Effects of dimensionless stand-off distance (h/d) and jet-to-jet spacing (s/d) on area averaged Nusselt number (Nu) for an in-line array of four submerged and confined impinging jets with conical nozzles was investigated. Range of s/d tested was from 6 to 18.5 and h/d ranged from 2 to 8. Reynolds number based on the jet exit diameter (Re) ranged from 3300 to 10600. The working fluid was a 60% to 40% (by volume) ethylene glycol - water mixture with an inlet temperature of about 80°C. Computations were validated against experiments that were carried out for the case of h/d = 5 and s/d = 18.5. A heat transfer correlation is proposed to correlate Nu with Re, Pr, h/d, and s/d for the in-line array. The correlation proposed in this work is compared with those of Martin and Meola which are derived from square and staggered array types. Correlations of Li et al. for single impinging jets were also compared. Nusselt number predictions from Li et al. were within 15% of that predicted from the proposed correlation which indicated weak jet-to-jet interactions. At large h/d such as 8 and small s/d such as 6, jet-to-jet interactions can't be neglected. As such, the correlations of Meola and Martin tend to deviate from the proposed correlation due to the differences in the way the jet-to-jet spacing effects are being captured. The jet-to-jet spacing effects can't be ignored since jets can interfere before impingement and wall jets can mix leading to an enhanced entrainment effect.
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