ENERGY BALANCE

ENERGY BALANCE

Nur Istianah,ST.,MT.,M.Eng THP UB 2017

Energy Balance

Total energy entering the system

Total energy leaving the system

Change in the total energy of system

=

The first law of thermodynamic states that energy can be neither

created nor destroyed.

Overall View of an Engineering Process

Using a material balance and an energy balance, a food engineering process can be viewed overall or as a series of units. Each unit is a unit operation.

Raw

materials Unit

Operation Further Unit Operation Previous

Unit

Operation

By-products Product

Wastes Energy Wastes Energy

Capital

Energy

Labor

Control

Conservation Law

E _in = E _out

ΣQ _in = Σ Q _p + Σ Q _bp + Q _loss

Efisiensi = Σ Q _p : ΣQ _in

Process

Heat exchange

• Heating (pasteurisation, blansing, sterilisation)

• Cooling

Separation

• Evaporation

• Drying

• Distillation

Mixing Chemical reaction

HEAT BALANCE OF

MIXING PROCESS

M1, CP, T1, Q1

M2, C2, T2, Q2

M3, C3, T3, Q3

M4, C4, T4, Q4

Neraca energi

An dairy industry produce 100 kg of low fat cream (18 % fat, 82% water, w/w) which the ingredients are double cream (48

% fat, 52% water, w/w) and milk(3.5 % fat, 96.5% water, w/w). If double cream 30°C was mixed with milk 50°C.

Calculate the final temperature of product!

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Excercise

Double cream 30 ⁰C

Milk 50 ⁰C

low fat cream

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Solution

Mass balance:

m in = m out

Define double cream as y kg and milk as x kg Total mass balance:

y + x = 100 kg ………. Eq.1

Fat mass balance:

0.035x + 0.48y = 100(0.18) ………. Eq.2 Eq. 1 dan 2 : 0.035(100-y) + 0.48y = 18

3.5 - 0.035y + 0.48y = 18 y = 32.58 kg So ………. X = 67.42 kg

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Q in = Q out Q in: (T ref=0 K)

a. Double cream

Cpdouble cream: 1674,72(0,48)+4186,8(0,52)=2981 Jkg^-1.K Qindouble cream= mCp(Tm-Tref)

= (32,58 kg)(

2981

^Jkg-1.K)(30-0 K) = 2.913.630,96 J b. Milk

Cpsusu: 1674,72(0,035)+4186,8(0,965)=4099 Jkg^-1.K Qinsusu= mCp(Tm-Tref)

= (67,42 kg)(

4099

^Jkg-1.K)(50-0 K) = 8.290.389,02 J

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Q out:

Cplow fat cream: 1674,72(0,18)+4186,8(0,82)=3735 Jkg^-1.K Qindouble cream= mCp(Tm-Tref)

= 100(3735 Jkg^-1.K)(T-0°C)=37350(T-0°C) Kesetimbangan energi:

Qindouble cream + Qinsusu= Q out low fat cream

2.913.630,96 J + 8.290.389,02 J = 37350(T-0°C)K T = (2.913.630,96 J + 8.290.389,02 J) /37350 Jkg^-1 T = 44,80 °C

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THANKS FOR YOUR ATTENTION

The best person is one give something useful always

28/04/2017 Nur Istianah-KP1-neraca energi-2015