The Acoustic Drying Of Cloth In Drum-Type Washing Machines

Acoustic Processes and Devices Lab
The Acoustic Drying Of
Cloth In Drum-Type
Washing Machines
Biysk Technological Institute (BTI)
www.u-sonic.com

Drying
The drying is a final stage of every cloth washing
processes. Combining washing and drying process in
unified machine provides full automation of cloth
maintenance process at home
Imperfections of
convective drying:
•Long time and big
power consumption.
•Limited minimal size of
washing machine.
•Impossibly to dry
“delicate” cloths.
•Probability of parch of
garments.
Humidity
Comparison
characteristics of
different drying
methods
Key advantages of
acoustic drying:
•Decreasing power
consumption.
•Possibility to carry
out qualitative cloth
drying with low
temperature .
Ultrasound Convection VHF
Time
2

Conceptions Of Acoustic Drying Physical
Mechanism
• At present day uniform conception of
acoustic drying physical mechanism is
absent, but exists set of hypothesis: by
Boucher, by Soloff, , by Greguss. . Each taken
separately it is enough describes some
mechanisms.
• This hypothesizes are based on knowledge
about physical effects that taking place in
drying materials and in material-air
air
interface under high-intensity intensity acoustic
wave propagation. This effects are driving
forces of acoustic drying.
3

Driving Forces Of Acoustic (Ultrasound)
Drying
Driving forces
Hydrodynamical Mechanical Calorific
Acoustic
cavitation
Radiation
pressure
Acoustic flows
Water atomization
Turbulization and
reducing thickness
of diffusion interface
Sound-capillary
effect
Pressing-out water
from capillaries
Heating the material
by means of oscillation
absorption
Pressure differences
above material surface
Arising and collapsing
of cavitation bubbles
in capillaries
Pulsation of vapor
in water-free capillaries
Decreasing
liquid viscosity
4

Pressure Differences Above Surface
• Acoustic wave, during
propagation above material
surface, arises quickly-changing
changing
zones of increasing and
decreasing pressure.
• Accordingly Boucher hypothesis,
in the increasing pressure zones
drying speed do not decreases,
while in the decreasing pressure
zones arises additional effect of
vacuum drying
Increased pressure
Decreased pressure
Increased pressure
Decreased pressure
Moisture
5

Acoustic Flows In Closed Space
• The flows in liquid and gas
mediums, during intensity
acoustic wave propagation, are
caused by liquid (gas) viscosity.
• Into infinite mediums the acoustic
flows are laminar and directed
lengthways wave propagation
vector.
• In the stationary waves conditions
acoustic flows are closed. Near
the interface layer acoustic flows
rises a turbulence.
• The velocity of acoustic flows
secondary-degree depends from
sound pressure and in range 140-
150 dB is 6-10 m/s
Scheme of acoustic flows in closed space
The acoustic flows is main driving force of acoustic drying in 1401
40-150 dB sound
pressure level range. Acoustic flows speeding up evaporation and provides humidity
removal from drying zone
6

Microflows Near Obstacle
• When the acoustic wave interacts
with drying cloth, in immediate
proximity to humidity fibers the
microflows are arises.
• Low intensity waves provides
laminar microflows that do not
influence to drying speed.
• When intensity of acoustic waves
reach a critical value, the
microflows turn into turbulence and
displace a bound laminar flow, that
assists for mass transfer process.
Laminar mode
Re1200
Microflows near the obstacle along with acoustic flows appreciably intensify mass
changes processes at 140-150 150 dB range
7

Reducing Thickness Of Water-Air
Interface Layer
Air flow
Air flow
Evaporation
Diffusion
Interface
Layer
Water
Convective drying
Water
Acoustic drying
• Near the wet material surface are presence the interface layer, that is impediment for mass changes
process
• Reducing the interface layer thickness provides increasing the evaporation speed.
• The thickness of interface layer depends from diffusion and hydrodynamic processes.
• During the convective drying air flows in interface layer are laminar and thickness of interface layer
defines by diffusion processes
• In the high-intensity acoustic fields thickness of interface layer seriously decreases that caused by
turbulent flows and microflows
8

Radiation Pressure
Radiation
pressure
Ultrasound
Removed water
Water in material
• Radiation pressure is steady component of total pressure that influence to
solid in acoustic wave.
• The cause of radiation pressure is a transfer a part of wave mechanical
impulse to a solid during absorption or reflection the acoustic wave.
• The radiation pressure, that arises in intensity acoustic field (more than 135
dB) capable to squeeze out water drops from material
9

