| Experiments have been performed investigating the effect of gas-phase turbulence on the evaporative heat and mass transfer of suspended heptane droplets. Comparisons are made to previously established correlations relating heat transfer and evaporation rate to characteristic flow properties such as Reynolds number, mass transfer number, and turbulence intensity. A previously developed heat transfer correlation (Yearling (1995)) accounts for gas phase turbulence level as follows, Nuf1+BH,f 0.7=2+0.58 Re1/2MPr1/3 f1+0.07TI0. 843 for the ranges, 100<ReM<1500, 0.7<Prmix,f<1.0, 0<BH,f<0.1. The convective heat transfer correlation degenerates to the laminar form in the absence of turbulence Nuf1+BH,f 0.7=2+0.58 Re1/2MPr1/3 f. ; Experiments were conducted at the Applied Energy Research Laboratory (AERL) at North Carolina State University. The AERL test facilities consist of a heated wind-tunnel capable of producing a range of mean flow velocities (0.5 to 7 m/s), grid-generated turbulent integral length scales (2 to 7 mm), and turbulence intensities (0.6% with no grid to 15% with grid installed). Flow velocity and turbulence characteristics are determined using a one-component laser Doppler velocimetry (LDV) system. The droplet evaporation rate equated with the supplied mass-flow rate necessary to maintain a constant diameter (volume) droplet. The supply flow rate is directly measured using a precision syringe pump.; Previous investigations at AERL (Yearling (1995)) have indicated that mild free-stream turbulence enhances heat transfer by as much as 30 to 50% over laminar free-stream conditions. The goal of this investigation is to quantify the interaction between the free stream turbulence structure and the evaporating droplet. A primary objective of the current investigation is to probe the validity of Yearling's turbulent correlation over a broader range of free-stream flow conditions. Experimental data is presented for laminar and turbulent free-stream over a Reynolds number range of 75 < Re < 320 and blowing regime range of 0.038 < BH < to 0.141. Although good agreement has been found with the established laminar correlation, the heat transfer data in turbulent free-stream conditions did not indicate augmentation over laminar to the extent predicted.; The effects of an in-situ droplet temperature measurement, droplet support system, internal circulation and downstream wake structure are considered and discussed. Results indicate that the free-stream turbulence strongly influences the droplet wake energy and structure. |
