EXPERIMENT NO 1
Objective:
To study the drying characteristics of solids in a tray
dryer under forced conditions.
Working Principle:
In tray dryer hot air is continuously
circulated. Forced convection heating takes place to remove moister
from the solids placed in trays.
Apparatus:
Tray dryer apparatus
Sand
Water
Theory:
A tray Dryer is an enclosed insulated chamber in
which trays are placed on top of each other in trolleys. Tray Dryer
are used where heating and drying are essential parts of
manufacturing process in industries such as Chemicals, Dye stuff,
Pharmaceutical, Food Products, colours etc.
The material to be dried either wet or solids are placed
in the trays. Heat transfer is by circulation of hot air by electric
heaters or steam in radiator coils. Blower fans are installed inside
to ensure proper circulation and transfer of heat.
A control panel to control the temperature and other parameters is
fixed outside the dryer. These dryers are available in Mild Steel,
Stainless Steel or construction. Tray dryer is used for drying of
pigments, food, bakery, electrodes, chemical and plastic powders.
Drying of solids is considered in two stages, a constant rate period
followed by a falling rate period. Rate of drying correspond to the
removal of water from the surface of solid. Falling rate period
corresponds to the removal of water from the interior of surface.
Rate in either case depend upon;
Flow rate of air
Solid characteristics
Tray material
Further conditions should resemble as closely as possible those
expected to prevail in the contemplated large scale operation.
Sample should be
similarly supported in a
tray.
It should have the same
ratio of drying to non
drying surface.
It should be subjected to
similar conditions of radial
heat transfer.
Air should have the same
temperature, humidity and
velocity.
Drying Rate is calculated from;
N = S(dx/dθ)(1/A)
Line Diagram:
M M
an
anomeome
t
Temp. Sensor 1
Temp. Sensor 2
Sample
Heater
Section
Blower
Procedure:
1. I load the pre-weighed tray with solid and record the weight of
sand and tray.
2. I start the blower and heater.
3. I fix the air flow rate and let the system to achieve steady state
as the air flow rate would make the temperature steady.
4. When the desired conditions of temperature and air velocity is
reached I remove the sample tray and put desired amount of
water in it until the sand in the tray is fully wet.
5. I turned on the stopwatch.
6. I started to take temperature readings with time at about 3-5
min interval.
7. It assumed to be complete when at least 3 consecutive readings
are unchanged.
8. The temperature at the inlet and outlet of the drying chamber
and the air flow rate are recorded at least three times during
the course of a run to give avg. operating conditions.
9. The same steps can be repeated for different flow rate of air.
Observations and Calculations:
Surface area of solid = A = 0.0706
m2 Weight of dry solid = S = 0.366
kg Weight of tray = 0.15 kg
Table:
t G W X= delX delθ N = S(dx/dθ)
(W-S)/S (1/A)
0 91 420 0.1475 - 300 0
300 91 408 0.1148 0.0328 300 0.404031022
600 91 406 0.1093 0.0055 300 0.067338504
900 91 403 0.1011 0.0082 300 0.101007756
1200 91 400 0.0929 0.0082 300 0.101007756
1500 91 394 0.0765 0.0164 300 0.2020115511
1800 91 385 0.0519 0.0246 300 0.303023267
2100 91 380 0.0383 0.0137 300 0.168346259
2400 91 375 0.0246 0.0137 300 0.168346259
2700 91 370 0.0109 0.0137 300 0.168346259
3000 91 365 0.0027 0.0082 300 0.101035364
3300 91 360 0.0164 0.0137 300 0.0168331445
3600 91 358 0.0219 0.0055 300 0.067406516
3900 91 357 0.0246 0.0027 300 0.033678612
4200 91 357 0.0246 0 300 0
4500 91 357 0.0246 0 300 0
t = Time = θ
G = Mass Velocity
W = Weight of Solid
X = Moisture Content
N = Drying Rate
Graphs:
delx VS N
0.45
0.4
0.35
0.3
0.25
0.2
del x
0.15
0.1
0.05
0
N VS X
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
X
0.04
0.02
0
0 0.010.020.030.04 0.05 0.060.070.080.090.1
N
Applications:
Tray dryer are used in pharmaceutical industries.
Used where moisture content is low.
Precautions:
Do not open the door of the chamber during experiment.
Do not disturb the balance during experiment.
Never switch on heater before blower.
Results:
Moisture content decreases w.r.t time and also the
moisture content in sand will decrease.
References:
www.slideshare.com
www.wikipedia.com