Cavitation
• The acoustic cavitation arises in
liquid during propagation high-
intensity acoustic wave.
• The cavitation is a key driving
force, that speeding-up many
physiochemical processes in
acoustic fields, includes drying
process.
• The cavitation connects with liquid
continuousness violation in
decreased pressure phase, arising
vapor-gas bubbles in gaps and its
collapsing in next increasing
pressure phase.
• When the bubble collapsing, on
account of bubble skewness, , arises
a jet stream that excite micro
shock wave in liquid
Increased pressure
Decreased pressure
Decreased pressure
SHOCK WAVES
Increased pressure
Increased pressure
Decreased pressure
10

Cavitation Atomizing Of Liquid
• Collapsing of cavitation bubbles near
free surface excites capillary-gravitation
waves. Wave crests splints up to little
drops.
• Detached drops make up an aerosol.
When other influences (e.g. air flows)
are absent the aerosol is in equilibrium.
• The air flows, acoustic flows and
radiation pressure provides effective
removing of aerosol from surface.
• Cavitation atomizing provides water
removal without evaporation. It
decreases power consumption of drying
process
• Cavitation atomizing arises only in
conditions of high cloth humidity
(more than 60%) and high-
intensity ultrasound – more that
160 dB.
• For the cloth drying in washing
machines cavitation atomizing is limited
applicable
Cavitation
Water
aerosol
Capillarygravitation
waves
aerosol
11

Sound-Capillary Effect
• If cavitation bubble arises at
capillary entrance, the shock wave
will be directed into capillary.
• The overpressure in capillary, that
excited by shock wave, squeezes
out liquid outside. This
phenomenon named as “soundcapillary
effect”.
• Sound-capillary effect promotes to
accelerated water transfer from
deep layers to surface, that
provides drying speeding up
Water squeeze out
Capillary
Cavitation bubble
12

Pulsation And Explosion Of Vapor-gas
Bubbles Into Capillaries. Decreasing
Liquid Viscosity
• With a increasing acoustic wave intensity a
part of bubbles does not have a time to
collapse in increasing pressure phase. In
the next decreasing pressure phase these
bubbles again swell. The process may to
repeat continuous time. These bubbles
named as “resonant bubbles”
• Pulsation of resonant bubbles in capillaries
excites low-frequency oscillations of
capillary walls and speeding up water
transfer from deep layers to surface
• Explosions of bubbles into capillary also
promote water transfer process
• Cavitation bubbles provides “loosening” of
liquid and, as result, decreasing the
viscosity, that is additional factor of mass
transfer too.
Water
Water
squeeze out
Borders
vibration
Cavitation
bubbles
13

Effect Of Radiation Pressure
Objects “hover” over acoustic radiator
by means of radiation surface
14

Calorific Effect
• Absorption of ultrasonic oscillations
in wet material provides its heating
• Acoustic heating arising almost
uniformly on all deepness of
material, that promote water
transfer from deep layers.
• Calorific effect observes only under
high-intensity intensity ultrasonic (more 165
dB) and may be effectively using
for poured materials (e.g. sugar,
corn or silica).
• In the acoustic cloth drying calorific
effect show weakly and do not
influence to drying speed
Ultrasound
Heat
Wet material
15

Pulsations Of Vapor In Water-free
Capillaries
• Due to decreasing humidity, part of
capillaries become water-free.
• In the water-free zones a vapor locks
are arising. That fact is a hinder for
transfer humidity remnants to surface.
• High-intensity oscillations excites
pulsations of vapor in water free
capillaries, that breaks a vapor locks.
• Accordingly with Simonian hypothesis,
vapor pulsation and vapor locks
removal provides drying speeding up
Ultrasound
Vapor
squeeze
out
Capillary
16

Industrial Applications Of Acoustic
Drying
• Low-temperature drying of bioactive
substances
• Drying of thermolabile vegetables raw
(corn, mushrooms, herbs)
• Drying of flammable and explosive material
• Drying of wood
• Drying of thermolabile chemical and
medical preparation
• Drying of tissues in textile fabrics industry
17

