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Applications of Dielectric Heating
The process of heating in which a high-frequency alternating electric field or radio waves or microwave electromagnetic radiation are used to heat the dielectric materials is known as dielectric heating.
Applications of Dielectric Heating
Since the dielectric heating is an expensive method of heating, therefore, it is only used where other methods of heating are not possible. Some of the applications of the dielectric heating are described as follows −
The plastic is used for making many appliances. If the pre-heating of the plastic is uniform, then the molding of plastic becomes faster and fault free. This pre-heating of the plastic is done through dielectric heating and takes very small time to give the desired heat to the plastic compounds before sending into the molding section.
In the plywood industries, the dielectric heating is used for drying the glue lines. It is used because under normal conditions the glue lines may take a day or more to dry and setting of the joint. However, when these joints are heated through high frequency dielectric heating, the drying and setting of the joints takes a few minutes. As, the process of making of multilayer plywood needs faster gluing and hence the dielectric heating is a necessity for uniform heating in the plywood industry.
The high quality books are passed through alternating electrostatic fields between tubular electrodes. This dries the glue on the cover binding in a fraction of time (about 5 to 10 seconds), through dielectric heating. Therefore, the book can be packed and dispatched without waiting for the covers to dry. Hence, the dielectric heating is used of book binding.
Sand Core Baking
The sand cores made of dry sand, water and some resin have to be backed before being used in molding processes. The drying of these sand cores is done when the cores are placed on a conveyor belt and are made to pass through an alternating electrostatic field. The sand cores are placed on a core plate which is further carried by a conveyor belt moving between a pair of electrodes connected to high frequency voltage source.
The automatic machines used in the modern bakeries use dielectric heating for backing of biscuits, cakes and other bakery products.
The dielectric heating is also used for making plastic garments like raincoats. As the raincoats cannot be stitched with ordinary sewing machine, otherwise rain water can enter the stitching holes. Therefore, for uniform and faster heating of these materials, the cold rollers fed with high frequency supply (i.e. dielectric heating) is used.
In the tobacco industries, the dielectric heating is used for drying of tobacco after mixing with glycerin, etc.
For Removal of Moisture from Oil Emulsions
The dielectric heating is also used for removing the moisture content from the oil emulsions. As certain chemical preparations require mixing of oil and water. Then, the water content has to be removed for giving desired life to the product.
For this purpose, the dielectric heating method is used because the dielectric constants of oil and water are much different, when the heating is done through dielectric heating, water will boil off while the temperature of oil will remain quite lower than the boiling point of water. In this way, the emulsion is dried safely, quickly and effectively.
Dehydration of Food
The dielectric heating process is also employed for dehydration of food so that they can be preserved for a long period of time. Dehydrated peas, packed sweets etc. available in the market are the examples of dehydration of food by dielectric heating. This process involves passing of the food through alternating electrostatic field resulting in dehydration through dielectric heating of the food.
The dielectric heating is also used in medicine for treatment of various disease. For example, the process called diathermy, in which a part of human body suffering from certain type of pain can be cured by heating the inner parts of the effective area through dielectric heating.
In this process, the part of the body is clamped between two electrodes which remain insulated from the body. The electrodes are then energized from high frequency high voltage source of power which generates dielectric heat in the tissues and bones of the body between the electrodes.
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