Heat transfer to a row of impinging circular air jets including the effect of entrainment

An experimental investigation is performed to characterize the convective heat transfer from a flat surface to a row of impinging, circular, submerged air jets formed by square-edged orifices having a length/diameter ratio of unity. Distributions of recovery factor, effectiveness, and local heat transfer coefficient are determined. Spanwise-average and surface-average heat transfer coefficients are calculated from the local heat transfer coefficients. The heat transfer coefficient is independent of the temperature difference between the jet and the ambient, if it is defined with the difference between the (heated) wall temperature and the adiabatic wall temperature. The effectiveness is independent not only of the temperature difference between the jet and the ambient but also of the jet Reynolds number in the range studied. Spanwise-average and surface-average heat transfer coefficients have the largest values on the impingement line and decrease with increasing distance away from it.