physical principles of food processing
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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 - PowerPoint PPT PresentationTRANSCRIPT
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 President, Australian Food Engineering
Association Mr Luong Hong Quang Lecturer, Food Engineering, Nong Lam
University
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
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
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
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
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
Derived SI unitsQuantity name symbol In SI base In other
unit
Force newton N m kg s-2
Power, radiant flux
watt W m2 kg s-3 J/s
Illuminance
lux lx m-2 cd sr lm/m2
Conductance
siemens S m-2 kg-1 s3 A2 A/V
Dynamic viscosity
pascal second
Pa s m-1 kg s-1
Surface tension
Newton per meter
N/m kg s-1
Exercise: Unit conversion British units are still used in countries
like the USA or in old machineriesSee Textbook table A1.2 for example 1.1
solution
foot ft 0.3048 m
British thermal unit BTU 1055 J
Pound lbm 0.454 kg
Pound per square inch absolute
psia 6.895 kPa lbf /in2 abs
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
Density = mass/unit volume
Solid density, table 1.6 Particle density Bulk density, table 1.7 Porosity Interparticle porosity
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
Temperature
Ice point = 0 Celsius= 32 Farenheit
Boiling point= 100 oC= 212 oF Kelvin & Rankine scale ΔT (K) = ΔT (oC)
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
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!
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
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)
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
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
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
The END of Lecture One !
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