This paper reports an experimental study focused on the impact of chevrons (serrations on the trailing edge of the nozzle) on the mixing process of an incompressible jet issuing from a convergent nozzle. The study also explores enhancement of the mixing performance by a novel approach to geometry modification. Profiles of mean velocity were used to characterize the extent of mixing. For a comparative assessment, studies were carried out with a base line circular nozzle, a conventional chevron nozzle and an improvised tabbed chevron nozzle. Flow visualization studies were carried out for jets issuing from chevron nozzles and the results corroborate well with quantitative measurements. The impact of confinement on mixing of jets issuing from chevron nozzles is also studied. The results show that the proposed geometry modification can significantly improve the rate of mixing in the range of Reynolds numbers considered in the study. In confined jets, presence of chevrons was found to accelerate the process of jet breakdown .

No abstract

No abstract

This paper aims at (a) improving the distribution, for the vertical velocity in the wake of a rising isolated bubble, for isothermal water layers, and (b) evaluating the proposed distribution for thermally stratified therminol layers, before and after the initiation of vortex shedding. To address these objectives, numerical investigations are performed, for the rise of an isolated bubble rising in isothermal and thermally stratified liquid layers, with the combination of Monotonic Upwind Scheme for Conservation Laws (MUSCL) and Pressure Implicit with Splitting of Operators (PISO) numerical scheme. The analysis revealed that the vertical velocity, in the wake of a rising isolated bubble, for isothermal and thermally stratified liquid layers, differs remarkably from the Gaussian distribution. Based on the detailed investigations, region-wise, wake velocity distribution, comprising a linear superposition of Gaussian approximation with Burr distribution, is proposed. Furthermore, this distribution is utilized to predict the rise velocity for a chain of rising bubbles, with the different frequencies of departure. Thus, the findings will be useful for the design of heat exchangers or cooling devices, which rely on the heat transfer augmentation with rising air bubbles, from a heated surface in isothermal (buoyancy suppressed) and thermally stratified (buoyancy assisted) liquid layers.

No abstract