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Physical Principles of Food Processing

Physical Principles of Food Processing. Introduction. Ayes Rock , Uluru, 384 m high, 9.8 km circumference. Contents. Staff Aims Topics Activities Assessment. Staff. Dr Associate Professor Minh Nguyen Fellow, Australian Institute of Food Science and Technology

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Physical Principles of Food Processing

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  1. Physical Principles of Food Processing Introduction

  2. Ayes Rock , Uluru, 384 m high, 9.8 km circumference

  3. Contents • Staff • Aims • Topics • Activities • Assessment

  4. Staff • Dr Associate Professor Minh Nguyen • Fellow, Australian Institute of Food Science and Technology • President, Australian Food Engineering Association • Mr Luong Hong Quang • Lecturer, Food Engineering, Nong Lam University

  5. Aim: Develop working knowledge in Physical Principles of Food Processing Objectives: • To be familiar with units and dimensions • To understand fundamental principles of mass and energy conservation • To understand and to apply basic engineering charts • To use physical properties of foods in process design • To comprehend basics of fluid flow, Newtonian and non Newtonian fluids • To predict pressure drops, power and to select pump

  6. Why Study Physical Principles ? • Numerous ways to process foods • Grouping into Unit Operations • Fundamentals for each operation are called Principles depending on aspects: physical, chemical or biological ... • Example: heat transfer principles cover cooking, drying, cooling, freezing etc

  7. How to engineer a food process • What are the quantities involves? • What is the rate of heat/ mass transfer ? • What is the kinetics of chemical changes? • Quantitative approach needed for analysis and design • Review basic physical & chemical concepts

  8. Dimension • To define a physical entity: time, area... • To measure the entity, dimension is expressed as Units: hour, square metre... • Primary dimensions: time, length... • Secondary dimension: length/time= velocity • Equations must be consistent in dimension

  9. Engineering SI units • Based SI units: length=meter, mass= kilogram, time= second, electric current= ampere, temperature= kelvin, amount of substance= mole, luminous intensity= candela • Supplementary SI units: plane angle= radian, solid angle= steradian

  10. Derived SI units

  11. Exercise: Unit conversion • British units are still used in countries like the USA or in old machineries See Textbook table A1.2 for example 1.1 solution

  12. System & state • Region or quantity enclosed by a boundary, away from surroundings • Open, closed or isolated system • Adiabatic or isothermal • In equilibrium or changing state  process via path of many states • State described by properties, extensive or intensive

  13. Density = mass/unit volume • Solid density, table 1.6 • Particle density • Bulk density, table 1.7 • Porosity • Interparticle porosity

  14. Concentration & Moisture content • Mass per unit mass as % or unit volume • Molarity, mole fraction & molality • Moisture content, wet & dry basis, • See examples 1.4 & 1.5

  15. Temperature • Ice point = 0 Celsius= 32 Farenheit • Boiling point= 100 oC= 212 oF • Kelvin & Rankine scale • ΔT (K) = ΔT (oC)

  16. Pressure • Pressure, atm=1.013 bar = 101.3 kPa • Pabsolute =Pgauge + Patmosphere • Pvacuum =Pgauge – Patmosphere • normal stress, static head P=ρgh • See fig 1.9, atm water column= 10.2 m • Static pressure & impact pressure • Bourdon tube

  17. Enthalpy • Sum of internal energy and product of pressure and volume, H=Ei + PV • Specific enthalpy is per unit mass • Steam table reference state = enthalpy of saturated water at 0 oC as zero!

  18. Equation of State • = Functional relationship between the properties of a system • Perfect gas equation of state • PV’ = RTA • P = ρRTA • PV = nRoTA Ro = M R • R = universal gas cont 8314 m3 Pa/kg mol K

  19. Phase diagram of water • To study pressure –temperature relationship between various phases of pure water • Check fig 1.11 for saturated vapour, saturation pressure, saturated liquid, subcooled liquid, quality of the steam (vapour)

  20. Conservation of Mass Principle • Matter can be neither created nor destroyed. However its composition can be altered from one form to another • (rate of mass entering boundary of system) – (rate of mass exiting...) = (rate of mass accumulating within...) • See fig 1.13 for open system • Assume uniform flow of incompressible fluid at steady state, mass flow rate • Σinlet ρun dA = Σoutlet ρun dA • Volumetric flow rate = Σinlet un dA = Σoutlet un dA • Closed system, msystem = constant

  21. Material balances • Collect all known mass & composition of in & out streams • Draw process block diagram with streams. Draw boundary • Write all data on block diagram • Select a convenient basis (mass or time) for calculations • Write mass balance for each unknown • ṁinlet - ṁexit = dmsystem / dt • Solve material balances for each unknowns • Check fig 1.14

  22. Practicing material balances • In class, examples 1.6, 1.7, 1.8 • At home, examples 1.9, 1.10 • Start Reading the textbook • Begin working on part of the ASSIGNMENT

  23. The END of Lecture One !

  24. Revision

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