To reduce water content from fibres, yarns and fabrics drying is necessary after wet processes. There are mainly two Drying – water evaporation techniques:

1. Mechanical Drying: This process used to remove water particles which are mechanically bound to fibres.
2. Thermal Drying: In this process heat is transferred by different processes like convection, infrared radiation, direct contact or radio frequency to convert water into steam.

What is Radio Frequency Drying?

Here water content from fibres, yarns and fabrics are removed through Radio Frequency. Apart from textile industry this process is used in paper industry, foundries, Chemicals, pharmaceuticals and ceramic industry.

Principle of Radio Frequency Drying Process:

In radio frequency drying system alternating electric field between two electrodes is created by RF generator. The material to be dried is put acrossed between the electrodes, where the alternating energy causes polar molecules in the water to continuously re-orient them to face opposite poles - much the same way magnets move in an alternating magnetic field. This movement causes the friction and due to this water in the material to rapidly evaporate throughout the material.

Figure 1 show, a radio frequency drying system. There is a product between the electrodes. The product’s polar molecules are represented by the spheres, with "+" and "-" signs connected by bars.

To determine amount of heat generated in the product frequency, the dimensions of the product, the square of the applied voltage and the dielectric "loss factor" of the material is required. The dielectric loss factor is essential to measure the ease with which the material can be heated by this method. The main reason for this is water, which is far more amenable than other materials. This reduction in loss factor or receptivity to RF energy provides valuable protection against overheating to the material dries. Where uniformity of product dryness is essential RF Drying is the ideal drying process.

Why Radio Frequency Drying?

» Water is more receptive than any other dielectric material. So in process of RF drying RF power will absorbed in higher amount from wetter areas which resulting Uniform Moisture Distribution.
» In conventional drying process many times, uneven shrinking consequences into surface cracking. In RF drying due to uniform moisture distribution Surface Cracking is reduced.
» In RF drying Radio Frequency is direct form of applying heat so in this process No Wastage of Heat.
» Radio Frequency Dryer required one fifth or one eighth space required over conventional dryer.
» RF drying is 2 to 20 times Faster than conventional drying methods.
» Here heating begins directly to the product so the Dwell Time is far less than in a conventional dryer.
» This process is Eco Friendly process.
» Maintenance Cost is low as compare to other drying process.

Some Manufacturers of RF Dryer Machine:

The Figure 2 shows, Thermex Tharmatron’s computer control RF Drying Machine. This machine can produce sustained power output levels of 120 KW to a suitable dielectric load in a stable high voltage, high frequency environment. And also capable of Fifty different recipes for automatic process control, Self diagnostic and calibration functions, Ethernet data acquisition with both real-time and historical reporting.

The system is also provided with the necessary features to 1) continuously transport your product during the heating process, 2) separate and remove the unwanted moisture, and 3) report quality-oriented results over time periods that you select. This is all done while providing for the uniform introduction of heat, or product profiling.

The Technical Specifications of this machine is as follow:

Figure 4 shows, Hong Kong Goworld International Industrial Holding Limited’s GWRF-85KW radio frequency dryer. It is suitable for all fibres and yarns such as synthetics (polyester, acrylic, and nylon), artificial fibres (rayon, viscose) and natural fibres (wool, cotton, silk, etc).

References:

▪www.radiofrequency.com
▪www.mongagroup.com
▪www.thermex-thermatron.com

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