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Convection and surface radiation heat losses from modified cavity receiver.pdf

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Convection and surface radiation heat losses from modified cavity receiver

ORIGINAL Convection and surface radiation heat losses from modified cavity receiver of solar parabolic dish collector with two-stage concentration K. S. Reddy ? N. Sendhil Kumar Received: 21 October 2007 / Accepted: 28 August 2008 / Published online: 16 September 2008 Springer-Verlag 2008 Abstract Numerical analysis of solar dish modified cavity receiver with Cone, CPC and Trumpet reflectors is presented. Three-dimensional modeling is carried out to estimate the convective and radiative heat loss from the receiver for different angles of inclination and operating temperatures. Incorporating reflectors in the modified cavity receiver for second stage concentration, the natural convection heat losses are reduced by 29.23, 19.81 and 19.16%, respectively. The receiver with the trumpet reflector has shown better performance as compared to other configurations. List of symbols A area (m2) D diameter of receiver (m) d aperture diameter of the receiver (m) E emissive power (W/m2) F view factor h heat transfer coefficient [W/(m2 K)] J radiosity (W/m2) k thermal conductivity [W/(m K)] L length of the secondary reflector from the base of cavity receiver (m) N number of radiative surfaces Nu Nusselt number P pressure (Pa) q energy flux (W/m2) Q heat loss (W) Ra Rayleigh number T Temperature (K) V velocity (m/s) X body force (N/m3) Greek symbols h angle of inclination of receiver () t kinematic viscosity of the fluid (m2/s) q density of the fluid (kg/m3) a absorptivity aa half cone angle () e emissivity r Stefan–Boltmann constant (5.67910-8 W/m2 K4) r Laplace operator Subscripts Atm atmospheric pressure Cav cavity Conv convection c1 inner surface of the receiver eff effective ij surface i to surface j in, i surface in i out, i surface out i Rad radiation f fluid Total combined convective and radiative vel velocity w inner surface wall of the receiver ? ambient 1 focal image/aperture of the receiver 1 Introduction Solar concentrators are promising technologies for attain- ing