Heat transfer and friction of rough ducts carrying gas flow with variable physical properties

Abstract

The paper presents the results of an experimental investigation into the local heat transfer and friction of gas (air) flow in annuli with the inner rough tube for the following ranges of parameters: Re = 5 × 10 3−5 × 10 5, temperature factor T w / T f = 1−2.8, relative height k/ d e = 0.0028−0.021 and nearly optimum relative pitch s/ k ~ 10 of rectangular and rounded trapezoidal roughness elements. The correlations have been developed to calculate the heat transfer and friction of rough annuli with allowance for the effect of variable physical properties of a coolant and also the relationships for the hydrodynamic and thermal functions of roughness to determine the thermohydraulic characteristics of rough tube clusters. It has been established that, in contrast to smooth tubes, the effect of variable physical properties of the gas on heat transfer in rough tubes depends on k/ d e and Re and diminishes with the increase of these parameters.