Industrial Drum-type Acoustic Dryers
• Drum-type acoustic dryers are
used for poured materials
drying
• Operation mode of drum-type
dryers is periodical
• Wet material is placed into
drum, where undergo acoustic
influence (including with
heating).
• Rotation of drum promote
uniform acoustic influence
onto all volume of material.
• Wet air from drum-type
dryers removes by airexhauster.
• Acoustic field in drum-type
dryers excites by gas-jet
radiators
1 – case, 2 – air-heater, 3 –
chamber, 4 – drum, 5 – door, 6 –
gas-jet radiator, 7 – air-exhauster, 8
-filter
18

Industrial Tunnel-type Acoustic Dryers
• The tunnel-type
type
dryers, as a opposed
to drum-type
dryers, are
continuous action
apparatus.
• Wet material moves
by transporter
through tunnel,
where presence
high-intensity
intensity
acoustic field
• Tunnel-type dryers
are used for poured
or sheet materials
and also wood
1-wet material, 2– acoustic
radiators, 3- air inlet, 4- air
exhaust
19

Industrial Ellipsoidal-type Acoustic
Dryers (Project)
• Chamber of ellipsoidal dryers
are generated by truncated
ellipsoid of revolution, at that
revolution axel passing
through one focus of
generatrix ellipse.
• Acoustic radiator is allocated
on revolution axel of ellipsoid.
• Wet material allocated along
line that circumscribed by
another generatix ellipse
focus.
• As well known, ellipse collects
in one focus a radiation,
emitting from other focus.
1 - container with wet material, 2 – drying
chamber,
3 – acoustic radiator
20

Contact-Type Acoustic Dryers
• In the contact-type
type
acoustic dryers,
oscillations are
leading into
material under
direct contact with
acoustic radiator.
• Contact-type
type
acoustic dryers are
used for sheet and
roll materials (e.g.
paper, cardboard,
tissues) and wood.
• Contact-type
type
acoustic dryers
based on solid
acoustic radiators
(magnetostrictive
or piezoelectric)
21

Problems Of Acoustic Drying
• In spite of evident advantages of acoustic drying method
its broad distribution are restrained by set of technical
problems:
1. Low efficiency of existent gas-jet radiators
2. High cost of compressors for pressured air feeding
3. Short life-time of gas-jet radiators
4. Necessity to protection a humans from harmful acoustic
radiation
• Existent constructions of acoustic dryers has been
specified only for industrial applications and absolutely
unfit for household
22

The Acoustic Drying Of Cloth In Drum-
Type Washing Machines
Acoustic Drying of Cloth
in Drum-Type Washing
Machines
Contact method
Noncontact method
Drum-walls
oscillations
exciting
Aerodynamically
radiators
Piezoelectric
radiators
Directly
acoustic influence
to cloth
Dynamic
Sirens
Gas-Jet
radiators
23

Gas-Jet Radiators:
Advantages And Imperfections
+ Good acoustic
matching with air
medium
+ Small dimensions
+ Capability to
change working
frequency
- Necessity of high air
flow ratio
- Low efficiency
- Wear of nozzle and
resonator
24

Action Of Gas-Jet Radiator To Wet Material
25

Piezoelectric-Type Radiator
Advantages
Imperfections.
+ More high effectiveness
in comparison with gas-
jet radiator
+ Simplicity of electronic
generator in mass
production
+ Possibility to focusing
and beam forming
Electronic E; generator
- Complicacy to oscillator
system production
- Necessity to final tuning of
electronic generator with
oscillatory system
- High Q-factor Q
of
piezoelectric radiator
requires special means of
acoustic and electric
matching
- Complicacy
electromechanical
construction
26

Operation Principle Of Piezoelectric-type
type
Radiator
Russian patent #2059239,
V.N. Khmelev et. al.
Russian patent #2141386,
V.N. Khmelev et. al.
27

Distribution Of Oscillations Of Radiating
Surface During Working Frequency Change
28

Piezoelectric-Type Radiator
Key features:
Radiating surface diameter,
mm
Weight, kg
Working frequency, kHz
Material:
-of radiating disk
-of acoustic concentrator
Acoustic waves intensity in
focus, dB
Focal length, mm
Radiator size
(length*diameter), mm
Cooling
200
1,8
22±1,6
steel 40Х13
titanium alloy BT5
≤200
140..200
150*200
Air, forced by
ventilator
1 – disk, 2 – phase changing
riffles, 3 – oscillatory system
29

