Turbulent heat transfer and flow characteristics in a horizontal circular tube with strip-type inserts. Part II. Heat transfer

This paper is the second of two papers that presents the results of an extensive study of turbulent heat transfer and pressure drop in a horizontal tubes with strip-type inserts. Experimental data were taken for air for a class of strip inserts (longitudinal strip and crossed-strip). The insert was characterized by the parameters of 1<=AR<=5 and R* (=0.5 and 1). Friction factor data (from Part I) and temperature measurements were used to understand the underlying physical phenomena responsible for the heat transfer enhancement for 6500<=Re<=19 500. Nusselt numbers were between four and two times the bare tube values at low Re and high Re, respectively. Performance evaluation index R1 (constant pumping power) and R2 (constant heat duty) were made and an optimum condition would be thus found.