In this book, a mathematical model to analyze the heat exchanges in two different types of solar air collectors was developed. The effect of placing a barrier inside a flat plate solar air heater was also investigated and all of them were simulated in two and three dimensions using the commercial software FLUENT. When building the thermal mathematical model it was shown that for each collector, at quasi steady state, the energy balance equations of the components of the collector cascade into a single first-order non-linear differential equation that is able to predict the thermal behavior of the collector. The heat transfer model clearly demonstrates the existence of an important dimensionless parameter, referred to as the thermal performance of the collector, which compares the useful thermal energy which can be extracted from the heater to the overall thermal losses of that collector for a given set of input parameters. An analysis of the thermal models was performed for the most significant input parameters such as the incident solar irradiation, the air mass flow rate, the depth of the fluid channel, in order to measure the impact of each of these parameters on the model.