1. The study compared the power consumption of air cooling versus water cooling for an extrusion process using four different resins. 2. Water cooling used slightly more energy than air cooling for all resins, with the greatest difference seen in PET where water cooling used 80% more energy. 3. Air cooling is recommended for dedicated processes as it provides sufficient cooling with less energy use than water cooling, however the screw design must match the resin to avoid excessive heating or cooling needs.

1. COMPARISON OF TWO DIFFERENT COOLING METHODS FOR EXTRUSION
PROCESSES
Timothy W. Womer
Walter S. Smith
Richard P. Wheeler
Xaloy Corporation, New Castle, PA
Abstract
This paper will compare the total power consumption of
two different means of heating/cooling systems: air and
water. For a single 90mm extruder, the total power
consumption, output rate, and thermal control will be used
to compare the two cooling means. Four different resins
will be used.
Introduction
Heat can be added or removed from the extruder barrel
with air or water cooling. Air cooling is ideal for
processes that do not require high energy removal. It is
less expensive for the hardware, easier to maintain, has
lower operating costs, and requires less space compared
to fluid cooling. Air cooling provides for slower changes
in temperature compared to water cooling.
Water cooling is best suited for processes that require
high energy removal. Compared to air cooling, the
equipment is more expensive, requires higher
maintenance to prevent fouling, and requires more space
and a water pump. Thermal instability can also occur if
the cooling water flashes to steam. Large thermal
gradients produced by water cooling can also contribute
to excessive thermal strain and stress in the extruder.
shown in Figure 2. A continuously running water pump is
shown in Figure 3. This pump is a 1000 Watt.
Figure 4 shows one zone of the air cooled setup. Each of
the five zones contains a set of 3000 Watt heaters (6000
Watts per zone). Each heater is cast aluminum with cooling
fins. The 205 Watt blower is to the right in Figure 4. Each
blower is activated by the zone controllers. Each blower is
rated at 7.5 cmm (265 cfm). Each zone is isolated by
baffles. Figure 5 shows an overview of the air cooled
system with all heaters, baffles and blowers installed. The
top cover has been removed in Figure 5. The heated air
exits in an air gap just under the top cover shown in Figure
6.
Also shown in Figure 6 is the 711mm (28”) Flex-lip Sheet
die and the Dynisco Screen Changer. The die was set to
2.5mm (.100”). The Screen Changer was loaded with a
breaker plate and a 20/40/60/20 screen pack. A melt probe
was inserted in the melt stream between the screen changer
and die.
A low shear barrier mixing screw was used for all testing. It
was specifically designed for polypropylene with a long
feed section.
A Fluke Data Acquisition System was used to acquire data
from the process. It will be referred to as NetDAQ.
Resins
Equipment
The extruder used for this study was a 90mm (3.5”) x
24:1 NRM Extruder with five temperature zone
controllers. It is equipped with a 112 kW (150 Hp) DC
motor. Max screw speed is 129 rpm. Figure 1 shows the
extruder.
Four resins were used for this study.
• ExxonMobil LDPE LD100BW, MFR of 2.0 g/10
min
• Novachemicals Novapol HD-2007-H HDPE, MFR
of 8.5 g/10 min
• ExxonMobil PP 9852EI, MFR of 2.1 g/10 min
• Eastar EB062 PETG, IV of .75 dl/g
The water cooled system consisted of five zones. It is a
closed loop system. Each zone has a set of 3000 Watt
heaters (6000 Watts per zone). Cooling of each zone is
controlled by a solenoid that opens and closes a valve.
Heat is pulled from the system through a heat exchanger
and discarded. The solenoids and heat exchanger are both
Experimental Procedure
Each of the four resins was extruded with water cooling and
then with air cooling for a total of eight one-hour tests.

