A numerical study of the forced convection of a two-dimensional laminar air flow through a rectangular pipe with a shoulder is presented. The profiles and contours of velocity and temperature were analyzed in detail. The effects of the location of this shoulder on the insulation and on the absorber, and its height on the variations of the temperature and the velocity at the exit of the collector were also studied and compared with the case without shoulder, for a flow rate varying between 20 and 80 m(3)/h. The results show that the use of a shoulder placed on the insulator or on the absorber contributes to increasing the dynamic and thermal performance of the flow compared to the simple case; an average temperature gain of 25.52 degrees C at 56.6 degrees C is obtained for the low and high flow rates, respectively. The study also revealed that the use of the largest height h(3) rated absorber can significantly increase the velocity (of the order of 222) compared to the simple case. In addition, this location allows to direct the flow at the entrance of the drying chamber downwards, which leads to better evacuation of moist air at the chimney outlet.
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