Abstract
Abstract This paper reports the results of a comparative study on a low concentration eccentric evacuated tube solar collector with two different absorber tubes of circular and rectangular cross sections. The two arrangements are intended for flow through applications although the collector with rectangular section can be adapted for PV applications. The governing equations of the model are approximated by the finite volume control method (FVM) in association with the SIMPLE algorithm. A home-built numerical code is developed to simulate both a single tube and a collector arrangement of 18 tubes of circular and rectangular cross sections. The evacuated tubes are connected to operate in single flow-through arrangement. The working fluid is aluminium oxide/water nanofluid to enhance the heat absorbed by the collector. It is assumed that the sealed inner and outer parts of the glass cover are in adiabatic condition. The model and the simulation predictions are validated against available results showing good agreement. In the case of a single tube arrangement with water as the heat transfer fluid, it was found that the efficiency of the evacuated tube with circular absorber was 8% higher than that of the collector with rectangular absorber at the same conditions. The simulations for the collector arrangement were conducted for a nano Al2O3 volume fraction ( ϕ ) in the range 0.01 ≤ ϕ ≤ 0.1 and fluid velocities between 0.005 ≤ u ≤ 0.010 m/s. The results showed, for the case of nanofluid with velocities of 0.015 , 0.01 , 0.007 and 0.005 m / s , maximum efficiency enhancement of the collector with circular absorber of about 1.1%, 2.5%, 5.2% and 8.8%, respectively. For the rectangular absorber the enhancements were 0.5%, 1.14%, 2.41% and 4.79%, respectively.
Published Version
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