Numerical modeling and experimental validation of Back-Pass rectangular ducts solar air heaters

Abstract

A numerical model for predicting the thermal performance of solar air heaters has been successfully developed. This model uses the control volume finite element method with discretization in both longitudinal and axial direction using general empirical correlations to solve the equations in a short time. The numerical model gives the following information: thermal efficiency curves (linear and quadratic), incident angle modifier, temperature distribution in solid parts (back insulation, absorber plate, and transparent cover), and both temperature and humidity values in the airflow along the ducts. The relative humidity is a significant parameter in drying processes, and other numerical models do not calculate it. The model was statistically validated using 84 experimental thermal efficiency data points obtained with three different solar air heaters arrangement. As a result of this validation, the average relative error between experimental and numerical data for thermal efficiency was ±5.38%. Based on statistical method, a linear regression analysis comparing the experimental thermal efficiency data against the thermal efficiency data predicted by the numerical model was carried out by a weighted least-squares regression model. With this, it can be concluded that the numerical model is a reliable tool to design and optimize back-pass rectangular ducts solar air heaters.