Sheathed electric heater
Sheathed electric heater (also known as armored electric heater, sheathed electric heating tube) is an industrial heating equipment with a metal sheath added outside the tubular electric heating element. The core design concept is to isolate the heating core from the heated medium, balancing safety, maintenance convenience, and heating uniformity.
Core structure
The sheathed electric heater is divided into three layers from inside to outside:
Heating core: The center is a high-temperature resistant alloy heating wire (Ni-Cr wire or Fe-Cr-Al wire), filled with high-purity magnesium oxide powder as insulation and thermal conduction filler, densified through tube reduction process.
Sheath tube: Made of cold-drawn seamless steel tube or stainless steel tube (304/316L), with large heat dissipation area and fast heat transfer, isolating the heating element from the medium to prevent local overheating and carbonization of the medium.
Wiring device: Divided into ordinary type (iron shell) and explosion-proof type (bolted flameproof shell), the explosion-proof type can reach explosion-proof mark dⅡCT4, protection level IP65.
Main features
Easy maintenance: Connected to oil tank/container via flange, no need to drain the medium during maintenance, just pull out the heating core for replacement, greatly reducing downtime.
Anti-carbonization design: The sheath increases the contact area with the medium, low surface power density, avoiding oil coking and carbonization due to local high temperature.
Safe and reliable: Good insulation, special types have explosion-proof function, and the shell can be effectively grounded to prevent electric leakage.
Long lifespan: The sheath tube isolates the medium from direct erosion of the heating element, extending service life.
Common model series
Table
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Series Typical use Rated voltage Surface power density Heat transfer temperature
HRY1/2/3 Hydraulic/lubricating oil heating 220V/380V ≤1.8W/cm² ≤300℃
HRY5 Hydraulic/lubricating devices 220V/380V Multi-core reduces load ≤300℃
SRY6/SRY9 Thermal oil and temperature control heating 220V/380V ≤0.7W/cm² ≤300℃
Main application scenarios
Hydraulic and lubrication systems: Heating hydraulic oil and lubricating oil, the most typical application scenario.
Thermal oil systems: Used with temperature control devices for thermal oil heating, SRY9 type is specifically designed for this scenario.
Chemical containers/reactors: Flange-mounted, used for heating liquids in reactors and storage tanks.
Heating non-corrosive gases/liquids: Such as air heating (requires fin structure).
Selection points
Medium matching: Mineral oil choose 304 stainless steel sheath; corrosive media choose 316L or titanium tube; water media pay attention to scale prevention, power density controlled at 510W/cm².
Surface power density: Strictly control oil media at 13W/cm², thermal oil recommended ≤0.7W/cm² to prevent coking.
Installation method: Hydraulic oil tanks mostly use threaded type, large storage tanks/reactors choose flange type, pipeline heat tracing choose insertion type.
Explosion-proof requirements: Petrochemical and dusty environments must use explosion-proof certified products, matching corresponding explosion-proof level and temperature group.
Power calculation: Based on medium mass, specific heat capacity, target temperature rise, and heating time, follow the principle of "sufficient but not redundant".
