Prediction of thermal and flow behaviour of a Solar Air Heater – A numerical study

Global population growth, industrialization, and urbanization have increased the importance of freshwater with only 3% of Earth’s surface safe for human consumption. A promising solution is solar water desalination, which improves performance through preheating air entering the evaporator using a solar humidification-dehumidification (HDH) technique. To predict the thermal and flow behaviour of a v-corrugated serpentine structure type solar air heater (SAH) design a numerical model of SAH is created, and experimental data from Ameri et al. [1] is used to validate the model. Predicting the thermal and flow characteristics allows for the assessment of the solar air heater’s performance and helps in optimising the design. In this context, various turbulence models such as standard $\mathrm{k}-\varepsilon$, realisable $\mathrm{k}-\varepsilon$, $\mathrm{RNG} \mathrm{k}-\varepsilon$, standard $\mathrm{k}-\omega$, and SST $\mathrm{k}-\omega$ are employed to compare the outlet air temperature of the SAH. The result shows that in all these turbulence models, the RNG k-$\varepsilon$ model outperforms the other models, and the values are as accurate as the experimental results. Variation in relative roughness pitch (P/e) ranging from 4.04 to 12.12 has been considered to get the optimum design of SAH. For a Re value of 15000 with P/e of 8.08, the highest values of Nusselt number and THPF obtained are 175 and 1.21, respectively. The friction factor has an average absolute variance of 3.33%, whereas 2.41% for the Nusselt number. Further, we can develop the correlations for the proposed SAH design with this study, which will help us to optimize the SAH design.