Engineering formula for pressure loss in an oscillating-triangular-jet nozzle

Abstract

A nozzle consisting of a circular inlet orifice and a short chamber with an exit lip can produce a naturally oscillating jet flow if the expansion ratio from inlet to chamber (D/d1) is larger than five. As an industrial natural-gas burner, the device offers advantages over simple nozzles of equivalent capacity. However, its usefulness as a pulverised solid-fuel burner is constrained because it requires a high supply pressure. This is due to the high energy-loss coefficient of the inlet expansion ratio, D/d1. If an equilateral-triangular inlet replaces the circular inlet, oscillating flow occurs at equivalent expansion ratios as low as D/d1¼2, and the supply pressure is much lower. An engineering model of the loss coefficient is obtained from measurements of supply pressure over a wide range of nozzle geometries. To begin, we split the overall loss coefficient K into three components, one for each of the inlet oriffice, chamber and exit lip. A formula representing each component of K is then determined from dimensional analysis, inspection of the data, and least-squares curve fitting. Combining these component formulae gives K as a function of four geometric parameters and seven numerical coefficients. When the numerical coefficients are optimised simultaneously, the r.m.s. difference between the model and the data is 2.2%.