itp uns semester 2 jenis bahan dan sifatnya
TRANSCRIPT
Classification and characterization of foodstuffs
Bambang SAJur. ITP FP UNS
Konduksi
)( 21 TTL
kAq
Persamaan Umum :
dimana T = suhu di beberapa titik x = tebal permukaan
A= luas permukaan k= thermal conductivity (Btu/hr.ft.ºF)
-dT/dx = perbedaan suhu
dx
dTkAq
3
Convection heat transfer untuk bidang datar
Flow
qTw
T∞
wall
Transfer panas pada dinding mendekati nol.
)( TThAq w
Classification according to source and state
Raw materials : originating from animal and vegetable sources
Semi-Raw materials Processed food
Classification according to source and state
Solids : (a) homogeneous (gels, protein terlarut) (b) heterogeneous : (1) capillary porous rigid materials : wheat kernels, (2) capillary porous colloidal materials : meat and vegetables
Classification according to source and state
Powders Liquids : (a) Low-viscosity (b) High-
viscosity Slurries or dispersions : milk or peas
in water Emulsions : milk Foams : whipped cream
Foods Contains
Water : 60 – 70 % Proteins Lipids Carbohydrates Vitamins and minerals
Food Properties : Physical properties
Density : density dan bulk density Energy : specific enthalpy Specific heat (cp) or specific heat
capacity Latent heat Thermal conductivity
Density (kg/m3)
drymeter
bulkPorositas
Specific enthalpy
Sum of internal energy and the kinetic energy (unit : J/kg or N m/kg or W s/kg
Specific heat (cp) or specific heat capacity
The amount of heat necessary to raise the temperature of 1 kg of the material by 1o C or 1 K (unit : J/kg. K)
T
pdTch0
Tch pJika Cp konstan)
Cp composition
piip CCC
Dimana :Ci = mass consentration
Termal properties of food constituents
Component Mass cons(kg/kg)
Density(kg/m3)
Spec. Heat(kJ/kg)
Thermal conduc. (W/m K)
Water Cw 1000 4.182 0.60
Carbohydrate Cc 1550 1.42 0.58
Protein Cp 1380 1.55 0.20
Fat Cf 930 1.67 0.18
Air Ca 1.24 1.00 0.025
Ice Ci 917 2.11
Inorganic minerals
Cm 2400 0.84
Foodstuffs containing mainly water
Cp = 4.18 Cw + 2 Cd for fish and meat Cw < 0.25
Cp = 1.67 + 2.5 Cw for fruit and vegetables Cw > 0.5
While Cd = spesific heat dry matter
(Cw = 1 – Cd)
Foodstuffs containing mainly water
Cp = 1.40 + 3.2 Cw for cereals low water content
Latent Heat
The amount of heat removed to frozen the water at 0oC is 334 kJ/kg at
The amount of heat necessary to vaporized the water at 100 oC and 101,3 kPa is 2256 kJ/kg
Depending on composition, the freezing point of most foodstuffs is between -0,5 oC and -4 oC.
Boiling point
Boiling point of foodstuffs is higher than 100 oC, depending on the concentration of solids.
XTBPR 52.0
Where X = the mole fraction of solute
Thermal conductivity
If thermal conductivities in a two-component material are k1 and k2, the total effective conductivity depends on the heat flow derection
Thermal Cond. Effective
ckckkeff 21 )1(
(a) (b)
21
21
)1( kcck
kkkeff
Where c = the volume fraction of material 2
If random material
1
2
21
2121 )1(
)1())1((kcck
kkbckckbkeff
21
11
kb
kb
keff
(2)
(1)
Terima kasih
Semoga bermafaat