Investigations on thermal performance of non-evacuated single tube receiver with concentric glass tube and Compound Parabolic Concentrator (CPC)

Simplified model to analyze the thermal behavior of a non-evacuated receiver tube integrated with a Compound Parabolic Concentrator (CPC) for Linear Fresnel Reflector systems is presented. Unlike evacuated receivers, CPC-based systems avoid high manufacturing costs and vacuum maintenance. An experimental investigation is conducted for a non-evacuated receiver to measure surface temperatures of the absorber tube, glass tube, CPC, and Flat Glass Cover (FGC) under steady conditions. The absorber temperature is varied between 323–493 K. The overall heat loss coefficients (U₁) are estimated for five configurations: (1) Absorber tube, glass tube only (2) Absorber tube, glass tube, CPC without insulation and without FGC (3) Absorber tube, glass tube, CPC with insulation and without FGC (4) Absorber tube, glass tube, CPC without insulation, and FGC at the CPC aperture (5) Absorber tube, glass tube, CPC with insulation, and FGC at the CPC aperture. Compared to (1), U₁ is reduced by 9–16% in (2), 14–31% in (3), 16–40% in (4), and 21–45% in (5). Configuration (5) showed the best performance with 10.8% lower U₁ than (3). A numerical model using surface-to-surface radiation and realizable k–ε turbulence, together with an analytical model, predicted results within 6.6% of experiments.