Experimental study of heat transfer and phase change condensation in a developing, two-dimensional wall jet flow field with an isothermal boundary condition

Benchmark data were obtained in a developing wall jet flow field as a means to validate computational models utilized for automotive defroster/demister flow design. A non-impinging, two-dimensional wall jet flow was utilized due to the relatively simplicity of the flow geometry and the similarity of the boundary conditions to the actual defroster flow field.; Isothermal, non-isothermal, non-condensing and non-isothermal, condensing flow regimes were measured and compared to results obtained from a two-dimensional computational model. The experimental, mean velocity profiles at streamwise locations greater than 7.62 slot widths downstream agreed with results in the literature to within 1% [Launder and Rodi, 1981]. The computational models tended to over-predict velocity and temperature gradients at the wall surface and over-predicted growth of the inner shear region by as much as 60% while under-predicting the jet-spreading rate. The model predictions of the mean velocity and the streamwise-normal stress agree within 10% and 20% respectively throughout the developing region investigated here. A new technique was developed to measure small aliquots of water utilizing headspace gas chromatography with a flame ionization detector. This measurement technique provided measurements of water from 0 to 3 mg with an accuracy of ±0.038 mg at a 95% confidence level for the regression model. This technique is more robust and exceeds the capability of gravimetric equipment that is readily available. The development of this technique was essential to provide an accurate measure of condensate in the required range and to meet other requirements, such as specimen isolation, of the experimental program.; A novel optical technique was developed to measure transient, local condensate thickness on reflective surfaces. Surface reflectance measurements to 8–12 μm wavelengths (infrared) were correlated with H₂O condensate thickness present on the surface. This technique proved to be highly sensitive with a dynamic range from 0 to 5 μm. Measurement accuracy depends on the target utilized. Accuracy of ±0.17 μm at a 95% confidence level was attained for ensemble surface calibrations (multiple target average). It appears that a single calibrated target would provide greater measurement accuracy. This technique was utilized to provide measurements of transient condensation development in the wall jet flow and estimates of the local, instantaneous mass transfer coefficient were calculated. Results indicated that the technique is an extremely sensitive condensate thickness indicator but that uncertainty in the mass transfer coefficient can be of the same order of magnitude or larger than the measurement due to the potential error in determining the concentration difference in the flow field.