2. For each test, the barrel and screw were completely
cleaned. The die was pre-heated two hours prior to each
one hour test, and the barrel was pre-heated for one hour
before the testing started. Steady thermal conditions were
then assumed to prevail throughout each hour long test.
The four resins were run with the water-cooled system
first. Once the water-cooled trials were completed the
extruder was retrofitted for air-cooling. The same
controllers used for water-cooling were used with the air
cooling. Between switching of the systems the heater
amperage and voltage were checked on each zone.
For each one hour test, the extruder was started and set to
a speed of 75 rpm. The thermocouple temperatures, the
amount of time the heaters were on, motor amps, screw
speed, melt probe temperature, and the amount of time the
blowers ran (air cooling) were all monitored and recorded
every .02 seconds a NetDAQ. Melt temperature was
measured every ten minutes with an IR gun and a handheld melt probe. Output rates were measured and
recorded every twenty minutes.
The data were then extracted from the NetDAQ and
compiled with a spreadsheet program. The amount of
time the heaters and blowers were on was used in
conjunction with the heater amperage and voltage to
calculate the energy (kilowatt-hours) consumed by each
heater and blower during the hour long test. The same
was done for the drive motor energy. The energy added
to the polymer was calculated from the difference
between the polymer product melt temperature and the
feed temperature.
Presentation of Data and Results
The water-cooled system used slightly more energy than
the air-cooled system for all four polymers as shown in
figure 7.
There was little difference between the HDPE runs shown
in Figure 8. Power consumption for the drive was almost
equal. The main difference was power used between the
cooling systems. The water cooled used about 22% more
energy compared to the air cooled.
The same patterns are seen with the other tests. Please
reference Figures 9 and 10. LDPE tests had similar
values between the systems with the water using 7% more
energy. The PP runs had the lowest total power
consumptions with comparable values. The air cooled
used 20% less energy than the water cooled.
Figure 11 shows the highest power required for all the
runs. This came during the PET trials. The major
difference was the power usage for heating/cooling. The
water cooled used 80% more energy than the air cooled.
Output rates were higher for the water-cooled system on 2
out of the 4 resins. Please see Figure 12.
Temperature control varied according to resin. With respect
to only the heating/cooling system LDPE had the highest
power consumption for all resins mainly because of power
needed in zone 3. This zone was cooler during the whole
trial for both systems. Please see Figure 13. HDPE
exhibited a similar pattern of a cooler zone 3 for both
systems as well. Please see Figure 14. PP had no apparent
differences between the two systems. This is confirmed in
Figure 15. PET was the only resin that required extensive
cooling in Zone 1during the trials. The air system couldn’t
maintain the actual temperature to the set point. This is
illustrated in Figure 16.
Discussion of Data and Results
One of the major differences between the water and air
systems was the continuous running of the water pump.
This consumed 1kWhr for all water cooled tests. Since
water cooling is an abrupt mean of heat extraction energy is
removed quickly and many times resulting in excess energy
removal. So energy must be added back into the system to
keep the barrel at temperature. Air cooling is more gradual
and doesn’t over cool a barrel section as easily as water
cooling. So unless extensive cooling is needed then water
cooling can be avoided. Air cooling should be a sufficient
system for most properly designed extruders.
Water cooling would be useful when many different
polymers are to be processed by the same extruder. With a
given screw design, some polymers may require extensive
cooling or heating to produce the desired product
temperature. This may require the added heat capacity the
water provides. But it is versatility at the cost of thermal
stability and excessive energy consumption.
This can be seen by the high energy consumption values for
HDPE and LDPE. Zone 3 actual temperature values were
low during the whole test. This zone required constant
power for both resins and both cooling systems. A different
properly designed screw would alleviate this problem. The
screw was specifically designed for PP.
More cooling was required to run the PET resin on Zone 1.
The air cooling system could not control this zone. However
the water cooling could control this zone, but naturally used
more energy to do so. The PET output rates were 5% higher
for the air cooled. The water lowered the temperature of the
first zone which lowered the solids conveying to reduce the
output. So, output rate can also be affected by the cooling
means, especially as it affects solids conveying.

