Modelling of Heat Transfer in a Trapezoidal Cavity Receiver for a Linear Fresnel Solar Collector with Fixed / Narrow Reflectors

摘要

In this research, the optical and thermal behavior of a Compact Linear Fresnel Receiver is studied with the aid of Computational Fluid Dynamics (CFD) and ray tracing methods respectively. This study aims at developing a new type of Linear Fresnel Collector (LFC) with azimuth angle tracking system. The optical analysis is performed using TracePro, a mature ray-tracing tool, in which the optical performance of the reflectors and receiver are simulated in order to obtain the optimum geometry along with the heat flux distribution on the receiver surfaces. The result of the optical analysis is used as a boundary condition for CFD modeling where the receiver located in the air stream is modeled in ANSYS Fluent. The main objectives of the thermal analysis are, firstly, to study the heat loss rate from the receiver at different absorber temperatures, and secondly, to determine the stagnation temperature under no-flow condition as an important factor contributed to thermal expansion and durability of the materials used. Further optimization is performed through examining the impact of the inner pressure and type of the gas content including air, argon and nitrogen over stratification and heat dissipation mechanism. The results indicate that a well-stablished stratification is achievable even in the atmospheric air-filled cavity. Once the conductive and convective losses are efficiently suppressed in a well-insulated receiver with a proper inner stratification state, the radiative part becomes dominant by allocating 82% of the overall heat loss. This study highlights the importance of reducing the long-wave radiative losses from the receiver to the surrounding to achieve high performance.