THE TRANSITION AND MIXING BEHAVIOURS OF SLIGHTLY HEATED PLANE JETS ISSUED FROM NOZZLES OF DIFFERENT INLET GEOMETRIES
Studying a heated jet where temperature act as a passive scalar is important in turbulent shear flows. Most of the works in this area are done in circular jets and in majority of the cases vertical orientation is studied. The influence of nozzle selection and consequent impact of momentum thickness is rarely investigated in heated horizontal plane jets. In the present work experimental study is performed using a two dimensional converging nozzle and then by attaching a channel attached to the nozzle with air issued at a moderate Reynolds number of 4000 at an inlet air temperature of 60 °C. Air is supplied from a compressed air storage tank and then issued through a series of screens ,honey comb structure and turbulence intensity in both cases is controlled below 0.5%.Dantec СТА and CCA modes of hotwire anemometer with five micron probes of platinum coated tungsten is used to measure velocity and temperature fields. The ratio of heat to momentum transport is 1.33 for nozzle jets and 1.4 for channel jets. The Spread rates of both mean velocity and mean excess temperature are estimated. Half widths based on mean excess temperature and velocity is higher for channel jets. A possible reason could be difference in coherent structure development as seen by the spectral development and integral length scale estimates. The results shows that there is a scope for improving transport properties by modifying momentum thickness, a possibility less explored for plane jets.