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Performance analysis and comparison of glazed and unglazed solar air collector

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Abstract

Glazed and unglazed solar collectors are now well-recognized solar collectors. Analysis of glazed glass tube solar air collector (GGTSAC) and unglazed glass tube solar air collector (UGGTSAC) is presented by developing a mathematical model in JAVA script language. The effect of five parameters (wind speed, mass flow rate of air, absorber tube diameter, length of glass tube and ambient temperature) is investigated by considering outlet air temperature and thermal efficiency as performance indicators. The agreement between theoretical and experimental data is good. Results show that out of five parameters, mass flow rate of air and length of glass tube are most critical parameters for GGTSAC and UGGTSAC. Outlet air temperature difference decreases from 49.7 to 38 and 28 to 24.1 °C and thermal efficiency increases from 0.67 to 0.71 and 0.33 to 0.42, when mass flow rate of air increases from 0.0074 to 0.0118 kg/s for GGTSAC and UGGTSAC. Outlet air temperature difference increases from 4.3 to 43.6 and 3.2 to 26.5 °C and thermal efficiency decreases from 0.74 to 0.71 and 0.52 to 0.38 when length of glass tube increases from 0.3 to 1.2 m for GGTSAC and UGGTSAC. The present work reflects the importance of transparent glazing in the design of solar air collector.

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Abbreviations

A :

Nusselt number

B :

Constant

C :

Reynolds number

D :

Diameter (m)

E :

Prandtl number

ƒ:

Interchange factor

h :

Heat transfer coefficient (W/m2 K)

I :

Solar intensity (W/m2)

j :

Element along the tube axis

K :

Thermal conductivity (W/m K)

L :

Length of tube (m)

:

Air mass flow rate (kg/s)

M :

Number of elements

r :

Radius, m

S :

Specific heat of air (J/kg K)

T :

Temperature (°C)

u :

Velocity (m/s)

U :

Overall heat transfer coefficient from absorber coating to ambient (W/m2 K)

x :

Constant

y :

Absorber glass tube thickness (m)

Δz :

Length of a slice along tube axis (m)

α :

Absorptivity

Ɛ :

Emissivity

ρ :

Density of air (kg/m3)

∅:

Dynamic viscosity of air (kg/ms)

τ :

Transmissivity

σ :

Stefan’s Boltzmann constant (W/m2 K4)

η :

Thermal efficiency

GT:

Glass tube

GTSAC:

Glass tube solar air collector

GGTSAC:

Glazed glass tube solar air collector

HTF:

Heat transfer fluid

UGGTSAC:

Unglazed glass tube solar air collector

g:

Glass

tg:

Transparent glazing

ac:

Absorber coating

at:

Absorber tube

f:

Fluid (air)

a:

Ambient

i:

Inlet

o:

Outlet

exp:

Experimental

sim:

Simulation

p:

Pressure

tg–a:

Transparent glazing to ambient

ac–tg:

Absorber coating to transparent glazing

at–f:

Absorber glass tube to flowing fluid (air)

w:

Wind

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Correspondence to Vishal Dabra.

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Dabra, V., Yadav, A. Performance analysis and comparison of glazed and unglazed solar air collector. Environ Dev Sustain 22, 863–881 (2020). https://doi.org/10.1007/s10668-018-0223-y

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Keywords

  • Glass tube
  • Glazed
  • Solar air collector
  • Performance
  • Unglazed