Numerical investigation of natural convection heat loss in modified cavity receiver for fuzzy focal solar dish concentrator

• Published in: Solar energy 2007-07, Vol.81 (7), p.846-855
• Main Authors: Sendhil Kumar, N., Reddy, K.S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Equipments, installations and applications; Exact sciences and technology; Heat; Heat transfer; Natural energy; Solar energy; Solar thermal conversion
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2006.11.008

In the present work, a 2-D-model is used to investigate the approximate estimation of the natural convection heat loss from an actual geometry of the modified cavity receiver (hemisphere with aperture plate) of fuzzy focal solar dish concentrator. The analysis of the receiver has been carried out based on the assumption of the uniform and maximum solar flux distribution in the central plane of the receiver. The total heat loss from the receiver has been estimated for both the configurations “with insulation” (WI) and “without insulation” (WOI) at the protecting aperture plane of the receiver. The convection heat loss of the modified cavity receiver was estimated by varying the inclinations of the receiver from 0° (cavity aperture facing sideways) to 90° (cavity aperture facing down). The convection heat loss is maximum at 0° and decreases monotonically with increase in angle upto 90°. The effect of operating temperature on convection heat loss for different orientations of the receiver was studied. The results of the numerical analysis are presented for a modified cavity receiver “with insulation” (WI) and “without insulation” (WOI) in the form of Nusselt number correlation: Nu D ( WI ) = 0.0303 Gr D 0.315 ( 1 + cos θ ) 3.551 ( T w / T ∞ ) - 0.086 ( d / D ) 0.878 , 10 6 ⩽ Gr D ⩽ 10 7 and Nu D ( WOI ) = 0.503 Gr D 0.222 ( 1 + cos θ ) 1.231 ( T w / T ∞ ) - 0.165 ( d / D ) 0.304 , 10 6 ⩽ Gr D ⩽ 10 7 . The maximum convection heat loss occurs at 0° inclination for both cases of the receiver, which is 63.0% (WI) and 42.8% (WOI) of the total heat loss, though the heat loss in WI configuration is lower than that of WOI configuration. Upon increasing the inclination of the receiver, the convection heat loss reduces to a minimum of 12.5% (WI) and 24.9% (WOI) of the total heat loss at 90°. The result of the present numerical model of standard receiver configuration (modified cavity receiver with insulation at bottom) is comparable with other well-known models.