This paper describes part of a continuing thermal-hydraulic study of inserts to enhance turbulent convective heat transfer in tubes, with particular application to fire-tube boilers. An electrically heated flow facility was used to deliver hot air to a water-cooled steel tube of 2.675 in (0.0679 m) i.d. and 71.75 in (1.823 m) length. Tube wall temperatures, fluid temperatures, and flow rates were measured to obtain sectional average heat transfer coefficients for four segments of the tube. Three new geometrical variations of one type of bentstrip insert were tested. A study of the insert entrance region was conducted in order to assess the insert length required for developed augmented conditions. Correlations to predict the average heat transfer and pressure drop are given. To differentiate the wall and core regions one insert was cut apart to provide core and wall inserts that were tested separately to provide more insight into the mechanisms of enhancement.

Units: Dual