Heat transfer in a confined impinging jet with swirling velocity component

Karel Petera,Martin Dostál

doi:10.1051/epjconf/201714302091

Karel Petera, Martin Dostál

Open Access

https://doi.org/10.1051/epjconf/201714302091

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Abstract

Heat transfer measurements based on an infrared experimental method (TOIRT) are compared with CFD simulations of a confined impinging jet with tangential velocity component. The tangential velocity component added to a pure impinging jet introduces into the flow field and heat transfer some similarities with real industrial processes like agitated vessels with axial-flow impellers. The tangential velocity component significantly influences the velocity field and heat transfer intensity in the stagnant region when compared to the classic impinging jet characteristics. Several turbulence models were used in numerical simulations of an agitated vessel with axial-flow impeller in a draft tube. Heat transfer coefficients at the vessel bottom were evaluated using the TOIRT method and compared with numerical results. The lateral heat conduction in the impinged wall was analysed with the conclusion that it has relatively small impact on the measured heat transfer coefficients. Quite good agreement of experimental data and simulation results was achieved concerning the size and position of the heat transfer maximum at the vessel bottom.

Highlights

High heat transfer intensities at relatively small surfaces can be achieved with impinging jets putting them in the focus of industrial interest
Many impinging jets are generated by devices with rotary parts some tangential velocity component is always present at the jet nozzle which has a significant impact on the velocity profile
The results presented here show that the values based on Wandelt and Roetzel method [8] have quite good agreement with correct heat transfer coefficients in regions with values greater than 1000 W m−2 K−1, that is in the prevailing part of the measured profile

Summary

Introduction

High heat transfer intensities at relatively small surfaces can be achieved with impinging jets putting them in the focus of industrial interest. A large drop in Nusselt number values is visible at the center of the stagnation region which is a consequence of small values of the axial velocity components there It is in accord with some of the literature data [6], even though as pointed out by [7], the flow and heat transfer characteristics show drastically different results depending on the type of swirl generators. The axial-flow impeller produced a jet with tangential (swirling) velocity component at the outlet of the draft tube, which, in addition, belongs to the category of confined impinging jets because it is placed in a cylindrical vessel. We compared CFD simulation results with experimental data measured by the TOIRT (infra-red temperature-oscillation) method [8]

Numerical simulation of agitated vessel

TOIRT experimental method

Experimental

Numerical simulation of the Wandelt and Roetzel method

Conclusions