Heat transfer and pressure drop in triangular ducts

Abstract

Heat transfer and pressure drop characteristics were determinded for triangular ducts with apex angles of approximately 10°, 20° and 30° and corresponding flow passages of 2.74, 2.75 and 2.68 square inches. The ducts, arranged vertically, had a height of five feet. They were heated by steam and maintained at a constant temperature of 218°F. The test facility was made to suit the upward as well as the downward flow of the air through the ducts. The pressure drop across the duct and the temperatures of the air at the duct inlet and the duct outlet were measured fro mass flow rates of air between 19.5 and 236.0 lb[subscript m]/hr. The Nusselt number, the Reynolds numbers, the Graetz number and the friction factor were calculated from the test data to find the heat transfer and the pressure drop characteristics for the triangular ducts. No appreciable change in the heat transfer was obtained between the upward and the downward flow of the air. The Nusselt number was found to vary approximately linearly with the Reynolds number. The pressure drop was higher for the downward flow than the upward flow. The friction factor was related to the Reynolds number with an equation of the Blasius form f = C'/N[subscript re][superscipt 0.25]. A new parameter for the pressure drop was developed. This parameter d³[delta]P₀/L[mu]² eliminates the necessity for a trial and error solution in the design of a fluid flow system. The results were compared with the available information in the literature.