Experimental study on convective heat transfer from a rectangular flat plate by multiple impinging jets in laminar cross flows

Convective heat transfer from a flat plate impinged by a row of air jets in laminar cross flows was studied experimentally. Several parameters, including the jet-to-cross-flow velocity ratio (1 ≤ r ≤ 30), Reynolds number (Re = 250-1750), and relative jet height (10 ≤ L/d ≤ 80), were explored. Results show that convective heat transfer can be enhanced significantly by a row of circular impinging jets. A critical jet-to-cross-flow velocity ratio exists for each experimental profile. Above this critical ratio, the relative Nusselt number, Nur, increases linearly with the jet-to-cross-flow velocity ratio. A large Reynolds number results in good convective heat transfer under the condition that the other parameters are unchanged. Furthermore, the relative Nusselt number decreases with the relative jet height when the jet-to-cross-flow velocity ratio and Reynolds number are small; meanwhile, it increases with the relative jet height initially and decreases afterward when both the jet-to-cross-flow velocity ratio and Reynolds number are sufficiently large. An empirical correlation, Nur (r, Re, L/d), with an uncertainty of 17.2% was developed.