Dissertation Report on

“A COMPARATIVE EXPERIMENTAL STUDY OF THERMAL PERFORMANCE OF THREE SOLAR AIR HEATERS HAVING DIFFERENT ABSORBER AREA’’

In partial fulfillment for the award of degree of MASTER OF TECHNOLOGY

In MECHANICAL ENGINEERING

With specialization ENERGY ENGINEERING

Centre of excellence, Solar energy research and utilization

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SURESH GYAN VIHAR UNIVERSITYJAIPUR

BYVIKAS KUMAR

Guided ByMr. HARI KUMAR SINGH

INTRODUCTION 2

Solar air heaters are unique type of heat interchange that absorb and converts solar radiant energy into heat.

The main focus is on the use of Renewable energy.

It is pollution free device and very much environment friendly.

It provide a healthy environment with low cost air heating.

Basically solar air heaters are classified in the following two categories:a. Air heaters with porous absorbers and

b. Air heater with non porous absorber Ceof

solar collector and the cost of equipment is very less as compare to other devices for heating air.

PROBLEM FORMULATION3

In earlier year the entire world has become more and more dependent on fossil fuels such as coal , oil and natural gas.

These resources are limited and it is created by natural processes over millions of years.

The whole world focusing on Shortage of fuel and emphasizes the need for alternate energy sources.

The Solar energy is one of the low cost and easily available energy source in the world.

Solar energy is most pollution-free and limitless source

OBJECTIVE 4 To compare the thermal efficiency of three different solar air heaters, type-

I, type II and type III respectively.

To investigate the effect of mass flow rate in thermal efficiency of solar air heater.

To show aluminum wire mesh and aluminum fins ensure more air flow above and below the absorber plates, generate the turbulence and decrease the dead zones in the collector.

To prove solar air heater as potential device for harnessing energy from the sun.

MATERIALS & METHODS 5Components of solar air heater:The main component of solar air heater are following:-

The casing or containerInsulationAbsorber plateCover plateFan Stand

The casing or container 6 It is made by strong plywood box. The thickness of plywood was 12mm. The internal dimension of box was 1476mm×726mm×186mm

Casing of plywood box

It is made by strong plywood box. The thickness of plywood was 12mm. The internal dimension of box was 147686

Insulation7

The thermo Cole and aluminum sheet were used (Scientific name Polystyrene) for insulating the plywood box from sides and bottom.

The insulation is necessary for the solar air heater for minimizing the heat loss from sides and bottom of the collector box.

Thermo Cole for insulation

Absorber plate8

The aluminum sheet of 22 gauge thickness were used for absorber plate.

The sheet was painted by black dark rubber coating for absorbing heat and provides durability.

absorber plate before coated absorber plate after coated

Cover plate 9 The two normal transparent window glass cover of 5 mm thickness were

used for cover plate. The length of glass cover was 1474 mm and width was 723 mm so that it

could sit over container box. Thermal conductivity of glass is 0.96W/m K

Glass cover used for solar air heater

Fan 10

The two computer exhaust fan of 12v each were used to force the air through the collector.

It was connected by voltage divider to regulate and maintain the speed of fans.

Fans used for inlet of solar collector

Stand11

The SAHs stand were making by 260 slope shape rectangular stand to sit the SAHs.

stand for holding SAHs at an angle

Measuring instruments 12

Following measuring instruments used for experiment:

LM-35 temperature sensor

Digital (TENMARS TM- 207)

Digital anemometer (METRAVI AVM-05)

alcohol thermometer

Magnetic base

Magnetic bas for measuring tilt angle of SAHsDigital anemometer (METRAVI AVM-05)

Digital solar power meter (TENMARS TM- 207)LM-35 temperature sensor

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Technical specification of measuring instruments LM-35

