Contents. Preface... xvii

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1 Contents Preface... xvii Chapter 1. Rotary Calcination Kiln: Heat Exchange by Radiation General points Purpose of calcination kilns Specific characteristics of heat transfer Gas heating in kilns Description Basic principle of the kiln Gas circulation in the kiln Support Lining Seals at drum ends Kinematic drive train in calcination kilns Feeding a rotary dryer Grain breaking Shaft power of the electric motor Axial transport of products in a bare drum in the absence of gas Determining the angle of progression α Expression of time spent in the drum Accounting for the presence of gas Fill ratio Heat transfer by radiation: basic concepts Working hypothesis Key concepts Kirchoff s law for surfaces

2 vi Heat Transfer in the Chemical, Food and Pharmaceutical Industries Luminance and emitted flow density Specular reflection and diffuse reflection Radiosity of a perfect exchange surface Equivalent direct transfer surface Equivalent trajectory and average trajectory through a gas Emissivity, absorptivity and transmissivity of the gaseous mixture (calculation) Distribution of direct radiation Energy flow density emitted by each wall element Net flow received by surface Ai Difference between net received flow and absorbed flow Net flow for a gray surface surrounding a gray gas Net flow for two surfaces in close proximity Evaluating EDTS. Some simple specific examples Heat transfer in rotary calcination kilns Transfer mechanism Equivalent direct transfer surface for the bare wall and free surface of the product Net flow densities received by the wall and the product Regeneration from the wall Expression of additional coefficients for heat transfer Solution to the wall equation Overall thermal power transferred to the product for calcination Chapter 2. Tubular Heat Exchangers and Flat-plate Heat Exchangers Description of exchangers Possible configurations Tube characteristics Shell diameter and tube bundle diameter. Number of tubes Transversal baffles (characteristics)

3 Contents vii 2.2. Calculations on the tube side Heat transfer inside the tubes (clear liquid or gas) Heat transfer inside the tubes (liquid-solid dispersion) Pressure loss inside the tubes Calculations on shell side Gross transfer coefficient, shell side (Bell method) Coefficient correction for leakage Pressure loss due to crossflow current Pressure drop: shell side Overall heat transfer coefficient Practical data Usual pressure drop values Computerized exchanger calculations Note: caloric temperature Plate exchangers Description Number of transfer units The pressure loss coefficient Plate grouping and correction coefficient Fouling Construction materials Chapter 3. Finned Tube Exchangers General points Purpose of finned tubes Types of finned tube exchangers Definition of the frontal area Technical data Bundle layout Air cooler header boxes Finned tube characteristics for air coolers Fin efficiency Preliminaries Temperature range in a fin Calculation of zero- and first-order modified Bessel functions Definition of efficiency Theoretical efficiency calculation Approximate calculation of efficiency

4 viii Heat Transfer in the Chemical, Food and Pharmaceutical Industries 3.4. Other thermal parameters Transfer coefficient: gas side Overall coefficient for bare tubes Output temperatures (pure crossflow current) Outlet temperature (pure counterflow current) Crossflow current (multiple passes in relation to gas) Determining geometry Number of rows and frontal surface Mathematical functions Number of tubes per pass Width of tube layers Number of tubes per layer and per pass Simulation and direct calculation Simulation Direct calculation Fans General points Position Diameter Number Fan power Implementation of air coolers Regulation Frost-proofing Air-side fouling Chapter 4. Scraped Surface Heat Exchangers, Spherulation Towers and Solidification on a Moving Surface General points Benefits when using viscous products Possible designs and heat transfer Types of scraped surface heat exchanger Quasi-gapless mechanisms, almost completely immune to wear Mechanisms with small gap size, subject to wear Mechanisms with a wide gap between the blade and the wall Spherulation towers Introduction Droplet formation

5 Contents ix Practical data Dimensioning Pollution Continuous solidification on a moving surface Principle Elements involved in a calculation Chapter 5. Efficiency of Single-phase Heat Exchangers: Fouling Number of transfer units and efficiency Mean logarithmic temperature difference (MLTD) Number of transfer units (NTU) Efficiency Applications of the notion of efficiency Multipass exchangers and coefficient F Fouling Heat transfer design Common types of fouling Practical consequences of fouling Typical fouling values Calculation of wall temperatures Chapter 6. Condensers, Traps and Condensate Lines Surface condensers Structure Assembly Isothermal condensation coefficient of pure vapor Calculation of a pure vapor condenser Heat flow densities for mixed vapors Case of condensable vapor in the presence of non-condensable elements Mixture of two condensable vapors Evaluation of D am /δ and D AB /δ Evaluation of y Ac and x Ac Coolant flow Calculation of the surface of a condenser

6 x Heat Transfer in the Chemical, Food and Pharmaceutical Industries 6.2. Overcooling of the condensate General points Transfer coefficient for overcooling Contact condensers General points Calculation of contact condensers Trap types Use of condensate traps Thermostatic bimetallic trap Balanced liquid expansion thermostatic trap Balanced pressure steam trap Inverted bucket steam traps Free-float traps Thermodynamic traps Trap selection and assembly Trap installation (classic assembly) Direct draining to the atmosphere Bypass to the condensate network Banging in vapor pipes Flowrate of condensate for drainage in steam pipes Trap selection Condensate lines Evacuation and use of condensates Chapter 7. Boiling and Heat Transfer Stagnant boiling Definitions Density of heat flowrate through the wall Calculation of overheating of the wall Drying of the wall Convective boiling Heat transfer coefficient Chapter 8. Thermosiphon Reboilers Manual method Operating principle Identifying the level where boiling starts Calculation of pressure drops and verification of driving height of liquid in the reservoir or column bottom Verification of heat transfer intensity

