RF Heating System

8/12/2019 RF Heating System

1/16


2/16

RADIO FREQUENCY HEATING

In a radio frequency heating system the RF generator creates an

alternating electric field between two electrodes. The material to beheated is conveyed between the electrodes , where an alternating

energy field causes polar molecules in the material to continuously

reorient them to face opposite electrodes much like the way bar

magnets move to face opposite poles in an alternating magnetic field.

Friction resulting from this molecular movement causes the material torapidly heat throughout its entire mass.

The illustration below depicts a radio frequency drying system with

material between the electrodes. Polar molecules within the material

are represented by the spheres with plus (+) and minus (-) signs

connected by bars.The amount of heat generated in the product is determined by the

frequency, the square of the applied voltage, dimensions of the

material and its the dielectric loss factor which are essentially measures

of the ease with which the material can be heated by radio frequency

waves.

INTRODU

TION


3/16


4/16

DIAGRAM OF RF EQUIPMENT SCHEMATIC

A basic schematic of a Radio Frequency dryer is shown below. The dryer receives standard

power (i.e. 480V, 60 Hz) through the Switchgear. In the Power Supply section, line voltage is

stepped up to high voltage AC through a transformer and then changed to high voltage DCthrough rectifiers. In the Oscillator section, high voltage DC is changed to high frequency, high

voltage RF energy and transmitted to the applicator or electrodes where it is applied to the

work. All of this is controlled by a modern control system.An RF Dryer works very much like a microwave oven which creates high frequency

vibration of water molecules which thereby selectively heats materials containing water while

other materials heat very little.


5/16

The key to effective application of RF energy for drying is the rightapplicator, or electrode design. Traditionally, heating was accomplished

by creating a uniform electric field between two parallel plates. This

approach is capable of heating thicker materials uniformly because ahigh voltage gradient can be established in the material. However, it

does not work well for thin materials such as webs. In order to establisha high voltage gradient in a thin web material, the plates must be very

close together which can cause arcing between the plates.

For thin materials, the KERONE electrode design was developed. Thisdesign creates an electric field between alternating parallel rods that

gives a higher voltage gradient in the web for faster heating. A variationon this electrode design for thicker webs is the staggered KERONE

design. This allows for more uniform heating of thicker webs. This hasalso been used for thin beds of ceramic powders. As a general rule,

materials under 1/4 thick use the KERONE design, materials 1/4 - 1/2use the staggered KERONE design, and materials over 1/2 use the

parallel plate design. In all of these electrode designs, the material canbe either self-supporting or can be transported on a conveyor.


6/16

Materials have a major effect on the success of RF heating. Some materials heat very

well and some do not heat well at all. The key measure of heatability is the loss

factor of the material. The loss factor is a material property that determines how

well the material absorbs the RF energy. If the material has a high loss factor, it

absorbs energy quickly and thus heats quickly. If a material has a low loss factor, it

absorbs energy slowly and thus heats slowly. In general, polymers tend to have low

loss factors and thus do not heat well. Water, on the other hand, has a high loss

factor so it heats rapidly. This is why RF lends itself to drying so well, it heats the

water quickly but does not heat most base materials.

It is important to remember every material reacts differently and loss factors (theability to absorb RF energy) can change with frequency and temperature. A material

that does not absorb RF energy at room temperature might absorb the energy at

higher temperatures. This is especially importantin a composite product with a high

loss factor material (RF heats rapidly) and low loss factor material (RF heats slowly).

As the high loss factor material is heated by the RF energy, it will heat up the low loss

factor material through normal conduction. If this heat raises the temperature of the

low loss factor material to where it now absorbs RF energy, both products are heated

and could be overheated. In rare cases, this can lead to a runaway situation where as

the temperature increases, it absorbs more energy, which increases the temperature,

which increases the energy absorbed, and it continues until the material overheats.


7/16

In most cases, the product can be heated faster than the solvent

can be removed so the heating rate must be scaled back to get the

right balance of heat transfer and mass transfer. If the heat

transfer rate is too high, steam will be generated which can

damage the product.The complexity of the interaction between materials and the RF

field is why it is critical to consult with an expert in RF drying and

conduct trials on your product.


