Hemodialysis Modelling

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Thesis on dialysis modelling

Text of Hemodialysis Modelling

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    MODELING OF HEMODIALYSIS OPERATION

    A Thesis Submitted to the Graduate School of Engineering and Sciences of

    zmir Institute of Technology in Partial Fulfillment of the Requirements for the Degree of

    MASTER OF SCIENCE

    in Chemical Engineering

    by Hasan Erbil ABACI

    August 2008 ZMR

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    We approve the thesis of Hasan Erbil ABACI

    ________________________

    Prof. Dr. Sacide Alsoy ALTINKAYA Supervisor

    ________________________

    Assoc. Prof. Dr. Ali hsan NESLTRK Committee Member

    ________________________

    Assist. Prof. Dr.Committee Member

    01 August 2008

    ________________________ ____________________

    Prof. Dr. Devrim BALKSE Prof. Dr. Hasan BKE Head of the Chemical Engineering Department Dean of the Graduate School of Engineering and Sciences

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    ACKNOWLEDGMENTS

    First and foremost, I would like to thank my advisor Dr. Sacide Alsoy Altnkaya, who has shown a large and consistent interest in my project during the times. Beside this work, I have learned so many useful things from her, that will help me to become a part of academia. I would also like to express my appreciation to my thesis committee; Dr. Erol eker, and Dr. Ali hsan Neslitrk. Their constructive comments have greatly improved this work.

    All of my friends, thank you for your patience and understanding throughout my study. One of my most special thanks goes to my dear friend, Pnar, who had always time to help me and let me use her personal computer no matter how busy she is. Last but not least, my family, I feel so privileged to have parents like you, giving me your unconditional support and love through all this work.

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    ABSTRACT

    MODELING OF HEMODIALYSIS OPERATION

    Recent studies have shown that the effectiveness of hemodialysis is based on module geometry, membrane properties and operating conditions. Various experimental work exist in the literature concentrated on the synthesis of new hemodialysis membranes. However, optimization of membrane structure requires extensive and time consuming experimentations. Therefore, mathematical models are neccessary that can be used to predict the performance of hemodialysis operation. In this study, a predictive theoretical model was developed to predict the solute concentrations in patients blood and optimize the efficiency of hemodialysis operation. The model takes into account simultaneous mass and momentum transfer along with the adsorption of rejected protein molecules on the surface of the membrane. Model predictions show that blood and dialysate flowrates are effective for all sizes of molecules. The change in structural properties of the membrane makes no effect on the total removal of urea beacause of its high clearance. On the other hand, a considerable increment in the clearance of larger molecular weight solutes occurs as the pore size and porosity of the membrane increases. The most important design parameter for dialysis unit which influence the solute clearances significantly is found to be the effective diameter among the fibers in the dialyzer. The model is extended to investigate the use of urease immobilized membranes on the efficiency of the hemodialysis operation. The results have shown that urease immobilization enhances the removal of urea from the blood and decreases the protein adsorption capacity of the polysulfone membrane. Model predictions are compared with different sets of clearance data available in the literature. The agreement is found to be satisfactory which suggests that the model can be used as a tool to design or test the performance of dialysis units.

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    ZET HEMODYALZ LEMNN MODELLENMES

