Effects of inlet velocity profile and swirl on the cooling characteristics of a laminar jet

The outcomes of numerical and experimental studies performed on a laminar circular swirling jet impinging on a flat surface is presented. In the numerical studies the computational domain is three-dimensional, which aids in predicting the complexity of the swirl flow field. The impact of inlet velocity profile is also studied. The Reynolds number is between 250 and 1500, with normalized jet outlet to surface spacing ranging from 2 to 12, and swirl number varying from 0 to 0.8. The configuration of the inlet velocity profile greatly influences the cooling characteristics. It was found that the cooling diminishes with rise in normalised nozzle to plate distance, due to the negative effect of increased entrainment and reduction in impingement velocity. The optimum distance from the nozzle to the plate is twice the diameter of the nozzle. In the range of Reynolds number and normalised nozzle to plate distance investigated extreme cooling happens at the point of stagnation. The cooling is superior with a parabolic velocity profile, compared to uniform profile. At a Reynolds number of 1000, the Nusselt number at the stagnation point for the parabolic velocity profile is 30% higher than that of the uniform profile. The stagnation Nusselt number rises by 275% as the Reynolds number increases from 250 to 1500. The relationship between the stagnation Nusselt number (Nus) and the Reynolds number (Re) can be expressed as Nus ∝ Re0.7. From a cooling perspective, pipe nozzle is less responsive to the introduction of swirl than orifice nozzle. Introduction of tangential velocity to a cylindrical jet can either improve cooling or reduce it, contingent on the swirl number and the Z/D. In the scenario of parabolic velocity, the average Nu rises with the swirl number, peaks at a swirl number of 0.4, and then declines thereafter. The average Nusselt number rises by 20% upon the introduction of a swirl with a swirl number of 0.4. With a uniform profile, swirl has a detrimental effect on the heat transfer on the entire area.