STUDIES ON
COILED FLOW INVERTER HEAT EXCHANGER
by
VIMAL KUMAR
DEPARTMENT OF CHEMICAL ENGINEERING
Submitted In fulfillment o f the requirements o f the degree o f
DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
MAY, 2007
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Dedicated to
My Parents
CERTIFICATE
This is to certify that the thesis entitled, ‘Studies on Coiled Flow Inverter Heat E xchanger’
being submitted by Mr. Vimal Kumar to the Indian Institute o f Technology, Delhi for award o f Doctor o f Philosophy is a record o f bonafide research work carried out by him under my guidance and supervision in conformity with the rules and regulations o f Indian Institute o f Technology, Delhi.
The research report and results presented in this thesis have not been submitted, in part or full, to any other university or institute for the award o f any degree or diploma.
Professor
Department o f Chemical Engineering Indian Institute o f Technology, Delhi New D elhi-110016
ACKNOWLEDGMENT
A t this m om ent, available word seem to be inadequate to express my deep sense o f gratitude to Professor K. D. P. N igam Departm ent o f Chemical Engineering, by w hose inspiration, keen interest and kind o f support, I had the opportunity to conduct this study. I shall be indebted to him forever for inculcating within me the qualities o f confidence, perseverance and a sense o f com m itm ent tow ards one’s work. He is a teacher par-excellence. W ithout his support, this task co u ld n ’t have been so easy for me. I specially thank him for being kind and considerate tow ard m e throughout the course work. It was a fortunate and unforgettable experience to w ork under his reflective and revered guidance. His endless kindness and incom parable support cannot be thanked adequately here.
I am profoundly thankful to all the Heads o f Chemical Engineering Prof. A. K. G upta, Prof.
B. K. G uha and Prof. S. K. G upta for providing me with all the necessary laboratory facilities during my tenure. I am extrem ely grateful to Prof. A. K. G upta for his concern about my w ork and clarifying certain doubts about heat exchanger design and his tim e to tim e valuable suggestions. Encouragem ent and constant support given by all the faculty m em bers o f the D epartm ent o f C hem ical Engineering, particularly P rof V. K. Srivastava and P rof A. N.
Bhaskarw ar, Dr. K. K. Pant throughout my research work is greatly acknow ledged.
I thank Dr. Y annick H oarau for all the time and advice that you gave tow ards the modeling aspect o f this project.
I w ish to thank the laboratory and office staff o f the Departm ent. I am especially grateful to Mr. N.K. Gupta, Mr. K rishan Kumar, Mr. Bisham ber Dayal, Mr. Vijay Pal Singh and Mr.
Azmal D asthagir for their encouragem ent and help and assistance in laboratory, which enabled me to com plete this research work.
W hen one ow es so m any, it is alm ost impossible and invidious to single out nam es. H ow ever I acknow ledge my friends Mr. R. N. Maiti, Ms. Subhashini Vashisth, Ms. M onisha M ondal, Mr. A rnab Atta, Ms. N andini Pechimuthu, Mr. Azad Singh, Mr. A m it G aikw ad, Ms.
A kanksha, Mr. K anthi V arm a and all the research scholars for their love, concern and help during my PhD.
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There are so many other people to thank: the many undergraduate students whom I had the pleasure o f discussing the projects, fellow graduate students, and the list goes on. Thank you all for your kindness.
And w hen it comes to personal support, I want to express my heartfelt thanks to my dear parents for their support and advice throughout my work. This thesis is as much yours as it is mine. I also remember the valuable words o f encouragement from my brothers Dr. Mukesh Kumar, Mr. Dinesh K um ar and my beloved sister Ms. Anju Singh.
I greatly acknowledged the Ministry o f Chemicals and Fertilizers for funding the research to install the heat exchanger on such a big pilot plant scale. I express gratitude to M/S Xytel India Private Limited, Pune for fabricating, testing, commissioning and developing software for the pilot plant.
Herewith I would like to thank for all o f those, who have directly or indirectly contributed to the realization o f this thesis.
(V IM A L K U M A R )
ABSTRACT
Heat transfer is an essential com ponent o f nearly all industrial processes, ranging from pow er production, chem ical and food industries, electronics, environm ent engineering, w aste heat recovery, m anufacturing industry, air-conditioning, refrigeration and space applications.
Consequences o f im proper heat-transfer include non-reproducible processing conditions and lowered product quality, resulting in the need for m ore elaborate dow nstream process system and increased heat-transfer area. H elically coiled tubes find applications in various industrial processes like solar collectors, com bustion system s, heat exchangers, and distillation processes due to their sim ple and effective means o f enhancem ent in heat and mass transfer, narrow er residence tim e distribution and com pact structure.
