# Thermal Performance Analysis of a Double-Pass Solar Air Collector: A CFD Approach
###### Abstract
Ray tracing was applied to analyze the radiation distribution on the receiver tube at normal incidence, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Solar Technology** & **TES Fluid** & **CFD Model** & **Radiation Model** \\ \hline
[16] & CPCs with tubular receivers and flat-plate receiver & Air in cavity & \
\begin{tabular}{c} 2D pseudo-transient model \\ Incompressible ideal gas \\ Buoyancy forces \\ k\(-\epsilon\) turbulent model \\ \end{tabular} &
\begin{tabular}{c} IR: S2S radiation model \\ ER: Solar radiation is \\ completely absorbed by the receiver \\ \end{tabular} \\ \hline
[17] & Panels of CPCs with tubular receiver & Air in cavity & \
\begin{tabular}{c} 2D pseudo-transient model \\ Incompressible ideal gas \\ k\(-\epsilon\) turbulent model with the \\ enhanced wall treatment \\ \end{tabular} &
\begin{tabular}{c} IR: S2S radiation model \\ ER: Receiver temperature as a \\ boundary condition (solar radiation \\ is not simulated) \\ \end{tabular} \\ \hline
[18] & CPC with flat-plate receiver & Air in cavity & \
\begin{tabular}{c} 3D steady-state model \\ Incompressible ideal gas \\ Thermo-physical \\ properties constants \\ Non-Boussinesq approximation \\ Standard k\(-\epsilon\) turbulence model with \\ enhanced wall treatment \\ \end{tabular} &
\begin{tabular}{c} IR: Discrete-ordinate radiation model \\ ER: Thermal boundary condition \\ with the surface external \\ emissivity specified \\ emissivity specified \\ \end{tabular} \\ \hline
[19] & Multi-pass flat-plates & Air & \
\begin{tabular}{c} 2D and 3D steady-state models \\ k\(-\epsilon\) turbulent model \\ Standard k\(-\epsilon\) turbulent model with \\ realizability constraints in the \\ vicinity of walls \\ \end{tabular} &
\begin{tabular}{c} IR: S2S radiation model \\ ER: External Radiation Source \\ sub-node is applied to contribute to \\ the incident radiative heat flux on \\ the solar spectral bands \\ \end{tabular} \\ \hline
[20] & \begin{tabular}{c} Three-pass and \\ quadruple-pass \\ flat-plates \\ \end{tabular} & Air & \
\begin{tabular}{c} 3D steady-state model \\ k\(-\epsilon\) turbulence model \\ \end{tabular} &
\begin{tabular}{c} IR: Discrete-ordinate radiation model \\ ER: Energy equation and Discrete \\ Transfer radiation model \\ \end{tabular} \\ \hline
[21] & Double-pass flat-plate & Air & \
\begin{tabular}{c} 2D steady-state model \\ Incompressible flow \\ k\(-\epsilon\) turbulence model \\ \end{tabular} &
\begin{tabular}{c} ER: Uniform heat flux \\ \end{tabular} \\ \hline
[22] & \begin{tabular}{c} Double-pass \\ flat-plates with three \\ fin configurations \\ \end{tabular} & Air & \
\begin{tabular}{c} 2D steady-state model \\ k\(-\epsilon\) turbulence model \\ \end{tabular} &
\begin{tabular}{c} ER: Constant heat flux \\ \end{tabular} \\ \hline
[24] & \begin{tabular}{c} Double-pass curved \\ collectors \\ \end{tabular} & Air & \
\begin{tabular}{c} 2D steady-state model \\ k\(-\epsilon\) turbulence model \\ \end{tabular} &
\begin{tabular}{c} ER: Constant solar radiation flux \\ \end{tabular} \\ \hline \hline \end{tabular}  
\end{table} 
Table 1: _Cont._with a correlation of the absorbed solar energy as a function of the angle along the perimeter of the tube. Both models were experimentally validated, and relative errors of less than 3.7% in temperature and 1% in efficiency were obtained. On the other hand, [PERSON] et al. analyzed the air heat transfer inside the cavity of a collector with a tubular receiver and with a flat-plate receiver and developed some correlations to express the Nusselt over the receiver [16]. Subsequently, [PERSON] and [PERSON] performed the numerical analysis of a panel with several tubular receiver CPCs to determine the influence on the thermal efficiency of the number and position of the CPCs along the panel, the use of a second transparent cover, the spacing between collectors, and the truncation of the reflectors [17]. For their part, [PERSON] et al.