No-vacuum Mono-Tube Compound Parabolic Collector Receiver for Linear Fresnel Concentrator: Numerical and Experimental Approach for Dynamic Behavior Assessment

Abstract

The present paper aims to develop a novel simplified transient model to investigate the dynamic behavior of a no-vacuum mono-tube receiver equipped with a compound parabolic collector. Considering the intermittency of solar radiation, predicting receiver thermal behavior is critical for linear Fresnel concentrator design and operation. From this standpoint, this research focuses on determining whether or not the steady-state assumption influences the receiver’s performance. Unlike the current models accounting for all the receiver components, the proposed model considers the absorber tube as the primary node and focuses on the heat transfer fluid temperature distribution. The remaining components form an equivalent thermal resistance through which heat loss occurs. The global heat losses are then characterized using an experimental receiver prototype with tube diameter of 70 mm, an aperture of 500 mm, and a secondary reflector. The overall receiver heat loss coefficient was determined at different absorber temperatures ranging between 60 and around 265 °C. The heat loss coefficients measured varied from 4.7 to 8.5 W/m2 K. The model computes receiver performance using the measured overall heat loss coefficient based on real solar data. The receiver response at steady and transient states has been conducted and discussed according to several design parameters, including the heat transfer fluid nature and mass flow rate, the receiver length, and the absorber tube thickness. For the same working conditions, synthetic oils fluid allows achieving higher efficiencies whereas molten salts enable reaching higher outlet temperatures. For the metal wall thicknesses ranging between 2 and 3 mm and the fluid outlet temperature varying between 250 and 300 °C, the receiver thermal efficiency during the day remains relatively close to 75 %. The impact of the absorber tube thermal inertia has been investigated by analyzing the dynamic behavior under various close-to-real-world scenarios. Results have shown that the steady-state assumption does not influence if the metal wall tube thickness is lower than 3 mm.