--- title: "Dielectric heating vs induction heating" subject: "Industrial Power Distribution and Illumination" chapter: 5 key: "semester_6/industrial_power_distribution_and_illumination:dielectric-heating" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/dielectric-heating site: BCT Engineering --- # Dielectric heating vs induction heating Industrial Power Distribution and Illumination · Chapter 5: Electrification of Industrial Building - Asked in: 2068 Jestha (old course), 8 marks - Video: [Dielectric Heating (Basics, Working, Applications, Block Diagram & Applications) Explained](https://www.youtube.com/watch?v=R5ecGEVXtUQ) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/dielectric-heating - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-5 ## Question What is dielectric heating? How is it different from induction heating? State the applications of dielectric heating. ## Short answer Dielectric heating uses a high-frequency electric field (10–50 MHz) to heat insulating materials via molecular friction. Unlike induction heating which heats conductors by eddy currents and hysteresis, dielectric heating provides uniform volumetric heating. Applications include drying wood, gluing plywood, welding plastics, and food processing. ## Answer **Dielectric heating** is the heating of an electrically **non-conducting (insulating) material** by placing it between two metal plates (electrodes) connected to a high-frequency AC voltage (about 10–50 MHz, a few kV). The alternating field makes the molecules of the dielectric flip and rub repeatedly (dielectric hysteresis loss), so heat is generated **uniformly throughout the material** itself. ```text HF oscillator (10–50 MHz) | | ===+=== electrode | [ material (charge) ] ← heat produced inside ===+=== electrode | |________________| ``` Heat produced: P = 2π f C V² tan δ ≈ 2π f C V² cos φ, so heat rises with frequency f and voltage V. The material behaves like a lossy capacitor (loss angle δ). #### Difference from induction heating | Point | Dielectric heating | Induction heating | |---|---|---| | Material heated | Insulators (wood, plastic, rubber, food) | Conductors (metals) | | Heating principle | Dielectric (molecular) loss | Eddy current and hysteresis loss | | Field used | Electric field between plates | Alternating magnetic field of a coil | | Frequency | High: 10–50 MHz (RF) | Low to medium: 50 Hz – 500 kHz | | Heat distribution | Uniform through the whole volume | Mainly near the surface (skin effect) | | Device | Capacitor plates (electrodes) | Induction coil (inductor) | | Typical use | Drying, gluing, plastic welding | Melting, hardening, brazing metals | #### Applications of dielectric heating - Drying of timber, paper, textiles and tobacco. - Gluing of plywood and laminated wood (heat cures glue uniformly inside). - Welding of PVC and plastic sheets (raincoats, bags). - Pre-heating of plastic moulding powder and vulcanising rubber. - Food processing: baking, dehydration, sterilisation; the microwave oven works on the same principle at 2.45 GHz. - Medical diathermy (heating body tissue). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is heat produced in dielectric heating? A. Eddy currents in a metal charge B. An insulator between electrodes at 10-50 MHz; molecules flip and rub (dielectric loss), heating the whole volume C. Burning of fuel near the material D. Current passing through a resistance wire Answer: B. The HF field makes molecules of the insulator oscillate, producing heat uniformly inside the material. (Key point: Dielectric heating principle) 2. On what does dielectric heat P = 2 pi f C V^2 tan delta increase? A. Only the material colour B. Frequency and voltage C. Only the plate area being smaller D. It is independent of frequency Answer: B. P is proportional to f and V^2 (and C and tan delta), so higher frequency and voltage give more heat. (Key point: Heating formula) 3. Which statement correctly contrasts dielectric with induction heating? A. Dielectric heats conductors with a magnetic field B. Dielectric heats insulators with an electric field uniformly; induction heats conductors with a magnetic field mainly at the surface C. Both heat the same materials at the same frequency D. Induction uses capacitor plates; dielectric uses a coil Answer: B. Dielectric uses electrodes (capacitor) on insulators with uniform volume heating; induction uses a coil on metals with skin-effect surface heating. (Key point: Difference from induction) 4. Which is an application of dielectric heating? A. Melting steel B. Gluing plywood and welding PVC sheets C. Hardening gear teeth D. Brazing copper pipes Answer: B. Dielectric heating suits insulators: gluing plywood, plastic welding, drying timber, food processing (microwave oven). (Key point: Applications) ## Related in other subjects - [Dielectric vs infrared vs microwave heating](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Adielectric-infrared-microwave-heating) — Utilization of Electrical Energy, chapter 5 - [Dielectric heating of laminated wooden board](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Adielectric-heating-wooden-board-30mhz) — Utilization of Electrical Energy, chapter 5 - [Dielectric heating: power, voltage, current (board to 160°C)](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Adielectric-heating-board-160c-power-voltage) — Utilization of Electrical Energy, chapter 5 - [Induction heating advantages; induction furnace](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Ainduction-heating-advantages-furnace) — Utilization of Electrical Energy, chapter 5