Heat loss investigation of 125kWth solar LFR pilot plant with parabolic secondary evacuated receiver for performance improvement

Numerical investigation is carried out on the secondary reflector system of the pilot solar linear Fresnel reflector module of 154 m2 in Vallipuram, Tamil Nadu. Initially, optical investigation on the design of the Linear Fresnel Collector module and the secondary reflector system is carried out. The optimized flux thus obtained is applied as a boundary condition to the thermal loss analysis. Investigation of the total heat losses (convective, radiative and conductive) with three different boundary conditions namely, the constant flux, variable flux and non-uniform flux distribution is carried out. The heat loss study has been carried out when the absorber is under non-evacuated and evacuated state. The study has been carried out with the DNI ranging between 250 W/m2 and 1000 W/m2. Uncoated and selectively coated absorbers with the emissivity of 0.01-1 are analyzed. Comprehensive analysis on the influence of wind flow on the receiver system is carried out. The variation of wind velocity from the ground level is incorporated in the forced convection. Investigation on the effect of the wind speed (0 m/s-10 m/s) and the wind direction (0°-90°) on this second stage reflector system is analyzed. The deviation between the different flux boundary conditions is comprehensively analyzed under different DNI and wind conditions. The variable flux distribution shows less deviation of about 15% from the non-uniform flux distribution for the DNI of 1000 W/m2 and is found to be less than 5% for 500 W/m2 under evacuated conditions. To avoid the computational complications in applying non-uniform flux boundary conditions to the absorber for DNI greater than 500 W/m2, variable boundary flux condition can be applied as an equivalent flux condition by augmenting 15% non-uniform error percentage to the final heat loss value.