In the present study a new device “C oiled Flow Inverter” has been introduced based on the phenom enon o f flow inversion by changing the direction o f centrifugal force in helically coiled tubes. The m ain m echanism generating the flow in the production o f spatially chaotic path by changing the direction o f flow in helical coils (alternating D ean flow). If the direction o f centrifugal force is rotated by any angle, the plane o f vortex form ation also rotates with the same angle. Thus in coiled flow inverter (CFI) com plete flow inversion is achieved by 90° shift in the direction o f centrifugal force, w hich also produces the stretching and folding in flow and therm al profiles.
The attempts have been made to investigate the hydrodynam ics and heat-transfer characteristics o f a coiled flow inverter (CFI) as heat exchanger on pilot plant scale. The experiments have been carried out in counter-current m ode operation w ith hot fluid in the tube side and cold fluid in the shell side o f coiled flow inverter heat exchanger (CFIHE).
Experimental study has been carried out over a wide range o f R eynolds num bers using DM water in the tube side o f the heat exchanger. The shell side fluids used is either cooling water or am bient air. The tube side o f CFIHE com prised o f alternate helical coils and 90° bends which are inserted in a closed shell. The heat exchanger is fitted with three types o f baffles (central rod, square m em bers and w edge shaped cut plates) to provide higher turbulence and avoid channeling in the shell side. The bulk m ean tem peratures at various downstream positions are reported for different flow rate on tube side. The heat transfer efficiency o f the heat exchanger is also calculated. Pressure drop and overall heat-transfer coefficient is calculated at various tube and shell side process conditions. The outer and inner heat-transfer coefficients are determ ined using W ilson plot technique. The results show that at low Reynolds num ber, heat-transfer in CFIHE is higher as com pared to coiled tubes, while at high Reynolds num bers, the configuration has less influence on heat transfer enhancement.
N ew em pirical correlations have been developed for friction factor and N usselt number predictions in the (CFIHE).
The convective heat transfer in CFIHE has been num erically investigated by varying Dean number, Prandtl num ber and num ber o f bends under lam inar flow conditions with constant wall tem perature (Tw) and constant wall flux (®w) as a boundary condition. The three- dimensional governing equations for m om entum and energy under the lam inar flow conditions are solved with a control-volum e finite difference m ethod (CV FD M ) w ith second- order accuracy. The stretching and folding phenom enon in Coiled flow inverter is observed and discussed for flow and therm al developm ent, heat transfer coefficient and flow resistance in the coiled flow inverter. The cyclic oscillation behavior in the heat transfer coefficient with dow nstream distance in the coiled flow inverter and coiled tube is also observed and
discussed. It appeared that heat transfer is strongly influenced by flow inversion. The effect o f boundary conditions on heat transfer perform ance in the Coiled flow inverter as well as in the coiled tube has also been studied. The effect o f Prandtl num ber on fully developed heat transfer coefficient is also reported. It is observed that heat transfer increases with increase in Prandtl number.
The study has been further extended to predict hydrodynam ics and heat transfer with tem perature-dependent properties (density, viscosity, therm al conductivity and specific heat) in the coiled tube and coiled flow inverter. The secondary flow induced due to centrifugal force distorts the velocity and tem perature profiles when the effect o f tem perature-dependent properties is taken into account. It is observed that the heat transfer under heating condition with tem perature-dependent viscosity is higher as com pared to the constant viscosity result while friction factor shows the reverse phenom enon in CFI. A new model is also developed in the present study based on the property-ratio technique for both friction factor and N usselt number.
In another study the hydrodynam ics and heat transfer characteristics o f a tube-in-tube helical heat exchanger at the pilot plant scale has also been investigated both experim entally and numerically. The experim ents are carried out in counter current mode operation with hot fluid in the tube side and cold fluid in the annulus area. The outer tube is fitted with sem icircular plates to support the inner tube and also to provide turbulence in the annulus region. The heat transfer coefficients are calculated in the inner as well as outer tubes using Wilson plots. The flow and therm al developm ent in tube-in-tube helical heat exchanger are carried out num erically for both inner and outer tubes. The num erically obtained N usselt num ber and friction factor values in the inner and outer tubes are com pared with the
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experim ental data collected in the present study as well as reported in the literature. The num erical predictions are in good agreem ent w ith the present experim ental data. The perform ance o f C FIH E and tube-in-tube heat exchanger is com pared.
