Abstract: An electric immersion heating apparatus for heating highly corrosive liquids includes a flexible cable-type immersion heater having a continuous coiled resistance heating element disposed in axially spaced pitches and being enclosed in a continuous tubular outer jacket formed of a flexible plastic material, such as polytetrafluoroethylene with a PFA side chain, resistant to chemical attach by highly corrosive liquids. The outer jacket is received over the coiled heating element in closely fitting relationship and has a wall thickness sufficiently thin to provide efficient heat transfer from the coiled element to the liquid being heated. Because of its thinness the outer tubular jacket is subject to permeation of damaging corrosive vapors through the jacket to the coiled heating element.

Abstract: A continuous flexible cable heater having a coil continuous conductor in a plastic casing. The conductor has uncoiled regions spaced therealong between coiled regions to permit bending at a radius less than twice the jacket outside diameter. A heater assembly has the cable disposed on a support in closely folded serpentine planar array. A sensor portion of the continuous cable is folded over and adjacent the upper surface of the planar array and includes fusible protective means to cut off the heater in the event of overheating of the liquid or excess current draw.