Impinging flames are used in industrial heating and melting, safely research, and aerospace applications. Multiple modes of heat transfer are commonly important in those processes. However, the derailed heat transfer mechanisms are not well understood. The available semianalytical heat transfer solutions have only limited applicability. Therefore, researchers and designers have either made measurements or used empirical correlations to determine the heat flux rates. Here, the empirical correlations are reviewed. The correlations are first arranged by the flow geometry. Four geometries have been studied. These include flames impinging: (1) normal to cylinders in cross-flow; (2) normal to hemispherically nosed cylinders; (3) normal to plane surfaces; and (4) along plane surfaces. The correlations are then arranged by the size of the region on the target under consideration. Correlations that apply to a small region on the target, such as the stagnation point, are referred to as the local beat flux. Correlations that apply to a large region of the target, such as the, entire body of a cylindrical target, are referred to as the average heat flux. Next, the correlations are arranged by the type of heat transfer. Correlations for natural and forced convection, thermochemical hear release (TCHR), radiation, forced convection with TCHR; and forced convection with radiation have been reported for some combinations of geometry and operating conditions, Finally, the correlations are arranged by the flow type, either laminar or turbulent. Correlations do not exist for many combinations of geometry and operating conditions; therefore, recommendations are given for further research.