The technology transfer o f CFIHE has also been done for the fertilizers industry in INDIA.
The basic engineering package (BEP) and detailed draw ings o f the CFIH E is prepared and given to the concerned fertilizers industry. The design o f the CFIHE is carried out for the following two process streams: (a) installation o f a new w ater cooler in C 0 2 com pressor suction knock out drum and (b) replacem ent o f a liquid-liquid heat exchanger for heat recovery in U rea Plant. It is found that the there will be a 25 % energy saving if the CFIHE is replaced with the existing heat exchanger in the fertilizers industry.
TABLE OF CONTENTS
C ER T IFIC A T E i
A C K N O W L E D G E M E N T ii
A B ST R A C T iv
LIST O F FIG U R ES xiv
LIST O F TA BLES xxii
N O TA TIO N S xxiv
C H A PTER 1 IN T R O D U C T IO N
1.1 Background 1
1.2 H ypothesis 8
1.3 O bjectives 11
1.4 O verview o f dissertation 13
CH A PTER 2 LIT E R A T U R E R EVIEW
2.1 Introduction 14
2.2 Coiled T ube A pplications 14
2.3 Fluid Flow in Curved Tubes 15
2.3.1 Flow developm ent at low D ean num ber 15
2.3.2 Fluid flow at high Dean num bers 19
2.3.3 D evelopm ent o f flow fields 21
2.3.4 Effect o f torsion on secondary flow 23
2.4 Friction Factor in C urved Tubes 28
2.4.1 Lam inar flow in coiled and curved tubes 28
2.4.2 Transition from lam inar to turbulent flow 30
2.4.3 Turbulent flow 35
2.4.4 O rientation o f the coiled/curved pipes 38
2.5 M ass T ransfer and M ixing in Curved Tubes 38
2.5.1 A xial dispersion in curved tube 38
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2.5.2 M ass transfer in curved tubes 40
2.6 H eat T ransfer 48
2.6.1 Therm al developm ent in curved tube 48
2.6.2 Fully developed heat transfer 53
2.6.3 Effect o f pulsatile Flow 62
2.6.4 Influence o f pitch on heat transfer 63
2.6.5 Effect o f buoyancy force 65
2.6.6 U nsteady state fluid flow and heat transfer 67 2.7 N on-N ew tonian Fluid Flow and H eat T ransfer 68
2.8 H elical Flow w ith Curved A nnulas 71
2.9 C haotic C onfiguration (com bination o f coils and bends) 74
2.10 C onclusions 77
C H A PTER 3 E X PE R IM E N T A L SETU P A ND M E T H O D O L O G Y
3.1 E xperim ental A pparatus 82
3.1.1 L iquid-feed section 82
3.1.2 H eating section 86
3.1.3 Inter-stage cooling and pressure regulating section 86
3.1.4 U tility section 89
3.1.5 Instrum entation 89
3.1.5.1 Tem perature m easurem ents 89
3.1.5.2 Pressure m easurem ents 91
3.1.5.3 F low m easurements 92
t 3.1.5.4 L iq u id level m easurem ents and control 92
3.2 H eat E xchanger 92
3.3 Softw are D escription 97
3.4 Process Fluids and C onditions 97
3.5 E xperim ental Procedure 99
3.6 Therm al E quilibrium Criterion 100
3.7 C alculation o f H eat Transfer C oefficient 101
3.7.1 G raphical W ilson plot technique 103
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3.8 Fluid Flow ing in Shell Side: The Equivalent D iam eter 106
3.9 Prelim inary R esults and D iscussion 107
3.9.1 Flow and tem perature profiles in coiled flow inverter heat 107 exchanger
3.9.2 Rise in tem perature o f the tube side fluid 107
3.10 C onclusions 108
C H A PTER 4 PR E SSU R E D R O P AND H EA T TR A N SFE R IN C O ILED FLO W IN V E R T E R H EAT EX C H A N G E R
4.1 Introduction 111
4.2 Pressure Drop O bservation and Friction Factor C alculations in 112 C oiled Flow Inverter Heat Exchanger
4.2.1 Tube side pressure drop and friction factor 112 4.2.2 Shell side pressure drop and friction factor 120 4.3 Heat T ransfer in C oiled Flow Inverter H eat E xchanger 122 4.3.1 V ariation o f bulk mean tem perature at various banks 122
4.3.2 Effectiveness o f CFIHE 123
4.3.3 Overall heat transfer coefficient 125
4.3.4 Tube side heat transfer coefficient 127