7 Contents xi 8.2. Computerized method Reboiler calculations through simulation Reboiler calculation by direct determination Operational stability of thermosiphon reboilers (breathing) Mechanism of the phenomenon Practical factors affecting boiler stability Chapter 9. Concentrating Solutions by Vaporization Introduction Terminology Boiling delay Definition Calculating boiling delay Multiple-effect evaporation Ideal specific consumption Specific consumption in practice Possible layouts Liquor preheating Thermal balance of an effect Material and thermal balances of a multiple effect system (manual method) Computerized calculation of the material balance Computerized calculation of overall thermal balance Heat losses Vapor recompression Thermocompression of vapor Mechanical vapor recompression (MVR) Description, choice and calculation of evaporators Short tube evaporators (sugar refiners) Climbing evaporators Forced circulation evaporators Falling film evaporators Other evaporator types Evaporator calculation Vapor separators Physical properties used in the calculation of vaporization devices Order of magnitude of heat transfer coefficients

8 xii Heat Transfer in the Chemical, Food and Pharmaceutical Industries Chapter 10. Falling Film Vaporizer (Evaporator) General points Types of falling film evaporator Performance Advantages of falling film evaporators Tube wetting Minimum linear charge Maximum linear load Vapor velocity in the tubes Rising current for vapor Descending current for vapors Heat transfer Partial transfer coefficient: tube side Overall transfer coefficient Distribution plate Description Computerized calculation Vapor pressure drop along the tubes Dimensioning an evaporator Tube length (preheating a cold feed) Tube length (vaporization part) Chapter 11. Heat Transfer in Stirred Tanks Coil transfer General points Definition of the coil Coefficient for the reactor wall Turbines and paddles Marine propeller Coil Double jacket: internal coefficient Viscous fluids: laminar regime Ribbon Anchor Thermal conditioning of tanks and reservoirs Operating principle Heat transfer using a coil Heat transfer via the double jacket wall Internal configuration External configuration Mixed configuration

9 Contents xiii Chapter 12. Cooling or Heating of Simple-form Solids and Plant Products: Blanching Thermal conditioning of simple-form compact solids Temperature expressions theoretical study Auxiliary variables Thermal conditioning of simple-form solids: semi-empirical study Introduction Plates and rectangular parallelepipeds Finite or infinite cylinders Sphere Thermal conditioning and hydrothermal processing Roasting plant products Hydrothermal processing of oilseed Drying Blanching Chapter 13. Thermal Insulation of Piping: Tracing Thermal insulation Insulation types Types of insulation material Coefficient for heat loss to the environment Heat flow density Temperature of the wall in contact with the atmosphere Calculating the thickness of insulation Pipe tracing Principle Heat transfer coefficient Practical data Chapter 14. Combustion and Sulfur Dew Point Characteristics of combustion Combustion air Fuel Stoichiometric air requirement Smoke generation and smoke composition by volume SO 3 content and dew point Calculation of the partial pressure of sulfur trioxide Calculating the sulfur dew point temperature

10 xiv Heat Transfer in the Chemical, Food and Pharmaceutical Industries Chapter 15. Heat Supply by Microwave or Infrared Radiation Microwave heating (theory) Maxwell s equations Energy balance of electromagnetic radiation Electric field propagation equation Penetration depth in a dielectric layer Dielectric conductivity Wave impedance Microwave heating (practical) Energy consumption and heating time Heating power output: runaway Transmission coefficients between two dielectrics Electric field in the oven and energy flow density Practical arrangements and use Infrared drying Radiation production Absorption of radiation Practical data Chapter 16. Freezing, Deep-freezing and Thawing Introduction Product properties Industrial freezing apparatus The deep-freezing principle Batch freezer cabinets Tunnel freezers Continuous blast freezers Contact freezing Freezing with refrigerant spray Deep freezing with refrigerant spray Continuous double band freezer Fluidized or fixed bed freezers Cooling units Coolant fluids Thermal balance Freezing time (Planck s equation) Case of a plate

11 Contents xv Case of a sphere Generalization I Generalization II Freezing and thawing times (numerical calculation) Freezing time: practical method Introductory note Definitions of characteristic dimensions Cleland et al s. method (1987) Average freezing temperature Precooling correction Thawing Microwave thawing External heating Contact heating Exudation losses Calculating thawing time Chapter 17. Freeze-drying General points The freeze-drying principle Heat supply Freeze-drying: implementation Thermodynamics of freeze-drying Activity of solvent water in equilibrium with ice Empirical expression of water activity for prefreezing Expression of enthalpies for freeze-drying Conclusion: the freeze-drying process Migration equations Free mean path Flow through a tube in the Knudsen regime Viscosity of a gas Migration equations Mean pore radius Relationship between instantaneous porosity and water content Simulation of freeze-drying

12 xvi Heat Transfer in the Chemical, Food and Pharmaceutical Industries Appendices Appendix 1. Characteristics of Exchanger Tubes Appendix 2. Resistance, Conductance, Diffusance Bibliography Index

Heat Exchanger. The purpose may be either to remove heat from a fluid or to add heat to a fluid.

Heat Exchanger. The purpose may be either to remove heat from a fluid or to add heat to a fluid. HEAT EXCHANGERS Heat Exchanger Heat exchanger is an apparatus or an equipment in which the process of heating or cooling occurs. The heat is transferred from one fluid being heated to another fluid being