This presentation consist of general introduction, structure, mechanism, operating process of vacuum dryer

1. CONTINUOUS VACUUM DRYER
FOR ENERGY SAVING

2. INTRODUCTION:
In recent years, there has been a general trend to use powdered foods.
×Spray drying: is not a suitable method for drying highly viscous foods
×Freeze drying: suitable for highly viscous food but has high operating cost.
New drying method required to dry heat sensitive foods with high viscosity at a
reasonable operating cost.

3. Continuous vacuum dryer:
• For energy saving
• High quality dried products
• Reasonable manufacturing cost.
• Dried in a enclosed vacuum chamber  Oxidization free product
and with good dispersibility .

4. STRUCTURE:
1.Vacuum chamber
2. Feed nozzle
3. Driving roller
4. Transport belt
5. Heating plate
6. Scraper
7. Recovery tank 11. Flow meter
8. Feed tank 12. Rolll guide 15.automatic discharging device
9. Dosing pump 13.preliminary vessel 16. Needle valve
10. Temp. Indicator 14.closure valve 17·pressure gauge

5. MECHANISM:
Five independent, overlapping transport belts are constructed with
combined returning passage.
The enclosed heating plates between the transport belts will supply
conductive heat toward the upper side belt and radiant heat downward to
the material on the transport belt.

6. COMPARISON:
• Thermal efficiency of this system is highly improved than conventional vacuum
dryer.
• Unutilized space can be reduced to a minimum, giving cost advantages.

7. OPERATION PROCESS:
 Wet product, coming from the pre-treatment plant
 Brought into feed tank.
 Fed into the vacuum chamber, under constant pressure.
 Evenly distributed to the 5 nozzles, is uniformly spread on the respective
moving belts.
 Dried while passing through the drying sections.
 The moving belts slide on the Heating plates, divided into 4 to 6 parts.
 Temperature of each part can be controlled independently according to the
drying characteristics of the materials.
 The dried products on the moving belts are crushed
 Discharged through the automatic discharging device.

8. CHARACTERISTICS:
1.DRYING METHOD:
Continuous vacuum dryer is efficiently treats the products.
1.Nozzle can spread the material uniformly on the moving belt.
2. heat from both radiation and conduction is simultaneously applied to the
product by the upper and lower heating plates.
Advantages:
 Heat sensitive foods of high viscosity can be dried more efficiently in a short
time.
 The time required for drying with in a few minutes.
Temperature of the product is kept below 40ᵒc throughout the drying process.

9. 2.DEVELOPED FEED NOZZLE:
(1)Preliminary Experiments For The Nozzle:
The qualities of products depend on vacuum and heating condition as well as
distribution of wet product . If the distribution of raw material is not uniform, it
does not make a good quality product because the material either received
excessive heat or was not completely dried. Therefore, when the test nozzle was
designed the following characteristics had to be considered.
(I) Flow rate must not fluctuate with time.
(II) Weight distribution must remain constant on the belt.
(III) Material must be distributed in a thin layer on the belt in order to increase
relative surface area.

10. (2) DOUBLE CYLINDER TYPE NOZZLE:
The nozzle is designed to prevent any fluctuation in the flow rate and non-
uniform distribution on the belt.
The raw material overflows from a part of
the cylinder to the orifice on an upper
portion of inner cylinder, and the material
flows uniformly to the outer cylinder, and
the material flows uniformly to the outer
cylinder in the direction of length. DESIGN OF FEED NOZZLE
 The role of the inner cylinder is to prevent excessive flow at the feed pipe for raw
material and to keep uniform feed distribution on the belt.

11. Newtonian liquid:
Sweetened condensed whole milk in the experiments resembles a nearly Newtonian
liquid.
Newtonian liquids are the ones whose shear stress is proportional to shear rate.
𝑭
𝑨
= 𝝉 = −µ(𝒅𝒖/𝒅𝒚)
τ=Shear stress or force per unit area(N/mm²);µ=Coefficient of viscosity(N-
s/m²);du/dy=Velocity gradient(s -¹).
Therefore the milk is described by the Hagen-poiseuille equation as follows:
Q=R4∆Pg/(8µL)
Where,Q=Flow rate(m3/h);R=radial of cylinder(m);∆P=Pressure difference(kg/m2);
µ=viscosity(kgf.s/m2);L=Length of cylinder(m); g=gravitational acceleration (m/s2).