4.3.5 Shell side heat transfer coefficient 131
4.4 C onclusions 135
C H A PTER 5 N U M E R IC A L M O DELLIN G OF C O ILED FL O W IN V E R T E R H E A T EX C H A N G E R
5.1 Introduction 136
5.2 M athem atical Form ulation 136
5.2.1 G overning equations 136
5.2.2 B oundary conditions 138
5.2.3 Param eter definitions 139
5.3 N um erical C om putation 140
5.3.1 N um erical m ethod and grid topology 140
5.3.2 C onvergence criteria 141
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5.3.3 Grid system 141
5.4 R esults and D iscussion 142
5.4.1 D escription o f velocity fields 143
5.4.2 D escription o f tem perature fields 153
5.4.3 Effect o f num ber o f bends 161
5.4.4 D evelopm ent o f local friction factor and N usselt num ber 161 5.4.5 D evelopm ent o f average friction and N usselt num ber 167
5.5 Flow R esistance in Coiled Flow Inverter 169
5.6 H eat T ransfer E nhancem ent 170
5.6.1 D ata com parison 170
5.6.2 H eat transfer under constant wall tem perature and wall flux 172 conditions
5.7 Effect o f T em perature-D ependent Properties on Fluid Flow and 175 H eat T ransfer in C urved Tubes
5.7.1 M athem atical M odel 17 5
5.7.2 Results and D iscussions 178
5.7.2.1 Velocity fie ld s \ 78
5.7.2.2 Tem perature fie ld s \ 84
5.7.2.3 Therm o-physical property distribution 189
5.7.2.4 F low resistance 189
5.7.2.5 H eat transfer variation fo r tem perature-dependent 192 properties
5.7.2.6 M odel developm ent 192
5.7.2.7 E ffect o f tem perature-dependent properties fo r 194 viscous flu id s
5.8 C om parison o f P resent Experim ental and N um erical 198 Predictions
5.8.1 Axial bulk m ean tem perature 202
5.8.2 Friction factor com parison in coiled flow inverter heat 202 exchanger
5.8.3 H eat transfer com parison in coiled flow inverter heat 203 exchanger
5.9 C onclusions 206
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C H A PTER 6 PR E SSU R E D R O P AND H EAT TR A N SFE R IN T U B E -IN - TU B E H E L IC A L H E A T E X C H A N G ER
6.1 Introduction 208
6.2 M odelling o f T ube-in-T ube Helical Heat E xchanger 208
6.2.1 M athem atical form ulation 208
6.3 N um erical C om putation 215
6.4 D evelopm ent o f Flow and Therm al Fields 218
6.5 E xperim ental Study 222
6.5.1 Tube-in-tube heat exchanger 222
6.5.2 Experim ental procedure 223
6.5.3 Calculation o f heat transfer coefficients 224
6.5.4 Fluids Flow ing in Annuli: The Equivalent D iam eter 224
6.6 R esults and D iscussion 225
6.6.1 Friction factor in tube-in-tube heat exchanger 226
6.6.1.1 Inner Friction factor 226
6.6.1.2 O uter Friction factor 226
6.6.2 Fully developed heat transfer 228
6.6.2.1 Inner N usselt num ber 228
6.6.2.2 O uter N usselt num ber 230
6.7 C om parison with C oiled Flow Inverter Heat E xchanger 232
6.8 C onclusions 232
C H A PTER 7 D ESIN G OF C O IL E D FLOW IN V E R T E R H E A T EX C H A N G E R FO R INDUSTRY
7.1 Introduction 235
7.2 Design o f W ater C ooler in CO2 C om pressor Suction K nock O ut 236 Drum
7.3 D esign o f L iquid-L iquid H eat Exchanger 243
7.4 C onclusions 246
CH A PTER 8 C O N C L U SIO N S AND R E C O M O N D A T IO N S
8.1 Sum m ery o f C onclusions 248
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8.1.1 Experim ental Study for heat transfer enhancem ent 248 8.1.2 M echanism o f heat transfer enhancem ent in coiled flow 249
inverter heat exchanger
8.1.3 H eat transfer and pressure drop in tube-in-tube helical heat 250 exchanger
8.1.4 D esign o f coiled flow inverter heat exchanger for the industry 251
8.2 R ecom m endations for Future W ork 252
B IB L IO G R A P H Y 255
A N N E X U R E A 282
A N N E X U R E B 288
A N N E X U R E C 295
A U T H O R ’S B IO D A T A 302
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