    Son almalar, hemodiyaliz ileminin verimliliinin, model geometrisine, membran zelliklerine ve ilem koullarna bal olduunu gstermitir. Literatrde, yeni diyaliz membranlar sentezlemek amacyla yaplm eitli deneysel almalar yer almaktadr. Ancak membran yapsnn optimizasyonu, kapsaml ve uzun sreli deneyler gerektirmektedir. Bu nedenle, hemodiyaliz ileminin performansn ngrebilmek iin matematiksel modellere ihtiya duyulmaktadr. Bu almada, hasta kanndaki znen madde konsantrasyonunu tahmin etmek ve hemodiyaliz ileminin verimini optimize edebilmek amacyla teorik bir model gelitirilmitir. Model ierisinde, ktle ve momentum transferi ezamanl olarak ele alnmakla birlikte, membran yzeyi tarafndan reddedilen protein molekllerinin adsorpsiyonu da dikkate alnmtr. Model sonular, kan ve diyalizat zeltisi hzlarnn, tm boyuttaki molekller iin etkili olduunu gstermitir. renin yksek temizlenme hzndan tr, membrann yapsal zelliklerindeki deiikliin, re uzaklatrlmasnda etkisiz olduu saptanmtr. te yandan, gzenek boyutu ve gzeneklilik arttrldka, daha byk boyutlardaki molekllerin uzaklatrlmasnda art gzlenmitir. Kandan madde uzaklatrlmasn belirgin bir ekilde etkileyen en nemli dizayn parametresinin, fiberlerin arasdaki efektif ap olduu bulunmutur. Model, reaz tutturulmu membranlarn, hemodiyaliz ileminin verimini arttrmak iin kullanmn incelemek amacyla geniletilmitir. Sonular, reaz tutturulmasnn, re uzaklatrlmasna katkda bulunduunu ve polislfon membrannn protein adsorpsiyon kapasitesini azalttn gstermitir. Model tahminleri, literatrdeki farkl deneysel sonularla karlatrlmtr. Tutarllk, tatmin edici olup, modelin diyaliz nitelerinin tasarlanmas ve performansnn snanmas iin bir ara olarak kullanlabileceini gstermitir.

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    TABLE OF CONTENTS

    LIST OF TABLES.......................................................................................................... viii

    LIST OF FIGURES ........................................................................................................ ix

    NOMENCLATURE ....................................................................................................... xi

    CHAPTER 1. INTRODUCTION ............................................................................................ 1

    CHAPTER 2. GENERAL INFORMATION ABOUT HEMODIALYSIS............................. 4 2.1. Properties of Fluids in Hemodialysis.............................................. .... 8

    2.1.1. Blood.............................................................................................. 8 2.1.2. Dialysate ........................................................................................ 9

    CHAPTER 3. LITERATURE REVIEW ................................................................................. 11

    CHAPTER 4. PROTEIN ADSORPTION KINETICS............................................................ 17 4.1. Factors Affecting Protein Adsorption............................................. .... 18

    4.1.1. Membrane Material and Morphology............................................ 18 4.1.2. Hydrophobicity .............................................................................. 20 4.1.3. Operating Conditions and Electrostatic Interactions ..................... 20

    4.2. Protein Adsorption Models............................................................. .... 22

    CHAPTER 5. THEORY.......................................................................................................... 24 5.1. Whole Body Clearance Model....................................................... .... 24 5.2. Plain Membrane Model .................................................................. .... 25

    5.2.1. Model Geometry and Assumptions ............................................... 25 5.2.2. Total Continuity and Conservation of Momentum . Equations ....................................................................................... 27 5.2.3. Protein Adsorption Model ............................................................. 30 5.2.4. Species Continuity Equation.......................................................... 32

    5.3. Enzyme Immobilized Membrane Model ........................................ .... 35 5.3.1. Species Continuity Equation in Enzyme Layer and Solute . Fluxes in Each Layer............................................................. ........ 36 5.3.2. Protein Adsorption Kinetics.......................................................... 37

    5.4.Estimation of Model Parameters...................................................... .... 43 5.4.1. Membrane Characteristics .............................................................. 43 5.4.2. Pore Size of Adsorbed Layer ......................................................... 44 5.4.3. Mass Transfer Coefficient on Dialysate Side ................................. 45

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    5.5. Numerical Methods.......................................................................... .... 46 5.5.1. Transformations for Jump Mass Balance ....................................... 46 5.5.2. Numerical Solution Algorithm ....................................................... 48

    CHAPTER 6. RESULTS AND DISCUSSION....................................................................... 51