solar air heater

A Seminar on Advances in Solar Air Heater 1

Prepared by,Hardik V. Ramani

13 MMET 16M. Tech Mechanical Engineering

(Thermal Engineering)

Guided by,Prof. S. V. Jain

Department of Mechanical Engineering Nirma University

Advances in Solar Air Heater

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Power of Sun [1]

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SOLAR AIR HEATER [12]

Location: At some where in Canada

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Content..

• Principle• Application• Types• Low Cost Solar Air Heater• Effective Solar Air Heater by Roughness • Summery• References

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Principle [7]

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Description

• 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.

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Weather cladding– Reduced heat loss

through wall

– Better air quality

SAH systems provide..[12]

School, Yellowknife, Canada

Solar Collector

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Examples: Canada and USA [12]

Ventilation Air Heating Systems

• Improved air quality at low cost

• Size ranges from a few m2 to 10,000 m2

• Ducts should be located near south wall

• Paybacks of 2 to 5 years typical

Apartment Building, Ontario, Canada

Portable Classroom, Ontario, Canada

Brown Collector on Industrial Building, Connecticut, USA

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Example: Indonesia [12]

Process Heat Systems

• Normally constant flow rate systems with very simple controls

• Used for drying crops that are harvested throughout the year

Tea Drying Shelter, West Java, Indonesia

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Application

• SAH provides ventilation and process air heating

• Locations throughout world have solar energy available with out any cost.

• SAH serves as weather cladding and feeds into conventional ventilation systems

• Efficiency and cost are the biggest barriers for any solar product.

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Types of Solar Air Heater [7]

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Non-Porous [5]

In this type air does not passing through below the absorber plate but air may flow above the plate.

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Porous Type [5]

It has porous absorber which may include slit and expanded metal, overlapped glass plate absorber.

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Advanced

Solar Air Heaters

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1.Low Cost Solar Air Heater [2]

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General

• Two low cost solar air heaters viz. single glazed and double glazed were designed, fabricated and tested.

• Thermocole, ultraviolet stabilized 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.

• 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.

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Cost Comparison

• Single and Double Glazed Solar Air Heater are low cost.

• Packed Bed Solar Air Heater is comparatively 30% costly than the Single and Double Glazed Solar Air Heater.

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A Seminar on Advances in Solar Air Heater 1802-December-2013


Single Glazed Solar Air Heater

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Double Glazed Solar Air Heater

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Packed Bed Solar Air Heater

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Tested at No Load

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Tested at Load-Rise in Temperature(During Summer Season )

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Tested at Load-Thermal Efficiency(During Summer Season )

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Tested at Load-Rise in Temperature(During Winter Season )

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Tested at Load-Thermal Efficiency(During Winter Season )

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The Efficiency

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The Energy gain for Flow Rate

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The Bill of Material with Cost

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Summery

• Single glazed low cost solar air heater gives better thermal effi-ciency 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.

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• 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.

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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, turbulence increase and heat trnsfer

coefficient also increase.

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CFD Analysis[8]

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2. Effective Solar Air Heater by Improvement in Roughness

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[3]

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• 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.

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• The application of artificial roughness, by using different shapes has been recommended to enhance the heat transfer coefficient by several investigators.

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Types of shapes of Roughness [3]

• V-shaped• Wedge shaped • Expanded metal mesh• Angle circular rib

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Objective of Experiment [4]

• Our objective is to investigate the effect discrete v & v-groove shaped roughness on the absorber plate of solar air heater, on the heat transfer coefficient and friction factor and to compare it with smooth absorber plate to know the actual increase in performance of flat plate solar air collector by using this particular artificial roughness on absorber plate.

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Basic Equation [4]

• The useful heat gain of the air is calculated as:

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Where,m’ is mass flow rate of air through the test duct Cp is specific heat of air Tfo is fluid temperature at exit of test duct

Tfi is fluid temperature at inlet of test duct

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• The heat transfer coefficient for the test section is:

• The Nusselt number is:

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• The friction factor was determined from the measured values of pressure drop across the test length:

• Thermo hydraulic performance hp= (Nu /Nus) / (fr/fs)1/3

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S. Reynolds Inlet Average Average Average Heat Convectiv Nusselt Friction Thermo

No. no. temperatu outlet air plate transfer e heat no. Factor hydraulic

(Re) re of air temperatur temperatu temperat Q (Watt) transfer (Nu) (f) performa

(ti) OC e (toav)

OC re (tfav) OC ure (tpav) coffecient nce

OC (h) W/m2-

oK

1 5387 34.00 46.00 40.00 72.28136.80

14.12 22.57

0.032 0.5

2 7604 33.50 44.00 38.75 70.48169.00

17.75 28.37

0.0275 0.69

3 9315 33.00 42.00 37.50 66.00178.00

20.81 33.230.025 0.853

4 10788 33.00 41.00 37.00 63.00 182.00 23.33 37.26 0.023 1.0

5 12051 32.00 39.50 36.00 61.20 191.30 25.26 40.37 0.022 1.1

6 13211 31.50 39.00 35.2 60.00 209.00 27.80 44.400.021 1.07

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OBSERVATION TABLE [4]


EXPERIMENTAL RESULTS [4]

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SUMMERY

( 1 ) 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.

( 2 )On increasing the roughness on the plate the friction factor also increase.

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( 3 )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

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REFERENCES

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1. The Solar Thermal Air Heating and Cooling Association (STA), 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.

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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

12. Rate Screen International www.ratescreen.com

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THANK YOU…….