Through analysis on five parameters

including the Nusselt number Nu

Rayleigh number Ra

vortex intensity ?

axial velocity u and average thermal efficiency η

the three-dimensional unsteady flow and heat transfer performance of the fluid in glass evacuated elliptical tube solar collector with different short-long half shaft ratios(? =0.6

0.9 and 1.0) was numerically simulated. The results show that

the η

Nu and Ra increases with the ?. The η

Nu and Ra of the circular cross section tube(? =1.0) is 3.50%

21.97% and 30.64% higher than that of the elliptical cross section with ? of 0.6

respectively. Therefore

the flow and thermal performance of circular cross section tube is excellent. Additionally

vortex exists inside the collector tubes and the vortex intensity declines from the joint face of tube and tank to the end of the tube. The vorticity inside the tube elliptical cross section is stronger than that in a circular cross section tube. The axial velocity distribution is consistent with the cosine function inside the tube.