RECOMMENDATIONS

CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS

7.2 RECOMMENDATIONS

The following recommendations are given on the basis of experience gained out of this research:

i. The performance of the receiver can be increased by using a selective surface of high absorptivity and low emissivity for wavelength.

ii. Performance can also be improved by using two layers of transparent covers. The transparent cover should be vacuumed properly.

iii. Transparent connector pipes between tank and collector can also be used, so that the fluid flow through the pipes can be able to be observed.

iv. Fluid flow rate is necessary for the calculations of amount of energy absorbed and efficiency. In our study we were not able to measure this parameter because we considered steady-state condition of fluid. But for more precise performance analysis there should be provision to measure flow rate of fluid.

v. Due to time shortage, we were not able to measure the temperature of storage tank. If we could do this, there might be a possibility to transfer the heat energy to another more efficient fluid.

vi. Thermal fluids like ethanol, methanol, acetone and so forth which have low saturation temperature and high specific heat can be used for performance analysis of the parabolic concentrator.

vii. We used mirror strips which were arranged one by one on a parabolic structure as a reflector. Instead of this if we could use a parabolic shaped mirror without strips, we might have obtained better performance but it would cost more.

viii. The year round performance characteristics of the parabolic concentrator should be studied.

ix. The performance characteristics for various depths and various sizes of the collectors should be studied.

x. Parabolic reflector structure should be manufactured with maximum amount of precision and accuracy possible.

APPENDIX A

Table A.1: Collected data during the experiment on 26 September 2012 Working Fluid: Water

Sky condition: Normal Weather Collector tilted angle: 22°

Ambient Temperature: 30°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr (⁰C)

End 1 Temp, T1

(⁰C)

Mild Temp, T2 (⁰C)

End 2 Temp, T3

(⁰C) 10:00

(initial)

32 30 31 30

11:00 57 55 56 54

11:30 60 58 60 57

12:00 67 65 66 63

12:30 63 58 61 58

1:00 60 55 56 54

1:30 62 59 60 57

2:00 59 54 57 53

2:30 54 50 54 50

3:00 49 44 47 42

3:30 44 40 44 43

4:00 39 37 39 36

Table A.2: Collected data during the experiment on 30 September 2012 Working Fluid: Water

Sky condition: Sunny Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr (⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2 (⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

28 27 28 27

8:30 35 33 34 32

9:00 46 44 45 43

9:30 54 50 52 49

10:00 58 53 56 53

10:30 63 59 61 58

11:00 69 67 67 66

11:30 70 67 68 67

12:00 79 76 78 75

12:30 78 75 76 72

1:00 (rain)

63 61 61 62

Table A.3: Collected data during the experiment on 1 October 2012 Working Fluid: Water

Sky condition: Sunny Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr (⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2

(⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

30 28 30 28

9:00 47 44 45 44

10:00 52 49 50 48

11:00 65 61 63 59

12:00 76 71 73 68

1:00 72 69 70 67

2:00 69 68 67 67

3:00 59 55 57 54

Table A.4: Collected data during the experiment on 2 October 2012 Working Fluid: Water

Sky condition: Gloomy Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr

(⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2

(⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

29 27 28 27

8:30 35 31 33 31

9:00 39 35 36 33

9:30 42 38 39 36

10:00 48 44 46 43

10:30 55 49 51 47

11:00 (rain)

45 41 42 40

11:30 55 48 49 46

12:00 63 56 59 53

12:30 76 61 68 61

1:00 69 61 64 59

Table A.5: Collected data during the experiment on 3 October 2012 Working Fluid: Water

Sky condition: Sunny Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp,

Tr (⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2 (⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

28 26 27 26

8:30 38 34 36 33

9:00 47 43 46 42

9:30 52 45 50 43

10:00 55 51 53 49

10:30 63 57 61 52

11:00 66 58 64 55

11:30 68 61 65 58

12:00 78 69 76 68

1:00 74 70 72 65

1:30 65 58 63 58

Table A.6: Collected data during the experiment on 7 October 2012 Working Fluid: Water

Sky condition: Sunny Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr (⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2 (⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

