Multiple impinging jet arrays - TU Delft Institutional Repository

184 Pages·2004·9.86 MB·English

Multiple impinging jet arrays:
an experimental study on
flow and heat transfer
L.F.G. Geers
Multiple impinging jet arrays: an
experimental study on flow and heat
transfer

Multiple impinging jet arrays: an
experimental study on flow and heat
transfer
Proefschrift
ter verkrijging van de graad van doctor
aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. dr. ir. J. T. Fokkema,
voorzitter van het College voor Promoties,
in het openbaar te verdedigen op maandag 9 februari 2004 om 10:30 uur
door
Leonard Ferdinand Gerard Geers
scheikundig ingenieur
geboren te Tilburg.
Dit proefschrift is goedgekeurd door de promotor:
Prof. Dr. Dipl.-Ing. K. Hanjali´c
Samenstelling promotiecommissie:
Rector Magnificus, voorzitter
Prof. Dr. Dipl.-Ing. K. Hanjali´c, Technische Universiteit Delft, promotor
Prof. dr. ir. J. Westerweel, Technische Universiteit Delft
Prof. dr. R. F. Mudde, Technische Universiteit Delft
Prof. M. Yianneskis, King’s College, London
Prof. dr. ir. Th. H. van der Meer, Universiteit Twente
Dr. ir. C. C. M. Rindt, Technische Universiteit Eindhoven
Dr. ir. M. J. Tummers, Technische Universiteit Delft
This research project was sponsored by The Technology Foundation (STW), TNO-TPD,
and Rademaker - Den Boer BV.
ISBN 90 901 7774 4
Copyright (cid:13)c 2003 by Leon Geers
Printed in the Netherlands
Voor Pa, Ma en Natasja
’The life of a scientist is one of vast periods of tranquility, punctuated by brief and sudden
moments of drama and excitement.’
Prof. Ian Stewart – Does God play dice?
vi
Contents
1 Introduction 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Theoretical background and literature review 5
2.1 Turbulent flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Conservation laws . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Heat transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.3 Structure identification . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Impinging Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1 Hydrodynamics of a single jet . . . . . . . . . . . . . . . . . . . . 14
2.2.2 Multiple jet flow characteristics . . . . . . . . . . . . . . . . . . . 19
2.2.3 Heat Transfer to a single impinging jet . . . . . . . . . . . . . . . 21
2.2.4 Heat transfer to multiple jet arrays . . . . . . . . . . . . . . . . . 23
3 Measurement techniques 27
3.1 Laser Doppler Anemometry . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.1 Principle of the technique . . . . . . . . . . . . . . . . . . . . . . 27
3.1.2 Fringe model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1.3 Tracer particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.1.4 Velocity bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 Particle Image Velocimetry . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.1 Principles of the technique . . . . . . . . . . . . . . . . . . . . . . 33
3.2.2 Advanced techniques . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 Liquid Crystal Thermography . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.1 Liquid Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.2 Colorimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.3 Lighting and camera . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.3.4 Image processing . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.5 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4 Experimental Apparatus 55
4.1 Single impinging jet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
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viii CONTENTS
4.2 Multiple impinging jet array . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.1 Wind tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.2 Heat transfer experiments . . . . . . . . . . . . . . . . . . . . . . 60
4.2.3 Liquid crystal calibration . . . . . . . . . . . . . . . . . . . . . . . 66
4.2.4 Flow experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 Results 75
5.1 Single impinging jet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.2 Multiple impinging jet array . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.2.1 Fluid mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.2.2 Heat transfer and the effect of turbulence . . . . . . . . . . . . . . 102
5.2.3 Vortical structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
6 Conclusions 143
A Specification of the wind tunnel 149
Bibliography 153
Nomenclature 161
Summary 167
Samenvatting 169
List of publications 171
Dankwoord 173
About the author 175
Chapter 1
Introduction
1.1 Background
Impinging jets are jets of fluid impinging on a surface that needs to be cooled or heated.
Because of their high efficiency and their ability to provide high heat transfer rates,
these jets are applied in a wide variety of rapid cooling and heating processes. Figure
1.1 presents a sketch of a jet issuing from a round pipe and impinging on a flat surface.
Arrays of impinging jets are applied in, for instance, steel and glass quenching, textile
drying, paper processing, baking. Figure 1.2 shows a schematic of another example: the
internal cooling of turbine blades. Due to the high temperatures in gas turbines (1400–
1500◦C), the blades are subject to high stresses that can cause severe damage to the
blades. While cooling of the mid-chord and trailing edge sections is being established
by ribs and pin fins, respectively, the leading edge is cooled with swirling flow created
Figure 1.1: Jet issuing from a pipe and impinging on a flat surface (Peper et al., 1995).
1