Turbulent heat transfer and pressure drop in an internally finned equilateral triangular duct

Abstract

Experiments were carried out to determine average heat transfer coefficients and friction factors for turbulent flow through equilateral triangular ducts with pin fins. The measurements were made by using a triangular duct heat exchanger. The fluids in the heat exchanger were air and water, and the average heat transfer coefficients were determined by measuring the overall heat transfer coefficients of the heat exchanger. To attain fully developed conditions at the entrance and exit, the heat exchanger was built with additional lengths before and after the test section (30 hydraulic diameters). The triangular ducts of the heat exchanger consisted of two metal walls (brass) and a wall of a less conductive material. The metal walls of the air side were finned with an array of short pin fins. Due to their high thermal conductivity and the small temperature variation of the water, these two walls were practically isothermal. The third wall of the duct was well insulated and can be considered adiabatic. The results are presented in dimensionless form, in terms of Nusselt numbers and friction factors as functions of the Reynolds number. The pin fin efficiency, which depends on the heat transfer coefficient, is also determined as a function of dimensionless parameters. It was found that the fins increase both the heat transfer and the pressure drop compared with an unfinned (smooth) duct. A better comparison between finned and smooth ducts was made for the same pumping power and heat transfer area. The results show that the Nusselt number for the finned duct, in the present work, is always greater than the one for the smooth duct.