Performance of radial flow vaneless diffusers with diverging walls

PERFORMANCE OF RADIAL FLOW VANELESS DIFFUSERS:

WITH DIVERGING WALLS

by

RATAN LAL GUPTA

Thesis submitted to the Indian Institute of Tecbnology,Delhi for the award of the ^{Degree of}

DOCTOR OF PHILOSOPHY

Department of Mechanical Engineering Indian Institute of chnology,Delhi

December, 1974

(1)

CERTIFICATE

This is to certify that the thesis entitled

"Performance of Radial Flow Vaneless Diffusers with Diverging Walls" being submitted by Mr. R.D. Gupta

to the Indian Institute of Technology, Delhi, for the award of the Degree of Doctor of Philosophy in Mechanical Engineering, is a record of bonafide research work carried out by him. He has worked under my _guidance and has fulfilled the requirements for the submission of this thesis, which has _reached

the requisite standard. 1)

The results contained in this thesis have not been submitted in part or in full, to any _other University or Institute for _{the award} of any degree or diploma.

( S.M. AHYA )

Mechanical Engineering Deptt.

Indian Institute of Technology New Delhi-110029.

ACKNOWLEDGEMENTS

It is with great pleasure that the author records his deep sense of gratitude to Dr. S.M. Yahya who sug- gested the research problem and ' supervised the work

reported in this thesis. Dr. Yahya's unceasing enthusiasm, fruitful discussions and constant encouragement inspired the author at all stages of this work.

Thanks are due to the _{staff of} carpentary section, I.D.D.C. and Mechanical Workshop, in particular to

Mr: Karam Singh, for their efforts in fabricating a number _of components for the experimental rig. Thanks are also due to the staff of Steam and Turbomac hinery Laboratory _for their co-_operation and help during _the experimental work.

The support rendered by the Ministry of Education, Govt. of India, for the financial help under the scheme

of Quality Improvement Programme is gratefully acknow- ledged.

The author thanks all his friends who have helped in one way or the other.

Finally the thanks are due to Mr. V.P. Sharma who typed the manuscript.

N 0 TA TI ONS

A Area of cross-section at any section of the flow.

AR Area ratio = . A - 2 b Width of diffuser.

C Fluid velocity.

Cr,C9,Cx Velocity components in r-, 8-, and x directions.

CP = (p3-p2)/

ip 2 ,

AC Gain of pressure recovery over non-swirl. flow.

D Diameter of the pipe.

d Diffuser diameter.

f Friction coefficient.

g Acceleration due to gravity.

L Length of flow path of air.

N Speed of wire gauze rotor.

p Static pressure.

po S tagna ti on pressure.

R Gas constant.

R _ CX2.b2

e — , Reynolds number based on hydraulic mean diameter (2b).

r Radial distance.

T Static temperature.

To Stagnation temperature.

Axial distance measured across the width.

R kinematic viscosity.

P

Angle of divergence of the diffuser walls.

Angle between absolute velocity and tangen- tial component.

Density of air.

~po2- po3y PC22 , loss coefficient.

/1 - 1 , loss coefficient.

A2 R

Diffuser efficiency based on stagnation pressure loss.

Diffuser efficiency based on the static pressure rise.

SUBSCRIPTS

1. Entry to the test rig.

2. Entry to the diffuser.

3. Exit of the diffuser.

w At the diffuser wall.

SUPERSCRIPTS

- Average value.

Ideal value.

x

V

A a

1

T'd2

(v)

CONTENTS

CERTIFICATE ACKNOWLEDGEMENT NOTATIONS

CONTENTS

CHAPTER I IWJRODUCTION

1 .1 Definition and types 1 .2 Applications

1 .3 Flow process in a diffuser 1 .4 Brief history

1 _.5 'The radial diffuser

1.6 Losses, pressure recovery and coefficients

1.7 Dimensional analysis CHAPTER II LITERATUREE SURVEY

2.1 Diffusers for hydraulic systems 2.2 Gas diffusers

2.2.1 'Pressure recovery coefficient 2.2.1.1 Effect of Reynolds number on

pressure recovery

2.2.1.2 Effect of boundary-layer on pressure recovery

2.2.1.3 Effect of swirl on pressure recovery

2.3 Incompressible flow analysis

1 1 3 3 4 8 9 11 13 . 13 14 22 22 23

23

24

3.4.4 Method of calculating friction

coefficient

59

CHAPTER IV EXPERIMENTAL RIG AND INSTRUMENTATION 61

4.1 Experimental rig 61

4.1 .1 Design and manufacture of the

diffusers .62

4.1 .2 Suction rings 67

4.1.3

68

4.2

Instrumentation 69

CHAPTER V EXPERIMENTS 71

5.1

72

5.1 .1

= 2° ) 72

5.1 .2 Diffuser B(A = 30

74

5.1 .3

5°) 75

5.1 .4

= 5

⁷⁵

5.1 .5

50

75

5.2

75

5.3 Presentation

'results 76

CHAPTER VI DISCUSSIONS 82

6.1 Non-swirl

6.1 .1 Diffuser A(

=

6.1 .1 .1 Velocity profile 82

6.1 .1 .2 Pressure recovery 82

6.1.1.3 Efficiency 83

6.1.1.4

84

6.1 ,1 .5

and efficiencies

85

6.1 .1 .6 Conclusions 86

6.1 .2 Diffuser B(8 = 30

) 87

6.1.2.1 Velocity profile 87

6.1.2.2 Pressure recovery

87

6.1.2.3 Efficiency 88

6.1.2.4 Loss coefficient

88

6.1 .2.5

and efficiencies 89

6.1.2.6 Conclusions 90

6.1 .3 Diffuser C (A = 50) 91

6.1 .3. Velocity profile 91

6.1.3.2

6.1.3.3 Efficiency 93

6.1.3.4 Loss coefficient 93.

6.1.3.5 Comparison of loss coefficients

and efficiencies 94

6.1.3.6 Conclusions

95

6.2 Swirl tests on diffuser A(ø = 2°) 96

6.2.1 Range of swirl angles .96

6.2.2 Velocity and swirl profiles at

diffuser entry 97

6.2.3 Pressure recovery C,, -98

6.2.4 Loss coefficient A 101

6.2.5 Efficiency i 103

6.2.6 Comparisons at Re =0.5,1.2 and

1.8X.105 105

6.2.7 Conclusions 106

6.3 Comparative performance of diffusers 108 6.3.1 Pressure and velocity profiles 108

6.3.2 Pressure recovery

C PR

6.3.3 Loss coefficient & 112

6.3.4 Loss coefficient A 115

6.3.5

6.3.6

6.3.7 Diffuser size 121

6.3.8 Friction coefficient 121

6.3.9

FUTURE WORK 128

7.1 Main conclusions 128

7.2 Suggestions for future work 130

REFERENCES 131

APPENDIX 137