8/16

APPLICATIONS

Conventional mode of Drying Textiles after they have been dyed is a slowprocess. Textile industries can increase Throughput and fill orders moreprominently using Radio Frequency (RF) Dryers. RF system has capability toaccelerate the drying process and shorten production time. RF drying offersHigh Volume, High speed and High quality drying which is what exactlyneeded in textile industries. As wet garments of Acrylic, Cotton, Nylon and

Polyester Blends pass through the drying chamber , the radio waves vibratesthe contained Water molecules million times per second, vaporizing them.Ventilator Fans are used to remove damp air from the Drying Chamber.

The dryer system comprises the 125kW industrial high frequency generatorin conjunction with a drying chamber incorporating an electrode applicatorand air extraction system. The equipment is suitable for drying most types of

Fabric which have had prior mechanical moisture extraction in either, cone,muff, bump or loose stock form. Many types of fibcriccan be dried. Themachine incorporates a modular polypropylene conveyor band and conveyorsystem.


9/16

Conventional mode of Drying Textiles after they have been dyed is a slowprocess. Textile industries can increase Throughput and fill orders moreprominently using Radio Frequency (RF) Dryers. RF system has capability toaccelerate the drying process and shorten production time. RF drying offers HighVolume, High speed and High quality drying which is what exactly needed intextile industries. As wet garments of Acrylic, Cotton, Nylon and Polyester Blends

pass through the drying chamber , the radio waves vibrates the contained Watermolecules million times per second, vaporizing them. Ventilator Fans are used toremove damp air from the Drying Chamber.

The dryer system comprises the 125kW industrial high frequency generator inconjunction with a drying chamber incorporating an electrode applicator and airextraction system. The equipment is suitable for drying most types of fibreswhich have had prior mechanical moisture extraction in either, cone, muff, bumpor loose stock form. Many types of fibre can be dried. The machine incorporatesa modular polypropylene conveyor band and conveyor system.

Because of the RF waves concentrate in the wettest, densest portion of thegarments. RF drying has a leveling effect that practically eliminates any

problems of uneven shrinkage and over drying. The RF drying times depend onthe type of fabric, the percentage of moisture in the fabric going in to the dryer,and the degree of dryness desired.

ONLINE RADIO FREQUENCY (RF) DRYER


10/16

ADVANTAGES:

The major advantage is that it gives thorough,

consistent drying in less time and also occupies less

space. In addition to these following advantages are

prominent:Faster DryingFaster ProductionIncreased Labor ProductionLess work in progressEnergy SavingLess Down TimeLower MaintenanceSpace savings

FEATURES:

Energy applied by radio waves at a frequency of 40.68 MHz.

Volumetric heating keeps the temperature low and uniform throughout the web to

prevent overheating.BARRIERS TO MARKET ACCEPTANCE

price

risk of failure

benefits not understood

priorities not on benefits of new technology

lack of technology awareness


11/16

TEXTILES INDUSTIRIES

1.ONLINE TEXTILE RF DRYERS Conventional mode of Drying Textiles after they have been dyed is a slow process. Textile

industries can increase Throughput and fill orders more prominently using Radio Frequency(RF) Dryers. RF system has capability to accelerate the drying process and shorten productiontime. RF drying offers High Volume, High speed and High quality drying which is what exactlyneeded in textile industries. As wet garments of Acrylic, Cotton, Nylon and Polyester Blendspass through the drying chamber , the radio waves vibrates the contained Water moleculesmillion times per second, vaporizing them. Ventilator Fans are used to remove damp air fromthe Drying Chamber.

The dryer system comprises the 125kW industrial high frequency generator in conjunctionwith a drying chamber incorporating an electrode applicator and air extraction system. Theequipment is suitable for drying most types of fibres which have had prior mechanicalmoisture extraction in either, cone, muff, bump or loose stock form. Many types of fibre canbe dried. The machine incorporates a modular polypropylene conveyor band and conveyorsystem.


12/16

2.DRYER FOR NONWOVEN WEBSThe RF Web Dryer rapidly removes moisture from the web at low temperatures and prevents the

migration of coating solids caused by conventional drying which increases web strength and

product quality.

This dryer eliminates the need for accumulation rollers required by festooned convectionand infrared type dryers and saves floor space by generally requiring one-fifth of the floor space

needed for hot-air and IR dryers as well as lowering maintenance costs.