29 28 28 27

8:30 35 32 34 32

9:00 39 38 39 36

9:30 44 41 43 40

10:00 49 46 47 44

10:30 53 50 51 48

11:00 56 51 53 49

11:30 62 59 61 57

12:00 70 66 69 63

12:30 78 74 76 72

1:00 72 71 72 69

1:30 69 67 68 65

2:00 65 61 63 61

Table A.7: Collected data during the experiment on 9 October 2012 Working Fluid: Water

Sky condition: Gloomy Weather Collector tilted angle: 22°

Ambient Temperature: 31°C Here,

Tr = Fluid temperature of the receiver tube (°C)

T1 = Fluid temperature at the one end of the receiver tube (°C) T2 = Fluid temperature at the middle of the receiver tube (°C) T3 = Fluid temperature at the other end of the receiver tube (°C)

Time Surface Temp, Tr

(⁰C)

End 1 Temp, T1 (⁰C)

Mild Temp, T2

(⁰C)

End 2 Temp, T3 (⁰C) 8:00

(initial)

29 28 29 28

9:00 35 32 34 32

10:00 39 37 38 36

11:00 45 41 44 42

12:00 62 56 59 54

1:00 59 57 58 57

APPENDIX B

Two model calculations are shown here.

The useful heat gain can be found from the Eq. 2.1:

Q_U=AaIbργτα−ULAr(Tr−Ta) A_a

Where,

Ta = ambient temperature, °C Tr = receiver temperature, °C Aa = aperture area, m²

Ar = receiver area, m²

Ib = direct beam insolation, W/m²

UL =loss coefficiet from the receiver, W/m² °C = reflectance loss

⍴

γ = interceptor factor

τα = transmittance and absorptance product Qu = useful heat gain, W

Experimental thermal efficiency is found from Eq. 2.5 η_{th ;exp}=mC´ _pw(T_o−T_i)

I_bA_a

Theoretical thermal efficiency is found from Eq. 2.7

η_{th ;theo}=ταργ AaIb−ULAr(Tr−Ta) I_bA_a

Theoretical thermal efficiency is found from Eq. 2.7

η_{th ;theo}=ταργ A_aI_b−U_LA_r(T_r−T_a) I_bA_a

Where,

Ti = initial temperature, °C To = final temperature, °C

Cpw = specific heat of water, J/kgk m´ = mass flow rate of water, kg/s ρ_w = density of water, kg/m³ Vw = volume of water, m³

t = time taken to raise the temperature, s

Performance Test of Parabolic Solar Concentrator on 26 September (11.00am):

Concentrator’s useful heat gain calculation:

From Table A.1, Ambient temperature, ^Ta

=

30°C, Receiver temperature, ^Tr =57°C From Figure 4.1, Solar insolation, I_b =200 W/m²

Aperture area = (width of concentrator-diameter of receiver cover) X length of concentrator = (55-2) X 36 in² [From Table 3.2 and 3.3]

= 1908 in²

=1.23 m²

Receiver area = π X diameter of receiver X length of receiver

= 3.1416 X 1 X 36 in² [From Table 3.2 and 3.3]

= 113.0976 in² = .073 m²

From Table 2.1.1 we take velocity of wind V = 6 km/h = 1.666 m/s From Eq 2.3 we find

h_wind = 5.7 + 3.8V =5.7 + (3.8 X 1.666) = 12.03 W/m²°C From Eq 2.4 we find

Or,

^hr

= 4 ε σ

^(Tr+Ta

2 ) ³

= 4 X 0.91 X 5.67 X 10^-8 X (57+30

2 ) ³

[From Table 2.1.1, ε=0.91]

= .017 W/m²°C From Eq 2.2 we find

U

L

= (

_h¹

wind

+

_h¹

r

)

^-1 W/m²°C =

(

_12.03¹

+

_.017¹

)

^-1

= 0.01697 W/m²°C

From Table 2.1.2 and Table 2.1.3, α = 0.91, τ = 78.6 τα= 0.762

γ = 0.94

⍴ = 0.85

So useful heat gain,

Q_U=A_aI_bργτα−U_LA_r(T_r−T_a) A_a

= 1.23X225X.85X.94X.762−.01697X.073X(57−30) 1.23

=

136.96 W/m²

Concentrator’s theoretical and experimental efficiency calculation:

