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Performance assessment of evacuated U-tube solar collector: a numerical study

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Abstract

This paper presents a finite element method based three-dimensional thermal model for predicting the performance of evacuated U-tube solar collector. Numerically predicted working fluid outlet temperature is compared with the experimental data available in the literature and a good agreement is observed between them. The influence of average solar irradiance on efficiency and useful heat gain rate of the solar collector is studied for two different evacuated tube configurations. Employing water and air as working fluid, copper, aluminium and brass as U-tube material, and graphite, magnesium oxide and aluminium oxide as filler material and the performance of the evacuated tube solar collector is investigated in detail.

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Abbreviations

Ac :

area of the collector (m2)

cp :

specific heat at constant pressure (kJ/kg–K)

kg :

thermal conductivity of the glass tube (W/m–K)

kfr :

thermal conductivity of the filler material (W/m–K)

ka :

thermal conductivity of the inner glass tube/absorber tube (W/m–K)

kf :

thermal conductivity of the fin material (W/m-K)

ku :

thermal conductivity of the U-tube (W/m–K)

LHS:

latent heat storage

\( \dot{\hbox{m}} \) :

mass flow rate (kg/s)

P:

pressure (Pa)

Quseful :

useful heat gained by the working fluid (W)

T:

temperature (°C)

\( \vec{v} \) :

velocity (m/s)

α:

absorptivity of the inner glass tube/absorber tube

λ:

average solar irradiance (W/m2)

ρ:

density (kg/m3)

μ:

dynamic viscosity of working fluid (Pa–s)

ε:

emissivity of the outer glass tube

η:

solar collector efficiency (%)

σ:

Stephen Boltzmann constant (W/m2–K4)

τ:

transmissivity of the inner glass tube/absorber tube

amb:

ambient air

ini:

initial

i:

inner

o:

outer

w,o:

working fluid outlet

w,i:

working fluid inlet

wf:

working fluid

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Authors and Affiliations

  1. Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, India

    B Kiran Naik & P Muthukumar

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  1. B Kiran Naik
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  2. P Muthukumar
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Correspondence to P Muthukumar.

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Naik, B.K., Muthukumar, P. Performance assessment of evacuated U-tube solar collector: a numerical study. Sādhanā 44, 23 (2019). https://doi.org/10.1007/s12046-018-0974-z

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  • DOI: https://doi.org/10.1007/s12046-018-0974-z

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