Experimental Assessment of a Modified PTC with Aluminum Tubes on the Reflector Surface

Despite significant advancements in solar collector technology, persistent challenges remain in improving the overall efficiency of solar systems. This paper investigates the use of mini-channel aluminum tubes mounted on the reflective surface as preliminary heating stages to enhance the overall system thermal performance. Experimental assessments were conducted with flow rates ranging from 0.1 to 0.8 LPM and tilt angles of 180° South and 225° Southwest in Al-Kut, Iraq, from 9:00 AM to 2:00 PM. Fluid flows sequentially through five flat aluminum tubes totaling 50 channels, named stage-1, then flows through four aluminum tubes totaling 40 channels, named stage-2, and lastly through the copper tube receiver, named stage-3. Results indicate that the copper tube contributes 65%–80% of total heating, while the aluminum tubes contribute 20%–35%. The maximum thermal efficiency reached 84% at a flow rate of 0.5 LPM and a tilt angle of 180° South at 1:00 PM. The pressure drop behavior was analyzed through three stages with different flow distributions. In stages 1 and 2, the pressure drop increased linearly with flow rate. In stage-3, the pressure drop rose more sharply with flow rate showing a nonlinear trend. The results contribute to the optimization of solar thermal systems by clarifying the roles of flow rate, collector orientation, and the use of mini-channel aluminum tubes in enhancing thermal efficiency. This study contributes to solar thermal technology by showing that the use of aluminum preheating tubes in a modified PTC can enhance thermal performance and provide sustainable energy solutions.