of
Reynolds number for smooth plate and rough surface. It is clear that Value of friction factor
drop proportionally as the Reynolds number increases due to the suppression of viscous sub-layer
29
with increase in Reynolds number.
Fig.4.5 Reynolds numbers vs Thermo hydraulic performance[4]
Figure shows as Reynolds No. increases Thermo hydraulic performance also increases and it
is max. for v groove plate and minimum for smooth plate.

SUMMERY
For the same initial investment, low cost solar air heaters collect more energy than packed
bed solar air heater.
In the entire range of Reynolds number, it is found that the Nusselt Number increases, attains
a maximum value for v groove roughened plate and increases with increasing roughness
geometry.
On increasing the roughness on the plate the friction factor also increase.
The value of the friction factor reduces sharply at low Reynolds Number and then decrease
very slightly in comparison to low Reynolds Number.
The experimental values of the heat transfer of the v groove Roughness absorber plate has
been compared with smooth plate. The plate having Roughness geometry v groove, gives the
maximum heat transfer
30

REFRENCES
1. The Solar Thermal Air Heating and Cooling Association (STA),
31
http://solarairheating.org.au/
2. R.S. Gill, Sukhmeet Singh, Parm Pal Singh, Low cost solar air heater, Energy
Conversion and Management,2012
3. M.K. Mittala, Varuna, R.P. Saini, S.K. Singal, Effective efficiency of solar air heaters
having different types of roughness elements on the absorber plate, Elsevier, Energy 32
(2007) 739–745, September 2005
4. Manash Dey Effect of Artificial Roughness on Solar Air Heater: An Experimental
Investigation, Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-
Oct 2013, pp.88-95
5. Sukhatme S.P., "Solar Energy: Principles of Thermal Collections and Storage", Tata
McGraw-Hill, New Delhi 2003.
6. Rai G.D., "Non-Conventional Energy Sources ", Khanna Publishers Delhi,1999
7. RREA Rural Renewable Energy Alliance,www.rreal.org
8. Akpinar Ebru Kavak, Kocyigit Fatih. Energy and exergy analysis of a new flatplate solar
air heater having different obstacles on absorber plates. Appl Energy 2010;87:3438–50.
9. Akpinar Ebru Kavak, Kocyig˘it Fatih. Experimental investigation of thermal performance
of solar air heater having different obstacles on absorber plates. Int Commun Heat Mass
Transfer 2010;37:416–21.
10. Ramadan MRI, El-Sebaii AA, Aboul-Enein S, El-Bialy E. Thermal performance of a
packed bed double-pass solar air heater. Energy 2007;32:1524–35.
11. Bansal NK, Uhlemann R. Development and testing of low cost solar energy collectors for
heating air. Sol Energy 1984;33:197–208

Report on Solar Air heater by Hardik Ramani

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Report on Solar Air heater by Hardik Ramani

Similar to Report on Solar Air heater by Hardik Ramani (20)

Recently uploaded

Recently uploaded (20)

Report on Solar Air heater by Hardik Ramani