η_{th ;theo}=ταργ A_aI_b−U_LA_r(T_r−T_a) I_bA_a

=

^{1.23X225X.85X.94X}.762−.01697X.073X(57−30) 1.23X225

=0.60871 = 60.871%

At ambient temperature density of water, ρ_w = 1000 kg/m³, specific heat of water, Cpw= 4200 J/kgk

Volume of water, ^Vw = π X (radius of receiver)² X length of receiver = 3.1416 X .5² X 36 in³

= 28.2744 in³ = 0.00046 m³ t = 1 hour = 3600 s

From Eq. 2.6

m´ = ρ_wV_w

t

=

¹⁰⁰⁰₃₆₀₀^X.00046

=

.000128 kg/s From Table A.1

Initial temperature, Ti = 31°C Final temperature, To = 56°C

Now experimental thermal efficiency is

η_{th ;exp}=mC´ _pw(T_o−T_i) I_bA_a = .00051X4200X(56−31)

225X1.23

= .0488 or 4.88%

Performance Test of Parabolic Solar Concentrator on 9 October (9.00 am):

Concentrator’s useful heat gain calculation:

From Table A.7, Ambient temperature, T_a

=

31°C, Receiver temperature, T_r =57°C From Figure 4.1, Solar insolation, ^Ib =225 W/m²

Aperture area = (width of concentrator-diameter of receiver cover) X length of concentrator = (55-2) X 36 in² [From Table 3.2 and 3.3]

= 1908 in²

=1.23 m²

Receiver area = π X diameter of receiver X length of receiver

= 3.1416 X 1 X 36 in² [From Table 3.2 and 3.3]

= 113.0976 in² = .073 m²

From Table 2.1.1 we take velocity of wind V = 6 km/h = 1.666 m/s From Eq 2.3 we find

h_wind = 5.7 + 3.8V =5.7 + (3.8 X 1.666) = 12.03 W/m²°C From Eq 2.4 we find

Or,

^hr

= 4 ε σ

^(Tr+Ta

2 ) ³

= 4 X 0.91 X 5.67 X 10^-8 X (35+31

2 ) ³

[From Table 2.1.1,

ε

=0.91]

= .0074 W/m²°C From Eq 2.2 we find

U

L

= (

_h¹

wind

+

_h¹

r

)

^-1 W/m²°C

=

(

_12.03¹

+

_.0074¹

)

^-1

= 0.0074 W/m²°C

From Table 2.1.2 and Table 2.1.3, α = 0.91, τ = 78.6 τα= 0.762

γ = 0.94

⍴ = 0.85

So useful heat gain,

Q_U=A_aI_bργτα−U_LA_r(T_r−T_a) A_a

= 1.23X225X.85X.94X.762−.0074X.073X(35−31) 1.23

=

136.987 W/m²

Concentrator’s theoretical and experimental efficiency calculation:

η_{th ;theo}=ταργ A_aI_b−U_LA_r(T_r−T_a) I_bA_a

=

^{1.23X225X.85X.94}_1.23^{X.762−.0074}_X225 ^{X.073X(35−31)}

=0.60883 = 60.883%

At ambient temperature density of water, ρ_w = 1000 kg/m³, specific heat of water, Cpw= 4200 J/kgk

Volume of water, ^Vw = π X (radius of receiver)² X length of receiver = 3.1416 X .5² X 36 in³

= 28.2744 in³ = 0.00046 m³ t = 1 hour = 3600 s

From Eq. 2.6

m´ = ρ_wV_w

t

=

¹⁰⁰⁰₃₆₀₀^X.00046

=

.000128 kg/s From Table A.1

Initial temperature, Ti = 31°C Final temperature, To = 56°C

Now experimental thermal efficiency is

η_{th ;exp}=mC´ pw(To−Ti) I_bA_a = .00051X4200X(35−29)

225X1.23 = .01 or 1%