Model- LM-35Accuracy

0.5 ensured Temp. operating

-55oC to 150oCOperating from

4V to 30VLess than

60 ᵤA

Solar power meter

Model – LM-100 Accuracy

-3% to 3% at 2854K

Range 20 to 2000 foot

candles Resolution 0.01 fc/lux Temperature -10 oC to 55 oC

Sensor Silicon Photodiode

Alcohol thermometer

Accuracy 1 oC

Range

-10 to 100 oC Organic liquid

Mercury Glass used

Normal

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Experimental set-up 15

In this experiment  following three types of solar air heaters were employed:

1. Simple single pass solar air heater (Type I)

2. Single pass solar air heater having aluminum wire mesh (Type II)

3. Single pass SAHs having aluminum fins (Type III)

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Outlook representation of simple single pass SAHs (Type I)

Absorber plate for Type III SAHs

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Type II Type III

Aluminum wire mesh used in absorber plate of Type II SAHs

Aluminum fins inserting on absorber plate of Type III SAHs

Calculation

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The thermal efficiency of all three types, I, type II and type III solar air heaters, were calculated using equation :

η = ṁCp (Ta, out – Ta, in)/I Ac

Where, ṁ = mass flow rate (kg/s)

Cp = Specific heat of air at constant pressure (kJ/kg K) Ta, out = Temperature of air at outlet Ta, in = Temperature of air at inlet

I = Solar radiation (W/m2)

Ac = Surface area of the collector (m2)

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Energy losses 

1/U = 1/ha + dx1 / k1 + dx2 /k2

Where,

dx1 = Thickness of thermo Cole

dx2 = Thickness of plywood

k1 = Thermal conductivity of thermo Cole

k2 = Thermal conductivity of plywood ha = Convective heat transfer coefficient for air

Q = UA∆T

Qtotal = Qsides + Qtop + Qbottom

Qtotal = 98.88 Watt

Total losses from Sun = 21600 kJTotal gain = 20318 kJ

RESULT & DISCUSSIONS 20Simple single pass solar air heater (Type I) at exit air

velocity is 4.20 m/s on May 30, 2015

1. The highest daily solar flux is obtained as 965 W/m2.

2. Daily mean solar flux is measured as 800 W/m2.

3. The difference between the exit and inlet temperature is measured by 33°C.

Thermal efficiency 21

The mean thermal efficiency is calculated as 42.02%.

Single pass solar air heater having aluminum wire mesh (Type II) at exit air velocity is 4.20 m/s on June 05,2015 2

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The highest daily solar flux is obtained as 995 W/m2.

Daily mean solar flux is measured as 805 W/m2.

The mean thermal efficiency is calculated as 43.26%.

The difference between the mean daily exit and inlet temperature is measured as 31°C.

Single pass solar air heater having aluminum fins (Type III) at exit air velocity is 4.20 m/s on June 15, 2015 2

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The highest daily solar flux is obtained as 1025 W/m2.

Daily mean solar flux is measured as 871 W/m2.

The mean thermal efficiency is calculated as 41.44%.

The difference between the mean daily exit and inlet temperature is measured as 33°C.

Thermal efficiency comparison among Type I and Type II 2

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Thermal efficiency comparison among Type I and Type III

Thermal efficiency comparison graph of Type I, Type II and Type III solar air heaters at exit air velocity 4.20 m/s

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CONCLUSIONS26 Single pass solar air heaters having aluminum fins higher thermal efficiency

compare to single pass solar air heaters and single pass SAHs with aluminum wire mesh.

Single pass solar air heater with aluminum wire mesh and aluminum fins has improved thermal efficiency as wire mesh and fins increase the heat transfer area.

The maximum mean thermal efficiency obtained as 46.12% in single-pass solar air heater with aluminum fins (Type III) at exit air velocity 4.20 m/s.

The maximum peak thermal efficiency obtained as 46.12% in single-pass solar air heater with aluminum fins (Type III) at exit air velocity 4.20 m/s.

The wire mesh and fins or obstacles guarantee a superior air flow above and below the absorber plates, generate the turbulence and decrease the dead zones in the collector.

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