Also known as sheathed electric heater, armored heater, or tubular electric heater, it is an industrial heating device that encapsulates electric heating elements within a metal sheath to heat liquids, gases, or solids.
Due to its robust structure, safety, durability, and ease of maintenance, it is widely used in petrochemical, electric power, machinery manufacturing, wind power, and HVAC fields.
The following is a summary of core information about sheathed electric heaters:
1. Core Structure and Working Principle
Structural Composition: A typical "sandwich" structure.
Central Heating Element: Usually a resistance wire made of nickel-chromium alloy (Ni-Cr) or iron-chromium-aluminum alloy, arranged in a spiral pattern.
Insulating Filling Layer: Magnesium oxide powder (MgO) is tightly filled between the heating wire and the sheath. This material has excellent thermal conductivity and insulation, rapidly transferring heat to the sheath while preventing electrical leakage.
Metal Sheath: The outer protective tube, typically made of stainless steel (such as 304, 316L), carbon steel, titanium, or copper. The sheath not only protects internal components but also directly contacts the heated medium for heat exchange.
Working Principle:
Based on Joule's law, current passing through the high-resistance heating wire generates heat, which is conducted through the magnesium oxide powder to the metal sheath, and then transferred from the sheath surface to the surrounding medium (such as oil, water, or air) via convection, radiation, or conduction.
2. Main Features and Advantages
Safe and Reliable: The live parts are completely enclosed within the metal sheath, achieving isolation between electricity and water/gas, with no risk of electric shock, and good explosion-proof performance (explosion-proof types can be customized).
Easy Maintenance (Core Advantage):
Most industrial sheathed heaters use flange connections or threaded connections.
Cartridge-type design: When the heating core is damaged, there is no need to drain the medium in the container (such as oil in a tank); simply remove the flange bolts and directly extract the damaged core to replace it with a new one, greatly reducing maintenance costs and downtime.
High Efficiency and Energy Saving: High thermal conversion rate (close to 100%), and some designs come with temperature control systems for precise temperature regulation, preventing localized overheating and carbonization of the medium (especially when heating heavy oil or lubricating oil).
Strong Adaptability: Shapes (straight, U-shaped, W-shaped, circular, etc.), power, voltage, and sheath materials can be customized to suit corrosive, high-temperature, or high-pressure environments.
3. Common Application Fields
Petrochemical: Heating crude oil, heavy oil, lubricating oil, resins, etc., to prevent solidification or reduce viscosity.
Electric Power Industry:
Wind Power: Specifically used for heating lubricating oil in wind turbine gearboxes to ensure normal startup in low-temperature environments (often with explosion-proof and IP65 protection ratings).
Power Plants: Boiler feedwater heating, fuel oil heat tracing.
Machinery Manufacturing: Hydraulic station oil heating, mold heating.
HVAC: Duct air heating, air duct heating.
Water Treatment: Water tank heating, flowing water heating.
4. Selection and Maintenance Considerations
Material Selection:
Heating ordinary water/air: Can choose stainless steel 304 or carbon steel.
Heating corrosive liquids (such as acids and bases): Need to choose 316L stainless steel, titanium tubes, or fluoroplastic coatings.
Heating high-temperature oil: Pay attention to surface load design to prevent coking.
Installation Requirements:
Strictly prohibit dry burning (unless it is a specially designed air heater). Liquid heaters must be fully immersed in the medium before powering on; otherwise, they will burn out instantly due to poor heat dissipation.
The junction box should be properly waterproof and moisture-proof.
Regular Cleaning: When used in poor water quality or oil prone to coking, scale may form on the sheath surface, affecting heat transfer efficiency; regular cleaning or descaling is required.