Action Of Piezoelectric Radiator To Wet
Material
30

Electronic Generator
Electric
Power
Acoustic
Energy
1 – regulated power supply, 2-output inverter, 3-matching
circuit, 4-oscillatory system, 5-driving oscillator, 6,8,10-
feedback, 7-controller, 9-control panel
Maximal power consumption, W (RMS)
Dimensions, mm
Weight, kg
Working frequency, kHz
Power grid voltage*, V
Output power adjusting range %
* - in mass production may be in 100-240 V range
Key features:
630
250х25
250х110

First Mock-up
(Based On “Vyatka” Washing Machine)
Appearance
Gas-jet radiators
Piezoelectric typeradiator
32

Test Procedure
• Testing and comparison gas-jet and piezoelectric-type type radiators.
• Testing possibility to drying different materials.
• Testing soundproofing
Drying speed (grams per minute) per weight unit
Pants (wool)
Material
Towel (double)
Thin linen tissue
Sport shirt (cotton)
Gas-Jet radiator
5
5,1
9,5
4
Piezoelectric-type type radiator
13
11
11
8,7
Average speed, gpm
8,2 (7,7)
12,3 (11,6)
33

Obtained Results
Acoustic power, W
Drying speed, gpm
200
14
12
150
10
100
8
6
50
4
2
0
1GJR
PZT
0
GJR1
PZT
Energy, consumed for removal 1 gram of water, kJ
Consumed power, kW
12
1,6
1,4
10
1,2
8
1
6
4
0,8
0,6
0,4
2
0,2
0
1GJR
PZT
0
GJR 1
PZT
34

Selecting Radiator Type
Feature
Gas-Jet Radiator
Piezoelectric radiator
Power consumption
≥1000
W
≤500
W
Efficiency
Problems of realization
Cost of acoustic drying
system
Life-time
≤25%
Absence of “domestic”
compressors with high air flow
ratio
10..20$ + compressor cost
≤100
hours
≤50%
none
≤100$ $ in mass production
≥ 1000 hours
Noise level
Over safety level
In safety range
Conclusion: Piezoelectric-type radiator is more effective and has
better parameter in comparison with gas-jet radiator
35

Results Of Experiments With First Mock-up
(Based On “Vyatka”)
1.Necessity of integrating acoustic radiator into
washing machine with convective drying
system
2.Necessity to make up acoustic drying unit
3.Necessity to investigate soundproofing features
of washing machine
4.Necessity to search optimal drying conditions
For the solving this problem has been build
second mock-up, based on LG WD14124RD
washing machine
36

Second Mock-up, Based On LG
WD14124
14124RD Washing Machine
Scheme of mock-up
Appearence
1 – case, 2 – inner drum, 3 – outer drum, 4 – drum drive, 5
–convective drying system, 6 – PZT, 7 – front door, 8 –
case soundproof, 9 – outer drum soundproof, 10 – front
door soundproof
37

Sound Pressure Meter
Standard SPLmeter
Developed
SPL-meter
Imperfections:
Measured SPL – less than 130 dB
Frequency range – less than 20kHz
Single channel
Realized features:
Measured SPL -up to 175 dB
Frequency range – up to 25 kHz
Dual channel
38

Testing Soundproofing System
Scheme of soundproofing system
and SPL measurement
First
channel
SPL-meter
Second
channel
Reducing the level of outside
harmful acoustic radiation and
noise the washing machine was
been soundproofed used special
sound absorption material
SPLAN-8
SPL level into washing
machine and outside was
measured used standard and
developed SPL meters.
Results:
1. Average SPL into drum – 130
dB.
2. Outside SPL at distance 1
meter from washing machine –
less than 70 dB.
* - SPLAN-8 – is a trademark of CG
“Standartplast”, Russia, http://en.stplus.ru/
39

Experimental Studies Method
1. Drying same-type tissues samples in different
conditions:
• without ultrasound - temperature 120°С
• without ultrasound - temperature 60°С
• with ultrasound - without heating
• with ultrasound - temperature 120°С
• with ultrasound - temperature 60°С
2. Measuring the humidity over same time intervals.
3. Analysis of results.
40

