Experimental investigation of the conduit slope impact on mixed convection in solar collectors

• Main Authors: Al-Sammarraie A.T., Al-Jethelah M., Ibrahim T.K., Salimpour M.R., Alnaimi F.B.I.
• Other Authors: 57195757756
• Format: Article
• Published: Taylor and Francis Ltd. 2024
• Subjects: experimental; inclined pipe; Mixed convection; solar collector; uniform heat flux; Copper pipe; Heat flux; Nusselt number; Solar collectors; Circular conduit; Experimental; Experimental investigations; Heat rate; Inclination angles; Inclined pipes; Length to diameter ratio; Mixed convection heat transfers; Pipe inclinations; Uniform heat flux
• Institution: Universiti Tenaga Nasional

An experimental investigation on the mixed convection heat transfer of air flowing in circular conduits of a solar collector is conducted. The test rig consists of three different copper pipes with a length of 70 cm. The pipes are heated at constant heat flux. The effect of the pipe inclination angle (? = 0�, 60�, and 90�), length-to-diameter ratio (L/D = 13.8, 18.4, and 36.7), and heat rate (Q = 5, 11, 19.6, 30, 40.5, and 57.8 W) is studied in the present study. The influences of Richardson number (Ri), inclination angle, and length-to-diameter ratio on the average Nusselt number are examined as well. The results show that the Nusselt number (Nu) is improved by 41.5% as the inclination angle is changed from 0� to 90� at L/D = 13.8. Further, as the length-to-diameter ratio was reduced from 36.7 to 13.8 at 90�, up to 54.9% enhancement in heat transfer is found. Also, it is seen that by increasing the heat rate from 5 W to 57.8 W at 90� and L/D = 13.8, the exchange in heat is improved by 44%. Three empirical correlations were proposed for each studied pipe inclination angle. A good agreement was found between the measured Nu and the calculated Nu from the proposed correlations. � 2023 Taylor & Francis Group, LLC.