Viscous dissipation effects analysis in a nanofluid circulating through a porous flat-plate solar collector.*

In this work, the velocity and temperature fields inside the channel of a flat plate solar collector (FPSC) is invesitgated, applying the following passive techniques for enhancing heat transfer: porous media and nanofluids. The research is justified since flat-type collectors work in the temperature range of various industrial processes, as well as residential applications; and it would not posed a problem to implement the studied techniques, if implemented. The mathematical models were solved by the finite element method, incorporated in the FreeFEM++ programming language. From the development of the mathematical models, several parameters were obtained which have an influence over the nanofluid velocity and temperature profiles; however in this study, the six most relevant parameters were selected. Different cases were solved numerically to measure the effect of the chosen parameters on the study variables. From the results obtained, it was concluded that, in the case evaluated from the most real or practical conditions, there is an increase of around 20% in the average temperature of the nanofluid (with a 5% concentration) at the outlet of the porous channel, compared to the case of free flow without nanoparticles. All temperature increase was produced by the effect of the porous medium, and, surprisingly, there is a slight reduction in temperature with the particles concentration. The latter is reversed when the heat generated by the viscous dissipation effect is enhanced