The document discusses drying techniques used in dairy engineering. It focuses on drum drying, which involves removing moisture from milk or other dairy products through indirect contact with a heated drum. Drum drying reduces the moisture content through evaporation to increase shelf life and reduce bulk. Key factors that affect drum drying include temperature, contact time, rotation speed, and pressure. Drum dryers come in different configurations depending on the number of drums, surrounding pressure, feeding arrangements, and materials of construction. Precautions must be taken to control temperature and contact time to prevent scorching or protein denaturation during drum drying.

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2. DRYING
Removal of moisture to a
desired m.c in equilibrium
with normal atmospheric air.
Why drying??
• Increased shelf life (inhibiting bacterial
activity and enzyme activity)
• Reduction of bulk
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3. GENERAL DRYING BEHAVIOUR
m.c of milk(X) = mw TS(total solid mass fraction) = ms
mw + ms mw + ms
mass of amount of
water dry matter
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4. During concentration…..
𝑚 𝑤0
− 𝑚 𝑤
𝑚 𝑤0
= 1 −
𝑥 1 − 𝑥0
𝑥0 1 − 𝑥
𝑚 𝑤0
− 𝑚 𝑤 =
𝑥0
1−𝑥0
−
𝑥
1−𝑥
𝑚s
Subscript 0 – representing
the initial conditions
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5. PROBLEM
Skim milk of Xo = 0.91 is
evaporated to X=0.55.
Find out the % water
evaporated based on
the original water
content.
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6. Other
included
topics
• EMC (for milk 2.4% w.b
@ T=80c and R.H 50%)
• mechanism of drying
solids (constant and
falling rate period)
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7. Indirect
Also called -
>roller drying
->film drying
• Less space
• More economical than
spray dryers (small
volumes*)
• Steam consumption : water
evaporation :: 1.2-1.6:1
(120kg steam
to evaporate
100kg water)
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9. Construction
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doctor
Liquid enters
at 700 C
Heat
transferred to
the liquid by
convention
Vaporized
moisture
removed
through a
vapour hood
Milk is
generally
precondenssed
(<300C)
Doctor blade –
150-300
L : 360cm
D: 60-120cm
Rpm: 6-24
(contact with
drum < 3sec)

10. FACTORS
• Temperature difference (inside
drum temp as well)
• Time of contact
• Rotation speed
• Pressure inside vessel
• feed type and feeding
mechanism
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11. CLASSIFICATION
No. of drums
pressure surrounding
the product
feeding
arrangements
Material of
construction
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12. No. of drums
No. of drums
• Single drum
• Double drum
• Twin drum*
Pressure surrounding
Pressure
surrounding
Atmospheric vaccum*
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14. • Nip feed(simplest)
• Splash feed
• dip feed
• Roller feed
FEEDING
ARRANGEMENT
MATERIAL
CONSTRUCTION
• Alloy steel
• Stainless steel
• Nichrome steel
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16. Product may have a scorched
flavour
Solubility is much lower because of
protein denaturation (98% to (85%)
Power consumed little high as
indirect contact exists
control
temp
control
contact
time
use
polycab
wires
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17. Precautions
Smooth
drum
Sharp
knives
every
100h of
operation
Preconcent
rate 25%-
30%
Preheating
< 700 C
Not for
acidic
milk
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18. REFERENCES
Drum Drying Juming Tang Hao Feng Washington State University, Pullman,
Washington, U.S.A. Guo-Qi Shen Shanxi Agriculture University, Shanxi, People’s
Republic of China
DAIRY PLANT ENGINEERING AND MANAGEMENT, Tufail Ahmad
web REFERENCES
http://sites.bsyse.wsu.edu/tang/main/publications/pdfdocs/book-
drumdry-tang03.pdf
https://www.youtube.com/watch?v=JGb77K_K55M
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