Design consideration of a filled layer U-pipe evacuated tubular solar collector with flat diffuse reflector: energy and exergy analysis

Abstract

A lack of research about critical design factors, notably the center-to-center tube spacing-to-tube diameter ratio (C/D) and the relationship between length and diameter, is conspicuously evident in the context of U-pipe evacuated tubular solar collectors (ETSCs) employing the filled-layer approach. Furthermore, using a U-pipe configuration in ETSCs coupled with a flat diffuse reflector (FDR) remains conspicuously absent from the scientific literature as a potential enhancement strategy. This study evaluates the influence of collector tube length, diameter and the C/D on output parameters, including $T_{\mathrm{out}}$, ${\eta }_{\mathrm{En}}$ and ${\eta }_{\mathrm{Ex}}$. The findings reveal that while ${\eta }_{\mathrm{En}}$ experiences a decrease with increasing C/D, the ${\eta }_{\mathrm{Ex}}$ does not reach its minimum value when C/D was three due to the corresponding increase in outlet temperature. Furthermore, introducing the FDR into the filled U-pipe evacuated tubular solar collector enhances daily ${\eta }_{\mathrm{En}}$ and ${\eta }_{\mathrm{Ex}}$ by 12.91% and 0.65%, respectively. Moreover, a suggestion of the length and diameters of a filled type boosted with FDR is L = 2000 mm for D_g/D_p= 47/37 mm and L = 1800 mm when D_g/D_p= 58/47 mm, which has the maximum ${\eta }_{\mathrm{Ex}}$ per day of 2.87% and 1.87%, respectively. However, if the objective is to maximise ${\eta }_{\mathrm{En}}$ per day, lengths of L = 1450 mm for D_g/D_p= 47/37 mm or L = 1200 mm for D_g/D_p= 58/47 mm would be preferable.

Abbreviations: ESC: evacuated solar collector; ETC: evacuated tubular collector; DUFET: filled-type evacuated tube with double U-tubes; ETSC: evacuated tubular solar collector; FDR: flat diffuse reflector; C/D: center-to-center tube spacing to the collector's tube diameter (cover tube); D_g/D_p: diameter of cover tube and diameter of absorber tube

KEYWORDS:

• U-pipe
• filled type
• evacuated tubular solar collector
• exergy
• design parameter
• FDR

Disclosure statement

No potential conflict of interest was reported by the author(s).