12. OPERATING CONDITIONS OF CONTINUOUS
VACUUM DRYER:
VISCOSITY OF FEED 40 POISE
TOTAL SOLID OF FEED 73.5%(WET BASIS)
FEED TEMPERATURE 10 OC
GAS CONSTANT OF FEED 60 ml/l
FEED RATE 27.2 Kg/h
FEED NOZZLE Double tube type
DIAMETER OF ORIFICE 1.3 mm
CHAMBER PRESSURE 5 mm Hg
BELT SPEED 0.72 m/min
DRYING TIME 408 s
OPERATING TIME 11 h
PRODUCT RATE 21 kg/h

13. 3.HIGHER THERMAL EFFICIENCY:
The continuous vacuum dryer has a higher thermal efficiency than conventional
vacuum dryers. The reasons are mentioned below. In both method A and method B
in figure, radiant heat from the heating plate under the moving belt has been
absorbed by the return belt. On the contrary, radiant heat in this system is utilized to
warm the product on the lower belt. Since the enclosed heating plate can supply
heat to the upper and lower belts simultaneously, the thermal efficiency of the dryer
markedly improved.

14. CALCULATION OF THERMAL EFFICIENCY FOR
DRYER IS AS FOLLOWS:
Emissivity of generation side of heat, e1 = 0.5
Emissivity of receiving side of heat, e2 = 0.5
Heating temperature of plate = 170°C;
vacuum pressure = 5 mm Hg;
Heat transfer coefficient from plate to material through synthetic belt, h = 14.5
kcal/m2hᵒc (experimental value).

15. CALCULATION OF RADIATIVE HEAT FLUX ON
THE PLATE:
QR=4.88e1(T1/100)4 - (T2/100)4 Kcal/m2h
=4.88(0.5){( 273 + 170)/100}4 – {(273 + 1)/100)}4
=802 kcal/m2h
CALCULATION OF CONDUCTIVE HEAT FLUX:
QC=h A ∆t=h A (T2-T1)
where A, unit heating area of plate (m2)
h=heat transfer coefficient from plate to material through synthetic belt(Kcal/m2hoc)
T1 heating temperature (OC);T2 saturated temperature equilibrium to vacuum
pressure (OC) QC conductive heat flux (kcal/m2h)
QC=14.5(1)(170-1)=2451Kcal/m2h

16. CALCULATION OF MODIFIED ANGLE
FACTOR FOR THE HEAT EXCHANGE
OF INFINITIVE PARALLEL PLATE:
FAE=Interchange factor for the radiation from one surface to other.
1/F AE=(1/e1)+(1/e2) – 1
1/F AE=(1/0.5)+(1/0.5) -1
FAE=0.333
HEAT FLUX RECEIVED BY RADIATION:
QR´=4.88((T1/100)4 –(T2/100)4)FAE (Kcal/m2h)
QR ´=4.88[{(273+170)/100}
4
- {(273+1)/100}
4
](0.333)
=534 Kcal/m
2
h .

17. CALCULATION OF THERMAL EFFICIENCY FOR
THE METHOD ‘A’AND ‘B’:-
ᵠA= Thermal efficiency of method A(%)
ᵠA=[(QR´+QC)/(3QR+QC)]×100
=[(534+2451)/{3(802)+2451}]×100
=61.5%
If the heat loss is assumed to be 10% at the heating pipe from the heating source to
the dryer then net efficiency will be 51.5%.

18. CALCULATION OF THERMAL
EFFICIENCY FOR THIS METHOD
ᵠ0=[(5QC+5QR´)/(5QC+7QR)]×100
=[{5(2451)+5(534)}/{5(2451)+7(802)}]×100
=83.5%
If the heat loss is assumed to be 10% .
Actual efficiency = (83.5-10)%
=73.5%

19. CONCLUSION:
High thermal efficiency .
The space requirement in vacuum chamber can be reduced to minimum.
The processing cost is reduced in comparison with conventional vacuum dryer.
It costs approximately one third of that of freeze dryer.
The particle size distribution can be controlled by the screen opening of the
sizing material.
Acceptable products for this system are mainly highly viscous food such as
cheese, High fat milk ,fruit Juices , tomato Juice, honey etc.

20. REFERENCES:
• Hayashi, H. , Kumazawa, E. , Saeki, Y. Andlahicka, Y.(1983) “CONTINUOUS
VACUUM DRYER FOR ENERGY SAVING”, drying technology, 1: 2, 275 —
284.
• Copyright © 1983 By Marcel Dekker, Inc.
• Milk Products Co. Ltd. Technical Research Institute, Kawagoe-shi, 350 Japan.

21. Thank you….