Physical Systems Karwe Flashcards
Density of a simple mixture
Simple mixture ignores the chemical reactions
Calculations are on slides
Brix scale
Sugar content of an aqueous solution that is purely based on sucrose.
Plato or degrees plato
Measure weight of solids dissolved in water measured in %
Density of water-ethanol mixture
Adding two liquids of same polarities is not a simple mixture so net volume will be less
Non-Ideal Density of Water-Ethanol mixture
Water and ethanol do not mix ideally
Volumetric contraction occurs when mixing water and ethanol leading to a higher-than-expected density at intermediate ethanol concentrations
Alcohol by Volume (ABV)
Measured by hydrometers that measure specific gravity of liquid before and after fermentation
Use temperature and ethanol weight % to find density
How to calculate ABV
Measure original specific gravity and final specific gravity of ethanol
ABV = (OSG-FSG)x131.25 in %
131.25 is a constant
Density decreases as sugar is converted during fermentation
Specific gravity decreases
Sugar solution of alcohol before fermentation has a density is higher than water
Boiling of Water-Ethanol mixture graph
Boiling alcohol at certain temperature results in a different composition of vapor
Ex: 10% alcohol at 90 degrees results in vapor composition of 58% alcohol
Alcohol is more volatile
Alcohol vapor pressure at given temperature is higher than water vapor pressure
If you condense vapor, it will have a composition different from the starting position and the vapor position (move down on the graph to obtain this %)
If boiling move to the right to obtain new ration
Beyond a point (95.6% alcohol) you cannot purify it more through distillation
Bulk density
Total volume is the volume of bulk + volume of feed
The air space has no mass
Mass of solid/volume of hole
Density of solid part of porous material
Mass of solid/volume of solid
(Vb-Vs)/Vb = 1- (Vs/B) -> 1- ((M/rho solid0/m/rho bulk) = 1 - Rho(bulk)/Rho(solid)
Tells you how much air is in product
Different porosity foods
High porosity foods
Meringues, marshmallows, whipped cream
Medium porosity foods
Most meats, fruits and vegetables
Low porosity
Hard cheese chocolate
Overrun
Used in manufacturing of productions involving whipping or aeration
Density is important to consider for foaming
Volume increases far beyond original volume
A = (Vfoam - Vliquid)/Vliquid
Mass of foam is also the mass of the liquid
A in % = (Density of liquid/Density of foam)-1 x 100
Air pockets are necessary for ice cream
Density Measurement of Non-standard shape object by pycnometer
When valve 1 is open and valve 2 is closed
Measures porosity
Vcell - V sample is volume of the gas
P1(Vcell - Vsample) =n1RT
Fill sample with pressure
Gas expands
Solid Fat Index (SFI) and Solid Fat Content (SFC)
SFC: direct measurement of solid fat at various temperatures
SFI: determined by volume changes resulting from melting or crystallization
Dilatometer
Measures volume change caused by physical or chemical process
SFI calculation method adopted as convention
SFI
Solids and liquid fats expand with temperature
Melt liquid fat as a function of temperature (x axis) to see change in specific volume
Look at the distance between the liquid fat and solid fat
Mixture of two fats should be in between this line
Spreadability is directly a function of SFI (you want a more linear line with temp and SFI)
Tortuosity
Measures how complicated path is
Higher number, higher tortuosity
Tortuosity characterizes paths of particles transported through the medium
Resists mass transfer
Depends on internal structure and ingredients
Porosity
Porosity is fundamental number that describes fractions of voids in medium
Permeability
Permeability defines ability of medium to transport fluid
Mass transfer property
Gas has to adsorb to package via Henrys Law
Diffuses through because of concentration gradient and governed by Fick’s Law
Finally desorbs
Particle Size, Shape and distribution
Affects production and handling of ingredients and formulation
Particle size affects reactivity, solubility, and flowability of ingredients, and the texture, mouthfeel and processing of products
Surface topography
Primary waviness with valleys and peaks
Roughness is microscopic
Asperity is highest point on surface and two surfaces touch as asperities
Surface roughness
Subtracting the waviness from the primary profile results in roughness
Observe fluctuation around mean line
Integrate curve and square the number and divide this by the length
Why is surface roughness so important?
Microbes can get into surface and detergent can have issues getting into these surfaces
Control surface tension so water can penetrate surface
Little surface tension as possible
Resistance to flow is higher when surface is rougher
Use CLSM to quantify surface roughness
As surface roughness increased, maximum microbial survivor increased
Rheology
How and why the material flows and deforms
Rheological data needed for what reasons
Ingredient functionality
Shelf-life prediction and testing
Evaluation of food texture
Process engineering calculations
Stress and Strain
Normal stress: Force/Area
Normal strain: Fraction of elongation/original length
Relationship between normal stress and normal strain is a straight line and relationship is e
Slope is Hookes Law and the higher value of e, higher stiffness/elasticity
Young’s modulus of elasticity
Newtons/M^2 (PA) for stress
No unit for strain
E has as a unit of Pascals as well
Viscosity in relation to rheology
Viscosity is shear stress divided by shear rate
As viscosity increases, the time for air bubble to travel increases
Smaller bubbles take longer to go away
Shear
Shear stress is also Force/Area
Perpendicular
Different than stress
Shear modulus can be graphed
Shear Strain
Delta X/Delta Y
Y is surface not being strained and x is surface being strained
Strain rate
First derivative of the ratio of change in length
When y is a constant, it measures how fast top surface moves in relation to time
Velocity/gap is the strain rate
Elastic Solid
Finite proportional deformation
No flow
Returns to original shape upon removal of stress
Plastic Solid
Residual strain can occur where material may not return to its original shape
Some recovery upon removal of stress
Application of normal stress
Compressible materials show a decrease in volume when pressure increases
Water at 690 MPa compresses by 15%
If volume and mass doesn’t change, density is constant
Relationship between shear stress and shear rate
Shear stress/shear rate is viscosity
Should be a linear relationship
G is shear modulus and gamma is shear strain
G is how spring like substance and is measured in
Mu resents fluidity of substance and is measured in Pascals*seconds
Newtonian vs Non-Newtonian
If Mu is constant at a given temperature, it is Newtonian
Newtonian: water, air, oil, honey
Viscosity is glycerin is about 1 Pas while viscosity of water is around 0.0018 Pas
Non-Newtonian materials do not show a proportional change in viscosity while Newtonian materials do
Shear thinning or shear thickening can occur
Viscosity divided by density is kinematic viscosity
Mu/rho in M^2/s
How fast a disturbance will travel through fluid
Mu controls the property of the signal of disturbance traveling through fluid
Use depth to determine the time it takes for disturbance to reach inhabitants
Depth^2/Mu
If Mu is lower, the time it takes for signal to reach is higher
Mu decreasing as temperature increases
Corn syrup is Newtonian but highly temperature dependent: More starch is broken down into dextrose, dextrose equivalent number increases and viscosity decreases
Sucrose vs invert sugar: Invert sugar is formed from when glycosidic bond between fructose and sucrose is broken
Molecular weight decreases and thus viscosity is lower in invert sugar
Both temperature dependent
