Free and forced convection on the outer surface of vertical longitudinally finned tubes

• Published in: Experimental thermal and fluid science 2014-09, Vol.57, p.145-156
• Main Authors: Niezgoda-Żelasko, Beata, Żelasko, Jerzy
• Format: Article
• Language: English
• Subjects: Air flow; Airflow; Applied sciences; Devices using thermal energy; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Forced convection; Free convection; Heat exchangers (included heat transformers, condensers, cooling towers); Heat transfer; Heat transfer coefficients; Mathematical analysis; Tubes; Vertical finned tubes
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2014.04.014

•Experimental studies of the heat exchange process under free and forced convection.•Longitudinal and transverse air flow around longitudinally-finned vertical tubes.•Heat transfer coefficients for transverse and longitudinal air flow.•Influence of the Raleigh and Reynolds numbers on the values of Nusselt numbers.•Relationships enabling the calculation of heat transfer coefficients. The paper presents the results of experimental studies of the heat transfer process on the outer surface of longitudinally finned tubes. Experimental values of heat transfer coefficients under free and forced convection conditions were calculated for low air flow velocities. Two air flow patterns were analysed, i.e. airflow parallel and perpendicular to the axis of the pipe. The mean values of heat transfer coefficients obtained during the study amounted to 2–8.5 (Wm−2K−1) under free convection conditions, 4.5–19(Wm−2K−1) for forced transverse flow and 4–11(Wm−2K−1) for forced convection along the axis of the tube. Experimental values of heat transfer coefficients for transverse flow around the tube were 22% higher than heat transfer coefficients for airflow along the axis of the tube. The paper lists the dimensionless relationships which can be used to calculate the values of the heat transfer coefficient under free and mixed convection conditions, with transverse and longitudinal air flow around the outer surface of vertical longitudinally finned tubes.