Features: Volumetric heating keeps tEnergy applied by radio waves at a frequency of 40.68 MHz.

he temperature low and uniform throughout the web to prevent overheating.


13/16

FOOD PROCESSING INDUSTRIES

1.POST-BAKING DRYERThe combination of conventional oven heating with RF heating in the final stage of the drying process is an extremely

efficient way to produce many types of baked products, and it's easy to do. Radio frequency post-baking dryers are generallysupplied as stand-alone turnkey systems, which can be ordered for retrofit to an existing or new oven line.

RF post-baking dryers automatically adjust power to respond to varying moisture loads resulting from oven burner

failures, minor dough moisture and sheet thickness variations. A pre-adjustment assures that the product is still

produced within moisture specifications despite varying incoming moisture levels

BenefitsIncreased Throughput:

Up to 30% increase for crackers and often up to 40% for

cookies.

Elimination of Checking:By greatly reducing the moisture variation throughout the

thickness of the product, checking caused by differential

shrinkage is eliminated.

Excellent Control of Final Moisture Content:

Final moisture is controlled to approximately +/-0.25%.

Independent Color Control:

Since moisture is controlled in the RF dryer, color development

in the oven can be done without concern for final moisturecontent


14/16

ADVANCED BOOKBINDER DRYER

In-Line Radio Frequency Drying System for Sewn and Perfect-Bound Books Using Water-based

Adhesives

Features:1.Compact one-piece design saves floor space.2.High performance electrode arrays resist belt abrasion.

3.Automatic mechanical belt tracking.

4.Adjustable for books .5" (13mm) to 3.15" (80mm) thick.

5.Opposite-hand dryer configuration is available for dual installations handled by one operator.

6.Does not radiate heat or affect the working environment.Custom-design automated glue drying systems are also available for new and existing installations.

1.Fast and easy belt replacement.

2.Four-zone drying applicator for precise control of glue temperature

Benefits:Use water-based glue at high production speeds.Bind continuously in-line without handling and stacking before

trimming.Binder-to-trimmer time is reduced. Eliminates trimmer blade

fouling.Glued area of the book is selectively heated and dried, while dryareas receive little or no heating. Minimum cooling is required.Glue charring, blistering and skinning-over is eliminated.Requires a fraction of the floor space of conventional dryers.Efficient use of energy. RF power is instant-on-off.Improved book quality, flexibility and recyclability.


15/16

CHEMICAL INDUSTRY

1.VERTICAL RADIO FREQUENCY WEB DRYERS FOR ON-PRESS DRYING OF WATER BASED COATINGS, ADHESIVES AND INKS

Benefits:Wet areas on the web are selectively heated and dried, while

dry areas absorb little or no energy.Aqueous materials can be dried in the shortest line length to

production speed of any drying method known.Instant-on R.F. power eliminates start-up delays.

Requires a fraction of the floor space of conventional dryers.

Highest productivity is achieved with aqueous materials.

Solvent emission and disposal problems are eliminated.

Energy saving. The electrical power consumed by the dryer

automatically adjusts to the amount of water present on the

web.

Features:Convenient access doors facilitate web threading.Waste heat from the RF generator is channeled through the applicator to scavenge moisture

released by dryer.Solid State controller provides soft-start and maintains power at preselected level.Optional auto-threading system is available to minimize make-ready time.


16/16

BULK SOLIDS

This drying system uniformly heats filter cake material throughout the thickness of the product depth and rapidly

removes the water without overheating, at a fraction of the time and expense associated with conventional dryers.

BENEFITS:1.PRECISE MOISTURE CONTROL:

Selectively heats products where the moisture content is the highest. The product output will be uniform in moisture contentthroughout, regardless of the non-uniformity going in.

2.INCREASES PRODUCTION THROUGHPUT:

Product throughput on many applications can be increased 50% to 100%.

3.MINIMIZE DRYING TIMES:

Rapid volumetric heating eliminates the long dwell time required by conventional heating and is a suitable replacement for

tumble-, spray-, tray-, spin flash-, and belt/tunnel dryers.

4.OTHER BENEFITS:

Energy savings and floor space savings. Typically requires one-fifth the floor space of conventional drying systems.

Documents

RF Heating System