Effect of nozzle inclination on jet-impingement heat transfer in a confined cross-flow

This paper reports measurements of the heat transfer associated with discharge of a single circular jet into an essentially uniform cross-flow. The jet was discharged both orthogonally and at a range of angles of inclination upstream into the cross-flow. The convective heat transfer distributions beneath the jet were derived by means of the Chilton-Colburn analogy from mass-transfer measurements obtained by a 'thin-film' naphthalene sublimation technique. With weak cross-flows (i.e. jet to cross-flow velocity ratios, M>10) the maximum impingement heat transfer occurred with orthogonal discharge. This was expected, since, for jets discharging into initially quiescent surroundings it has been found by previous investigators that nozzle inclination reduces impingement heat transfer. However, at higher cross-flows the maximum heat transfer coefficients were obtained with the jet inclined at an angle of about 30° obliquely against the cross-flow. This appears to be associated with improved penetration of the jet into the cross-stream so that the jet is less readily deflected away from the impingement surface. Jet inclination can thus offer significantly enhanced heat transfer under severe cross-flow conditions.