3. Conclusions
1.
Cooling of the extruder barrel should be
minimized. Excessive cooling will require more
motor power.
2.
Heating of the extruder barrel should be
minimized. Excessive heating will produce large
thermal gradients in the melt and non-uniform
product melt temperature distribution.
3.
Air cooling is recommended for an extruder
dedicated to a given product. However, the
screw must be properly designed to not require
excessive cooling or heating to maintain product
temperature.
4.
Water cooling finds uses when a given extruder
is used to process multiple polymers and rates
with the same screw. Water cooling can provide
great energy transfer so that product temperature
can be maintained in spite of a screw that is not
optimized for a given polymer at a desired rate.
Figure 1-90mm x 24:1 NRM Extruder
with water cooled system
Solenoids
References
1.
2.
3.
C. Rauwendaal, Polymer Extrusion, Hanser
Publishers, NY, 1986
E. Steward; W. A. Kramer, Air vs. Water Cooled
Single Screw Extruders, ANTEC 2003
J. Wortberg; T. Schroer, Novel Barrel Heating
with Natural Gas, ANTEC 2003
Manifold
Heat Exchanger
Figure 2-Water cooled system
Heat Exchanger and Solenoids

4. Flow Meters
Water Pump
Figure 3-Water cooled system-Water
Pump
`
Figure 5-Air cooled system-Overview
Baffle
Air Gap
Air Cooled Heater
Blower
Screen Changer
Die
Figure 4-Air cooled system-Single zone
Figure 6-Die, Screen Changer and Air Gap

5. Total Energy Consumed for Each System
Comparison of Total Kilowatt-hours
for Processing PP
100
87.75
45
86.54
41.87
39.64
40
80
70.49
69.33
70
60
52.2
50
Water
Air
50.05
41.87
40
39.64
30
20
Power Consumption (KWh)
Energy Consumed (KWh)
90
35
30.27
Total
Drive
Heat/Cooling
25
20
15
11.6
9.36
10
5
10
0
0
HDPE
LDPE
PP
PET
Water
Resin Processed
Figure 10-Power Consumption for PP for
both systems
Comparison of Total Kilowatt-hours
for Processing HDPE
Comparison of Total Kilowatt-hours
for Processing PET
80
100
70.49
69.33
70
87.75
50
Total
Drive
Heat/Cooling
40
30
20
11.14
8.73
10
Power Consumption (KWh)
90
60.6
59.35
60
Air
Heating/Cooling System
Figure 7-Total Energy
Consumption for the 8 tests
Power Assumption (KWh)
30.28
30
Water
85.85
70
60
Total
Drive
Heat/Cooling
50
40
30
20
10
0
86.54
84.07
80
3.68
0.69
0
Air
Water
Heating/Cooling System
Air
Heating/Cooling System
Figure 8-Power Consumption for HDPE
for both systems
Figure 11-Power Consumption for PET
for both systems
Throughput Rate for Each System
Comparison of Total Kilowatt-hours
for Processing LDPE
350
307
60
Total
Drive
Heat/Cooling
40
34.21
33.25
30
20
17.99
Throughput Rate (kg/hr)
50.05
50
Power Consumption (KWh)
292
300
52.2
250
200
166
164
169
Water kg
Air kg
171
150
106
97
100
16.8
50
10
0
HDPE
0
Water
Heating/Cooling System
Air
Figure 9-Power Consumption for LDPE
for both systems
LDPE
PP
PET
Resin Type
Figure 12-Output Rates for all 8 Tests

6. Temperature Control for LDPE of both systems versus
setpoint
Temperature Control for PET of both systems versus setpoint
260
260
250
250
240
240
Temperature C
Water
Air
Setpoint
220
200
200
190
190
180
180
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Zone 1
Figure 13-Temperature Control of LDPE
for both cooling systems
260
250
240
230
Water
Air
Setpoint
220
210
200
190
180
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Figure 14-Temperature Control of HDPE
for both cooling systems
Temperature Control for PP of both systems versus setpoint
260
250
240
230
Water
Air
Setpoint
220
210
200
190
180
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Figure 15-Temperature Control of PP for
both cooling systems
Zone 2
Zone 3
Zone 4
Zone 5
Figure 16-Temperature Control of PET
for both cooling systems
Temperature Control for HDPE of both systems versus
setpoint
Temperature C
Water
Air
Setpoint
220
210
210
Temperature C
Temperature C
230
230