MASS TRANSFER. Theory and Practice. N. ANANTHARAMAN Professor Department of Chemical Engineering National Institute of Technology Tiruchirappalli

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2 MASS TRANSFER Theory and Practice N. ANANTHARAMAN Professor Department of Chemical Engineering National Institute of Technology Tiruchirappalli K.M. MEERA SHERIFFA BEGUM Associate Professor Department of Chemical Engineering National Institute of Technology Tiruchirappalli Delhi

3 MASS TRANSFER: Theory and Practice N. Anantharaman and K.M. Meera Sheriffa Begum 2011 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN The export rights of this book are vested solely with the publisher. Second Printing July, 2013 Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi and Printed by V.K. Batra at Pearl Offset Press Private Limited, New Delhi

4 Dedicated to my Mother N. Anantharaman Dedicated to my Parents K.M. Meera Sheriffa Begum

6 CONTENTS Preface... xv Acknowledgements... xix 1. INTRODUCTION TO MASS TRANSFER Introduction Classification of Mass Transfer Operations Gas Liquid Liquid Liquid Solid Liquid/Gas 2 2. DIFFUSION Introduction Molecular Diffusion and Eddy Diffusion Diffusivity or Diffusion Coefficient Steady State Molecular Diffusion in Fluids Molecular Diffusion in Gases Diffusivity Prediction in Gases Molecular Diffusion in Liquids Diffusivity Prediction in Liquids Pseudo Steady State Diffusion Diffusion in Solids Types of Solid Diffusion Unsteady State Diffusion 16 Worked Examples 16 Exercises MASS TRANSFER COEFFICIENT AND INTERPHASE MASS TRANSFER Introduction 42 v

7 vi Contents 3.2 Mass Transfer Coefficient Mass Transfer Coefficients in Laminar Flow Mass Transfer from a Gas into a Falling Liquid Film Mass Transfer Theories Film Theory Penetration Theory Surface Renewal Theory Combination of Film Surface Renewal Theory Surface Stretch Theory Analogies Reynolds Analogy Chilton Colburn Analogy Taylor Prandtl Analogy Von Karman Analogy Interphase Mass Transfer Equilibrium Two-phase Mass Transfer Overall Mass Transfer Coefficient Types of Operations Co-current Process Counter-current Process Stages Stage Efficiency Cascade 59 Worked Examples 60 Exercises EQUIPMENT FOR GAS LIQUID OPERATIONS Introduction Tray Towers General Features Type of Trays Bubble Cap Trays Sieve Trays Linde Trays Valve Trays Counter-flow Trays Tray Efficiency Venturi Scrubber Wetted-wall Towers Spray Towers and Spray Chambers Packed Towers Characteristics of Packings Types of Packings Random Packing 77

8 Contents vii Regular Packing Shell Packing Supports Packing Restrainer Liquid Distributors Entrainment Eliminators Channeling Loading Flooding Comparison of Packed Towers with Plate Towers HUMIDIFICATION Introduction Definitions Molal Absolute Humidity (Y) Saturated Absolute Humidity (Y s ) Dry Bulb Temperature (DBT) Relative Humidity or Relative Saturation (% RH) Percentage Saturation or Percentage Humidity (H p ) Dew Point Humid Heat Enthalpy Humid Volume Adiabatic Saturation Curves Wet Bulb Temperature (WBT) Theory of Wet Bulb Thermometry Gas Liquid Operations Adiabatic Operations Non-adiabatic Operations Design of Cooling Tower Re-circulating Liquid Gas Humidification Cooling Equipments Packed Cooling Towers Spray Chambers Spray Ponds 98 Worked Examples 98 Exercises DRYING Introduction Definitions of Moisture and Other Terms on Drying Moisture Content (Wet Basis), X Moisture Content (Dry Basis), X Equilibrium Moisture, X* 117

9 viii Contents Bound Moisture Unbound Moisture Free Moisture (X X*) Critical Moisture Content Fibre Saturation Point Constant Rate Drying Period Falling Rate Drying Period Funicular State Pendular State Hysteresis Drying of Soluble Solids Classification of Drying Operations Batch Drying Parameters Affecting Drying Rate During Constant Rate Drying Period Effect of Gas Velocity (G) Effect of Gas Temperature Effect of Gas Humidity Effect of Thickness of Drying Solid Moisture Movement in Solids Liquid Diffusion Capillary Movement Vapour Diffusion Pressure Diffusion Some More Aspects on Falling Rate Drying Unsaturated Surface Drying Internal Diffusion Controlling Through Circulation Drying The Rate of Drying of Unbound Moisture Drying of Bound Moisture Continuous Direct Heat Drier Material and Energy Balance Rate of Drying for Continuous Direct Heat Driers Drying Equipments Based on Contact between Drying Substance and Drying Material Based on the Type of Operation Based on the Nature of Substance being Dried Atmospheric Compartment Dryers Vacuum Compartment Dryer Tunnel Dryers Rotary Dryers Roto Louvre Dryer Turbo Dryer Conveyor Dryers 134

10 Contents ix Filter Dryer Combination Cylinder Dryers Festoon Dryers Mechanically Agitated Dryer Drum Dryer Vacuum Drum Dryers Spray Dryers Freeze Drying Infrared Drying Dielectric Drying 138 Worked Examples 138 Exercises CRYSTALLIZATION Introduction Crystal Geometry Classification of Crystals Invariant Crystal Principles of Crystallization Purity of Product Equilibria and Yield Yield Enthalpy Balance Super-saturation Nucleation Theory of Homogeneous Nucleation Heterogeneous Nucleation Crystal Growth DL Law of Crystal Growth Growth Coefficients Application to Design Population Density Function Number of Crystals per Unit Mass Crystallizers Super-saturation by Cooling Super-saturation by Evaporation Super-saturation by Evaporation and Cooling 173 Worked Examples 175 Exercises ABSORPTION Introduction Gas Solubility in Liquids at Equilibrium Ideal and Non-ideal Liquid Solutions Choice of Solvent for Absorption 187

11 Mass Transfer : Theory And Practice 25% OFF Publisher : PHI Learning ISBN : Author : ANANTHARAMAN, N., BEGUM, K. M. MEERA SHERI Type the URL : Get this ebook

OURSE TITLE : MASS TRANSFER OPERATIONS 1 COURSE CODE : 5071 COURSE CATEGORY : A PERIODS/ WEEK : 4 PERIODS/ SEMESTER : 52 CREDIT : 4 TIME SCHEDULE

OURSE TITLE : MASS TRANSFER OPERATIONS 1 COURSE CODE : 5071 COURSE CATEGORY : A PERIODS/ WEEK : 4 PERIODS/ SEMESTER : 52 CREDIT : 4 TIME SCHEDULE MODULE TOPIC PERIODS 1 Diffusion and Absorption 13 2 Humidification