Training in Food Engineering

Dr. Sirichai Songsermpong

Dept. of Food Science and Technology

Kasetsart University

Why we need to study food eng

• Design and model the process

• Design food processing equipment

• Evaluate new equipment and process

• Troubleshoot problems in plant processing

• Part of plant start up team

• Communicate effectively with engineers, designers, maintenance crews and plant operators which requires engineering methods and terminology

Objectives

• To understand the concept of material and

energy balances

• To understand the concept of thermodynamics

• To understand the concept of transport

phenomena in food processing

• To understand the engineering principles in

each unit operation

• To be able to calculate some parameters in the

process

References

Singh, R.P. and Heldman, D.R. 2001. Introduction to

Food Engineering. 3rd edition. Academic Press,

California.

Toledo, R.T. 2007. Fundamentals of Food Process

Engineering. 3rd edition. Springer Publisher, New

York.

Earle, R.L. 1966. Unit Operations in Food Processing.

Now available on line.

Heldman, D.R. and Singh, R.P. 1981. Food Process

Engineering. 2nd edition. AVI, Connecticut.

Others

Unit one: Material and Energy

Balance

Unit conversion

Conservation of mass and energy

Overall analysis

Unit analysis

A

B C

D

E

SI unit

• Meter

• Kilogram

• Second

• Kelvin

• Newton

• Joule

• Pascal

• Watt

• Ampere

Prefix

• Tera

• Giga

• Mega

• Kilo

• Milli

• Micro

• Nano

• Pico

Unit conversion

• Temperature conversion

R C KF

212 672 100 373boiling

freezing

32 492 0 273

0 460

F=1.8C+32 C=(F-32)/1.8 R=F+460 K=C+273Temp conversion

Temp. difference

conversion F=1.8C C=F/1.8 R=F K=C

180 100

Pressure

• Guage pressure based on atm. pressure

• Absolute pressure based on perfect

vacuum

Absolute pressure = Guage pressure + Atmospheric pressure

Absolute pressure (Pa)

Vacuum = difference between atmospheric and absolute pressure

1 atm=760mmHg=14.7 psi=406.8 in of water=101.3kPa

Pressure

Absolute pressure

Atmospheric

pressure

Guage pressure (Difference

between absolute and atm pressure

Vacuum (Diff between atm

and absolute Pressure)

Absolute pressure (less

than atmospheric)

0 kPa

101.3 kPa

100C

200 kPa

120C

Practice

• 150F = ?C

• 14.7 psig = ? kPa

• 1 lb/ft3 = ?kg/m3

• 1 kJ/kgK = ? Btu/lbF

• 1 Btu/hrftF = ? W/mC

• 1 centiPoise = ? mPas

Conservation of mass

Mass in = mass out + accumulation

Why we need to do mass balance?

• To see the loss

• To calculate the efficiency

• To plan how much raw material is needed

• To see how much product and waste are

generated

• To determine the size and number of machine

Conservation of mass in

blending process

• Flour A has amylose 15 %

• Flour B has amylose 30 %

• Blending of flour A and B to achieve

amylose 25% for 1000 kg

A

B

C

Conservation of mass in dilution

How many kg of a solution containing 10% sodium chloride can be obtained by diluting 15 kg of a 20% solution with water?

15 kg

20%NaCl

X =? kg

10% NaCl

Water

Conservation of mass in

dehydration

How much weight reduction would result

when a material is dried from 80% mc to

50% mc?

W

80% H20

20% solid

D

50% H20

50% solid

H2O

Conservation of mass in

concentration

How much water is removed from 1000 kg of juice?

Juice 10 BrixConcentrate

60 Brix

water

Multi components and various

compositions

Lean beef X kg

14%fat

67% water

19% protein

Pork fat Y kg

89% fat

8% water

3% protein

Water Z kg

Frankfuter 100 kg

20% fat

65% water

15% protein

Calculate mass of each component

Recycle

10,000 kg/h

Evaporator Crystallizer40% solid

Filtrated 45% solid

50% solid 95% Cake

5% (a 45% solution)

Energy balance

• Energy in = energy out + energy

accumulation

• Sensible heat Q=mCpΔT

• Latent heat Q=mL

energy balance: introduction

• Sensible heat

Q = m C ( T1 – T2)

C: heat capacity (p, v)

• Latent heat

Q = m L

L: latent heat of…

Solid Liquid Gas

Temperature

Solid Liquid Gas

Temperature

How to calculate Cp

• Water has specific heat of 4.18 kJ/kgK

• Air has specific heat of 1 kJ/kgK

• Specific heat of Food =

Mass fraction of water*Cp water +

Mass fraction of solid *Cp solid

Where Cp of solid = 0.837 kJ/kgK

Other equations

• Cp = 0.4F+0.2 SNF+1W

• Cp=1.424xcarbo+1.549xprotein+1.675xfat+0.8

37xash+4.187xwater kJ/kgK(Dickerson,

1969)

• Cp=xice*Cice+xsolid*Csolid where Cp of ice =

2.093 kJ/kgK

Latent heat

• Latent heat of fusion = 335 kJ/kg

• Latent heat of vaporization = 2257 kJ/kg

• Latent heat of sublimation

• Can be seen from steam table

Practice

• Calculate the heat removal from apple

juice 200 kg/hr at 25C to -20C

• Freezing point is -1C

• Latent heat of freezing = 281.5 kJ/kg

• Cp above freezing = 3.59 kJ/kgK

• Cp below freezing = 1.88 kJ.kgK

Steam table

• We can read enthalpy at state 1 and

enthalpy at state 2 from steam table and

then calculate the heat gain or loss

• Q = m (enthalpy at state 1- enthalpy at

state 2)

Steam table (saturated steam)

T

(C)

P

kPa

Spec

ific

(l)

volu

me

(g)

Enth

alpy

(l)

Enth

alpy

(g)

entro

py

0.01 0.61

100 101. 419 2676

120 198 503 2706

140 316 589 2734

Practice

• To heat mango juice 1000 kg/hr from 25 C

to 90 C, steam at 120 C is used and

condensate exit at 100 C. Calculate the

weight of steam needed.