The tubular electrothermal element (electrothermal tube) is made of magnesium oxide sand with good heat resistance, thermal conductivity and insulation by filling and compacting the holes of spiral electrothermal alloy wires (nickel-chromium and ferrochromium alloy) along the central axis of the tube with metal tubes as the shell (including stainless steel and copper tubes). The ends of the tube are sealed with silica gel and processed by other processes.
