Applied Sciences, Vol. 13, Pages 6345: Center-to-Center Distance’s Effect between Vertical Square Tubes of a Horizontal Array on Natural Convection Heat Transfer

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Applied Sciences, Vol. 13, Pages 6345: Center-to-Center Distance’s Effect between Vertical Square Tubes of a Horizontal Array on Natural Convection Heat Transfer

Applied Sciences doi: 10.3390/app13106345

Authors:
Zeyad Alsuhaibani
Mohamed Ali
Nader S. Saleh

An experimental study on natural convection heat transfer from the outer surface of a horizontal array of vertical square tubes in the air is investigated. The array consists of three vertical square tubes at equally different center-to-center distances. Each tube has a square cross-section with a side length of 2.00 cm, 100 cm length, and is filled with sand. Each tube is heated by inserting an internal heating element with a constant heat flux at the center. Five center-to-center separation distance to hydraulic diameter ratios (S/D) are used at different heat flux ranges of 70–360 W/m2. Results show that at small S/D, the Nusselt number of any tube in the array is lower than that of the single tube up to a specific S/D and then increases as the ratio increases. Empirical correlations are obtained for each tube in the array at different S/D using the modified Rayleigh numbers only. General correlations using S/D as a parameter are obtained for each tube, and an overall general correlation using both S/D and the tube number (n) as parameters is obtained. The difference between the predicted and experimental Nusselt numbers is in the reasonable range even at high Rayleigh numbers.

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