Heat transfer on the outer surface of vertical longitudinally finned tubes

Abstract

This paper analyses the heat transfer process on the outer surface of a vertical tube with eight longitudinal aluminium fins situated central-symmetrically along its perimeter. The goal of this experimental study is to determine the local heat transfer coefficients on the outer surface of vertical tubes with longitudinal fins during airflow under natural and forced convection conditions. The analysis concerned the distribution of heat transfer coefficients on the perimeter and along the pipe. It looked at various ranges of air velocity w = 0–2.3 m/s and a variety of air refrigerant temperatures ΔT = 24–40 K. Measurements taken for non-zero air flow velocity indicated the need to take into account the effect of the temperature difference between the heat transfer coefficients obtained for conditions of forced convection in the analysed range of flow rates. In addition, the study involved the determination of temperature distribution on the ribs, and their efficiency was verified numerically by CFD modelling of the heat exchange process for the ribs. Numerical calculations confirmed the correctness of the method for determining the efficiency of the ribs and of the method of measurement.