Experimental Results
(11 kg of cloth, maximal temperture 120°С)
Drying speed
Cloth humidity dynamics
16
45
15
14
40
Drying speed, gpm
13
12
11
10
9
8
w/o US
US var A
US var B
US var C
Cloth humidity, %
35
30
25
20
w/o US
US var A
US var B
US var C
7
6
15
0 5 10 15 20 25 30
0 5 10 15 20
Time, minutes
Time, minutes
Cloth humidity, %
45
40
35
30
25
Cloth humidity dinamics
US var C
w/o US
On the diagrams use following abbreviations: «w/o
US» -without ultrasound influence. «US var A» –
ultrasound influence by PZT #1 (steel acoustic
concentrator), electrical power 330W. «US var B» -
ultrasound influence by PZT #1 (steel acoustic
concentrator), electrical power 500W. «US var C»
ultrasound influence by PZT #2 (titanium acoustic
concentrator), electrical power 250-280W
20
15
0 5 10 15 20 25 30
Time, minutes
41

Experimental Results
(11 kg of cloth, temperature 60°С)
Drying speed dynamic
Cloth humidity dynamic
10
41
Drying speed, gpm
9
8
7
6
5
4
3
2
1
w/o US
US var C
Cloth humidity, %
39
37
35
33
31
29
27
w/o US
US
0
0 5 10 15 20 25
25
0 5 10 15 20 25
Time, minutes
Time, minutes
Since the requirements for final cloth humidity are absent, while it is known that exists
optimal humidity for following ironing of cloth and taking into account that equilibrium
humidity of cloth may alternates from 6% to 20% depends from air moisture, WE
SUPPOSES THAT OPTIMAL CLOTH HUMIDITY AFTER DRYING IS 25%
42

Experimental Results
(11 kg of cloth, temperature 60°С)
18
36
16
34
D ry in g s p e e d , g p m
14
12
10
8
6
4
US var C
w/o US
H u m id ity , %
32
30
28
26
24
US var C
w/o US
2
22
0
0 5 10 15 20 25
20
0 5 10 15 20 25
Time, minutes
Time, minutes
Since the requirements for final cloth humidity are absent, while it is known that exists
optimal humidity for following ironing of cloth and taking into account that equilibrium
humidity of cloth may alternates from 6% to 20% depends from air moisture, WE
SUPPOSES THAT OPTIMAL CLOTH HUMIDITY AFTER DRYING IS 25%
43

Experimental Results
(Removing 1 kg of moisture, temperature 120°С)
35
80
30
70
Drying speed, gpm
25
20
15
10
US var C
w/o US
Cloth humidity, %
60
50
40
30
20
US var C
w/o US
5
10
0
0 10 20 30 40 50 60
Time, minutes
0
0 10 20 30 40 50 60
Time, minutes
Influence
Maximal drying speed,
gpm
Average drying speed,
gpm
Drying time
Convective-Heat
24
21,3
47
Combined (convective-
heat + ultrasonic)
29
26,5
39
44

Optimal Drying Conditions Selecting
14
12
12
14
10
8,8
9
9,5
9,5
8
6
4
4,4
6,9
6
2
0
1,6
1 2 3 4 5
w/o US
with US
1 – Cold air, 2- Warm air at initial drying period,
3 –Warm air (temperature 60°С), 4 – Hot air (120°C), 5- Hot air
(120°C) + high-power of ultrasonic ( 500 W )
45

Analysis Of Experimental Results
1. Drying speed with acoustic influence always greater than
drying speed without acoustic influence at same air
temperature and air convection conditions
2. The drying speed non-linearly increases depends on
increasing acoustic influence power
3. Maximal drying speed under acoustic influence provides at
initial drying period when cloth humidity is maximal
4. In the conditions our experiments maximal drying speed
reach up to 14 gpm at maximal power of PZT 500W
5. Optimal drying speed is 12 gpm (at 350W for “steel” PZT
and 210W of “titanium” PZT)
6. More quick increasing the drying speed at initial period
when using acoustic influence one should be account for non-
inertial character of acoustic influence in comparison with
thermal influence
7. More quick decreasing the drying speed at final period
when using acoustic influence one should be account for more
quick decreasing of cloth humidity.
46

Conclusion
• 1. The integration of acoustic drying system into
washing drying machine provides increasing the
drying features by increasing the drying and
decreasing energy consumption.
• 2. The energy consumption of drying process
decreases with increasing the acoustic radiation
power.
• 3. Maximal growth of drying speed by acoustic
influence provides on initial drying period when the
cloth and air into drum are cold and cloth humidity is
high.
• 4. The most advantages of drying process with
acoustic influence in comparision with drying without
acoustic influence obtains when air temperature in
drum is low.
47