Two-step numerical simulation of the heat transfer from a flat plate to a swirling jet flow from a rotating pipe

Abstract

Purpose Impinging jets have been widely studied, and the addition of swirl has been found to be beneficial to heat transfer. As there is no literature on Reynolds-averaged Navier Stokes equations (RANS) nor experimental data of swirling jet flows generated by a rotating pipe, the purpose of this study is to fill such gap by providing results on the performance of this type of design. Design/methodology/approach As the flow has a different behaviour at different parts of the design, the same turbulent model cannot be used for the full domain. To overcome this complexity, the simulation is split into two coupled stages. This is an alternative to use the costly Reynold stress model (RSM) for the rotating pipe simulation and the SST k-ω model for the impingement. Findings The addition of swirl by means of a rotating pipe with a swirl intensity ranging from 0 up to 0.5 affects the velocity profiles, but has no remarkable effect on the spreading angle. The heat transfer is increased with respect to a non-swirling flow only at short nozzle-to-plate distances H/D < 6, where H is the distance and D is the diameter of the pipe. For the impinging zone, the highest average heat transfer is achieved at H/D = 5 with swirl intensity S = 0.5. This is the highest swirl studied in this work. Research limitations/implications High-fidelity simulations or experimental analysis may provide reliable data for higher swirl intensities, which are not covered in this work. Practical implications This two-step approach and the data provided is of interest to other related investigations (e.g. using arrays of jets or other surfaces than flat plates). Originality/value This paper is the first of its kind RANS simulation of the heat transfer from a flat plate to a swirling impinging jet flow issuing from a rotating pipe. An extensive study of these computational fluid dynamics (CFD) simulations has been carried out with the emphasis of splitting the large domain into two parts to facilitate the use of different turbulent models and periodic boundary conditions for the flow confined in the pipe.

Computational study of the application of Al2O3 nanoparticles to forced convection of high-Reynolds swirling jets for engineering cooling processes

“…The reason is attributed to two important facts. First, as stated in Granados-Ortiz et al (2019), this imbalance between experimental-computational works is also observed in classic literature on heat transfer by impinging air or water jets. It was discussed earlier in this section that the modeling of turbulence in impinging jets is challenging (it is considered a case of complex flow because of the sudden changes in velocity magnitude and direction, the shear-layer interaction and the transition to turbulence (Granados-Ortiz & Ortega-Casanova, 2020)).…”

“…The impinging jet considered in the present paper is turbulent. The existence of turbulence in wall jets is, in fact, recommendable since the radial Nusselt distribution strongly depends on this feature, as shown by several authors (Behnia et al, 1999;Granados-Ortiz et al, 2019;Uddin et al, 2013). These authors explicitly outlined the presence of secondary peaks in the Nusselt profile due to the transition to turbulent flow.…”

“…These authors explicitly outlined the presence of secondary peaks in the Nusselt profile due to the transition to turbulent flow. They also pointed out the complexity in turbulence modeling of impinging jets, where even high-fidelity simulations such as Large Eddy Simulations (LES) may have difficulties to reproduce accurately experimental results (Granados-Ortiz et al, 2019;Uddin et al, 2013).…”

“…Visualization techniques applied in Nuntadusit et al (2012) showed that heat transfer rates of the moderate swirling jets (S = 0.4) are found to enhance the non-swirling jet performance, whereas those of larger swirl numbers (S = 0.78 and 0.94) worsen the performance in comparison to the non-swirling jet. This is so due to flow momentum and velocity profiles of the jets, which are dependent on the device used for swirl generation (Granados-Ortiz et al, 2019). The most relevant phenomenon when dealing with swirling flows is recirculation bubble.…”

Desirable effects of cutting grooves on inner side of small cooling tower on reduction in ground level pollutant concentration

“…In some cases, the grooves were cut on the inner side of jet with different twisting angles to rotate the outlet flow of fluid. The effects of swirling jets on the flow and heat transfer of fluid were investigated by many authors [20][21][22]. The study of previous works on the effects of swirling jet on the flow and heat transfer of fluid led the authors to propose the idea of using swirling exhaust plume to disperse the pollutant.…”